RonFrank
Contributor
catherine96821:yea. I am having to buy the 400+ 8" dome port for my new 10.5 fish eye and unfortunately, I already have three other dome ports so the fact that the new pricey
8" works for them all doesn't really help soften the blow of the price. I wish I could see images from the 6" next to the 8" with the 10.5 to see the edges and the amount of distortion. Everyone is telling me there is no comparison for doing split images with the 8 VS the 6, so guess I will bite the bullet after 15th. I love split images so...
I hear exposure under/over is tricky. Ron, I need you to figure all this out, so I can ask you!
Catherine,
You may want to hold off on the 8" dome port, and see the results of the smallest 6" you have first. I'm guess you will get vingetting, but the question is how much, and do you care. If you change the image from a fisheye to a standard perspective, you crop in any event.
As for over/under, I know in *theory* how to accomplish it. There is really only one way, and than adding a strobe as a variable if desired
You never want to overexposure a digital image, so you will need to take a reading topside, and use that. Say it reads with 1/250 ISO 100 @ f8. So you can use that for the exposure. If the UW exposure is underexposed you can either mask it in PS, and brighten the UW section, or attempt to up the overall exposure RAW, and play with the shadow/highlights to see if that helps.
The only other thing one can do (other than using graduated nuteral density filters, which may not even be possible) is to add some flash to the UW exposure. This will only impact the stuff within the flash range, but it likely would not hurt to try. You would have to position the strobe UW, which would make this whole thing tricky.
The good news is that if the topside exposure is at value X, then the water is lighted by the same lighting, and should only have slightly less exposure. These would likely work best where you have subject matter to shoot in the first few feet of water, so a shallow reef for example.
L8R,