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Paul Romero
professor emeritus
Reged: 04/05/05
Posts: 537
Loc: Reno, NV
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Hi all,
Im getting equipment and reading up on astrophotography, but I dont understand a few words. Could someone tell me what these mean?:
"Sub" (as in "I took a couple subs of M31")
"Platesolve" (as in "I was able to use the Sky 6 to platesolve the targets")
thanks,
Paul
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Nexstar 11 GPS
8'x10' backyard 'skyshed'
and presenting...."Sweet Pudding", my AM 110mm FLT on 'Max', a MI-250 mount.
travel: BORG 45EDII on an Astrotrac.
"Pablito Clavo un Clavito en la Calva de un Calvito"--by Jose A.
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mathteacher
Pooh-Bah
Reged: 05/13/07
Posts: 1042
Loc: SF Bay Area
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A sub is short for sub-exposure (I think). Those are the individual pictures that are stacked digitally to make the final image. Stacking shorter exposures increases the signal to noise ratio of your image and allows you to bring out faint detail.
As for Platesolve, I haven't a clue.
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Regards, Mr. Wang
CR 150-HD - Gordie, Vixen ED100sf - Schipperke, Orion ST80 - The Pug, Orion 7x50 Scenix
Meade DSI Color
Vixen Porta Mount, Super Polaris, 2" pipe mount
Please join the International Dark Sky Association
My CN gallery
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Paul Romero
professor emeritus
Reged: 04/05/05
Posts: 537
Loc: Reno, NV
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thanks bud,
Anyone one want to solve the plate solve puzzle?
thx,
Paul
--------------------
Nexstar 11 GPS
8'x10' backyard 'skyshed'
and presenting...."Sweet Pudding", my AM 110mm FLT on 'Max', a MI-250 mount.
travel: BORG 45EDII on an Astrotrac.
"Pablito Clavo un Clavito en la Calva de un Calvito"--by Jose A.
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Bill W.
Pooh-Bah
Reged: 10/09/05
Posts: 1437
Loc: Western PA, USA
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A plate solve is when the image is taken of the night sky and compared using TheSky or a similarly capable software to where the mount thinks it is pointing. TheSky takes that image and matches it to the coordinates that the image really is point to... most software will then slew the mount to where it thought it was pointing. It allows for very accurate telescope point. I personally use it to point my scope when I am imaging. Sometimes the nebula, etc. is too faint to be seen in a short exposure so a plate solve comes in extremely useful in those instances. Plate solve are also useful for automated imaging, which I have used it for that too. Hope that helps... 
-Bill
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Orion Atlas EQ-G (EQMOD), SBIG ST-2000XM & AO7
Stellarvue SV66ED
Skunk Hollow Observatory
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s58y
Post Laureate
Reged: 12/12/04
Posts: 4832
Loc: Eastern NY
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Quote:
Anyone one want to solve the plate solve puzzle?
I've never done any plate solving myself, but apparently certain software packages can look at your exposures and automatically identify what's in the image (i.e. what direction the scope is pointing).
I'd like to hear more about this -- does the software need clues (like image scale, approximate area of the sky covered, etc. or can you just give it a random frame and it figures out everything?
I think this technique is used more by advanced imagers, so you might get a better response over in the CCD forum.
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Hutech 30D, SBIG ST-402 autoguider
SV80S, SV66 guidescope
AP900, G-11, Barndoor tracker
http://www.pbase.com/s58y
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jay52
Carpal Tunnel
Reged: 09/26/04
Posts: 2280
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Plate solve. Yes.
Let me give you an application. I use a program called "T-point" to refine my pointing accuracy and polar alignment within TheSKY6. What I do is take a picture of an area of the sky...any area. Because TheSKY knows generally where it is, it then compares the image with a set of images in its database. Because those images in the database have known coordinates and star names, it is able to match one to your image and then produce actual coordinates for your image, including naming which stars are actually there. Once it does this, within TheSKY, I can "map" that known coordinate as a "point." Once I have generated 6 such points, the software has enough information to begin correcting the pointing accuracy, as well as knowing how off your polar alignment is. 6 points isn't enough to be really accurate, so I normally do many more points than that, from 20 to 30 for a basic polar alignment to 300 or more for a very accurate pointing model...which then is so accurate that it can improve actual tracking and even counteract flexure.
While you don't have to do a platesolve for T-Point (I can just center a star on the screen and map to that), it's much more accurate to do the platesolve.
The other obvious application for this is for discovery. When you image a section of the sky, then do a platesolve, you generate a known list of objects in the image, including brightness values, locations, etc. With that, you can then find anomolies in your image, such as comets or asteroids, or do photometic (brightness comparisons). So, if you are doing something like variable star research, you have a way of measuring a star's brightness over time.
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jay
www.allaboutastro.com
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jay52
Carpal Tunnel
Reged: 09/26/04
Posts: 2280
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One more application that I use.
