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Paul Kay

Acceptable sharpness with wide-angles

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"My guess is the Nik 15mm would hold up pretty well on a FF sensor, if there was way to jury-rig one, but maybe there are other issues"

 

The sensors fitted to current dSLRs work best when struk by light as perpendicular to their surfaces as possible - which means that wide-angle lenses need to be of retrofocus design (in theory the latest Nikon lenses are - but there are no ultrawide (weitwinkel) fixed primes of say 12mm focal length so users are stuck with slower zooms so far). The Nikonos 15mm (even the later version) was not a substantially retrofocus design so the light paths would have neen very oblique in the corners - hence why it would probably not be a good lens for digital.

 

Leica's new M8 uses a sensor designed to work better with more obliqe light and if someone was enthusiastic enough it might be possible to use it with the Nikonos 15mm - that would be a very interesting idea BUT with a 1.3x sensor crop..... back to square one!

 

If we are lucky in the future sensors might be better designed for wide-angle lens work and have a higher dynamic range - rather than simply more pixels. But they cannot overcome the inherent problems with using simple domes underwater.

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how about a ultra wide (weitwinkel) lens (maybe the 15mmUW-Nikkor) on a FF sensor array that is laid down on the inside of a sphere rather than a flat surface as they are now. Sure it might only be good for the one wide lens, but hey, it might be sharp!

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Sounds like we're getting to the heart of the matter here. The Nikonos 15mm is a perfectly matched system where the main optic is designed to handle a curved virtual image from the dome. The only SLR lenses we have available that do this are the fisheyes.

 

You'd have a job fitting the 15mm Nikonos to an SLR, because of the short retrofocal distance. Bonk, bonk! There's the mirror. Same with most wideangle rangefinder lenses. See how the rear element sticks out:

uw15e.jpg

 

Yes, the 15mm is the same FOV as a 20mm housed topside lens, 94 degrees. By 20mm on a FF SLR we're getting back into sharp corner territory. Of course the upsides of the housed lens include the ability to do split level shots and being attached to a DSLR, providing immediate feedback, more than 36 shots, autofocus and all that good stuff.

 

Leica have done valuable work with their offset microlenses, but of course they had a bigger problem than the DSLR guys to start off with, namely a more extreme angle of incidence at the edge of the frame. Vignetting is largely a none issue for a FF DSLR like the 5D. If it deemed undesirable, it can be removed very easily at the RAW conversion stage.

 

 

Martyn

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