How compensate the loss with diffuser?

Using a Nikon D50 and Ike DS-50´s, I wonder how can I try to compensate the loss of 1 f-stop using a flash diffuser? settings? What everybody does? I search thru wetpixel but so far i found everybody use the diffuser but nothing about what settings changes you should do....

one option would be to increase the ISO and see if you can accept the potential affect it may have with the potential increase in noise.

example........ISO 200 without inclusion of 1 stop diffuser is equivalent to ISO 400 with 1 stop diffuser installed.

One other point, this increase in ISO will also have an effect on the background exposure.......

Generally speaking, the strobe illuminates the foreground (influenced by strobe power, aperture, and ISO) and ambient light illuminates the background (influenced by aperture, shutter speed, and ISO). Since the diffuser only influences the strobe power, it's inclusion has no effect on the background exposure. But by increasing the ISO to compensate for the loss of strobe output and its subsequent effect on the foreground exposure, the background exposure will also be increased. To offset the increase in sensitivity, the shutter speed may be increased (say from 1/100 to 1/200) to compensate. Increase of shutter speed will have no effect on foreground exposure as long as speed chosen is within the sync speed capabilities of the camera.

hth,

b

theoretically speaking, can I increase the EV to compensate for strobe diffuser?

theoretically speaking, can I increase the EV to compensate for strobe diffuser?

Do you mean the EV on the strobe or the camera?

What mode are you shooting in? The EV (on the camera) setting is only relevant in the auto modes P,A,S, and all the scene modes. Basically what it does is add or subtract a stop of exposure to what the meter suggests is the correct exposure for every EV you dial in. How it accomplishes this depends on what mode you are in. In A mode for example shutter speed is the independant variable and so it bumps down the shutter speed.

I would reccommend shooting in full manual mode M. In this case your four exposure variables should be used as follows.

Aperture: controls the depth of field you want in your photograph. Choose small apertures (large F#) to include all the background, large aperture for subject isolation. Very small apertures can make the background go black for normal shutter speeds (1/125-1/250). Increasing this will affect both the foreground and the background even with flash.

Shutter speed: Set to get the color of blue background water you want in your photo. Faster shutter speeds make the backround darker. Increasing shutter open time this only affects the background exposure assuming you are using flash because it takes a LONG exposure to equal the light from the strobes in 1/500 a second.

Strobe power: Controls the foreground exposure. for 1-about 8 ft max (probably 3 ft with the DS50). Adjust the power once you have fixed the two above to get the exposure you want. Increasing this will only affect the foreground.

ISO: adjust this to minimize noise to a level you can live with. Increasing this will affect both the foreground and the background.

So, if you want to increase the foreground exposure over a wider area with a narrow beam DS50 you could use the diffuser. Then you need to adjust the strobe power accordingly to compensate for the 1 stop loss of light. Usually this isn't a problem. You just dial in more with the strobe 10 step EV controller. Most shooting is in the midrange so there is usually some headroom.

If this isn't enough, then you could bump up the ISO and increase the shutter speed (faster, less light) so that you have re-balanced the background. ISO 400-800 is still fine with this camera.

You just dial in more with the strobe 10 step EV controller.

Can I do it with the iTTL controller in the ike housing? or this are 2 different things?

Ok, so if you have a TTL housing you don't need to do anything. The flash will fire its pre-flash, calculate how much flash it needs to give based on how much light it sees in the frame and fire accordingly. You don't need to know anything its all automatic. The flash doesn't know or care that there is a diffuser there. With TTL its all trial and error happenning automatically inside the camera at a fraction of a second.

If you are unhappy with the exposure you are getting, try adding some Flash Exposure Compensation (FEC) by pressing the +/- on the back of the housing in TTL mode. In this case it will measure what it thinks is the proper exposure and then add or subtract however many stops you have dialed in. So its like semi-auto. You have just calibrated it above or below what it thinks is right.

Now the DS50 is already a little strobe. It should work great for macro. You probably won't want the diffuser here. But may be a bit underpowered for wide angle. Adding the diffuser will broaden the beam and make it better for wide angle. If you find that even with max FEC you aren't getting good enough color in the foreground (and you are shooting less than 3' away!) then you should try to bump up the ISO and dial up the shutter speed. If that doesn't work the only solution is bigger strobes.

Remember no strobe will shoot more than about 8' into the water. So the most important advice is to get close.

Good Luck!