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Old 25-11-2008, 10:52 AM
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erick (Eric)
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New T-adapter

I know little about astrophotography, but I do have a HoTech laser collimator, purchased mainly because of the clever way of mounting in the focusser - their so-called SCA ("Self-Centering Adapter").

The HoTech have developed a T-adapter based on that technology:-

http://www.hotechusa.com/SCA%20T-Adapter.html

What do you imaging folks make of that?
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Old 25-11-2008, 02:34 PM
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bojan
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It uses expandable rubber rings to obtain grip around barrel (they probably expand because of axial pressure).
It might not be as repeatable and as rigid as claimed.. possible temperature issues? therefore too expensive...
But perhaps it is worth checking..

Last edited by bojan; 25-11-2008 at 02:52 PM.
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Old 26-11-2008, 06:39 AM
celstark (Craig)
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I've had a chance to use them a bit and posted a blog entry here:
http://www.stark-labs.com/blog/blog.php

They're very solid and I've not noticed anything changing with temperature. Once clamped on there, they're going nowhere...

Craig
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Old 26-11-2008, 07:38 AM
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erick (Eric)
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Hi Craig

Your blog suggests you are a happy customer!
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Old 28-11-2008, 09:32 AM
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multiweb (Marc)
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The best solutions are always the simplest ones. Such a clever design.
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Old 28-11-2008, 09:38 AM
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multiweb (Marc)
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Quote:
Originally Posted by bojan View Post
It uses expandable rubber rings to obtain grip around barrel (they probably expand because of axial pressure).
It might not be as repeatable and as rigid as claimed.. possible temperature issues? therefore too expensive...
But perhaps it is worth checking..
All hydraulic [oil] technology works at high pressure and high temperatures mostly. I remember in my short time working with Liebherr and Klem Hydraulic hammers that everything that had a moving piston had those centering groves and series of O'rings and composite material rings ... and these hammer drills used to hit at 2000 hits per minutes with pressures exceeding 400 bars so it was critical everything was aligned with very tight tolerances. So I recon the focuser grip with 3 O'rings will stay centered no matter what once it's "clamped in"
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Old 28-11-2008, 01:01 PM
DeanoNZL (Adrian)
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Hi Craig.
Welcome to IIS.

For those unaware, Craig is the author of PHD guiding & Nebulosity.
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Old 28-11-2008, 07:57 PM
Dennis
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Quote:
Originally Posted by DeanoNZL View Post
Hi Craig.
Welcome to IIS.

For those unaware, Craig is the author of PHD guiding & Nebulosity.
Thanks for the heads up Deano, it’s nice to know when an international luminary drops by, a name to be remembered and respected indeed. With the introduction of PHD Guiding, Craig irrevocably changed the landscape of auto guiding overnight!

Thanks Craig, for a terrific set of applications. Your prodigious output never ceases to amaze me, I’m sure there are at least 2 or 3 of you, or is it that you simply don’t require sleep!

Welcome to Ice In Space.

Cheers

Dennis
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Old 29-11-2008, 06:24 AM
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[1ponders] (Paul)
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to IIS Craig. If you've given it the then I'd guess it definitely one to look into then.

BTW Thanks for some great astro applications, I know I'd be lost without them.
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Old 02-12-2008, 04:14 AM
celstark (Craig)
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Thank you all, but "luminary" is a bit much, IMHO, unless you're referring to the effect of the bright Southern California sun bouncing off my bald head, temporarily blinding those around me

Anyway, it's hard for those getting their guiding rigs going to underestimate the role that flex can play in making us tear our hair out (did I mention I was bald?). A few weeks ago, I was looking at a new-to-me 8" f/5 Antares (Synta) Newt and the new "wsg" off-axis guide setup for my QSI camera. I ran some tests using my current guide rig (the Borg XY setup -- great, great setup) and the onboard "wsg", looking at the post-guiding error (what Nebulosity reports it had to do to align the frames).

With the "wsg", I averaged 0.14 pixels of error across a 25 minute run (this is error in the main image, so where it really counts). I could stack without any alignment and have no issues at all (using whole-pixel alignment, no frames were shifted at all).

Without and using a separate guide scope, the error was horrible. I was drifting at almost 2 pixels per minute!

Why? Does my guide scope suck? Nope, the Borg is a rock (previously tested as equal to at least 0.95 rocks). The focuser and the main tube itself flex a good bit under the load of this heavy camera. Move the camera around and you can watch the tube flex. Think that'll have an effect on your collimation and your guiding accuracy? You bet...

Anyway, that's why I like this HoTech setup. The coupling of the scope to the focuser is one place I've had to fight this (I had a really bad time of it on a TMB 105-LW I used to have). It's such a simple idea and it just plain works. That source of flex is just taken out of the equation (and you're left to fight the other sources...)

Craig
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Old 02-12-2008, 06:55 AM
Dennis
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Hi Craig

Thanks for the details on the flexure investigation – I am gradually taming my rig having iteratively minimised various contributing factors. I reckon the next step is to try one of Ho’s adapters – a Xmas present to myself!

Cheers

Dennis
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