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12-26-2013, 05:14 PM   #1
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Pentax Asahi f4 macro 100mm question

ok, here's the lens I got at a bargain. Some users say it's not fungus but cement or haze

Pentax M SMC Macro 100mm F 4 Lens Pleae Read K Mount 60 Day Guarrantee | eBay

Got the lens today. Took these photos. Tell me if you think the debris inside the last element is affecting the lens or not. All photos taken between f4 and f8 under a lamp. There is some yellowing that seems to occur in the images - just wondering if users thinks that's caused by debris or just lack of light


Last edited by Michael Piziak; 12-29-2013 at 08:20 AM.
12-26-2013, 05:26 PM   #2
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effect of fungus

Very difficult IME to detect the effect, if any, of fungus. The only occcasion I felt I had a clear effect was with a tamron zoom where I was able to make direct comparison with a clean lens. Fungus was effecting a number of elements and I felt I was seeing a clear loss of contrast. Thats the most likely effect.

Yellow pics? Indoor lights alwways a bit tricky to get white balance right. But in any case unlikely to be anything to do with fungus.

More often than not you can be a bit blase about a bit of fungus in a lens IME
12-26-2013, 05:51 PM   #3
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Had a lens with separation/haze on the back glass once. When shooting in good light conditions it would give a hazy image. Kinda dreamy effect.
12-27-2013, 10:01 AM   #4
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Under these lighting conditions I don't see anything out of the ordinary with these images. The color cast to the images is from the lights that were used to illuminate the subjects. The images are under exposed as the camera's light meter was fooled by the predominately white image. If these images are indicative of what you're normally going to use the lens for then I'd say your test is fine and you have nothing to worry about. However, if it isn't - say you're going to use it outdoors with the subject backlit, top and/or side lit, then you need to take more images to see if the lens will work under those situations too.

12-28-2013, 12:56 PM   #5
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I wouldn't be surprised if most of that damage isn't from cleaning. The center of the front element looks like a nice fat cleaning mark, and the damage at the edge is quite even.
01-01-2014, 04:59 PM   #6
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This lens continues to perform as is:
https://www.pentaxforums.com/forums/12-post-your-photos/247066-macro-water-droplet.html
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