UV filter and strange Bokeh

[I-S]

My colleague got into photography recently and bought a 450D, 18-55 and 55-250. He wanted more reach without paying canon prices, and bought a Sigma 150-500 OS. On both the 55-250 and the 150-500 we've seen a strange effect of diagonal lines in the bokeh. To begin with it seemed like camera shake, and was much more prevalent at the long end of the lens (in both cases). The direction seemed consistent (and after a while far too consistent for camera shake).

Here's an example of how the bokeh looked (this is one of the test shots from our final diagnosis of the problem):

As you can see, the bokeh shows strange diagonal lines, but the focused subject remains free of any camera shake problem.

Turning the filter a bit changed it to vertical:

And removing the filter entirely:

The effect, and solution, were identical on his 55-250 lens also.

This is not an effect that I've seen before, although I think it is probably tied in with cheaper filters (I use canon and Hoya HMC Pro filters, my colleague use(d) Jessops and Kenko filters). However, I do have a few shots that have displayed "odd" bokeh and I wonder if it might not be a similar effect. However, I have done some tests with my Canon 300F4L IS and the Canon Protect filter that is on it and couldn't tell any difference between the shots.

Anyone else seen similar effects?

 

[jamesoliverstone]

And this is why I hate UV filters with a passion...

 

[501cards]

I had the same problem with a Jessops 77mm UV that was fitted to a 100-400 I was using, caused same wierd Bokeh

Removed it problem gone, on checking the filter one of the metal clip rings that secure the glass was missing and the glass was sitting in the filter at a slight angle, (Probably only 1/4 MM off square) but still enough for what seemed to be the cause of the problem for me.

 

[arad85]

Had the same on my 70-200. It was supposed to be a B&W MRC Haze filter, but I did buy it cheap off fleabay and I concluded it must have been a fake (Although I didn't check if it was flush or not). Threw it in the bin - totally pointless ruining a decent lens

With IR filter:

Without IR filter:

 

[Gigabyte]

Reading a lot of people saying that a UV spoils images i have decided not to use one. I have had some glare on a pic with a UV. Its not an expensive lens anyway so i am going to give it a shot.

 

[I-S]

Interesting to see other people's images of this. Before I came across this with my colleague I had never heard of this sort of effect - of course I'd heard people saying that a filter could reduce contrast, increase flare, reduce sharpness, but this sort of bokeh weirdness was a new one on me. Hopefully this thread could help people suffering from this sort of a problem.

501cards - That's interesting. I think that the issue is mainly to do with flatness, and the use of rolled (rather than ground) glass in cheap filters, plus mounting issues with cheap filters and mechanical flexibility in large filters. From what I've found on the net, this issue crops up most often with the sigma xx-500 zooms, which require 82mm filters but with the low price of the lens people are unwilling to pay a high price for a filter. I think the combination of cheap, large filters and a high-magnification lens is the reason it crops up most on those lenses.

 

[Gigabyte]

Maybe a hood would be a better bet as lens protection?

 

[arad85]

I have to say that I'm NOT seeing the same effect on the 24-105L with UV filter attached - in fact, I can't see any difference at all with it on or off on that lens.

 

[dalex_257]

One thing that may explain regular patterns is that it the optical sandwich on top of the camera sensor has a slight polarising effect. This may expose some optical irregularities which are usually quite common in cheap filters.

I would not say it happens with every filters but I don't think UV/protector filter use is really helping at all - only causes more flare and adds more glass to the optical path. Hoods are much better protection and change nothing optically.

 

[trencheel303]

I have to say that I'm NOT seeing the same effect on the 24-105L with UV filter attached - in fact, I can't see any difference at all with it on or off on that lens.

probably because it's a decent filter. Well I'd hope so on that lens. Crap filters are obviously going to affect the image. I have a Hoya HD UV filter permanently on the end of my 17-40 - £50 for a piece of glass in a ring - but the pictures are tack sharp and clear with it on so it's worth it.

 

[I-S]

Indeed, it's not endemic to ALL filters. I have had no such problems with the Canon Protect filters on my lenses.

 

[arad85]

probably because it's a decent filter. Well I'd hope so on that lens. Crap filters are obviously going to affect the image.

On the 24-105L it's a Kenko Pro 1 UV filter. Came with the lens.

I also don't see the effect on the cheapo Jessops UV filter I have on the 18-55 IS either.

 

[I-S]

I think the effect is also tied into the magnification of the lens - you might not see it with the 18-55, but if you were to try the same filter on a longer lens (eg 55-250 or 100-300 USM, to think of a couple of longer 58mm thread lenses) you might see it. We found it much more prevalent at the long ends of the zooms where the problem was observed.

 

[arad85]

We found it much more prevalent at the long ends of the zooms where the problem was observed.

I seemed to remember it being an issue at longer zooms too

 

[HoppyUK]

I seemed to remember it being an issue at longer zooms too

Yes, it only really happens with long lenses, and cheap filters. Some lenses seem to be more prone that others.

Very easy to test. Zoom to max, focus about half way, and hold a pencil in front of the lens. Move it around. It will be so out of focus it effectively disappears, but check what's happening to the out of focus backgound!

 

[Moonrakerz]

Well I'd hope so on that lens. Crap filters are obviously going to affect the image. I have a Hoya HD UV filter permanently on the end of my 17-40 - £50 for a piece of glass in a ring - but the pictures are tack sharp and clear with it on so it's worth it.

Greetings everyone !

I just HAD to make a comment on the above.

I have always had a UV filter (Hoya) on my standard lens, 18 - 55mm. Always been completely happy with the results.
Yesterday after much 'umming and 'arring I bought a Sigma 18 - 200mm to replace my existing two "shorter" lenses.
Before I got rid of the other lenses I set up a quick trial of the new lens against the old ones just to compare.
I noticed a very slight milky cast at 55mm on my original lens compared to the Sigma. Then I noticed the same when comparing the 18 - 55mm to my 55 - 200mm.
Re-did a couple of trial shots, with and without the UV filter - it was definitely the source of the cast !

Glad I didn't buy the UV filter for the Sigma. Won't be buying any more for sure.