Officina Stellare RC360 Pro ... has arrived!!

[marc4darkskies (Marcus)]

Originally Posted by SkyViking

I wonder what they put in those scopes to make them so heavy? Is the construction lightweight, or does it just not matter on the big mount?
Btw, is that with or without counterweights...? If you have another 45kgs of metal sitting at the other end of the shaft then the inertia must be quite a bit when making fast guiding corrections. What guiding frequency to you plan to use?

Just for comparison, although mine is a bit smaller at 12.5" it's weighing in at 16kgs which rides very smoothly on the Losmandy G-11 I figure a 14" version would push it to maybe 18kgs.

Hope to see your first deep image soon Marcus

Thanks Rolf! Yes, you're spot on. Guiding frequency has a lot to do with it. The stiffness of the spring plungers is only part of the solution. My default minimum period was 2 seconds in CCDAP (way too quick), but have now increased that to 5 sec and reduced aggressiveness. I will probably increase the guide period further when I start imaging and/or guide stars are scarce - the PME doesn't need guiding that fast anyway. I have also yet to add the AO-L into the equation which will eliminate at least 95% of mount based guiding corrections (depends on polar alignment).

The bare weight of the OTA is 34kg and I have another 11 or 12 (as near as I can figure) in imaging train plus other accoutrements. So yes, the total payload is 90kg - a lot of inertia!

[White Rabbit]

OMG, this thread has been the biggest tease of the century. Hurry up and get yir kit off and show us some images already....

[SkyViking (Rolf)]

That's interesting Marcus. Although there are different schools of thought I'm personally in favour of fast guiding corrections. Except of course if you use AO so it doesn't matter, which you plan to do anyway
In my case (no AO) I typically guide at ~2 Hz (0.5s), and then only increase the guide exposure if the graph is not behaving well (this depends on seeing and wind), but always keep it between 0.5s and 1.5s.
Or put another way, if the guide star has moved then I don't want to wait, say, 5 seconds for an exposure before corrections are sent to the mount.

[strongmanmike (Michael)]

Originally Posted by SkyViking

That's interesting Marcus. Although there are different schools of thought I'm personally in favour of fast guiding corrections. Except of course if you use AO so it doesn't matter, which you plan to do anyway
In my case (no AO) I typically guide at ~2 Hz (0.5s), and then only increase the guide exposure if the graph is not behaving well (this depends on seeing and wind), but always keep it between 0.5s and 1.5s.
Or put another way, if the guide star has moved then I don't want to wait, say, 5 seconds for an exposure before corrections are sent to the mount.

Same here, usually stick with 2 sec as a rule, only when the seeing (or in the dreaded past THE WIND) is bad have I upped it to 3 or 4 sec

Mike

[SimmoW (SIMON)]

Originally Posted by White Rabbit

OMG, this thread has been the biggest tease of the century. Hurry up and get yir kit off and show us some images already....

Ha, corr, Astroporn!

[ericwbenson (Eric)]

Originally Posted by marc4darkskies

Guiding frequency has a lot to do with it. The stiffness of the spring plungers is only part of the solution. My default minimum period was 2 seconds in CCDAP (way too quick), but have now increased that to 5 sec and reduced aggressiveness.

Actually the integration time for the guider does not affect how fast the correction is applied. The "guide speed" of the mount is what determines the motor velocity, the angular distance is controlled by the length of the correction. So many small corrections can be better than fewer large ones.

When I had the PME under the 20" the guiding was ok, if not exceptional, if the wind was still. But too much breeze (even with a dome) would push the scope and stretch/sqeeze the mount components resulting in bad guiding. And worse often I think it would oscillate in RA, which is more cantilevered than DEC (7 x 20lbs counterweights on the extended shaft will do that !!!) So the PME is a great mount, but not impervious to aperture fever.

Best,
EB

[marc4darkskies (Marcus)]

Originally Posted by ericwbenson

Actually the integration time for the guider does not affect how fast the correction is applied. The "guide speed" of the mount is what determines the motor velocity, the angular distance is controlled by the length of the correction. So many small corrections can be better than fewer large ones.

