Depth of field on Zeiss 28mm/F2.8

oliverks

New Member
I have a 28mm F2.8 and a 50mm F1.4 lens on a Contax Aria. When I shoot film, I scan the negatives or slides at 4000 DPI. With B&W film, and the 50mm lens, I find the images are sharp even at the edges at 4000 DPI. As such I think my setup is working reasonably well. Both lenses were bought new through a reputable supplier.

My problem is with the 28 mm lens. I have several issues with it.
1) I find it hard to focus. The focus seems very soft, so I have trouble telling whether it is in focus or not in the view finder. I don't have this problem with the 50mm lens. As a disclaimer I should add I don't have the best eyesight, but I have no trouble focusing an F4 80-210 zoom lens with the camera.
2) The depth of field is less than I would expect for a short focal length lens, and certainly has no relationship to the markings on the barrel.
3) I have started focusing slightly before infinity with the lens even for distant objects. I find this produces better results.

I typically shoot between f5.6 to F11, as the performance of the lens suffers even more outside of this range.

The scanned images at 4000 DPI are never tack sharp, but can be good sometimes. Certainly nothing in comparision to the 50mm lens.

I have a 2 part question
Is this normal for the 28mm lens?
If not what might be wrong with the lens and how do I check it?

Thanks in advance

Oliver
 
J

jeter

Hello, Oliver,

In my opinion, your lens is probably in normal condition. I too have recently purchased the Aria and the same two lenses. All wide-angle lenses tend to be more difficult to focus because the image inside the viewfinder is so small, unless you are photographing objects very nearby. I find the 28/2.8 more difficult to focus than the 50/1.4 because of the 2-stop-darker view. For indoor, ordinary flash photography, I have been stopping-down to f8 in order to accommodate any focussing difficulties I might have when presented with moving subjects.

My eyesight is approximately 1/2-diopter off what the viewfinder offers me, so my focusing there is also compromised slightly. You should use a diopter-adjustment accessory lens or experiment with using your eyeglasses or not. I find that using a plain or grid screen is more reliable than the split/prism types.

If your photography is slow-paced, use a tripod or monopod and try a viewfinder magnifier.

Ensure that your testing methodolgy is strict. But weight your results on the "finished product" image, not so much on your lab testing.

The depth of field scale probably is not usable for enlargements past 5x7, in the context of print viewing. But sharpness is highly interdependent on many factors!! Read more about that elsewhere. I do not own a film scanner, so I cannot delve into using a scanner and how that affects what you are seeing in regards to sharpness.

Be sure to read Kornelius's lens PDFs at the Zeiss Web site, and search this and other sites in regard to sharpness of 28-mm or wider lenses.

The CZ 50-mm lens is one of the sharpest of all, and the 28 is not far behind, at least for most practical purposes.

You could ship your lens to Zeiss for testing, but you might first reconsider your situation further, such as by comparing your 28-mm lens with someone else's.

Best wishes,
Leon
 
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