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A new 290 mm F/2.5 Astrograph!

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#1 rik ter horst

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Posted 03 October 2012 - 12:42 PM

More than one year after having finished the optical design I had first light for the new 290 mm F/2.5 Astrograph! Not on the sky yet, but on earth-based targets a few kilometers away.

This instrument looks like a very short Newtonian with an optical window, but it is a bit more complicated than that. It uses an aspherical window and a field corrector and this specific combo provides a diffraction limited flat field of more than 50 mm diameter for a wide spectral range, see the accompanied matrix spot diagram below. The small black circles represent the airy disc. The visual and photographic tests confirm the total absence of chromatic errors and preliminary observations with a 13 mm Ethos convinced me that this instrument is not just a photographic instrument but it will also be a first class Wide-field telescope with coma-free images!
In the coming months the final (Carbon) housing will be made together with a brand-new focuser, specially developed for this instrument. At the end of this year we expect to have first light on the sky, untill then I'll post some updates so once in a while....
Cheers,
Rik

Attached Thumbnails

  • 5453560-matrix spots.jpg


#2 rik ter horst

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Posted 03 October 2012 - 12:51 PM

Below the protoype of the 290 mm F/2.5 Astrograph, shortly named LYNX. This set-up is used for testing purposes and here it is equiped with a 13 mm Ethos. The focal length of the instrument is 730 mm, so with this eyepiece you'll get a 56x power with a true field of 1.78 degrees on the sky (exit pupil 5 mm).

Attached Thumbnails

  • 5453575-LYNX small!.jpg


#3 dan_h

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Posted 03 October 2012 - 02:01 PM

Those are very impressive spots! I am looking forward to your future posts!

dan

#4 Mert

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Posted 03 October 2012 - 02:50 PM

Hoi Rik,

Ziet er zeer interesant uit!
Very interesting spot-diagrams, I hope to see more on this
project, especially images taken with it!
If it is only 1/10th as good as your 16", this will be
an absolute killer optic!!

Keep them coming Rik!! :waytogo:

#5 rik ter horst

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Posted 03 October 2012 - 03:10 PM

Thanks Dan and Mert!
As it will also be used as a visual instrument it needs to be very well corrected.
This front view shows the temporarily pole on which the flat secondary is attached. In the final instrument the flat mirror is directly attached to window by means of a mechanical solution.

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  • 5453795-front view small!!.jpg


#6 GlennLeDrew

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Posted 03 October 2012 - 03:31 PM

Even the prototype has a certain elegant charm! How many refractive elements are there?

#7 rik ter horst

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Posted 03 October 2012 - 03:59 PM

Thanks Glenn! There are in fact two groups: an aspherical window (is that a group??) and a group near the focuser with some exotic glass.
All refractive elements will have a broad band AR coating for maximum transmission. I‘ll still have to find a reliable company who can make these AR coatings, so suggestions are welcome!
Cheers!

#8 GlennLeDrew

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Posted 03 October 2012 - 04:23 PM

A cagey answer, Rik. :grin: How about the total number of individual refractive elements, if that's not giving away too much? I'm just curious to know the relative complexity (or simplicity.)

#9 Mike I. Jones

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Posted 03 October 2012 - 04:24 PM

You might try James Mulherin at Optical Mechanics, Iowa City, Iowa, http://www.opticalmechanics.com. I think he can do broadband AR coatings, and if not, he'd know who to contact.
Mike

#10 Mirzam

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Posted 03 October 2012 - 04:43 PM

Majestic Optical Coatings in New Jersey also does AR coatings. I think D&G may use them.

JimC

#11 siriusandthepup

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Posted 03 October 2012 - 07:05 PM

You don't need a Schmidt camera if you got one of these babies!

I want one... Comets are coming.

#12 rik ter horst

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Posted 04 October 2012 - 02:11 AM

Ok Dan, you win ;-) There are two lenses in the field corrector, all spherical. The complexity is more in the aspherical window... But for me that's just fun!

Mike and Jim, thanks a lot for the AR-coating companies! 15 years ago I had a disastrous experience here in Europe with one company that succeeded in destroying three finished 260 mm diameter Schmidt-correctors at once during cool-down after coating, so it is for that I look for experienced companies even if they are outside Europe.

#13 mconnelley

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Posted 04 October 2012 - 02:40 AM

Hello:

Could we ask for an optical prescription or Zemax file?

Cheers
Mike

#14 rik ter horst

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Posted 04 October 2012 - 08:53 AM

Hi Mike,
I'm sorry for not being able to publish all the design details (yet). A detailed publication is foreseen somewhere next year, so I hope you can wait that long ;-)
Cheers,
Rik


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