jgibson1@emich
sage
Reged: 06/11/06
Posts: 332
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I was up north this past weekend spending some time under dark skies. With loads of free time during the day to contemplate the meaningless things in life I began thinking about the procedures in acquiring quality astrophotos. I know what I personally do and it has been working for me for the most part but I am curious as to the method of madness of all you other imagers……
Typically my imaging sessions start with the typical polar alignment routines including the drift technique. After this I then run a P.E.C. training routine. This takes all of about 20-30 mins. After this I simply wait and watch as the skies darken. Once dark I double check the focus on both the guide scope and imaging scope via a bahatinov(sp?) mask. My next step is to find my target object, frame the target object, choose a guide star, begin auto-guiding, and finally begin capturing light frames.
After collecting an hour or two of light frames on a target I collect light frames for another target and then another depending on my plans for the session. I have in the past simply collected the darks at the end of my imaging sessions (ie- early morning just before sunrise). While taking the darks I sleep for a few hours and then setup and take my flats, by which time the sun has risen and with a white cloth (ie- t-shirt) I take my flats. After this I snap off a few bias frames and that’s the end of an imaging session.
My reason for thinking about my process arose from my trip this past weekend. The temperature drops throughout the night this time of year can be dramatic to say the least. At astronomical twilight the temps were around 60-65F. At about 1am they had dropped to 35-40F and possible even colder by 3am. As a result the darks as taken in the morning do not match the lights that I took much earlier in the evening with respect to temperature. In the future I think I may try taking a few darks ever 5 light frames of so as this would help in getting darks that match the lights. My quick initial calibration of some light frames as taken this past weekend show some of what I believe are side-effects of my approach of collecting the darks at the end of the night.
…………………  So my question is, what is your typical procedure in collecting the appropriate image data to create astrophotos?
Clear Skies,
Jason
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Clay Kessler
super member
Reged: 04/16/07
Posts: 151
Loc: Manchester MI
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Jason,
My system lives in the backyard so I do not have to polar align. I typically setup the computer and camera, find a target and align the DSC's, focus with a Stiletto unit once it gets dark, Pick an object, Gather light frames, switch, gather more light frames and take my darks at the end of the session - usually while I am covering the scope and packing up the movable equipment. Flats I take the next day. I usually don't image for an entire night so I figure one set of darks work for me. If I already have darks at a similar temperature I use them as well as if I have flats taken in the same camera position.
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Best Regards
Clay Kessler
www.ssoastro.org
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Mike Clemens
Post Laureate
Reged: 11/26/05
Posts: 4255
Loc: Wasilla, Alaska 61N
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I have an observatory now with remote control from the house, so it takes about 90 seconds to run out, roll the roof back and power up the mount. I then run back into the house.
My sequence now is this...
Initial setup:
slew to focus star near target
plate solve & set mount position exactly
slew to focus star near target
calibrate PHD guider
focusmax focus
slew to target
take (3) 8 minute exposures
(24 minutes pass)
slew to focus star near target
focusmax focus
slew to target
take (3) 8 minute exposures
(24 minutes pass)
every several sets I will do the plate solve and set mount position (since my mount is not super accurately polar aligned any more)
after meridian flip I repeat the initial sequence including the PHD guider calibrate and then go again
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historius apochromaticus
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Tonk
Post Laureate
Reged: 08/19/04
Posts: 4349
Loc: Leeds, UK, 54N
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My method is identical to yours Jason, except I stick to one target for the night - unless it sets before night is over. I don't worry to much about unmatched temperatures as bias substraction mean you can scale the darks in Images Plus if they are not too different in temp (I think DSS can do this as well?)
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Televue 85, GM-8/Gemini, Canon 40D (unmodded), Canon 450D (modded w/Astronomiks clip-ins - UV/IR, OWB)
Coronado SM60/BF10, Baader Herschel Wedge
Leeds Sky Clock Ripon Sky Clock
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zAmbonii
scholastic sledgehammer
Reged: 01/19/08
Posts: 836
Loc: Ypsilanti, MI
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For me, typical image acquisition involves 1) alittle cool down 2) rough levling and align of the mount 2) drift align 3) calibrate mount 4) put on camera focus on bright star with bhatinov mask, make sure guide scope is pointing in the same direction and foucs also 5) slew to target, mke sure it is centered or framed the way I want. 6) open up phd guiding and get that calibrated and run 7) start snapping off lights.
I usually only do one or two targets per night. I only switch targets if it dips below the trees in the backyard or I have to do a meridian flip.
