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02-03-2012, 09:45 AM   #1
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Unwanted soft-focus/blur on lens!

Hey everyone!

I'm a LONG time forum reader, but only recently found I needed to start a thread. I picked up a 28mm F2.8 Pentax lens from eBay for a steal of a price ($20). As far as I can tell, the glass is flawless and free from any dust/haze or fungus. I have owned dozens of lenses over the years (many of them from garage sales), and have owned a lens with all of these at one point in time, so I have a pretty good idea of what each one looks like.

The problem is that when using this lens (both on my K1000 and my Canon 1DS MkII with adapter) everything seems to have a soft focus/blur effect. I can see when it is "in focus" at an easy focal point, but the blur is quite evident all around. If you wouldn't mind, would you take a look at the example below and tell me what you think it might be? Aside from haze/fungus (which is not visible) I can't imagine what would be making this happen on both my bodies!




02-03-2012, 10:27 AM   #2
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could be fungus, do you see any web-like strands on any part of the glass or edges of the glass when you put the lens up to a light/background? It is pretty common in older lenses and can cause the haze you see

EDIT: I see you say it is not fungus, sometimes it can be difficult to see or can look like small scratches, fungus aside I am not sure...
02-03-2012, 10:28 AM   #3
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Is this same character present when stopping down? This effect where focus is achieved but haziness is present must be due to light being scattered within the lens. As you have identified, haze/fungus are frequent causes. Could also be caused by many fine scratches, poor lens coatings, or anything else that might scatter the light. It can also be caused by spherical aberration, sometimes intentionally as in soft focus or defocus control lenses.

What is the actual model of lens? Pentax did made an FA 28/2.8 soft focus lens.
02-03-2012, 10:33 AM   #4
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Element separation, maybe? At the far right the item in red looks like it has motion blur but at 1/200 speed I doubt that, but it still looks like multiple images.

You do not mention which 28mm this is, A, K or M?

It is also possible someone opened it up to try and repair or clean and reassembled improperly. I reversed a lens element once and the result was similar.

02-03-2012, 10:38 AM   #5
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A long time ago, I remember seeing a soft focus lens for "dreamy" portrait work. I don't remember if it was 28mm but it could be. Does it say soft focus anywhere?
Is there any wobble or rattle in the lens?

Thanks,
02-03-2012, 10:59 AM   #6
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Hey everyone,

Thanks for the super quick and helpful responses. Allow me to address each one:

1) I do not see any super fine strands at all, nor any other imperfection apart from two tiny specs of dust that are not visible especially when wide open. I used the loupe I use for contact sheets and held the lens in near-direct sunlight, and still couldn't see anything out of the ordinary.

2) The lens is the SMC Asahi (like this one: Pentax SMC Asahi-M 28mm f2.8 Pentax K Fit Prime Lens wide angle | eBay) I am almost positive it is not a soft-focus lens, nor does it have a soft-focus filter (something I double checked to make sure I wasn't losing my mind!

3) From my understanding, Chromatic Aberration is normally found in conjunction with colored lines on the edges of light lines (purple/blue/red) - but I may be wrong in this! Please correct me if so!

4)The effect seems to be lessened when stopped down (and also when taking a darker subject) but is still definitely present.


Now the most interesting comment was from jatax, as I had not noticed this before. Now that you mention it, the focus ring does have a little slip to it, and feels a bit loose. Could this also be an indication of element separation?

Thank you all for such detailed and speedy responses, several minds always make a problem much easier to tackle!
02-03-2012, 11:00 AM   #7
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Edit: I see you wrote spherical aberration, not chromatic. My apologies!
02-03-2012, 12:19 PM   #8
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Judah,

Here is a link to lens in the lens database. Some interesting reading especially about there being two versions.

What I mean by element separation is that some lenses have elements that are glued together. Here is a link to the lens diagram for version 1. Sometimes the glue used on these elements can deteriorate and cause both a clouding effect and a misalignment of the elements resulting in poor optical performance. But I am just speculating, I am not sure if this lens is prone to that or not.

The focusing ring slipping is probably not a sign of element separation but it could mean somebody opened it up and did not get things back in place properly. By using the lens diagram you could attempt to open and see what is wrong. Or you could send it off for repair but since you paid little I doubt that would be worth it. If your seller offers a guarantee or if they stated it was "in perfect working order" or similar I would send it back. It isn't worth the effort unless you want a project to play with and try to fix.

02-09-2012, 10:11 PM   #9
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Well I just wanted to update everyone - this was my first successful lens tear-down and cleaning! My buddy owns a car-painting shop (a GOOD one), so of course they have a (semi) clean room. I simply used a micro-fiber cloth and a watered-down lens cleaning solution (wasn't sure how delicate coatings are). Again, I didn't find any fungus, but there was a very interesting and barely noticeable film on one of the lens elements, that I could only really see under a jewelers lighted loupe when I opened it all up.

I didn't end up fixing the slipping focus ring, but I got it clean and back together without any major disaster. A couple of specks of dust on the inside that aren't noticeable in images!

For contrast, here is an image I took today with the lens - glow and blur is all gone! (Clarity and levels were pushed a little)



Thanks for all the ideas and input!
02-09-2012, 10:38 PM   #10
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Good for you! It takes quite a bit of courage to tear down a lens that far, and a lot of skill to get it back together without losing the little ball in the f-stop ring!

Last edited by newarts; 02-09-2012 at 11:09 PM.
02-09-2012, 10:40 PM   #11
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Thanks!

Luckily I did plenty of research beforehand on Pentax servicing, and read about that EXACT thing! I have ruined two lenses in the past, so I am very pleased to have this working!
02-10-2012, 06:19 AM   #12
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Wow, excellent work.
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