snowdragonusa
Pooh-Bah
Reged: 09/04/07
Posts: 1125
Loc: Denver, CO
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Heya Dave - Back on page 5 of this thread, about halfway down, you will see a post by me with a screen shot. The files and instructions are right there for you. In addition, have a look at David's mask generator which you will find links for right around that same post.
Cheers,
Adam
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Adam
12" LX200R, AT80LE
Lunt 60mm Ha & CaK solar scopes
DMK41.AS, DSI Pro, DSI-C, LPI
Denver Astronomical Society
Brighton Astronomical Group
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WhistleStop
sage
Reged: 09/07/07
Posts: 425
Loc: Grafton, Ontario
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Just used a Spike-a mask for the first time...WOW ! This is what I've been waiting for...perfect focus in one minute through 8nm Ha filter...made my night ! Pavel Bahtinov deserves a medal...and our sincere thanks
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WHISTLESTOP
Whistle Stop Observatory (44N78W)
TV NP101is, C9.25, WO ZS66,
G11 with Gemini, EQ6 with EQMOD
FLI ML8300 with CFW-2-7
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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Quote:
Just used a Spike-a mask for the first time...WOW ! This is what I've been waiting for...perfect focus in one minute through 8nm Ha filter...made my night ! Pavel Bahtinov deserves a medal...and our sincere thanks
I'm glad this is working for you. I'll pass along your thanks to Pavel Bahtinov on my next conversation with him.
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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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dsnay
sage
Reged: 07/02/06
Posts: 268
Loc: Massachusetts
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Quote:
Heya Dave - Back on page 5 of this thread, about halfway down, you will see a post by me with a screen shot. The files and instructions are right there for you. In addition, have a look at David's mask generator which you will find links for right around that same post.
Cheers,
Adam
Last night I was bored and made one up in Adobe Illustrator based on the calculations provided by the original poster, which had me making my "bars" 4mm wide for my little ole 80mm. I printed it on Velum and then cut out the openings and mounted it on an old needlepoint hoop I have been using for focusing by having string across it. It worked out pretty well, I think.
I've attached a copy of the jpg for use by anyone that wants it.
Dave
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rguinamard
member
Reged: 12/26/07
Posts: 24
Loc: south of Lyon, France
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Hi everybody,
This Bahtinov mask seems great!
I'm thinking of a mask for my (only visual) 24" dob.
If I keep the Bahtinov factor to 150, it leads to a very difficult to do and weak resistance mask:
So I made other simulations :
Bahtinov factor 100:
Bahtinov factor 80:
Bahtinov factor 50:
The factor 50 or 80 seems best to be both strong and easy to make but do you think it will be as efficiency as the 150 ?
I do not wan't to make several 24" mask...so long job to do!!!
Thanks in advance
Raphaël
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South of Lyon, France
24" dob f/d3.3
Edited by rguinamard (10/11/08 02:57 AM)
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snowdragonusa
Pooh-Bah
Reged: 09/04/07
Posts: 1125
Loc: Denver, CO
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Hey Raphaël,
Yep, anytime you end up with a mask with very tiny cut outs you can also use the Divide by 3 Rule and get an appropriately sized mask...
So if you took your 150 factor and divided by 3... voilà! 50 
That is going to be one monster mask for the 24" dob! Be careful not to drop it on your toe!!!
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Adam
12" LX200R, AT80LE
Lunt 60mm Ha & CaK solar scopes
DMK41.AS, DSI Pro, DSI-C, LPI
Denver Astronomical Society
Brighton Astronomical Group
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pubquiz
sage
Reged: 10/07/04
Posts: 469
Loc: Lancashire England
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Hi All
Been reading this thread over the last week or so with great interest...just a couple of questions...apologies if they have already been asked but there are quite a few pages to look through
1) Is it ok to put the mask at the end of the dew shield or must it be close to the lense?
2) I printed a mask for my Megrez 72 tonight (will cut it out tommorrow) but I also want to do one for my 12" LX200...Is there a facility in Inkscape (not familiar with it just downloaded tonight for this) to print onto 2 sheets of A4 paper to fit a 12" mask on? and is it easy to do?
Thanks
Tom
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Losmandy G11 with Celestron 8" SCT & William Optics Megrez 72 side by side with Argo Navis
Pier mounted in observatory.
