Astrotrac First and Second Light

[Digz]

At the weekend I ordered an Astrotrac to try and give me something that was portable and easy to set up. I have been a little frustrated with how long it takes to set up my EQ mount and get going and it will be a while before I am in position to think about a pier and obsy. That, combined with some local holidays around the UK coming up (to places which promise dark skies) I decided to get something that was more portable, and also easier to set up to get me back out imaging.

Well on Tuesday it arrived!

I had looked at various items such as a Polarie and GPDX after advice from various people here, but settled on the Astrotrac as it satisfied my thirst for well constructed kit but also had increased capacity over its closest rivals.

In the past week we have had two clear nights and on both nights I have been out imaging!

Night 1

Set up was easy. A Manfrotto geared head sits on my tripod and the Astrotrac atop this. This allows adjustment in the three major axis to help balance and polar alignment. On top of the Astrotrac a Manfrotto ball head and my camera, allowing the camera to shoot any part of the sky.

Aligning is quite simple, the polarscope is mounted to the unit and rotated so the constellation orientation matches whats overhead. The geared head is then tweaked to bring the pole star into the gap as marked. This can be further refined if you have good skies using the second and third star epoch markings in the polar scope.

Once aligned the unit can be powered with its supplied cigar lighter and powerpack or via AA batteries. After pressing the start button the screw unwinds about 25mm to balance and get itself ready, a further press of the button will see a green pulsing light and your away tracking.

Now, In my haste to get imaging I forget to actually set the Astrotrac tracking so ended up with an hours worth of subs all with star trails. Still, seeing was terrible with high level cloud so the data collected wasnt usable.

Night 2

Hold on, two clear nights in a row, this has to be some kind of record!

After the failure of the first night this was a lot easier. Set up was quicker and I managed to set the Astrotrac to track this time.

My target was Orion with my Nikon D7000 and 105 macro lens. I have only captured an hours worth of data as my batteries werent fully charged by the results can be seen below:

18 x 3min subs

ISO 1200

Nikon D7000

Nikkor 105 Marcro

No flats or darks.....

It was so refreshing to be out imaging again with a quick set up and tear down time and I cant wait to take it away to some real dark skies. What it has told me, however is I need to work on my editing skills as Ive made a pigs ear of removing the gradient and there is a massive dust bunny there! I also need to be patient and ensure I capture flats and darks.

Anyway, hope you enjoy the above as much as I have, and I look forward to any comments you may have.

[iksose7]

Nice image Digz, although it looks like you may of had some dew form on the lens while imaging? I also just recieved my AT a few days ago. Great piece of kit (apart from the polar scope). I will be posting my results soon.

[cfpendock]

This is a great piece of kit, and I am sure you will get some excellent shots with it. And the best thing is, it is seriously portable!

chris

[Digz]

Thanks guys. Im very impressed with the AT, easy to set up and gets me out imaging more, even when we go on holiday.

iksose7 - I don't think there was any dew (I could be wrong) as I didnt notice any on the lens. I think the effect is from my poor processing skills.....

I found the polarscope to be ok to be honest. Sure the connection could easily result in a dislodged scope is knocked, but I managed to align relatively easily and quickly with it.

[iksose7]

I found the polarscope to be ok to be honest. Sure the connection could easily result in a dislodged scope is knocked, but I managed to align relatively easily and quickly with it.

Yeah, mines not bad now but i had alot of problems when it arrived. Starting with the collimation and removing the grub screws. Took me about two hours, i had to file down and make my own allen key! But its ok now that i have replaced them with thumb screws. All i need now is a slip joint washer to stop the scope falling out the arm again.

Anyway, all that is forgiven because of the quality of the AT. Got it set up outside now waiting for darkness...

[Digz]

Oh crikey haven't even thought about collimation of the polar scope.....

ive seen people just a piece of pipe lagging above to prevent any accidental slippage, but a slip joint washer sounds a neater solution. As you say, can be forgiven because of the quality and precision of the AT itself.

[iksose7]

Oh crikey haven't even thought about collimation of the polar scope.....

You're in for a treat

[StuartJPP]

A great start Lee, hope you enjoy your AstroTrac, I think it is a great piece of kit, but like most things you have to get to know it intimately to get the most out of it.

You can ignore the following advice if you wish

Depending on focal length and exposure duration I'd say collimation of the scope is essential. It isn't too difficult to do, I have done two now, but it can be frustrating. Just take your time and only make small adjustments to the grub screws and never loosen all 3 at once. After loosening the opposite 2 slightly, the "tight" screw is tightened more to push the reticule over. Ensure that all the screws are tight(ish) after you have finished. I also found that the actual barrel can be a bit loose as well, so make sure it is tightened up a bit and straight before collimation. Once collimated, make sure that you treat it relatively carefully.

Another thing to look at in future is to check that the folding polar scope arm is also true. I found that getting Polaris aligned with the folding arm at 3 o'clock was slightly off at 12 o'clock and 9 o'clock. That was much more fiddly to adjust than the polar scope collimation and in the end involved 2 pieces of tape on the polar scope holder to correct. This was however a 2nd hand AstroTrac so I can't complain too much.

See this thread...

http://tech.groups.y...ac/message/5473

The above might not be strictly necessary, because if you find the best arm position (12 o'clock for instance) and always stick with that for aligning, you should be fine. I always try to be consistent so as to eliminate any variables.

