Photography / Tips and Solutions

Understanding Crop Factor


There is a great deal of confusion surrounding crop factor, and it is particularly difficult to explain, but let’s give it a try, shall we?

Before we dive in, let me dispel two vicious rumors related to crop factor that are circulating through the photography (Internet) world today:

  1. Crop factor does NOT affect a lens’s focal length.
  2. Crop factor does NOT affect a lens’s aperture.

Before you scroll to the bottom of the screen to leave a comment to the contrary, let me explain why I am stating these facts…

Focal Length The focal length of a lens, expressed in millimeters, is the distance along the lens’s optically central axis (beginning at the rear nodal point) to the image plane in the camera (often illustrated by a "Φ" on the top plate of a camera body) when the lens is focused at infinity. The image plane in the camera is where you will find your digital sensor or film plate.

Therefore, a 50mm lens can measure 50mm from the point where light rays begin to exit the lens in the same direction as they entered the lens until they arrive on the image plane. Some “pancake” lenses and mirror lenses have optical tricks to shorten them, but in general, the focal length is that physical measurement.

A zoom lens can change the physical focal length of a lens. Sometimes this movement is contained inside the lens—the lens body does not physically change length—and other times the lens does change its size.

However, regardless of what kind of camera or sensor you place behind the lens, the focal length will not change just because you have a larger or smaller sensor or frame of film. I will explain later how sensor size (or film size) changes the equivalent focal length—not the true focal length of the lens.

Aperture  is the size of the opening in the lens. Some lenses have fixed apertures that cannot be changed, but most photographic lenses have variable apertures to control the amount of light entering the lens. This opening is regulated by a diaphragm comprising blades that can be adjusted to vary the size of the hole (aperture) through which the light passes.

In photography, aperture is expressed as a ratio of the focal length to the diameter of the aperture opening. The ratio is commonly referred to as an f/number, f/stop, focal ratio, f/ratio, or relative aperture.

This ratio is based on physical measurements and is completely independent of the size of the camera’s sensor or the size of the film you are shooting. Sensor size has an effect on depth of field, but not because it changes aperture. Aperture is independent of film frame or sensor size.

35mm Format

The first thing to know about crop factor is that, as with all “factors,” we need to have a base reference from which to work. In the photography world, this reference is a piece of 135 film. In the digital photography world, “full-frame” sensors are the same size as this film; a film frame with a width of 35mm. Cameras of this photography format are collectively known as “35mm cameras.”

A 35mm film strip measures 35mm across

One source of crop factor confusion is the use of “35mm” when discussing the reference. The value in this case is used not as a focal-length measurement, but as a measurement of the dimensions the frame of film. The film image area measures 24 x 36mm, but the strip is 35mm wide. So, when you think of “35mm” when it is used in reference to film or the size of a camera sensor, know that you are not referring to lens focal length. You can mount a lens of any focal length, even a 35mm lens, on a 35mm camera. The focal length is the focal length. Film and sensor dimensions are different.

For years, the 35mm camera has been, by far, the world’s most popular camera format. Because of this, for those of us who grew up in the world of 35mm cameras, when we think of the field of view given by a lens of a certain focal length, we can visualize what the photograph should look like. In the 35mm camera world, a lens with a focal length of around 50mm will provide a “normal” view with its human-eye-like field of view. Lenses with shorter focal lengths will provide a wider view and lenses with longer focal lengths will provide narrower or telephoto views.

Digital Sensors

Life was simple back when almost everyone was shooting 35mm cameras and 35mm film. Sure, there were those making magic with medium format and large format cameras, and there were point-and-shoot cameras that took specially made smaller films. My first camera, handed down from my grandmother, was a Kodak Instamatic 30, with its 13 x 17mm 110 film. Back then, no one really paid attention to “crop factor,” even though it existed. I’d bet most photographers didn’t know the dimensions of their 110 film, nor did they know the focal length of the tiny lenses! You just looked through the camera and took the picture it gave you.

Then, digital photography arrived. In its early days, most sensors were smaller than 35mm film, and a virtual can of worms was opened. Why? Because the sensors were smaller than 35mm film, the images seen through a lens of any particular focal length had a different field of view than that of the same lens on a 35mm film camera. Suddenly, a 50mm lens no longer had a “normal” field of view; it was a bit more of a telephoto.

The cropped sensor “sees” a narrower field of view

If you never shot 35mm film, this was no big deal because your mind’s eye did not have a 35mm film reference for different lenses. But photographers entering digital imaging decided that they needed to know the “35mm equivalent” field of view of various lenses when attached to a camera with a digital sensor smaller than 35mm film. The reality of it is, “crop factor” serves to translate a measurement into a language in which many of today’s photographers were never fluent to begin with. And, because of this, many of you out there have been very confused and frustrated by the mention of crop factor. Hopefully this article will end your confusion!

