explain strobe diffusers to me

[diverrick]

I am looking for a diffuser for my Inon D2000 because I can't turn it down enough for macro work, or even semi macro. I end up holding the strobe behind my head just to get it far enough away. Even at the lowest setting it bakes the picture white in the middle. I can only use manual settings so I have to fiddle with each shot to get the flash intensity correct.
I started looking for a diffuser but there are so many choices.
I was just thinking of a white diffuser but even that is broken down to -.5 and -1.5. What do those numbers mean?
Then they have all sorts of colored ones I normaly shoot in full Auto mode with the flash, and white balance in manual for natural ambient light.

 

[Warmwater Wank]

DRick--You don't mention the camera but I'd look there first, at least for the exposure problems. What ISO camera setting are you using? Go for the lowest setting you can make (80 or 100 for starters) and you'll get not only less noise but less light sensitivity. You mention you shoot in "full Auto mode" but can you choose otherwise? I would start by using Av or an aperture adjusting mode and set a high f/stop number (at least f/5.6 or f/8 on a p&s). You might look at the EXIF data on your overexposed shots and see what has been getting set previously for f/stop, ISO etc. then try alternatives.

You did mention "even at the lowest setting" you are getting over-exposure so I presume you are adjusting the strobe manually. If it is dialed to it's lowest output setting adding a diffuser is reasonable for spreading and softening the light. IA diffuser shouldn't be necessay to avoid serious overexposure though. Your camera settings need to play a bigger role here.

The diffuser numbers mentioned tell you how much light the diffusers "lose" or absorb. So, .5=1/2 stop, 1.5=1.5 stops. For a seriously over-exposed shot even the 1.5 stop loss wouldn't be enough. Sure, it would help but from the sounds of it that still wouldn't fix things.

Post your camera type and a better solution can be offered for adjusting exposure but for now, I'd say lose the Auto mode if possible and set the ISO as low as you can. // ww

 

[Warren_L]

I'd agree with Wank on this - it sounds like a settings problem. Adding a diffuser isn't likely to reduce the strobe output significant enough to solve your problem if your images are consistently over exposed. Half a stop maybe?

One interim solution may be to keep turning the strobe outwards until you reach a point where the lighting is reasonable. As you reach the edge of the strobe beam, the intensity lessens you as you catch the fringe of the strobe light, it should reduce the amount of strobe light caught in your shot. This wouldn't be a permanent solution, but it may work in the meantime.

 

[diverrick]

Fuji F810 with a optical cable to the strobe, not TTL. Not all pics come out OE, just the ones where I am trying to get a close up, such as less than two feet. The strobe lights up the center,sometiimes too much but the edges are darker I manually turn the strobe down to adjust the flash intensity, but sometimes it is not enough or the spotlight effect is still present though the illuminated sections are perfect, it is not uniform

 

[Warmwater Wank]

Ok, so the F810 has aperture priority. It still will auto adjust shutter speeds in that mode but for now that's not critical. You'll control the exposure much better by setting a higher f/stop--and the camera does go to f/8 so this should get solved easily enough.

With strobe exposures you are up against the inverse square law, meaning it will be signicantly brighter the closer you get. Thats why you have more problems in close. Start at f/8 and see what happens, check your camera manual if you aren't familiar w/ using Aperture Priority AE mode.

The shutter speeds will affect the background and areas not hit by the strobe but, in close, they won't really affect the strobe lit areas. You may still need or want a diffuser, they do help avoid hot spots by softening and spreading the light, but I'd lean toward the -.5 (1/2 stop loss) vs the -1.5 (1.5 stops) diffuser. When you have a way to reduce the exposures using the camera controls why lose the output of the strobe by an extra stop? (One stop meaning cutting the exposure in half in this case.) Just my opinion on the diffuser choice. Chances are when you get the exposures more correct the "hot spot" will be less objectionable.

Check out a couple topside test shots in macro and see what you think. (Just 1 or 2 shots, don't overheat the strobe above water!) Check back in when you've had a chance to mess with all this--and good luck! // ww

 

[bvanant]

I would start with the Inon diffuser (it should have come with your strobe) at the 0.5 setting. This diffuser will eliminate much of the hotspot from the strobe. Set up something to shoot macro on your kitchen table and take a bunch of pics of that with the strobe at various powers. Make sure that you are using the appropriate f stop on the camera i.e. the smallest one (biggest number). Let us know how that goes.
Bill

 

[Wisnu]

If you set properly, should not have any problem even if the distance is only few inch.
I'm not familiar w/ Fuji F810, I use D2000 with G9. You can try in the pool, say set a full manual, F8, 1/500, iso 100, macro on, adjust strobe manually until you happy. Make a note about strobe power vs distance. Once familiar, will be easy.
If you feel the lighting is too harsh you can make your own diffuser from milk plastic bottle or (new) thick white condom.

 

[diverrick]

I'll try some of those adjustments. My strobe never came with any diffusers.
If I use the -1.5 instead of the -.5 won't that just make me turn up the strobe a few more stops to compensate?
I was taught that on auto settings the camera will make all the adjustments for me, but I will try using the Manual F stop (AP) adjustments and let the camera set the shutter speed.

I was told that I had to use all the lenses under water to make them work properly. I guess I can not use any lenses for these tests.
What is the difference about all the different colors? I was struck that must be for above water use, as the last thing I need is more blue under water.

And Just a quick other question, seeing as I seem to have found someone who knows something about U/W cameras, How can I attach my two extra lenses to my strobe mount base or elswhere? I hate carrying them in my BC pockets too much hassle, to much chance of loosing them, covers float off while fumbling with installation etc. I have yet to find anything online that would work.

 

[Warmwater Wank]

The critical thing here is to set the highest f/stop number you can (F/8 or f/8.4 depending on where you are zoomed). Once you do that I doubt you would need to dial down the strobe all the way, even when close up. If you run your tests and feel like you still want to lose more light, then yes, you are correct. The -1.5 diffuser loses a full stop more light than the -.5. Run the tests first though.

For the testing you are only checking for the exposure, not trying to make a sharp picture so you don't need the aux. lenses on. (You don't mention which lenses you have but you can Google "lens caddy" and probably you'll see what you need for securing them to your tray set.) I'd use a smooth toned wall or similiar for the test exposures so you can see how even the coverage is. Approximate the distance where you have encountered the over-exposure previously and try a few shots as discussed. When you get back UW you'll need to tweak the exposure perhaps but you should have a reasonable strobe adjustment range to do that with.

Inon sells their diffusers as an accessory, I don't believe they toss them in for free. These other filters you mentioned are not needed, you can adjust the color balance later fairly easily using the post-processing software that came w/ your Fuji. You may want to tell whomever sold you the color filters about Wisnu's "one size fits all" stretchable diffuser solution--but I leave that to you... ww

 

[diverrick]

Cool Thanks for all the info.