OzAndrewJ
professor emeritus
Reged: 11/30/10
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Re: Why no commercial source for "Duncan" Mask?
[Re: gnowellsct]
#5372467 - 08/17/12 01:19 AM Attachment (36 downloads)
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Gday Greg
Quote:
Jim, they don't bring out product because they know they can't beat the Sheer Genius Collimation Device.
It's priceless.
Unless you have bicycle spokes 
About 5c each.
This allows you to adjust the collimation easily whilst looking through the EP and no risk of hitting the corrector with your fingers or allen keys etc.
Andrew
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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: Bart]
#5372731 - 08/17/12 08:37 AM
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Bart asks "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."
No. As you approach focus, whether collimated or not, the three little spikes (produced by diffraction through the three open arcs) converge. If you have ever used a Hartmann mask it behaves the same way. If you are collimated, the three little spikes all arrive at the center at the same time. Conveniently, there is a tiny dot at the point where they converge, presumably the Airy disk of the star. If you are not quite collimated the spikes do not arrive at the same time. In my case, two of the three spikes touched the dot together while the third spike hadn't quite made it. Luckily it was the spike at the 12:00 (or 6:00) position so I knew which knob (Bob's) to turn. I gave the "top" knob maybe 1/8th of a turn. Checking the spikes again the errant spike now reached the dot before the other two, so I knew I had gone too far. I moved the top knob back a little at a time, checking the spikes' behavior, until they appeared to arrive at the dot in unison. By "checking the spikes' behavior" I mean making small movements of the focus knob and watching the spikes move radially towards or away from the little central dot.
Edited by Steve OK (08/17/12 08:39 AM)
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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: Steve OK]
#5372769 - 08/17/12 09:06 AM
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I guess I'm getting confused with the idea of collimation and focusing being the same thing.
So as represented with the third picture, second from right, when all the lines converge at the beginning of the lines, collimation has been achieved. Then when you focus, the lines move on top of each other as suggested in pic number four, first from right. Is that correct?
Thanks
Bart
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HeyJP
sage
Reged: 12/11/10
Loc: Boulder, CO
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Re: Why no commercial source for "Duncan" Mask?
[Re: Bart]
#5372812 - 08/17/12 09:42 AM
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Now you have it, Bart. When you collimate,, you intentionally de-focus your scope, then adjust the collimation screws until an endpoint of the three lines just touch in the center. You can then re-focus your scope which causes the three lines to overlap and cross their centers.
Jim
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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: HeyJP]
#5372861 - 08/17/12 10:14 AM
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Thanks.
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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: Bart]
#5373590 - 08/17/12 05:41 PM
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Does anyone know if a cheapo video eyepiece (made by Orion) is good enough to use with a Duncan mask?
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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: OzAndrewJ]
#5376553 - 08/19/12 08:29 PM
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Now *that* truly is sheer genius. Makes the stick look, well, unimaginative and rather antiquated. 
- Jim
Edited by jrbarnett (08/19/12 08:30 PM)
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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: jrbarnett]
#5379453 - 08/21/12 01:53 PM
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I made one today for a C11 out of cardboard , I wasn't to sure of measurements so I guesstimated and this is what I came up with
[image]http:// [/image]
If it works , I'll make one from 1/4" plywood.
Edited by nevy (08/21/12 01:55 PM)
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end
super member
Reged: 08/31/11
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Re: Why no commercial source for "Duncan" Mask?
[Re: nevy]
#5379474 - 08/21/12 02:03 PM
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Looks great! I will be very interested to hear how well this works. In particular I'm interested to know how fine of collimation can be achieved. In my opinion there are many ways to get rough or good collimation, but the final adjustment to very good or great collimation is much more difficult and usually involves analysis of a sharply focused star and its airy disk.
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gnowellsct
Postmaster
Reged: 06/24/09
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Re: Why no commercial source for "Duncan" Mask?
[Re: OzAndrewJ]
#5379554 - 08/21/12 03:14 PM
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Quote:
Gday Greg
Quote:
Jim, they don't bring out product because they know they can't beat the Sheer Genius Collimation Device.
It's priceless.
Unless you have bicycle spokes
About 5c each.
This allows you to adjust the collimation easily whilst looking through the EP and no risk of hitting the corrector with your fingers or allen keys etc.
