What causes this? UPDATED FINDINGS!

One of the reasons I rarely use a filter. If I was in a similar position to Arkady or shooting in adverse conditions then yes as protection, but for normal shooting I personally don't like putting anything in front of good glass!
 
I'm guessing then that I could use the 50D's calibration thingy to stop the front focussing of the lens?:help:
 
squizza said:
I'm guessing then that I could use the 50D's calibration thingy to stop the front focussing of the lens?:help:
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Yes, that's what its for, you will have to do it twice once without the 1.4x and again with.

Ideally you need to be a minimum of 50x the focal length, so for a 300mm lens you need to be about 15 mtrs away and with the 1.4x added about 21 mtrs away.

You need to choose a nice contrasty subject and then it's a case of trial and error, I focus on a roadsign, then dial in some adjustment and see what happens. live view is good to check. Good luck, the more time you can spend doing each lens the better the results. Don't just take one shot at each adjustment, take a few and turn the lens OOF before taking the next shot.
 
EdBray said:
One of the reasons I rarely use a filter. If I was in a similar position to Arkady or shooting in adverse conditions then yes as protection, but for normal shooting I personally don't like putting anything in front of good glass!
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Nor do I, my Zuiko 90-250 2.8 comes with an Olympus supplied and branded protection filter, this is the first lens I've ever had where a manufacturer supplies one as part of the kit.

Paul
 
EdBray said:
Yes, that's what its for, you will have to do it twice once without the 1.4x and again with.

Ideally you need to be a minimum of 50x the focal length, so for a 300mm lens you need to be about 15 mtrs away and with the 1.4x added about 21 mtrs away.
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I think I'd do both tests at the same distance Ed - with and without the converter. The converter doesn't actually change the focal length or the minimum focusing distance, being basically just a magnifying glass placed behind the lens?
 
OK...I'm going to have to say this is the first time I've ever seen this - since Nikon tele and ultra-tele lenses don't have this problem...
I've used 300 f/2.8 IF-ED and 600 f/4 IF-ED with filters attached (made by Nikon - I doubt they'd make a filter for a 600mm lens if it conflicted with the optics) and have never had this happen...
We did lots of - how shall I put it...? Oh well...surveillance work in Northern Ireland where extreme ranges and high-crop ratios were the norm.
If this had been an issue, believe me, we'd have picked up on it sometime in the past 20 years...

I can only conclude that it's a Canon problem...sorry guys...
 
Never had this issue on any of my Zuiko glass either. I use UV or plain multi-coated filters on all of them.

Are we saying the bokeh fringing is normal for the 300/4 lens? Or does this only happen with the 1.4x TC?

Andy
 
loplyg said:
I feel somewhat vindicated in having never spent more than £12 for a UV/skylight filter now.
I just never saw how a £50 filter could be better than a cheap one, and I've done quite a bit of pixel peeping.
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In ideal conditions, shooting with the light behind you and no high-contrast areas in your field of view, providing the glass is perfectly flat and consistent in optical density, that is true. The more expensive filters have multi-coatings on a par with the lens elements themselves and coated edges to reduce internal reflections within the filter. In addition, they are usually mechanically better, with threaded rings securing the filter rather than a sprung clip - which is better for keeping crud out from between the lens and the filter. If you shoot against the light, or with bright subjects, flare will be more evident on the cheap filters.

It would seem that the optical formula of the 300/4 is sensitive to things in front of it. I still struggle to see how the particular diagonal striping in the bokeh of the dunnock and deer shot arose. I would guess that the filter has made things worse, but there may still be a problem.

Andy
 
Arkady said:
OK...I'm going to have to say this is the first time I've ever seen this - since Nikon tele and ultra-tele lenses don't have this problem...
.....I can only conclude that it's a Canon problem...sorry guys...
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Do you mean the fringing or the striped bokeh?

Bob
 
Striped Blokey...

But looking hard at the images, I would say the fringing may also be associated with that as well...
It also may be a rogue-filter - obviously the OP didn't buy two so there's no way of knowing without trying one in a shop...

Neither should appear in a lens of this quality...
 
Arkady said:
OK...I'm going to have to say this is the first time I've ever seen this - since Nikon tele and ultra-tele lenses don't have this problem...
.....I can only conclude that it's a Canon problem...sorry guys...
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Canon Bob said:
Do you mean the fringing or the striped bokeh?

Bob
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Arkady said:
Striped Blokey...

But looking hard at the images, I would say the fringing may also be associated with that as well...
It also may be a rogue-filter - obviously the OP didn't buy two so there's no way of knowing without trying one in a shop...