Crop Factor

A round lens produces a circular image circle—not rectangular. The sensor, or film, at the back of the camera captures a rectangular portion of this image circle. When we use 35mm film as a standard, any camera with a sensor smaller than a frame of 35mm film will cover a smaller portion of the image circle produced by a given lens and will thereby change the field of view of that lens. This is the “crop” part of the crop factor.

However, because traditionally, the field of view produced by a given lens has been described not as a measurement of degrees, but by the focal length (kind of the “name”) of the lens, we need to translate the cropped field of view into an equivalent lens focal length.

For example, if you attach a 50mm lens to a camera with a smaller-than-35mm film sensor, you will have to multiply the focal length of that 50mm lens by a factor derived from the size differential of the sensor to calculate the 35mm equivalent focal length. This will then give you the means to figure out the lens’s field of view based on that new equivalent focal length. This is the “factor” part of crop factor.

This multiplication factor is the ratio of the size of the digital sensor to the dimensions of the 35mm film negative.

Formula: The diagonal of a rectangle can be determined by a2+ b2 = c2

Full Frame: 24mm2 + 36mm2 = c2

576 +1296 = 1872

Square root of 1872 = 43.3mm

Full-Frame or 35mm Diagonal / Crop Sensor Diagonal = Crop Factor

So, if you have a camera with an APS-C-sized sensor (circa 15.6 x 23.5mm or 14.8 x 22.2 on Canon), plug in the numbers and you will get a crop factor of 1.5x (or 1.6x for Canon).

Then, to find the equivalent focal length of the new field of view afforded by the smaller APS-C sensor, multiply the true focal length of the lens by 1.5x to get the 35mm equivalent focal length of the lens. A 50mm lens on a camera with a 1.5x crop factor APS-C sensor gives a field of view equivalent to that of a 75mm lens on a full-frame or 35mm film camera.

Remember, the actual focal length of the lens is unchanged, as is its aperture.

In our example, if you weren’t familiar with a 50mm lens’s field of view in the first place, this doesn’t really matter. But if you were familiar with the 50mm lens’s field of view, you will know that this same lens, when placed in front of the smaller sensor, has a narrower field of view than your normal vision has.

A comparison of relative sensor sizes.


If you have a zoom lens on a smaller-than-full-frame camera, you can figure out the effective focal-length equivalent by multiplying both focal length numbers by the crop factor. For example, a 70-200mm lens becomes a virtual 105-300mm lens on a 1.5x APS-C sensor.

Cameras with sensors or films larger than a 35mm frame will have sub-one crop factors. For instance, a medium-format Pentax 645Z’s sensor measures 33 x 44mm. This gives it a crop factor of 0.78x. A 50mm lens on this Pentax camera gives an equivalent field of view of a 39mm lens.

Full-frame versus The Rest

The crop factor discussion inevitably leads us to the full-frame versus smaller-sensor debate. For my take, click here.

So as not to drive down the well-trodden path here, in summary, full-frame cameras are ideal for landscape images because there is no crop factor and wide-angle lenses maintain their wide-angle field of view. Smaller-sensor cameras give lenses a virtual telephoto effect that is ideal for some sports, wildlife, and macro work. Both formats have advantages and disadvantages.

Another thing to mention: there are “regular” lenses and there are lenses specifically designed to operate on smaller-sensor cameras. These small-sensor lenses may not work well on their full-frame cousins. On a 35mm film or full-frame digital camera, you may experience heavy vignetting. If the small-sensor lens does work on a full-frame digital camera, the camera might simulate the smaller sensor the lens was designed for and automatically provide the crop factor field of view. A regular lens will work happily on a full-frame digital, 35mm film, or smaller-sensor camera. The crop factor will only apply to a lens if it is used on a small-sensor camera. Today, some manufacturers refer to their “regular” lenses as “full-frame lenses” to emphasize that they are not designed specifically for smaller-sensor cameras. But, before digital photography, all 35mm format lenses were “full-frame.”

The Final Word

Crop factor is really quite simple. The confusing thing is that, as I said earlier, it exists to translate an angular measurement (degrees of field of view) virtually into a linear measurement (millimeters of lens focal length) so that old-school 35mm photographers can figure out the real field of view of a lens based on an equivalent focal length resulting from using sensors smaller than 35mm film. Get it? Got it. Good!

I suppose that is useful in many ways, but I have seen many frustrated photographers over the years try to understand and explain this concept. Sprinkle in some bogus information on the Web about magically changing focal lengths and apertures, and everything has become a mess!

I hope this has cleared things up for those who are new to photography or who were confused a few minutes ago. If not, I stand by to take your questions! And, in case you were wondering, the Instamatic 110 film camera has a crop factor of 2x. 

For more information about the theory behind crop factor, be sure to watch this engrossing video.