If I have time before the sun rises I may snap off some darks. Flats usually has to wait for the next night. I have recently also ran into problem with my darks not matching and I can't completely figure it out. I am seeing some residual hot pixels and amp glow with the darks that I am taking on the same night.
My question for all of you is *just how* are you taking your lights. If you are going for say 6 minute exposures, how long inbetween exposures are you waiting. I am currently doing 6 minutes exposures, wait 11s for it to write to disk (with my 300D) then for another 6 minutes. (I want to maximize the lights I can get per night). Do you guys snap off as many lights as you can or do you let the CCD "cool down" for a minute or two inbetween?
I have a sneaking feeling that my camera is constantly heating up with my scheme and that my darks are significantly warmer than my lights, causing a mismatch in processing. Need to figure it out because I have a couple of pics I need to finish processing because I am running a backlog of them...
Edit: Wanted to add, I spend a bit of time drift aligning. That may take me a good half hour to 45 min. I seem to have some weird DEC drift periodic error when aligning that I want to make sure I don't have a drift....Usually let it go 5-10 min after adjustments to make sure it is on.
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Check out my Astrophotos on Flickr
C6-N 150mm f/5 Newtonian
CG-5 ASGT mount
Canon 300D self modded + IDAS LPS-P2 FF
Meade 70AZ + Meade DSI for autoguiding
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lawrie
Carpal Tunnel
Reged: 01/31/06
Posts: 1742
Loc: Okanagan Valley
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I have a roll off roof with a permanent pier, so I'm lucky I don't have to lug everything out and do the initial setup, (level mount, polar align, drift align).
I start up my planetary program and EQMOD.
After the programs have loaded I then slew to a bright star in the region I am planning to image, usually I have to center the star using a red dot finder then use live view to get it right on.
Then I sync the star in the planetary program.
Time then to put on my Bmask and take a 5-10s image, depending on how dark it is.
I open DPP (Digital Photo Professional) so I can use the 200% page to get the spikes right. I focus my guide scope at this time also.
Then hopefully I rememmber to take the mask off, but not always.
I then slew to another star in the target region, at this point I can center and sync it with just live view.
I do this on at least one more star, this puts the target center of the camera chip.
I then open PHD and calibrate. After calibration I set PHD to 2.5 - 3 s and let it warm up.
While PHD is warming I open my image capture program and set it up (how many, how long)
Usually I don't let this exposure reach its full term and
this is when I look at the first image I find out if I left the mask on, and if I like the framing.
I then start collecting the images for the night (in the summer its one target, in winter can be two).
I can go back into the house then and monitor everything with Teamiewer (with Teamviewer you have control over the other comp, you can change settings or shut down whatever you want)
After a couple of hour, or sooner if the temp changes faster, I will refocus)
After I have collected all the lights I can, I change batteries and reprogram to collect the darks for the night.
Close it up and go to bed. Bias and flat frames are collected the next day.
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Clear Skies
Lawrie
Ultima 8
Atlas EQ-G
ZenithStar 80 FD
DSI Pro - Pro II
Canon 350D
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Mike Clemens
Post Laureate
Reged: 11/26/05
Posts: 4255
Loc: Wasilla, Alaska 61N
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I snap them as fast as it can download the last image, record to disk and begin the next exposure.
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scully1234
sage
Reged: 09/04/07
Posts: 309
Loc: Rush, NY
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Hey Zambonii,
You might want to let the camera cool down for a full minute between lights.
After a 6 min exposure the CCD is going to get pretty warm.
I have my Phottix remote programed for a 1 minute delay between exposures to let the camera cool off.
My darks match my lights very nicely.
I also wait 1 minute between the dark exposures as well.
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Astrophotographer ! Finally ! (thanks to everyone's help on CN)
My webpage = www.starsinmybackyard.com
Celestron C8 XLT on the CG-5GT mount
Meade 70mm AZ guide scope
Canon EOS 450D (xsi)
DSI color (guide cam)
Acer mini-laptop (for guiding and xsi tethered shooting)
Canon A530 point-n-shoot
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jgibson1@emich
sage
Reged: 06/11/06
Posts: 332
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Thanks everyone for the info. I have found a few things that I will definately try in the future and maybe a couple others that are intersting.
Thanks,
Jason
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Clay Kessler
super member
Reged: 04/16/07
Posts: 151
Loc: Manchester MI
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Jason,
My autoguider guides in RA and DEC.
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Best Regards
Clay Kessler
www.ssoastro.org
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jgibson1@emich
sage
Reged: 06/11/06
Posts: 332
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Hello Clay,
I can guide in both directions too but for whatever reason I selected to disable the guiding in dec this past weekend when I was setting up. I could kick myself in the a$% for having done that but then again I jsut didn't know that this noise pattern was a result of the dec drift.