Neither should appear in a lens of this quality...
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The striped "blokey" is neither a lens nor filter problem per se, it's a mis-match between the two. Although you state "since Nikon tele and ultra-tele lenses don't have this problem", it most certainly does occur with Nikon tele's and tele-zooms...search Google for "bokeh", "lines" and stripes" and you'll find similar reports....more often with the 70-300VR but likely due to it being a popular lens (not my sphere)

Lens designers add coatings to the surface of the glass to combat reflections. The coating is generally Magnesium Flouride and the thickness of the coating will determine the wavelength of light that is affected most. Visible light tends to be in the range 475-650nm and a single coating is usually pitched to deal with 550nm and effeciency deteriorates either side of this. Having multiple elements (and two surfaces/element) allows the designers to put coatings of different thickness on differnet elements and get a better spread of the visible light spectrum covered. The coatings will reflect a portion of the light at 1/4 of the wavelength and use this to cancel the reflections....the chance to have 6 surfaces coated would likely lead to coatings aimed at 475, 500, 525, 550, 575 and 600nm (too simplisitic, but you get the drift).
Everything should be nicely balanced and hunky dorey. Then someone sticks a multi-coated filter on the front that's nicking some of the light at a certain frequency and using it for its own purposes. Now we're buggered....the light at frequency X is missing and the deisgners best efforts have gone up effluent creek sans paddle.
The circumstances leading to the lines/stripes are very specific....a combination of light temperature, the colour of the background blurr and the level of blurr (cirlce of confusion and Airy disk...don't get me started on that please). Longer focal lengths and wider apertures will increase the chance of it appearing but, in theory, it also occurs at shorter lengths to a lesser degree if the same relationships exist.

All this based on my understanding of the physics which may well be flawed.

Okay folks....rip your filters off now :thumbs:

Bob
 
I mentioned specific Nikon lenses that I've personally used and not found any evidence of the phenomenon...Aslo that we used Nikon filters, which I have to assume since they come in that filter size, were designed with those lenses in mind...

I concur with the theory behind what you're saying, just that I have no personal experience of it and neither has anyone else in my organisation. I'd have heard if it by now if they had.
Those lenses I used were primes - I have no idea if that is a factor...?
 
There's only merit in removing the filter if it causes a problem. I have to admit to checking several before and afters with my ZD 300/2.8, as I wasn't prepared to compromise a hand-built £5k lens. No issues whatsoever. This problem - and I only think Sarah has demonstrated that the bokeh gets worse with the filter - is particular to certain lenses only. The test shot didn't show the diagonal weirdness, just the bokeh getting worse.

Andy

Edit: you got me thinking now... I'm going to upload a series of images with and without the filter. Shooting at the closest focussing distance, a candle sitting on the floor in a darkened room. To the right, about 50cm behind, another candle, to the left, a further 50cm behind the 2nd candle, a third candle. Hopefully a good test as I can't think of anything that is higher contrast (the candles are lit!!). First test is here, the Zuiko 14-35mm at each end of the range, wide open at f2.0: http://picasaweb.google.com/elliott.aje.andy/1435BokehTestFilterNoFilter# - manual focussing on wick of first candle, aperture priority with EV comp to get an optimal exposure. The only difference in this test is a slight ghost image with the filter on with the lens at the widest angle. I think you will agree though, this is an extreme test!
 
I'm not sure there is any great mystery to this. Filters cause more problems with longer lenses because any surface defects are just magnified much more. I'm thinking it's more a simple glass quality (plano-parallel) issue rather than a coatings thing. And I don't think Nikon are immune either. On top of that, I'm guessing Sarah maybe has a rogue filter.

Perhaps we don't often see it because you need a certain kind of subject to show it (eg bright background bokeh) and most people just dismiss it without doing with/without filter comparisons. Plus I'm guessing that filters are generally not as common on longer lenses?

Easy enough to check on a long lens shot with bright back-lit background bokeh.
 
HoppyUK said:
...Plus I'm guessing that filters are generally not as common on longer lenses?
...
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Probably because they are large and expensive!!

Bring back the days when most of my OM glass had 49mm filter threads!

Andy
 
HoppyUK said:
I'm not sure there is any great mystery to this. Filters cause more problems with longer lenses because any surface defects are just magnified much more.
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I think the optical formula must play a major part - as it seems to rear its head a lot with this lens and the 100-400 from what others have said. Being so near to the front of the lens, your should expect it to be thrown right out of focus. I've shot with a tele all day and then realised I had a big greasy fingerprint on the front - without being able to notice the effect to a definite degree. I would expect something like this to be worse than rogue filter.

Andy
 
Looks almost like an interference pattern there. I wonder if its internal reflections inside the lens from the filter forming an interference pattern on the sensor?

That is very weird though as bokeh depends on the aperture shape so lines are strange

sid
 
Sarah,

Just out of interest, back in post #38 you showed with and without filter, was IS on too in both?
 
Sarah, can you try an experiment for me - shoot your filter on and filter off test again, but add two shots with "filter on, IS off" and "filter off, IS off". Remember to write down which ones are which :D

Am just curious.

I have seen this before - on my Canon 300 f4 IS.

And if you look on this forum, both Dod and CT have posted about it with sample images from 100-400's and 300 f4 IS's.
 
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