Andrew
Those are very clever, though from the point of view of indicating which screw needs adjustment you need one shadow. Three would be confusing.
Greg N
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OzAndrewJ
professor emeritus
Reged: 11/30/10
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Re: Why no commercial source for "Duncan" Mask?
[Re: gnowellsct]
#5379656 - 08/21/12 04:11 PM
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Gday Greg
Quote:
Those are very clever, though from the point of view of indicating which screw needs adjustment you need one shadow. Three would be confusing.
I dont use a finger/arm shadow.
Once you understand which way the star needs to be moved in the FOV when collimating, you just try each spoke to find the one that best fits the direction required.
Andrew
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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: OzAndrewJ]
#5379690 - 08/21/12 04:39 PM
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Can you put little rubber angry birds on the ends of the spokes to make them look more imaginative?
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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: elwaine]
#5379866 - 08/21/12 06:43 PM
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Larry, I hope you'll post a report on the Duncan mask and Orion eyepiece video cam combination. I think you're on the right track.
Geoff
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Gavin Bray
sage
Reged: 12/31/06
Loc: Australia
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Re: Why no commercial source for "Duncan" Mask?
[Re: barasits]
#5381624 - 08/22/12 07:25 PM
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I made a Duncan mask and tested it last night. A little while ago I'd collimated using CCD Inspector and I believe my collimation is reasonably good. The Duncan mask worked as described. I tried an eyepiece at 355x but found the image to be fairly small and a little hard to discern the relative positions of the three bars. I then barlowed this up to 711x but of course things were bouncing around a bit. However, as far as I could tell, my collimation was fine. I also tried with a Lodestar guide camera and feel it or something similar could be used to make adjusting and checking collimation a lot easier.
Regards
Gavin
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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: Gavin Bray]
#5381730 - 08/22/12 08:39 PM
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Hi Gavin,
Thank you for that report.
Quote:
The Duncan mask worked as described.
Was the collimation equal to, or better than the collimation you achieved with CCD Inspector?
Regards,
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Gavin Bray
sage
Reged: 12/31/06
Loc: Australia
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Re: Why no commercial source for "Duncan" Mask?
[Re: elwaine]
#5381791 - 08/22/12 09:13 PM
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Hi Larry
The collimation looked good to me so I didn't make any adjustments.
It was relatively easy to make the mask though I'm not sure if it's quicker or more accurate than CCDI.
I'd certainly recommend making one and trying for yourself.
Regards
Gavin
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Adam E
Pooh-Bah
Reged: 06/29/09
Loc: Orlando, FL
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Re: Why no commercial source for "Duncan" Mask?
[Re: Gavin Bray]
#5382214 - 08/23/12 06:36 AM
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Apologies if everyone already knows about this collimation / focusing aid, but anyone have any personal experience with one of these (GoldFocus)?
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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: Adam E]
#5382282 - 08/23/12 08:25 AM
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Quote:
Apologies if everyone already knows about this collimation / focusing aid, but anyone have any personal experience with one of these (GoldFocus)?
No experience with that mask, but in reading about it on their website I note that it has to be used with a CCD camera... which in turn requires a computer, etc.. The Duncan Mask is simpler to use, requiring only a high power eyepiece.
I've made a Duncan Mask for my C9.25. It is very easy to make. I used black foam board that I bought at Office Depot. The foam board is flat black, fairly ridged, and very easy to cut with an Exacto knife. However, the night time clouds may not clear SW Florida skies for another month. (Hurricane Isaac will definitely ruin the next week or two.) So I hope others continue to report on their experiences with the Duncan Mask.
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BlueGrass
Carpal Tunnel
Reged: 07/25/09
Loc: Wasatch Front, UT
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Re: Why no commercial source for "Duncan" Mask?
[Re: Adam E]
#5384079 - 08/24/12 08:01 AM
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Adam,
Thanks for the post and link. This looks very interesting. I've often found the accuracy of my various Bahtinov masks can depend on a number of things... most notably my eye's own ability to focus depending on how tired I am ... 
If I read the web site correctly, the mask can be used without the analysis software...?
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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: BlueGrass]
#5384224 - 08/24/12 10:06 AM
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I've noticed a few people saying the image is a little dim with the Duncan mask, so I was thinking would the image be brighter if the depth of the 3 slits was a little deeper to allow more light of the star in ?
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