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dscarpa
Post Laureate
*****

Reged: 03/15/08

Loc: San Diego Ca.
Re: Red Hot New Concept OTA's new [Re: mikey cee]
      #5617164 - 01/11/13 12:14 PM

Impressive! Will you be using this design with any of your APOs? I'm definitely interested in the 140 F-7.5 APO you're working on. Do you know when the 140 F-7.5 will be available? I'm fine with a regular OTA on that scope but a lighter one would be a plus. David

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tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Red Hot New Concept OTA's new [Re: dscarpa]
      #5617196 - 01/11/13 12:31 PM

Keith Lawson won a Merit Award at RTMC in 2010 for an open tube refractor he'd built. He was camped across the road from me, so I had a chance to look through it a number of times. A very nice performer, actually. Very good contrast.




-Tim.


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tim53
Postmaster
*****

Reged: 12/17/04

Loc: Highland Park, CA
Re: Red Hot New Concept OTA's new [Re: tim53]
      #5617202 - 01/11/13 12:34 PM

As for thermal plumes off the observer?

Perhaps installing a fan would help?



-Tim.


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Pinbout
Postmaster
*****

Reged: 02/22/10

Loc: nj
Re: Red Hot New Concept OTA's new [Re: tim53]
      #5617227 - 01/11/13 12:48 PM

Quote:

Keith Lawson won a Merit Award at RTMC in 2010 for an open tube refractor he'd built.




Cool pics Tim, thanks.


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ISTAR Optical
Vendor- IStar Optical
*****

Reged: 08/09/09

Loc: Page, Arizona
Re: Red Hot New Concept OTA's new [Re: tim53]
      #5617483 - 01/11/13 03:44 PM

Dear Tim,
Im aware of this rail scope. This consruction is known and Keith made a superb job putting this thingn together. He used Istar 204 F8,8 achromatic doublet if I remember correctly. Thank you so much for sharing!!
cheers,
Ales


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ISTAR Optical
Vendor- IStar Optical
*****

Reged: 08/09/09

Loc: Page, Arizona
Re: Red Hot New Concept OTA's new [Re: tim53]
      #5617496 - 01/11/13 03:54 PM

Gotta love some of these... right? Personally I suggest four independent fans with controlled variable speeds and a 4-stage Marlow Ind. thermo-electric (TE) cooling device attached directly to the operators' forhead.

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johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Red Hot New Concept OTA's new [Re: ISTAR Optical]
      #5617560 - 01/11/13 04:29 PM

Quote:

Dear Tim,
Im aware of this rail scope. This consruction is known and Keith made a superb job putting this thingn together. He used Istar 204 F8,8 achromatic doublet if I remember correctly. Thank you so much for sharing!!
cheers,
Ales



Ales that is what I was talking about earlier, I like Keith's short dewshield/back extension offering protection for the lens as well as shielding stray light.


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mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Red Hot New Concept OTA's new [Re: johnnyha]
      #5617673 - 01/11/13 05:56 PM

Yes I agree with that short dewshield and rear extension. I'd get awfully up tight with a big lens exposed both front and rear. Couldn't really enjoy or relax without that provision at a starparty with the public involved. Nervous like a cat on a hot tin roof! Mike

Edited by mikey cee (01/11/13 05:58 PM)


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ISTAR Optical
Vendor- IStar Optical
*****

Reged: 08/09/09

Loc: Page, Arizona
Re: Red Hot New Concept OTA's new [Re: johnnyha]
      #5618513 - 01/12/13 06:41 AM

Hello Johnny,
this is exactly what we have planned for the dew shield construction. We are looking into two versions so give us some tim to experiment and decide. The bottom line is that if anyone buys one of these TCR scopes, they will be given a choice of a dew shield later on this year, I suspect second half of 2013, possibly sooner.


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Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Red Hot New Concept OTA's new [Re: ISTAR Optical]
      #5618575 - 01/12/13 08:16 AM

I think the dew problems is not something a rolled up newspaper cannot solve... I often make makeshift dewcaps out of a newspaper, which I roll around the dewcap or end of the scope, then hold in place with tape or rubber bands. Works extremely well and is very inexpensive. When it gets too ugly, I just throw it away and make a new one.

I once tried to make a prettier dewcap from some soft, thin bubble foam plastic. I thought it was going to be perfect, as it was longer than the newspaper tube, but imagine my surprise, when the scope often dewed up, when it never did so with the old newspaper tube!

So, bad news (on print) can be good for something allright!


Clear skies!
Thomas, Denmark


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Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Red Hot New Concept OTA's new [Re: Astrojensen]
      #5618588 - 01/12/13 08:26 AM

BTW, I am impressed with the new OTAs. It's about time someone tried to do something serious to make a lightweight big achro. I've thought a great deal about making one with a traditional truss tube, with a centerpiece that attached to the mount and two ends with the objective and focuser that each attached to the centerpiece with truss tubes. The bad thing about this is that the truss angles become very narrow, if the centerpiece is not quite a bit larger than the objective, in which case the center of gravity sits quite far from the fulcrum at the RA axis, meaning you need a lot of counterweights or a very long counterweight shaft.

I also thought about making a single-pole refractor, much like the one Keith Lawson has made, but I didn't follow up on it in detail and thought that it would have problems if I wanted to attach a shroud, which is almost a neccesity in my climate, or so I thought at the time. Your solution is more elegant and also more solid.


