Astrotrac questions

[FuzzSummit]

My current astro setup is a Sirius EQ-G mount + either 5D2+lens or 5D2+AT6RC telescope+Orion Starshoot autoguider. While it gives great results, my only gripe is that the setup requires very careful alignment and calibration to get long exposures. Given the weight and setup requirements, it's not very portable (or as portable as I'd like it to be). Thankfully I live under relatively dark skies, but would like to travel and shoot from other darker locations too. Hence my interest in the Astrotrac. But I do have a few questions about the whole system...

1. Is this the only thing I need? The way I think it works is that the camera mounts on it, and the whole thing attaches to a tripod head. There must be a way to tilt the whole setup to the correct right ascension, either by using a ballhead or adjusting the tripod legs?

2. How easy/quick is it to set it up from scratch? Obviously the right ascension adjustment will depend on the tripod/ballhead. But what about the polar alignment? With the Sirius EQ-G, it does take a while to get it exactly right. How easy is the Astrotrac? With the EQ-G, getting everything balanced accurately takes time too -- does the Astrotrac need to be balanced or calibrated in any other way?

2. I don't see anything about counterweights -- does the Astrotrac not need any? The specs say that it can support up to 33lbs -- presumably without needing any counterweights?

3. Looks like it has a port for an autoguider. How does an autoguider attach to the system? I'm guessing the autoguider would attach on the Astrotrac first, and then the camera on top of the guider? Anyone have pics of a guided Astrotrac setup?

3. The AstroTrac website says it can achieve exposures of up to 5 minutes. Is that unguided? If it is indeed unguided, how realistic/frequent is that?

4. How delicate is the AstroTrac? Will carrying it in a padded camera bag as airline carry-on damage any of the built-in calibration?

Thanks a lot for any responses.

[cyberon]

I'll try to answer some of your questions:

1. It can be tilted with the ball head but the recommended way is to use the manfrotto gear head or the astrotrac wedge, it makes it a lot easier.

2. For widefield shot, it is not too hard but as your focal length increases, alignment needs to be a little more precise. The polarscope that comes with it is close to useless especially if you live in the Southern hemisphere because it is poorly made and rather dim. Drift alignment is recommended if your focal length is longer. Counterweights are necessary if you mount a small scope, you need another piece of accessory to fit a counterweight. As it is, you should only mount your camera and lens on the astrotrac.

3. Yes, the astrotrac can be guided but only on the RA axis only. I have never tried this. I guess 5 minutes may be possible unguided if you take the time to drift align and your focal length is not too long.

4. Astrotrac is quite well built and would be fine in a padded bag for air travel.

[FuzzSummit]

cyberon, thanks for your reply. What's the longest focal length you've used, and what's the longest exposure you've successfully (i.e. little/no trailing) captured at any focal length?

[cyberon]

The longest I've used is 500mm but only for short duration of 45s. I can't polar align it well enough because I am in the Southern hemisphere and the polarscope is close to useless here. Some of our members have made a green laser to mount on the screw thread where you mount your camera to assist and simplify polar alignment. You would have better luck aligning it to polaris.

[canadave]

Originally Posted by cyberon

1. It can be tilted with the ball head but the recommended way is to use the manfrotto gear head or the astrotrac wedge, it makes it a lot easier.

Can I ask you to elaborate on this? How much is "a lot"? The geared head/wedge is a fairly significant expense...if there were a way to get away without using the geared head/wedge to do the latitude adjustment, even if it's a LITTLE more work, it would put me closer to purchasing this.

FWIW, I would be using it with a 300mm focal length and max 1-2 min exposures.

[cyberon]

The wedge especially and the gear head to a lesser extent allows you to make tiny adjustments that are important when polar aligning, try doing that with a ball head and you will know the difficulty involved.

[Mark Brim]

Originally Posted by cyberon

The wedge especially and the gear head to a lesser extent allows you to make tiny adjustments that are important when polar aligning, try doing that with a ball head and you will know the difficulty involved.

Agreed, i tryed to do this it a non geared head when i first bought the astrotrac, i sharpish realised it was nigh-impossible to get a decent alignment without

[Mark Brim]

Originally Posted by FuzzSummit

cyberon, thanks for your reply. What's the longest focal length you've used, and what's the longest exposure you've successfully (i.e. little/no trailing) captured at any focal length?

