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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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03-26-2018, 02:50 PM - 2 Likes   #16
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QuoteOriginally posted by chrisliaskonis Quote
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?
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.

03-27-2018, 12:41 PM - 1 Like   #17
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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
03-28-2018, 12:53 PM - 1 Like   #18
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QuoteOriginally posted by BigMackCam Quote
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
So yes we found it! I did the tests on normal shutter speeds with efcs off and high shutter speeds with efcs on. When i use slow shutterspeeds without efcs the images look completely normal! Getting over 2000 shutterspeed with efcs on and you start to noticed the shadow thing. Very interesting! i would have never thoughout about it! Thanks BigMackCam and everyone! Case closed
03-28-2018, 01:01 PM - 1 Like   #19
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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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