Clear skies!
Thomas, Denmark


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jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: Red Hot New Concept OTA's new [Re: Astrojensen]
      #5618616 - 01/12/13 08:49 AM

How does the weight compare with a carbon fiber tube?

Just wonder'n


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Astrojensen
Post Laureate
*****

Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Red Hot New Concept OTA's new [Re: jgraham]
      #5618630 - 01/12/13 09:06 AM

I think the weight might be comparable, but carbon fiber tubes are quite expensive in the sizes we are talking about here. They are also not collapsible, unlike the new ISTAR tubes.

Looking at prices for newtonian carbon tubes at Teleskop-Service, I'd estimate that a raw carbon fiber tube for a 6" f/12 newtonian might be around $1000 and that one for a 8" f/12 could be $2k. I could be wrong, though.


Clear skies!
Thomas, Denmark


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opticsguy
sage


Reged: 02/02/09

Loc: Washington State
Re: Red Hot New Concept OTA's new [Re: Astrojensen]
      #5618738 - 01/12/13 10:18 AM

First; very impressive scope, nice design and I certainly want one.

Second; Not at all an original design when you look at the single element loooong focus refractors way back in the late 1600's (Hevelius' 140 foot telescope).

Thirdly, I would be very concerned with dew on the lens, a definate problem in my area.

Fourth; I want one. :-)


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ISTAR Optical
Vendor- IStar Optical
*****

Reged: 08/09/09

Loc: Page, Arizona
Re: Red Hot New Concept OTA's new [Re: opticsguy]
      #5619113 - 01/12/13 01:53 PM

Dew shields are being designed for these scopes and they will become available this year. We have two versions to test before we decide.
cheers,
Ales


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mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Red Hot New Concept OTA's new [Re: ISTAR Optical]
      #5619517 - 01/12/13 05:43 PM

I see this thread was been removed from "Refractors" forum. Well too bad but take a peek here folks! http://www.istar-optical.comGallery/Perseus/_TCR_150-12/index.html I believe anyone going to this effort in redesigning refractors to this extent is truly more interested in the hobby than in making a buck! I mean there must be less innovative and easier ways to make money off of amateurs in this hobby. When Istar got my attention as a customer they truly did make a believer out of me and I'm one picky SOB that is hard to impress! Mike

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ATM57
super member


Reged: 01/01/10

Loc: Tehachapi, CA
Re: Red Hot New Concept OTA's new [Re: tim53]
      #5619574 - 01/12/13 06:14 PM

Hey, thanks for the honorable mention. Cool. Yes, this was an Istar 8" F/8.8 lens. Super performer. I never had any issues with lens cooling, body heat problems or contrast issues. Properly designed/placed baffles will work quite well despite how the scope looks from the outside. An eyeball look through the focuser reveals only the light from the lens. If interested I can show a photo shot through the focuser with the scope aimed at a bright wall with the scope outside in the sunlight and the only thing you can see is the light from the lens. This scope was a lot of fun to build and use.

The new Istar design should work quite well. It looks like someone spent the time to "get it right". Good design, nice machine work, well baffled and light weight. If I had one I would put it through it's paces and give a detailed report (hint, hint)

Edited by ATM57 (01/12/13 08:14 PM)


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ISTAR Optical
Vendor- IStar Optical
*****

Reged: 08/09/09

Loc: Page, Arizona
Re: Red Hot New Concept OTA's new [Re: ATM57]
      #5620187 - 01/13/13 05:01 AM

Keith, is that you? Great talking to you after so many years (3 I think since you were one of our very first customers for larger lens). Anyhow, I looked at many tubeless refractor designs including yours. Me and our master optician spent countless hours discussing different options but the bottom line is this. If you put baffles in places exactly as you explained (what counts is what you see at the focuser end.. no matter what anyone else will argue with(. This is the reason I posted photo from the focuser so people can see that all you see is the lens up front.. everything else is filtered off by the cross-sections/baffles. What ever remaining stray light must enter the remaining 30 percent (overall scope length) which is a fully enclosed tube with its own set of baffles.
The bottom line is, when we tested the TCR tubeless sceletal scope against fully enclosed old fashioned scope and found no difference, I can say that Im happy and I achieved all what I hoped for. From incredible over 50 percent OTA weight reduction (the main objective)to unchanged resolution. Recently we even round out that now the ballance point is shifted heavliy towards the FOCUSER, not towards the lens as one would expect.... read more at our web site (not sure if I can openly advertize our web site here on CN Vendor forum...) but Im sure people will find it.
cheers,
Ales


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ATM57
super member


Reged: 01/01/10

Loc: Tehachapi, CA
Re: Red Hot New Concept OTA's new [Re: ISTAR Optical]
      #5620975 - 01/13/13 02:49 PM

Hi Ales,

It is interesting to read the comments of those who have never used a refractor designed this way. Their lack of experience causes them to question the validity of such a design. As an "end user" of an open refractor I know that, if well designed, the scope works quite welll. I can say just by looking at your design that you guys have done your homework. Great looking scope! When you take these scopes out to astronomy gatherings it will shut the mouths of the naysayers. There are a lot of advantages to the open design. Keep up the innovative work. It's nice to see something new and affordable in the refractor realm


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BillP
Postmaster
*****

Reged: 11/26/06

Loc: Vienna, VA
Re: Red Hot New Concept OTA's new [Re: ISTAR Optical]
      #5621032 - 01/13/13 03:11 PM

Ales,

What iStar optics is this new design going to be available with?

-Bill


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