On 9/11/2025 at 6:23 PM, Nemrod said:

I do not know. I do not see any difference in my limited trials turning that power knob in HSS using the Retra board switch position. I do see that the Backscatter HF-1 only has one power setting in HSS and I suspect the same here with the Apollo S, excerpt from HF-1 manual attached. I have the Apollo manual and I do not see this addressed therein. I think I am beginning to understand HSS.

I wish I had read this thread more closely earlier, as I wasn't aware of the single power setting. I went to try HSS with my HF-1's and UWT trigger today using f1.8 on a lens I'm testing. I set my ISO to 100 and shutter speed up high. The strobe completely overexposed the shot. I turned the power knob all the way down and it did not seem to have any effect. Next I began turning the shutter speed way up. This is a shot at 1/4000s. Turning the shutter speed up this high kind of works, but you can see all the horizontal flash lines in the shot if you look closely. I'm disappointed that the HF-1 'kind of' supports HSS with the UWT :(

11 minutes ago, JayceeB said:

I wish I had read this thread more closely earlier, as I wasn't aware of the single power setting. I went to try HSS with my HF-1's and UWT trigger today using f1.8 on a lens I'm testing. I set my ISO to 100 and shutter speed up high. The strobe completely overexposed the shot. I turned the power knob all the way down and it did not seem to have any effect. Next I began turning the shutter speed way up. This is a shot at 1/4000s. Turning the shutter speed up this high kind of works, but you can see all the horizontal flash lines in the shot if you look closely. I'm disappointed that the HF-1 'kind of' supports HSS with the UWT :(

I would expect you would need to play every card to try to use this strobe under the conditions you are mentioning, You should be able to to ISO 50 I think and perhaps you need to close down a stop on your lens? You could also try reducing output using the widest angle diffuser on the strobe. This is a downside of using a very powerful strobe, it's harder to turn down.

I would guess that what the strobe is doing is running at a set frequency for the duration the shutter is open and probably does that so it can work with any HSS system as the HSS protocols are likely different for each camera manufacturer.

On 8/29/2025 at 9:49 AM, Nemrod said:

... the Retra strobe with HSS selected at position 9.

If you mean TTL Converter switch position 9, - this is a mistaken choice.

Check the User Manual for TTL Converter: https://drive.google.com/file/d/1IpmCU-Ei8IeeApRnpLnTrDu8gVBUIzw9/view

There are three positions for HSS strobes:

Position '2" - for Apollo-III.

Position "3"- for Apollo-S,

Position "7" - for Retra Pro MAX.

Edited 15 hours ago15 hr by Pavel Kolpakov

1 hour ago, Chris Ross said:

I would expect you would need to play every card to try to use this strobe under the conditions you are mentioning, You should be able to to ISO 50 I think and perhaps you need to close down a stop on your lens? You could also try reducing output using the widest angle diffuser on the strobe. This is a downside of using a very powerful strobe, it's harder to turn down.

Lowest ISO on the Canon R5 is 100. I have a set of MF-2's I'm going to test out tomorrow with HSS. I'm assuming they use a single default power level too, but it should be much lower than the HF-1's. Thanks for the diffuser option, I hadn't considered that.

22 minutes ago, JayceeB said:

Lowest ISO on the Canon R5 is 100. I have a set of MF-2's I'm going to test out tomorrow with HSS. I'm assuming they use a single default power level too, but it should be much lower than the HF-1's. Thanks for the diffuser option, I hadn't considered that.

You should be able to access ISO 50 - it's called extended ISO, by default the camera goes to ISO 100, but enabling extended ISO alllows one stop lower and one stop higher to accessed, you need to menu dive to enable it. This video explains:

Going to ISO 50 will reduce dynamic range slightly but it might be worth trying it out - in most cases UW you don't need very wide dynamic range.

The MF-2 would also be worth trying out.

Thanks @Chris Ross for the information that I can go to ISO50 with my R5... I was somtetime blocked Many thanks