Author Topic: Bahtinov Mask  (Read 15863 times)

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MarkS

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Bahtinov Mask
« on: Oct 01, 2008, 23:40:28 »

I've just cut a Bahtinov Mask from cardboard and given it a test run on my Celestron C11.
This is the easiest way of focusing a DSLR I have yet come across (much much easier than the Hartmann Mask).

This thread on an astronomical website(and similar ones on the Cloudy Nights site) explains all:
http://www.iceinspace.com.au/forum/showthread.php?t=35676

Here is the one I made tonight:


And here's an animated GIF I created (using the DSLR on the C11) that shows it in action - it is the image of a single star with the Mask placed in the front of the scope:


When the vertical bar is central between the slanted ones then you have perfect focus.  The other great thing is that it even "tells" you which way to turn the focus knob - turn it one way to move the vertical line to the left, the other to move it to the right.   It couldn't be easier!



Ian

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Re: Bahtinov Mask
« Reply #1 on: Oct 01, 2008, 23:58:20 »
now that looks scarily useful...

RobertM

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Re: Bahtinov Mask
« Reply #2 on: Oct 02, 2008, 00:42:54 »
It's brilliant, I've been trying it out the last couple of sessions and it certainly works much better than the mask I've been using till now.  Mine's rather crudely made out of part of a cardboard box but still works a treat.

Tony G

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Re: Bahtinov Mask
« Reply #3 on: Oct 02, 2008, 12:17:55 »
I can feel a Blue Peter moment coming.
Might try this the weekend.

Thanks Mark.

Tony G
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Mike

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Re: Bahtinov Mask
« Reply #4 on: Oct 02, 2008, 14:27:54 »
Looks interesting. I will give that a go myself.
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Mac

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Re: Bahtinov Mask
« Reply #5 on: Oct 27, 2008, 16:19:10 »
Found this whilst searching for things astronomical.

http://astrojargon.net/MaskGenerator.aspx

it will generate your masks for you.
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Carole

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Re: Bahtinov Mask
« Reply #6 on: Nov 05, 2009, 11:13:50 »
I've made the 3 hole version focus mask.  Would any-one say that this mask is even better.  I found the 3 hole version worked perfectly for me when I used it. 
Just wondering whether I should make this one as well?

Carole

RobertM

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Re: Bahtinov Mask
« Reply #7 on: Nov 05, 2009, 11:50:53 »
For the extra accuracy it's definitely worth the effort.

mickw

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Re: Bahtinov Mask
« Reply #8 on: Nov 05, 2009, 16:02:31 »
How precise does the cutting have to be, or is it the pattern that does the trick ?

Cutting one for a 91 is doing my eyes in :(
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Mac

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Re: Bahtinov Mask
« Reply #9 on: Nov 05, 2009, 17:53:37 »
Quote
or is it the pattern that does the trick

Its the pattern that works, by using diffraction.
similar to the once you see round stars ;) :roll:

cutting dosent have to be that accurate, resonable should do.
all you will get is a slightly different difraction pattern.
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mickw

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Re: Bahtinov Mask
« Reply #10 on: Nov 05, 2009, 18:18:21 »
Thanks Mac

That's a relief  :) :oops:
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Mike

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Re: Bahtinov Mask
« Reply #11 on: Mar 09, 2011, 10:54:08 »
Just realised I can get these laser cut at the London Hackspace in perspex or MDF. Will have to make one for my ED80.
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RobertM

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Re: Bahtinov Mask
« Reply #12 on: Mar 09, 2011, 11:34:48 »
I have a couple that need doing, any chance of getting those done while you're at it ?

Mike

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Re: Bahtinov Mask
« Reply #13 on: Mar 09, 2011, 12:04:48 »
Sure. Give me the details.
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RobertM

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Re: Bahtinov Mask
« Reply #14 on: Mar 09, 2011, 12:34:47 »
Thanks, I'll need to get some perspex and mask layout to you.

When are you getting them done?

Mike

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Re: Bahtinov Mask
« Reply #15 on: Mar 09, 2011, 12:44:58 »
Some time next week.

Just give me the numbers for the generator, it will be a lot easier.

I will need to convert the .svg file to .dxf for the laser cutter.