I use 400mm on a regular basis with no problems wat so ever, I can see myself borrowing a 2x to see how far i can push the Focal length, but ive spoken to someone who helped design the mount who thinks 400+ is pushing it

[FuzzSummit]

Mark, where in the UK are you, and do you travel with the Astrotrac a lot? One of the main reasons for my interest in the Astrotrac is because I'll be moving to London (near Wimbledon) later this year. I have pretty dark skies where I live now, so all my imaging is done from my backyard (my astro shots) -- hence the current heavy astro gear is okay. But once I move, I'm guessing light pollution will rule out imaging from home, in which case I'll have to travel some distance for dark skies. And that's where the Astrotrac would come in handy.

EDIT: how power/battery-hungry is the Astrotrac (for field use)?
EDIT2: I assume all the astro pics on your Flickr were with the Astrotrac?

[Mark Brim]

Originally Posted by FuzzSummit

Mark, where in the UK are you, and do you travel with the Astrotrac a lot? One of the main reasons for my interest in the Astrotrac is because I'll be moving to London (near Wimbledon) later this year. I have pretty dark skies where I live now, so all my imaging is done from my backyard (my astro shots) -- hence the current heavy astro gear is okay. But once I move, I'm guessing light pollution will rule out imaging from home, in which case I'll have to travel some distance for dark skies. And that's where the Astrotrac would come in handy.

EDIT: how power/battery-hungry is the Astrotrac (for field use)?
EDIT2: I assume all the astro pics on your Flickr were with the Astrotrac?

Im in the northeast of england, Most of my shots are from the back garden. If i do travel its not often very far, Just sling it in the back of my car and off up the road.
Once youve attached the astrotrac to your tripod...and plugged it in...it takes about 1 minutes to align (depending on what kinda FL your gona be using....im pretty sloppy with my alignment as my patients is low when imaging the stars! haha) so were talking under 5 minutes and your ready to image. It is remarkably quick to set up.
Ive never had problems with batterys, but im yet to have a hardcore imaging session. Ive done a couple of hours in cold conditions with no problems. Since i bought the mount 6 months ago(ish) id say ive only replaced the batteries 4 times. It does come with a car adapter for field work, the cable isnt massive so you couldnt stray too far.
Yeah most of the recent astro pics on my flickr are with the astrotrac.

As ive never used any other mount im pretty amazed at what the astrotrac lets you do!
Maybe because your used to using a more hardcore mount, it will seem like a step down for you as this mount has obvious limitations. Im yet to really push my imaging skills so my images arent the best example of what the mount can do. If you get your alignment down i think youll find getting 3/4 mins easy
In terms of easy of use and mobility the astrotrac gets a serious thumbs up!!

[dmf]

Living in Wimbledon and using an Astrotrac I may be able to answer some points.

You can do some back garden imaging, up to 2 minute exposures @ISO 800, F4, 280mm. But everything does end up a little orange at that point. A light pollution filter really helps but I still haven't managed to get rid of that annoying blue hue to my photos now
It really comes down to how much light pollution you can put up with.

But having the ability to throw it in the passenger foot-well of the car and drive outside of the M25 is so handy.

I have managed 5 minute exposures with only slight elongation of the stars. My polarscope is not that useful after I stripped the threads on the barrel by mistake. It's threaded together with PTFE tape at the moment.

It isn't too battery heavy, I've been running mine off of a 12v sla battery for the past few months and I've not had any issues. I'm not sure I would want to do long imaging sessions with just the AA battery pack.

[FuzzSummit]

This is great info - thanks both Mark Brim and dmf.

dmf, that makes me very hopeful.

I am definitely leaning towards getting the AstroTrac now. Just need to figure out what lens to use. Trying to decide between 70-200 f/2.8 II + 2x teleconverter or Sigma 150-500. I already have the 70-200, so that would be the cheaper option, but not sure of the IQ difference; plus the Sigma would give me longer reach. Hmm, decisions, decisions!

[canadave]

Originally Posted by FuzzSummit

Just need to figure out what lens to use. Trying to decide between 70-200 f/2.8 II + 2x teleconverter or Sigma 150-500. I already have the 70-200, so that would be the cheaper option, but not sure of the IQ difference; plus the Sigma would give me longer reach. Hmm, decisions, decisions!

Would it not be simplest to just try the 70-200+TC first, see how well it works, and then make a decision on buying the 150-500 based on that?

[FuzzSummit]

Originally Posted by canadave

Would it not be simplest to just try the 70-200+TC first, see how well it works, and then make a decision on buying the 150-500 based on that?

Yup -- I already have a 2x TC rental coming next week.

[hollis_f]

I'm thinking about asking for one of these for my birthday in July. What's the heaviest setup you can realistically use?