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Gabriel,? Just a note on how the ST4 guide port works as implemented in the ServoCAT.? First off both the AZ and the ALT tracking rates are changing continuously on an ALT/AZ mount. They will go from zero as, for example, AZ crosses over directly south in which case the ALT will go from UP through 0 speed and then back to down... it will of course be decrementing (on the east side of the meridian) and slowly incrementing on the west side. I believe the equivalent location in the sky for the same action only in the AZ axis is at a position of 90 - LAT in both AZ and ALT. So if you are at 40¡ã LAT it would be at a position of AZ=50, ALT = 50. Just below that in ALT and the AZ will be slowing down, just above that it will be speeding up.? Second of course if you reverse direction you will due to the nature of mechanics in gearing, introduce backlash and have to unwind the gears going in the opposite direction.? The way ST4 applies guiding is to add a fixed amount (programmed in GUIDE 2 speed value and used only when the HC is in GUIDE and the command is coming from/through the ST4 port). It does not replace the actual track rate. It simply modifies it. So if at a particular location in the sky the AZ track rate is 12.52123 arcsecs/second and the ST4 AZ GUIDE 2 speed is 10 then an ST4 command to go west (in the direction of sidereal movement) the track speed will increase to 22.52123. If the east command came in it would go to 2.52123. So it speeds up - or it slows down. NOTE however that if the ST4 rate were, for example, 15, then in one direction it would go to 25.52123 and in the other direction it would go negative to -3.47877 AND in the process lash will be introduced.? Hindsight says I should have designed it not to go below 0 speed... but it is what it is currently (and there are more than likely additional complications if it were done that way).? So you can see that ideally the GUIDE speed (ST4) values should, as well, be fluid as the AZ changes drastically going through infinity as one approaches dead-center to the zenith and passes through it. In 0 time it has to go from pointing directly east to directly west. Because of this for any and all factors related to tracking with a dob - avoid the pole! It works extremely well visually even as high as say 86¡ã Alt... but you're getting in to some very high numbers and rapid changes so from an imaging standpoint I'd stay a good distance from the pole - probably a good 10 - 15 degrees away.? If I were to do it again, now having actually used it and experimented with it... it would be different than what it is. But when i did it very few were using it (I had a handful of people that would talk about it over nearly 20 years or so). But now that CMOS cameras have made very short exposures possible (down to sub 1 second on very large apertures) it becomes something that ideally would be optimized.? I don't say this as any pressure on Bill.... he is doing fantastic work both in keeping up production as well as working on new and exciting products... but maybe a "what could I have done... " statement on my own part and accordingly: an explanation of what I did probably way way back in about 2004 or so.? Gary Myers
------ Original Message ------
From "Gabriel Wiklund via groups.io" <gabriel.wiklundholeshot@...>
Date 2/14/2025 9:47:26 AM
Subject Re: [ServoCAT] Promising Autoguiding results in PHD2
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Hello Gary,
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Thank you for the info, interesting and helpful! I have read some about guiding on Cloudy nights and it seems other systems do the same, they add to the current track rate, so when they mention "0.5 x sidereal" they have stated that the current rate increases or decreases by 7.52 arc seconds, as i am writing this i realize that EQ mounts always are very close to the sidereal rate which would mean that the guidespeed would have to be greater than 1x sidereal for the RA to change directions, that explains why you can't enter more than 1.01x sidereal in the PHD2 guide section, and why backlash only was a problem in DEC when i used my EQ mount.
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By the way, i saw some posts about the Mesu 200 mount with ServoCat Argo with insane tracking accuracy, so it seems, like i think you have written somewhere already - the scope and installation is the limiting factor not the ServoCAT when it comes to Astrophotography.
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/Gabriel |
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Dear all,
Thanks Gary to have explained the way the guiding correction works.
You say "The way ST4 applies guiding is to add a fixed amount (programmed in GUIDE 2 speed value....".?
OK
Then in his message /g/ServoCAT/message/7395 I see Gabriel has lowered the guidespeed in ServoCAT Sky to 6 arc seconds per second to achieve a good auto guiding
But I see at same time the classical guide2 values are around 160 arc sec/sec for obsessions scopes, whatever their diameter, which is very far away from the 6 arc sec/sec that found Gabriel.
There is a conflict here : if the guide2 value is 6 arc sec/sec for autoguiding, it will be way too slow for visual observing.
Gabriel, how do you manage this if you want to observe visually ?
Changing the rate settings in servocat sky each time you change from autoguiding to visual would be boring...
With your guide 2 being 6 arc seconds/sec, did you change your guide 1 speed -which is classicaly in the 250-280 arc sec/sec - to 160 arc sec/sec to use it for visual observation ? Then you also need to reajust the slew and jog rates also to have smooth ratio change...
In this case the guide 2 will be only allocated to autoguiding and guide 1, slew, jog for visual observing.... Right ???
Unless I miss something ???
Regards?
Rapha?l
Gabriel : I send you a private email to discuss your scope settings and avoid polluting this group. I hope you have received it.
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I am not using my scope for visual anymore, but if you leave the guide 1 values as they are and the switch on the ServoCAT is flipped to "1" visually you will not be using the guide 2 values when using the handpad, if you decide to image the Autoguide port uses the guide 2 value regardless if you have the switch to 1 or 2 (as i have come to understand it, Gary correct me if i am wrong).
