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

[Dennis]

This looks like a very interesting add-on product; Telescope Drive Master, offering 1 arc-second tracking ability without using conventional auto-guider or PEC software!!!

Some parts of the website are still under construction and the outfit appears to be based in Hungary although I understand they have some commercial arrangement with Meade in Europe?

The Telescope Drive Master Encoder/Black Box product appears to be available for the following mounts at the time of this post:

• Synta EQ-6 non-goto or goto / Skywatcher EQ-6 Synscan / Orion Atlas EQ-G (both old and new versions)
• Synta HEQ5 /Skywatcher HEQ5 / Orion Sirius EQ-G
• Celestron CGE
• Fornax 50 / 51 / 100 / 150
• Astro-Physics 1200
• Losmandy G11 (both old and new versions)
• Meade LXD 75
• Vixen GPDX

Visit the website for more specific details on the Synta products listed above.

Cheers

Dennis

[acropolite (Phil)]

Looks like an exciting new development Dennis, hopefully the pricing will be affordable.

[bojan]

I do not think it will be affordable.
This is the closed loop system with high resolution encoder directly on RA shaft, nothing new in principle, but never cheap (because of the price of such encoders).
Classic guiding (with additional telescope and camera) is still a good enough and cost effective solution for amateurs.

[Peter Ward]

I read the manufacturers website with some interest.

I remain very skeptical however.

A super accurate RA shaft rate simply does not make a perfectly guided image.

I have seen stars randomly drift in RA *and* Dec for various reasons, and while RA rate errors are one cause, there are many others, well like: refraction, convective cells, mirror flop, differential flexure, wind buffeting
and thermal expansion/contraction of the telescope and telescope mount components, plus sag in the camera mountings etc.

In short, if you think one of these new wunderkind devices will deliver perfectly round deep sky stars at 2500+ mm... with no guiding...I think you'd also be in for a big disappointment.

[Wavytone]

This isn't a helpful solution. The website also shows the author has a very naiive understanding of the causes of tracking errors.

- it assumes a stellar rate only, it makes no provision for lunar or solar rates; most good drive correctors from 30 years ago could do that;

- it doesn't have any ability to track in declination, ie it is not able to cope with a mount that is not perfectly aligned with the pole. The effects of refraction mean it is impossible to eliminate the need for declination tracking at all parts of the sky. This alone makes it useless as to solve this you will have to use another drive corrector for declination;

- it has no capability for fine adjustments even in RA. Which also makes it useless.

- it makes no corrections for geometric errors in the mount (angles that are not perfect right-angles);

- it makes no corrections for atmospheric refraction;

- it makes no corection for the flexure of the mount and telescope assembly - which may change during an exporure if these are cooling or warming;

- there is no adequate explanation as to how it compensates for periodic errors in the geartrain.

It might be adequate for driving an equatorial platform for a Dob being used visually, or perhaps a small mount with a piggyback camera with a short lens taking short exposures of a few minutes, but thats about all.

A closed-loop feedback system (autoguider) solves all of the above.

[allan gould]

Interesting but the caveats of Peter and Wavytone are well made. A good autoguider and software will probably be cheaper in the long run

[Dennis]

Originally Posted by Peter Ward

In short, if you think one of these new wunderkind devices will deliver perfectly round deep sky stars at 2500+ mm... with no guiding...it think you'd also be in for a big disappointment.

Did you see the following example on the website?

E.g. the attached photograph below (NGC1161) was captured by a 10 minutes' (!) long exposure using a 16" LX200R OTA (and SBIG ST-8) with 2.5m (!) reduced focal length on around 70 degrees horizon altitude without conventional autoguider and, as you can see, the shape of the stars are free of any kind of visible elongation or distortion.

Cheers

Dennis

[Wavytone]

Originally Posted by Dennis

without conventional autoguider

That claim is simply not credible as anyone with some astrophotography experience (i mean manually guided film shots) should know.

[Dennis]

Originally Posted by Wavytone

That claim is simply not credible as anyone with some astrophotography experience (i mean manually guided film shots) should know.

The claim was made by the author on the website and an image was provided as evidence to substantiate the claim. Maybe it was a fluke or maybe only someone with advanced skills or a certain set up can do this? However, I have no reason at this stage to question the authenticity of the claim or the image.

Cheers

Dennis

[Peter Ward]

Originally Posted by Dennis

Did you see the following example on the website?

the shape of the stars are free of any kind of visible elongation or distortion.

Cheers

Dennis

Yes, of course.

Bisque also have a similar shot on their PME website, but either shot proves very little...other than on a good night you can jag round stars at long FL's. In reality it simply doesn't always work that way.

Autoguiders are a very inexpensive, effective and proven solution
for the reasons already mentioned.

[Peter Ward]

I think it's also worth mentioning here there is much more to a mount's suitability for astro-imaging than an super accurate RA rate.

High machining accuracy, mechanical stiffness and high natural frequency of vibration are...pardon the pun..paramount. Having a super accurate drive on a bowl of jelly is simply a recipe for astro-imaging misery.

[Dennis]

Originally Posted by Wavytone

- it assumes a stellar rate only, it makes no provision for lunar or solar rates; most good drive correctors from 30 years ago could do that;

From the authors website:

"If the angular velocity of the RA shaft deviates from the prescribed (sidereal or King Rate) velocity value, it accelerates or delays telescope's driving clock. In this way, a high precision, feedback regulated, real-time rotational speed control has been created. Corrective action happens via autoguider input port of telescope's driver unit if its own."

