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Jupiter 21m-200mm blocks light and stripped screw help.
Posted By: chrisliaskonis, 03-25-2018, 09:06 AM

I have noticed after some white skies today that my jupiter 200mm and possibly every 21m lens blocks some light in the area where the metal plate is at the bottom of the lens. Although i thought this was only producing reflections i found that it also blocks some light, because the dark part of the photos are excactly where the metal plate is. I have covered it with some very thin mat fabric (last pic is not mine) to avoid reflections, but even when i remove it the darkness on top of the image when into landscape still appears. So i decided to remove the plate completely, only to find out that the screws were incredible diffucult to unscrew. After some time i removed the first one but the other one is completely damaged as you can see. Any advice on what i can do to remove the screw andthe metal plate is appreciated!
Thank you!

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03-25-2018, 10:20 AM - 1 Like   #2
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Hmmm... that's odd. I've never noticed that happening with my own Jupiter-21M.

Here's a full-frame white wall photo taken with mine just now on the Sony A7II, using a Pixco M42-NEX adapter, aperture set to f/4 (wide open):



Mine shows a little more corner vignetting to the right hand side of the image, but that's almost certainly because my adapter has some lateral movement - it's not precisely engineered.

This is how my lens looks at the rear (you can see that I've also done the anti-reflection mod with thin black foam on the plate):



I'm wondering if the plate on yours is bent out of position? With the aperture at f/4 and set to focus at infinity, look through the lens from the rear - it should look like this:



Notice how the plate (just inside from the aperture pin) is nowhere near the optical path?

Also check your adapter and make sure there's nothing getting in the way. I'm not sure what camera you have... As I said, I'm using the A7II. My adapter looks like this from the rear:



As for the screw, that should be a simple inset flat headed set screw. It looks like yours has been covered or filled with adhesive or varnish, and I think I can see the groove for the screw head just below the surface. Try using a pin or needle to scrape away anything covering the screw head.

Last edited by BigMackCam; 03-25-2018 at 10:34 AM.
03-25-2018, 11:18 AM   #3
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i am using an a6000 I dont think thats the cause, it should be the other way around. But it doesnt matter if the plate isnt getting in the way of the optical path as you see it. Mine is the same, i cant see it near the optical path, but when i take a flash light shine through it, the light that comes from the other side has a shadown at the spot where i see it in my photos.
03-25-2018, 11:32 AM   #4
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QuoteOriginally posted by chrisliaskonis Quote
i am using an a6000 I dont think thats the cause, it should be the other way around. But it doesnt matter if the plate isnt getting in the way of the optical path as you see it. Mine is the same, i cant see it near the optical path, but when i take a flash light shine through it, the light that comes from the other side has a shadown at the spot where i see it in my photos.
I'm aware that the plate causes a slightly flattened edge of the image circle. That's normal with the Jupiter-21M - it happens with mine too... if I shine a flashlight through it from the front, the circle of light projected from the rear is very slightly flattened at one point on the circle. But it doesn't cut off enough of the image circle for it to be noticeable on 35mm film or a full-frame sensor, and it *definitely* shouldn't by noticeable on an APS-C cropped sensor camera which uses a smaller area of the image circle. That's what makes me wonder if the plate is bent out somehow...

You're not using it with either a teleconverter or focal length reducer, are you?


Last edited by BigMackCam; 03-25-2018 at 11:45 AM.
03-25-2018, 11:41 AM - 1 Like   #5
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Precision Screw Extractor Set USA - iFixit
03-25-2018, 11:44 AM   #6
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QuoteOriginally posted by UncleVanya Quote
Those look very useful. Have you tried them, or any like them? I could do with a set of those myself.

I only wish I had the tools and capability to make my own replacement set screws too... I save what I can from old lenses that are beyond repair, but it would be nice to have some stock of the various common screws used in Soviet lenses...
03-25-2018, 11:55 AM   #7
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QuoteOriginally posted by BigMackCam Quote
I'm aware that the plate causes a slightly flattened edge of the image circle. That's normal with the Jupiter-21M - it happens with mine too... if I shine a flashlight through it from the front, the circle of light projected from the rear is very slightly flattened at one point on the circle. But it doesn't cut off enough of the image circle for it to be noticeable on 35mm film or a full-frame sensor, and it *definitely* shouldn't by noticeable on an APS-C cropped sensor camera which uses a smaller area of the image circle. That's what makes me wonder if the plate is bent out somehow...

You're not using it with either a teleconverter or focal length reducer, are you?
no i dont use a teleconverter or a focal length reducer, its definitely the plate but its not bend up or something and with the screw damaged i think am in bad luck! Thanks for answering !
03-25-2018, 12:16 PM   #8
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QuoteOriginally posted by chrisliaskonis Quote
no i dont use a teleconverter or a focal length reducer, its definitely the plate but its not bend up or something and with the screw damaged i think am in bad luck! Thanks for answering !
The other thing to check is the alignment of your M42-to-NEX adapter. I've had several adapters where the mount was misaligned and non-central. This can be for a number of reasons... the adapter-to-camera mounting piece isn't centered, the inset into which the M42 threaded ring isn't centered, or the hole and threads in that ring aren't centered. All of these can happen due to poor machining. If your adapter isn't centered properly, it's possible that it could be off-setting the lens just enough to bring the plate into the path between the rear element and the camera sensor.

Do you have a different adapter you can try, or can you borrow one? If not, it might be worth ordering another inexpensive one, just to test this.

