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11-30-2018, 06:05 AM - 2 Likes   #1
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Are glass blemishes really affecting performance of vintage lenses?

Today I went through a huge number of pics I had saved in my laptop in jpg format.
I was trying to clean the clutter and free some space, as I have transferred long ago both raw archives to USB drives and posted some of the most relevant online, on different fora/sites. Which actually means that I have no use for many jpg's that are just eating up precious space on internal HD's (I have two, one SSD and one traditional, in place of the DVD).
Erasing dozens and dozens of jpg files I found a test I did long time ago, whose very existence had completely slipped out of my memory.
One interesting set was a test of three M42 lenses, made with a K10D camera (which I still have, equipped with a chinese plastic ground glass with diagonal stigmometer and microprisms).
The lenses that were tested were a Meyer Lydith 30mm, its Pentacon successor with identical optical layout, and a Panagor 2.5/28mm. The latter is practically identical to the Kino-made Vivitar that of course is present in the Vivitar 28mm Bestiary Internet page.
Examining the shots at 100% I found that the best lens is the oldest of the three, the Lydith.
It beats by a small margin the Pentacon (which should have a slightly better coating), and by an important margin the Panagor.
It's not what I would have expected, as the Pentacon and the Panagor are in very good shape, while the Lydith example I tested has a small scratch and some coating blemishes on the front glass.
Recently I am trying to buy vintage lenses in perfect shape, while in the past I wanted to try them, and I was happy to acquire examples that were in less than ideal conditions.
Well, it seems I was right!
The images from that quick test seem to confirm what I have learnt with practice: a spotless glass (especially the front one) is not a necessary precondition to punchy, detailed pictures.
Some vintage lenses have so-and-so front glass and work great, while others look perfectly fine... but they are out of whack, and perform accordingly!
Some might even be like that from day one. It is widely believed that soviet lenses had QC problems towards the end of the Soviet Union.
The same way, some historical german brands had slowly worsening assembly standards towards the end of their activity.
However, I guess that most lenses were perfectly fine when they left the factory, but over a long period of time they might have been wrongly/carelessly reassembled. Others sustained strong impacts, which could have left no traces, because some lenses were built like tanks!
All in all, most vintage optics are quite impervious to "accidents", unlike modern AF zooms with plastic zoom and focusing sleeves.
Though some are actually totally out of spec, and it happens that every now and then I realise I got a lemon.
Sometimes it's just hazy, and it's easy to restore it to its former glory.
Sometimes the optics are misaligned, or (even worse) there are missing distancing rings or other major problems.
I think I have never found a hugely disappointing lens that is underperforming because of glass damage, unless it's a real disaster, like a front glass practically sanded down by repeated attempts to clean the lens without blowing off sand particles.
I have seen few lenses in that conditions, but I have seen some that had large part of the very soft coating completely removed.

I am asking for some stories that would confirm my point (or eventually disagree).
Maybe some funny/extreme story. I know of a micro Nikkor that was etched with the tip of an iron nail by a child, and was tested afterwards by my repairman, proving as sharp and with practically no decrease in contrast!
It would be interesting to understand if you would ever buy a lens with a visibly damaged front glass, knowing for sure that it would not affect the performance.
In all sincerity, I got a bit snobby under this point of view. I guess because half of my brain thinks as a collector, and not in practical terms of photographic output (the actual quality of the final image).
At the same time, it is also true that I recently bought a few vintage lenses, knowing that they had fungus/haze problems, because I wanted to take the chance to fix them, and because a mint example would cost a little fortune...
I realise that I always carefully check the pictures OF the lens, but I almost never have the chance to actually see any picture made WITH the lens I am going to buy. I should try to ask for sample images, but it's not always possible.
Despite taking some risks, and ending up with optics in far worse condition than I expected, fortunately I found that some of the objectives that have some glass imperfection are among my favorite.
Maybe I would never buy any of them now, if I was aware of the problem, but I am glad I did when I was more interested in trying new vintage lenses at a decent price than having collector grade examples... which by the way may even get less use because of their value.
I am not sure I would carelessly throw in a soft groceries bag (together with a low value K10D or K-01) my recently CLA'ed Primoplan or my beautiful 8-elements Super Tak, as I often do with other low value or very "experienced" optics.
An imperfect lens is always better than no lens at all. I found that some of the best shots come unexpected, and having a camera/lens you are not afraid to lose or ruin can make those shots possible... and it's great if when you get home you find that the "imperfect" glass works pretty well!