When I had the PME under the 20" the guiding was ok, if not exceptional, if the wind was still. But too much breeze (even with a dome) would push the scope and stretch/sqeeze the mount components resulting in bad guiding. And worse often I think it would oscillate in RA, which is more cantilevered than DEC (7 x 20lbs counterweights on the extended shaft will do that !!!) So the PME is a great mount, but not impervious to aperture fever.

Best,
EB

You're quite right to remind me of the guide speed - something I hadn't adjusted yet - thanks. Yes, I know the guide period has no effect on on guide speed - the theory was that if the mount is oscillating in RA then it will spend less time oscillating with a lower guide frequency. As it happens I've reduced, but not eliminated the elongation, so guide rate might be the clincher. Once I've got everything right I'll do a large model and activate protrack as well.

[Joshua Bunn (Joshua)]

By ''guide rate'' do you mean the aggressiveness of the guide corrections?

[gregbradley]

Never considered changing the guide speed. That could be worth checking out.
For what its worth I find best results vary when it comes to guide exposures.
In poor seeing I get better results with fast corrections like 2 seconds. On a stable night 5 or 6 works well.

I got better guiding with a 300point t-point model and Protrack activated as well as PEC and autoguiding. Which is what I use now.

I think a Pempro PEC curve might even tweak it a tad more compared to Precision PEC or Sky X.

If you are getting oscillating guide errors my suggestion is to make your balance slightly off to the east to load the gears a tad so the backlash doesn't cause a bing bang effect. That worked on my PMX when I encounter that which I have the last 2 times I used it.

Greg.

[marc4darkskies (Marcus)]

Originally Posted by Joshua Bunn

By ''guide rate'' do you mean the aggressiveness of the guide corrections?

No. The guide rate is the speed of the correction that is applied to the telescope's position expressed as a fraction of the sidereal rate. The default rate for SB mounts 0.5. I.e. on the RA axis this means that the tracking rate will change to either 0.5 or 1.5 times the sidereal rate depending on whether the tracking error is west or east. On the Dec axis corrections will be +-0.5 times the sidereal rate. Aggressiveness is the proportion of the computed correction that is applied. I.e. a 1 second computed correction will be only a 0.6 second actual correction if aggressiveness is set at 6 (10 = full correction applied) ..... I think! .

Originally Posted by gregbradley

If you are getting oscillating guide errors my suggestion is to make your balance slightly off to the east to load the gears a tad so the backlash doesn't cause a bing bang effect. That worked on my PMX when I encounter that which I have the last 2 times I used it.

Greg.

Tried that with no effect. There is no backlash per se. My theory is that this is more a vibration set up when starting and then stopping (via a guide correction) a large mass. The measures I've taken support this theory - adjusting the spring plungers (small effect), reducing aggressiveness and increasing guide period. I suspect now, if I'm right, that correct guide rate + aggressiveness settings will solve the problem. However, I won't do any more testing until I've got my collimation sorted out.

[gregbradley]

Tried that with no effect. There is no backlash per se. My theory is that this is more a vibration set up when starting and then stopping (via a guide correction) a large mass. The measures I've taken support this theory - adjusting the spring plungers (small effect), reducing aggressiveness and increasing guide period. I suspect now, if I'm right, that correct guide rate + aggressiveness settings will solve the problem. However, I won't do any more testing until I've got my collimation sorted out.[/QUOTE]

Was adjusting the spring plungers hard or easy? I should look at that. Is it in the manual or is there a paper about it?
Yeah that was only on my PMX not PME. I am running similar or more mass and I use aggressiveness at 6 and with good seeing and no reducer but with MMOAG 6 second guide exposures with PEC. Min move .1 max move 2. I get round stars routinely. With guide scope and reducer I have to be a little careful of flexure but as long as guide scope is locked down hard I get round stars 10minutes, occassionally a small amount of elongation in 10 minute subs. Enough for me to consider an OAG/FW thin combo from Starlight Express at some point.

With Protrack I got an additional slight gain.

Greg.

