Thanks Alex. That's helpful. What's your preferred extension ring, same as you used previously?
Hey Jeff, these are with Subal FE2 port and ext ring. I haven't actually had time to go through all the test images, yet, once I do I let you know which ext ring dioptre combo is best. But actually my aim was to determine acceptable limits in various configs. I took close to 100 images (3 domes, 3 ext rings, 3 dioptre options, range of apertures means a lot of variables).
A very nice comparison of the 17-35mm lens with and without diopters. So interesting that I'll have to do a similar set of tests with my own Seacam domes.
I think it might also be interesting to see center sharpness comparisons of the same shots so we can see how much (if any) sharpness is lost to the center of the image by adding the diopter to the prime lens.
Hi Fred, I used 3 domes, but the shots above (and below) these were taken with the Subal FE2 dome - usually referred to as a 8" dome. Considerably smaller than Seacam superdome.
Here are the centre frame details from the same shots. All F5.6. The no dioptre case is perhaps marginally sharper - although it may just be a bit brighter (i shot on auto exposure in the failing light) - these are totally unprocessed crops from the NEFs. These images are the same scale (100%) as the ones above - and the size of the tiles shows the pincushion distortion from the dioptres (bigger tiles at edge of frame, the examples above). But the main observation is the drop off in sharpness at edge of frame with no dioptre (top image above vs top image here).
We have 2 Seacam shooters in our group here. I shot the Superdome and Canon 16-35mm Mk2 in the pool (no dioptre) earlier in the week. I don't have the files, but it seemed to be pretty good in the corners without a dioptre when stopped down. At F2.8 - even through the viewfinder the corners were clearly blurred.
I agree on the need to go shooting rather than worrying too much about these things - which is exactly what I intend to do now. The squid are waiting!