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Forum: Maintenance and Repair Articles
03-28-2018, 01:01 PM
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Great news! Thanks for letting us know :)
Incidentally, as I'm sure you've found, you can still use high shutter speeds - just not with EFCS. If you only use EFCS at lower shutters speeds (I don't know the limit, but I'd guess 1/1000s or less), you should be fine. Above that, stick with the mechanical shutter.
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Forum: Maintenance and Repair Articles
03-27-2018, 12:41 PM
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Just thought I'd add one more thing here...
I tested my own A7 MkII + Jupiter-21M today, using EFCS at high shutter speeds, and I get *exactly* the effect you've experienced. If I drop the shutter speed and/or switch to mechanical shutter, the effect disappears.
I'm now confident EFCS is the cause of your problem, and you've no need to open up that Jupiter-21M and remove the plate :p
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Forum: Maintenance and Repair Articles
03-26-2018, 02:50 PM
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Sounds like we might have a possible solution, then. Let me know how your tests go, please?
As for why EFCS can cause this, I don't honestly know as I've never read up on it - I just remember reading it somewhere. It's even mentioned (though well-hidden!) in various Sony camera manuals, as follows:
When you shoot at high shutter speeds with a large diameter lens attached, the ghosting of a blurred area may occur, depending on the subject or shooting conditions. In such cases, set this function to [Off].
When a lens made by another manufacturer (including a Minolta/Konica-Minolta lens) is used, set this item to [Off]. If you set this function to [On], the correct exposure will not be set or the image brightness will be uneven.
From what I've read, it may be something to do with the scan speed vs shutter speed, and limitations of this at higher shutter speeds. But I really don't know the technical details.
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Forum: Maintenance and Repair Articles
03-26-2018, 12:44 PM
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OK, well it was worth trying! :o
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! :)
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Forum: Maintenance and Repair Articles
03-25-2018, 01:18 PM
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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 :p
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 :o
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Forum: Maintenance and Repair Articles
03-25-2018, 12:16 PM
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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.
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Forum: Maintenance and Repair Articles
03-25-2018, 11:44 AM
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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...
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Forum: Maintenance and Repair Articles
03-25-2018, 11:32 AM
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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?
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Forum: Maintenance and Repair Articles
03-25-2018, 10:20 AM
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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.
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