OAG or Gude Scope Poll

[Bart]

I thought I would run a thread and get an idea of how many use OAG or guide scope and who uses ST4 or pulse guiding.

[Peter.M]

OAG, and pulse guiding for me. Nothing better than registering 30 minute subs from a chinese mount and them being within 1-2 pixels of each other due to dithering.

[frolinmod]

When I voted I assumed PulseGuide and Directguide are the same thing (i.e., not using an ST4 cable).

[Rod771]

OAG for long focal lengths (C11 - 2800mm and 1960mm with reducer)

Just bought the Orion mini guide scope for guiding with the Hyperstar lens.

Camera - SX Lodestar

ST-4

[Bart]

I guess it is the same, there are only two ways that I know of. :)



Interesting. I have often heard that it is not worth an OAG on faster scopes. :thanx:

[Bart]

So far I think the results are very informative.

I am surprised at the low use of PEC. I know that EQMOD does suggest that PEC is better used with pulse guiding than ST4.

Is this correct or is it that people are unsure of PEC and its properties/value or even how to create and use it?

[Rod771]

Nothing fast about F10 or F7, I use the OAG at these ratio's.

I just started using the guide scope to guide at F2 (Hyperstar)

[PRejto]

I cannot see any reason why PEC would have anything to do with guiding other than to improve guiding by making fewer corrections possible. Why would the use of PEC make one method of guiding (relays or direct) better?

I'm going to guess that the statement from EQMod is possibly misinterpreted. I think direct quide has advantages over relays whether PEC is on or off. Turning on PEC probably increases the advantage but I still fail to see how it could hurt relay guiding.

Peter

[Bart]

Hi Peter,

I think you like you, I cannot see it as being a problem, I would have thought it better to use PEC than not. Here is an excerpt form the EQMOD guiding section.

Do PEC and AutoGuidng fight?
Running PEC and autoguiding simultaneously should, in theory, deliver the best of both worlds. The PEC
keeps the mount on track. The only errors observed are non periodic ones which the autoguiding makes
corrections for. Many folks are successfully using PEC and autoguiding.
So where does the widely held opinion that PEC and Autoguiding fight come from? The answer lies in how
ST-4 and/or PulseGuiding has actually been implemented for your particular mount – here's why:
Consider the case where PEC is doing its job and keeping the guide star centred. To do this
PEC is overriding the mounts tracking rate. The Autoguiding software however is totally
unaware of any rate corrections made by PEC it assumes that the mount is tracking perfectly by
itself.
Now consider what happens if a “non periodic” error occurs. The Autoguiding software see the
error and when it deems it significant will calculate a pulse duration needed to correct it.
Remember this correction is being made in response to an error observed with PEC already
active and potentially already making a significant correction of its own. The Autoguiding
software issues its correction by setting the appropriate ST-4 signal. This is where it all goes
wrong. As soon as the mount sees the ST-4 override it moves at a fixed “preset guiding rate”.
Any existing speed correction made by PEC is immediately lost and, because the autoguiding
software has no knowledge of PEC, the ST-4 correction made will not be sufficient to hold the
guide star on track. Effectively we have introduced a step change into the closed loop
autoguiding system. In due course the autoguiding software should be able to recover the
situation by making further corrections but now it is having to correct for periodic error as well.
Eventually the guidestar is brought back on target at which point control passes back to PEC.
Some folks assume that all that is happening is that PEC is lost for a short period whilst autoguiding takes
over and that having PEC operating 80% of the time must be better than not having it at all. What they fail to
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The EQMOD Project
EQASCOM & AutoGuiding
take into account is the level of disturbance to the control system that occurs whenever ST-4 corrections are
made. This can result in a greater error than would have occurred if simply using autoguiding alone.
Although ST-4 is used in the example above the same problem could also apply to ASCOM Pulse Guiding.
The key is in the implementation. In order for Guiding and PEC to operate together the guiding rate
corrections must be made as relative corrections to the PEC tracking rate rather than as absolute rate
overrides.
If your mount/driver cannot provide relative corrections then PEC+Guiding is not a useful combination (those
selling PEC applications may try to convince you otherwise, but then they would wouldn't they!).
For those using the EQMOD EASCOM driver the good news is that the Pulse Guiding implementation
has been carefully designed to work alongside PEC. I would not however advise the use of PEC with
ST-4 guiding for the Synta mounts.

Thanks for dropping in and having a say,

Bart. :)

[PRejto]

Hi Bart,

Thanks for posting that info from EQMod. It is most interesting, and as a result, I probably stand corrected in my first post saying perhaps that their info had been misrepresented.

I wonder if high end mounts running off TheSkyX are also possibly subject to this effect? I would imagine not everyone would agree on this subject!

Peter

[Bart]

Hi Pete, everyone that voted,

Thanks for taking the time to stop by. I have seen quite a bit of info in the results and will move forward from here.

Have a great weekend,

Bart. :thumbsup::thanx::D:)

[Bassnut]

You bet not everyone agrees on this subject!.

To Guiding and PEC, now add Tpoint super model. 3 feedbacks all at once :P.

That EQmod response is very interesting.

Anicdotally, some say (say on a PME), alls good, all work together in majic harmony and produce amazing results for them, others much smarter than me say nope, all 3 together are a problem and dont work, they fight each other. Statements like "PEC is for high freq corrections, supermodel for low freq", are bull I say, sounds good, but unless there is some really fancy control going on doesnt make sense for a bunch of reasons to hard to mention in short.

That EQmod response is the 1st proper technical explanation ive seen on guiding/PEC conflicts. I have yet to see the same for a guiding/PEC/pointing model combo.

[gregbradley]

After I did a 300 point -point model and turned on ProTrack I did see an improvement in already excellent tracking. That was already using PEC and an OAG. That was on a PME and using Sky X supermodel function.

I see an improvement from PEC, Protrack and of course an OAG has given me the best autoguiding of any setup. OAG can be a pain in terms of backfocus distance, weight but they work really well and once setup tend to be a set and forget sort of accessory.

Greg.

[Bassnut]

Many have found that it all works Greg, many others havent. Your lucky.

Its possibly a set up issue for those that it doesnt work for.

Id like to see a proper description of how for instance protrack makes a mount correction for the next exposure, and guide (and PEC) also make seperate counter corrections. That is say guiding via DL says move this much via ST4 and Sky is doing something different. Id like to know if they constantly communicate the corrections they both have in mind to each other..(am I wrong?) "frequency" is irrelavent IMO, correction per guide exposure is the same frequency for all.

[LewisM]

Guidescope / ST4

Used to dither, don't now, may again.

My Vixen GPD2 mount tracks so accurately, I can blink 4 hours of subs and there will be no noticeable movement between each sub (stacking is a BREEZE - everything is just about already lined up!). Not the best for noise reduction, but that mount sure impresses me. Now I found the settings for mount settle in MaxIM after dithering, i am going back to 0.5 pixel dither.

[Nico13]

Just in the middle of altering all this, going away from the SBS with the RC8 and ED80 with piggy back ST80 guide scope.
That's been fun but getting a bit more serious now.
First stop is RC8 with ED80 rigid piggy back guide scope with SX Superstar camera. Check the improvemments
Option two is OAG with the SLR interchangable between scopes for some wider field through the ED80. Check for improvements again.
If still not happy look at implementing PEC.
Step by step we'll see how it goes.

[LewisM]

My guidescope is rigidly mounted in non-adjustable rings. I use a Lodesar camera. Not a single solitary issue.