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Dust Catcher

 
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Craig Gerard



Joined: 01 May 2010
Posts: 2877
Location: Australia

PostPosted: Tue Jul 06, 2010 8:38 pm    Post subject: Dust Catcher Reply with quote

Dust Catcher.

In an earlier discussion we were talking about protecting the sensor from dust when usings bellows:
http://www.photomacrography.net/forum/viewtopic.php?t=7433&start=0

Is anyone using some type of dust protection method they would like to share?

Currently looking at using a M42 to Nikon adapter with infinity focus element; but removing the infinity focus glass element and replacing it with SternKreuz watchmakers glass of appropriate dimensions.

My concerns are that this approach may introduce a 'hotspot' on the sensor or bounce-back effect between sensor and glass; there may also be a possible loss of contrast, etc.

Any thoughts, solutions, suggestions?










Hot Spot definition for clarification: ref: Jenoptik Optical Systems

Quote:
Hotspotting is an optical issue. Specifically, a central hotspot is a ghost image of the aperture stop created by two ghost reflections. These reflections can occur between any two lens surfaces, or it can be a reflection off the sensor or coverglass followed by a reflection from a lens surface.

Craig
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g4lab



Joined: 23 May 2008
Posts: 1434

PostPosted: Tue Jul 06, 2010 9:46 pm    Post subject: Reply with quote

If the watch crystal is in fact crystal as the label seems to imply then you may have some odd responses due to the fact that mineral crystal (ie quartz) may be doubly refractive. I say may because it could be synthetic or natural singla crystal structure in which case it is definitely doubly refractive, or it may be so called fused quartz which is amorphous in structure and therefore only singly refractive, like other glasses.

You can find out by taking two linear polarizers and crossing them to extinction (darkness) and then rotating the window in between. If it doesn't affect the extinction then it is singly refractive and amorphous and usable.

If it blinks between bright and dark several times as you rotate it then it is a slice of single crystal quartz and may confuse the exposure meter and autofocus if any. It also would interact with any polarizers you might use.

But otherwise seems like a pretty good idea.
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Charles Krebs



Joined: 01 Aug 2006
Posts: 5805
Location: Issaquah, WA USA

PostPosted: Wed Jul 07, 2010 12:26 am    Post subject: Reply with quote

Quote:
My concerns are that this approach may introduce a 'hotspot' on the sensor or bounce-back effect between sensor and glass; there may also be a possible loss of contrast, etc.

Very real concerns. Would vary considerably with subject/lighting. I think you would want the best multi-coatings possible on that piece of glass.

In that other thread Wisniewski said:
Quote:
(it later dawned on me that I could have built up a spacer that tilted the filter about 5 degrees, reducing the possibilities of long reflections from filter to lens or sensor to filter)
This would be effective as well... but I can't help but wonder what it might do to the image quality.
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seta666



Joined: 19 Mar 2010
Posts: 866
Location: Castellon, Spain

PostPosted: Wed Jul 07, 2010 3:01 am    Post subject: Reply with quote

I did a test using an eos-52mm male adapter (those ones for reversing lenses) a 52mm UV filter and a male 52mm-M42 female ring to adapt it to my M42 bellows. First test did not show any CAs but testing my M plan 20x some CAs apeared. I broke the UV filter as it was over thightened and at the end those CAs where normal on the M plan.
I do not have any more 52mm UV filter but I will get one and do further testing. My EOS 5D is a dust magnet.
What I do to remove the dust trails is I open all the files in camera raw, synchronize them and use the Spot Healing Brush to clean all the dust spots/dead pixels from one frame, automaticaly camera raw cleans all the frames. This will clean the dust trail but may cause spots with wrong data, but this will be much smaller than the dust trails and easier to deal with.
Any way, this is my set-up, you will see the adapter and UV filter thin; in this picture I used a Eos-M42 adapter, M42-52mm, Uv filter, 52mm-M42 and then the bellows



Here you have the full description
http://www.flickr.com/photos/seta666/4761091535/
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