Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1298
Loc: Kiev, Ukraine
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150 to 200, so that you don't need to cut exactly 7.34579mm but round to 7 or 8mm  (Just a number from my head).
Those are empirically derived numbers. 35-45 will work too, but you'll probably need a bit different cut sizes.
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snowdragonusa
Pooh-Bah
Reged: 09/04/07
Posts: 1125
Loc: Denver, CO
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I was reading back over some of the original posts from Dennis and noticed his red mask had a hole cut out in the center.
While Maks, SCTs, and Newts will see no difference I started thinking about refractors. If we were to cut out the center obstruction hole that would allow more light to enter we would be able to focus on dimmer stars. However, I also wonder if the increased central portion of light would start 'washing out' the defraction patterns.
Any thoughts? I think I might try that experiment out at home tongiht with my papaer cutout for the 80 mm and see if there is a big difference.
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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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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1298
Loc: Kiev, Ukraine
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The hole in the center is just for the secondary mirror. For refractor you don't need it. Just continue cuts where the hole is.
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ayiomamitis
super member
Reged: 02/10/07
Posts: 191
Loc: Athens, Greece
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Dennis,
Thanks to both yourself as well as the gentleman who came up with this ingenious creation.
I would like to ask you about the "f/s = 150-200" rule of thumb ... can I assume that it refers to the sum of the slit and the ensuing bar? In other words and using my AP refractor with focal length of 1200 mm, the above rule of thumb yields a value of "s" which is between 6 and 8 mm ... therefore, are the slits one-half of this amount (3-4 mm) and another similar amount for the bar?
As for the angle of the slits for one of the two sides which are not 90 degrees, is this fixed (ex. 20 degrees) or do we have a similar equation for a suggested angle?
Thanks again for your time and attention to this creative tool!
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Clear skies,
Anthony Ayiomamitis
Athens, Greece
http://www.perseus.gr
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Gus_Smedstad
Pooh-Bah
Reged: 07/02/06
Posts: 1108
Loc: Boston 42° 16' N 71° 08' W
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Post #5 makes it fairly clear that you have the numbers correct. A 1200mm focal length gives you a total width S of 6-8mm, so the slits need to be 3-4mm and spaced by the same amount.
I'm not clear at this point whether this is a major improvment over an ordinary Hartman mask which has 6 diffraction spikes. The triangular version gives 18 diffraction spikes, which is really unusable, but if you paint three toothpicks black and attach them to the holes of a 3-circle Hartman mask, you get much the same effect I'm seeing in the animations.
The main difference would seem to be that there are a lot more slits and the specifics of the slit spacing. Perhaps this yields brighter diffraction spikes?
- Gus
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Gus Smedstad image gallery
Orion Atlas 8 EQ-G
Celestron Onyx 80EDF (guiding / widefields).
Orion Starshoot Autoguider
QHY8
Philips SPC900NC
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Elliot
super member
Reged: 09/12/06
Posts: 123
Loc: Medford NJ
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Hi John - I ordered one from your website today http://www.spike-a.com/# but did not see where it will take 2-4 weeks for deleivery. Why so long? Is that accurate?
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Celestron CPC 1100
APT Wedge
Celestron ED80 GuideScope
SkyShed
SBIG ST9XE
Celestron Ultima 2000
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John Wunderlin
Vendor - Spike-a Focusing Mask
Reged: 10/01/04
Posts: 655
Loc: Mineral Point, Wi
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Hi- yes, I just added that to the site. The 1st batch of masks I have were prototypes. The 1st production run will be done next week. I'm hoping it will be less than 2 weeks, but I want to manage expectations. If you're interested in a prototype, PM me or email me directly.
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
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Elliot
super member
Reged: 09/12/06
Posts: 123
Loc: Medford NJ
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I will anxiously wait. 
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Celestron CPC 1100
APT Wedge
Celestron ED80 GuideScope
SkyShed
SBIG ST9XE
Celestron Ultima 2000
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John Wunderlin
Vendor - Spike-a Focusing Mask
Reged: 10/01/04
Posts: 655
Loc: Mineral Point, Wi
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One additional suggestion for the DIYers, I experimented with wide ribbon of the type you use for wrapping presents. It showed some promise. You could potentially make a 'dreamcatcher' type mask with perhaps a wood slat down the middle and attach ribbon to it in this pattern. I gave up on this path after Jerry & I hooked up.
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
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Gus_Smedstad
Pooh-Bah
Reged: 07/02/06
Posts: 1108
Loc: Boston 42° 16' N 71° 08' W
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As long as you're following this thread, Josh, if you're going to offer these masks, are you going to give any consideration to the slit spacing? I'm unclear how important this is because, not knowing Russian, I haven't read the original thread. But my 8" OTA is an Orion 1000mm, and your site doesn't say whether the slits on an 8" mask are 3mm (for 1000mm f/4.9) or 5-6mm (for a 2000mm f/10).
- Gus
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Gus Smedstad image gallery
Orion Atlas 8 EQ-G
Celestron Onyx 80EDF (guiding / widefields).
Orion Starshoot Autoguider
QHY8
Philips SPC900NC
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John Wunderlin
Vendor - Spike-a Focusing Mask
Reged: 10/01/04
Posts: 655
Loc: Mineral Point, Wi
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Quote:
As long as you're following this thread, Josh,
I assume you mean me- John?
