New product - 1 arc-second tracking ability without using conventional auto-guider

[Peter Ward]

Originally Posted by Dennis

Gee Peter, lighten up and give the guy a break!

Dennis

Hey, I have no axe to grind here.

Any product that effectively improves the tracking of a mount is a good thing.

What I do find annoying is: on the referred website, the implication is this device removes the need for guiding.

I've found just he opposite to be true.

The better you can guide, the more flux you can lay over fewer pixels, and the better the result.

[Dennis]

For those interested in seeing the results when this system was fitted to a Vixen GPDX mount, and if you can access the Cloudy Nights Forum, here is a link to one user’s experience.

The results look very promising although the user indicated a price of around 1,000 Euros, so you won’t get much change out of $2000 Au.

Cheers

Dennis

[bojan]

Originally Posted by Dennis

For those.... a price of around 1,000 Euros, so you won’t get much change out of $2000 Au.

Cheers

Dennis

That was exactly my point.
Too expensive... guiding does the same job ( PLUS it allows for not-so-accurate alignment) for much less money.

[Bassnut (Fred)]

Somethings wrong here, the site shows the encoder fitted directly to RA as an output encoder. To resolve 1 arcsecs, it then needs to have at least 1.2million ticks per rev. Ive seen Heidehain encoders a lot over the years on CNC machines, they are top shelf, and, very expensive. I scaned Heidenhains site for prices and anything like the model they used, to no avail unfortunately (the picture res of the encoder frustratingly doesnt allow reading of the model number), but at a guess an encoder alone of that res would be many times more than 1k euro. So, Im thinking they have gear reduction on a lower res encoder, which then raises questions of machining accuracy/variability between examples and PE within its own gearing.

[AlexN]

I must admit, the most interesting thing on the site to me was a 20min unguided exposure using a 160mm F/8 refractor on an EQ6... A 160mm F/8 refractor would have one hell of a moment arm, be fairly heavy, especially in the front end, I know I've managed 5 minute unguided shots through my 102 F/7 refractor, after nearly a full night tweaking the polar alignment.. 5 minutes at 700mm is pretty good in my books.. 20 minutes would just be out of the question without guiding, or perhaps, this new device..

Thanks for bringing it to our attention Dennis... Its great for the people with paramounts to say its rubbish, but for those of us not made of money, this might be an option... I will however be waiting for some real world results...

Post the link on Cloudy nights and let the americans try it first!

Cheers.
Alex.

[leon]

Interesting stuff, but I might just stay with the set up I already use, it's not perfect but it dose the job pretty well.

Leon

[AlexN]

Ooooh... here we go...

Checked on Cloudy Nights.. Someone already has one... Heres a link to his results with his GPD/GPDX mount... Looks like it worked as described...

http://www.cloudynights.com/ubbthrea.../o/all/fpart/1

[AlexN]

Oh, forgot to mention... He paid 1000 Euros for it, however the creator has now signed a deal with Meade...

3 things could come of that...
-Bigger company, manufacture in bulk, cheaper product for all end users.
-Bigger company, manufacture in bulk, sell unit only for Meade mounts/intergrate into meade mounts...
-Bigger company, Manufacture in bulk on the cheap, sell to everyone at inflated prices and because they are the only company selling it, we cant do anything about it..

[bojan]

It will never be cheap.
Encoders with that sort of resolution are on the market for a long time.. and price never dropped.
The only thing that can drop is quality.
Stick to auto-guiders guys, that what they were designed for.

[Dennis]

I’ve just dug up some receipts and invoices for my side-by-side auto guiding set up for a quick cost comparison.

Orion Deep Space Star Shooter:….. $569
WO 66mm F6.1 Petzval:…..$349
WO Diagonal for short tube OTA:…..$100
WO Guide Rings:…..$100
Scopestuff side-by-side plate:…..$100
WO Saddle/Plate combo:…..$200

The above comes to around $1400 and was purchased over a period where the Aussie/US $ exchange rate fluctuated, so the figures can only be a rough guide. The Orion camera is the original Peltier cooled model as I wanted it for noise-free, long guide star exposures and for this, it works really well. I’m sure that someone could cobble together a less expensive kit, but the above is just what I’ve ended up with over the years.

So, technical/performance issues and flexibility/versatility issues aside, this makes roughly $600 difference between my rough costs above and the guesstimate of $2000 for the TDM kit.

However, if I were building a new system from scratch, I would probably double the budget and would likely lean heavily towards an SBIG dual chip camera, as I have enjoyed much more reliable results with my SBIG ST7E dual chip ccd camera compared to my side-by-side set up; the overall set up, complexity and operation is simpler too, a single camera on a single scope looking at one section of the sky.

Just some thoughts; not trying to convince anyone to take my position which is simply where I am through historical factors, opportunities and trial and error, which will no doubt change as I get wiser and hopefully, wealthier!

Cheers

Dennis

[Peter Ward]

Arrgh..... so are there really people out there that will pay
"1000EUR + shipping + VAT" .....so at about $A2200? for a device that
*will not* correct for:

polar alignment error
intrinsic sidereal/king rate error
mirror flop
mount flexure
OTA felxure
atmospheric refraction
atmospheric convection
camera sag
mount /OTA thermal expansion
mount/OTA thermal contraction
mount non-orthogonality
intrinsic gear indexing errors
etc. etc.

But...by crikey...the constancy of RA shaft rate is brilliant!

Humm.... I seem to recall a dual chip, self guiding CCD camera was introduced to the market nearly 20 years ago, that solved all of these problems....nah...I must have been deluded

[AlexN]

Peter - Agreed... At 2200 AUD I'd be looking for an ST7XME / ST8XME, not an RA drive corrector...