Discussion 143

Add new comment

Add comment Cancel

Hi todd

i thought I had this, but after rereading again, I may have confused myself

i have a Nikon  APS-C crop body and shopping for lenses   I bought a FX 70-200 lens, which I understand from your explanation will give me an 35mm equivalent of 105-300 at the 1.5 CF.  So far, so good.   

What is getting me now is the difference between buy a FX lens and a DX specific lens.  Originally, I had thought that the CF applied only to the FX lens when used on a APS-C body, and that design of the DX lens meant that the "focal length" as stated did not need the CF "adjustment".   Thus, for example, an FX 24-80 lens on my camera would yield the 35mm equivalent of 36-120mm, but if it was a DX 24-80,  it would give the 35mm equivalent as "stated", just 24-80, no CF adjustment needed as it was a DX lens on a APS-C body

ok - that is what I thought, but now thinking the CF applies to both lens.  The only difference between the two lenses being that the image circle in the DX lens is smaller and thus will not work well on an FX body

so, is my understanding right now, or was it correct the first time?    I think it is right now - the CF applies to FX AND DX lenses.   Why is this important.    I am trying to by 1-2 shorter lenses and want to make sure I have he right "overlap" with a shorter zoom I am considering 

thsnks in advance

Any ideas of the crop factor of a Nikon P900 with 83mm - 2000mm optical and digital zoom please. And how to work it out as am very confused by this. Trying to take an on-line photography course and struggling a little bit. Thanks for your help. Regards. 

Hey Iain,

The crop factor of the P900 is 5.62x. Pretty extreme to get that much telephoto action!

Also, don't worry about digital zoom, that really isn't a function of crop factor. Digital zoom is simply zooming on on the optically zoomed image.

Check out this link for some help with your course (hopefully):

Good luck!

Thank you Todd. Much appreciated 


No worries, Iain! Cheers!


I have been researching for hours and have been reading so many articles and I still cannot comprehend this:

I use a Canon T2i (crop sensor, 1.6x crop factor), and a 50mm 1.8 EF lens.

I understand why a focal length of a 100mm on an ef lens on a crop sensor would technically make it 160mm...

So why isn't my 50mm technically an 80mm? Why in this case does a 50mm stay a 50mm, and doesnt get an increased focal length? Is it because it's a prime lens?

Hey Karlie,

You are not alone in your confusion.

The focal length of a lens is a fixed measurement. If you take a 100mm lens and put it on a bookshelf, it is a 100mm lens. If you attach it to a large format camera, it is a 100mm lens. If you tape it on the front of a disposable point-and-shoot camera, it is still a 100mm lens. Prime lens or zoom...same thing. The focal length is a measurement.

The size of the sensor of the camera changes the field of view of the lens—not the focal length. We (well, not I) invented the 35mm-equivalent focal length moniker to translate the lenses into a system where most people were familiar—that of the 135 (35mm film) format.

More confused now? Basically, when we talk about crop factor, we translate focal lengths into a "language" that pretty much only those who shot 35mm film understand. I think I am digressing...

I hope that clears things up and I didn't tell you too much!

Let me know!

Thank you for replying, so let me see if I got this right now.

So, same as before, my 50mm on my T2i gives a field of view of 80mm, yet it is still a 50mm lens? Is that what you are trying to say? From the article you said: "any camera with a sensor smaller than a frame of 35mm film will cover a smaller portion of the image circle produced by a given lens and will thereby change the field of view of that lens. This is the “crop” part of the crop factor." So in this case, that is the 80mm that I'm trying to figure out, yet it's on my 50mm lens.

So when I say, my 50mm on my t2i is technically 80mm, how is that still wrong? Because it's only the field of view in the lens that makes it 80mm?

So the 80mm is the "equivalent focal length of the new field of view afforded by the smaller APS-C sensor" since "a 50mm lens on a camera with a 1.5x crop factor APS-C sensor gives a field of view equivalent to that of a 75mm lens on a full-frame or 35mm film camera." Except mines a 1.6x, so hence the 80mm.

Did I get it right this time?

Also, to clarify, does the 1.6x mean that my T2i sensor is 1.6x smaller than the full frame; hence giving me the field of view of an 80mm, yet its with my 50mm. Is that correct? 

Hey Karlie,

You are close to a breakthrough! :)

All of what you said, is correct. Except, you cant really call a 50mm lens an 80mm lens. You cannot call a honeycrisp apple a red delicious apple. Both are apples, but they are very different. Right?

You can say that your "50mm lens has a 35mm-equivalent field of view of an 80mm lens." That is still confusing, right?

Here is the missing part that I did not mention in my reply yesterday. Field of view is labeled in degrees, not in linear millimeters. So, when we talk about 35mm-equivalent focal lengths based on changes to field of view, we are translating degrees of measurement into a focal length that provides that field of view when used on a 135 format (or 35mm format or full-frame) camera.