[Joshua Bunn (Joshua)]

Originally Posted by marc4darkskies

No. The guide rate is the speed of the correction that is applied to the telescope's position expressed as a fraction of the sidereal rate. The default rate for SB mounts 0.5. I.e. on the RA axis this means that the tracking rate will change to either 0.5 or 1.5 times the sidereal rate depending on whether the tracking error is west or east. On the Dec axis corrections will be +-0.5 times the sidereal rate. Aggressiveness is the proportion of the computed correction that is applied. I.e. a 1 second computed correction will be only a 0.6 second actual correction if aggressiveness is set at 6 (10 = full correction applied) ..... I think! .

Thankyou Marcus

[rat156]

[QUOTE=marc4darkskies;1055591 My theory is that this is more a vibration set up when starting and then stopping (via a guide correction) a large mass. The measures I've taken support this theory - adjusting the spring plungers (small effect), reducing aggressiveness and increasing guide period. I suspect now, if I'm right, that correct guide rate + aggressiveness settings will solve the problem. However, I won't do any more testing until I've got my collimation sorted out.[/QUOTE]

Hi Marcus,

By your own post earlier, you don't actually start or stop the mount in RA when guiding unless the guiding rate is set above 1, which would be silly to do, the mount slows down or speeds up only, so this should not cause oscillation. Don't forget to do the calculations to work out you minimum guide correction, depends on your image scale, it's something many people have set way to small.

http://www.ccdware.com/resources/autoguidercalcv4.cfm

Cheers
Stuart

[marc4darkskies (Marcus)]

Originally Posted by rat156

Hi Marcus,

By your own post earlier, you don't actually start or stop the mount in RA when guiding ...

Pardon my imprecise language Stuart! I meant starting and stopping a guide correction or better, speeding up / slowing down tracking!!

Originally Posted by rat156

... Don't forget to do the calculations to work out you minimum guide correction, depends on your image scale, it's something many people have set way to small.

http://www.ccdware.com/resources/autoguidercalcv4.cfm

Cheers
Stuart

I appreciate this advice. I've never imaged at 3100mm and it's become increasingly clear that I need to pay more attention to tuning my guiding to achieve an optimal result - a learning experience. I confess I hadn't even realized that the minimum move setting is important. It's conceivable that if set it too low the mount will constantly be trying to apply tiny corrections, possibly contributing to artifacts.

[PRejto (Peter)]

Hi Stuart,

Thanks for pointing out that calculator!

Would you be able to post some "rule of thumbs" for the MX and various seeing conditions? (Peak to peak max allowable error & max movement)

Thanks!

Peter

[gregbradley]

Originally Posted by PRejto

Hi Stuart,

Thanks for pointing out that calculator!

Would you be able to post some "rule of thumbs" for the MX and various seeing conditions? (Peak to peak max allowable error & max movement)

Thanks!

Peter

Interesting calculator. I plugged in some figures for my setup and it said .5 min move. I normally set it to .1. That mean more corrections are taking place than may be needed. I'll try that out tonight with .5 to see if I can see a difference on my PME (about to start imaging).

This is with both PME and PMX. I usually set max move to 2 as I find prolonged guide errors greater than 1-1.5 result in unacceptable stars.

With poor seeing I have gotten good results going either way. Shorter exposures with more rapid corrections and also with longer exposures hoping the seeing fluctuations don't last that long. So a bit inconclusive. Perhaps raising the min move in poor seeing would be another tool to battle it rather than only adjusting guide exposure length like I have.

Greg.

[rat156]

Originally Posted by PRejto

Hi Stuart,

Thanks for pointing out that calculator!

Would you be able to post some "rule of thumbs" for the MX and various seeing conditions? (Peak to peak max allowable error & max movement)

Thanks!

Peter

I'd love to Peter, but it all depends on the your image scale. I'll note down my settings next time I'm imaging, that's about all I can do. I'm by no means an expert on this. If we all share our guiding settings and the reasons for them we may all be able to gain experience and come to some consensus, probably in a new thread though.