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So it's only if you flip the ServoCAT switch to "2" your handpad will have the very slow value.
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When i got my scope the Guide 1 and 2 values where 110 arc sec/sec.
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I have not seen anybody recommend a guide 2 speed lower than 25 arc sec/sec, but the guide deflections where so massive even when i had 20 arc sec/sec it looked like windgusts where hitting my scope, so i had no choice but to try other values even if no one had recommended them, and autoguiding works very well now! Yesterday i did tests all over the sky and also let it guide for 1 hour on M106 with 10 second subs, no problems so far! I did not even have any problems with backlash, and to be precise.. the measured guidespeed in PHD2 is not even 6 arc seconds per second, but 2.5 arc seconds per second, and for some strange reason it even worked when i did test exposures at about 74 degrees in altitude.
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My theory is that the unguided tracking already is so good that the corrections need to be very subtle to make things better instead of worse.
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Rapha?l i found your email now, it was in the junk mail, i will read it and respond soon!
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/Gabriel
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Raphael,? Good question.? First the main intention of GUIDE speeds is for visual use. At the eyepiece. It is there to allow you - looking into an eyepiece, to move around a field at a comfortable rate. That field size might typically be say 25 arcmins. The GUIDE1 speed might be 250 arcsecs/sec. So it would take just over 3 seconds to move from the edge of the field to the center. You can very conveniently select GUIDE fast or GUIDE slow to customize this depending on the actual power and field size... I designed the system to be extremely flexible and conveinent for this action which is probably near 100% of what one does - uses the hand controller for. AND if you go to high to really high power on say a night of good seeing you can flip the SPEED switch from 1 to 2 and have slower speeds available. So as long as the user has taken the time to understand how GUIDE works and programmed the speeds according to their particular telescope (FL) ... they should be quite comfortable using it.? When you use ST4 AG you now dedicate Speed2 to AutoGUIDING. This, too, isn't an issue as the vast majority of users never flip the Speed switch from 1 to 2 and thus it goes unused for the most part. You can leave the Speed 1/2 switch set to 1 ... have the comfortable guide speeds as discussed above when looking through the eyepiece (or centering on a camera frame) and yet still have the programmed speed2 values for AG. No flipping of switches needed! Maximum convenience.? Now that all stated - I personally would not set the AG speed to anything less than 10 or so. That is because most of the time the AZ track value is going to be around sidereal (just over 15 arcsecs/sec). But as mentioned in the last note - it is very dynamic and having a "right" speed depends heavily on where you are in the sky.? Gary?
------ Original Message ------
From "Raphael Guinamard via groups.io" <rguinamard@...>
Date 2/16/2025 3:52:29 AM
Subject Re: [ServoCAT] ST4 Guide Port action
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Indeed! The tracking can be extremely good. I had nights where I could measure it using a 240mm guide scope and a camera... and know what it was ... and in AZ it stayed UNDER 1 arcsec for a long period of time.? We have to remember that this is ALT/AZ. Field rotation is GOING TO BE dominate. MY goal in playing with ST4 was only - only to reduce severe drift in either axis. If the alignment was not great and/or if there are mount errors causing the model of the sky in the DSC to differ from reality - that WILL cause tracking to be off ... and for me it was purely a matter of keeping the view roughly centered to maximize field size with field rotation nibbling away at the edges. This would reduce the necessary cropping that inevitably has to be done. So the intent and hope was to keep 'the center' within maybe 1/2' of total movement over the full time of the desired image capture (15 - 60 minutes).? I've unfortunately only been able to use it a few times due to mostly weather and the fact that I'm now in a 55+ community with no backyard to set up in... thus limited as to what I can test.? Gary?
------ Original Message ------
From "Gabriel Wiklund via groups.io" <gabriel.wiklundholeshot@...>
Date 2/16/2025 4:29:02 AM
Subject Re: [ServoCAT] ST4 Guide Port action
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Dear both,
Thanks to your message, I realise I made a confusion :
I though the guide 1 was used for guide fast value and guide 2 for guide slow value. But this is completely wrong as you explained and as written in the manual :
"Guide speeds:
With SPEED 1/2 set to 1: GUIDEslow = GUIDE1 GUIDEfast = 2X GUIDE1 With SPEED 1/2 set to 2: GUIDEfast = GUIDE2 GUIDEslow = 1/2 x GUIDE2" ?
Sorry for my mistake and thanks for explanations !
Regards
Rapha?l
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Raphael, Yes indeed! Since there was only the one GUIDE switch position on Gen1/2 hand pads I had to come up with a system that would support the dual buttons. It is as the labels suggest, though one need not have to know the particulars.? So if Speed 1/2 is set to 1 which is what probably 90%+ of users use (and most never touch the switch - to my chagrin as it is handy when going to really high/narrow fields) then GUIDE fast is faster than GUIDE slow (by a factor of 2:1, although again one need not know the particulars)!? Likewise if in Speed 2 once again?GUIDE fast is faster than GUIDE slow (by a factor of 2:1)!? The programmed GUIDE 1 speed is the reference (base if you will) for slow vs fast The?programmed GUIDE 2 speed is the reference (base if you will) for fast vs slow(er)
g. ------ Original Message ------
From "Raphael Guinamard via groups.io" <rguinamard@...>
Date 2/16/2025 4:34:47 PM
Subject Re: [ServoCAT] ST4 Guide Port action
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Gabriel Wiklund