Preventing sensor dust when using bellows

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AlxndrBrg
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Preventing sensor dust when using bellows

Post by AlxndrBrg »

Hello!

I recently got my brand spanking new (and thus clean, in contrast with my old Nikon D70 - which had significant parts of the Sahara desert on the sensor) Canon 6D, in parts thanks to commenters on this forum.

The camera will be mostly used for studio stacking in combination with a bellows unit. My worry now is that the sensor, while certainly clean now, will soon become dusty due to using live view (or tethered) + EFSC and a dusty old bellows.

Is there any way around this? I was wondering if its possible to put a filter between the bellows and the camera, to prevent air and dust to enter the camerahouse?

My setup is as follows:
Canon 6D
Canon EF-to-42M adapter
Pentacon 42M bellows
Reversed lens

Would it be possible to find a filter (UV/skylight, ie something close to transparent) with 42M threads to put between the adapter and the bellows? I might simply try and glue an old skylight to the adapter and see how it works out, if the picture quality is unchanged it works I suppose...

Or is there some other solution to separate the camera house "air" from the bellows "air" ?

/Alex

Pau
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Post by Pau »

I think that putting a filter to cut dust is a good idea. I recall somewere in the forum a post about it. For best quality a multicoated filter will be better.
Maybe to avoid sensor reflections (digital sensors are pretty reflective and lenses with rear flat elements often produce some glare issues) you could place the filter angled about 5 degree (this tric is bundled in some microscope systems)
The sensor autocleaning system in Canon cameras, despite not perfect, is very good. I still have my 7D sensor clean after 3 years shotting (even after multiple lens changes in Africa during the dry season), very different than my old 20D.
Pau

enricosavazzi
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Post by enricosavazzi »

A filter parallel to the sensor plane and placed at the rear of the lens creates reflections, usually visible as a magnified and offset/reversed ghost image of bright light sources (a filter at the front of the lens may have a similar but not identical effect). This is often a problem with digital cameras used with legacy telephoto lenses (and some specialist lenses) that use a filter mounted at the rear of the lens. Remove the filter regardless of recommendations to the contrary by the manufacturer, and the problem is gone.

A multicoated filter will lessen this problem, but not completely eliminate it.

Nikon 1 users can expand/correct me on the following: I handled Nikon 1 bodies a couple of times in camera shops, and I seem to remember seeing a filter/transparent window placed a few mm in front of the sensor (not the usual IR/antialias filter). Perhaps the shorter filter-sensor distance, coupled with lenses telecentric on the sensor side, reduces/eliminates this reflection problem?

If I am correct about the presence of this internal filter in the Nikon 1, I believe its main function is to make dust particles on this filter invisible or less visible (by defocusing them) than dust directly on the sensor window, which is the goal we are discussing here.

However, one thing to remember that DOF on one side of the lens is complementary to DOF on the opposite side. When focusing on a distant subject, DOF on the subject side is large, but on the sensor side it is very small, so dust a short distance from the sensor plane becomes defocused. In photomacrography, the situation is the opposite: small DOF on the subject side, large DOF on the sensor side. So the filter needs to be quite far from the sensor to be effective in defocusing the dust particles. Maybe too far to be practical.
--ES

Pau
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Post by Pau »

http://www.photomacrography.net/forum/v ... 7575#57575
http://www.photomacrography.net/forum/v ... 672#102672

and searching for bellows dust and filter will give you more results and discussions.
Pau

pierre
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Preventing sensor dust when using bellows

Post by pierre »

Tested: cutting the liveview BEFORE extending / contrating the bellows helps a lot reducing this dust problem.
Regards

Pierre

AlxndrBrg
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Post by AlxndrBrg »

Thank you for your replies! Much appreciated

Pau: I found the threads by using some better searching (including AND between the terms cut down the hits from 2000 to a manageable 20), but thanks for the links - now I know which threads you referred to :)

Ok, so the "filter" idea I had is viable, but not without potential drawbacks, lessened by tilting the glass at a small angle.

1) How would you go about attaching such a filter? I dont have anything between my camera house and the bellows except the very thin adapter. Should I try and find some canon (or perhaps M42) extension tube to place the filter in? I rarely use the bellows at short extension so some extra length its no problem.

2) What kind of filter or glass would be the best option, if I had to buy a new item? I dont want anything that will affect the image quality if it can be helped, but at the same time I dont know if a cheap filter will do or if I should try and get something fancier?

/Alex

Charles Krebs
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Post by Charles Krebs »

Alex,

With the last new body I purchased (a few years ago now) I felt exactly the same. So I got a high quality B+W clear filter (UV of some type... don't remember) and sealed it into a T-mount adapter I use on some equipment (it was mounted "squared", not angled in any way). Frankly I expected to encounter flare and reflection problems but I experienced none at all. (But as a rule all interior surfaces of my equipment are very scrupulously checked for reflective surfaces and for some lenses I have mounts with special flare-cut diaphragms... so this undoubtedly helped avoid problems).