[Dennis]

Within the stated limitations of TDM as documented on their website, it would appear that the system is targeting the amateur astronomy community who may want to manage one or more of the following scenarios:

• It does not need to find bright guide star for tracking (the observation process can be automated on much easier way).
• High density filters (e.g. H-alpha) do not have any influence to the performance of tracking.
• TDM is a standalone application so it does not need any PC support or other external device for using it.
• TDM is firstly recommended for the observers who intend to take a lot number of shots per night about different parts of the night sky quickly and easily. (E.g. supernova patrols, comet and/or asteroid hunters, observers of cataclysmic variable stars, etc.)
• TDM can be an extremely advantageous application for robotic telescope owners who needed to find bright enough guide stars within the field of view manually so far.
• For "tourist amateurs" who do not want to drag an extra tube and CCD just for autoguiding purposes up to the peak of the mount escaping from light-polluted regions.
• If you want to use a narrow band filter (e.g. H-alpha) but you have a dual chip CCD or just an AO-7/AO-8 adaptive optics as guiding equipment, your guiding chip will be in almost total darkness... But TDM will help.
• If you have just a tiny guiding chip at the bottom of a small aperture tube, you probably will not always be able to find an appropriate guide star... TDM will help you again.
• TDM together with AO-7/AO-8 adaptive optics is the best equipment that you can have!!! TDM will eliminate the periodic error of your mount (independently of the magnitude of its amplitude) and AO-X will eliminate the rest of the deviations like scintillation and/or refraction. This is the ideal, ultimate set of serious astrophotographers!
• Who is not satisfied with his/her mid-ranged telescope mount's tracking ability but does not want to spend another couple of thousands of euros/dollars for a top rated one (which has much more PE then TDM...), those will appreciate this cheaper solution.

Cheers

Dennis

[bojan]

If someone is really annoyed by the presence of PE, in my opinion the much more cost-effective way to minimize it is illustrated here:
http://groups.yahoo.com/group/EQ6/ph...78408/pic/list
To polish the worm, there is no real need for lathe, it can be done with simpler, ad-hoc arrangement.
Also, the replacement of original gearbox (or total elimination of gears between motors and worm gear by using timing belts) does help a lot, some reports are talking about 5"pp and even better (for EQ6).

However, as Peter said, all this *will not* correct for items on his list.
So, all this effort does not make much sense .. when at the end, some sort of guiding is still needed for longer focal lengths imaging.

This discussion reminds me of a similar thread, about direct drive stepper motors on both shafts.. like ideal solution for ideal mount. Yes, we can and we should aim for the better.. but we have to take into account the cost of this, sometimes irrational urge... IMHO of course.

[multiweb (Marc)]

I read this thread and the cloudy night forum with great interest. It's quite a revolutionary approach to guiding. I have to join the skeptics though
We look at the sky and we guide accordingly in reference to what we're imaging right? Putting aside what Peter already pointed out that we have orthogonality problems, wind, flop, flexure, etc... you name it: still if we had resolved all of the above it would still be like being bolted solid to a boat deck and taking pictures of the sky right? I mean, you can't compensate only one RA rate when there are so many other variables at work? Sounds just like common sense to me to use the stars as a reference?

[Dennis]

Originally Posted by Peter Ward

Arrgh..... so are there really people out there that will pay "1000EUR + shipping + VAT"...

Yes – at least one person on CN!
It appears that the owner of the GPDX in question seems quite pleased with:
“The PE on my mount is typically +/- 15-20arcsec, the TDM can reduce this down to +/-1 arcsec without any significant setup effort”.

Originally Posted by Peter Ward

But...by crikey...the constancy of RA shaft rate is brilliant!

Hmm, does my radar require re-calibrating, or is it picking up the sparks from the grinding of an axe?

Cheers

Dennis

[Peter Ward]

Originally Posted by Dennis

Yes – at least one person on CN!

PT Barnum, of Barnum and Baileys circus had a great saying:

"We've got a little something for everyone"

........ (like Fornax 50, 51, 100, 150, Synta EQ6, SkyWatcher EQ6, Orion Atlas G, Celestron CGE, Astro-Physics 1200, Losmandy G11 owners?? )

Now looking at the "happy" CN reviewer's linked data for this device


http://www.cloudynights.com/ubbthrea...t%20090109.jpg


we see, despite some impeccable RA tracking, there is close to half an arc minute of Dec drift in 1200 sec (!!)


Barnum had another great saying: "There's a sucker born every minute"

[Dennis]

Originally Posted by Peter Ward

Barnum had another great saying: "There's a sucker born every minute"

Peter, thanks for confirming that my radar does not require calibration.

Cheers

Dennis

[Wavytone]

Originally Posted by Dennis

“ the TDM can reduce this down to +/-1 arcsec”.

Another very dubious claim. Very few telescope owners have the foggiest idea what order of magnitude their PE is, and even fewer have the ability to measure it accurately.

Many here need to be reminded that the US does not have any laws about misleading advertising and manufacturers can and will say anything.

As for the CN "review" that could have been posted by the designer of the device, for all we know.

[AndrewJ]

“ the TDM can reduce this down to +/-1 arcsec”.
Another very dubious claim.

With my Mech Engineer hat on,
if the encoder used is of good enough accuracy, and the motor feedback loop quick enough, this claim is probably valid,
but getting a perfect RA Axle "tracking rate" doesnt help synchronise the "entire mount" to the sky, which is where all the argument comes in.
An absolute encoder on the RA shaft will certainly "proactively" remove the bulk of PE and backlash from the drivetrain, but some form of guiding ( albeit now much smoother ) will still be required to give round stars
And its round stars that count.

Andrew