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Unguided with pointing model
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I'm really appreciating reading about Roland's work to get pointing
models into the keypad.
I've been doing a lot of imaging from home, LA County, with a Traveler, and an AP180EDT with 1100GTO. My biggest bugaboo in these skies is finding a suitable guide star. PHD2 will lock onto any clump of noise and hunt around the sky trying to guide on it. I'm presuming that the same feat as Roland is developing for the keypad is available now if I go buy the advanced version of APCC. I never did so because I stack my setup every evening and take it down every morning, whether I'm working from Sawpit Wash at home or GMARS in the desert. If my assumptions are correct, how much additional setup time am I adding if I plan to create a new pointing model after every setup? (Is THAT assumption correct as well?) Aside: I'm amazed at the results I'm getting from home. I never bothered to try it from here because I just assumed it would be a waste of time. Under the circumstances, I'm not interested in traveling anywhere (and having to use a public restroom perhaps along the two-and-a-half hour trip to get there). I just decided I'd run the Messier catalog for a quarantine project, and it's been fabulous. I'm documenting it all at http://mojo.whiteoaks.com Best regards, Mojo |
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Hi Mojo
PHD2 will lock onto any clump of noise and hunt around the sky trying to guide on it.My biggest bugaboo in these skies is finding a suitable guide star. I'm not sure what issue you are having, but i image in the san fernando valley (the worst) and i have no problems finding guidestars, even with a simple lodestar x2. PHD has a number of techniques and filters to rule out non-stars for star selection, so i'm surprised you are having these kinds of issues you might consider posting your logs to the PHD forums for feedback? Brian On 5/28/2020 12:48 PM, Mojo Jones wrote: My biggest bugaboo in these skies is finding a suitable guide star. PHD2 will lock onto any clump of noise and hunt around the sky trying to guide on it. |
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Roland Christen
If my assumptions are correct, how much additional setup time am I adding if I plan to create a new pointing model after every setup? A pointing model is something completely different from a drift model. A simple pointing model can get you to various objects fairly accurately and takes just a few minutes per point. You can do 3 on one side, 3 on the other plus a quick Orthogonality model. The whole thing takes maybe 10 - 15 minutes. However, that won't do a proper drift compensation.
If you want to do unguided imaging you need to do either a full sky model using APCC Pro (takes maybe 1/2 hour during twilight), or you need to model the path along which the object tracks during the night. That can take 20 - 30 minutes depending on how many points you wish to measure.
Rolando
-----Original Message-----
From: Mojo Jones <mojo@...> To: main@ap-gto.groups.io Sent: Thu, May 28, 2020 2:48 pm Subject: [ap-gto] Unguided with pointing model
I'm really appreciating reading about Roland's work to get pointing
models into the keypad.
I've been doing a lot of imaging from home, LA County, with a Traveler, and an AP180EDT with 1100GTO. My biggest bugaboo in these skies is finding a suitable guide star. PHD2 will lock onto any clump of noise and hunt around the sky trying to guide on it. I'm presuming that the same feat as Roland is developing for the keypad is available now if I go buy the advanced version of APCC. I never did so because I stack my setup every evening and take it down every morning, whether I'm working from Sawpit Wash at home or GMARS in the desert. If my assumptions are correct, how much additional setup time am I adding if I plan to create a new pointing model after every setup? (Is THAT assumption correct as well?) Aside: I'm amazed at the results I'm getting from home. I never bothered to try it from here because I just assumed it would be a waste of time. Under the circumstances, I'm not interested in traveling anywhere (and having to use a public restroom perhaps along the two-and-a-half hour trip to get there). I just decided I'd run the Messier catalog for a quarantine project, and it's been fabulous. I'm documenting it all at http://mojo.whiteoaks.com Best regards, Mojo |
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Thanks for chiming in Brian! I'm sure much of my difficulty comes
from using the built-in off-axis guide camera on my ST-4000XCM, so I
don't have the privilege of a wider-field guide scope. Quite often
this past week I haven't had a wide enough field to find a bright
enough star to peek up above the sky glow. PHD2 presents a gnarly
grey noisy field, and "auto select" latches onto something that's
often not a star at all.
I'd love to tweak PHD2 so it doesn't latch onto non-stars. I built a bad pixel map. On 5/28/2020 12:58 PM, Brian Valente
wrote:
Hi Mojo |
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dvjbaja
Mo, You might be surprised to learn you can use a small guide scope and guider array where it becomes easy to find a guide star. Just say'n. J Sent via the Samsung Galaxy Note9, an AT&T 5G Evolution capable smartphone -------- Original message -------- From: Mojo Jones <mojo@...> Date: 5/28/20 4:01 PM (GMT-08:00) To: main@ap-gto.groups.io Subject: Re: [ap-gto] Unguided with pointing model I'd love to tweak PHD2 so it doesn't latch onto non-stars. I built a bad pixel map. On 5/28/2020 12:58 PM, Brian Valente
wrote:
Hi Mojo |
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Hi Mojo We're not so far apart on our setups: i have an OAG with Lodestar that is 752 x 582 8.4u @840mm focal length Your camera has the TC-237 tracking CCD (657 x 495 pixels at 7.4u) @ 1620mm focal length yes of course you're imaging at 2x focal length (yes i'm jealous :) ) but PHD also has noise reduction, star saturation detection, minimum star size, etc. to eliminate erroneous star selection. might be worth a visit to PHD forums? i'll stop on this now haha On Thu, May 28, 2020 at 4:01 PM Mojo Jones <mojo@...> wrote:
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I'll be spending my next few days surfing the PHD2 forum. Thanks
Brian :)
On 5/28/20 7:02 PM, Brian Valente
wrote:
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willsonjared
A tracking model that’s good enough for five minute unguided images with your 180 should be possible without losing much imaging time. That is, you should be able to do it during twilight. A good polar alignment probably takes about as long as building the model. Maybe an hour total for the two? Depends on the number of points you choose. If you start as soon as possible after sunset, you may not lose any imaging time at all. If you do lose any, it could easily be less than the accumulated time lost waiting for a guider to settle after dithering twenty or thirty times during the night. Then you could skip the guiding entirely. Assuming you have the AE version of the 1100 you should get results that are equal to or Possibly even marginally better than a well guided image. Based on testing with my 1100GTO AE the other night (I bought it a year ago but have only been using it for the past couple months), typical star eccentricity at 1,160mm focal length with a 5 minute unguided images is between 0.45 and 0.55. That’s using a model that’s probably better than you would build “in the field”, but still. It works quite well with a moderate number of points. When I spoke with Ray G at the last Advanced Imaging Conference he recommended starting with, say, a 70 point model for field use.
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