Eventually I gave up on it. The camera was moved around to a wide variety of equipment some of which did not use the T-mount (and regular Canon lenses as well) so inevitably I reached a time where sensor cleaning was needed.

If I had a setup where a new camera would be "permanently" attached to a piece of gear and not moved around I would try it again. I would use a B+W filter with their "Multi-Resistant Nano Coating" which is superb and incredibly easy to clean.

AlxndrBrg
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Post by AlxndrBrg »

Charles,

Thanks, I might acutally try that exact setup - some 25€ I can spend on keeping my sensor clean if its a close to perfect solution. And if it isnt I'll have to angle it some 5 deg's and cross my fingers.

Did you remove the glass from the filter thread somehow (is that even possible without cutting away the metal?) or did you simply not bother? And roughly how long was the distance from the filter to the sensor?

/Alex

AlxndrBrg
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Post by AlxndrBrg »

Got my 39 mm B+W UV-Haze Nano filter and stuck it between two M42 extension tubes that I put closest to the camera. The filter was small enough to simply fit inside of the female M42 threads, and is held tight between the two ET's when they are screwed together.
Seems to work a charm, no degradation of the sharpness, might have some reflexes though - but I havent seen any yet. I couldnt mount it non-parallel to the sensor, but it seems fine. If I ever get any problems with reflected light I'm sure I can angle it a bit, could simply file down the threads on the filter to make the glass appear tilted compared to the front and back threads.

Will update on the dust situation after I've used it for a while.

Once again, thanks for your input guys! :)

/Alex

AlxndrBrg
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Post by AlxndrBrg »

Belated update:

Have been using the camera for a couple of years now, for the first 3 years the rig was used in a horizontal setup, and recently in a vertical (for stability and also to reduce the chance of dust floating up to the sensor)

Considering how much I have used the camera, and how exposure heavy live view stacking is, I'm happy how it's been working. Of course I dont have a control to compare with, and I dont know how much the cameras own sensor cleaning helps either.


The dust shows up way more than usual in this picture, in shots with a black or close to white background the dust specks are not visible at all. They are also not showing up when there's detail for ZereneStacker to single out instead.

Maybe I should actually send in the house for some spring cleaning...

Edit: I tried to estimate the number of exposures, the lower bound would be 20k, but I wouldnt be surprised if its around 35k

Image


/A

ChrisR
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Post by ChrisR »

I don't have a link to hand, but there do exist filters designed to sit in the throat of a DSLR body, for use by folk who have IR filters removed from their sensor. I believe astro-photographers use them too.
Chris R

Rudi
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Post by Rudi »

ChrisR wrote:I don't have a link to hand, but there do exist filters designed to sit in the throat of a DSLR body, for use by folk who have IR filters removed from their sensor. I believe astro-photographers use them too.
But I have :D :D (look for the MC clear filter)
http://www.astronomik.com/en/clip-filte ... m.html?p=2

Just noticed that you have a full frame body, look at:
http://www.astronomik.com/en/clip-filte ... t.html?p=1

hope this helps....
Last edited by Rudi on Thu Apr 05, 2018 12:02 pm, edited 1 time in total.
Always looking at the bright side of life,
Kr, Rudi

ChrisR
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Post by ChrisR »

Well found Rudi :D, that's probably the one I had in mind. There may be others.
Chris R

Rudi
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Post by Rudi »

ChrisR wrote:Well found Rudi :D, that's probably the one I had in mind. There may be others.
As usual, not hard to find iff you know where to look... :D :D

I have two clip in filters. One is the MC clear for my 7DII.
Can't really comment on the pros/cons as I am just started about a month ago (one need to start somewhere, isn't it ??) with bellows/reversed lens setup.
But my experience with the other clip-in filter I have, and (mis)used for astrophotography, is that the clip in system works nicely.
Always looking at the bright side of life,
Kr, Rudi

lonepal
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Post by lonepal »

Rudi wrote:
ChrisR wrote:Well found Rudi :D, that's probably the one I had in mind. There may be others.
As usual, not hard to find iff you know where to look... :D :D

I have two clip in filters. One is the MC clear for my 7DII.
Can't really comment on the pros/cons as I am just started about a month ago (one need to start somewhere, isn't it ??) with bellows/reversed lens setup.
But my experience with the other clip-in filter I have, and (mis)used for astrophotography, is that the clip in system works nicely.
Hi Rudi;

Is there any exposure change or IQ lost when you use clip-in filter?
Have you ever make a comparison with filter vs without filter?

Thanks.
Regards.
Omer

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