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Ex&le of corner sharpness 80mm CF lens

H

hackum

New Member
My favorite lens is the 80mm Planar. However I never use it at f2.8
Corner sharpness is awful and the resolution in center and corners is no good.

But at 4.0 it looks amazing - sharp as tack in the corners. I was surprised to find this out after I scanned an image yesterday on a Canoscan flatbed scanner: 3.0 DMAX.

Shot at f/4.0

http://www.purelook.com/full.jpg

http://www.purelook.com/detail.jpg

Is there anyone who shoots at f2.8? Can you post some pictures please, the problem could be with my lens afterall.
 
Yes, I do shoot Planar CF 80 mm f:2,8 at f:2,8 and I can not call the results bad. Sorry, I am not able to mail any ex&les. But still, lens performance should not be the limitting factor, even at f:2,8.

Kerkko K.
 
Atanas, I use mine at f2.8 often and concur with Kerkko - very good BUT as is normal optical physics, it improves most by one stop at f4 and a bit more at f5.6, but after f5.6 (to the eye) there is no improvement that I can see at f8 and it logically drops of a bit at f11.

It's performance in this regard is exactly as one would expect.

Zeiss does not optimise performance (my view) wide open but achieves excellent performance on axis towards the field when wide open - all improving noticeably one to two stops down.

IMHO, only in Leica M lenses are there focal lengths that perform optimally wide open with no visible improvement stopped down (axis and in the field) - the legendary Apo-Telyt-M 135mm.

BUT, I cannot see from the 2 s&les where you have an issue with "no good". Maybe your ex&le has some focus or mount issues or your Canon scan has added to the lower sharpness.

IMHO (and I will stand corrected here by more knowledgeable people on scanning technology), you can only judge lens performance accurately bu looking at a slide on a light box.

So, since it concerns you, shoot slide film, process it and examine under a 5x loupe and see if you still feel there is an issue.

BUT, overall, of course you should see a noticeable improvement in image quality in the field and all the way to the edges from wide open for 1 or 2 stops.
 
Film flatness is often an issue with desk-top scanners. It's the reason there are glass mounts, fluid mounts, etc. ... it's also why an Imacon scanner uses the concept of "virtual drum" to assure film flatness, and costs 10X as much as a Canon scanner.

I have scanned Hasselblad films from the 80/2.8 and encountered no problems with edge sharpness that would warrant comment.
 
My 80mm f/2.8 Planar C T* exhibits quite visible coma in the corners wide open. This is most obvious when I have used the lens for astrophitigraphy. Bright stars in the corners appear as pincushioned triangles. Mind you, astrophotography is one of the most severe tests for a lens. I expect the results from a CF lens would be very similar.

There was an ex&le of a night photo on another discussion board where a photographer using the 80mm Planar was inquiring about the aberrations in the corner where a light was distorted. That photo was also shot at f/2.8. This is usually not an issue, as when shooting wide open, the corners usually contain images of items that are out of focus anyway.

> IMHO, only in Leica M lenses are there focal lengths that perform optimally wide open with no visible improvement stopped down (axis and in the field) - the legendary Apo-Telyt-M 135mm.

The 250mm f/5.6 Sonnar is best wide open, and maybe the longer Hasselblad/Zeiss lenses as well.

Taras
 
Those who suffer from the coma of the 80 mm lens may consider buying a 100 mm lens (and as I happen to have two of them one is FS, black C-lens with silver front ring, location Germany)

Ulrik
 
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