Lens scratches/image quality

[stephen_vaughan3]

At what point do scratches, cleaning marks etc. (on the front and rear

elements of a lens) begin to cause a loss in image quality?

Have just bought a lens which has some marks on the outer surface of

front and rear - how much should I be concerned?

Thanks in advance for your replies........

[light-zone]

Stephan, without seeing the amount of damage involved, it's tough to guess as to the image quality the lens can provide. A test film is really the only way of knowing what damage has been done if any. Take shots in a variety of lighting situations, including backlighting and shots at dusk or dawn, with lots of shadow detail. That should give you a good idea of wether the lens is a keeper or not. Polishing out the scratches will more than likely cost you more than you paid for the lens in the first place, and most repairmen will advise you against it, especially if the lens is coated.

 

I can relay a story about one of my worst ebay experiences though. I bought a Rolleiflex 2.8C for about $350. The taking lens was described as having some cleaning marks. Sounded harmless enough. After buying the camera, I soon discovered that the "cleaning marks" were created by cleaning the lens with what looked to be a steel wool pad. OK, that's a bit exaggerated, but the results of my test film concurred with my initial reaction. The negs were a disaster. I contacted the seller, (a photo store) and arranged for an immediate return. I considered myself lucky to get out of this situation none the worse for wear. But what I did learn from the whole ordeal was this: one mans light cleaning whisps are another mans soft negatives.

As with all things used, buyer beware.

[brian_ellis3]

I don't think there is a fixed "point" where there's a "loss" in image quality. It depends on the number of scratches, location of the scratches (towards the edges of the lens is better than at or near the center), the length of the scratches, the depth of the scratches, whether they're on the front or rear glass (scratches on the rear are supposedly worse than scratches on the front as I recall), and the lighing conditions under which you're photographing. Even if you use the lens and conclude that the scratches have no noticeable effect on image quality under a variety of lighting conditions, they will adversely affect the resale value of the lens so you hopefully got a good discount on your purchase. Personally I wouldn't buy a lens with any scratches anywhere, it's too easy to buy lenses without them.

[tim_hicks]

I like to try old lenses and if they are cheap enough I have bought ones with small cleaning marks. The rules I follow are:

 

1)Marks on the front are less likely to affect the image than marks on the rear element

2)Avoid balsam seperation - it will probably get worse

3)Is a fair price considering the condition?

4)Is it just dirt? I have bought a lens with marks only to discover it just needed proper cleaning with suitable lens cleaning fluid

5)How rare is the lens?

6)As a percentage of the overall area of glass how much is the damaged area? For example lots of minor cleaning marks may affect the image more in terms of flare and loss of quality than a scratch near the edge that is only 1% of the area

7) Try before you buy if possible.

[roger_michel]

the question is really impossible to answer. the only way to assess the loss in quality due to the scratches would be to compare negs pre and post scratch. needless to say, lenses are not designed to be used scratched, and so presumably any marring of the surface will result in stray light with concomitant loss of resolution and contrast. having said that, there is also a tremendous amount of overkill built into lenses. i have owned lenses, scratched them, and then not noticed a post scratch degradation. the only real answer here is to use the lens and see if you are happy with the results -- preferably as compared with other similar lenses. without a benchmark of comparison you are just guessing. it would be a pity to use the lens for a few years, be reasonably happy with the results, only to use a pristine example and suddenly see what you'd been missing. one final point: with the huge volume of unscratched second hand LF lenses out there, why bother with a scratched lens unless you get a REALLY good deal?

[nick_morris]

Stephen, I have found the comments already given to be good advise. I would like to relate my experience with a a real mess of a lens. It is an old Wollensak Series IV Velosigmat 6.3/9 1/2" in an Optimo shutter. It came with the Eastman 2D 8x10 I bought. This lense has scratches on both front and rear elements, some "grunge" around the outside of the front element, and a chip at the edge of the rear element. But, you know what, it doesn't take bad pictures. A bit on the soft side, particularly in low contrast situations, but reasonably sharp, if a bit unpredictable. It sort of confirms what I'd heard years ago about 8x10s, that you could shoot through the bottom of a Coke bottle, and still get a good image.

Not that I would suggest such a lens for professional work, or where good quality, dependable results are required. But alot a people seem to be buying older, messey lenses to experiment with (a la Sally Mann), and they can be fun, if they can be acquired for a reasonable price.