So, here are your questions, one by one:

  • So, same as before, my 50mm on my T2i gives a field of view of 80mm, yet it is still a 50mm lens?
    • Yes, a 50mm lens will always be a 50mm lens regardless of what you do with it.
  • Is that what you are trying to say?
    • Yep! :)
  • So when I say, my 50mm on my t2i is technically 80mm, how is that still wrong?
    • It is not technically an 80mm lens. It simply provides the same field of view on your camera as an 80mm lens would on a full-frame camera. It is still a 50mm lens.
  • Because it's only the field of view in the lens that makes it 80mm?
    • The field of view makes it the equivalent of an 80mm lens on a full-frame camera, but the focal length of the lens is still 50mm.
  • Did I get it right this time?
    • Yep. Mostly. B+ :)
  • Also, to clarify, does the 1.6x mean that my T2i sensor is 1.6x smaller than the full frame; hence giving me the field of view of an 80mm, yet its with my 50mm. Is that correct? 
    • Yes. Exactly.

Here is the other thing to keep in mind. Just because we use focal length to describe the field of view of camera doesn't mean it is important to photography, in a sense. The field of view of the camera is what you see when you look through the lens—the number assigned to it doesn't really matter. We could use "wide-angle," "normal," and "telephoto" instead of numbers, but the numbers allow us to be more precise when describing the angular field of view (by using linear measurements...ugh). :)

Get it? Got it! Good! ....right? Let me know if this is clear as mud now. 

Thank you Todd for answering all my questions! So in order for my 50mm to have a field of view of 50mm, looks like I need to get a full frame?? ;)

No worries, Karlie!

Yes, if you want your 50mm to have a 50mm field of view, you will have to shoot full-frame.

If you want the 50mm field of view on your APS-C camera, you need to get a lens with around a 35mm focal lenght.

Check out this article!

Good chat!

Hi Todd! I currently have a Canon T3i and I am going backpacking through southeast Asia in a few months and I am thinking about upgrading, I am just starting out with photography and am trying to learn myself. I'm getting to the point to where I need some new gear so I've been shopping around before the trip. I received my camera as a gift and for some reason, I have been unhappy with it lately. I've been researching different cameras and I'm having trouble deciding what to get, especially between a full frame vs. an apsc. After reading I sort of understand (I think) but I still am not sure which would be best for what I need it for, I was leaning toward full-frame but now I'm not sure. I shoot a little bit of everything so it's been hard to narrow it down. I would love a recommendation for a camera if you have one or at least a little help deciding between full-frame or aspc. (If you want to throw in a couple lens recommendations too that would be great)

Hey Lauren!

I am here to help, but your question is more complicated than you might think. I could recommend some cameras and lenses, but I would like to know more about what you photograph and why you are unhappy with the T3i and what lenses you have currently. May you share some more info?

Also, some homework for you:

And, if you want to skip to the end, I would say you will find the Canon T6i or T6s a nice upgrade for your T3i. Before we dive into full-frame versus APS-C, we need to chat more.

Standing by for follow-ups!

Thank you! Also, I'm sorry I meant a Canon Rebel T4i not a 3i. I  Mostly I like to photograph nature, landscapes but also close ups of flowers or animals. I also travel a lot so most of my photos come from my trips. I have a lot of architectural photos, portraits, and landscapes. Really just a little of everything. I suppose I have just been disappointed with the quality of some of my photos, I feel like the images aren't as clear or bright as they could be and I felt like they were always cropped in farther than I remember when I took them. I especially noticed this when I started shooting portraits. I would be careful to make sure to crop at a certain point to not cut off finger tips or toes or something in a portrait and then when I went to edit the photos the toes or whatever I was trying to keep in the image would be much closer to the edge or even touching the edge of the frame. I started trying to shoot from farther out but it kept happening. When I started reading about crop sensors I thought that might be the problem, but then I read a little more and I wasn't so sure. I might also be unhappy with my camera because I started with traditional film and solely used my film Nikon for a couple years until I moved out of my home town and didn't have access to a darkroom anymore. Then I learned digital on my moms Nikon, I forget what she has but I think it is a bit nicer than mine. It took me a long time to adjust to digital, and I must admit I am a little resistant to technology so I thought I was just unhappy with my photos because I didn't quite know how to use my camera. I felt like I could never get the settings quite right and the images always came out just a little dull or not as sharp as I would like. I read all the tutorials I could find and kept trying to play with settings and figure out the problems and it got a little better but then I went on a camping trip to Colorado and my uncle lent me his Canon EOS 70D and I loved it. I'm not sure why but I never had trouble with the settings, everything seemed so much simpler to use and more natural and the images turned out bright and crisp, I barely had to edit anything, I didn't notice much on the cropping but I was shooting more for fun so I wasn't paying as close attention. So I was thinking I was going to try and get one of those but then I started looking up more articles and reviews and got very confused. As far as lenses I have 50mm 1.8 and then the lenses that came with the camera. I know I want to get a few more lenses and I think I picked out a few but I really don't know if it is worth upgrading the body. Thank you again for your help!

