jrbarnett
Eyepiece Hooligan
Reged: 02/28/06
Loc: Petaluma, CA
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Why no commercial source for "Duncan" Mask?
#5346779 - 08/01/12 11:08 AM
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Most of you probably know what a Duncan Mask is. For those that don't, it's a collimation tool for catadioptrics conceived of by UK amateur Duncan Evenden. It consists of an aperture mask with cut-outs opposite of the collimation screws. Here's an example together with basic instructions on its use:
http://stargazerslounge.com/index.php?app=core&module=attach§ion=attach&attach_id=65090
My question is this. Given the exorbitant prices fetched for SCT collimation tools like the Hotech unit, why hasn't any commercial producer bothered to manufacture Duncan Masks for commercial SCTs? Heck, Celestron and Meade could *include* them with their scopes. Producing a solidly mounted, precision mask would literally cost pennies.
Orion? Astrozap? Scopestuff? Are you listening? 
- Jim
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brianb11213
Postmaster
Reged: 02/25/09
Loc: 55.215N 6.554W
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Re: Why no commercial source for "Duncan" Mask?
[Re: jrbarnett]
#5346851 - 08/01/12 11:40 AM
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Heck, Celestron and Meade could *include* them with their scopes. Producing a solidly mounted, precision mask would literally cost pennies.
For a few pennies they could upgrade the power cord connector to a reliable type.
For a few dollars they could stick a dew shield in the retail box (SCTs and Maks are essentially useless without a dewshield) and add forced ventilation fans.
These companies are more interested in what they can pay their shareholders now than in whether or not they have a repeat customer in five years.
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nevy
sage
Reged: 02/07/12
Loc: UK
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Re: Why no commercial source for "Duncan" Mask?
[Re: brianb11213]
#5346934 - 08/01/12 12:36 PM
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I was thinking of making one of those masks, do they work and if they do does it get collimation spot on ?
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bilgebay
Post Laureate
Reged: 11/06/08
Loc: Türkiye - Istanbul and Marmari...
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Re: Why no commercial source for "Duncan" Mask?
[Re: nevy]
#5347114 - 08/01/12 02:36 PM Attachment (57 downloads)
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I built one for my C11 but didn't like it as the pattern it produced was too dim. Maybe I didn't understood the formula and made a mistake during the design phase. I will produce another one asap.
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gnowellsct
Postmaster
Reged: 06/24/09
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Re: Why no commercial source for "Duncan" Mask?
[Re: jrbarnett]
#5347290 - 08/01/12 04:44 PM
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My question is this. Given the exorbitant prices fetched for SCT collimation tools like the Hotech unit, why hasn't any commercial producer bothered to manufacture Duncan Masks for commercial SCTs? Heck, Celestron and Meade could *include* them with their scopes. Producing a solidly mounted, precision mask would literally cost pennies.
Orion? Astrozap? Scopestuff? Are you listening?
- Jim
Jim, they don't bring out product because they know they can't beat the Sheer Genius Collimation Device.
It's priceless.
http://www.astromart.com/articles/article.asp?article_id=718
Greg N
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gnowellsct
Postmaster
Reged: 06/24/09
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Re: Why no commercial source for "Duncan" Mask?
[Re: gnowellsct]
#5347328 - 08/01/12 05:04 PM
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There's a close up in this thread.
sheer genius collimation device
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bluedandelion
Carpal Tunnel
Reged: 08/17/07
Loc: Hazy Hollow, Western WA
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Re: Why no commercial source for "Duncan" Mask?
[Re: gnowellsct]
#5348049 - 08/02/12 01:13 AM
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You should have said, "The SGCD is so simple, it cannot be invented. I am not the inventor." 
The uses of a stick are many, but how does one invent one? You found a new use for an old device.
Ajay
Edited by bluedandelion (08/02/12 01:15 AM)
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nevy
sage
Reged: 02/07/12
Loc: UK
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Re: Why no commercial source for "Duncan" Mask?
[Re: bilgebay]
#5348290 - 08/02/12 08:02 AM
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I built one for my C11 but didn't like it as the pattern it produced was too dim. Maybe I didn't understood the formula and made a mistake during the design phase. I will produce another one asap.
I think it should be a round disc with 3 cutouts In the shape of the grey area, it should look like a 11" cats eye hotspot
http://i1172.photobucket.com/albums/r563/nev19/ccd762f7.jpg
Edited by BRisley (08/02/12 10:26 AM)
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jmiele
Patron Saint?
Reged: 12/04/10
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Re: Why no commercial source for "Duncan" Mask?
[Re: nevy]
#5348332 - 08/02/12 08:39 AM
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Exactly. The grey is what should make up the mask. Light grey that is.  Also the edge should account for the retaining ring so as not to make the 3 arc's become to slender.
Joe
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Mary B
Vendor - Echo Astronomy and Electronics
Reged: 05/21/10
Loc: Minnesota
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Re: Why no commercial source for "Duncan" Mask?