Strathspey 20x90 Binos, Vixen Ark 20x80 Binos
Virgo Novamount parrallelogram mount
Meade Mysky, Meade DSI Pro, Meade LPI, Canon 450D un modded (for now), QHY5 Autoguider
Bahtinov Masks
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FarmerDave
sage
Reged: 09/07/07
Posts: 412
Loc: Northern Virginia
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Quote:
Is there a facility in Inkscape (not familiar with it just downloaded tonight for this) to print onto 2 sheets of A4 paper to fit a 12" mask on? and is it easy to do?
I don't think there is a way to do it automatically - what I suggested to someone else (I actually tried it just for fun) is to
1) set the paper size
2) "grab" and drag the mask in SVG until at least half of it (or a quarter of it) fits on a piece of paper. Print it, move it to do the other half (or quarter), and print that (repeat if necessary), and then cut and paste the physical pieces of paper together.
If you're using the generator, setting the "Center line color" option will print a center crosshair, which will make cutting and aligning the component pieces much easier.
I still want to give the option of generating 2 halves or 4 quarters as separate files, but haven't gotten to it - in fact, I just moved hosting providers today. Hopefully no one is running into any issues.
HTH,
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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jgraham
Postmaster
Reged: 12/02/04
Posts: 6695
Loc: Dayton, Ohio
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I use mine out on the end of my dew shield and it works fine.
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-John
================================================
Homebuilt scopes from 4.25-16.5"
Meade LXD75-N6/SN6/SC8, DSX-90, ETX-60BB, ETX-125PE, DS-2130
Orion StarBlast, BinoViewers, Coronado PST
Rebel XT/XTi, DSI Pro (I, II, & III), DSI, LPI, Electronic Eyepiece, Phillips SPC900NC
Tasco 60mm Refractors
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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:
This Bahtinov mask seems great!
I'm thinking of a mask for my (only visual) 24" dob.
I've used my mask a couple of times now visually for public presentations where I want to be close to '20/20' focus. A couple of points on this- if you wear glasses, the focus point with and without your glasses will change. This may seem obvious, but I tested this just to be sure.
Also, I noticed that some of my eyepieces will change the focus point depending on the position of your eye in relation to the eyepiece. I found if you move around in the eyepiece, the center diffraction spike will move as well! Maybe that's not true for the really good eyepieces, but my moderately priced eyepieces had this tendency.
Maybe I need to buy an Ethos now just to test this theory... anyone want to back me up with my wife? 
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
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rguinamard
member
Reged: 12/26/07
Posts: 24
Loc: south of Lyon, France
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Adam wrote:
Quote:
Yep, anytime you end up with a mask with very tiny cut outs you can also use the Divide by 3 Rule and get an appropriately sized mask...
Hi Adam, the 150 factor mask are not that tiny to cut (each cut is 12 mm), but so boring and the main problem I see is that the mask would also seems too weak to put on the dob.
So I agree in my case the bhatinov factor 50 seems better. I'm just wondering if the factor 50 mask will be as efficient as the factor 150 mask.
Quote:
Be careful not to drop it on your toe!!!
You're so right...! look what happens to my secondary last week that fell on the wooden floor.
It was not on my toe but maybe it would have been preferable...
...aarrgghh!
It is in french but the pictures are self-explicites...
http://www.astrosurf.com/ubb/Forum2/HTML/028211.html
Raphaël
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South of Lyon, France
24" dob f/d3.3
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pubquiz
sage
Reged: 10/07/04
Posts: 469
Loc: Lancashire England
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Thanks for that David..good idea re the red centre line.
Yes I used your generator....thanks for doing it, it makes things easy.
John..glad about that as it will be easier at the end of the dew shield.
Tom
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Losmandy G11 with Celestron 8" SCT & William Optics Megrez 72 side by side with Argo Navis
Pier mounted in observatory.
Strathspey 20x90 Binos, Vixen Ark 20x80 Binos
Virgo Novamount parrallelogram mount
Meade Mysky, Meade DSI Pro, Meade LPI, Canon 450D un modded (for now), QHY5 Autoguider
Bahtinov Masks
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snowdragonusa
Pooh-Bah
Reged: 09/04/07
Posts: 1125
Loc: Denver, CO
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Raphaël
OUCH! Sorry to hear that mate! 
