[Wheatfield]

Then why does Pentax tell us to cover the viewfinder for long exposures?

This should onlky be an issue with the LX when working in automatic, since it meters continuously during exposure.
Every other camera, the metering is done prior to exposure starting.
What can affect things is light entering the viewfinder during metering, which can happen if the photographer doesn't have his eye to the finder, and it is possible for some stray light to get past the raised mirror and enter the mirror box and perhaps find it's way to the sensor.
However, this is not the case with the pictures at hand, which are cause by reflection from sensor to lens and back to sensor.
I've seen this before, BTW.

[snostorm]

Most likely, that is a reflection off the sensor to the rear lens element and then back to the sensor as image forming light.
If this is the case, the cure, such as there is one, is to use a less bright background for your macro shots.

I agree with this explanation. I see this when I try to turn the FA 35/2 into a DA 35/2.8 by using a 25mm extension tube. It doesn't show in the viewfinder at all. I tried a lot of shading and hood techniques without affecting the problem.

I concur with this explanation too, when you're shooting macro there is a lot of light which doesn't hit the sensor due to the large mag factor, this can get reflected off the wall of the mirror box and of the surfaces of the lens and sensor.

I'll add my 2 cent's worth, and agree with you three.

I have an old Rikenon 135 F2.8 screw mount that has the same issue. It is the only lens I have that exhibits it out of 30 lenses in total.

I concur. I think this is a (pretty extreme) example of "digital" flare which the "optimised for digital" coatings are supposed to deal with. I have not experienced it with any of my many lenses, and the only times I recall seeing it mentioned was in macro shooting where the center of the image circle has been magnified significantly.

Scott

[eccs19]

Just for the record, the images that were really bad were done using my Takumar 55mm 1.8. I also tried it with my 100mm tak F4, but it wasn't nearly as bad. Maybe it existed with the 100mm before, but because it wasn't that noticeable, I just didn't see it. Could be that I'm just paying more attention, as it's a new camera, and I want to make sure it's not a camera issue. I think I'll try my 50mm 2.0 Pentax K mount and see.

[jeffkrol]

Except that it was there on 2 different lenses.

As others have stated it's lens flair (or sensor ghosting) and it occurs on many lenses... Older Tamron 90's do it, some Sigma zooms do it.. some Pentax macros do it as well......
The window test... smaller you stop down the more you see the shape..

[distudio]

Then why does Pentax tell us to cover the viewfinder for long exposures?

Well they have to keep it simple for the plebs I guess. The metering is affected by light spill through the finder, (most modern DSLRs meter off the finder prism) so if you are shooting using automatic metering with your eye away from the finder then it's advisable to use an eyepiece blind.

[suzuki-j]

also have same thing happened to me with 90mm 2.8 tamron macro and k-x with 2x TC ...

[eccs19]

I tried another lens out last night, and it wasn't as bad as with the 55mm, but it was still there. Maybe the new series of camera's (K-X & K-7) are just more sensitive. Never saw this happen with my *istD. I guess it would be a good excuse to keep my old one just for macro work.

[jeffkrol]

My shot was w/ a *ist-D. If the LENS has the sensor flair issue it seems to make little difference as to the camera....
Re: LBA Tamron SP AF90mm F/2.8 Di Macro: Pentax SLR Talk Forum: Digital Photography Review
Re: Rear coatings and real sensor reflections proiblem: Pentax SLR Talk Forum: Digital Photography Review

[snostorm]

I tried another lens out last night, and it wasn't as bad as with the 55mm, but it was still there. Maybe the new series of camera's (K-X & K-7) are just more sensitive. Never saw this happen with my *istD. I guess it would be a good excuse to keep my old one just for macro work.

It's possible that the newer anti-dust coatings on the sensor filters might have some effect. . .

Scott

[Canada_Rockies]

Then why does Pentax tell us to cover the viewfinder for long exposures?

Because it affects the meter.

[jeffkrol]

Pentamirror is basically the same.
If you follow the exit arrow straight back, that is the metering cell (and other display stuff).


In case your wondering the AF sensor is 11