Last time I looked at the Pentax-M 20mm f4, the tiny, pancake like lens that's one of my favourites. It performed very well on the A7, considering its age. My other 20mm lens, the Canon FD 20mm f2.8 S.S.C, is a stop faster, but how does it stack up against the Pentax? I wouldn't do a extensive comparison in this post, because I intend to shoot them side by side in a later date.
The Canon 20mm f2.8 vignettes very heavily at f2.8, but it's still very sharp, and even the corners are very respectable. The picture below was how it came out from the RAW file. I would say at least 3 stops of light loss in the periphery. It's definitely not desirable in most situations, unless you want vignettes in the picture.
Downtown toronto - Sony A7 & Canon FD 20mm f2.8 @ f2.8. Click for larger.
But, the vignette mostly goes away by f5.6. At about f8, the lens is very sharp and the corners are relatively sharp, but not as good as the centre. I would say it's on par with the Pentax-M 20mm f4.
Very wide angle lenses are hard to control, and I am terrible at it. The fact that it captures so much information in the frame, finding a balanced composition is not an easy task to me.
Untitled - Sony A7 & Canon FD 20mm f2.8 @ f5.6. Click for larger.
Last Rays - Sony A7 & Canon FD 20mm f2.8 @ f8. Click for larger.
Sugar Beach - Sony A7 & Canon FD 20mm f2.8 @ f8.
glad to see this is a general issue with wide angle lenses and not caused by 36MP sensor's high density. I have similar issues with my OM21F3.5 lens which I feel unable to focus properly. I do much easier with my OM24F2.8 which looks extremely sharp compared to the 21mm lens. Even vignetting is similar.
ReplyDeleteI was very surprised at the amount of vignette of the lens. I guess f2.8 was considered very fast on a lens this wide.
DeleteSee Roger Cicala's two recent blog posts at lens rentals.com regarding the heretofore largely obscure glass sensor-cap thickness variable -- it matters, particularly with wide angle lenses. Yep, something else to worry about, optical adaptologists! Perhaps this factor is relevant here...
ReplyDeleteFred, I take with a pinch of salt Rogers claims. Especially when he published that stuff about adapter alignment, its just not borne out in real world testing with tilt adapters on 43rds which are even more "misaligned"
DeleteIt's true that some lenses are designed with a filter as part of its optical path.
DeleteI tried the Makinon 300mm f5.6 mirror lens with and with the rear filter and it made absolutely no difference.
Interesting, vignetting is quite strong. I am of the view that I have seen similar vignetting reported on film with FD users saying stop down to 5.6 to clear that up. My OM21f3.5 does similar at these fstops.
ReplyDeleteWith full frame one needs to be more careful with hoods too. I find that get dark corners with just a slightly longer hood.
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