Hey Lauren,

Thanks for all of that. It is very helpful.

Here are a couple of thoughts and suggestions...

"Closer crop." First of all, you are doing everything right by paying attention to the edges of your frame and composing with keep it up! What I think you are discovering is the fact that the T4i's viewfinder is a 95% viewfinder. It doesn't show everything the lens sees. What you see is not exactly what you get. So, start helping yourself by leaving a bit more room around the edges of your shot...5% worth!

Canon vs. Nikon. Go with what you are comfortable with. Having come from Nikon, those cameras should be easy for you, but you expressed that your uncle's Canon and your T4i settings are working for you, so you can flip a coin if you want.

When you mention the "lenses that came with the camera," I assume you mean something like an 18-55mm and 55-200mm kit lens, correct? Do you use your 50mm f/1.8 much? My guess is that you are getting better sharpness and color with that lens than the kit lenses. If it is sitting on your shelf, take it out for a spin!

Why do I mention this? My guess is that your kit lenses, not the camera, are holding you back. The T4i is a bit long in the tooth, so it might be time to upgrade, but my guess is that if you stayed in the APS-C world and upgraded your optics, you would be just as happy as if you went full-frame and upgraded your lenses as well. After all, your uncle's 70D is APS-C as well. What lenses were on his camera?

So...the 70D is an option as is the T6....for an APS-C upgrade. The 7D is a great camera as well.

If you want to jump to full frame, the 5D is going to be your go-to option...and you could probably save a good bit of money by getting the superb Mark III instead of the Mark IV.

For upgrading lenses, I would start looking at Canon L-series glass. Expensive, but lenses are a long-lasting investment.

Standing by for follow-ups!

[Continued from previous post]

Also, does crop factor act the same while filming as compared to still photography? Thanks.


Hey Nicholas,

Good questions!

To answer your first: No, the focal length of the lens is its physical focal length. Manufacturers will not describe a lens by its full-frame equivalent focal length. So, a 50mm lens is a 50mm lens regardless of what kind of camera you mount it on.

And, when shooting video, the crop factors are also factored in, but, in video, there are many different formats, so, for example, if you are shooting Super 35 like Sissy in the conversation below, there is a different crop factor.

Thanks for stopping by!

Hi Todd!

I am about to buy a Sony A6300 and am a film student so I am just trying to understand cameras down to every detail. Crop factor is a little confusing to me (go figure). My question is, when I go to buy my Sony E-Mount lenses will they have the crop factor already factored into the listed focal length. For example, when I buy a 50 mm prime lense I am truly getting a 50 mm prime lense for the APS-C censor? Or do I still have to keep in mind the 1.5x crop factor when I try to get an exact look/exact focal length? Very beautifully written article though, thank you!


Thanks for the kind words, Nicholas! See my reply above!

I don't understand you language " Therefore, a 50mm lens can measure 50mm from the point where light rays begin to exit the lens in the same direction as they entered the lens until they arrive on the image plane."

What is the significance of light rays exiting the lens? 

Shouldn't your sentence just be " Therefore, a 50mm lens can measure 50mm from the point where light rays enter the lens until they arrive on the image plane."

Hey Richard,

Fair point, but light rays have to exit the lens in order to get to the image plane. As far as I know, there is always a gap between the back of the lens and the film or sensor. That gap is often filled by the shutter mechanism and, in the case of a SLR, a mirror.

Maybe I could have been less wordy!

Thanks for reading!

Hey Todd,

I am curious, if I am standing at point A shooting with a crop sensor and 85mm lens to point B, also standing at point A shooting with a full frame sensor and a 135mm lens, I should have roughly the same framing. My question is, is the crop sensor a lower quality image and how does it differ from say zooming in post on the same A to B shot with a 85mm on a full frame? Hope that makes sense! 

Hey Brandon,

Great question, and it does make sense...assuming a Canon APS-C 1.6x crop factor.

The answer is a bit complicated, but, in general, there will not be a difference in image quality and, yes, the framing will be nearly identical.

On the full-frame image, the background may be a bit less in focus for a given aperture as the focal length is increased and depth of field changes.

If both cameras are 20MP, for the sake of argument, the full-frame will show a bit less resolution on the crop as you are discarding pixels while cropping. The cropped area will be approximately 12.5MP where as, on the APS-C camera, you will still get the full 20MP. Does this make a huge difference? No. I would say not.

One last comment. This is a pretty good thought experiment, and many of us have pondered this when thinking of the advantages/disadvantages of certain sensor sizes, however, it isn't usually a real-world exercise, right? Framing and composition are determined by the focal length of your lens and what you see in the viewfinder—not the sensor size of your camera.