Cheers
Stuart

[gregbradley]

Just by way of feedback. I used that calculator for my CDK and Trius. I set the min move to .5 like it recommended up from .1 that I normally use. It worsened the images quite a bit. My guide errors even with PEC and Protrack on are .05 to .3 for 80% of the corrections and the rarely over .5. So that meant it was not being corrected for 85% of the time if not more.

The bottom line very often with these types of calculators etc is its hard to beat empirical testing - ie. the actual performance as opposed to a theoretical. Trial and error whilst slow tends to get you involved and you know what is best for your system under various conditions.

For my PME with a guide scope at 2 metres its 2 second guide exposures, .1 min 2 max move. aggressiveness 6.
At 3 metres and a MMOAG it is 5 or 6 second guide exposures and same min/max.
Both with PEC and Protrack (300 point model) on.

For PMX I use about 5 second exposures with MMOAG, 6 or 7 aggressiveness, .1/2 min/max at 1260mm focal length and PEC on (no Protrack as I don't have a good enough model yet). If its a bit windy I would reduce guide exposures to 2 secs. No delay on any of these. Direct guide on all of them. Quite an accurate polar alignment on both and of course this is the first step to get perfect and worth the effort.

Greg.

[marc4darkskies (Marcus)]

Just a short recap.

I'm about a month behind but it's been well spent learning new things. Hopefully by the time the moon has gone I'll be imaging!

Here's a list of the things I've had to think about & address:

Stray light issue: Resolved:

• OS primary baffle add-on (pending delivery)
• Flocking and a couple of makeshift ring baffles

Guiding issues: Resolved. The guiding artifacts observed were never visible with shorter FLs of the TOA-150 and can easily be hidden by seeing. At 3130mm and at the image scale of the internal guider - a TC-237 built into the STL (0.98 arcsec/pixel (binned 2x2)) - any issues stand out like dogs b*lls:

• Spring Plunger stiffness adjustment because of increased payload (45kg)
• Auto-guide tuning - increase the minimum move from 0.01 to 0.2 arcsec
• Auto-guide tuning - PME guide rate reduced from 0.5 to 0.3 x sidereal
• Auto-guide tuning - Aggressiveness. Not so much a change but a greater awareness that this can be variable depending on conditions
• PME tracking rate too fast(??!!) Stars constantly drifting west - quite rapidly. I had noticed this before using the Tak but let it be guided out. At the longer FL it's now very obvious. Reducing the rate to 99.85% eliminated all residual drift in RA. I've seen others report this on the SB site but they were dismissed with the catch-all recommendation to invoke Protrack to remove polar alignment issues
• Redo PEC training
• Still need to redo TPoint model and adjust mount altitude to remove dec drift.
• Still need to invoke ProTrack and see if this addresses part or all of the tracking rate issue mentioned above (if I restore it to 100%)
• Attach the AO-L and do some proper guiding!

Collimation: Almost resolved

• Really a result of my ignorance on how to collimate. Now gradually homing in on the optimal settings after ruining the initial factory settings. Learning how to use the Takahashi Collimation scope has helped a lot.

Tilt of the imaging train - not sure if this is a problem yet - will know when all of the above are put to bed

Hardware & software: Amost resolved.

• I had to get the OTA, Atlas, Pyxis Rotator working in TheSkyX and CCDAutopilot. Most of this was pretty easy but have been spinning my wheels on the rotator + CCDAP integration (can't seem to remove an offset).

Lappy BSODs:

• A simple overheating issue - probably because of a greater load on the CPU (?). Easily fixed by better ventilation. A very annoying distraction though!!

This was a big migration for me from the ultra simple days of imaging with the TOA (relatively light, perfectly collimated and short focal length). I underestimated the time and effort required, especially having to hold down a demanding job and being slave to the weather . As a result I can safely say that this kind of upgrade is not for the faint of heart or the impatient!!

A big thank you to those who have contributed their thoughts & suggestions along the way!

[gregbradley]

Did you see much improvement increasing min move from.01 (very low anyway) to .2?

I changed mine from .1 to .5 and it made things worse by quite a bit. But that's a more subtle change. It implies minor errors .2 and below are not really errors at all that can be guided out? Or are below the seeing so it could be just as easily as seeing rather than a gear imperfection?

Greg.