28/1.9 Ultron focus shift?

[Philip Whiteman]

I wonder if anybody else has found this: I am confident that there's no underlying problem with my R-D1 (all my Leica M lenses focus accurately and consistently) but my brand new 28/1.9 Ultron seems to actually focus further behind the subject as it is stopped down.

Happily, it appears to be set up to focus correctly at f1.9 – where you need it to be accurate. I wonder if it's the optical design that is causing the problem – or have I a dud one?

I'd be interested in your comments!

 

[Jim Watts]

My 28 Ultron is fine wide open and I don't notice any front/back focus problems on stopping down, but there does seem to be collimation problems with individual examples of VC and other lenses on the R-D1. My 40mm Nokton very slightly back focusses and my 35mm Cron (3rd type) front focuses by 3 inches at 1 metre.

Epson only claim +/- 1 inch close-up setting the focus with the 35mm f2.5.

 

[x-ray]

Never seen a focus shift with mine and I shoot a good bit at 1.9 to 4.

 

[sonwolf]

I do not have this problem with my 28mm Ultron. You need to shoot a controlled focus test before declaring the lens defective. Lock the camera down on a tripod and focus on a flat surface with sharp, clear high contrast details. Set the rangefinder focus to proper alignment and slightly in front and behind the subject. Shoot all the apertures but be mindful of diffraction at smaller apertures. At f/1.9, the Ultron is a relatively fast lens so its optimum apertures are in the f/4-5.6 range. After 5.6, the quality begins to decline; f/16 will be noticeably less sharp than f/5.6.

If you notice a significant focus shift after doing this test, I would exchange this lens for a second copy. Voigtlander produces excellent lenses at good prices but their quality control can be mediocre. The first 50mm Nokton I received had a hair the size an eyelash inside the lens. I exchanged it and received an unflawed second copy. The 28mm Ultron is a great lens for the R-D1 and definitely worth owning. Don't be discouraged if this copy of the lens is sub par.

 

[Philip Whiteman]

Done precisely that kind of test, sonwolf – plus lots of field testing – and it's a consistent problem with the Ulton (and not with any other lens I have in regular use). Sounds like take it back and ask for a replacement time!

 

[sonwolf]

Definitely do a lens exchange. A good copy of the 28 Ultron is really a beautiful match for the R-D1. Considering that the 28/35 Ultrons have been discontinued, now is the time to buy these lenses before they become scarce.

Hopefully, fate will smile on you with the second lens. Good luck.

 

[pvdhaar]

Focus shift when stopping down does occur, and some lenses are notorious for it. There's some info on why it happens here: http://www.vanwalree.com/optics/spherical.html

Faster lenses seem more prone to it than slower ones..

 

[Chavo]

Good find Peter!

Learn something every day!

Chavo