Good question!

Hi Todd,

Thanks for this, I was wondering if you would be able to help me with this. If I adapt lets say a Mamiya sekor C 645 lens to EF mount for a super 35mm video camera (Black magic Mini U Pro for instace), what would the crop factor/equivalent be there? Im just having trouble getting the conversion from medium format to super 35mm, I assume it could be more than double. Anyhow, my second question is, do you know of any optical reducer/converters like the speedbooster types from medium format to super 35mm, or at least 35mm? In case the crop is too much. Thank you!

Hey Sissy,

Ugh. I forgot to mention, in the above article, how bad at math I am! So, definitely check my work!

645 film dimensions: 56 x 41.5mm  (Ratio 8:5.2) (Diagonal 69.7mm)

135 film dimensions: 36 x 24mm (3:2) (Diagonal 43.27mm)

Super 35 film dimensions (varies): 25.34 x 14.25mm (on the Black Magic camera you mentioned) (16:9) (Diagonal 29.07mm)

645 to 135 format (full-frame) crop factor is: 0.62x

645 to Super 35 format crop factor is: 0.42x approximately...slightly different ratios...and I am not sure how that factors in. My calculations were based on the diagonal measurements.

I hope someone better at math than me can crunch the numbers in a more precise way!

As far as speed boosters for that conversion, there are definitely 645 to full-frame adapters, but I don't see any with optics...they are only straight adapters.

We are looking for other options, but have come up dry so far.

I hope this helps!

hi. if i have an apsc specific lens for a cropped camera sensor say for argument sake its at 50mm focal distance. are these lenses designed so that 50mm focal distance gives a field of view that is a true 50mm or is it still 75mm? 

ie. 50mm apsc lens designed so that field of view is true 50mm not 75mm as you would get on a full frame lens. 

Hi john,

Good question. The answer is, "No."

A 50mm lens is a 50mm lens regardless of what kind of camera (or sensor) it is attached to. If it is sitting on a bookshelf, it is always a 50mm lens. The field of view is dependent on the sensor or film size. So, a lens that is made for APS-C cameras still has a focal length number is a fixed measurement.

So, a 50mm lens is a 50mm lens. 

Thanks for stopping by!

Hi Newer to photography and still understanding the crop factor. I have a mf/3 camera (gx85) and an old 35 lense with an adapter( just hallow not boster) its a 50mm 1.8 i was told it would look like a 100mm(in terms of the frame it would capture). why dose my 45-150 set to 50mm take the exact same pic as the 50mm vintage shouldnt it be zoomed in like if i set the zoom in the 45-150 to 100mm?

Hey James,

Welcome to photography!

So, on the MFT camera, an old 50mm focal length lens will have the same field of view as a 100mm lens on a full-frame or 135 format film camera. The lens, however, is still a 50mm focal length lens.

Your 45-150mm lens can achieve the same field of view as that 50mm vintage lens when you zoom in to the 50mm mark. The 45-150mm has the equivalent field of view as a 90-300mm lens on a full-frame camera.

Focal length is focal length. It is a measurement that is not dependent on the type of camera the lens is mounted on. A 45-150mm lens is a 45-150mm lens when it is sitting on a shelf and not mounted on a camera. The different sensor sizes changes the field of view of the lens, not the physical focal length.

Does that make it clear?

Let me know if you have more questions!


Thanks for the in-depth explanation. I was familiar with most of it, but was hoping to find something about Fujifilm x series sensors. I was looking into buying the XE2 or XPro2 and went to Professional Photo Resources in Atlanta to have a hands-on look at one, and possibly rent one to try out. I also tried out the 23mm and 35mm lenses to compare angle of view and similarity to "fullframe" format. The staff at PPR is extremely knowledgable in several formats and brands. The person who helped me used the X series cameras personally and could navigate through the menus and controls on all the models I asked about, and did an excellent job guiding me through the finer points of the cameras. I asked about the crop factor for the X series and he said it was 1.3. I told him I thought it was 1.5 for APS-C and he insisted it was 1.3 and that the 35/1.4 lens would be exactly 50mm equivilent field of view on the X series bodies. If that were the case, it would actually be 46mm rather than 53mm with a 1.5 crop factor. We both agreed that the important thing was that the photog liked what was seen through the viewfinder, regardless of numbers. So, I was wondering if you have ever heard of the 1.3x crop factor with the X series?



Hey Dean,

Thanks for your question! Interesting.

If the Fujifilm X-series sensors were 1.3x, that would make a lot of websites (including ours and Fujifilm's site) incorrect!

The Fujifilm X sensors are APS-C. 1.5x crop factor.

Thanks for stopping by!

