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I am reproducibly getting the kind of rainbow-streak flare seen in the attached image on my copy of the Industar 50-2 (a russian 50mm f3.5 tessar-ish M42 pancake). The pattern does rotate when focusing the lens (which has a rotating front element).

Shot wide open, on a 24MP Sony APS-C, no post except scaling down

Is this an effect inherent to the Industar design or manufacturing process, or a lucky manufacturing defect, or an acquired defect, and what is optically happening here?

There is no recognizable damage to the optics, nor are there notable performance problems with this copy.

Not looking for advice on fixing or avoiding the effect since it seems quite useful - if anything, looking for advice on how not to accidentally fix it.

  • Is this image cropped at all? – scottbb Mar 12 at 20:31
  • APS-C sensor, not cropped. scaled jpeg to jpeg in RT, SOOC otherwise. – rackandboneman Mar 12 at 20:43
  • Tested: Not about the adapter. Usually have the Industar on a secondary helicoid to have it even more collapsible, but same effect can be reproduced with a bright lamp and plain M42 adapter. – rackandboneman Mar 12 at 20:48
  • FYI - the reason I asked about whether is was cropped was because the "flare circle" was off-center, and didn't appear to be at least diametrically opposed to the light source through the optical center. So my hunch was perhaps the image was cropped. But my hunch was wrong (see the screenshot and/or video review of the lens in my answer). – scottbb Mar 12 at 20:58
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I think the lens flare is a side-effect 2 things: simple Tessar lens design, and little or no coatings on the lens elements. There's probably nothing you can do to "accidentally fix" the flare on this lens. (edit: nothing normal, that is. I supposed if you were to have anti-reflective lens coatings applied to the lens elements internally, you'd reduce some/most of the flare. But that's a lot of effort and cost for such an inexpensive lens)

Here's a screenshot from this video review of the 50-2. It exhibits the same sort of flare:

enter image description here

So don't be afraid, go ahead and clean the lens. You won't wipe its character away. =)

  • My copy is single coated by the looks of it. What is really odd is how the flare rotates with the front element. Aperture edge roughness? ... I have actual 50/2.8 single coated tessars too (both the east german and the voigtländer-do erived formulae), never noticed that kind of flare on them, will have to experiment.... – rackandboneman Mar 12 at 21:04
  • It's not surprising the flare rotates with the lens element rotation. The imperfections in the grinding/manufacturing process show up in the flare as sort of a fingerprint for your particular lens. The overall character of the flare is the same copy-to-copy, but the exact appearance of the flare in your lens is as unique as your eye's iris, and your own fingerprints. – scottbb Mar 12 at 21:11
  • ... a completely uncoated lens probably would not have taken the original scene without completely drowning in veiling glare - that light close to the center is brutally bright (for guiding rhine ships through fog I assume). – rackandboneman Mar 12 at 21:18
  • @rackandboneman That's probably true. But a coating on the front or rear exterior lens surface(s) won't contribute to the flare reduction, so unless you're going to disassemble the lens and clean the internal lens surfaces, you don't have to worry about changing the flare character from simple lens cleaning. – scottbb Mar 12 at 21:21

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