Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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Bill. The cut size you would need for f2 would be 1.9mm or about .075 inches. In your case use the native focal length of 2800 and Bahtinov factor of 150. This will give you a cut size of 9.3mm or .366 inches. You will use the third order for most of you focusing.
Are you going to split the mask so it can be removed without removing the camera? If so make sure the alignment is kept symmetrical when the mask is in place. A small error in angle will give you trouble.
Hope this helps.
jerry
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Meade LXD75-SN-8, SN-10, C11
DSI Pro
Canon XSi 450D unmod
www.spike-a.com Bahtinov Style Focus Mask
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Bill Richards
journeyman
Reged: 04/19/07
Posts: 5
Loc: Tucson, Arizona
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Jerry. Great information - Thanks. I was going to mount the mask on the end of a dew shield but splitting the mask is a great idea. As you suggest, I'll need to make it fit precisely. Thanks again.
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Bill Richards
Celestron C11
William Optics ZS-105, ZS-80ST
Hyperstar 3
Canon/Hutech 350D
CCD Labs Qguide
Tak EM-200 Temma II
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shurik
member
Reged: 10/07/07
Posts: 36
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I am looking for Bahtinov Mask for Tak 180ED f/2.8 can someone name their price or make one and I will pay, or maybe has a drawing for this scope. Thank you ! Alex
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bilgebay
newbie
Reged: 11/06/08
Posts: 3
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Hi anat,
Is this for the 18-55mm lens that comes with 450D. If yes, can you please advise the values to enter into Bahtinov mask generator?
Thanks and best regards
Sedat
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anat
sage
Reged: 06/03/04
Posts: 235
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Sedat:
I tried the mask on a 200mm lens but spikes could not be seen. I think the spikes are undersampled in lenses with a focal length less than about 200 mm. However, I successfully use it at a focal length of 350mm.
For the values, I simply scale it up or down. No rule 
Anat
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Astro-physics 155EDT
Borg 60ED
Losmandy G11 Gemini
Hypermodded Canon 450D
LVI SmartGuider
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joejoe
member
Reged: 08/04/08
Posts: 96
Loc: Australia
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For anyone who doesn't have a Bahtinov mask yet, I made a quick video of my home made one in action:
Watch here
Once again, thanks to David. Your generator made it so easy...
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MN152, ED127, WO72FD, EQ6
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fourstars
sage
Reged: 07/12/06
Posts: 365
Loc: Wild West.
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Hey, cool thread! Good thing I got my new glasses cause that was a read. I have used the generator for my 5" refractor, but now need one for my 10" cave. Is there a way to print out on regular printer?? Also I can use the cave at f/16 or as a newt at f/4 What is this 3rd order thing? must of missed the post on that.
Thanks for everybody help and time here!
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Staring off into space is highly underated!
Edited by fourstars (12/17/08 06:52 PM)
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FarmerDave
sage
Reged: 09/07/07
Posts: 412
Loc: Northern Virginia
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Quote:
Is there a way to print out on regular printer??
The easiest way to do it is to download Inkscape, then print the mask image to get one half, slide it to the left to get the other half, trim each of the halves, and paste them together.
You might have to do each quarter separately, depending on the size of your scope, the outer edge thickness you use, and the size of your paper. Under the print options, putting in a "Center line color" of red or black can help you line up the halves/quarters.
I keep saying I'm going to add an option to produce multiple files, but I haven't gotten to it. I'm off for almost two weeks for the holidays, so I might spend some time upgrading the generator.
Quote:
Also I can use the cave at f/16 or as a newt at f/4 What is this 3rd order thing? must of missed the post on that.
Hopefully, John W (or someone else who actually knows about/understands the physics) can weigh in on this, but I think this is in reference to the wave harmonics that create the interference patterns we see, that line up so pretty when we're in focus. The 3rd order is what makes the "divide the Bahtinov factor by three" thing still produce a workable mask/pattern.
David
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Celestron C6/C9.25/CG-5GT Mount
Orion 80ED/EON 72/Supercharged Atlas EQ-G
Garrett Optical Signature Series 10x50
Canon XTi (soon to be modded)/Canon 40D (unmodded)
Meade DSI/Meade DSI Pro/Philips SPC900N
1944 Ford 2N/1948 Ford 8N
Bahtinov Mask Generator * AstroCataLink * 40DShutterCount
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John Wunderlin
Vendor - Spike-a Focusing Mask
Reged: 10/01/04
Posts: 658
Loc: Mineral Point, Wi
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Quote:
Quote:
Also I can use the cave at f/16 or as a newt at f/4 What is this 3rd order thing? must of missed the post on that.
Hopefully, John W (or someone else who actually knows about/understands the physics) can weigh in on this
I'm afraid I don't understand the physics well on this- maybe Jerry does, but I have tested the same mask with f4 and f10 and found the pattern to be easy to use with both. I suspect that you will be able to use the same mask even with that wide of a range of f ratios. It's extremely forgiving.
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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Is this Physics or Quantum mechanics?  My answer is neither! The Bahtinov mask is just pure magic.
Okay, seriously- the light waves travel past the sharp edge of the mask and causes a diffraction spike in a wave form. As each peak of the wave aligns it creates a bright spot. This is the first order in the spectrum. As each third peak aligns, a third order spectrum spot is illuminated. Then a 5th, 7th and so on until the aptitude of the wave has dissipated. So this is why the math formula uses focal length to calculate the optimum distance between the cutouts. The nice thing is that you can align the spectrum on the rising, falling, or peak of the sin wave and still get a nice diffraction spike pattern. It is only a minor difference in the third order spectrum from a mask that is dead on optimal and one that is way off. This is why I always recommend that you spend more time on getting nice straight lines with a sharp edge, and not get too caught up with the focal length.