Last edited by cyberjunkie; 11-30-2018 at 06:15 AM.
11-30-2018, 06:38 AM - 2 Likes   #2
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Minor surface defects, including easily-fixed ones such as dust and smudges, have very little impact on IQ unless directly struck by a strong light source, mainly because they are so out of focus. Front and rear surfaces are probably damaged more by compulsive cleaning than anything else. Sharpness freaks may disagree but kids, sharpness is overrated.
11-30-2018, 07:29 AM   #3
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What you say is largely true. Many types of minor blemishes (internal dust, scratches, fungus, damaged coatings, haze, etc.) have no obvious effect on lens sharpness.

The reason is that blemishes do not affect the overall bending of the light (refraction) which is controlled by the curvature of the lens surface and the physical properties of the bulk glass.

Blemishes don't affect bending of light but they do effect scattering of the light. Thus, blemishes will fog the blackest blacks in heavily backlit scenes and affect shadow recovery and HDR.

Other effects:
1) scratches and dirt can create tiny repeating patterns in the bokeh
2) scratches and internal dirt can cast faint shadows on the image when stopped-down

Solutions:
1) keep the sun or any direct light off the blemished elements of the lens
2) a good petal hood reduces the amount of stray light being scattered
3) stopping down can reduce the effects of blemishes on the periphery of lens elements such as fungus and balsam separation

Used carefully, many an ugly lens can take beautiful pictures!
11-30-2018, 08:13 AM - 1 Like   #4
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Muy dad used to show buyers in his camera store that compulsive cleaning wasn't needed... He would take a small square of lens cleaning cloth and wet it, then he'd stick it on the front element and have them ok through the viewfinder. Most couldn't tell it was there!

11-30-2018, 08:44 AM - 1 Like   #5
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Scratches on the front element have little effect on the final photo. Common wisdom back in the day was to buy up heavily used pro telephotos cheap, and to fill any scratches in the front element with black paint - making them less likely to light up and scatter light. If you take a photo with such a lens and you have an out-of-focus "bokeh bubble" highlights, you can see the scratch in each one! Otherwise, you don't see it.

But .... but .... scratches on a small rear element are much more catastrophic in my experience. Carelessly setting an ultra-wide angle down without a rear cap, can leave a mark that makes every photo a flarey, fuzzy event.
11-30-2018, 08:46 AM   #6
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QuoteOriginally posted by Ontarian50 Quote
But .... but .... scratches on a small rear element are much more catastrophic in my experience. Carelessly setting an ultra-wide angle down without a rear cap, can leave a mark that makes every photo a flarey, fuzzy event.
Agreed!
11-30-2018, 10:42 AM   #7
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QuoteOriginally posted by Ontarian50 Quote
Scratches on the front element have little effect on the final photo. Common wisdom back in the day was to buy up heavily used pro telephotos cheap, and to fill any scratches in the front element with black paint - making them less likely to light up and scatter light. If you take a photo with such a lens and you have an out-of-focus "bokeh bubble" highlights, you can see the scratch in each one! Otherwise, you don't see it.
I've got a Tamron 90-300mm with a "substantial" scratch on the front element that I'd not worried about simply because it didn't seem to make any difference (I almost invariably used a hood).
I had a vague memory about the black paint trick, but couldn't convince myself if it was fact or not. Given this confirmation I'll be digging out the ultra-fine brush an having a go. The lens only cost £5 in a charity shop, so I'd nothing really to lose, but I'd not wanted to risk spoiling an otherwise functioning lens


Thanks
11-30-2018, 10:47 AM - 1 Like   #8
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My Helios 44M has a scratch on the inner surface of the rear element that almost certainly originated at the factory. If it affects the photos, I have never noticed. I have a few Zeiss Jena lenses with tiny bubbles, but those are common enough for German lenses of the time. I have not yet used those lenses, but don't anticipate any issues.

I did have a Super-Takumar 28/3.5 (v1) that I had to return, however. The lens was cosmetically quite clean as were the front and rear elements, but photos taken with it were impossibly "smeary". On close examination with a magnifier and bright light, it was obvious that several of the internal surfaces had been scoured with some sort of abrasive and were significantly marred. I took that to be the smoking gun (refraction happening at the lens surface after all) with the scratches probably having been made during an attempt at fungus removal. The seller reluctantly agreed to accept the return after sending me a link to an article about how scratched lenses work fine.

