Filter Reflections in Images

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Filter Reflections in Images

Postby biggerry on Sun Aug 22, 2010 10:19 pm

I was going thru a few images from the recent Ivo Rowe sunrise and came across an image with an interestign effect in it - now its not post processing, but could not think of better location to put this thread in. I have attached two images one is obviously a crop of the noted reflection. On teh day I had a Lee GND and a screw on ND8, so my first culprit would be one of teh filters. Anyone else experienced reflections in their images when filters are installed?

Image

Image
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Re: Filter Reflections in Images

Postby aim54x on Sun Aug 22, 2010 10:29 pm

I've never seen anything like that, and here i was thinking you were talking about reflected light causing glare...
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Re: Filter Reflections in Images

Postby surenj on Mon Aug 23, 2010 1:12 am

I think you are right. It has to be one of the filters. I usually get reflections with a symmetrical(ish) shape though.
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Re: Filter Reflections in Images

Postby DaveB on Mon Aug 23, 2010 1:22 am

Definitely it's light bouncing around between the filters. In fact it might be bouncing off the camera sensor, back up through the lens, then back down off a filter. Notice how the reflections are diagonally opposite (across the centre axis of the lens) which would match such a scenario.

Same thing is sometimes obvious with bright light sources and "normal" UV filters.
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Re: Filter Reflections in Images

Postby methd on Mon Aug 23, 2010 5:30 am

Screw the reflections, 1st one is epic. love it.
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Re: Filter Reflections in Images

Postby biggerry on Mon Aug 23, 2010 2:50 pm

DaveB wrote:In fact it might be bouncing off the camera sensor, back up through the lens, then back down off a filter. Notice how the reflections are diagonally opposite (across the centre axis of the lens) which would match such a scenario.


the diagonally opposite reflection makes alot of sense, I have had a brief read up on sensor reflections and with DSLR cameras this is certainly more of a concern than with their film counterparts. Lens are typically designed and coated to prevent sensor reflection, however this appears to be a prime example of throwing in a couple filters and just right conditions to achieve teh reflection.

A couple of interesting webbies regarding this, although I was unable to find some real world examples of this type of reflections, so if anyone knows of some let me know!

http://thesybersite.com/minolta/sensor-reflection/
http://www.canon.com/camera-museum/tech/report/200308/report.html#t9

Screw the reflections, 1st one is epic. love it.


nah, its over exposed and I did not achieve the beautiful green colour of the moss under the water which I was looking at..next time :up:
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Re: Filter Reflections in Images

Postby DaveB on Mon Aug 23, 2010 4:28 pm

biggerry wrote:the diagonally opposite reflection makes alot of sense, I have had a brief read up on sensor reflections and with DSLR cameras this is certainly more of a concern than with their film counterparts. Lens are typically designed and coated to prevent sensor reflection, however this appears to be a prime example of throwing in a couple filters and just right conditions to achieve teh reflection.

A couple of interesting webbies regarding this, although I was unable to find some real world examples of this type of reflections, so if anyone knows of some let me know!

Here's one example off the cuff: http://dslrusers.com/viewtopic.php?p=395609#p395609

The common examples I see (not online) are in the work of first-year photography students who go out and photograph the bright lights of town in the evening...
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Re: Filter Reflections in Images

Postby surenj on Mon Aug 23, 2010 6:47 pm

Very interesting. So this scenario was potentially avoidable if Gerry zoomed in a little (thus avoiding the lateral sunlight entering the lens/filter or used a lens hood of the sorts?
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Re: Filter Reflections in Images

Postby gstark on Mon Aug 23, 2010 7:00 pm

DaveB wrote:Notice how the reflections are diagonally opposite (across the centre axis of the lens)


I'm not so sure that they are.

I agree that these are internal reflections of some sort, but while they are easily visible in the crop image presented, that crop image also presents an incorrect view of the area from where the reflection originates.

If you look at the crop, the source might seem to come from where the water flows down over the rocks, which is roughly in the diagonal location indicated by Dave.

But if you go back to the full image, you will see that this is probably not correct. Rather, this seems to me to perhaps be some flare coming in from the top lh side of the image, where the waves are crashing against the rocks.

Gerry, could you please present a crop that includes those rocks and the waves' motion above them?
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Re: Filter Reflections in Images

Postby biggerry on Mon Aug 23, 2010 8:06 pm

gstark wrote:Gerry, could you please present a crop that includes those rocks and the waves' motion above them?


of course, I think this is the area you are talkign about

Image

there is also teh full res image below, just click the link for larger etc.
Image

and the image I took immediately before the one in question, it was at a slightly different compo and you cant ses the reflection.

Image
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Re: Filter Reflections in Images

Postby DaveB on Mon Aug 23, 2010 11:00 pm

The whole-frame image is the one you want to check to put things into perspective, but keep in mind that with the GND there's the possibility that it wasn't perfectly tangential to the lens axis (i.e. any reflection from it might be offset).

surenj wrote:Very interesting. So this scenario was potentially avoidable if Gerry zoomed in a little (thus avoiding the lateral sunlight entering the lens/filter or used a lens hood of the sorts?

Not really, no. If the bright thing that's involved in the reflection is actually part of your image, cropping it out by framing/shading could be counter-productive to achieving your target result. ;)
Lens hoods are important to avoid flare from bright things outside the sensor's field of view, but as we can see there can be issues with flare/reflections from things INSIDE the sensor's field of view.

Lenses "designed for digital" (Sigma tags theirs as "DG", Canon and Nikon don't distinguish these with a nametag) generally have extra coatings on the rear element of the lens, to avoid reflections from the sensor coming back up through the lens and causing problems like this. Note that the tags "DC"(Sigma)/"DX"(Nikon)/"EF-S"(Canon) are about the image circle size, NOT whether they have these coatings on the rear elements.

But such coatings aren't perfect (although they do stack the odds in your favour) and in some cases you're forced to avoid having flat filters on your lens (the curved meniscus shape of the lens' own front elements avoids the reflections). Sometimes you really need the filters though, and good anti-reflective coatings on the filters (both the front and the back) can help (part of the differences between cheap filters and good filters).

I have seen in one situation a funky GND mount that was deliberately tilted in order to send reflections off to the side (just enough to miss the sensor) but it seemed rather unwieldy to me. We have enough problems with vignetting issues as it is...
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Re: Filter Reflections in Images

Postby biggerry on Mon Aug 23, 2010 11:19 pm

DaveB wrote:
surenj wrote:Very interesting. So this scenario was potentially avoidable if Gerry zoomed in a little (thus avoiding the lateral sunlight entering the lens/filter or used a lens hood of the sorts?

Not really, no. If the bright thing that's involved in the reflection is actually part of your image, cropping it out by framing/shading could be counter-productive to achieving your target result. ;).


best course of action imo, is take half a step in either direction and re-compose. there ain't no hoodie thats gonna cover these filters, not one that I am gonna pay for anyway!
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