Lens VR unit IR leakage affects long exposures - cont'd.

Started Feb 17, 2008 | Discussions thread
Ravncat Senior Member • Posts: 1,109
Re: Lens VR unit IR leakage affects long exposures - cont'd.

There seems to be a rather large difference between the effect that occurs on the sample above and on the 70-200 when compared to the 18-200 images posted in the prior thread.

The 18-200 image shows a very clear gradient from the right frame to the left, while the above images are much more pinpoints or scratches of light. This would seem to suggest a different cause, or some other design difference that's altering the effects of the same cause.

I have to wonder if it's related to the 18-200's VR/AF servo's and the circuitry between the lense and camera, since the gradient (if you look in photoshop and use the gradient tool to cancel it out) appears to be at a very simmilar angle to the location of the electrical contacts on the lense mount, perhaps a natural continuation of those circuits. If those run hot interior to the camera, providing internal heat on the right side of a greater amount than the other lenses, it could be a cause.

It's not too surprising that the gradient appears to correlate with the heat equation (see calculus / boundary value problems / thermodynamics) Unfortunately, I have not done any kinds of density tests or actual angle checks to verify the above conjecture, so please do remember that it is conjecture.

It's clear that it has something to do with the A/F and VR lenses, unless I missed something on my 18-70 images, I didn't pixel peep those tests, because I was looking for a large obvious gradient effect, that was separate from Ampglow. The 18-70 lacks the VR function but does have a M/a override. I'll have to test again with that third combination. (Camera AF off, M/A on lense, Camera AF on/M on lense, Camera AF off, Lense M/A set to m)

This certainly makes me wonder why the shown effects on the 70-200 and the OP's tests show up as nearly specular. The theory that it's internal IR bouncing off the blades seems to make sense. This however, tends to point to the idea that the 18-200 issue is different from the other lenses, in a fundamental way. Unfortunately without dissasembling the lense, doing proper reflection analysis, it's hard to tell if it's being diffused, but even if that were the case, it seems awfully strange that it's the entire right side of Maxk's photos.

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A poor photographer blames his tools.

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