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12-19-2012, 03:32 PM   #1
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Flaring issues with 645 lenses on K mount

Recently I've been using Pentax A 645 lenses on my K20d. I have a generic 645 to K mount converter with no communication between the lens and camera. I had been shooting an A 55, A75, A135, and now an A 150 lens. I'm noticing that I get a white haze in the center of the image (yes, I know, and example would be nice...I'll see if I can post something with this in effect in a bit) on daylight shots. I first thought it was because I didn't have a sunshade on my lenses but today in seeing this again with the A150, I'm getting it when the camera is pointed towards the sun and when it's pointed away from the sun in broad daylight. In trying to work with it, I've found (at least on my A 150) that if I open up to maximum aperture (f3.5 in this case) to a couple of stops down, the haze seems to clear but if I go at say f8 or smaller, I get more and more haze. Note that I'm shooting in manual mode and doing the stop down metering properly. I've also gotten some help rolling in -1ev or so. All of that aside, although my shooting with these 645 lenses is not critical, I can't explain what's going on other than apparently, something is happening optically that I don't understand. It doesn't seem to matter to if I meter with grid or spot metering as well. For me it looks like the kind of hot spots I get with some lenses on my IR converted digital camera.

So...anyone got a clue on this? and if so, how do I avoid this.

TIA

12-19-2012, 03:59 PM   #2
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Not specific to your lens, but often the light reflects of the closed diaphragm and then back again--so shooting wide open can resolve that. The next thing to check is the generic adapter--if not properly blackened/baffled it may be the additional factor.
12-19-2012, 04:57 PM   #3
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I have the same problem with my Pentax-645 FA300mm/5.6, Pentax-67 M*400mm/4, Takumar (6x7) 75mm/4.5, Takumar (6x7) 200mm/4 . It doesn't always happen, only in some occasions. With my P-67 M*400mm since i use it most of the time at f/5.6 the problem is not frequent.
12-20-2012, 06:13 PM   #4
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I've also seen this problem when using generic adapters. Applying flat black paint to any shiny surface on the interior of the adapter should eliminate the flare/haze.

12-21-2012, 03:20 AM   #5
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18 months ago I got a SMC Takumar 200/4 which had the light absorbing matte painted tube at the back fallen out on arrival. I had exactly this effect.

https://www.pentaxforums.com/forums/general-technical-troubleshooting/152972-...-function.html

In that case gluing the tube back in remedied the problem.

Check your generic adaptor - does it have matte light absorbing aint on all the internal surfaces. If there are any shiney surfaces you get this problem.

I also got a similar effect with an Auto Tak 35/3.5 which has a glossiy back end, unlike the later series which have matte black paint on the film/sensor facing surfaces. From that I concluded that digital sensors reflect much more light than film, thus enabling this 'fogging' problem with dSLR where a fild SLR did not have the problem.
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