See my post above for a photo I made with a mask that was way off of optimal cutout as calculated by the formula. You see the first order is a mess, but the third order still is quite useful in getting good focus.
I hope I explained this okay.
And by the way- I’m not a big time banker, just a guy that works on engines by day and takes time out on clear nights to enjoy the cosmos. Once and a while I’ll climb on my 1952 8N tractor and ride for the fun of it. 
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Meade LXD75-SN-8, SN-10, C11
DSI Pro
Canon XSi 450D unmod
www.spike-a.com Bahtinov Style Focus Mask
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FarmerDave
sage
Reged: 09/07/07
Posts: 412
Loc: Northern Virginia
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Thanks for the explanation, Jerry!
Quote:
Is this Physics or Quantum mechanics?
I'll take "Subjects I didn't do altogether well at in college" for $800, Alex.
Quote:
Once and a while I’ll climb on my 1952 8N tractor and ride for the fun of it.
Ha! We might have to ask the admins for a tractor subforum.
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Celestron C6/C9.25/CG-5GT Mount
Orion 80ED/EON 72/Supercharged Atlas EQ-G
Garrett Optical Signature Series 10x50
Canon XTi (soon to be modded)/Canon 40D (unmodded)
Meade DSI/Meade DSI Pro/Philips SPC900N
1944 Ford 2N/1948 Ford 8N
Bahtinov Mask Generator * AstroCataLink * 40DShutterCount
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fourstars
sage
Reged: 07/12/06
Posts: 365
Loc: Wild West.
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Yes, thank you. I even kind of get it. Well I'll be spending the weekend with the trusty old scroll saw!
I've always wanted a tractor!
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Staring off into space is highly underated!
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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Fourstars you are a brave man to cut a bahtinov mask with a scroll saw. You must be highly skilled. Please post a photo after you get it cut.
David- A tractor sub? good idea. For now I posted a photo of my tractor in the Gardening thread. i did use it to dig a hole for my pier also.
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Meade LXD75-SN-8, SN-10, C11
DSI Pro
Canon XSi 450D unmod
www.spike-a.com Bahtinov Style Focus Mask
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FarmerDave
sage
Reged: 09/07/07
Posts: 412
Loc: Northern Virginia
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Quote:
David- A tractor sub? good idea. For now I posted a photo of my tractor in the Gardening thread. i did use it to dig a hole for my pier also.
Nice pic - I don't go into the gardening forum much - if they called it the "planting things and watching them die" forum, maybe.
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Celestron C6/C9.25/CG-5GT Mount
Orion 80ED/EON 72/Supercharged Atlas EQ-G
Garrett Optical Signature Series 10x50
Canon XTi (soon to be modded)/Canon 40D (unmodded)
Meade DSI/Meade DSI Pro/Philips SPC900N
1944 Ford 2N/1948 Ford 8N
Bahtinov Mask Generator * AstroCataLink * 40DShutterCount
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fourstars
sage
Reged: 07/12/06
Posts: 365
Loc: Wild West.
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Well I cut out my 5" mask on the scroll this afternoon. Was so proud of how straight it turned out. Thought I'd wash off some of the left over glue I used for the pattern. Better yet set it by the wood stove to dry out. NOT a good idea! I guess that wood will warp:-) I decided to still try it out and WOW! This is going to save me tons of time. I'll cut out a new mask and post a picture of both just for a good laugh. At least the saw is sharp!
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Staring off into space is highly underated!
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bilgebay
newbie
Reged: 11/06/08
Posts: 3
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Thank you Anat. I will try and see what happens if the clouds permit of course...
Sedat
Edited by bilgebay (12/21/08 07:53 AM)
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greeps
member
Reged: 02/04/06
Posts: 52
Loc: Chattanooga, TN
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Post deleted by greeps
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fourstars
sage
Reged: 07/12/06
Posts: 365
Loc: Wild West.
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Here's a couple shots of the ones I cut out of birch.
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Staring off into space is highly underated!
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fourstars
sage
Reged: 07/12/06
Posts: 365
Loc: Wild West.
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And this is for the five inch F/9. Sure was a fun project, and what a time saver
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Staring off into space is highly underated!
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greeps
member
Reged: 02/04/06
Posts: 52
Loc: Chattanooga, TN
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Does anyone know the difference in the focusing image between the mask with the wider vs the narrower cutouts?
My understanding thus far is that you get 3rd order spikes with the wider slots and if you use the narrowest, you get 1st and second in addition. Are the spikes narrower and is the central image smaller with the narrower slots?
I cut one out of Kydex yesterday for my 80mm with a field flattener. It took a couple of hours with razors and a chisel. It turned out OK and works very well, but I did use the wider slots so I'm wondering if there are benefits to the narrower slots.
For the wider slots, I used Astrojargon's site with a value of 50. I've printed patterns for all my scopes. I just wonder if the narrower slots are worth the extra trouble to cut.
Thanks for any help with this.
Also thanks for all the help, messages, and links that have been provided. I've found them enormously helpful. I've read all 23 pages of posts and I'll go through them again. I hadn't made the mask when I read them the first time so maybe I missed something.
David
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