advice with a 65mm caltar, soft corners

Hello all,

I am new to this forum. I am a fine art photographer in Phoenix and teach at Arizona State University. I've been doing some architecture work as of late and have been working with a 65mm Caltar IIN f4.5. According to what I know, this is a Rodenstock badged by Calumet, though the quality control may not be the same.

When photographing a large building, the lens is super sharp in the center and appears to get a bit soft at the edges wide open. With a loupe right in the corner the softness seems to stay until the lens is stopped down to f45, where it almost feels as sharp as the center of the image. This is understandably not a good aperture for such a wide lens. The center looks best from f8-f16. At those apertures however, the edges still appear unsharp. It is difficult to tell on the glass as the corners are a bit dim. I just dropped some film off at the lab shot at f8, f11 and f16. Does anyone have any thoughts on this? I was planning to purchase an APO grandagon 55mm f4.5 but if I can keep the caltar I wouldn't mind saving the cash.

thanks

Mike

First off, softness at the edges of the GG may not necessarily mean softness on the negative at the edges, so it is certainly worth burning a few test frames to confirm the actual performance of the lens before drawing any concrete conclusions.

Next, the lens probably will be soft at the edges wide open, though should perform reasonably well in the center. Typically any LF lens will perform best in in the center at about three stops down from wide open.

Lastly -- and especially with wideangle lenses -- the best performance in the center is probably going to happen at a wider aperture than the edges, so the edges may need a bit smaller aperture than the center to crisp-en up. IOW the edges may need say f32 where the center is good at 16. F45 is probably still usable across the field for 4x5, but you will certainly start to see some deleterious effects from diffraction.

Re the 55 APO Grandagon. I own one (actually, I am currently selling it on eBay since it isn't quite wide enough for my extreme wideangle needs) and it is an exceptional optic. It tested exceptionally well on a resolution target, making over 60 LPmm, which was far sharper than any 65 I compared it to and on par with the 110 SSXL -- IMO the APO really makes a difference in the extreme wideangle designs. Offered FWIW only...

Cheers,

I've used the Rodenstock badged version of this lens and found it to be acceptably sharp right out to the corners of 4x5. Of course ALL lenses degrade in performance as you move away from the center, but "not in focus" is not acceptable. One thing you might check... is the lens being kept parallel to the film plane? A small misalignment (tilt) can produce the effect you are describing. I've experienced this myself (didn't seat the lensboard properly) also using a WA lens, and didn't see it on the GG because the corners are too dark to see. The center was sharp because that is where I focused, but acceptable sharpness ultimately evaporated before the image area did.

Thanks for the quick replies.

Jack, good advice and oddly enough, I think I may be bidding on that lens!

So, just now, after reading about Paul's experience with his Caltar I took the lens off the board and gave it the old gentle shake test, The rear element had a slight rattle to it. I thumbed the inner glass and it was loose! I tightened it up and just shot another test at f16 and f 22, the optimal apertures for this lens. On the GG the image appears sharp all the way across. Ain't it something how the way things go. I'll know tomorrow if its any good. thx Paul.

Jack, we'll see if I own a 55 as well as the 65 caltar...

best

Mike

It is the nature of wide angle lenses to have a curvature of field of optimum focus. Therefore, for maximum sharpness over the whole field you need to "focus in." Instead of focusing on a specific spot set the lens to a distance in front to the object and stop down.

As an example, if you are focusing at something (with your 65mm lens) at a distance of 100 feet away set the focus at around 25 feet instead and stop down to F16 or F22. If there is no defect with your lens it should give you pleasing sharpness over the entire field.