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Old 18-12-2008, 10:15 PM
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Omaroo (Chris Malikoff)
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Thumbs up 50mm DSLR Bahtinov mask

For an experiment, I asked Clinton (chunky) to come up with a down-scaled Bahtinov mask that I could slip onto a 50mm daylight filter, so that I could focus my DSLR's standard lenses properly for widefield. The plan was to be able to loosely screw the filter/mask on to my lens, focus, take some 3-sec shots (oh for live view) and then remove it after achieving focus - all without losing the focus I'd just attained.

He obliged (thank you Clinton) and sent me a laser-cut sticker cut to 51mm OD in double-time by post. It just sits inside the rim of a standard 50mm filter and is adhered to the glass. I removed the backing paper and kept it - I made another mask in its own right with it. As another experiment, I cut out and continued the slots towards the center of the backing paper to eliminate the central obstruction and see if it makes a difference - which is all just development!

Both worked fine - the original as well as the re-cut version. I had the filter on my 105mm Nikkor f/2.5 and obtained the following focus patterns. Once I had it in perfect focus, unscrewing the filter carefully didn't rotate the focus assembly so it stayed put. Lovely. Being such short focal length, the centrally-obstructed mask is quite noticeable on a 105mm lens (dim), but less so on the 50's and down. A secret is to open your aperture right up to ensure that the iris in the lens is lrger than the obstruction.

One thing for Tak owners - the 50mm Bahtinov filter mask fits on the front of your Taks "man hole cover" of a lens cap. The removable centre step-down aperture accepts a 50mm filter and is threaded to suit. I didn't know that until now. This means that a 50mm Bahtinov mask mounted in a filter should do both your lenses and telescope! I haven't tried it yet, admittedly, but i can't see why it won't work.

The diffraction pattern is chunkier than normally seen through a device with longer focal length, but still very recognisable. Being that these masks are designed (optimally) for a fixed focal length, I think it goes to show how flexible the design is, in that they manage to work at all over a range of my lenses.

Pic 1: The mask mounted in a 50mm filter, about to be attached to my 105mm Nikkor prime and 350D.

Pic 2: In focus

Pic 3: Out of focus
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Last edited by Omaroo; 19-12-2008 at 09:59 AM.
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  #2  
Old 19-12-2008, 06:16 AM
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h0ughy (David)
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looks ok Chris
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Old 19-12-2008, 08:11 AM
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dannat (Daniel)
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i want one
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Old 19-12-2008, 08:23 AM
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Me too,
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Old 19-12-2008, 10:16 AM
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great idea
alex
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Old 21-12-2008, 04:05 PM
cfranks (Charles)
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If someone could PM me with details on how to get one (77mm in my case) I would be grateful.

Charles
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Old 21-12-2008, 09:08 PM
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madwayne (Wayne)
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Hi Charles

If you pm chunky (Clinton) with the details of what you need he can laser cut one for you, and send you a bill too .

Regards
Wayne
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Old 22-12-2008, 08:30 AM
chunky (Clinton Wood)
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filter masks

Hi there all,

Thanks for the great write-up Chris. Sorry I haven't looked at the thread in a few days - I have fallen a bit behind.

They are $40 including freight, and I need the exact glass measurement, so they fit straight on.

Just PM me for the payment details.
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Old 09-01-2010, 11:32 AM
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Thanks for the detailed report there Chris.
I have just ordered one of these and was wondering what would be the clearest and /or cheapest filter to stick it on to?


Cheers Daniel.
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Old 09-01-2010, 04:00 PM
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Omaroo (Chris Malikoff)
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Quote:
Originally Posted by danielsun View Post
Thanks for the detailed report there Chris.
I have just ordered one of these and was wondering what would be the clearest and /or cheapest filter to stick it on to?


Cheers Daniel.
G'Day Daniel

I just used an old 52mm Skylight filter that was knocking around in my camera bag. Works well
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Old 09-01-2010, 09:54 PM
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Thanks Chris.
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