One last tiny bit of advice, using some method to ensuring that the polar scope doesn't drop out of the magnetic holder if knocked can help immensely. I attached a lanyard to mine which I thread through the polar scope hole. It has saved my polar scope on two occasions from connecting with the ground due to bumping it with my head torch.

Polar scope properly aligned through 360 degrees rotation.

Polar scope arm rotated 90 degrees without moving the polar scope shows that it is off by quite a bit.

My correction, two pieces of sticky copper tape, this took a number of hours to get correct:

[Digz]

Excellent advice mate. When I get time ill be sure to collimate.

[iksose7]

My correction, two pieces of sticky copper tape, this took a number of hours to get correct:

Hi Stuart. Although i know about collimating the polar scope, i'm not too sure about all this polar arm buisiness. Are you saying that you should be able to centre a target in the polar scope, and move the polar arm while the target stays centered?

I have you as a contact on Flickr and you have some really impressive images, would love to be able to get something similar but i'm having a little bit of trouble with star trailing. I'm wondering if maybe my polar arm is out as yours was?

[StuartJPP]

Hi Stuart. Although i know about collimating the polar scope, i'm not too sure about all this polar arm buisiness. Are you saying that you should be able to centre a target in the polar scope, and move the polar arm while the target stays centered?

I have you as a contact on Flickr and you have some really impressive images, would love to be able to get something similar but i'm having a little bit of trouble with star trailing. I'm wondering if maybe my polar arm is out as yours was?

Yes, the proper alignment of the polar scope arm to me is important to squeeze as much out of the AstroTrac as possible, without using drift alignment that is, which may be my next method of alignment. Remember that I am using a lens with a focal length that is longer than recommended (weight is within limits), but it really is pushing the limits of the AstroTrac.

If you think about it, you have to have the tripod head screw on the AstroTrac pointing exactly at the North Celestial Pole (NCP), if it isn't pointing exactly there then some drifting will be present. When doing polar alignment, you are aligning your polar scope arm, not the actual screw thread. If the arm was bent by 10 degrees you would easily see that you are not aligned with the screw thread even though the polar scope is aligned with NCP. However we are talking a very small amount here, invisible to the naked eye. My "fix" was a piece of tape, basically the thickness of a piece of thin paper.

If you align the cross hairs in the polar scope on Polaris or any other bright star or distant object (not the gap where Polaris goes) and you rotate the arm through 270 degrees, the position of the cross in the centre of the polar scope should not change otherwise your arm and thread is not properly aligned and hence you will not be actually pointing towards NCP.

Are you also using the 2nd and 3rd star in the alignment as well? I can usually only see the 2nd star.

Another thing that can also happen is that the sidereal tracking rate can be a little bit fast or a little bit slow. This can be caused by the camera equipment not being balanced properly or even tolerances of the unit itself which will probably change slightly due to temperature. There is not much you can do about this without having the AG version.

[iksose7]

If you align the cross hairs in the polar scope on Polaris or any other bright star or distant object (not the gap where Polaris goes) and you rotate the arm through 270 degrees, the position of the cross in the centre of the polar scope should not change otherwise your arm and thread is not properly aligned and hence you will not be actually pointing towards NCP.

Thanks for clearing that up. Looks like i'm going to have to give this a go soon. Going to take quite a while i'm guessing with alot of trial and error.

I am doing 3 star alingnment but is pretty tedious. I can only see the 3rd star if i'm not looking directly at it making it hard to line up. Also, i have the AG version so i may look into setting that up.

Cheers Stuart.

[Digz]

Great discussion and information guys, helps clear things up for me as well

[StuartJPP]

I firmly believe that no matter what equipment you have got, there will be some improvements that can be made. Even though the AstroTrac is a precision instrument and not strictly speaking a mass market item, engineering tolerances can't be expected to be 100% spot on for the price paid. If every single unit that came out of the AstroTrac factory was 100% spot on, they would be a lot more expensive than they are. This applies to any manufacturer. You pay a lot of money for expensive mounts because they have been engineered to extremely tight tolerances and tested against them, that is why you can spend £10k's on a mount.

I am doing 3 star alingnment but is pretty tedious. I can only see the 3rd star if i'm not looking directly at it making it hard to line up. Also, i have the AG version so i may look into setting that up.

If everything isn't aligned with each other I can't see the point of doing 3 star alignment, unless you just happen to be consistently using the polar scope arm position that is optimal. This may explain why we sometimes have good sessions and other times bad sessions, because one time we are all aligned because we chose the arm at 12 o'clock , and the next time at 9 o'clock which isn't the same thing. Since the AT can only track in RA, you would still need accurate polar alignment, all that guiding would do is correct for sidereal tracking errors.

I just wish it would clear up out there so that I can actually use it and not just talk about using it

[iksose7]

Yes, i suppose that makes sense. Maybe one day i will be able to afford one of those 10k mounts...

I'm just about to go outside and see if i can get the polar arm lined up properly. I had a clear night last night but had to throw away 2 hours of data due to a focus slip and light pollution creeping into the bottom of the image. Dropped the PS again aswell so that will need collimated. Weathers looking 50-50 for tonight.

[starman1969]

Great advice on the Astrotrac here. I hope to take some of that on board.

Lee, I hope you manage to get some great images with your astrotrac. I bought one last year & can now take images I never thought I could possibly do before.

I've only been doing astrophotography for about a year or so.

Also, I used a Nikon D7000 & 70-200mm f2.8 lens mounted on an Astrotrac for this shot of the Andromeda Galaxy.