The larger cut outs for the mask might make the spikes a little less pronounced... not sure though.
Has anyone tried larger cutouts?
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Adam
12" LX200R, AT80LE
Lunt 60mm Ha & CaK solar scopes
DMK41.AS, DSI Pro, DSI-C, LPI
Denver Astronomical Society
Brighton Astronomical Group
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rguinamard
member
Reged: 12/26/07
Posts: 24
Loc: south of Lyon, France
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Quote:
The larger cut outs for the mask might make the spikes a little less pronounced... not sure though.
It's what I'm worrying also...
Raphaël
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South of Lyon, France
24" dob f/d3.3
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 498
Loc: Lexington NC
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No worries Raphael. Your 50 will work just fine.
If it were me I would try 60. Shoot for 17 horizontal slots. This will make a very good mask for your 22 inch Dob. The large aperture scopes put a beautiful diffraction pattern. You will have not trouble getting focus on a 6th magnitude star.
You have a big advantage on material choice with that big of a scope. If you have a router you can cut a Bahtinov mask out of ¼ inch plywood. I would go with a Birch or Oak.
If you use real French oak then save me the chips, I’ll use it to age my wine. 
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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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rguinamard
member
Reged: 12/26/07
Posts: 24
Loc: south of Lyon, France
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Hi Jerry, and thanks for your comments about the diffraction pattern that blown away my worries.
I have a router.
I hadn't think what material to use for the mask, but you're right : plywood precisely cut by the rooter is certainly the good way to go.
I can buy 5 or 9 mm plywood.
Sorry for the chips, the classical -easy to find- plywood is not in oak....
Thanks again
Raphaël
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South of Lyon, France
24" dob f/d3.3
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rguinamard
member
Reged: 12/26/07
Posts: 24
Loc: south of Lyon, France
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Hum, I'm just thinking that if I use the rooter, it's certainly more simple to have the wide of the line the same as the drill (don't know if this is the correct word for the french "mèche") of the rooter.
For example I have a 9.5 mm diameter drill. With the 600 mm optical diameter of my scope the number of lines would then be 600/(2*9.5)=31 lines.
This lead then to a Bhatinov factor = 100 and Horizontal stripe count = 16
9 mm plywood is certainly needed in this case to avoid a mecanically too weak filter. Or better a 5mm plywood with a large "Structural bar thickness (mm)"=50 and maybe a wooden reinforcement in the middle of the horizontal stripe(no cutout in the middle of the horizontal stripe):
Raphaël
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South of Lyon, France
24" dob f/d3.3
Edited by rguinamard (10/11/08 04:18 PM)
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btieman
sage
Reged: 07/24/08
Posts: 466
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Quote:
Quote:
I've used my mask a couple of times now visually for public presentations where I want to be close to '20/20' focus. A couple of points on this- if you wear glasses, the focus point with and without your glasses will change. This may seem obvious, but I tested this just to be sure.
I don't understand this statement...I thought the point of the mask was that you use the position of the spike to determine focus. The position shouldn't change just because the eye focuses differently--should it?
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CPC 1100
Orion 120st
Milburn Wedge
QSI 520i
Meade DSI Pro
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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:
if you wear glasses, the focus point with and without your glasses will change.
Quote:
I don't understand this statement...I thought the point of the mask was that you use the position of the spike to determine focus. The position shouldn't change just because the eye focuses differently--should it?
Yes, it does. As you probably know, nearsighted individuals can use telescopes without their glasses by changing the focus slightly from the position when they are wearing their glasses. The perfect focus point for when they have their glasses on will be different from the point when they take them off. The diffraction spikes with the mask are centered when the perfect focus is achieved for whatever imaging device is at the eyepiece- whether a CCD or your eyeball- with or without glasses. So when you look through the scope and have the spikes centered with your glasses on, then take them off, the center spike will move. Kind of strange, but true!
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
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dmdouglass
super member
Reged: 12/23/07
Posts: 143
Loc: Tempe, AZ
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Jerry, I saw you reference to the site:
www.spike-a.com
I had just found this site also, via an advertisement in:
www.astrophotoinsight.com
Are you and spike-a one in the same? Just curious. Thought I would mention it, as others may be interested in the mask, but not want to "make it".
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David M. Douglass
Tempe, Arizona
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