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RobertM

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Re: Bahtinov Mask
« Reply #16 on: Mar 09, 2011, 13:49:56 »
Ok, will do

Fay

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Re: Bahtinov Mask
« Reply #17 on: Mar 09, 2011, 13:52:06 »
I have an 8" one I can sell
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The Thing

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Re: Bahtinov Mask
« Reply #18 on: Mar 09, 2011, 15:11:27 »
I used the web generator (Mac's link below) and printed it on an A4 self adhesive photo sticker, sprayed it with photo shield stuff, then stuck it on an old plastic folder cover then cut it out with a craft knife. I believe sharp edges are crucial rather than perfectly straight lines as its the edge that causes the diffraction. I have tried a couple of configurations and fewer slots seems to be better. 8" masks must be easier to cut than one for Mick's Burgess.
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mickw

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Re: Bahtinov Mask
« Reply #19 on: Mar 09, 2011, 15:40:34 »
Quote
8" masks must be easier to cut than one for Mick's Burgess.

I still see diffraction spikes when I look at a lightbulb  :o

At least I know it's in focus  :lol:
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Carole

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Re: Bahtinov Mask
« Reply #20 on: Mar 09, 2011, 20:27:44 »
Wish I'd seen this revived thread a couple of days ago, might have saved some blisters on my fingers from all the pressing with the cutting blade.

 :(

MarkS

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Re: Bahtinov Mask
« Reply #21 on: Mar 09, 2011, 20:45:33 »
I've just seen the animation at the beginning of this thread.  I was dead impressed until I realised it was my own!
« Last Edit: Mar 09, 2011, 21:42:42 by MarkS »

Carole

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Re: Bahtinov Mask
« Reply #22 on: Mar 09, 2011, 22:08:17 »
 :lol:

Mac

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Re: Bahtinov Mask
« Reply #23 on: Mar 09, 2011, 23:53:47 »
 :cheesy:
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Mike

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Re: Bahtinov Mask
« Reply #24 on: Mar 15, 2011, 12:33:41 »
Note that the maximum size of the cutting bed for the laser is 310mm x 585mm so nothing over 310mm in diameter. Suitable materials - thin MDF sheeting or acrylic.

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mickw

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Re: Bahtinov Mask
« Reply #25 on: Mar 15, 2011, 12:42:05 »
So the Lightbridge is out then   :D

When would you want the materials by ?
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Mike

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Re: Bahtinov Mask
« Reply #26 on: Mar 15, 2011, 12:54:34 »
Acrylic can be cut up to 4mm depth and MDF up to 3mm. I can get materials from Hamar Acrylic which is just a short walk from London Hackspace. I'm doing some for Robert tomorrow (if he gives me the dimensions) so I'll let you know an idea of prices then. I know it is £3 per hour to use the cutter plus cost of materials on top.
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mickw

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Re: Bahtinov Mask
« Reply #27 on: Mar 15, 2011, 14:58:57 »
PM on it's way
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Mike

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Re: Bahtinov Mask
« Reply #28 on: Mar 16, 2011, 23:52:15 »
Did a few tests today cutting some of the 3mm MDF Mick gave me:



This was using the 80mm dimensions Robert gave me for his scope.

The acrylic Mick gave me was useless though, it just burnt. It needs to be branded Perspex apparently if you want smooth edges. I shall pick up some in black from Hamar Acrylic some time this/next week and do some more tests.
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Mike

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Re: Bahtinov Mask
« Reply #29 on: Mar 17, 2011, 00:17:21 »
Just for a laugh I made some planetary gears (tenuous astronomy link) too.

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mickw

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Re: Bahtinov Mask
« Reply #30 on: Mar 17, 2011, 07:39:38 »
Love the gears  8)

The reason the acrylic I gave you didn't work was because it was polycarbonate - Sorry  :oops:

I'd better get some numbers to you soon as well
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RobertM

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Re: Bahtinov Mask
« Reply #31 on: Mar 17, 2011, 08:50:00 »
Neat gears  8)

Those 80mm masks look ok, were they with the original figures I gave?

Robert

Mike

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Re: Bahtinov Mask
« Reply #32 on: Mar 17, 2011, 08:55:53 »
Robert, they were with the second set of figures. The original set had the slits so close together that the supporting struts also got burnt away during the cut. You might want to look at the designs for the other two as they may need adjusting too.

Once you are happy with the design I will cut them for real.
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Re: Bahtinov Mask
« Reply #33 on: Mar 17, 2011, 11:08:04 »
Just for a laugh I made some planetary gears (tenuous astronomy link) too.
What sort of diffraction pattern would that create!
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Re: Bahtinov Mask
« Reply #34 on: Mar 17, 2011, 11:16:38 »
I have an 8" one I can sell

Is it an SCT one with the big hole in the middle?

Chris