Although I admit to not doing a thorough inspection of the lens above, my usual practice is:
  • Do a close inspection of the glass in a dimly lit room using a small flashlight and magnifying loupe from both front and rear. Any scratches, fungus, or internal water spots will be quite evident as might damage to external coatings.
  • Inspect the aperture blades for damage and oil contamination and check the aperture function (snappy and proper without hesitation) at all settings
  • Confirm smooth and easy action for all controls (focus, aperture, A/M switch, preset mechanism, zoom)
  • Confirm that the mount is free of excessive wear and damage to thread, tang, and coupling levers. Pay particular attention to alignment and appearance of coupling tabs/levers.* Do this before attempting to mount to a body...yes, even on new lenses.
  • Confirm that the filter threads are whole and thread properly
  • Confirm that the lens is free from excessive play in any of its parts. This may be somewhat difficult to assess on some older zooms, but if there is obvious lapse of optical alignment it may be best to pass on the purchase.
Additional notes:
  • Mild scratches on the front element are often of little concern. The same is not true of the rear element. Deep scratches either end are reason to not accept the lens except perhaps for parts or for household decorating.
  • A bent or broken filter ring is often evidence of a hard impact, hard enough to potentially damage the lens internals, particularly with zooms
  • Never buy when the description says "slight cleaning marks...will not affect performance", unless you are willing to accept creative rendering
  • Never buy when the description says "converted to clickless aperture, parts to restore included" unless you are willing to accept that it cannot be restored.**

Steve

* I learned the hard way on this point when a factory defect on a Russian lens permanently munged the aperture actuator of one of my 35mm SLRs, turning a favorite body into a parts camera. Not happy.

** I have a CZJ Pancolar 50/2 in Exakta mount that was hopelessly damaged due to a botched declicking.


Last edited by stevebrot; 11-30-2018 at 11:07 AM.
11-30-2018, 12:16 PM   #9
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Most of my lenses have come to me in less than stellar condition due to my eternal poverty. I have removed mould from a few, have some with scratches or water spots and some that are wobbly. I have never been disappointed by a lenses performance compared to examples from presumably mint copies that I have seen online.

This includes my da15 with a long scratch on the rear element. Also my fa50 showed no improvement after I cleaned the mould off the rear element, so I wouldn’t even be too worried about defects on the rear of a lens either.
11-30-2018, 12:51 PM   #10
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QuoteOriginally posted by Ontarian50 Quote
But .... but .... scratches on a small rear element are much more catastrophic in my experience. Carelessly setting an ultra-wide angle down without a rear cap, can leave a mark that makes every photo a flarey, fuzzy event.
Used to see people do that taking a lens off their camera. I would literally cringe and shudder with horror but they usually say "Oh, I always do that".....Aaaaargh!
11-30-2018, 01:47 PM   #11
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A family member of mine who was a professional in the 70's told me about a friend who used to produce amazing images with an ethereal quality and no one knew how or why.

One day during an outing with him they looked at his lens and realized why.... super dirty!
11-30-2018, 04:20 PM - 4 Likes   #12
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I sandpapered the front element of my 18-55mm WR to try to get some light scatter across the glass and take some of the hard edge off the rendering. I'm not suggesting that it's something that a sane and normal person would want to do, but I'm happy with the results:







11-30-2018, 04:49 PM - 2 Likes   #13
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QuoteOriginally posted by Dartmoor Dave Quote
I sandpapered the front element of my 18-55mm WR to try to get some light scatter across the glass and take some of the hard edge off the rendering. I'm not suggesting that it's something that a sane and normal person would want to do, but I'm happy with the results:







Would doing it on a filter have similar effect?
11-30-2018, 05:01 PM - 2 Likes   #14
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I'm holding the rear element group to my Zeiss 25/2 lens. Initially, the rear element had a couple of scratches on it. Those scratches bugged me, so I used a Dremel tool and some fine polish in an attempt to buff out the scratches.

Well, the rear element group got hot (very hot), and the entire rear element group cracked clean through, right in the center.

I put this scratched, cracked optical group (with the coating partially removed) back into my adapted Zeiss 25mm f/2 lens. I took some photos with it on my K-1. To my surprise, I was able to take the attached half-way decent photos with this lens. For mid-range and distance photos, I can see a degradation of the image. However, when I use this lens at it's closest focus point, I really can't see any degradation of the image..




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Attached Images
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PENTAX Q7  Photo 
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PENTAX K-1  Photo 
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PENTAX K-1  Photo 
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View Picture EXIF
PENTAX K-1  Photo 

Last edited by Fenwoodian; 11-30-2018 at 05:14 PM.
11-30-2018, 05:25 PM   #15
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QuoteOriginally posted by Dartmoor Dave Quote
I sandpapered the front element of my 18-55mm WR to try to get some light scatter across the glass and take some of the hard edge off the rendering. I'm not suggesting that it's something that a sane and normal person would want to do, but I'm happy with the results:







Those are very cool, so I guess the answer is that marks of this sort definitely affect performance.


Steve
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