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Gear Talk => Technical Support => Topic started by: triise on February 18, 2013, 06:14:18 PM

Title: Strange pattern in long exposure images
Post by: triise on February 18, 2013, 06:14:18 PM
I was out shooting the Aurora Borealis tonight, and when I got my images on the computer screen I noticed some strange circular patterns in most of the images. Anyone seen this before?

It appears dead center in all the images where there is some light.

EXIF: 5D3, EF 17-40L 4.0 @ 30.0 sec f/ 5.0 ISO 800.

See cropped screenshot attached.
Title: Re: Strange pattern in long exposure images
Post by: Drizzt321 on February 18, 2013, 06:27:36 PM
Oh no! The Aliens! They're coming! First crop circles, now photo circles!!

Seriously, no clue, but I couldn't resist.
Title: Re: Strange pattern in long exposure images
Post by: thebowtie on February 18, 2013, 06:49:48 PM
I was out shooting the Aurora Borealis tonight, and when I got my images on the computer screen I noticed some strange circular patterns in most of the images. Anyone seen this before?

It appears dead center in all the images where there is some light.

EXIF: 5D3, EF 17-40L 4.0 @ 30.0 sec f/ 5.0 ISO 800.

See cropped screenshot attached.
I think this pattern is caused by your lens - or something inside it.
My dim recollection of physics tells me this is a pattern caused by phase interference between curved and flat elements in your lens.

Patterns like this are seen in "interferometry" - I have seen this used by opticians profiling the surface of the human eye for visual correction purposes.

I'm sure it's also used in camera lens analysis and alignment.

Possibly your lens has a defect or alignment issue between some of the elements?

I'm sure there's someone much more knowledgeable (Dr @neuroanatomist?) that can answer this.
Title: Re: Strange pattern in long exposure images
Post by: Don Haines on February 18, 2013, 07:22:13 PM
Definitely an interference pattern....

Two questions.... Do you have a filter on the lens and are you using a lens hood?

Title: Re: Strange pattern in long exposure images
Post by: sturdiva on February 18, 2013, 07:22:46 PM
If you are using Lightroom try turning off lens corrections, I noticed something similar at high iso with a 50mm.
Title: Re: Strange pattern in long exposure images
Post by: neuroanatomist on February 18, 2013, 07:53:56 PM
You're seeing a 'Newton's rings' artifact (let the Googling begin  ;) ), not sure of the cause but most likely a combination of the monochromatic light of the Aurora and antireflective coatings on either a filter (if you were using one), the lens itself, or the filter stack on the sensor.
Title: Re: Strange pattern in long exposure images
Post by: tron on February 18, 2013, 08:07:21 PM
http://www.dpchallenge.com/forum.php?action=read&FORUM_THREAD_ID=168176 (http://www.dpchallenge.com/forum.php?action=read&FORUM_THREAD_ID=168176)
Title: Re: Strange pattern in long exposure images
Post by: Don Haines on February 18, 2013, 08:52:33 PM
You're seeing a 'Newton's rings' artifact (let the Googling begin  ;) ), not sure of the cause but most likely a combination of the monochromatic light of the Aurora and antireflective coatings on either a filter (if you were using one), the lens itself, or the filter stack on the sensor.

brings back memories of a mis-spent childhood and helium-neon lasers.....

each ring represents a one wavelength different length of the path from the source to the sensor. My bet is that if you remove the filter from the lens that the pattern will go away, but then again, it's been 40 years since I was playing with lasers.... I am NOT going to test my guess because the only laser I have access to now is one used to cut steel.... and shining that at my camera is probably not a good idea.
Title: Re: Strange pattern in long exposure images
Post by: triise on February 19, 2013, 02:29:15 AM
Definitely an interference pattern....

Two questions.... Do you have a filter on the lens and are you using a lens hood?

Both an UV-fliter and a lens hood is attached yes.
Title: Re: Strange pattern in long exposure images
Post by: triise on February 19, 2013, 02:30:24 AM
If you are using Lightroom try turning off lens corrections, I noticed something similar at high iso with a 50mm.

Actually, lens corrections in LR is not used on this (ora any of the other images) - but it gave me an idea to try with it on...
Title: Re: Strange pattern in long exposure images
Post by: Don Haines on February 19, 2013, 05:07:03 PM
Definitely an interference pattern....

Two questions.... Do you have a filter on the lens and are you using a lens hood?

Both an UV-fliter and a lens hood is attached yes.

I'd try again without the filter, that's the only possible source of the interference pattern that you could change.... if it is inside the lens, you are stuck.

The hood is not the source of the pattern, but without it you can get strange ghost light from sources off to the side, looks like a faint blotch. I think they are only noticeable when shooting in the dark. I tend to always use the lens hood when shooting night skies.
Title: Re: Strange pattern in long exposure images
Post by: agierke on February 19, 2013, 06:27:15 PM
Quote
I am NOT going to test my guess because the only laser I have access to now is one used to cut steel.... and shining that at my camera is probably not a good idea.

oooo....pretty please! if we take up a collection to cover the costs of replacement will you do it and post a video of it?

i would love seeing a laser slicing through a DSLR. not mine of course....just someone elses.
Title: Re: Strange pattern in long exposure images
Post by: emag on February 19, 2013, 09:25:32 PM
I've had a similar interference pattern occur when using a filter on my EF300/4 (non-IS), which has an almost flat front element.  Back when I was a young man with a full head of dark hair, we would look for interference fringes when checking optical flats and precision gauge blocks under a monochromatic light.  Neuro mentioned 'Newton's rings'....that's a phenomenon of similar cause, in the context we used it was an indicator that cemented lens elements were beginning to separate.  We'd re-cement them with Canadian Balsam, nowadays replaced for the most part with different adhesives.  This thread has conjured up memories of the smell of hot Canadian Balsam and hours of rebuilding Navy binoculars....a pleasant memory.  Thanks!