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Two Kowa Prominar 883 samples (1 Viewer)

BoldenEagle

Well-known member
Hi,

today I had a chance to briefly star test two Prominar 883 samples. I also did a basic comparison using 20€ bill as a target with my own Prominar 883 sample and Zeiss Victory Diascope 85 FL as a reference scopes. I tested these all with their zoom eyepieces @60x. I have earlier posted star test pictures of my Prominar 883 sample in to this thread: https://www.birdforum.net/threads/kowa-prominar-883-star-test-pictures.392589/

Now today the first sample showed quite obvious astigmatism and maybe little coma, SA was at least not any better than in my sample but I think not obviously worse either. It didn't show as sharp image as my sample (or Diascope). I think it still was better than the worst 883 sample I have tested so I don't think it could be regarded as a lemon.

Second sample didn't show any obvious astigmatism, SA was about the same as in my sample but it seemed to have more obvious coma (my sample also has just little). When comparing with my sample, it was very close but I had strong impression that it was at least not any better, maybe just slightly less sharp if I would have been forced to make a difference by this test.

Both of these samples and also my current sample shared one obvious defect in a star test; all had distinct yellow prism roof line vertically accross the diffraction pattern. I think it may be quite common defect with 883 since I think both samples tested here by Henry Link show that very same yellow vertical line: https://www.birdforum.net/threads/tests-of-two-tsn-883-scopes.125302/ If very carefully observed at least two samples I tested, showed also faint dark vertical bands on both side the yellow line (my sample and another of these two I tested today).

I think the sample I have now is quite good actually but it could be better because the reference scope Diascope 85 is sharper and resolves better even if it has smaller aperture. I think Diascope has just some SA but is otherwise quite excellent sample. I think only IQ area where my Kowa 883 sample seems to be obviously better is contrast and maybe more vivid colours.

Regards,

Juhani
 

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