it's possible but then i would expect asymmetric patterns in many things. so far, i haven't observed any but then i haven't done shooting of targets or anything to detect that kind of thing and i am too lazy to rig up my test targets and measure the MTF of my instance. i have the targets and software to do so but after measuring some lenses and then testing in the field, i concluded that i learned little from the target shooting that really mattered in day to day shooting at the settings that i normally use.
Herb...
denoir wrote:
It's possible that Herb's 21 is not correctly centered. It's very common. The 21 has an immensely complex design (18 elements or so IIRC) and misaligned copies are commonplace. If I remember correctly Lloyd Chambers had to send back several copies of the 21 ZF before he got one that was correctly aligned. It's one of the disadvantages of the 21 compared to the much more simple design of the 25.
A star test would be in theory good for a limited number of aspects if you could get the stars to stand still. Now as you are forced to use higher ISO you'll have difficulty telling anything because of the noise.
It won't tell you anything about lens resolving capability, nothing about distortions, nothing reliable about CA.. You can perhaps say something about field curvature - but it's hardly an optimal test.
Stars are excellent to test a lens' mechanical infinity stop, but I can't really think of what else it would be really good at..
True it would be a good coma test. As for corner sharpness, only if there is significant field curvature so that the focus is not at the infinity in the corners. As for regular resolution, that would be the spacing between the stars and they too much spaced apart to make it useful.
and if everything in the optical train is nice and square. Field curvature might be explored as well. I have not tried, but I will. There is nothing stopping you from focusing on an object close to the corner.
With some experience of various lenses there is much to be learned. But not _every_thing, which is a bit much demanded of something free, isnīt it? As always you have to be open to the benefits and shortcomings, and perhaps show a genuine interest in the subject, perhaps even dear to try it out yourself, to really get a fair chance to find out something new, good or bad, brilliant or worthless.
Optics is very complex, as you all know. The startest is a rather clean and simple test that anyone can perform. Get best focus by focusing in live view x10 on any bright star in the center of the view. Perform the test against a star field as close to one of the poles, where the rotation of the sky is a small as possible. I usually center on the Polar star that is over 63° high, as Iīm at 63° north myself.
carstenw wrote:
Erm, huh? Wouldn't you want a flat field to test corner sharpness? Points in focus staying points and all that?
Huh? What I said was that you could check for deviations in sharpness due to field curvature but not just a regular drop in resolution. Weak corners don't always imply field curvature.
Dear ONΞant,
At the moment we are still working on a complete redesign of a Distagon lens with 25 mm focal length.
The new 25 mm Distagon lens will be available as ZE (for EF bayonet) and as ZF.2 (for F bayonet) version. Unfortunately we cannot specify at the moment when the new lens will be available. Sorry.
Best regards,
Carl Zeiss Lenses Team
I think its important to keep this news current, would be a shame for any zf25 buyers to not be aware.
OTOH what you actually pay for a lens is the price you pay for it minus the money you get when you sell it. As used Zeiss lenses are comparably expensive, the actual cost for a lens may very well be lower than what you would pay for any plastic phantastic that is almost impossible to get rid of.
trusty wrote:
...
LC made a test involving many lenses and bodies. After his D3X has been fixed he said he didn't exactly know if one of the 4 samples of ZE provided (at the same time for testing) ZE was really faulty even if somes did not provide exactly the same results.
...
By the way this story has made me to check my lens. I now suspect mine to have the same problem than the one reported by L.C here :
It's also like L.C on the right side. In indoor scene, with curvature of field this is not evident to see. But with proper tests and inspecting pictures, taking one picture rotating 180° the camera and taking the same picture reversed helps to diagnose the problem.
I will more investigate and if it confirms I will return the lens.
Do someone have encountered a misalign with any of your zeiss ?
It's also like L.C on the right side. In indoor scene, with curvature of field this is not evident to see. But with proper tests and inspecting pictures, taking one picture rotating 180° the camera and taking the same picture reversed helps to diagnose the problem.
I will more investigate and if it confirms I will return the lens.
Do someone have encountered a misalign with any of your zeiss ?
My advice would be, if the decentering wasn't obvious since day one, forget about it. If you look for something hard enough, you will always end up finding it. The perfectly centered lens doesn't exist yet. You will go nuts comparing 100% crops from left and right corners.
a great discussion here! I had sold my 25mm some time ago, but when I saw one going cheap on ebay I could not resist the temptation. If only I had an FF camera to to use it on! However, I can note, that when shooting people I preferred the 35mm f2. it is hardly relevant, as obviously 25mm is designed for different purpose.
edwardkaraa wrote:
My advice would be, if the decentering wasn't obvious since day one, forget about it. If you look for something hard enough, you will always end up finding it. The perfectly centered lens doesn't exist yet. You will go nuts comparing 100% crops from left and right corners.
You'right. this kind of tests can someone go nuts. I'm aware that no lens is perfectly aligned but some pictures make me perplexed. That's the reason, i'm coming here to get some little help. For those who have a little time to spend, I'll try to post somes pictures on the dedicated thread : https://www.fredmiranda.com/forum/topic/991515
met that beauty on a walk today. When I looked at the pics at 100%, I could not believe how sharp the details were. The ZF 25/2,8 seems to like metallic surfaces.
