#1  
Old 18-12-2008, 10:15 PM
Omaroo's Avatar
Omaroo (Chris Malikoff)
Let there be night...

Omaroo is offline
 
Join Date: Aug 2006
Location: Sydney/Cooma
Posts: 7,628
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
Attached Thumbnails
Click for full-size image (50mm_bahtinov_1.jpg)
115.2 KB644 views
Click for full-size image (50mm_bahtinov_2.jpg)
37.4 KB774 views
Click for full-size image (50mm_bahtinov_3.jpg)
50.9 KB736 views

Last edited by Omaroo; 19-12-2008 at 09:59 AM.
Reply With Quote
  #2  
Old 19-12-2008, 06:16 AM
h0ughy's Avatar
h0ughy (David)
DOGHOUSE REBORN

h0ughy is offline
 
Join Date: Apr 2005
Location: NEWCASTLE NSW Australia
Posts: 30,747
looks ok Chris
Reply With Quote
  #3  
Old 19-12-2008, 08:11 AM
dannat's Avatar
dannat (Daniel)
daniel

dannat is offline
 
Join Date: Sep 2007
Location: Macedon shire, Australia
Posts: 3,382
i want one
Reply With Quote
  #4  
Old 19-12-2008, 08:23 AM
leon's Avatar
leon
Registered User

leon is offline
 
Join Date: Apr 2006
Location: ballarat
Posts: 10,849
Me too,
Reply With Quote
  #5  
Old 19-12-2008, 10:16 AM
xelasnave's Avatar
xelasnave
Gravity does not Suck

xelasnave is offline
 
Join Date: Mar 2005
Location: Tabulam
Posts: 13,023
great idea
alex
Reply With Quote
  #6  
Old 21-12-2008, 04:05 PM
cfranks (Charles)
Registered User

cfranks is offline
 
Join Date: Feb 2008
Location: Tungkillo, South Australia
Posts: 599
If someone could PM me with details on how to get one (77mm in my case) I would be grateful.

Charles
Reply With Quote
  #7  
Old 21-12-2008, 09:08 PM
madwayne's Avatar
madwayne (Wayne)
Registered User

madwayne is offline
 
Join Date: Jun 2007
Location: Robertson NSW
Posts: 517
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
Reply With Quote
  #8  
Old 22-12-2008, 08:30 AM
chunky (Clinton Wood)
Registered User

chunky is offline
 
Join Date: Nov 2007
Location: Sydney
Posts: 36
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.
Reply With Quote
  #9  
Old 09-01-2010, 11:32 AM
danielsun's Avatar
danielsun
Canon collector

danielsun is offline
 
Join Date: Oct 2005
Location: Taylors Lakes Melb
Posts: 1,965
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.
Reply With Quote
  #10  
Old 09-01-2010, 04:00 PM
Omaroo's Avatar
Omaroo (Chris Malikoff)
Let there be night...

Omaroo is offline
 
Join Date: Aug 2006
Location: Sydney/Cooma
Posts: 7,628
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
Reply With Quote
  #11  
Old 09-01-2010, 09:54 PM
danielsun's Avatar
danielsun
Canon collector

danielsun is offline
 
Join Date: Oct 2005
Location: Taylors Lakes Melb
Posts: 1,965
Thanks Chris.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:52 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
Astromechanics
Advertisement
Testar
Advertisement
Celestron RASA
Advertisement
EQ8-R
Advertisement
Star Adventurer
Advertisement
Lunatico Astronomical
Advertisement
Astronomy and Electronics Centre
Advertisement