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Not sure if rangefinder or lens is "out of focus"
Old 12-16-2014   #1
azkay
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Not sure if rangefinder or lens is "out of focus"

My LTM f/1.2 50mm Canon lens came in today.
Previously I was using a 35mm f/2.8 Jupiter-12.

As far as I can tell, the 35mm worked fine. I think the patch was just a tiiiiny bit off. But with the 50mm it's maybe 3mm or so off.

Not sure if it's the lens or the rangefinder that needs modifying.
I set it to minimum focusing distance on tripod and kept taking pictures then moving the tripod back a few cm.

The minimum focusing distance I can get it to focus has the rangefinder patch unaligned (if that makes sense)

Should I look at the lens or rangefinder first?

This is the lens: https://www.youtube.com/watch?v=qMRnqIysGAk
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Old 12-16-2014   #2
Sid836
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First try the rangefinder. A quick test at infinity and then, set it on a tripod, aim at a target at one meter (or at 1.5 depending on the min focus distance of your lens) focus the lens and look at the distance reading on the barrel of your lens. If the distance scale on your lens reads 1m and your target is at 1m then it is most likely that you are on the spot.
Now open the back of your camera. stick a piece of tracing paper on the rails of the film plane, focus on your target and with a magnifying glass check the sharpness of the image on the paper. If it is sharp enough then you are ready to go. If not, you will have to adjust the cam of the rangefinder so that you get a sharp image focused on the paper, and after that, the rangefinder itself so that focusing at 1m gives you a reading of 1m on the lens barrel.
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Old 12-16-2014   #3
azkay
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If I focus the lens "correctly" according to the rangefinder I get this (at 1m)


The lens focus ring goes further back than 1m (I think it's *supposed* to stop at 1m, but it keeps going for a bit). If I focus it further, to <1m (which shouldn't be possible) I get:



Which is better, but still isn't sharp.
Using an Epson R D1, so I can't take the back off, sensor is in the way :P
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Old 12-17-2014   #4
AndersG
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Having a digital camera makes it even easier to asses the accuracy of the lens distance scale as you can look at the images immediately (like you do above).

Where do you get the focus if you set the lens distance scale to 1m? Set some items at varying distance with one exactly 1m from the sensor plane of the camera (hopefully there is a symbol on the camera). Use increasingly larger apertures to get narrower fields of depth.

If the lens distance scale turns out to be off I'd be wary of changing the rangefinder calibration as that could ruin its calibration with other lenses.
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Old 12-17-2014   #5
Sid836
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Sorry, I have missed that you have been talking about that digital rangefinder camera.
I guess that you are using an adapter to mount the LTM lens on that camera. You have stated that focusing was perfect with the J-12 lens. It could be that the rangefinder had been adjusted to accommodate focusing with that lens and now it needs to be re-calibrated for use with the Canon Lens.
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Old 12-17-2014   #6
azkay
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I'll have to do some more sciency experiments in the morning
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Old 12-17-2014   #7
Sarcophilus Harrisii
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Set the lens to infinity and the highest output quality your camera permits. Use a tripod and cable or self timer. Take several shots preferably including high contrast subjects eg power poles against sky etc.

Examine the images critically for sharpness. If they are unsharp your lens is off.

Next check the RF image at infinity. If that is also sharp/unsharp it may be coupled correctly to the lens. If they deviate the RF is out.

