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Dave Smith

Testing my new astrotrac TT320X-AG

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About a year ago I decided that I wouldn't attempt to take my imaging gear to astrocamps such as Kelling as it was so much hassle getting it out of my obs and then getting it all to work at the camp. I do like observing so thought I would be happy just doing that away from home. I recently decided that I did want to do some sort of imaging and widefield imaging seemed particularly suitable for a dark site. Hence the astrotrac.

It arrived very quickly from FLO but regretably so did the cloud and rain. I did consider getting a Vixen Polarie but decided that I may wish to exceed the weight limit of 2 kg. The weight limit for the astrotrac of 15kg and the fact that they have been around for a while decided it for me. There was little difference in price. (Both expensive :))

I already had a 410 geared head and tripod but decided to get a Manfrotto 460MG head to go between the AT and camera as it gives easier control over where it is pointing. A ball head would also be good for the job.

Here are some pics of my setup. When at home or at camp withing the UK I am using my otherwise redundant NEQ6 tripod. The fixing bolt with handle came from astroboot. If I go overseas I have a carbon fibre tripod that I use for birdwatching. Similarly I use a SkyWatcher power station to power the AT but will use batteries if overseas.

AT01.jpg

I have the tripod fully extended to enable me to polar align without having to bend too much (showing my age) but it seems plenty stable enough.

AT02.jpg

AT03.jpg

The last two evening I have been testing the setup. It is extremely easy to polar align - the geared head makes it a dream. I initially kept on knocking the polar scope off so added a piece of pipe lagging to keep it in place (grey).

On the first night I had trouble getting focus, but it turned out that the CLS clip filter I was using changed the position of focus on the lens so that the dial indicated only 1.5m. I found this out by testing in daylight. It just didn't occur to me to try at such an apparent distance. So last night I did achieve focus with the CLS filter in place and here is the result. The star in the middle is Arcturus. I have identified M3 and the blackeye galaxy in the picture but only as blobs. This was the result of stacking 7 x 5 minute subs and darks were also taken. Aligned and stacked in MaximDL and processed in photoshop.

ArcturusAT01.jpg

Dave

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Looks good Dave, good results too. Was that with your 24-105 ?

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Nice results Dave...

Another thing to watch is that the zoom lens are no longer parafocal across their zoom range when you use a clip in filter...its important to focus at the imaging focal length ratehter than zoomign in focusing and them zooming out to the imagign FL...

I wasted a few nights with the 24-105 f4L and 70-200 f4L before sussing that out :)

Peter...

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Thanks Dave, John and Peter.

Yes, John it is with my 24-105 f4L lens set on 24mm.

Thanks for the tip Peter. Hopefully at a dark site I won't need to use the CLS filter.

I'm off this weekend to a club astrocamp at a dark site in Suffolk. Just hope for some clear skies on Fri and/or Sat.

Dave

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Neat results Dave. :)

The clip filter makes a huge difference, I like how that pic has come out.

Good first report.

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Neat results Dave. :)

The clip filter makes a huge difference, I like how that pic has come out.

Good first report.

Thanks Pibbles.

One problem I had with the focusing was that a Bahtinov mask just didn't seem to work with such a short focal length. However, APT came to the rescue with it's focusing routine, especially the ability to nudge the focus via the software and not have to touch the lens.

Dave

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Looking good Dave and thanks for the pipe lagging tip.

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Looking good Dave and thanks for the pipe lagging tip.

No problem. The first time I had it out I knocked and dropped the polar scope so tried to come up with a solution. It still isn't that firm but at least doesn't drop out.

Dave

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Very nice image. I have a similar setup but used a prime canon lens. (300mm). Found it quite difficult to nail the focus even with live view.

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