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08-14-2013, 11:32 AM   #1
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Lens haze/flare issue

I'm really not sure if this issue is what is called "flare" or not. But I have a Pentax-F 35-70mm af lens. It's really a great piece, nice and sharp and good colors, generally one of most liked zooms. But when I compare it to many of my other lenses, this one seems prone to an issue that I'll try to describe. When I'm shooting into medium/low light and there's a bright, high contrast area, say bright sky behind trees or similar, that bright light casts a washed out hazy area around the light section and smears across the darker areas, it kind of washes out the image to a degree. My other lenses don't do this nearly as much or at all. It's a diffuse and washy, hazy light, not rings or points that I'd typically associate with "flare". Is this an issue that varies from one example to another, or is this the nature of the -F 35-70mm lens in general.

When I shoot in brighter or lower contrast light, this lens excels nicely, but in these lower light with points of bright, this washed out thing happens. And I'm using a hood. This light is well inside the image when it's causing this problem.

Thanks,
Brad

08-14-2013, 11:41 AM   #2
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Here are two cropped images that demonstrate what I'm talking about, both at f8. The first/flared image is the Pentax-F 35-70mm. The 2nd, less flared is the Pentax DA 18-55mm II.
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08-14-2013, 11:57 AM   #3
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Haze, Flare or Glare?

Hello Brad,
I have the same lens and like it a lot. I've noticed that it's a bit prone to flare, but no worse than other lenses of it's generation and better than some.
But I did find that a regular wide-angle hood didn't help much. With the APS-C crop, this is more like a 52-105mm, a medium-to-short-tele zoom.
So, I tried a short generic hood, the type with no 'flare' (excuse the expression!) or bell-shape, just a straight, no-taper hood, normally called a telephoto hood.
I measured mine and it's 20mm or roughly 3/4" from the filter thread to the outer rim. Cut the remaining flare down to virtually zilch. FWIW, I also use this hood on my M 50's, M85 and M100mm. No vignetting or light cutoff on any of these lenses
So, that's one option, these hoods are cheap Hong Kong specials, no problem getting them.
Next, are you using any filters? If so, ditch' em. Well, save the CPL, nothing else.
Last, I'm assuming you've checked the front element for any cloudiness, stain or smears, right? If so, try this; Check the rear element just as carefully. Somehow, don't ask me why, the back glass gets dirt or other contaminent on it and will affect the I.Q. much more than crud on the front glass.
If all else fails, try using a magnifying glass to look through the (wide-open aperture) lens front-to-back and back-to-front at a strong light. Could be a delamination of an inner optic, but I sort of doubt it.
That's about all I've got for suggestions, good luck!
Ron
08-14-2013, 12:02 PM   #4
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Are you shooting with a filter mounted? What this looks like is called "veiling flare" and filters are a common cause.


Steve

08-14-2013, 12:26 PM   #5
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No filters used. I never use one. And thanks for the replies. I guess I'd never really, CLOSELY looked inside this lens, but I just did. I noticed that one of the elements had a distinct hazing with some veiny lines in it. So I pulled the front two elements out. The front piece looks like a pair/group. The second and much smaller piece very well could also be a pair/group. That's the one with the hazing on the rear. I cleaned it and while I got some dust off, the hazing won't change at all, so maybe it is in between the pair of elements. Everything else in the lens looks great, but this one piece has the issue, and it surely looks like it could diffuse the light that passes thru it a bit. Fortunately, these lenses aren't all that expensive, so I think I'll hunt down a hopefully cleaner example.

Thanks for the replies.

Brad
08-14-2013, 12:35 PM   #6
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QuoteOriginally posted by bradsarno Quote
distinct hazing with some veiny lines in it
Sounds like this could be the dreaded fungus having a go at your lens.
08-14-2013, 01:02 PM   #7
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Yeah, could be fungus. Sadly, it's sealed between two pieces of glass in a "group".


B
08-14-2013, 01:42 PM   #8
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It could be fungus, but I also think that modern (DA) coatings are just superior to older (F series) coatings for reducing flare and other aberrations.

I used to have an F 28 2.8, and when I would test it around my house, I could induce that washed-out look in it quite easily from a lamp. A hood reduced it by about 95%.

Contrast this with my DA 35 2.4. I have purposely tried to induce flare and other aberrations in it by shooting it towards a lamp/from several different angles in the lamp's direction. Nothing.

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