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Astro-Tech AT90EDT review ???

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#1 bouffetout

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Posted 03 January 2013 - 11:38 AM

So far,I'm leaning towards the AT90EDT to buy this coming summer.I only found one review about it ,and the dude likes it a lot but didn't have it since a long time...
Can anyone owning one and do astrophotography with it tell me about it ?? I will mostly use it for astrophoto.
Thank you !
Maxx

#2 JonM

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Posted 02 May 2013 - 01:03 AM

I'd be interested in these questions too as I am looking for a wide field scope with a robust focuser for Ap and the 90EDT could be a player.

#3 orlyandico

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Posted 02 May 2013 - 04:45 AM

I have one. I am using it for AP.

It needs a flattener. I use both the WO 66mm type II flattener/reducer and the Orion 1.0X flattener (with no reducing capability). Both work fine.

I used to use an Orion 100ED with the WO flattener. The AT90EDT produces tighter and whiter stars. The star test is also better than the Orion doublet.

The focuser is not a Feathertouch. I toyed with the thought of buying an FT focuser for my Orion (the WO focuser I put on my Orion wasn't up to a heavy imaging load). But the cost of the FT focuser was about the same if I sold the Orion and got the AT90 (used) so that's what I did.

There is a good bit of image shift in the AT90 focuser when you reverse directions - in this case the WO and GSO crayfords are actually better because they have no image shift. But the AT90 focuser can lift anything. It can also crush fingers, etc. due to the rack-and-pinion.

If you approach focus from one direction only, you won't need to deal with the focus shift. Also if you tighten the focus lock knob, this reduces image shift substantially.

The focuser doesn't slip, so it's good enough for me, but I'm not an expert.

Note though that I don't have any "premium" optics - the other refractors I had were a WO 70mm and the Orion 100ED. The Orion's generally have good optics, and the long slow f/9 doublet means there's not much that can go wrong with them.

That said.. the AT90 is the best refractor I've had. Maybe my story would be different if I got an NP101... or Tak... or...

#4 JonM

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Posted 05 May 2013 - 04:44 PM

Thanks for that input. Very helpful. I guess for AP we just have to consider the cost of upgrading focusers or getting a used scope that already has a Feathertouch or a Moonlite. Just can't seem to trust the Chinese focusers to be all we want them to be.

#5 dhaval

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Posted 06 May 2013 - 10:00 AM

The AT90EDT is a wonderful scope for imaging. It is F6.7 that makes a great focal length, is relatively heavy for its size, but that's a good thing making it a lot stable than some of the other 90mm scopes that I have seen out there. The best part about the scope though is its focuser - it's a 2.7" R&P focuser and will handle around 8-9lbs of load easily - it is one of the best standard focusers that I have seen on any Chinese made scopes, much in the class of what I got when I bought the TEC110FL. You can see some of the images that I have on my Astrobin/Flickr page. If you add a $150 flattener it makes a wonderful scope - much rivaling scopes made by SV or other named manufacturers.

That being said, Astronomics has stopped manufacturing the AT90EDT and the AT106, so you have to get them from other companies that sell the 90EDT version - SharpStar optics is one of them. Their focuser is a 2.5" R&P and in the same class as the AT90EDT.

I recently posted on these forums that I would consider the AT90EDT a much better scope for people beginning AP simply because it scores very highly on a lot of the metrics that make a good scope for AP, even higher than the TEC110FL that I just recently sold.

Hope the above helps.

Thanks,
Dhaval






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