Telescope Reviews: 10" f/3.5 Astrograph with Rosin focal reducer

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Mike I. Jones
Carpal Tunnel

Reged: 07/02/06

Loc: Fort Worth TX

Re: 10" f/3.5 Astrograph with Rosin focal reducer [Re: MKV]
#5549065 - 12/01/12 04:32 PM

Visually, yes, the system focal ratio does not affect limiting magnitude. The retina is a non-integrating detector, so staring continuously at an object does not make it appear brighter, unless you happen to still be dark adapting at the time.

At lower powers and large eyepiece exit pupils, though, high-brightness light pollution increases the background brightness, and can also interfere with dark adaptation, both of which affect limiting magnitude.

Photographically, the f-number and T-number directly impact photographic exposure times, as cameras are integrating detectors.

Mike

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Ed Jones
Carpal Tunnel

Reged: 04/06/04

Loc: Sin-sin-atti

Re: 10" f/3.5 Astrograph with Rosin focal reducer new

[Re: Mike I. Jones]
#5553474 - 12/04/12 07:37 AM Attachment (17 downloads)

I deleted my previous post, Zemax found a better design. This is a telecompressor/coma corrector for a F/5 Newt primary. It makes it an f/2.8.

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kfrederick
Carpal Tunnel

Reged: 02/01/08

Re: 10" f/3.5 Astrograph with Rosin focal reducer new

[Re: Ed Jones]
#5553485 - 12/04/12 07:45 AM

Great work .Will it work for all size telescope?

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Mark Harry
Vendor

Reged: 09/05/05

Loc: Northeast USA

Re: 10" f/3.5 Astrograph with Rosin focal reducer new

[Re: kfrederick]
#5553549 - 12/04/12 08:40 AM

Duel of the Joneseys! I'm eatin' popcorn.....
M.

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MKV
Carpal Tunnel

Reged: 01/20/11

Re: 10" f/3.5 Astrograph with Rosin focal reducer *DELETED* new

[Re: Ed Jones]
#5553868 - 12/04/12 12:18 PM

Post deleted by MKV

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MKV
Carpal Tunnel

Reged: 01/20/11

Re: 10" f/3.5 Astrograph with Rosin focal reducer *DELETED* new

[Re: MKV]
#5553964 - 12/04/12 01:14 PM

Ed, could you show the spots?

Mladen

Edited by MKV (12/05/12 04:33 AM)

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Ed Jones
Carpal Tunnel

Reged: 04/06/04

Loc: Sin-sin-atti

Re: 10" f/3.5 Astrograph with Rosin focal reducer new

[Re: MKV]
#5554430 - 12/04/12 06:43 PM Attachment (17 downloads)

Mladen,
Here is the spot diagrams. I optimized it for C,F and D so the deep blue 405 isn't so good but it could be optimized for other ranges. With 5 lenses it there won't be too many ATMs that can do this but it shows what's possible. It works with most focal length mirrors that can have enough BFL space.

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MKV
Carpal Tunnel

Reged: 01/20/11

Re: 10" f/3.5 Astrograph with Rosin focal reducer new

[Re: Ed Jones]
#5554551 - 12/04/12 08:02 PM

Quote:

Mladen,
Here is the spot diagrams. I optimized it for C,F and D so the deep blue 405 isn't so good but it could be optimized for other ranges. With 5 lenses it there won't be too many ATMs that can do this but it shows what's possible. It works with most focal length mirrors that can have enough BFL space.

Thanks Ed. Looks really nice. Obviously this type of corrector is the way to go with bigger mirrors.

For some reason OSLO didn't get the same results with your original configuration. I believe it's the limitation of OSLO.EDU to 10 surfaces, so in order to include the airgap between the two N-PSK57 lenses you'd need 11 surfaces in OSLO.

Also, I don't see why a five-lens corrector would be impossible for an amateur and a four or a three element wouldn't. It wouldn't be cheap, but results are great, and the shapes are not exotic.

Mladen

Edited by MKV (12/05/12 04:35 AM)

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Ed Jones
Carpal Tunnel

Reged: 04/06/04

Loc: Sin-sin-atti

Re: 10" f/3.5 Astrograph with Rosin focal reducer new

[Re: MKV]
#5554599 - 12/04/12 08:31 PM

Mladen,
I only have 10 surfaces, seems like it should work. I've played around with this design and it can be pushed even better including 405nm.

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MKV
Carpal Tunnel

Reged: 01/20/11

Re: 10" f/3.5 Astrograph with Rosin focal reducer new

[Re: Ed Jones]
#5554779 - 12/04/12 10:33 PM

Quote:

Mladen,
I only have 10 surfaces, seems like it should work. I've played around with this design and it can be pushed even better including 405nm.

I just noticed that I was using a wrong glass for the third lens, so disregard any previous attachments.

No doubt the performance can be pushed even better, but what's really attractive and practical about this configuration is that the primary mirror is a relatively slow paraboloid (f/5) and therefore relatively easy to figure to high precision, yet the system operates at f/2.8.

Mladen

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