What autoguider are you using?
Jason
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Jerry Lodriguss
Vendor
Reged: 07/19/08
Posts: 542
Loc: Voorhees, NJ
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Hi Jason,
You do need to guide in declination. If you have consistent drift in dec in the same direction, then you are not accurately polar aligned.
Even after you are accurately polar aligned, you still need to guide in dec because of things like flexure and differential atmospheric refraction.
The diagonal noise you are seeing is most probably because the temperature of your darks does not exactly match the temperature of your lights.
When the darks are subtracted, some stuff that looks like noise is left behind. It can be light or dark "holes" or spots depending on whether the dark was hotter or colder than the light.
So this "noise" is present in each frame, but it's not really noise, it's really incorrectly removed thermal signal. So it's in the exact same place from frame to frame.
But then you move each frame to align it to stack the images. So the "dark holes" move, marching across the frame.
If your drift was in dec, then the "dark holes" march in dec.
If you have a combination of drift in dec and periodic error, or flexure, they can move diagonally, or any which way.
The perfect solution is to shoot darks at exactly the same temp as the lights. But this is literally impossible with DSLR cameras because they heat up during use and each frame is at a different temperature. Not to mention falling ambient temperatures during the night.
So, what can you do?
You can just use a program like Images Plus, which as automatic dark frame matching, which will solve this problem.
I have a library of dark frames every 10 degrees. I use a LOT of darks to make a master dark. I shoot them in my garage on cloudy nights.
Then pretty much whatever ambient temp I run into, I have a dark within 5 degress of it. And if the camera heats up and they don't match, Images Plus takes care of it, no problem.
Also, you should shoot bias frames so you can scale your darks to different exposure times.
The secret here is LOTS of darks and bias frames to make really good, low-noise thermal frames, and Images Plus automatic dark frame matching.
Jerry
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A Beginner's Guide to DSLR Astrophotography
http://www.astropix.com
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guyroch
sage
Reged: 01/22/08
Posts: 253
Loc: Ottawa, Canada
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Quote:
The secret here is LOTS of darks and bias frames to make really good, low-noise thermal frames, and Images Plus automatic dark frame matching.
Jerry, how much is LOTS of dark and bias frames? Would you say 15 each or something closer to 50?
Thanks
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750mm 6" Skywatcher Reflector f/5
Celestron CG-5 GT mount
SSAG autoguider mounted on Orion 80mm short tube
Canon 40D unmodified / TC-80N3 remote timer
Orion SkyGlow for Astrophotography light polution filter.
Orion AccuFocus & Bahtinov mask
Bushnell 8x42 h2o® Waterproof Binoculars
Sky Atlas 2000.0 Field Version (Laminated)
Plenty of patience and a wife that doesn’t quite understand my love for clear skies, but let’s me go out anyway ~ thanks honey bunny 
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Jerry Lodriguss
Vendor
Reged: 07/19/08
Posts: 542
Loc: Voorhees, NJ
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Quote:
Jerry, how much is LOTS of dark and bias frames? Would you say 15 each or something closer to 50?
It depends on how many lights you shoot. You need more darks and bias frames if you shoot a lot of lights.
But, in general, I would say 16 minimum.
I use up to 64 in some of my master darks and master bias frames.
You just set the timer up to run all night long in your garage (or even refrigerator) and go to bed... :-)
Jerry
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A Beginner's Guide to DSLR Astrophotography
http://www.astropix.com
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Tonk
Post Laureate
Reged: 08/19/04
Posts: 4349
Loc: Leeds, UK, 54N
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I too would endorse 50+ dark and bias masters. Over the last 6 years my best images are those with a rediculous number of lights (100+) calibrated with low noise dark/flat/bias masters. At the end of the day the quality of the dark deep sky has a profound impact on everything else in your image. People tend not to pay attention to this aspect of the image, but it is just as important as the main subject matter
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Televue 85, GM-8/Gemini, Canon 40D (unmodded), Canon 450D (modded w/Astronomiks clip-ins - UV/IR, OWB)
Coronado SM60/BF10, Baader Herschel Wedge
Leeds Sky Clock Ripon Sky Clock
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Clay Kessler
super member
Reged: 04/16/07
Posts: 151
Loc: Manchester MI
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Jason,
I use the Orion Starshoot autoguider. It works very well and is quite simple.
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Best Regards
Clay Kessler
www.ssoastro.org
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