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05-26-2010, 09:21 AM   #1
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My K20D takes terrible images with my 645 lenses, why?

I just got a 645 to K adapter from Cirrus, and my K20D takes useless images with it. I've only tested three lenses so far (120mm A f/4 macro, 150mm A f/3.5 and 200mm FA f/4), but all three can't just have broken in the same way, so it must be the adapter. (Or the lenses are really useless on digital, which seems unlikely.)

I've attached the same thing taken through my open window just now, first with a Sigma 55-200mm f/4-5.6 at 150mm f/5.6 (to see that the camera works), then 645 150mm f/3.5 at f/5.6, then 120mm macro f/4 at f/4 and finally 120mm at f/8.

It seems to get worse if I stop down. (I didn't bother to upload anything from the 200mm, the problem is the same.) I'd guess it's reflections from the large image circle, but while the adapter is shinier than the camera I don't think it's that shiny. So what else could it be?

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05-26-2010, 09:36 AM   #2
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I'm going to have to say that it's the adapter's fault. I'll go out and take some test shots with my 645 gear now and get back to you on the quality

Could you post some close-up pictures of the adapter so that we can compare it to the Pentax one?

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05-26-2010, 09:45 AM   #3
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I get the same behavior with an old XR rikenon 135F2.8 (M42 mount) lens that I bought. I believe it is a reflection off the sensor.

There have been some other posts showing this as well.

Perhaps there is an issue with a bright exposed surface between the lens and sensor on the adaptor that is causing reflections, but that is the only other guess I have.

I have not seen this problem reported by any other users of Medium Format lenses in the forums.
05-26-2010, 10:55 AM   #4
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Here are images of the adapter. Sorry about the light (flash), I got lazy.

In the first one you can see the irregular ring that presses the aperture lever and the silvery tab that moves when you press the release button.

As you can see the parts that might reflect are painted black, but it's a fairly shiny black.

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05-26-2010, 11:01 AM   #5
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Since it is concentrated more in the center, I think Lowell may be right. I don't know for sure but I would think that if it were reflections off of the sensor it would occur uniformly across the image.
05-26-2010, 11:24 AM   #6
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You said that you were shooting through a window- maybe try taking that out of the equation and trying again? I'm taking a look at my adapter and comparing them now.

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05-26-2010, 11:25 AM   #7
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Would you mind putting the camera on a tripod and taking a few shots with a cover on the viewfinder? Just an outside chance that it is light coming through that path that is screwing up the shots, even though that path is supposed to be blocked when the sensor is exposed.
05-26-2010, 12:12 PM   #8
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I suspect the adapter. I use the 645 150/3.5 on my K20D and get fine images.

05-26-2010, 12:54 PM   #9
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Adam: Open window, so it really just means it was a bit darker where the camera was.

jbinpg: I don't see how that could affect only my 645 lenses, but I did make a slightly different test: Lens cap on, take a 30 second exposure. The image is black, both with a 645 lens and a K lens, without covering the viewfinder. If I fire a flash through the viewfinder I do get a pattern on the image, but that's pretty extreme, and just the same regardless of lens.

bkpix: So do I. I suppose I'll have to try to make it less reflective somehow.
05-26-2010, 04:49 PM   #10
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try putting a peice of black construction paper between the lens and the adaptor to hide the shiny black surface

since the lens covers a lot more than a 35mm film lens, it could hit that black shiny surface and reflect off it back at th erear of the lens, causing the issue.

otherwise, and I can't explain it, you have refletions off the sensor, even though others report no issue,.
05-26-2010, 07:19 PM   #11
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QuoteOriginally posted by drougge Quote
I just got a 645 to K adapter from Cirrus, and my K20D takes useless images with it. I've only tested three lenses so far (120mm A f/4 macro, 150mm A f/3.5 and 200mm FA f/4), but all three can't just have broken in the same way, so it must be the adapter. (Or the lenses are really useless on digital, which seems unlikely.)
It seems to me very likely that the problem is reflections off the surface of the central tube, I would flock it or even paint it with some really black matt paint.
05-26-2010, 08:00 PM   #12
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I have the Pentax adapter. The black paint inside is exceedingly dull, offering almost no reflection even when you hold it up to a bright light.

The inside cylinder surface is also -- how to describe this? -- finely corrugated, as if the inside of the tube were milled for a very fine screw. That, of course, would also serve to reduce internal flare.

The inside surface of the adapter in your photo looks quite reflective.

Perhaps some very careful application of some very flat black paint....
05-27-2010, 05:08 AM   #13
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Today I tried putting some cloth (a piece of sock) in the adapter, and the improvement is considerable. I'll have to get something better of course, but there's definitely hope. Same 120mm at f/8 as in the first post but now with sock attached, and an image of the sock in the adapter, to show how completely professional it looks while still working acceptably. (The sock isn't even black, but dark blue.)
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05-27-2010, 05:27 AM   #14
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Interesting

You should look to apply some paint to this surface.

I would suggest getting an "antique" flat black paint that has a wrinkled surface, followed by regular flat black paint or black primer.
05-27-2010, 10:44 AM   #15
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Interesting. I always knew internal flare could be a problem, but had no idea it might ever be this severe. Thought it was more in the realm of a little shift in contrast.
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