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jjongmans

Mission accomplished: 20 minuted UNGUIDED with ASA DDM60!

14 posts in this topic

The weather wasn't good, lots of thin cirrus clouds, but I could see some stars. I was a bit skeptical about this mount, not any more... Unguided imaging IS possible with an ASA Direct Drive Mount. Look at the image below, the Ha signal isn't good, but the stars are round!

Attempt 1: 10 minutes unguided

IC410

2000mm f/8 reduced to 1383mm f/5.53

1.608"/px = FOV 33.6' x 44.6'

Unguided

1x 600s (10 min) 3nm Ha 2x2

-40°C

manual focus

no calibration

HistogramTransformation in PI

ic410_600s_small.jpg

Full resolution - 10 min

Attempt 2: 20 minutes unguided (a bit more clouds, so less Ha signal)

IC410

2000mm f/8 reduced to 1383mm f/5.53

1.608"/px = FOV 33.6' x 44.6'

Unguided

1x 1200s (20 min) 3nm Ha 2x2

-40°C

manual focus

no calibration

HistogramTransformation in PI

ic410_1200s_small.jpg

Full resolution - 20 min

I'm really impressed! It's very important to have accurate balance and a precise sky model, after that it's point and shoot. Who needs guiding? :grin:

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I bow to your set up skills. 20 mins unguided! Respect Sir!!

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I bow to your set up skills. 20 mins unguided! Respect Sir!!

All credits go to the ASA mount.

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Very nice indeed. One thing you may want to check out is whether the 20 minute non-guided accuracy holds up at different positions across the sky - usually when near the zenith it's less demanding however 20 degrees or so above the horizon is a bigger test - would be interesting to see if there is any difference or not. It's good though to see the ASA mount coming back into favour, there were some hit & miss comments a while ago on these, but they now seem to be reliable & very high quality mounts. I've still not seen any reviews on the smaller 10 micron mount GM1000 mount which is in the same price bracket though.

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Excellent - well done :)

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Good to see that you are making it work well for you.

As mentioned, precise alignment and accurate sky mapping is important, and really should be the standard everybody aims for to reduce the need for guiding adjustments. With close attention to the fit and pointing of the mounts there is no reason even a trusty old EQ6 can't do unguided subs for 20 mins at this sort of focal length.

Cheers

Tim

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The mount needs to track in both axis in order to get unguided performance, unless you have perfect polar alignment, no dec slack and no atmospheric refraction...

My 10micon GM2000HPS does half-hour unguided subs at FL 1500mm, and I expect my incoming GM1000HPS will too. Dual axis tracking and a reasonably good alignment model are musts.

/per

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The mount needs to track in both axis in order to get unguided performance..........Dual axis tracking and a reasonably good alignment model are musts.

/per

Is this true? I was always under the impression that once the mount had arrived at its target, then the DEC drive was more or less done with. Quite often I guide with DEC guiding turned off.

Or is that just the advertising blurb that comes with the mount? Looks nice btw ;)

Tim

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Well, if you have absolute orthogonality on your mount and it is perfectly polar aligned it shoud do a zillion hours unguided. But, let's face it, who gets the polar alignment perfect and who has a perfect mount?

A drift alignment will get you very far and you can probably get some pretty good long exposure subs unguided, but it is not something I would feel comfortable with. Suppose you have a good pier for your mount and you leave it there, perfectly polar aligned. With all the mechanics involved, how long will it retain that alignment? It doesn't have to be many arc-seconds off before tracking becomes a problem.

So, I'll stick with stuff that has a reasonable software support for an advanced sky model, preferably in-mount and not in a PC on the side. Unfortunately, that doesn't leave many products to choose from :(

All the best,

Per

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No manufacturer makes a perfect mount and no astrophotographer can do a perfect polar alignment. The reason this mount can track unguided isn't only the direct drive design, encoders, etc. but also the software to model sky. With this model I can compensate for flex (mirror and focuser), refraction, polar alignment error, orthogonality error, deviation optical axis and RA axis, etc.

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It is of great interest to me as I like to image at long focal lengths and for very long exposures. Having a mount as capable as yours would be extremely useful for me, especially when taking the 2-3 hour long subs that I do when chasing the extremely faint outer regions of planetary nebulae and supernova remnants.

Keep up the good work!

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I want to rejuvenate this topic.

I am looking to buy one of these mounts. Do you recomend it jjongmans?

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