Because my scope has a automated camera rotator, I can keep TheSKY6 in sync with the actual camera angle. So, when using a scripting program, like CCDAutopilot4, that program can platesolve to know how the camera is oriented, which is important when it goes to find it's own guidestar with SBIG cameras. So, because of the platesolve, such a program can spin the camera as required for the guidestar, but also reacquire that guidestar after a meridian flip or reframe the image precisely after that flip, or in a new session.
Cool stuff.
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jay
www.allaboutastro.com
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s58y
Post Laureate
Reged: 12/12/04
Posts: 4832
Loc: Eastern NY
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Quote:
so I normally do many more points than that, from 20 to 30 for a basic polar alignment to 300 or more for a very accurate pointing model...
How long does it take to do 300 points?
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Hutech 30D, SBIG ST-402 autoguider
SV80S, SV66 guidescope
AP900, G-11, Barndoor tracker
http://www.pbase.com/s58y
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Bill W.
Pooh-Bah
Reged: 10/09/05
Posts: 1437
Loc: Western PA, USA
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Quote:
I've never done any plate solving myself, but apparently certain software packages can look at your exposures and automatically identify what's in the image (i.e. what direction the scope is pointing).
I'd like to hear more about this -- does the software need clues (like image scale, approximate area of the sky covered, etc. or can you just give it a random frame and it figures out everything?
I think this technique is used more by advanced imagers, so you might get a better response over in the CCD forum.
As Jay said, yes, the software does need to know the scale and approximate location the scope is point. TheSky can 'ask' your mount where it thinks it is pointing as a starting point to start the search. The software typically searches out from that point in a circular pattern trying to find a matching star field in it's database. Plate solving for me saves a lot of time in that I don't have to center the object manually. I tell my software the coordinates that I want my imager to center on and voila! This is really very useful on dim objects or as Jay said to improve pointing accuracy using TPoint.
-Bill
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Orion Atlas EQ-G (EQMOD), SBIG ST-2000XM & AO7
Stellarvue SV66ED
Skunk Hollow Observatory
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Bill W.
Pooh-Bah
Reged: 10/09/05
Posts: 1437
Loc: Western PA, USA
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Quote:
Quote:
so I normally do many more points than that, from 20 to 30 for a basic polar alignment to 300 or more for a very accurate pointing model...
How long does it take to do 300 points?
I haven't used TPoint to do this. But, plate solves typically only take a couple of seconds to do from beginning to end. I'd say 10 seconds or so per point. So 10 X 300. There is the variable of how long the plate solve exposure is in that mix. I use 5 second exposures for my plate solves.
-Bill
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Orion Atlas EQ-G (EQMOD), SBIG ST-2000XM & AO7
Stellarvue SV66ED
Skunk Hollow Observatory
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jay52
Carpal Tunnel
Reged: 09/26/04
Posts: 2280
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300 points can take a while, though Ron Wodaski developed a utility called "Automapper2" to make it faster. It works with CCDSoft and TheSKY6 in order to develop a point list and then automate the process of slewing the scope, platesolving, and then mapping the point.
Still, it takes time. Lets say a 5 to 10 second image, an 8 second download (3x3 binned), a couple of seconds for auto-dark application and mapping, then perhaps a 10 second slew to go to the next point (including settling time).
Plus, not every point is mapped correctly, for whatever reason, but usually because not enough stars are available to plot a solution...or perhaps due to a north angle error. But I'd say that each point takes around 45 seconds on average.
In total, a 300 run will take a few hours.
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jay
www.allaboutastro.com
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Galaxyhunter
scholastic sledgehammer
Reged: 01/02/06
Posts: 880
Loc: Northern Illinois
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There is another use for Plate Solve. Comet & Asteroid hunters need to "Solve the Plate" so they know exactly where there target is located.
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Carl
Hawkeye Observatory
Observatory - "Hawkeye"
Scope - 18"f4.5 on a GEM
8" f4.9 Orion piggy backed
Drive - Sitech Technology
DSC - Sky Commander
Planetarium - MegaStar
Camera - ST2000XM
Desire - comes & goes
Talent - ZERO, NONE, NADA (But I can Wish)
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Paul Romero
professor emeritus
Reged: 04/05/05
Posts: 537
Loc: Reno, NV
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Hi again,
I can confidently tell someone that any of my shots that will combine to form a final image is a 'sub'. Great
Plate solve sounds very interesting. I had a hint that it might be where you plan out an imaging session, and then you move the rectangle representing the sensor coverage around on a sky background to 'frame' your image. So, it isnt this, but it is much more fascinating than I had presumed.
thx,
Paul
--------------------
Nexstar 11 GPS
8'x10' backyard 'skyshed'
and presenting...."Sweet Pudding", my AM 110mm FLT on 'Max', a MI-250 mount.
travel: BORG 45EDII on an Astrotrac.
"Pablito Clavo un Clavito en la Calva de un Calvito"--by Jose A.
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walt r
Carpal Tunnel
Reged: 02/13/07
Posts: 2394
Loc: Doylestown, PA
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Google is your friend.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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