June 27th, 2006, 09:12 PM
Iím looking for a super wide angle with no barrel distortion (Nikon mount), was thinking of going for the Sigma 20mm f1.8. Does anyone have experience with one of these on an adapter? Does it vignette badly? Will I be able to control the aperture manually?
I had a look at the 14mm Tamron in the shop and it looked awesome through an SLR but itís f2.8 so I think it will vignette and be no good for available light indoors (didn't have adapter with me and it was more than I wanted to spend anyway).
Is there a super wide angle camcorder adapter without barrel distortion that someone can recommend (i.e. bypass 35mm adapter)?
June 28th, 2006, 01:46 AM
As for the Sigma 20mm f1.8 yes you will be able to control the aperture straight from the lens barrel and as far as I know all those modern, Sigma wide primes have non-vignetting optical construction, in order to obtain adequate peripheral brightness with open aperture.
Another good thing about those Sigma bright wide primes is that they can obtain focus from very close distance that is a good thing specially for UWA lens.
One thing to mention is that Sigma QC varies so sometimes some lenses are not as good as others.
BTW vignetting depends on adapter design too. For example focusing screens with frensel lens on the other side vignette sometimes with some wide lenses.
June 28th, 2006, 02:32 AM
Thanks for the info, yes obviously the adapter design influences vignetting I really meant relative to say a 50mm lens that doesn't vignette on the same adapter. For example I have no vignette on my 50mm f1.2 but I do have some on my 24mm f2.8.
June 28th, 2006, 05:46 AM
I am using a 28mm wide image off the groundglass for a 16:9 frame.The width is limited by my prism path. I get some reflection artifacts from the prisms if I go the full 30mm wide.
Groundglass is finished with 5 micron aluminium oxide.
Lenses tested as good are :-
f2.8 14mm Sigma. (Seems slightly softer wide-open).
f1.8 20mm Sigma.
f1.8 28mm Sigma.
f2.8 20mm - 35mm Tokina.
f1.8 50mm Nikon.
f1.8 85mm Nikon. (the best for sharpness).
f1.8 105mm Nikon.
f2.8 135mm Tamron Adaptamatic.
Usable with some issues.
f8 500mm Nikon mirror telephoto. (soft).
f10.5 1084mm MTO mirror telephoto. (soft).
Usable with some flicker problems in high contrast outdoors.
f4 12mm - 24mm Nikon.
Usable with a little brightness falloff in corners.
f4 - f5.6 50mm - 500mm Sigma.
f3.5 55mm Micro-Nikkor.
The full frame lenses which are optimised for digital SLRs seem to have an added benefit. This"optimisation" is apparently some optical process which causes the angle of incidence of the light from the optimised lenses to fall onto the imaging sensor at a less acute angle which apparently leads to less edge falloff in brightness.
In "magic hour" lighting conditions, the f2.8 Sigma 14mm lens aperture can be closed to f11 before some groundglass artifacts and edge falloff become a problem.