Interfit S1a 500Ws HSS TTL AC Powered Monolight

Interfit S1a 500Ws HSS TTL AC Powered Monolight
Key Features
  • Optional Transmitter for Canon/Nikon TTL
  • AC Power
  • 300' Wireless Range
  • High-Speed Sync to 1/8000 Sec
Interfit joins the wave of manufacturers producing studio-quality TTL flash heads with the introduction of the S1a 500Ws HSS TTL AC Powered Monolight.
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Interfit S1a Overview

  • 1Description
  • 2Compatibility and Firmware Updates
  • 3S1a TTL Remote
  • 4Power Supply
  • 5Shooting Modes
  • 6Manual Mode and High-Speed Sync
  • 7IGBT

Interfit joins the wave of manufacturers producing studio-quality TTL flash heads with the introduction of the S1a 500Ws HSS TTL AC Powered Monolight.

The S1a has 3 shooting modes: Wireless TTL for Canon or Nikon, Manual Mode, and High-Speed Sync. Wireless requires purchase of a Nikon or Canon dedicated transmitter, but once that's done, you can basically treat these studio strobe units as you would your on-camera flash. In TTL, the camera's flash technology takes stock of the scene and automatically adjusts the power from 7.8 to 500Ws across a 7-stop range. If you want to fine tune your exposure, there's +/- 3 stops exposure compensation adjustable in 1/3 stops, and you can do it all at distances up to 328' thanks to the S1a's built in radio receiver.

Traditional manual mode is also available for those who want complete control. Manual mode is also how you access HSS (High-Speed Sync). This mode uses the flash's top 4 power levels (from 62.5 to 500Ws) to allow you to access sync speeds as short as 1/8,000. HSS presents a new world of exposure possibilities whether you're trying to overpower the sun, control the background's brightness or use wider apertures.

The S1a recycles to full power in 3 seconds and a fraction of that time at reduced power levels. Thanks to the incorporation of IGBT technology, the flash can also reach flash durations as short as 1/9000 sec. for the ultimate in stop-action while still maintaining a steady 5700K color temperature. The S1a includes a 7" Bowens S-Type reflector, AC power adapter and a mini USB cable for firmware upgrades.

Compatibility and Firmware Updates

In order to ensure maximum compatibility with your system, Interfit offers firmware updates for download on their website. These updates can be easily installed by the user by connecting the monolight to their computer over USB.

S1a TTL Remote

The S1a's TTL remotes give the users direct control over any S1 light in any shooting mode from the camera position. This camera-mounted transmitter is available for both Canon and Nikon cameras and supports E-TTL II and i-TTL protocols. Having three individual groups gives users the freedom to control lights individually to create dynamic lighting ratios with a working range of up to 300' (100 m).

Power Supply

The S1a ships with an AC power pack (adapter). This multi-voltage (100-240VAC) adapter can be used anywhere in the world.

Shooting Modes

The S1 has three different shooting modes, each to serve a different purpose and shooting style. Interfit's S1 Remote for Canon or Nikon enables photographers to take advantage of their camera's TTL system just like they would with a speedlight. This automated light output uses the S1a's entire 7 stop power range (500 - 7.8Ws), automatically calculating the light in 1/10th stop increments and allowing for +/- 3 stops of exposure compensation

Manual Mode and High-Speed Sync

For those that prefer to have complete control over their light and have time for fine-tuned adjustments, the S1a can be used in the traditional manual mode. Manual shooting mode also utilizes the entire 7-stop power range, controllable in 1/10th stop increments. While in manual mode, users gain access to the S1a's High Speed Sync mode, reaching shutter speeds up to 1/8000th of a second. High-Speed Sync mode utilizes the top 4 stops in the power range (500Ws - 62.5Ws) and is manually adjustable in 1/3 stop increments


Utilizing IGBT technology, the S1a is able to offer short flash durations while maintaining color accuracy throughout the power range. Flash duration ranges from 1/1000 at full power, down to 1/9000 at minimum power. While shortening the flash durations, Interfit was also able to improve color accuracy, giving the S1a a consistent 5700K (+/-100K) color temperature throughout the entire power range

Interfit S1a Specs

Flash Head
Maximum Power500 Ws
Power Control7 Stops in 1/10-Stop Increments
Guide Number160' / 48.7 m at 9.8' / 3 m, ISO100
Flash Duration1/9000 to 1/1000 Sec
Recycle Time3 Sec (Full Power)
Color Temperature5700K ± 100K
Accessory Fitting TypeBowens S Type
Modeling Light
Wattage10 W
Control ModesFull On, Off
Sync TypeCable, Infrared, Optical, Radio
Sync Speed1/1/250 Sec
1/1/8000 Sec (High-Speed)
Wireless Frequency Bands2.4 GHz
Wireless Range328' / 100 m (Radio)
Auto DumpYes
Fan CooledYes
Dimensionsø: 5.1 x L: 12.6" / ø: 13.0 x L: 32.0 cm, Including Handle
Weight4.9 lb / 2.25 kg
Packaging Info
Package Weight7.9 lb
Box Dimensions (LxWxH)18.1 x 11.3 x 10.2"
See any errors on this page? Let us know


does this come with a remote trigger?

does this come with a remote trigger?
Asked by: James
Unfortunately, a transmitter is not included since they are camera dependent. Here is a list of compatible transmitters.
Answered by: Kirk
Date published: 2019-01-08


Anyone tried HSS with Buff cybercommander remote? I really only need to fire the strobe, not control it. Only outdoor action shots with Canon 5D miii and 5D mIV. Cant believe that Paul C Buff has turned their backs on the need for HSS.
Asked by: Sean
I havent tried with that remote but with others it has fired. For the extra $99... totally worth it. I have five !
Answered by: Anonymous
Date published: 2018-10-24


The box of the flash and the specs says that it's multivoltage - but the case if the actual flash says 110/120volts has anyone tried them with 220volts
Asked by: matias p.
I have not tried them for 220. There is a pretty hefty transformer in the direct feed system. It is supplied with a 110 cord and plug. It may well be supplied with a 220 cord and plug where appropriate. interfit has a good support line you can call or email. They are happy to answer questions.
Answered by: jeffrey l.
Date published: 2018-08-26


Will my Canon ST-E3-RT remote controller trigger this flash or do I need to buy interfitS1 TTL remote controller?
Asked by: Zia
No, the Canon ST-E3-RT will not control the S1. In order to have the remote power control, TTL functionality and HSS functionality, you must use the Interfit S1 TTL remote.
Answered by: Steven S. Interfit Expert
Date published: 2018-08-26


Will HSS functionality on this strobe work only in conjunction with Interfit S1 TTL remote controller or can I use any generic radio controller? Description says HSS works only in manual mode. So what is the point to buy TTL controller? Main reason For me to buy this is HSS.
Asked by: Zia
TTL and HSS can only be achieved using the Interfit S1 TTL remotes.
Answered by: Steven S. Interfit Expert
Date published: 2018-08-26


Can you change modes(ttl,manual,hss, ect) on the flashhead or only via remote?
Asked by: kevin t.
You must have the Interfit S1 remote to switch between HSS, manual, and TTL modes.
Answered by: Steven S. Interfit Expert
Date published: 2018-08-26


Can The Vagabond Extreme Lithium Battery power these? I have one and Im curious if these will give it enough power.
Asked by: Anonymous
From our understanding, the Vagabond Extreme would power a strobe up to 3200 W/s. However, there are no tests that we are aware of that confirm the compatibility between both units. Your results may vary.
Answered by: Kirk R.
Date published: 2018-08-26
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