Astrotrac

I forgot Trevor was ahead of you in the 'queue' Keith! Thanks for posting Trevor, some quirks there. I wonder about the polarscope? Is it a flaw or could you have a bad one? If it's a flaw, you'd think it would have weel been corrected at this stage.

Seanie.

TrevorDurity wrote:

One word of warning though be careful with the polar scope, it dropped out of the mount any time I moved the tripod as the magnet is not very strong, so I'll only be attaching that at the end once everything else is setup.

Thats prudent Trevor.
It only needs to be done last so no need for the magnet to be heavy.
Because it is a portable set up the last thing you should do,
(even after setting the arm to track)
is do a polar alignment.

I spent some time talking to Richard of Astrotrac regarding a few issues,
another issue was the Polar scope reticle.

VERY important thing to know here...
The first couple of thousand Polar Scopes he ordered have the wrong
magnification on in the reticle.
Not a total disaster but you'll need to follow his
'alternate' method for fine tuning alignment.
(he has this on the Astrotrac Yahoo Group)
Now this is not an issue if you are just doing wide field shots
but if you want to set it up to have the tracking as accurate
as possible for deep field work then this is again VERY important to know!

This just about explains the issue.

www.eanet.com/kodama/astro/equipmnt/polefind/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!
I spent hours in Mt Parnon struggling with this!

I'd reccomend joining the Astrotrac Yahoo Group also as it's a
great resource for tec issues.

Hopefully you will have recieved one of the new batch polar scopes
and this will all be redundant but just in case, hope it helps.

Some other things I found out the hard way.

Rechargable AA batterys are no good (not enough juice)
Duracell batterys are good but have 8 spare fresh ones
because if they die mid track then you will not be
able to reset the arm.

If you are using a manfrotto head to mount your scope onto
youll run into issues with the gear handles hitting the astrotrac
at high altitudes or East / West targets.
(forget North if you are not using a ball head)

Another thing.
You may find the suggested position for the Astrotrac
gets in the way of using the camera.
I've gotten around this by swinging the unit
45 deg to the left or right (out of the way)
and this does not effect tracking.
(As in this pic)
www.frankryanjr.com/astrotrac_ETX-125.jpg
You'll also see here the potential issues with the
manfrotto knobs hitting the unit or else into each other
at high alts.

One final thing,
when the Astrotrac returns to the start position
after its two hour run,
it has a tendency to pull the arm up ever so slightly.
If you dont extend it back down fully (you'll hear a beep when
its making contact with metal) the gears will just
spin an there will be no movemnet.
Its easy to strip the worm gear this way so be careful.

All in all, it's rock solid and you'll no doubt have
hours of fn with it!

Seanie_Morris wrote:

I forgot Trevor was ahead of you in the 'queue' Keith! Thanks for posting Trevor, some quirks there. I wonder about the polarscope? Is it a flaw or could you have a bad one? If it's a flaw, you'd think it would have weel been corrected at this stage.

Seanie.

Hey Seanie!

I don't think it's a bad one but I have noticed that it has been disassembled and it looks like the front lens was replaced or moved - certainly it was a little loose and had fingerprints on the inside. I did find it difficult to look through with glasses on however but that's a very minor point.

Frank, many thanks for the link and all the other useful info. Gonna give it a shot tonight if I can get out of the office.

Thanks,

Trev

Did you buy it second hand Trevor? :huh:

Seanie_Morris wrote:

Did you buy it second hand Trevor? :huh:

Sure did Seanie. Got it off our old favourite astrobuysell in the UK. Same package as they sell direct but I got it without the tripod.

I just tried it out an hour ago. Straight off the bat it did a 4 minute exposure at 200mm with no trailing. I was pretty astounded as polar alignment was rough.

The only thing I don't like about it is the polarscope. For one thing I couldn't make it dim enough to see anything but Polaris (and you could just barely make Polaris out). I suspect there's just something wrong so I'll take it apart over the weekend as I was getting weird coma like effects away from the centre, but even with that the astrotrac really performed. Worth every penny for the quick setup alone I would say.

Trevor,
I'm delighted your up and imaging with her!
It sounds as though either Richard (or the owner) manually replaced the
dud retical in the polarscope with a correct one?
(as you said yourseld, it looked like it had been opened?)
I too found the bulb a little bright but you can get around
it by putting a tiny bit of tissue paper over the hole I shines thru.

Great night tonight (aside from the Moon)