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Killing a lens for experimental purposes?
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PostPosted: Mon Oct 19, 2009 8:54 pm    Post subject: Reply with quote
LucisPictor wrote:
Even then some lense are perfectly usable. I have got some lenses with clear cleaning marks at the rear element and they still perform excellently.


In my experience such glasses show evident lack of contrast and resolution.


PostPosted: Mon Oct 19, 2009 9:04 pm    Post subject: Reply with quote
mflex-on wrote:

In my experience such glasses show evident lack of contrast and resolution.


Lot of small ones, yes.


PostPosted: Mon Oct 19, 2009 9:43 pm    Post subject: Reply with quote
Mike Deep wrote:


Mike, how the heck did you shoot that, 10,000 frame video? Nice Image?

High power rifle, full metal jacket? how many groups/elements. Looks a Pentacon 135? Laughing


PostPosted: Mon Oct 19, 2009 11:30 pm    Post subject: Reply with quote
This guy did a systematic test of damaging the front element: http://kurtmunger.com/dirty_lens_articleid35.html

The conclusion is the same as the commonly accepted fact; scratches on front element don't matter. So testing on the rear element would be more interesting… I personally have one good lens with a scratch on the rear element, and my feeling is that it doesn't matter but might cause some irregularities in bright out of focus highlights, but of course I don't know if the scratch is the cause.


PostPosted: Mon Oct 19, 2009 11:48 pm    Post subject: Reply with quote
Arkku wrote:

The conclusion is the same as the commonly accepted fact; scratches on front element don't matter.


Not always. It depends on some factors of which the most important is the focal lenght. A couple of years ago I bought on Ebay a used Distagon 18mm from a Sicilian guy. He described the lens as "perfect". When the lens arrived, it showed a big scratch exactly in the centre of the front glass.
I mounted on the 5D, and took some test shots. The scratch was visible in all pictures. When wide open, it showed up as a large smudged area. When stopped down, as a clear detail reproduction of the scratch itself. When shooting against the sun, the scratch image was visible as flare in all the shots. In other words, the lens was a piece of junk.

So the correct statement to make is: a scratch on front glass MAY not be visible in the photos, depending on the lens type and the circumstances. With telephoto lenses, the chances for a scratch to become visible are small, actually close to non-existent at wide open. Stopped down after f/8 may reveal something.
The shorter the focal lenght, the more the chances to see the scratches in the picture.
With a super wide lens as a 18mm lens, the percentage for a scratch to be visible in the pictures is near 100%.


PostPosted: Tue Oct 20, 2009 12:10 am    Post subject: Reply with quote
Obviously, the wider angle a lens is, the more impact scratches or other deformities will have on an image. For example, a fisheye lens typically doesn't even have a focusing ring because everything from the lens surface to infinity is in focus. Thus I am not surprised that an 18mm suffers a lot from scratches.

But for longer focal lengths they can largely be ignored. I've owned two Nikkor 28mm lenses, which are reasonably wide, and both of them had rather obvious scratches on the front element. I still own one of them, in fact. I would challenge anyone to be able to notice any image degradation from that 28mm due to the scratches on its front element.

I used to own a Nikkor 180mm f/2.8 ED -- bought it from a press photographer, and that lens had been through the press wars! It had a really ugly ding in the surface of the front element, but because of this ding he sold it to me for a really great price. He promised me that the ding wouldn't affect my photos, and you know what? He was right. I don't recall ever using the 180 in a situation where a bright light was in the frame that might have caused gouge-related flare; all I recall about that lens, especially when I go back and look at slides I took with it was how amazingly sharp it was.

Try this -- take a piece of string and hold it across the front element of your lens, then focus on whatever you want. Okay, we're assuming the lens isn't an ultra-wide angle or a macro, okay? Try it with a 28mm or a 35mm or longer. Anyway, try this. Stop the lens down to taking aperture. Chances are, you won't even be able to see the string. And if you can't, neither will your photos.

Here's a little trick that I learned from astronomers -- to eliminate flare and internal reflections caused by a scratch or scratches, they would fill them with India ink. The scratch remained undetectable on the images, but any chance of flare or ghosting or whatever was eliminated.


