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M42 Adapter Ring Anonymous
First of all, I'm very sorry for this thread. It's not about photos, it's about gear. Help me now, stone me later. Or even better: help me now and have a lot of photos to rip apart when I get this fixed.

I'm using a 350D with an adapter ring to mount my older M42 lenses. For a long time, I've been wondering if my eyes are fucked or if its just bad luck or the shaking of my hands. The focus is always slightly off, even though I could swear that it was right when I saw it trough the viewfinder.

Now, I've finally conducted a small test. Pic related. I focussed on the block of equations, which are now horribly out of focus. The part which appeared to be out of focus (in front of the equations) is sharp.

I've had another person verify my settings and the focus as seen through the viewfinder.

I had already abandoned all hope when I remembered the adapter ring. It was pretty cheap (eBay) and had no further specifications. I redid the test with the 18-55 canon lens and it turned out just the way I saw it in the viewfinder. So, my camera is okay. The old lenses must be okay since I've seen the awesome (and awesomely sharp) photos my mom took years ago. The only culprit left is the adapter ring.
I've read about other lens types which should not be used on modern cameras since they lose the ability to focus on infinity. And a second test confirmed that this doesn't work very well either.

Bad luck? Is that what I deserve for buying stuff off eBay? Are there adapter rings which are guaranteed to work without those problems?
EXIF data available. Clickhereto show/hide.
Camera-Specific Properties:Equipment MakeCanonCamera ModelCanon EOS 400D DIGITALCamera SoftwareDigital Photo ProfessionalImage-Specific Properties:Image OrientationTop, Left-HandHorizontal Resolution350 dpiVertical Resolution350 dpiImage Created2008:09:11 15:36:08Exposure Time1/500 secF-Numberf/0.0Exposure ProgramManualISO Speed Rating100Lens Aperturef/infExposure Bias0 EVFlashNo Flash, CompulsoryFocal Length0.00 mmColor Space InformationsRGBImage Width1000Image Height667RenderingNormalExposure ModeManualWhite BalanceAutoScene Capture TypeStandard
>> Anonymous
tl;dr
>> Anonymous
I have noticed this type of issue as well.

Try this: get an M42 lens with a distance scale (preferably a macro or a telephoto, since their scales are more accurate), then focus on something at a known distance. Compare the distance to what it says on the lens. Use the optical center of the lens (guess halfway down the barrel if you don't know) rather than the film plane.

If the distance scale on the lens is pretty close to accurate, then something about your focusing screen is out of alignment. If it's not, and the distance scale says something other than what you've measured, then your adapter ring is wrong. Not sure which way, though.

Another test: focus on something at infinity. Check the scale. Are you currently reading something like 30 feet or so? And if you set the lens to infinity, you overshoot? This means that your adapter is too thin (a common way of making sure the lens can focus at infinity, at the expense of some close-focus ability). This millimeter or so that they shave off might have an effect on your focusing, especially wide open. I'm not an optical technician, so I don't know if it actually changes the optical path to the sensor to a different extent than the path to the ground glass (if they both change the same amount, then it shouldn't make a difference).

I have two M42 adapters. One works properly with the distance scale, and one does not. Look at the flange around the outside edge, where it mounts to the outermost part of the EF mount -- it should be fairly beefy looking, about as thick as a piece of matboard. I measured both of mine with vernier calipers...the thicker, accurate one is 1.42mm thick, while the thinner one is 0.91mm. That makes enough of a difference that the scale is significantly off on the thinner one.

Another thing to consider might just be that it's hard to get critical focus on the crap screens in the xxxD series of cameras. I know that I really, really miss the split-prism in my Spotmatic.
>> Anonymous
>>252288

same anon...I should add that I have noticed that the thinner adapter has some focusing issues with fast lenses wide open. I have occasionally thought "damn, I was sure I got that shot" then realized the subject was out of focus. These mostly happen at night, though, or in a moving car or something, and the screen in my 300D is pretty bad -- so there's really no objective way to tell if it's completely accurate without setting up some kind of test bench and looking at the files at full res.

