To Diffuse or Not?

[Ardy]

This was such a silly question to me up until recently. Of course you use a diffuser! but as I have just bought a YS-D1 with a guide # of 32 I am wondering if I can shoot those fish that were always an f-stop too far.

Prior to about 10 years ago I always used a large flash without a diffuser and I could photograph fish and macro stuff easily and never gave a diffuser much thought. As soon as I went to a digital setup and bought a new SnS 110a with a diffuser I put it on straight away and assumed it would improve light spread therefore it was needed. Same with the Inon 240z, but I had problems getting enough light to get that great fish shot 2m+ away.

Anyone done any testing of flashes without diffusers? Or any thoughts about the impacts? Are the newer flashes with smaller tubes more likely to create a 'hot spot' and how significant is it anyway?

 

[Steve_C]

I have a different camera with a sealife digital pro flash. Diffuser really helps with fish that have highly reflective scales and similar targets.

 

[bvanant]

Sure you can get a bit further away for that fish, but you could also either open up your f:stop or you could up your ISO. The GN for the D1 is 32 on land and approximately 10 in the water without the diffuser and is 24 on land and approximately 8 under water. Remember that GN = Distance x f:stop. So for a GN of 10 and a distance of 2 meters, you need to shoot at f5 while for GN 8 (with diffuser) and a distance of 2 meters you need to shoot at f 4. Not such a big difference. All of this at ISO 100. Going to Iso 200 means one stop better for each etc.

Bill

 

[Ardy]

Sure you can get a bit further away for that fish, but you could also either open up your f:stop or you could up your ISO. The GN for the D1 is 32 on land and approximately 10 in the water without the diffuser and is 24 on land and approximately 8 under water. Remember that GN = Distance x f:stop. So for a GN of 10 and a distance of 2 meters, you need to shoot at f5 while for GN 8 (with diffuser) and a distance of 2 meters you need to shoot at f 4. Not such a big difference. All of this at ISO 100. Going to Iso 200 means one stop better for each etc.

Bill

Hi Bill thanks for the post - I am assuming over 2m and I normally set my ISO to 200. I know I can slow the shutter down to 1/40th or maybe a bit less, I normally shoot in manual.

So if I read you correctly the diffuser (100) drops one f-stop. Is that correct? So as the YS-D1 is ± one stop higher than the Z240, it should be a net improvement.

 

[rob1967]

Hi Bill thanks for the post - I am assuming over 2m and I normally set my ISO to 200. I know I can slow the shutter down to 1/40th or maybe a bit less, I normally shoot in manual.

So if I read you correctly the diffuser (100) drops one f-stop. Is that correct? So as the YS-D1 is ± one stop higher than the Z240, it should be a net improvement.

It is important to keep in mind that slowing down your shutter is only going to increase the ambient light in the shot without affecting the exposure from your strobe, as your strobe is much shorter than your shutter speed, on the order of 1/2000 of a second or less. Generally speaking, you will want a fast shutter (say 1/200 or faster) so that most (if not all) your light is coming from your strobe. You generally don't really need strong strobes (unless shooting wide-angle SLR in daytime), because as Bill points out, you can always open up your aperture or increase your ISO to give your strobes more reach. But the fall-off from your strobes is even more pronounced underwater than on land, so generally you will want to be closer than 2 m to your subject.

Generally it is better to leave the diffusers on, as you only lose one stop of light, but the quality of the light is improved (softened).

 

[AZTinman]

When I first started shooting underwater, I seldom used the diffusers on my strobes. I've got a lot of early photos that have 'hot spots' from the strobes. Eventually, I decided to experiment with the diffusers. Now, I seldom remove the diffusers. I like the lighting effects with the diffusers much better.

-AZTinman

 

[KeithG]

i do not use diffusers. in the early days of my TTL life i tried them a couple of times but did not notice any change.

i now shoot manual only and do not even think about diffusers. my macro shots seem fine and i want more light for shots further away. i see no need for a diffuser.

i use a pair of S&S YS110 on wired sync cords with a canon G16.

 

[bvanant]

There is a lot of info/speculation going on here. On the Z240 vs. D1 info, yes the D1 has a GN one stop better than the Z240 but the Z240 native (without diffuser) beam angle is wider so if you use the D1 and the Z240 with the same beam angle the powers are mostly indistinguishable since the 1 stop d1 diffuser gets to the same beam angle as the Z240 with no diffuser. In general shutter speed has NO effect on strobe illumination since the strobe is on for say 1/1000 sec or less. That being said, shutter speed is your "dial a blue" control, it generally sets the background color, fast shutter is black, slow shutter is bluer etc. Also most modern cameras are so good at Higher ISO that we should all think of changing ISO to shoot further away stuff allowing us to keep control of DOF by not changing aperture.

Bill

 

[Ardy]

There is a lot of info/speculation going on here. On the Z240 vs. D1 info, yes the D1 has a GN one stop better than the Z240 but the Z240 native (without diffuser) beam angle is wider so if you use the D1 and the Z240 with the same beam angle the powers are mostly indistinguishable since the 1 stop d1 diffuser gets to the same beam angle as the Z240 with no diffuser. In general shutter speed has NO effect on strobe illumination since the strobe is on for say 1/1000 sec or less. That being said, shutter speed is your "dial a blue" control, it generally sets the background color, fast shutter is black, slow shutter is bluer etc. Also most modern cameras are so good at Higher ISO that we should all think of changing ISO to shoot further away stuff allowing us to keep control of DOF by not changing aperture.

Bill

HI Bill - I am now wondering what ISO I should be using. Having come from film I was always looking for the lowest ISO (currently 100) but I have moved to 200 in the last couple of years. Are you suggesting that the quality would be excellent even at 400 ISO on my Oly EM5? I get so little diving in these days that I do take things a bit conservatively as I don't want to up my ISO and find the dive was a loss in Photographic terms.

I will take a dive without the diffusers to see what difference there is but that won't be until Sept/Oct which will be my next dive trip to Bali. Only get 2 trips a year and try to make the most of them. Can't stand cold water diving anymore!

 

[bvanant]

I routinely shoot at ISO 800, with excellent results.
Bill