What sort of tracking performance can you achieve?

[g__day]

I curious what sort of tracking performance folk achieve, particularly if they use permanently mounted gear.

Using a C9.25 (plus two other scopes) on a Vixen Atlux I check tracking by taking 3 seconds shots of a star - one minute apart for an hour or two and see how much drift occurs (with no guiding on the mount).

After PE correction I generally hope to see less than a stars diameter in drift over an hour- so for me that is about 12 arc seconds of drift an hour. What sort of tracking performance do folk experience here when their gear is set up well?

Many thanks,

Matthew

[g__day]

No one wants to try this and post what they get - image the moon to get your scale, track Achernar for an hour or two and report how much drift you have RA and DEC by type of mount so we develop a resource - how well users mounts perform tracking wise?

[Starkler]

To gain meaningful results you would need to have perfect polar alignment:shrug:

[bojan]

It seems most people guide... so tracking error is irrelevant.
However, the imperfect polar alignment contribution should be possible to take into account, it will manifest itself as a drift in one direction - easily identifiable and measurable.....

Edit:
And yes, I can expose up to 30sec with standard EQ6 (no PEC), lens 1000mm, Canon 400D, without visible trailing. That means, error is less than 5" (judging by the size of star images (not overexposed)

[centroid]

I can generally expose for around 90-120 secs, with the guiding switched off, before evidence of 'trailing' starts to show.

That is with the Periodic Error Correction (PEC) switched in. (12" LX200R)

My PEC data was obtained, and calculated using Pempro.

Dave

[AlexN]

last time I tried, I ran 200 seconds unguided with my Megrez 102 + QHY8, stars appeared round to me...

Thats not to say thats the EQ6's limit, just the limit of my polar alignment..

[Lester]

With my Goliath EQ mount unguided, I can expose for 2 minutes with 14" LX200 at f6.3 without any star trailing. = FL of 2205mm

I have gone 7 minutes with FS102 and focal reducer. = FL of 690mm

[gary]

Hi Geoff,

Thanks for the post.

As I have mentioned several times before, including on IceInSpace,
the concept of "perfect polar alignment" is a myth and is widely misunderstood
by amateur observers.

Due to the effects of atmospheric refraction, there is no magic point in the
sky to which one can align the polar axis of the scope so that when the
scope rotates around the polar axis only, field rotation will no longer exist.

At best, for any one fixed point in the sky, there is a corresponding optimal
elevation of the polar axis. Unless one has an observatory at the North or
South Pole where the polar axis then corresponds exactly with the zenith.

As a whole sky compromise, it is optimal to align with the refracted pole
rather than the true pole.

However, before rushing out and adding an electrically controlled
jack that will dynamically adjust the elevation of the polar axis, which is one
way to solve the problem, or moving to the North or South Pole, which is another
way to lick it, then if autoguiding is used, the field of view not overly large and
the imaging time kept appropriately short enough, then from a practical standpoint,
there will be no problem.

But as for looking for that "perfect polar alignment", unfortunately there are
only two points on Earth from which it might be done and as for the rest of
us, like most of life, all one can do is reach some best compromise. :)

Best Regards

Gary

[montewilson]

I'm going to IIS camp this year - YEAH!!!!

Anyway I'm not planning on imaging something really difficult, no masterpieces thanks. I think I will play with new software and test new systems, chat and drink wine. So hey, why not do some tests with my Takahashi EM-200 mount?

I can turn off the corrections in both axies and see what the error readout tells me after a while.

Also Jase if you stumble across this thread, I have finally got FocusMax installed on my system and it seems to be talking to CCDSoft after I installed at that ASCOM stuff. I wont know until I get the system under the stars but here's hoping.

Also I have done something radical. I have installed a series of Nichrome heaters along the length of my FSQ tube these are controlled by two digital temperature controllers, one for the tube and one for the objective. The whole tube has been insulated with neoprene.

Why? Well now I can control the temperature of the tube down to
about 0.1 deg. That should be the end of the focus change I suffer from so much at f5 especially with demanding filters like the Ha over 20 minute exposures. I will post some pictures of the set up soon.

[AlexN]

Update - After tweaking the living hell out of it tonight in preperation for my imaging project, I ran a 7min unguided sub @ 714mm. Lovely round stars..

I am impressed with both myself and my mount. :)

[jase]

Rock on Dude! Knew you come to the dark side. @Focus/2 is good, but difficult to beat the accuracy of FocusMax. You'll hit the CFZ everytime. Look forward to seeing more of your work. If your M45 is anything to go by, you're on the money.:thumbsup:

[montewilson]

Hi Jase - Can you tellme your settings for RoboFocus / Focusmax as you and I have the same systems it will be helpful and probably save me a lot of time.

My backlash is set to 2 with final direction set to IN

Duty cycle is set to 0
Microstep pause is 8
Step size is 8

My max travel is 300

Regards

Monte

[jase]

RF Settings
Backlash: 20
Direction: In
MicrostepPause: 5
StepSize:2

Actually there are differences considering the FSQ-106N has a smaller back focus distance than the FSQ-106ED. The FSQ-106ED can accomodate additional items such as an inline third party focuser (FLI PDF) or large filter wheels and still reach focus. This difference is evident in the max travel setting. You've got yours set to 300, while mine is 1100. I could of course also configure mine to 300 - providing at some point along the 300 steps the focuser moved in and then back out of the CFZ - this is all that is important when configuring the max travel setting.

tip - If you're looking to speed up your auto focus routine, use filter of offsets.

[montewilson]

Backlash of 20? I can detect that the slack has been taken up in the cogs after 2 pulses of 8 (ie 16 microsteps) where as you are at 2x20. Interesting.

Do you know how many steps you have within the CFZ before you pass back out of it?

I have a dial gauge at work I can use to measure travel in the micron range. I will have a look to see where I am with it.

I have found that microsteps under 4 and my motor becomes unreliable. It seems to falter sometimes. 4 and above no problem.

PS what do you think about the tube temp control idea?

[jase]

Never had any backlash issues with the focuser. Keep in mind that the Q has the Tak 1:10 micro focuser - not that it should make a huge difference.

The FSQ has a theoretical CFZ of 55 micron so you've got a "little" room as you make a pass. To be honest, I've never determined how many steps it takes to move through the CFZ. Sure you could do the math based on the figures provided if you're keen.

Temp. comp. - Nice. Yes, I've used it, but don't any more. I use ACP for data acquisition which refocuses at predefined intervals or between filter changes.

Sorry to hijack the thread Matt.

[g__day]

No worries - anything that improves things for folks is good. Really I wanted this thread to be about how good you can get your raw tracking to be on various set-ups, before you overlay guiding.

Any thoughts on what folk can realistically do - and the delta - how much it improves things (raw tracking both before mods applied and after all mods implemented) - is well worth covering.

Matt

[Benny L]

never tried long un-guided exposures, but I am getting sub 1.00 pixel error according to CCD-SOFT through a 14" Meade and Losmandy Titan mount. (No PEC)