03-25-2018, 12:57 PM   #9
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actually i have one! i just did a quick test but didnt see anydifference between the shots. i cant really tell any difference between the adpaters, except that the metal ring at the top of one of the adapters is a little bit bigger. I will do some more testings in daylight with the 2 adapters hopefully its the new adapter thats causing this, didnt really noticed it with the old one.
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03-25-2018, 01:18 PM - 2 Likes   #10
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QuoteOriginally posted by chrisliaskonis Quote
actually i have one! i just did a quick test but didnt see anydifference between the shots. i cant really tell any difference between the adpaters, except that the metal ring at the top of one of the adapters is a little bit bigger. I will do some more testings in daylight with the 2 adapters hopefully its the new adapter thats causing this, didnt really noticed it with the old one.
Great! Good luck with the testing, and please let us know how you get on, as it might be helpful for others here. It'll help me maintain my sanity, too, as I'll probably keep thinking about this until we get you a solution

As an aside, but related... Some months ago I bought a brand new Peleng 8mm fisheye lens in M42 mount, direct from the BeLOMO factory. Nice lens, but it wouldn't screw all the way into my adapters, and when I looked carefully, the M42 threads on the lens mount weren't fully cut. The factory rep was very helpful, and quickly sent me a new mount which I duly fitted. At first glance, it looked perfect, and indeed it screwed all the way into my adapters as it should.

However, when I took numerous test shots, I noticed they were off-centre. The Peleng 8mm is a circular fisheye, and on full-frame the image should show as a circle with the top and bottom cut off by the same amount... but on mine, only the top of the circle was cut off, and quite significantly so. Looking at the mounting component, and measuring with calipers, I noticed that it was off-center. So, I got the original mount - the one that wasn't cut fully - and using brute force over several minutes with a cheap (and, if need be, disposable) adapter, eventually managed to screw it fully into the adapter. When I removed it, I sanded off any swarf, then I fitted it to the lens and took some more test shots. They were PERFECT!!

I mention this only to confirm that this kind of thing can, and does, happen - even at the lens
03-25-2018, 02:07 PM   #11
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QuoteOriginally posted by BigMackCam Quote
Great! Good luck with the testing, and please let us know how you get on, as it might be helpful for others here. It'll help me maintain my sanity, too, as I'll probably keep thinking about this until we get you a solution

As an aside, but related... Some months ago I bought a brand new Peleng 8mm fisheye lens in M42 mount, direct from the BeLOMO factory. Nice lens, but it wouldn't screw all the way into my adapters, and when I looked carefully, the M42 threads on the lens mount weren't fully cut. The factory rep was very helpful, and quickly sent me a new mount which I duly fitted. At first glance, it looked perfect, and indeed it screwed all the way into my adapters as it should.

However, when I took numerous test shots, I noticed they were off-centre. The Peleng 8mm is a circular fisheye, and on full-frame the image should show as a circle with the top and bottom cut off by the same amount... but on mine, only the top of the circle was cut off, and quite significantly so. Looking at the mounting component, and measuring with calipers, I noticed that it was off-center. So, I got the original mount - the one that wasn't cut fully - and using brute force over several minutes with a cheap (and, if need be, disposable) adapter, eventually managed to screw it fully into the adapter. When I removed it, I sanded off any swarf, then I fitted it to the lens and took some more test shots. They were PERFECT!!

I mention this only to confirm that this kind of thing can, and does, happen - even at the lens
interesting! I dont have much experience with adapters i only have two m42 and one pk adapter for nex. My pk adapter works flawless but the 1st adapter i got for m42 got loosen very quickly and the metal ring that was holding the screw mount broke somehow with the little screws on the side not able to screw all the way in resulting in loose fit of the lens. So i ordered another one that was great so far until i noticed that shadow . I am looking to shoot some deep sky photos with the jupiter in some weeks and i need all the light possible for that, i hope its just the adapter because this little screw aint gonna come out any time soon :P
03-25-2018, 10:11 PM   #12
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QuoteOriginally posted by BigMackCam Quote
Those look very useful. Have you tried them, or any like them? I could do with a set of those myself.

I only wish I had the tools and capability to make my own replacement set screws too... I save what I can from old lenses that are beyond repair, but it would be nice to have some stock of the various common screws used in Soviet lenses...
No, I have used drill bits designed to extract screws but nothing this small.
03-26-2018, 12:33 PM   #13
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QuoteOriginally posted by chrisliaskonis Quote
interesting! I dont have much experience with adapters i only have two m42 and one pk adapter for nex. My pk adapter works flawless but the 1st adapter i got for m42 got loosen very quickly and the metal ring that was holding the screw mount broke somehow with the little screws on the side not able to screw all the way in resulting in loose fit of the lens. So i ordered another one that was great so far until i noticed that shadow . I am looking to shoot some deep sky photos with the jupiter in some weeks and i need all the light possible for that, i hope its just the adapter because this little screw aint gonna come out any time soon :P
So i did some daylight testings and as you can see its the same with both adapters the first one is a bit darker because the sun was dimmer at that time. I dont know what it might be....
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03-26-2018, 12:44 PM   #14
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QuoteOriginally posted by chrisliaskonis Quote
So i did some daylight testings and as you can see its the same with both adapters the first one is a bit darker because the sun was dimmer at that time. I dont know what it might be....
OK, well it was worth trying!

I've been thinking some more about this. I wonder, are you using EFCS, and a fast shutter speed? If you are, make sure EFCS is disabled and only use mechanical shutter. See if that helps... I have a good feeling that this might be the culprit!
03-26-2018, 02:28 PM   #15
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QuoteOriginally posted by BigMackCam Quote
OK, well it was worth trying!

I've been thinking some more about this. I wonder, are you using EFCS, and a fast shutter speed? If you are, make sure EFCS is disabled and only use mechanical shutter. See if that helps... I have a good feeling that this might be the culprit!
Yes actually i notice it more on very fast shutterspeeds! i always use efcs, i will try tomorrow slower shutterspeeds and no efcs. But how these 2 factors could produce something like that?
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