I thought that the King Rate was the drive rate taking into account atmospheric refraction? However, the author does go on to write:

“if you are hunting just about 25-30 degrees above the horizon (and far from the local meridian) with a 1000-1200mm APO refractor, you will be able to apply around 1 minute exposure time only due to the exponentially increasing refraction rate at low altitudes”.

Maybe he's referring to those higher altitudes at which advanced imagers normally image at?

Cheers

Dennis

[Dennis]

Originally Posted by Peter Ward

I think it's also worth mentioning here there is much more to a mount's suitability for astro-imaging than an super accurate RA rate.

High machining accuracy, mechanical stiffness and high natural frequency of vibration are...pardon the pun..paramount. Having a super accurate drive on a bowl of jelly is simply a recipe for astro-imaging misery.

Which is probably why the author, in the documentation on the website writes?

"It is not rational (and no cost-effective at all) to purchase TDM for low priced and weak quality beginner mounts. At the same time, if you have a sturdy and rigid hi-quality or semi-pro mount, the price of TDM is just on a gadget-price level. (The weakest mount which can be rational to use with TDM is the Synta/SkyWatcher EQ6 or Orion Atlas EQ-G. This is why there is no TDM adopter offered for cheap mounts.)"

Cheers

Dennis

[Zuts]

Originally Posted by allan gould

Interesting but the caveats of Peter and Wavytone are well made. A good autoguider and software will probably be cheaper in the long run

Maybe, my autoguiding setup runs to nearly 1000 AUD. It still has differential flexure and adds over 2kg plus cables to the imaging rig.

Orion autoguider AUD 469
102 mm achro AUD 250
side by side losmandy mounting AUD 300

Also I have to set it up, it requires a laptop connection etc. If this item was around AUD 1000 I may be tempted to sell my autoguiding gear.

I have a self guided camera but need the autoguiding for Ha shots; and believe me its a joy to use the self guiding on the SBIG without the hassle of connecting all the autoguiding stuff; and this to me seems an equally simple solution for non SBIG cameras or narrowband shots; depending on price and suitability.

Cheers
Paul

[Dennis]

Originally Posted by Wavytone

It might be adequate for driving an equatorial platform for a Dob being used visually, or perhaps a small mount with a piggyback camera with a short lens taking short exposures of a few minutes, but thats about all.

From what the author has written, I would expect the system to be more capable that this, given the limitations he has addressed below:

"Unlike different conventional autoguider systems, Telescope Drive Master does not need and does not have any feedback from the sky during tracking. This means you need to minimize the mechanical and adjustment problems of your telescope OTA, mount and pier such as mirror flip, tube & mount flexure, dirty and improperly installed RA bearings, swinging cables of CCD & power supplies on OTA, instable and moving pier as the most common problem sources and, finally but chiefly, inaccurate polar alignment.

If you want to achieve less than 1" (arc-second) tracking error during your 5 (maybe 10) minute exposure on "photometric altitudes" of the sky (zenith distance is less than 40-45°) without position-corrections, you need to keep the axis of the RA shaft on the (refracted) pole (see explanation below) with the best accuracy you can achieve."

Cheers

Dennis

[Peter Ward]

Originally Posted by Dennis

From the authors website:

"If the angular velocity of the RA shaft deviates from the prescribed (sidereal or King Rate) velocity value, it accelerates or delays telescope's driving clock. .........

Dennis

The flaw in this system is it simply isn't looking at deviations at the imaging sensor level.

Perhaps they use a direct coupled encoder, or they couple the system via intermediate gears, either way there are still eccentricity, indexing and periodic errors.

The only way these can be accounted for is to accurately measure deviations against the sky, not the RA shaft.

[Dennis]

Originally Posted by Peter Ward

The flaw in this system is it simply isn't looking at deviations at the imaging sensor level.

Again, as the author openly acknowledges:

:There is no optical feedback from the certain part of the sky observed so your telescope needs to have a sturdy and rigid mount which is not cheap. (This system is insensitive regarding flexure of mechanical parts and weak quality RA bearings.)"

Cheers

Dennis

[Dennis]

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

All alone, sitting quietly at my desk, here is Uncle Dennis’ train of thought:

I found a new astronomy gadget – I think, “Gee, this looks like an interesting product, I’ll post a link on Ice In Space to see if anyone is using one and to see what others may think of the approach”. What happens next?

• I read some replies that say it cannot do certain things yet when I look at the website, there is evidence that is appears to work as described.
• I also read some replies that appear to “find fault” with the system and, maybe its how I interpreted the post, appear to “rubbish” the system. But upon further reading of the website, the author himself acknowledges those limitations.

Maybe it’s just me, but it seems the product appears to have been too strongly denounced, in quite forceful terms, prior to having seen any tests or results?

Cheers

Dennis

[Zuts]

Originally Posted by Peter Ward

The flaw in this system is it simply isn't looking at deviations at the imaging sensor level.

Perhaps they use a direct coupled encoder, or they couple the system via intermediate gears, either way there are still eccentricity, indexing and periodic errors.

The only way these can be accounted for is to accurately measure deviations against the sky, not the RA shaft.

Other people including Qui of QHY are looking at similar solutions so they must think these 'absolute' methods have some credence. In any case I wouldnt want to buy the first unit but if after reading some independant reviews it was found to perform as advertised then i would probably buy one, and at the risk of naming names I bet Houghy would!.

[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 only by RA shaft rate correction.

I've found just he opposite to be true.

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