[Gooshin]

i see this so many times

"dust inside lens, no affect on image quality"

"scratches on front element, no affect on image quality"

"lens missing aperture blades, no affect on image quality"




you get the idea. How much truth is there to this, surely ANY scratch or dust particle on a lens element means light bouncing/bending and hitting the film plane in a way that it was not meant to do.

otherwise lens manufacturers would save alot of money operating their assembly lines in a less clandestine manner.

[vievetrick]

Overal from what I have read and or heard it is true it has little or no impact on the picture. UNLESS (I BELIEVE BUT COULD BE WRONG)you are shooting at a high Fstop with long exposure.

[Gooshin]

if front element scratches dont affect picture quality

then why do so many people oversealously protect their lenses, some even go so far as to stick a UV filter just for the sake of protecting the actual lens!

silly people.

[ryan s]

I could post pics showing that small imperfections like dust don't have an effect.

I could also post pics from a lens with a severe fungal infection (if my other PC wasn't in a box).

I could post pics from a lens with lots of dust AND minor fungus.

I could post pics from a lens with a grain of sand inside.

You couldn't tell me which one was which

Things nearer to the rear of the lens tend to make more of a difference. FWIW...I don't use UV filters unless the front can be scratched...aka...using extension tubes with a lens at around 2:1 magnification with a close working distance.

[séamuis]

silly people.

im silly then.

[Gooshin]

im silly then.

so then you believe that dust particles and front element scratches DO affect image quality?

[Douglas_of_Sweden]

I could post pics showing that small imperfections like dust don't have an effect.

I could also post pics from a lens with a severe fungal infection (if my other PC wasn't in a box).

I could post pics from a lens with lots of dust AND minor fungus.

I could post pics from a lens with a grain of sand inside.

Do that, it would be interesting.

[Gooshin]

I could post pics showing that small imperfections like dust don't have an effect.

I could also post pics from a lens with a severe fungal infection (if my other PC wasn't in a box).

I could post pics from a lens with lots of dust AND minor fungus.

I could post pics from a lens with a grain of sand inside.

You couldn't tell me which one was which

Things nearer to the rear of the lens tend to make more of a difference. FWIW...I don't use UV filters unless the front can be scratched...aka...using extension tubes with a lens at around 2:1 magnification with a close working distance.

the point is that people inflate the sale price of an item by using such blanket statements as "like new"

and covering up obvious wear and tear signs, such as scratches, fungus, and dust, with dubious statements like "has NO affect on image quality"

if you did not get the intention of my first post, i will rephrase it for you, i do not care whether one could notice something or not, which is a dubious statement in itself as a blind man sees much less than you and me.

i am asking if scientificaly, in an absolute sense, lens defects affect image quality.

[Geekybiker]

i am asking if scientificaly, in an absolute sense, lens defects affect image quality.

Of course it does. anything other than an optically perfect lens would. The question really is- "Does it produce an effect noticeable by the average person."

[lithos]

if front element scratches dont affect picture quality

then why do so many people oversealously protect their lenses, some even go so far as to stick a UV filter just for the sake of protecting the actual lens!

Because dent filter rings are a bitch.

[Ivan Glisin]

Cut a small square or a tiny strip from a Post-It note (adhesive part) and stick it on the front element to simulate a ding or a scratch. Doesn't need to be too small. Then shoot and see for yourself if there is any difference. No worries, you can not damage anything and it is easy to clean if any adhesive remains (probably not). Then remove stickers and take another series of the same subject. Compare "damaged" and clean glass. Most likely you will not be able to see any difference.

Of course, this is not exactly the same as a scratch (no light refraction) but it is close enough simulation without damaging the lens.

[woof]

Of course it does. anything other than an optically perfect lens would. The question really is- "Does it produce an effect noticeable by the average person."

Agreed. More concretely, a wide angle lens with a front element scratch or scratches might be more apt to show at small apertures because depth of field will tend to bring the flaw close to focus.

I have a an old Retrofocus 28mm lens with a rather alarming scratch. At small apertures, this lens focuses from inches to infinity. So that scratch, while not in focus, sure is close to being in focus. I have never detected the scratch per se, but the effect I DO see is that the lens is a little prone to flare at times, and the scratch seems to be the culprit. The flare always seems to appear in just the quadrant where the scratch terminates and is deepest. Some day I'll probably get 'round to restoring this lens.

woof!

[WJW]

you get the idea. How much truth is there to this, surely ANY scratch or dust particle on a lens element means light bouncing/bending and hitting the film plane in a way that it was not meant to do

The biggest problem is usually that the dust/scratch causes extra flair. If the lens is properly shaded, the effects would not be noticeable unless you were comparing to a pristine version of the same lens. Having said that, I tend to stay away from very dusty or scratched lenses because you don't know how they acquired the problem and what else might be wrong.

Btw, one of my favorite examples of what a defective lens can do is here:
Vintage Folding Cameras

[ryan s]

Do that, it would be interesting.

If my PC had a place to be set up here, I'd do it

the point is that people inflate the sale price of an item by using such blanket statements as "like new"

and covering up obvious wear and tear signs, such as scratches, fungus, and dust, with dubious statements like "has NO affect on image quality"

if you did not get the intention of my first post, i will rephrase it for you, i do not care whether one could notice something or not, which is a dubious statement in itself as a blind man sees much less than you and me.

i am asking if scientificaly, in an absolute sense, lens defects affect image quality.

I realize that, and I realize what lens you're talking about. My post was that, while certain things make more of a difference, some are negligible in the grand scheme.

When I sell a lens, I will mention that there are small dusts specks and that these specks won't show in pictures. If it was anything more serious, I would mention it. I'm upfront so there aren't any surprises, and I don't stick someone like I got stuck last week

Now that I see what you meant, we see eye to eye. I didn't before replying the first time...

[Mike Cash]

The best example I have ever found of how it is not necessary to worry overly much about a few dust specks:

You won't believe this