Quote:
if you're going to offer these masks, are you going to give any consideration to the slit spacing?
The spacing gets smaller as the diameter of the mask gets smaller. I don't have an 8" with me right now, so Jerry would probably be a better person to ask about that. I suggest PMing him if you want to know the dimensions.
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
Edited by John Wunderlin (09/04/08 11:50 AM)
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Gus_Smedstad
Pooh-Bah
Reged: 07/02/06
Posts: 1108
Loc: Boston 42° 16' N 71° 08' W
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My apologies for the name mistake. For some inexplicable reason I saw "Josh" every time I read "John."
Arrrgh.
- Gus
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Gus Smedstad image gallery
Orion Atlas 8 EQ-G
Celestron Onyx 80EDF (guiding / widefields).
Orion Starshoot Autoguider
QHY8
Philips SPC900NC
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Dennis Sakva
Pooh-Bah
Reged: 10/19/04
Posts: 1298
Loc: Kiev, Ukraine
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s=slit+space
So S=10 the cut is 5mm and the uncut space is also 5mm
BUT!
As cuts get too small you can multiply the number by 3 and use 3rd order spectrum (no visual difference) instead of the 1st one. I described all that on 1st page.
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John Wunderlin
Vendor - Spike-a Focusing Mask
Reged: 10/01/04
Posts: 655
Loc: Mineral Point, Wi
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Quote:
My apologies for the name mistake.
No problem!
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
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Snow dog
Carpal Tunnel
Reged: 07/17/05
Posts: 1770
Loc: Alberta Canada
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Quote:
if you paint three toothpicks black and attach them to the holes of a 3-circle Hartman mask, you get much the same effect I'm seeing in the animations.
Gus
I'm interested in how you put the toothpicks in the holes. I just made a hartman mask for my LX-200 and was going to make one of these but if all I need to do is add a few toothpicks it would be great. Could you post a pic or a sketch of how you did it.
Thanks
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Marc
Someone get these crazy dogs off me
12" LX200 Classic
ETX-90PE
Meade DSI
Canon AE-1, EOS Rebel 350
My Home Page
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John Wunderlin
Vendor - Spike-a Focusing Mask
Reged: 10/01/04
Posts: 655
Loc: Mineral Point, Wi
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Here is a website that describes the process in quite a bit of detail for the Hartmann style.
http://starryvistas.net/Articles/FocusMask/FocusMask.aspx
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John Wunderlin
Vendor - Spike-a Bahtinov Focusing Mask
Empire Ranch Observatory
Iowa County Astronomers
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snowdragonusa
Pooh-Bah
Reged: 09/04/07
Posts: 1125
Loc: Denver, CO
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The thing I don't like about the Hartman Mask is I am taking my 12" scope and reducing the light gathering ability down to perhaps 1/5 or more. The triangles produce small diffraction patterns at best and even placing the toothpicks on I saw little difference (in my case).
This Pavel Mask really makes a HUGE distinction on focus by the placement of one spike compared to the other two. I also don't have to worry about zooming in on the star to get a good focus.
Oh, and I get to play with knives and glue to make a new mask!
Bonus all the way around!!! 
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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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Gus_Smedstad
Pooh-Bah
Reged: 07/02/06
Posts: 1108
Loc: Boston 42° 16' N 71° 08' W
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That article on Starry Vistas is where I got the idea for the diffraction toothpicks in the Hartman mask. The circles I used were a lot larger, and I have no trouble picking out the diffraction spikes, though I do typically zoom in with Live View.
More light, brighter spikes, and a clearer relationship between the spikes would be good, though. Eyeballing the focus is a lot better than a plain Hartman mask, but I still sometimes feel I'm guessing whether they're centered, since the intersection is obscured by the star itself.
- Gus
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Gus Smedstad image gallery
Orion Atlas 8 EQ-G
Celestron Onyx 80EDF (guiding / widefields).
Orion Starshoot Autoguider
QHY8
Philips SPC900NC
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Gus_Smedstad
Pooh-Bah
Reged: 07/02/06
Posts: 1108
Loc: Boston 42° 16' N 71° 08' W
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BTW, we should probably be calling these "Bahtinov Masks", not Pavel Masks. Oh, sure, Pavel rolls off the tongue, but it's sort of like calling something a "Paul Mask."
- Gus
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Gus Smedstad image gallery
Orion Atlas 8 EQ-G
Celestron Onyx 80EDF (guiding / widefields).
Orion Starshoot Autoguider
QHY8
Philips SPC900NC
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xumaxer
sage
Reged: 01/30/06
Posts: 249
Loc: 39º 45' N, 8º 48' W
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Wow! this sure looks promising! 
I got one question, though:
- shooting with a WO ZS80FD + 0.8x FR - the focal length on the formula will be the original one (555mm) or with the reducer on (444mm)? will it make a difference?
I also have a 2" extender and DSLR...
BTW, what if I want to get one for my C11?
Thanks!
xumie
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Ciao
xumie
________________________________
C11
FS-102NSV
G-11 Gemini
ST2000XM + CFW10
DMK21AF04.AS
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