Been researching all over the internet for a possibility to increase my cameras field of view. I know about speed boster gear, but I just want an adapter of some sorts to make my D7100s field of view the same as a Nikon FX camera's one. I've been looking everywhere for a possibility to do that but I keep bumping into the Speed Booster things. Either I don't know what to choose, or like i've thought till now, they only make adapters for different lenses than the cameras mounted on. Any suggestions other than getting wider lenses? I'd even like my 50mm to act like on and not a 70mm. I usually work in tighter spaces and also look for the aesthetics of a wider field of view. Thanks

Hey Mike,

Good questions.

Speedboosters are good when you are adapting your lenses to another type of camera, but there isn't one to change your DX lens into an FX field of view.

So, your option is to get wider lenses. If you want a "50" you should grab the amazing and inexpensive DX 35mm f/1.8. Also, there are a number of great wide angle zooms on the market like the Nikon DX 10-24mm and some great lenses around that focal length from Tokina and Tamron as well.

Let me know if you have follow up questions. Thanks for stopping by!

I have a dilemma and I am hoping you can help me out.  I have a Canon 5D Mark III and due to the cost of a repair needed for my Canon 7D, I am going to buy a new body but I'm not for sure if I should buy the 5D Mark IV (Full Frame) or the 7D Mark II (Crop Frame).  If I were to take a picture of let's say a bird with a full frame camera, and if I import that picture into Lightroom and crop it with a 1.6 crop factor (just like that of the 7D), would the quality of that cropped image be the same as if I shot it with a crop frame?  When I travel, I use a Cotton Carrier and always have 2 bodies on me at all times (the 7D with my 70-200 f2.8L II and my 5D with either a 24-70 or 16-35).  There are times when I wish I had the 70-200 on my full frame and find myself switching lenses (I keep it on the 7D just for those shots needed of birds or other wildlife), so I am contemplating getting another full frame body.  What do you suggest?  Thank you so much for your help with this.

Hey Floyd,

That is a solid dilemma.

So, to answer the question of cropping a full-frame image versus not cropping an APS-C really depends on the image and the sensors being used. If you took a crop from a 12MP full frame camera versus a 24MP APS-C camera, you might see a reduction in quality on the full-frame image. With the same pixel density, you should have similar images. 

Before I get jumped on by the mathematicians and scientists, out there, this can all be pretty subjective and sometimes you are starting down the road of a pixel peeper here. Cropping, in general, be it film or digital, reduces the quality of the image.

I like your system with the two different bodies. And, because you are using the 7D for telephoto work and birds, it makes total sense. Having 2 full-frame cameras will be fine as well, but you have to crop to get that extra "reach." Personally, I would be tempted to stay with the different sensors...the best of both world's. But, you really can't make a bad decision here. Coin toss?

Oh, if you don't want to keep switching lenses, you can buy a 70-200 for both bodies! :)

First class explanation - I'm no expert but have attempted to explain CF to others ever since digital cameras with replaceable lenses have been on the market - thanks

Thank you, mike! I am glad this helped!

Hi Todd,

I'm confused about whether a 50mm lens for a crop sensor camera, on a crop sensor camera, will give the same image as a 50mm lens for a full-frame camera on a full-frame camera (at the same distance and with the same settings applied). I think what I'm trying to ask is, to find the true value of a lens, do you need to do the mathematical conversion for crop sensor lenses on crop sensor cameras, or just for full-frame lenses on crop sensor cameras?

Thank you for a great article -- I'm still very new to all the terminology!

Hi Hannah,

Good question. A 50mm lens for a crop sensor camera is still a 50mm lens—the number "50" refers to the focal length, not the field of view. Therefore, it will only look like a "traditional" 50mm lens if it is placed on a full-frame camera.

The "true value" of a lens, to use your terminology, is focal length and aperture. A 50mm lens is a 50mm lens when it is on a store shelf by itself, attached to a camera, or flying through the air when you toss it to a friend. Things change depending on what sized sensor you put behind it.

So, if you want the classic "50mm" field of view with a cropped sensor, you need to apply the conversion factor to the lens focal length. On Nikon DX and Fujifilm X, for instance, the 35mm lenses will give the photographer the same classic "normal" 50mm field of view. This is why Nikon makes a DX 35mm f/1.8 lens...specifically to give DX shooters the 50mm experience.

I hope this clears things up for you! Let me know if you have any follow-up questions. Thanks for stopping by!

That really helped, thank you!

You are welcome! What are you shooting?

In a few days my "50mm" buying guide will be coming out...don't tell anyone!

Hello Todd,

I know I am asking a question that you have already explained, but maybe I am working the question differently.
If I am shooting wiht a Canon 7D, which is a crop sensor, and another photographer is standing beside me with a full-frame sensor, and we both shoot the same picture at the same time of the same subject with the same size lens, will both unedited files look exactly the same, left to right, top to bottom, or will the crop sensor have an increase of magnification, if that is the right word?
The way I am reading it is that both finished files will be the same.
Thanks again,

Dan of Troy
(No relation to Helen)

Hey Dan of Troy,

I miss Helen. She was great! I'd go to war over her. answer your question: the photos will look different.

