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Why no commercial source for "Duncan" Mask?

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#51 stuart keenor

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Posted 29 August 2012 - 04:33 PM

I made one for my little C130 Mak-Cass. It seemed to work just as well as with my C11.

sound intresting may do the 10" mak cass!!what do you guys think? stuy

#52 Steve OK

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Posted 30 August 2012 - 07:24 AM

Since it only takes 20 minutes and costs little or nothing to make, why not? :)

#53 stuart keenor

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Posted 30 August 2012 - 11:52 AM

Since it only takes 20 minutes and costs little or nothing to make, why not? :)

going to have a shot will let you know thanks stuy

#54 frolinmod

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Posted 04 September 2012 - 08:10 AM

Steve, I made one just like yours, but the three arcs did not become lines as focus was moved in. They stayed arcs all the way to focus and I did not get crossed lines at focus. With that in mind, doing it with the mask did not make collimation any easier than doing it without the mask. I'll have to try one more time before making a new mask in the shape as shown by pinbout and nevy.

#55 nevy

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Posted 04 September 2012 - 10:35 AM

I made a new one using Steves diamentions
[image]http://Posted Image[/image]
[image]http://Posted Image[/image]
The silver lines are so I can line them up with the collimation screws,
It did work as its suppose to , I thought my collimation was spot on using a star test ( concentric rings) , with the mask on , the lines crossed in the centre but one was slightly back a little bit so I adjusted it so they were all the same , I then took the mask off and looked at the defocused star , it showed not concentric rings (off to one side slightly ) so I collimated it back to perfect again without the mask , but then the clouds rolled in and had to cover the scope. I don't know why the two methods didn't agree , I'll have a go with it another time and try again . I found the lines to be bright enough but a bit awkward to see as they were very small ( I was using a 7.4 & 6.4mm eyepieces , 378x & 437x mag ) should I be using more power to make the image bigger?

#56 Steve OK

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Posted 04 September 2012 - 12:01 PM

Well, Frolinmod, I don't know what to tell you. How was the seeing when you tried this? My first try with the mask happened to coincide with some (rare) good seeing. In subsequent trials with more average seeing, the pattern has been less distinct. But in all the trials, the arcs do in fact become tiny radial lines just before focus is reached. High power is required to see them. I was using 560x on my C11 the first time.

And to Nevy, I got a little taste of that myself, trying to collimate using my webcam. The two patterns with and without the mask did not agree. I started wondering if having a not-perfectly-centered secondary could cause such a discrepancy. I can't quite get my mind around it. I'll keep messing with the mask, no doubt, but perhaps the tried and true "center the airy disk in the diffraction rings" will win out after all.

Thanks for the feedback, guys!

Steve

#57 stuart keenor

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Posted 04 September 2012 - 03:28 PM

Since it only takes 20 minutes and costs little or nothing to make, why not? :)

going to have a shot will let you know thanks stuy

made one out of cardboard worked very well on the intes micro mak cass ingenious ;)stuy

#58 Steve OK

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Posted 04 September 2012 - 03:43 PM

Good news! Thanks for the report, Stuy.

#59 nevy

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Posted 04 September 2012 - 04:29 PM

I was wundering about the secondary not being centred , sometimes when I've did star tests before , I have noticed that although I get nice concentric rings , now & again I think I'm noticing the tiny dot right in the centre might not quite be in the dead centre. But sometimes it looks like it is , I'm not sure if I'm convincing myself it is centred becaus I bellieve it should be. :confused:

#60 Mary B

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Posted 05 December 2012 - 08:41 PM

Added them to my product line!

#61 barasits

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Posted 05 December 2012 - 09:47 PM

Added them to my product line!


Great! I haven't had the time to make my own Duncan mask, so would you please provide a link to your web site.

Geoff

#62 Bart

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Posted 06 December 2012 - 11:30 PM

Ditto! I'd love to pick one up for a C11.

#63 Mary B

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Posted 07 December 2012 - 03:03 AM

No web site, send me a PM here. I found a web site was costing me more than I was making, this is a very small part time business. I will need dimensions of your scope in order to cut one. Scopes over 10 inches I have to farm out the cutting to someone with a larger laser and it isn't cheap.

#64 A. Viegas

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Posted 08 December 2012 - 04:27 PM

I have a friend who has a new 3D printer. I will see if we can figure out how to print one of these Duncan masks for my C8 and C11... already printed out Bahtinov masks, so should not be that difficult.

Ideally, if anyone has a .svg file with exact dimensions for the Duncan mask, that would make it easier, otherwise I will use the drawings from a few of the posts on this thread. ( I assume there is no "Duncan Mask" generator on the web? http://astrojargon.n...Generator.aspx)

Al

#65 jbalsam

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Posted 12 January 2013 - 08:57 AM

Bump.

I got an email recently from someone asking if I could add Duncan masks to my lineup, so I wanted to see if that would be a useful service to provide to the community. I've read some conflicting posts here about people being able to get results with them, and I've never owned an SCT so I don't know if methods like Greg Nowell's SGCD are easier/better. I don't want to sell something to people that isn't going to work well.

#66 m2k

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Posted 14 January 2013 - 07:16 AM

Mary B. (Echo Astronomy and Electronics) in a previous post stated that these masks can be laser cut up to 10" in diameter...
I'm wondering if a larger diameter disc can be used to "stop-down" a larger diameter scope to 10" and still work? I'm thinking here of my C-14. :confused:
-Mike






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