AstroTrac TT320

mikkelbo · Post by **mikkelbo** » Sat Jun 21, 2008 3:43 pm

Here a few of my shots from the Burren using my brand new AstroTrac. I really haven't had much time, so I haven't even stacked or properly processed the images, so what I show here is only the tracking accuracy of the AstroTrac. I am very impressed with it. I had far more problems with focusing and with dew than with the AstroTrac.

Beehive Cluster, 180mm lens @f/5.6, 168s exposure. Notice how nice and round the stars are.

Saturn, 180mm lens @f/5.6, 30s exposure.

See more at My Flickr astro pages

Frank Ryan · Post by **Frank Ryan** » Sat Jun 21, 2008 10:33 pm

Wow,
the AT really does the job!
Are you using a seagul focuser?
I bought one lately and it struck me you now have 2 focuses to deal with!

How do you think you will combat dew formation?

mikkelbo · Post by **mikkelbo** » Sat Jun 21, 2008 11:28 pm

I'm using the manual focus ring on the lens to focus. My 180mm lens is really smooth and the FOV with an 180mm is good for focusing. I had more problems with my 35mm lens. I couldn't judge anything through the viewfinder.

The right angle (RA) finder adds another focusing factor, but it is easy to judge the correct focus of the RA even if the lens is not focussed properly yet.

Here is another image -- 5 minutes exposure of M57 "Ring Nebula" in Constellation Lyra. Tracking is right on the money. I have to try longer exposures, but my Nikon D200 starts to get noisy (thermal) around five minutes, so stacking is a better option. But for fun, I'll try 10, 15, and 20 minutes exposures, just to see.

Now I lust for a 400mm or 600mm lens ...

John O'Mahony · Post by **John O'Mahony** » Sun Jun 22, 2008 8:40 am

Nice shots Mikkel. That astrotrac looks the business.

Dave Lillis · Post by **Dave Lillis** » Sun Jun 22, 2008 1:50 pm

Good tracking there Mikkel, although it looks like the lens might have very slight chromatic abberation.

mikkelbo · Post by **mikkelbo** » Sun Jun 22, 2008 2:41 pm

Yeah the lens does have some CA. I stopped down two stops (from f/2.8 max aperture to f/5.6) but I may have to stop down even more. But that makes it rather useless, if I have to stop down to f/8.

I'm looking at getting a Sigma 400mm f/5.6 APO for the AstroTrac. They sell used for around $400. The Sigmas have virtually no CA.

mikkelbo · Post by **mikkelbo** » Thu Jun 26, 2008 11:09 am

Instead of a Sigma lens (which I would be able to use in daylight as well), I am thinking about a small APO refractor.

Do any of you have experience with APO refractors in the range 66mm to 80mm apeture?

Specifically, I'm looking at these:

William Optics 72mm

William Optics 80mm

Orion EON 72mm ED APO

Apochromatic Refractor 80mm OTA (FPL53 glass)

Frank Ryan · Post by **Frank Ryan** » Thu Jul 24, 2008 2:36 am

This just about explains it all

http://www.eanet.com/kodama/astro/equip ... /index.htm

(scroll down to ;
Gotcha! #1 -- Wrong Finder Magnification)

I love the line...

These have the problem of incorrect magnification relative to the reticle. In my setup, the two stars end up sitting not in the gaps but on the lines closer to the center (indicated by red spots in the figure 3). If you don't know this, you'll undoubtedly have pulled out some hair trying to figure out why you just can't get the stars to fit.

Indeed!

Frank Ryan · Post by **Frank Ryan** » Tue Sep 09, 2008 11:20 pm

Frank Ryan wrote:Mikkel, i wonder have you noticed a problem with the polar scope?
I raised the issue on the astrotrac yahoo group and Richard replied
(to Roland, he seems to think he started the thread )
anyway,
He is essentially saying you can still use them with a 'modified' alignment procedure,
EG, ignore certain markings and
guesstimate 2nd & 3rd star positions relative to the alignment lines.

I have to say I feel a little miffed.
I'm also not happy that I should have to 'make do'
after paying a lot of cash for it.

I will email him and voice my concerns.

He seems like a really good guy and I'm sure the 'new alignment procedure' works fine for focal lengths no more than 200mm
but I want to go deeper if I can and I just don't want to be wasting my
time.

mikkelbo · Post by **mikkelbo** » Wed Sep 10, 2008 10:12 pm

Hi Frank,

Sadly I haven't had time to unpack my AstroTrac yet, and the weather has not been too good lately either.

However, I do remember having the same kind of aligning problems with the polar scope, and I was also somewhat disappointed about it.

Frank Ryan · Post by **Frank Ryan** » Wed Sep 10, 2008 10:48 pm

Hey Mikkel.
The weather world wide is a disaster!

I've been in touch with Richard at Astrotrac and he has explained the issue
to me.
I'm not going to get too caught up in the fact that the gaps are incorrect
because he assures me that once they are on the lines it will be fine.

Any word yet on weather you can make it to WSP08?