The photos taken with the 7D will look as if the photographer zoomed in on the image 1.6x. It isn't really an increase in magnification; think of it as a crop of the full-frame image that gives the appearance of magnification.

The images will look identical if the 7D (1.6x crop factor) is equipped with a 50mm lens and the full-frame camera has an 80mm lens, but if they both have the same lens, the 7D image will have a smaller angle of view, compared to that of the full-frame sensor.

I hope this clears it all up, Dan!

Let me know if you have any follow-up questions! Thanks for reading!

Hey Todd! Thanks for the information.

Just to be sure I comprehend, I am considering purchasing the Nikon 24-120mm lens for an upcoming trip. I have a basic DSLR, D3200 but it works! I've been reading that this lens could work on the camera but it may have a 'shortened' captured photo, ultimately the crop factor. Just ensuring I understand correctly that I can use this lens but my images will not be the same as i am viewing. And in order for me to capture a larger image, my distance would have to increase?

Hi Bea,

Good question! Great news for you...what you see in the viewfinder will be accurate to your image framing. On a DX camera, you are shooting a cropped section of the full-frame lens' image circle, but the DX camera only will show you that area of the lens—nothing more, nothing less. So just put the lens on and shoot what you see! Easy!

Thanks for reading! Sorry for the delay in replying...we were on break!

Hi Todd, Thanx for the article! So far it has been the best explanation I have found ;)

But I still wonder, what the big deal is? Does this mean that what you see through the viewfinder and/or the back screen, is not exactly what you will get in the picture? That would be my only concern to get a crop camera then.

If you want a wider angler, cant you just walk away from the subject? Do smaller focal length lenses, squeeze in more of the world into the 35mm film picture ratio?

I'm still a little puzzled :S

I would appretiate your feedback

enjoy your day!


Hey Daniel,

Thanks for the kind words! I am glad you enjoyed the article.

The my isn't a big deal. There are a lot of photographers that would disagree with me, and some have commented on this article! One reader (in this or another article) said that you absolutely cannot do professional work with a crop sensor camera. I hope no one tells my clients this!

So, yes, the viewfinder or LCD screen, in general, will show you the frame of the shot you are about to take (this is not true for rangefinders and full-frame cameras in crop mode).

And, yes, if you want to get further from a subject, you can just get further away...unless your back is to a cliff, a building, or a busy highway, right? Yes, lenses with shorter focal lengths provide wider fields of view...and cameras of all formats allow wide-angle shooting.

So, yes. Not a big deal...unless you over-spent on a full frame camera and you feel the need to try to feel superior in order to compensate for the overspending. 

I hope that answers your question. Let me know if you have follow-ups!

Thanks for reading!

Hey Todd!

Great article, one thing that isn't mentionned is how the crop factor affects the f/stops. And I'm having a hard time figuring it out. I have a panasonic GH4 with an Olympus 12-40mm lens with an 1:2.8 constant f/stop, which means I have an 24-80mm equivalent. But does it also mean I have a 5.6 constant f/stop?

If that is so, if I get an Aputure DEC LensRegain with a x0,75 crop factor combined with a sigma 18-35mm F/1.8 lens I will get an 27-52,5mm F/2.7?

Thank you in advance for your help!


Hey Henry,

Good question and you can read some confusion about this below in the discussion, if you want.

To answer your question, your aperture is not effected by the sensor crop factor. The aperture is determined by the size of the lens (diameter and focal length) as well as the amount that the aperture diaphragm opens. That ratio is consistent regardless of what sized sensor sits behind the lens. If crop sensor affected aperture, crop sensor cameras would have a different math for calculating exposure values and they do not. 

So, that 12-40mm lens is truly an f/2.8 lens.

Having said that, there is one thing that changes regarding crop factor and aperture—depth of field. I wont bore you with the math, but, basically, because the smaller sensor creates a different reproduction ratio for the image, an f/2.8 aperture on a crop sensor camera gives the same depth of field as a narrower lens on a full-frame camera. You can apply the 2x, 1.5x, 1.6x factor to the DOF math to get the equivalent. In summary, the f/2.8 lens on a Micro Four Thirds camera does not have the same depth of field as an f/2.8 lens on a full isn't as shallow when all other factors are the same.

[If you want to see the math:]

I am not familiar with that converter, but it may change the aperture...but not because of crop factor.

I hope this answered your question! Thanks for stopping by!

Cheers Todd, that was a brilliant answer.

Loved the math. Will not hesitate to come to you again with questions.



Cheers, Henry! Thank you very much! See you around!

Show older comments