lense scratch question

jbakerphoto

I am thinking about picking up a sigma 70-200 2.8 HSM APO. It has a scratch on the front element but the owner says it does not affect image quality. I asked for some sample images at different focal lengths.

At what aperture would you usually see a scratch? in other words do i need to tell him to stop it all the way down or somewhere else.

I guess the other question is am i making the right decision trading the canon 70-200 f4 l for the sigma 2.8. He want 325 for it so i could definitely come out ahead on if i sell the canon.
Thanks

ziggy53

unclejon wrote:

I am thinking about picking up a sigma 70-200 2.8 HSM APO. It has a scratch on the front element but the owner says it does not affect image quality. I asked for some sample images at different focal lengths.

At what aperture would you usually see a scratch? in other words do i need to tell him to stop it all the way down or somewhere else.

I guess the other question is am i making the right decision trading the canon 70-200 f4 l for the sigma 2.8. He want 325 for it so i could definitely come out ahead on if i sell the canon.
Thanks

Unless I could see the scratch first-hand, it's hard to make an assessment.

The scratch is probably not significant if it's off to the side. If it crosses the center of the element, it can have more impact. If you shoot towards a light source, a scratch can have more impact as well.

The effect of a scratch is not so much that the scratch itself will be visible, but that it increases dispersion and sometimes glare.

In olden times lens manufacturers would sometimes take a special black paint to fill in imperfections on the front element (usually bubbles). It is sometimes possible to use the same technique for scratches to reduce their impact on lens performance. I don't suggest that you do this yourself and I currently don't know anyone who does this anymore. You might do some searches if you feel it is needed.

You might contact Sigma to see what it costs to replace the front element.

From my own tests, I found that wide open the modern Sigma 70-200mm, f2.8 EX HSM had an odd inner reflection of extremely high contrast boundaries that neither the Canon EF 70-200mm, f2.8L USM nor the 70-200mm, f4L IS USM has that I own. I tried 2 copies of the lens. By f4 the problem goes away, but I needed the f2.8 for my purposes.

Supposedly, the "Macro" version of the lens is somewhat better in that regard. I have not tested the macro version.

I have an older Sigma 70-210mm, f2.8 APO (77mm filter) that does not have the problem. (It has other problems relating to modern Canon dSLRs and it is not HSM, but it is extremely high quality optically. Very close to the "L" lenses.)

jbakerphoto

Hey Ziggy,
Thanks for the reply. I contacted sigma and they said it cost somewhere around 240 for a new front element. I still havent heard from the guy selling it so who knows. I might get a lense i might not. It would be nice to get a 2.8 though.
Jon

pathfinder

One consideration is that a lens with a significant, visible defect will have considerably less re-sale value when you want to sell it later. Just a thought.

The Canon 70-200 f4 L is a dynamite lens, and a lot lighter to carry than the 70-200 f2.8 L. If I were to do it again, I think I would buy the f4 version over the f2.8 version that I do own, myself.

Tee Why

If it's a small scratch, I'd doubt you can see it. You may see some extra flare shooting into a bright light while stopped down IMO if the scratch is significant.

Not having seen the lens or images, it's tough to say though.

jbakerphoto

Looks like the lens has been sold out from under me. Owell, its probaly for the best. I had read a lot of reviews yesterday that said the sigma was not so great.

I do like my canon f4 L and haven t had a bit a problems with it. So looks like i am keeping it.....

Thanks all for commenting.