Guider exposure times?
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Mike Shade
Curious as to what people have for guider exposures for various systems. Was having some issues guiding my 1600/CDK 17/Maxim 5.18/STL6303E (guiding with camera) in that the stars were not always round...almost but not quite, just a few pixels but enough to oblong the stars. Always had somewhat longer guide exposures (7"-10") to try and even out seeing variations (which can be quite large with a 17" telescope). The system can go unguided with reasonably round stars for the 382" worm cycle near zenith but guided images were a different story (I do need to guide the system). So last night lowered the guide exposure to 2", aggressiveness to 5 and round guided stars. What I think might have been happening is that with a longer guider exposure, there would be centroid changes between exposures and the system was reacting to these. With a shorter exposure, this is not happening as the "deviation" is not allowed.
So, just curious as to what others have their systems setup for guiding and if my thinking on this makes sense.
Mike J. Shade Mike J. Shade Photography:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
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Stuart <stuart.j.heggie@...>
Mike, I use 3 or 4 seconds with my 12.5" Planewave / MMOAG. I "think" I'm running 4 seconds with my AP155 and Borg 60mm guidescope. Stuart Heggie
On Thu, 30 Apr 2020 at 11:52, Mike Shade <mshade@q.com> wrote:
--
Stuart http://www.astrofoto.ca/stuartheggie/
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Michael Hambrick <mike.hambrick@...>
It seems that I read somewhere that shorter
guide exposures are better, but I am not sure where I read that. In any
case I have always tried to go for 1 to 3 second guide exposures. I use
Maxim DL-Pro and sometimes CCDOps. My guider aggressiveness is typically
about 7 or 8.
I have never really experimented a lot with these parameters or taken the time to set up a PEC, but I suppose that I should. Best Regards Michael Hambrick ARLANXEO TSR Global Manufacturing Support PO Box 2000 Orange, TX 77631-2000 Phone: +1 (409) 882-2799 email: mike.hambrick@...
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My experience has been that guiding camera exposure times will vary according to how steady the sky is. You want to have exposures long enough to average out the seeing so you aren’t chasing a false centroid calculation by the guiding software. For me, I want to keep my guide exposures as short as possible because I dither the guide star every one or two exposures (for better pixel rejection during stacking, “walking noise” issues with my camera, and because I frequently use drizzle integration) so I want to minimize the settling time before the next exposers is started.
I generally use 3 sec for calm nights but will use 5 sec for nights with bad seeing. It is very instructive to watch seeing scintillation at longer focal lengths with an eyepiece and see how a star will move around. Then you can easily see how short guide exposures will give you an inaccurate result. Also, try taking a 1 or 2 sec exposure with your guide camera. If the star is misshapen or elongated then you might not be getting an accurate position calculation. -- Dean Jacobsen http://astrophoto.net/wp/ Image Gallery - http://astrophoto.net/wp/image-gallery/ Astrobin - https://www.astrobin.com/users/deanjacobsen/
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dnakic@...
I have AP 1600GTO with PEM training running around +/- 0.74. I have a 14” Edge HD @f11 and imaging with STXL 11K and guiding with its SXTL filter wheel/guider. I use Maxim DL with 8/8 X/Y aggressiveness. Guide calibration is 4 sec and 4 sec for guide exposure. My guiding is +/- .5 arcsec when watching the guiding trace. My imaging with narrowband is typically 20min in duration. Early on I noticed my STXL fan was creating vibration and causing oblong stars. I now run with fan off, but it does go on when it reaches a critical point. You may want to try running with fan off too.
I’m enclosing a sample of what I’m getting with this setup.
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I use 2 seconds for all my different scope/guidescope configurations in PhD2. I image from an area with considerable light pollution but don't know if that really matters. Thanks, Charles Sent from mobile device.