Which I think I just may do. I'll post results later if something interesting comes up.
>> tl;dr Anonymous
cool taylor polynomials, bro
>> ac !!VPzQAxYPAMA
What aperture are you shooting the M42 lenses at? And did you get the adapter ring with focus confirmation enabled?

The 350D's viewfinder doesn't work for crap with apertures wider than about f/2.5. It just flat out won't show any depth of field narrower than an f/2.5 depth of field. So it's easy to focus such that it looks okay in the viewfinder and have it come out blurrily unfocused in the final image. So if the reason you're using M42 lenses is because you've got some fast ones and you're shooting them wide open, that could be the problem.

(If you're shooting with, say, f/2.8 or f/5.6 lenses, then I've got nothin')
>> Anonymous
Thanks for the responses.

It's a 400D by the way. I always get those two mixed up since I originally wanted to buy a 350D. Does this change anything?

>>252310
It's consistent with all apertures. If anything, it gets worth with f/11 and higher as there seems to be absolutely NO sharp spot in the whole image.
I do love my fast lenses and use them very often. I can confirm that the depth of field as seen through the viewfinder seems to be rather large at f/1.8 etc. But that's not the problem as it's easy to work around. The big problem is that the focal point (is that the right word?) is always wrong.

The adapter is just a cheap black metal ring which does nothing really apart from pressing down the little pin of the lens to close the aperture blades. I do not have the means to measure its thickness but I will do so as soon as possible.


>>252288
Focussing on infinity works perfectly fine in the viewfinder. I can't make out where exactly the sharp part is in the resulting image, but it's surely not infinity. It seems to be rather nowhere, but I will conduct some more tests on it this weekend.
>> Anonymous
>>252310

>doesn't work for crap with apertures wider than about f/2.5

That makes a lot of sense, actually. It explains why I have so much trouble getting critical focus with my 35/2 but manage just fine with the 105/2.8 and anything slower than that. (I have a 300D but the viewfinder is probably the same). I never seemed to have any problems if I stopped down to f/4 or less, but I assumed that was just cause there was actually a greater depth of field.

Yet another reason to upgrade. Cmon Canon, I need that 5D mkII with a better mirror box!
>> ac !!VPzQAxYPAMA
>>252373
As I understand it, this is an issue with autofocus cameras in general rather than with crop cameras.

Here's a better explanation of it than I can give:
http://www.jayandwanda.com/photography/dslr_man_focus/man_focus.html
>> ac !!VPzQAxYPAMA
>>252387
(Rereading that seems to disagree with my assertion that it goes for full-frame DSLRs too. So I very well may be wrong about that)
>> Anonymous
>>252387
Well, ac, that's one of the most useful things I"ve ever gotten from /p/ (though really that's not saying a lot).

Now I can say DAMN YOU STUPID MARKETING making new problems where there weren't any before! I don't have any idea why manufacturers have gotten rid of the 50mm 1.4 (30mm now I guess) as a kit lens, since it was such a perfect design. No image stabilization needed to shoot at night, and the faster shutter speed freezes your subject's motion as well as your hand's.

bleh bleh. Well, another thing to hope for in the 5D MkII. Good focusing screens. If I can't get a split-prism, or at least a katz eye version, then I suppose it'll be a used 1Ds MkII for me...
>> ac !!VPzQAxYPAMA
>>252400
>I don't have any idea why manufacturers have gotten rid of the 50mm 1.4 (30mm now I guess) as a kit lens
The target markets for cheaper SLRs don't understand "f/1.8 maximum aperture"

The target markets for cheaper SLRs do understand "3x zoom".

Given the choice of a fast prime and a slow zoom, most people who don't really know photography will pick the slow zoom.
>> Serenar !m827jEgWi.
>>252400
It was a shame when film cameras started coming with slow zooms, but you can't really expect the manufacturers to crank out 30/1.4s for cheap crop cameras at kit lens prices. The design is quite a bit tougher than a 50, as far as I understand.