Telescope Reviews: Why no commercial source for "Duncan" Mask?

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Equipment Discussions >> Cats & Casses

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Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5384264 - 08/24/12 10:24 AM

The image might be dim on smaller scopes. With my C11, it was plenty bright...using Vega as the star. I'm thinking that making the openings wider might make the pattern less distinct. As easy as the mask is to make, it might be worth an experiment!

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5384356 - 08/24/12 11:12 AM

Quote:

The image might be dim on smaller scopes. With my C11, it was plenty bright...using Vega as the star. I'm thinking that making the openings wider might make the pattern less distinct. As easy as the mask is to make, it might be worth an experiment!

Hello Steve , I havnt had a chance to try mine yet , I just guessed the measurements for mine , I also have a C11 , would you be so kind as to tell me what the measurements are for the slits ( ie the depth of the slits between the edge of the plastic ring on the corrector to the edge of the slit on the mask also the length of the slits ) Thanks.

Edited by nevy (08/24/12 11:23 AM)

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Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: nevy]
#5384537 - 08/24/12 12:47 PM Attachment (75 downloads)

Here is what mine looks like. The measurements shown are the radii from the center to each relevant point. I divided the circle into 60° segments, then used a drawing compass to make the circles all from the same center. There is really no reason to leave the 10mm "ring" all the way around, but I think it is a good idea to cut the overall diameter to fit just inside the front ring. That way the mask rests on the corrector retaining ring, rather than the corrector itself. Hope this helps...let me know!

Steve

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nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5384580 - 08/24/12 01:15 PM

That's perfect , thankyou very much Steve

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Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5385238 - 08/24/12 08:48 PM

Steve,

Thanks for the instructions. I assume that's for the C11?

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Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5385876 - 08/25/12 06:46 AM

Hey, Bart...yes it is for the C11. It could be scaled proportionately for any size. I don't think these dimensions are all that critical, really. The diameter of the inner circle should allow an easy fit over the secondary housing with little slop, and the outer diameter should fit inside the front ring of the scope without binding.

Post Extras:

Bart
Carpal Tunnel

Reged: 05/28/06

Loc: Somewhere near Charlottesville...

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5385963 - 08/25/12 09:18 AM

Thanks, I'm going to make one.

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RodShea
member

Reged: 11/01/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: Bart]
#5390366 - 08/27/12 08:17 PM

Not to hijack the thread, but this would work on other cassegrains as well?

Thanks,

Rod

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Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: RodShea]
#5390924 - 08/28/12 06:37 AM

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

Post Extras:

RodShea
member

Reged: 11/01/09

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5392629 - 08/29/12 03:46 AM

Thanks,

Rod

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stuart keenor
member

Reged: 02/20/11

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5393702 - 08/29/12 05:33 PM

Quote:

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

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Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5394466 - 08/30/12 08:24 AM

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

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stuart keenor
member

Reged: 02/20/11

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5394887 - 08/30/12 12:52 PM

Quote:

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

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frolinmod
Pooh-Bah

Reged: 08/06/10

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5402540 - 09/04/12 09:10 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.

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nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: frolinmod]
#5402806 - 09/04/12 11:35 AM

I made a new one using Steves diamentions
[image]http://

[/image]
[image]http://

[/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?

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Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: frolinmod]
#5402953 - 09/04/12 01:01 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

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stuart keenor
member

Reged: 02/20/11

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5403387 - 09/04/12 04:28 PM

Quote:

Quote:

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

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Steve OK
professor emeritus

Reged: 09/22/07

Loc: OKC, OK

Re: Why no commercial source for "Duncan" Mask? new

[Re: stuart keenor]
#5403416 - 09/04/12 04:43 PM

Good news! Thanks for the report, Stuy.

Post Extras:

nevy
sage

Reged: 02/07/12

Loc: UK

Re: Why no commercial source for "Duncan" Mask? new

[Re: Steve OK]
#5403486 - 09/04/12 05:29 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.

Post Extras:

Mary B
Vendor - Echo Astronomy and Electronics

Reged: 05/21/10

Loc: Minnesota

Re: Why no commercial source for "Duncan" Mask? new

[Re: barasits]
#5556391 - 12/05/12 08:41 PM

Added them to my product line!

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