-------- Original message -------- From: Mike Shade <mshade@q.com> Date: 4/30/20 10:53 AM (GMT-06:00) To: main@ap-gto.groups.io Subject: [ap-gto] Guider exposure times? Curious as to what people have for guider exposures for various systems. Was having some issues guiding my 1600/CDK 17/Maxim 5.18/STL6303E (guiding with camera) in that the stars were not always round...almost but not quite, just a few pixels but enough to oblong the stars. Always had somewhat longer guide exposures (7"-10") to try and even out seeing variations (which can be quite large with a 17" telescope). The system can go unguided with reasonably round stars for the 382" worm cycle near zenith but guided images were a different story (I do need to guide the system). So last night lowered the guide exposure to 2", aggressiveness to 5 and round guided stars. What I think might have been happening is that with a longer guider exposure, there would be centroid changes between exposures and the system was reacting to these. With a shorter exposure, this is not happening as the "deviation" is not allowed.
So, just curious as to what others have their systems setup for guiding and if my thinking on this makes sense.
Mike J. Shade Mike J. Shade Photography:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
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Mike Shade
Thanks for the input on this. As we are now in the heat in SE AZ, there is a bit of ground heating during the day, in spite of my tree planting 20 years ago. I did notice with the shorter guide exposures, the error graph in Maxim looked better, smoother and there was significantly less variation. I did a series of tests last night pointing the scope at various elevations and doing a 1 minute unguided shot. I was testing for some sort of sag or flexure in the optical components. The results were interesting. I shot at 85, 75, 65, 55, and 45 degrees elevation, pointed E, W, and then S. In a series of several at the same location, the stars were all sorts of interesting shapes...round, ovoid in one direction, ovoid in another direction. As there was no guiding, the only "live" axis was RA and the deviations were not tracking errors as they were not in line with this axis. Interesting demonstration, at least to me of the effects of seeing variations.
Mike J. Shade Mike J. Shade Photography:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
From:
main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Mike
Shade
Curious as to what people have for guider exposures for various systems. Was having some issues guiding my 1600/CDK 17/Maxim 5.18/STL6303E (guiding with camera) in that the stars were not always round...almost but not quite, just a few pixels but enough to oblong the stars. Always had somewhat longer guide exposures (7"-10") to try and even out seeing variations (which can be quite large with a 17" telescope). The system can go unguided with reasonably round stars for the 382" worm cycle near zenith but guided images were a different story (I do need to guide the system). So last night lowered the guide exposure to 2", aggressiveness to 5 and round guided stars. What I think might have been happening is that with a longer guider exposure, there would be centroid changes between exposures and the system was reacting to these. With a shorter exposure, this is not happening as the "deviation" is not allowed.
So, just curious as to what others have their systems setup for guiding and if my thinking on this makes sense.
Mike J. Shade Mike J. Shade Photography:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
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Coma? Bright head towards center, tail opposite? I use 2-3" for guide exposure for a C11 w/reducer, 1750mm FL Steve
On Thu, Apr 30, 2020 at 4:52 PM Mike Shade <mshade@q.com> wrote:
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Mike Shade
No, that would be constant...the star shapes changed on each one minute exposure...round, oval from 7 o'clock to 1, then from 11 to 5, then from 9 to 3, it was random. At .63"/pixel, 2940mm fl, and a generous aperture it doesn't take much. It was quite interesting and eye opening.
Mike J. Shade Mike J. Shade Photography:
In War: Resolution In Defeat: Defiance In Victory: Magnanimity In Peace: Goodwill Sir Winston Churchill Already, in the gathering dusk, a few of the stars are turning on their lights. Vega, the brightest one, is now dropping towards the west. Can it be half a year since I watched her April rising in the east? Low in the southwest Antares blinks a sad farwell to fall... Leslie Peltier, Starlight Nights
International Dark Sky Association: www.darksky.org
From:
main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Steven
Panish
Coma? Bright head towards center, tail opposite?
I use 2-3" for guide exposure for a C11 w/reducer, 1750mm FL
Steve
On Thu, Apr 30, 2020 at 4:52 PM Mike Shade <mshade@q.com> wrote:
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Worsel
Mike
I almost always use 4 seconds with no delay between guider exposures. I have tinkered with up to 10 seconds and delays up to 20 seconds, but keep getting the best performance in terms of star quality and low RMS with 4 seconds and zero delay. OAG, 2500 mm F.L., full frame DSLR YMMV Bryan
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