PostPosted: Tue Oct 20, 2009 3:01 am    Post subject: Reply with quote
Bruce wrote:
Mike Deep wrote:


Mike, how the heck did you shoot that, 10,000 frame video? Nice Image?

High power rifle, full metal jacket? how many groups/elements. Looks a Pentacon 135? Laughing


Just a 1/2000 shot from my 30D. My friend has a high speed video though.

We used a run of the mill .22 (An M4 was on hand but wasn't sighted in) and that's actually the second time we shot the lens. The first shot didn't penetrate, see this image.

The lens in question is a Tokina-made TX-mount Vivitar 300/5.6, which I usually hear positive things about. I think I just got a lousy copy, even stopped down it was miserably soft and loaded with red fringe. So rather than pass on a dog, I threw it into the mix with the high-speed video and photography we were doing.


PostPosted: Tue Oct 20, 2009 4:50 am    Post subject: Reply with quote
2nd round with 22 makes sense to me, but who the better shooter, the rifleman or the cameraman, I cant say... nice timing!


PostPosted: Tue Oct 20, 2009 12:07 pm    Post subject: Reply with quote
cooltouch wrote:

Here's a little trick that I learned from astronomers -- to eliminate flare and internal reflections caused by a scratch or scratches, they would fill them with India ink. The scratch remained undetectable on the images, but any chance of flare or ghosting or whatever was eliminated.


I can testify to that - I once bought a Retina IIIC (the one with the interchangeable lens component) with a flake of glass missing from the front element - it had 'fallen out' according to the owner and hit the concrete pavement. The missing flake was an irregular shape about half an inch across the outside edge and one fifth of an inch into the lens itself - roughly12mm by 5mm - from memory. I think I paid him £5 for it, not much even then.

Shots in dull weather looked ok, but there was increasing flare on bright days and shooting into the light created REALLY bad flare. Matte black paint worked wonders! If I'd been sensible I'd have kept it, but the lure of quick profit was too much to resist Embarassed The buyer didn't really believe it would be ok and insisted on shooting a roll of film before he paid for it ... but I had to agree that to the uninitiated it must have sounded an unlikely story.


PostPosted: Tue Oct 20, 2009 4:29 pm    Post subject: Reply with quote
scsambrook wrote:
cooltouch wrote:

Here's a little trick that I learned from astronomers -- to eliminate flare and internal reflections caused by a scratch or scratches, they would fill them with India ink. The scratch remained undetectable on the images, but any chance of flare or ghosting or whatever was eliminated.


I can testify to that - I once bought a Retina IIIC (the one with the interchangeable lens component) with a flake of glass missing from the front element - it had 'fallen out' according to the owner and hit the concrete pavement. The missing flake was an irregular shape about half an inch across the outside edge and one fifth of an inch into the lens itself - roughly12mm by 5mm - from memory. I think I paid him £5 for it, not much even then.

Shots in dull weather looked ok, but there was increasing flare on bright days and shooting into the light created REALLY bad flare. Matte black paint worked wonders! If I'd been sensible I'd have kept it, but the lure of quick profit was too much to resist Embarassed The buyer didn't really believe it would be ok and insisted on shooting a roll of film before he paid for it ... but I had to agree that to the uninitiated it must have sounded an unlikely story.


Yes I have done the same on a Zuiko 2/24.
Even though it is a fast WA lens with 3 deep scratches.
The images are great with the scratches painted black.


PostPosted: Tue Oct 20, 2009 8:45 pm    Post subject: Reply with quote
Quote:
I used to own a Nikkor 180mm f/2.8 ED -- bought it from a press photographer, and that lens had been through the press wars! It had a really ugly ding in the surface of the front element, but because of this ding he sold it to me for a really great price.


I bought Nikkor 28mm f2.8 close-focus 0,2m lenses in batch in same condition , 20 EUR each or even less. They have scratch every where front, back ... I still have them and they are perform beautifully. I am not really worry about flair I rare shoot against sun..
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