[tony_galt]

As everyone else has said, it depends upon the nature of the scratches. There is a cheap repair that could be tried for small isolated deeper scratches in the glass itself (not the coating), especially if they are off axis. If you have a steady hand and some kind of a magnifier (the one time I did this, I used a low power binocular microscope I had access to), you might try filling the scratch, and just the scratch, with black paint using a very fine brush. I would try the lens with the scratch before doing this, perhaps shooting in situations likely to cause flare, to see if the current situation is objectionable. (It may not be; I have a 24mm Pentax lens with a 1 mm scratch close to axis, and I don't see much difference.) If you think it is, you might not have much to lose trying the paint trick, especially if it is an older inexpensive lens. The paint neutralizes the light scattering effect of the scratch. Obviously this won't work for cleaning or swirl marks and other kinds of hairline scratches. It is better for, perish the thought, "puncture wounds."

[kcrisp]

Stephen: A few suggestions based on my experiences. It depends. Shoot a contrasty scene with something white being hit by the sun. Does the image lose contrast and fuzz up around that object? If not, you're probably out of the woods. If it does, it may still work fine in less demanding circumstances, but specular highlights and bright objects will be trouble, every time. A few scratches don't matter, if they are a blur of scratches and take on the effect of an overall haze when you look through the lens at a bright light, this is serious. Chips and small but deep impacts are usually not much of a problem, especially on the front, but if they pick up light when you look through the lens from the back you can use a very fine point Sharpie to darken it and this incredibly dumb suggestion (gleaned from this forum) works well. Remember that cleaning marks ARE scratches, after all. Without seeing the lens in hand I don't think anybody can definitively answer your question.

[david_grandy5]

Although this isn't exactly on point I have a story to tell.

 

When I was a university a fellow photographer bought a used enlarger. He already had a set of EL-Nikkors and he looked at the "comes-with-the-enlarger" EL-Cheapo lens with some disgust. So for a lark (and probably after a beer or two) he took a hammer and smashed the front element of this $10 lens. After he had done that, it occured to us that this might produce some interesting results in the darkroom. So we grabbed it and a neg, an off we went to try a print.

 

When we made an exposure though this lens we were all amazed to see that it had no obvious effect! Was it sharp? It seemed to be. Was it contrasty? No worse than usual. And the ding that he put in the lens looked like what would happen when a rock hits a car window.

 

I'm sure that optical quaility WAS reduced. But after seeing how much damage was done to the lens and how little it affected the test print, I've decided that owing a pristine lens just makes me feel better and that a small ding on a lens wouldn't be the end of the world.

[roger_michel]

i assume you were assessing the quality of the resulting print "after a beer or two" as well.

[eric_mortensen3]

In my experience you will be hard pressed to find any degradation of image quality from superficial cleaning marks that only affect the coating, front or rear.

That said, there seems to be an inverse relationship between film size used and the level of anxiety experienced by the user when it comes to lens imperfections.

And, a linear relationship between user anxiety and user-induced marks to the lens while cleaning.

So, if this is true then 35mm lenses should on average have more cleaning marks than lenses that cover larger formats.

And those cleaning marks will be more likely to affect image quality.

In my opinion, life is much too short to worry about these things.Go shoot some film and enjoy the results!

[jim_galli4]

I'd rather have a Symmar with a few cleaning sleaks than an Optar that was New In Box. Give me a wispy EBC Fujinon over any Komuranon. I'm working myself into a polygon and a fight I'm sure to be a bringanon.

[light-zone]

Hey Jim, them be fightin' words were I come from....;-)

 

I think the point is, how the cleaning marks/scratches are described is a lot different than how they could potentially affect the performance of the lens. One persons "cleaning wisps" are another persons scratches.

 

Load some film and find out what, if any damage has been done to the lens.

[angel_justo]

I own 2 old Nikkor lenses with minor cleaning marks and I am quite sure they have no effect at all in my pictures. I also own an old pentax 35mm that has the front element completely broken (it fall out from my hands and hit a rock). Watching the lens you would surely say that it would be useless. Well, I still take pictures with that lens. I suppose you would be able to see the difference if you look carefuly enough, but if you're not told what to search for, it is just imposible to see any difference.

 

So cleaning marks were not and will not be a problem to me. I purchased a few days ago another Nikkor (300mm 2.8 ED AIS) highly reduced in price because of cleaning marks. I saved hundreds of dollars and still have nice and crispy pictures from my lens.