corner sharpness with digitar 35mm

[gebseng]

Hi everyone,

(I hope at least some of you are enjoying the holidays already!)

As I mentioned in earlier posts, I am shooting architecture with a Linhof Techno view camera, a Leaf Valeo 22 back (36x48mm sensor) and a Schneider Apo-Digitar 5,6/35mm.
Lately, I realised that rising more than 10 mm with the Digitar 35 gave me a strange corner effect: the image became quite blurry, and there was a notable amount of halo in contrasty areas (a sample image and a 100% crop are attached).
So, I sent the Digitar to Schneider Kreuznach, with a very detailed description of that problem and some example files.
They told me that the copal leaf shutter was misaligned and had to be changed, the service cost € 660.-, which is about 1/3rd of the price of the lens.
After receiving the serviced lens I repeated the test shot and, alas, the corner sharpness and halo had not increased in any way.
Now Schneider says that my lens is in perfect condition after the service, and there's nothing they can do about my problem.
The test shot was done with f8 and a rise of 15mm, which does not exceed the 90mm image circle in any way (i calculated that the upper corners are still within an 84mm circle)(I also tested with f5.6 and f11, with very similar results).
So, do you think that this is just something I have to live with, or is the lens faulty?

thanks for your input,

geb

[ced]

If I look at the centre crop of the full image my guess is that the focus is slightly out and the halo effect I think with a shift of 15mm is about normal.
You have reached the limits of the whole system camera included but check the focus!!!

[rhsu]

Can you try at f11/16 and see what happens with your digitar?  I know I used to own Digitar and I always stuck with what mfgr recommendation ie f11.  Whereas Rodenstock HR lenses recommend f8.  Good luck!

[gebseng]

thanks ced! I am glad to hear that you saw that kind of corner halo before, because I have not so far,

geb

[gebseng]

rhsu, thanks also! I tried f11 and f5.6, but the halo stayed pretty much the same.

geb

[ChristopherBarrett]

Regardless of the image circle size, you can easily run into diffraction softness with the 35mm.  I use the same lens with a P65+, which is a larger sensor and I try not to shift it more than 10mm because of the loss of sharpness.  If you shift it 15mm, take the back off the camera and look at how close the lens is to the plane of focus, you will be amazed that you get any image at all that far out.

If you really need to shift that much on a wide composition, I'd look into the new Schneider 28mm.  Its retrofocus design helps combat diffraction.  It's pricey and huge, but it will probably get your picture.

[archivue]

If you really need to shift that much on a wide composition, I'd look into the new Schneider 28mm.  Its retrofocus design helps combat diffraction.  It's pricey and huge, but it will probably get your picture.

there's plenty of color cast with this lens... doesn't work with IQ180 for example...

[BernardLanguillier]

You could also try to stitch 4 non shifted images with a pancake camera on a pano head.

That will generate perfectly sharp corners if that is important for your applications.

Cheers,
Bernard

[gebseng]

thanks for all the input!
I am otherwise quite happy with the 35 digitar. color shift is not a big issue with the leaf 22 and 33 mp backs.
My best guess is to use shift only up to 10 mm and do additional perspective correction in software...

best,

geb