[Re: jmiele]
#5348994 - 08/02/12 04:27 PM
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Be easy to laser cut, what is the math behind it?
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gnowellsct
Postmaster
Reged: 06/24/09
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Re: Why no commercial source for "Duncan" Mask?
[Re: bluedandelion]
#5349074 - 08/02/12 05:11 PM
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You should have said, "The SGCD is so simple, it cannot be invented. I am not the inventor."
The uses of a stick are many, but how does one invent one? You found a new use for an old device.
Ajay
No no Ajay, I didn't invent "the stick." I invented *the properly placed notch*! (TM)
Greg N
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shiner
super member
Reged: 11/04/11
Loc: England
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Re: Why no commercial source for "Duncan" Mask?
[Re: gnowellsct]
#5368338 - 08/14/12 01:10 PM
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I'm going to look into making one of these. The lid of a five gallon plastic paint tub should do the trick....
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Starhawk
Post Laureate
Reged: 09/16/08
Loc: Tucson, Arizona
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Re: Why no commercial source for "Duncan" Mask?
[Re: shiner]
#5369406 - 08/15/12 01:30 AM
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I've used the shadow of my arm in place of the stick.
It works. I think the reason no one makes one is it's like trivial. Print out a radiation warming symbol and get some scissors.
-Rich
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jrbarnett
Eyepiece Hooligan
Reged: 02/28/06
Loc: Petaluma, CA
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Re: Why no commercial source for "Duncan" Mask?
[Re: Starhawk]
#5370133 - 08/15/12 01:21 PM
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You mean "trivial" like commercially available flexible dew shades, Bob's Knobs, magnetic "speaker magnet" counterweights, Baader solar film ring filters, "shower cap" style solid tube Dob end caps, collimation caps, etc.?
There are loads of things that are utterly trivial to make yourself, yet they sell well when made available commercially. I would also like to see "stop down" dust caps for refractors with threaded concentric rings allowing reduction in aperture in 5mm increments (and corresponding extension of focal ratio).
Regards,
Jim
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Steve OK
professor emeritus
Reged: 09/22/07
Loc: OKC, OK
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Re: Why no commercial source for "Duncan" Mask?
[Re: nevy]
#5371142 - 08/16/12 06:52 AM
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I made one yesterday (20 minutes with an X-acto knife and a piece of photo matte board), and got to try it last night. I am very excited by how well it worked! I did have decent seeing, and my scope was within 2°F of ambient temp when I pulled it out of the shed. I used a 5mm EP on my C11 for 560x, and even then the pattern of three lines was pretty small. I could easily see the effect on the pattern of tiny movements of the collimation screws. I think I achieved the best collimation I've ever had for my C11. I don't think I'd be overreaching to say that the Duncan mask is to collimating an SCT what a Bahtinov mask is to focusing my camera, at least for me. It gives the same kind of feedback anyway. I'm sure that the purists out there that are blessed with consistently good seeing can get perfect collimation without a mask, but the feedback it gives is a huge help to me. I leaves me wondering...why did I just now find out about this? And what other wonderful tricks are hidden out there?
Steve
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Pinbout
Post Laureate
Reged: 02/22/10
Loc: Montclair
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Re: Why no commercial source for "Duncan" Mask?
[Re: Mary B]
#5371948 - 08/16/12 05:46 PM Attachment (25 downloads)
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Be easy to laser cut, what is the math behind it?
if you send me one for 8in I'll tell you the math...
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elwaine
Pooh-Bah
Reged: 06/18/06
Loc: S.W. Florida
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Re: Why no commercial source for "Duncan" Mask?
[Re: Pinbout]
#5372092 - 08/16/12 07:41 PM
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Good point Jim. A mask like that will certainly sell.
So which one of you guys are going to commercialize this?
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Bart
Carpal Tunnel
Reged: 05/28/06
Loc: Somewhere near Charlottesville...
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Re: Why no commercial source for "Duncan" Mask?
[Re: elwaine]
#5372122 - 08/16/12 08:21 PM
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I'd buy one for a C11, hint, hint, hint.....
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Bart
Carpal Tunnel
Reged: 05/28/06
Loc: Somewhere near Charlottesville...
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Re: Why no commercial source for "Duncan" Mask?
[Re: Bart]
#5372129 - 08/16/12 08:32 PM
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http://stargazerslounge.com/index.php?app=core&module=attach§ion=attach&attach_id=65090
With the above link you come across this sentence: "When they all meet collimation is achieved, when they cross evenly you are in perfect focus." I'm confused by it's meaning and hoping someone can clarify.
Would the sentence above be more accurate if it was written this way? "When the lines start to meet, collimation is almost achieved. When they all cross evenly, like the last picture, that is when you have achieved perfect collimation."
Thanks
Bart
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barasits
sage
Reged: 06/12/11
Loc: Chicago
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Re: Why no commercial source for "Duncan" Mask?
[Re: Steve OK]
#5372430 - 08/17/12 12:37 AM
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Thanks for the report, Steve. You've convinced me to put this at the top of my project list.
Geoff
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