Always check the lens first, it is the master adjustment. A RF should be dialled in to that. If the distance results are inconclusive repeat the test at close range with a suitable target which should inform you if the lens & RF track together. But if the lens checks out on infinity it should be OK at close range because you can enlarge the digital images to critically examine their sharpness. The close distance cross check is a lot more important with film because it's surprising how good infinity can look with a loupe and ground glass and be nearly correct but not quite. Hence, cross checking at close range; if both look good you're probably there.
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Old 12-17-2014   #8
Sarcophilus Harrisii
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I should add that if you need an adapter for the lens, I recommend conducting these tests with the standard lens for your camera which one would hope would have its infinity stop correctly calibrated to the focus plane and also to the RF. If this checks out good the next step is to test the lens involved with the adaptor. If this is out, but the RF previously tested good against the cameras OEM lens, then, once the lens is corrected for use with your adapter the RF should in theory fall into line with the Canon lens. My advice in my previous post is generally good, but the complication in your case may be the use of an adaptor if applicable? In which case the issue is quite likely dialling the lens(es) in to the adapter, not the RF in to the lens, as the RF itself may well be OK when correct lens register applies.
Cheers
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Old 12-17-2014   #9
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Quote:
Originally Posted by Sarcophilus Harrisii View Post
I should add that if you need an adapter for the lens, I recommend conducting these tests with the standard lens for your camera which one would hope would have its infinity stop correctly calibrated to the focus plane and also to the RF. If this checks out good the next step is to test the lens involved with the adaptor. If this is out, but the RF previously tested good against the cameras OEM lens, then, once the lens is corrected for use with your adapter the RF should in theory fall into line with the Canon lens. My advice in my previous post is generally good, but the complication in your case may be the use of an adaptor if applicable? In which case the issue is quite likely dialling the lens(es) in to the adapter, not the RF in to the lens, as the RF itself may well be OK when correct lens register applies.
Cheers
Brett
My body didn't come with a lens, I've used an adapter and an LTM lens since I first started using it (the Jupiter12) which tends to be fine, so I think it may be the lens.

I'll try what you said and come back with results'
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Old 12-17-2014   #10
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Taken at f/5.6

Infinity:


20m (correctly aligned in rangefinder):


3m (sharp picture, I tried at 10m, 7m, 5m, 4m. 3m is where it became sharp):


Rangefinder at 3m (the pole isn't aligned at 3m, you can see it on the right):
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Old 12-17-2014   #11
azkay
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After some more testing, setting the lens to infinity then unscrewing it from the adapter a little bit at a time I'm getting it sharper.

So I may just have to make some paper/aluminium shims to sit the lens further away from the sensor

Makes me think, maybe one of the previous owners added shims internally for their camera (as I'm sure I've read about people using the same lens on their R D1's).

Once I get it sharp with external shims I'll check to see if it fixes the coupling too'

EDIT::
This is the gap needed to take sharp photos at infinity:


EDIT::
So made a carboard shim, now it focuses at infinity, at minimum focus distance and the coupling seems to work fine now.
I guess next step will be to take apart the lens and find out how to shim it out internally. Not too happy with carboard shims on the outside (flimsy, rather not have the lens hanging off not completely threaded on, and with the "external" shims all the markings are on the bottom of the lens).

EDIT::
Scratch that- now infinity works but minimum is off ): So confusingggg
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Old 12-18-2014   #12
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Fixed took the back of the lens off and put the shims in there, now it couples correctly and focuses correctly. It might be .02mm off but I can live with that :P (My patience cutting thin paper can only go so far ha)

Still a little blurry here, but I'm 99% sure it's just my bad focusing at f/1.4 on a moving subject in low light. I think my next mission will be increasing contrast on the focusing patch :P

Thanks for all the help everyone, mission complete!
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Old 12-18-2014   #13
Sarcophilus Harrisii
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Well done! I usually use Champion brass shim stock for shimming Rolleis back to true, but you have quite a gap to adjust and the thickest size that seems commonly available on eBay is 0.25mm, so you may have to try a local engineering shop for something thicker to get you in the ballpark; the online stuff would then enable you to correct it bang on if desired. For examples of the type of stuff I'm referring to see here.
Cheers,
Brett
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Old 12-18-2014   #14
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Made two paper shims and tested them with the other 2 (one from tea cardboard, one from a thin-ish business card). Ended up removing the tea cardboard and adding the two paper shims and it's sharper than before. Taking one of the paper shims away makes it worse, so as it is:

1 thinnish business card
2x normal a4 paper

Together it's probably around .8mm?
Might just use these until I need a reason to move to metal shims (or go plastic), cheaper :P
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