Pentax Asahi f4 macro 100mm question

Michael Piziak · 12-26-2013, 05:14 PM

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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.

**marcusBMG** · 12-26-2013, 05:26 PM

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

striker_ · 12-26-2013, 05:51 PM

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.

FrankC · 12-27-2013, 10:01 AM

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.

Wheatfield · 12-28-2013, 12:56 PM

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.

Michael Piziak · 01-01-2014, 04:59 PM

This lens continues to perform as is:
https://www.pentaxforums.com/forums/12-post-your-photos/247066-macro-water-droplet.html

12-26-2013, 05:14 PM	#1
Michael Piziak Closed Account Join Date: Dec 2013 Location: West Virginia Posts: 2,815	Pentax Asahi f4 macro 100mm question Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here. 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
marcusBMG Site Supporter Join Date: Nov 2012 Location: North Wales Photos: Gallery \| Albums Posts: 2,870	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

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12-26-2013, 05:51 PM	#3
striker_ Senior Member Join Date: May 2011 Location: Sweden Posts: 158	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
FrankC Veteran Member Join Date: Dec 2011 Photos: Gallery Posts: 322	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
Wheatfield Moderator Join Date: Apr 2008 Location: The wheatfields of Canada Posts: 15,991	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
Michael Piziak Closed Account Join Date: Dec 2013 Location: West Virginia Posts: 2,815 Original Poster	This lens continues to perform as is: https://www.pentaxforums.com/forums/12-post-your-photos/247066-macro-water-droplet.html