Accurate mount pointing

[Peter Ward]

Up until recently, I used Sky6 and a few add-ons to keep my dome and scope automated.

It still works well, but having to solve various third party issues recently I really needed more than a cursory knowledge of SkyX.

So I went the whole enchilada and have mirrored Sky6 and SkyX systems for some time now.

One thing SkyX does *really* well is plate-solve/image link with T-point to build an excellent pointing model.

While I'm hardly the first, I encourage others who haven't been down this path to try it.

The attached image is from a mere 32 point auto-mapping run.

17arc seconds RMS all-sky pointing isn't too shabby! :)

[lazjen]

Nice accuracy.

I'm curious, and so need to ask a possibly dumb question: how important is it to having pointing accuracy like this, or even say less than around 1 arc min?

[RickS]

I guess it's nice and might save you some time plate solving and re-slewing but it's not critical for any application that I can think of. I'm a nomadic imager and I get by just fine without a pointing model. If I had a permanent setup I would do one, of course.

Cheers,
Rick.

[Peter Ward]

Actually, that's a really good question!

For most, an arc minute or ten would be sufficient: as long as it lands on the sensor/eyepiece you are happy.

But for those wanting to get, not just a guide star, but bright one at that, in a comparatively miniscule guider field, the SkyX performs magic.

You can slew to an object, *know* it is centred.
Direct or even automate a guide star capture and create a AO-guider/Megadata/awesome-mosaic .

But that's not all

Pro-track also accounts for pointing errors and corrects the tracking rate with error vectors previously measured for the part of the sky you are imaging in.

Now, if the Bisque clan could just clean up hardware interrupts and unexpected crashes when using a: camera/mount/dome/AO/guider/filter-wheel/focuser.....
..OK..all at the same time..

Well...Nirvana springs to mind

[Peter Ward]

Ultimately it comes down to repeatable, albeit narrow, fields of view.

e.g. If you don't need to go 0-100km/hr in 3.2 seconds, it's wasted horsepower :)

[RickS]

Not having a permanent obs is more like riding a push bike, albeit a very nice one in my case :lol:

[Logieberra]

Your next mission, should you choose to accept it, is Protrack and unguided work. You'll need a lot more points for that one, hundreds in fact, drawn from all across the sky. Check it out ;)

[lazjen]

Thanks for the answers, I didn't consider the guider aspect before.

[Peter Ward]

Yes, I've pondered whether it would be worth the effort....but seriously doubt unguided results would improve images from say, an AO equipped camera.

That said, the less corrections an imaging system has to make, courtesy accurate tracking, the better the resulting guided image. :thumbsup:

[Zaps]

...And that's why the gods invented direct drive mounts.

;)

(Standby for the upcoming fireworks.)

[gregbradley]

I would also add that after I did a 300 point super model in Sky X and turned on Protrack corrections I got even better guiding results than simply autoguiding with PEC on. So now I use PEC and Protrack in my guiding and I get better results.

I think though a periodic redo of the model may be required if you change cameras with a resulting slight rebalance etc. Its a bit like taking flats. If you change anything the model may go off.

Greg.

[Logieberra]

And that's why, as of January 2014, the price per KG of DD mount capacity is still astronomical.

FYI, an AP mount (or ME2) equipped with encoders all but eliminates PE... with the option of install at a later date when funds are available. Then I'd spend good coin on the latest AO unit after that.

Getting directly into a DD mount, today, in the 100+KG capacity range just ain't possible for most of us (Skywatcher, if you're listening - bring out that EQ9/10 with direct drive please, to keep em honest)...

[Paul Haese]

Agreed the speed of plate solving and super modelling in SkyX is fantastic. Pointing is very good too. Some glitch other stuff going on but bearable at this stage. The sky6 is stable by comparison but pedestrian.

My current model which got interrupted last week by a cable wrap is 113 points and pointing at 20.5 arc seconds with a R50. Every thing I point to hits the target pretty well right on the centre of the sensor.

[Peter Ward]

Unless the Chinese work out how to make high-res ring encoders for less that a few thousand a pop, (yep, that's the OEM cost) I can't see it happening.

BTW what happens to DD mount when it loses power? I've been told they simply fall limp.... :eyepop:

...but that sounds a bit risky/disastrous for 100Kg of telescope etc. so you'd hope there is some sort of fail-safe.

Anyone know for sure??

[Logieberra]

Getting a bit off topic, but:

DDM85
NO counterweight shaft
'Impressive' (?) carrying capacity of 100lbs/45kg
15.5K USD!
http://www.optcorp.com/a2-ddm85-ddm85-direct-drive-mount-85.html

P.S. don't own one, never used or seen one...

[marc4darkskies]

I'm also getting 17 arcsec RMS - 180 point model. Automapping is a breeze and fun to watch too.

It's VERY useful having accurate pointing for the reasons you mention - especially reliable and predictable automated guide star acquisition. Also, when automating, focus star acquition requires slewing and if you don't have accurate pointing when returning to your subject your data acquisition overall will slow down because time is wasted centering. If you don't center every sub and if all your subs are dithered by a ten arcmins because of poor pointing you'll end up cropping valuable camera FOV too.

Cheers, Marcus.

[Zaps]

Yup, fireworks every time.

:rofl:

Here's a better site for information:

ASA's DDM85 page (http://www.astrosysteme.at/eng/mount_ddm85.html).

[marc4darkskies]

I'd be interested to know the answer to this as well. I've seen the question asked but never answered properly. Usually someone says the scope has to be "balanced", but that can't be the answer because most people know perfect balance in all orientations is rarely possible.

[Peter Ward]

Soo...begging the question....and being Devil's advocate...:D..... how do you know if they any any good?

I suspect they are..... but the no power= unlocked mount remains a troubling question.....:question:

[Logieberra]

Good? For the astronomical price, I bet they're darn amazing! :)

Although... http://www.myastrospace.com/forums/forum/equipment-discussion/3734-

Peter, will we see ASA on your product line in the not too distant future?

[Peter Ward]

:lol: It's interesting to note that the user plonked it on a Losmandy Tripod :thumbsup:

While I'm sure ASA would take an order from my commercial venture..

...but I don't expect to be snowed under with inquiries any time soon....so it's probably not going to happen.

The reality is in Oz, sell cheap, or sell sporting gear (maybe both )

High end astronomy instruments are for a discerning few....and I'm not taking a swipe at those who are not in a position to drop $15-50K on a system...

You can buy a S-class Benz, or you can buy a "reasonably priced car" . Both will indeed safely get you from A to B.

It's simply a matter of whether that last few (and often costly) percent of engineering excellence matters to you. :thumbsup:

[MrB]

I have no idea, but if I had a hand in designing the mount I would have added a solenoid operated clutch/brake.
If power were lost, the solenoid can no longer hold the clutch/brake open.

[Peter Ward]

Indeed... one of a few practical solutions. The question however remains...:confused2:

[marc4darkskies]

Here's an interesting and recent ASA forum thread that pretty much answers the question IMO.

http://forum.astrosysteme.com/index.php?/topic/215-parked-scope-power-requirements/

Even if you manage to achieve perfect balance 100% of the time in all orientations, imagine what might happen if a power failure happens during slew or after a surge! :scared:

[Peter Ward]

I can see Today-Tonight's headline: "Astronomer crushed by run-away telescope with laser-finder and causes overflying Airliner Terror :eyepop: "

"Legislation banning them needed now !" :rofl: