UV filter and strange bokeh

Hello Mark,

 

Thank you for your post and the link - I must say, I winched, seeing Northrup hacking at his canon lens with a vengeance... Anyhow, perhaps the scratches on that lens did not affect later photos, but the lens on my Canon Powershot G9 most certainly did not perform well after being damaged, a big, deep scratch - all photos after the damage showed a slightly over-exposed area directly under the scratch.

 

Cheers,

 

Mabel A.

He should have clarified don't do this to plastic lenses.

He should have clarified don't do this to plastic lenses.

Wut? "Plastic" lenses?

Wut? "Plastic" lenses?

Your powershot doesn't have a plastic lens. For some reason I thought it did. On another note, I recall reading on a forum some powershots had a design flaw that caused the lens cover to scratch the len. Sorry if I mispoke. I am not a powershot owner. I have owned a Rebel 350D, 40D, 7D, 6D, 5D MK IV, I may have bought a powershot for my son 15 years ago. I never used it. I cant remember the last time I saw it.

Whenever I see a linear periodic structure like this in an optical system, I immediate think interference fringes. I suspect that it is caused by interference of refections of the out of focus rays between the filter and the lens elements. Try a higher quality filter with more coating layers that will have a lower value of %R.

Other people have been commenting on this being a good example extended to a more general comment that all filters have a negative impact on image quality. Which is not a valid. There are many ways in which filters can potentially impact and not impact image quality and it is highly dependent on the lens, filter design, illumination conditions and the observer.

Someone at the photo store too, figured that the weird effect was caused by some kind of interference between the layers of glass.

It became clear to me, after shooting some test shots outside the photo store with a tryout lens provided for the occasion, a Hoya, that a much more expensive filter of, obviously, a high quality, would not present the disturbing bokeh, however, at this moment I need to cough up money for other essentialities. Then I also tend to agree with the non-filter-is-best crowd. So I simply bought a lens hood for a low price. It provides protection and the image quality is great.