mikki Posted July 29, 2009 Share #1 Posted July 29, 2009 Advertisement (gone after registration) Hi! I've just bought a CV Color Skopar 35/2.5 for my M8, but i've noticed some softness in one of the corners. I've did a couple of test shots using Imatest-test-targets on the wall. The sample shown is at 2.8. At f4 it is less noticable, at f8 it is neglectable. I've used different M-mount adapters. Distance was 5ft, no postprocessing other that raw-conversion. What do you think, is this field-relevant? Should I send it back? Thank you, Micky Link to post Share on other sites More sharing options...
Advertisement Posted July 29, 2009 Posted July 29, 2009 Hi mikki, Take a look here Decentering of CV 35/2.5??. I'm sure you'll find what you were looking for!
Shootist Posted July 29, 2009 Share #2 Posted July 29, 2009 Could be the lens and if it is I'd send it back. But it could also be the sensor alignment, not that is is but it could be. Have you checked any other lenses for this same problem. If it shows up with other lenses then it is the sensor or mount alignment. Link to post Share on other sites More sharing options...
giordano Posted July 29, 2009 Share #3 Posted July 29, 2009 I've never worked out a good way of making sure that the sensor plane of the camera is guaranteed parallel to the wall. How do you do it? Link to post Share on other sites More sharing options...
LotharZhou Posted July 29, 2009 Share #4 Posted July 29, 2009 i had exactly the same problem with the same lens, only my case is much more serious, I had it sent back and got a new one, the blurry is better but still obvious in left corner. After all it's a 300 pound lens. Link to post Share on other sites More sharing options...
LotharZhou Posted July 29, 2009 Share #5 Posted July 29, 2009 I can almost certainly say it's not a sensor issue, all my other lens on M8 don't have this soft blurry corner apart from my CV 35mm/2.5, and from your test the issue is not bad at all compare to mine. Link to post Share on other sites More sharing options...
wlaidlaw Posted July 29, 2009 Share #6 Posted July 29, 2009 My CV 35/2.5 is quite soft everywhere and has a fair degree of static back focus but as I bought it on eBay for only just over £100, I was not too worried. It is also, like the OP's, better in one corner than the other, which must be due to misalignment of one variety or another. It now mostly sits on my M4 for use on B&W film where it gives a nice vintage appearance to the images. Wilson Link to post Share on other sites More sharing options...
Shootist Posted July 29, 2009 Share #7 Posted July 29, 2009 Advertisement (gone after registration) I've never worked out a good way of making sure that the sensor plane of the camera is guaranteed parallel to the wall. How do you do it? Simple. From the center of the test target measure out X distance, level to the vertical center of the target, and place a mark. Set the lens on the camera at that same heigth as the center of the test target and measure at a angle from marks you placed X distance out from the center of the test target to the center of the lens on the camera. Once you get all that fairly equal, it doesn't have to to the 1/128" or .001mm a 1/4" or 5-7mm (or even a little more) is find, the camera is as near center and perpendicular as needed. Link to post Share on other sites More sharing options...
lars_bergquist Posted July 29, 2009 Share #8 Posted July 29, 2009 Which version of the lens is it? The old man with a Pancake II Lens Link to post Share on other sites More sharing options...
mikki Posted July 29, 2009 Author Share #9 Posted July 29, 2009 Which version of the lens is it? The old man with a Pancake II Lens It's the Classic version, but I was told they're all the same. Recently I've sent back a 35/1.4 for similar reasons (it had no defined corners at-all). It will cost a lot of shipping costs to get it back again. Link to post Share on other sites More sharing options...
lars_bergquist Posted July 29, 2009 Share #10 Posted July 29, 2009 It's the Classic version, but I was told they're all the same. Recently I've sent back a 35/1.4 for similar reasons (it had no defined corners at-all). It will cost a lot of shipping costs to get it back again. The optical design is the same. Cosina are spiffing up their QC procedures however, probably with some prodding from Zeiss. My specimen is all right. So recent lenses may in general have better centering than earlier ones. The old man with a Pancake II Lens Link to post Share on other sites More sharing options...
giordano Posted July 29, 2009 Share #11 Posted July 29, 2009 Simple. From the center of the test target measure out X distance, level to the vertical center of the target, and place a mark. Set the lens on the camera at that same heigth as the center of the test target and measure at a angle from marks you placed X distance out from the center of the test target to the center of the lens on the camera. Once you get all that fairly equal, it doesn't have to to the 1/128" or .001mm a 1/4" or 5-7mm (or even a little more) is find, the camera is as near center and perpendicular as needed. I must be missing something. What you describe guarantees that the centre of the lens is on the line normal to the wall and passing through the test target, but it doesn't seem to guarantee that the sensor is actually parallel to the target. A good spirit level will get it vertical, but I don't understand how you ensure the horizontal alignment. Or is it just trial and error shooting until the centre of the target is exactly in the centre of the image? Link to post Share on other sites More sharing options...
Shootist Posted July 29, 2009 Share #12 Posted July 29, 2009 I must be missing something. What you describe guarantees that the centre of the lens is on the line normal to the wall and passing through the test target, but it doesn't seem to guarantee that the sensor is actually parallel to the target. A good spirit level will get it vertical, but I don't understand how you ensure the horizontal alignment. Or is it just trial and error shooting until the centre of the target is exactly in the centre of the image? Well if you measure off your floor to the center of the target and then set the center of the lens at the same heigth, and the camera is level front to back side to side, measured off your floor then the camera lens is centered on the target. That is if you live in a house that has fairly level floors. Now all you need to do is move it right or left to make it perpendicular, @ 90°, to the center of the target. That is what I was describing in my first reply. Measuring the hypotenuse of two right triangles. Or just use a large square like a sheetrock square. Although I've never found one of those that is actually square. Link to post Share on other sites More sharing options...
tashley Posted July 30, 2009 Share #13 Posted July 30, 2009 Hi! I've just bought a CV Color Skopar 35/2.5 for my M8, but i've noticed some softness in one of the corners. I've did a couple of test shots using Imatest-test-targets on the wall. The sample shown is at 2.8. At f4 it is less noticable, at f8 it is neglectable. I've used different M-mount adapters. Distance was 5ft, no postprocessing other that raw-conversion. What do you think, is this field-relevant? Should I send it back? Thank you, Micky The first one I had was just like yours so I got it replaced and the one I have now is good. My experience is that all lenses, by any maker, have sample variation and that you should test every one you buy and get the poor ones replaced immediately. It is so tedious but you do end up with a great bag of glass! Link to post Share on other sites More sharing options...
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