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Hubert
super member
Reged: 09/26/06
Posts: 122
Loc: Belgium
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Hi,
I have taken a picture of Eps Aur and would like to measure the magnitude of Eps Aur. The used camera is Canon Eos 400D. I have never done anything like this. I don’t know anything about photometry. I have downloaded C-munipack to process the picture. I have understand from some messages that I have to use the green channel.
How can I get that green channel?
I’m going to do this step by step so probably I will have a lot of other questions 
Clears skies, Hubert
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brianb11213
Carpal Tunnel
Reged: 02/25/09
Posts: 2076
Loc: 55.215N 6.554W
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Quote:
How can I get that green channel?
Well, I load the raw (.CR2) image file from my 40D into AIP4WIN v2.3.0 and use the colour tool to seperate out the red, blue & green images. I don't have C-munipack but could I respectfully suggest that you can effectively isolate the green layer by loading the image into Irfan View (freeware), go into the "Enhance Colours" menu (shift+G), move the red & blue sliders to the extreme left, then convert to grayscale & save (as TIFF).
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Hubert
super member
Reged: 09/26/06
Posts: 122
Loc: Belgium
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Thanks, it's working.
How can I get now the magnitude of the star? If possible with freeware.
Clears skies, Hubert
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brianb11213
Carpal Tunnel
Reged: 02/25/09
Posts: 2076
Loc: 55.215N 6.554W
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Sorry but I'm not competent to describe how to use C-munipack - but it looks as though it will do the job.
What I do is, using AIP4WIN which is not freeware, make the green image active then select the "single star" tool (Measure menu, Photometry submenu). The star aperture & annulus are adjusted suitably, I use radii 8.0, 14.0 & 20.0. I click in turn on the following stars: epsilon Aur, eta Aur, zeta Aur, lambda Aur and the "62" star just south of epsilon on the AAVSO chart. This gives five raw magnitudes which look something like this
4.235 3.969 4.656 5.549 7.141
But I know that lambda Aur is 4.705 so the magnitude of epsilon from this comparison is 4.705 + 4.235 - 5.549 = 3.391. Similarly it's 3.172 + 4.235 - 3.969 = 3.438 compared with eta Aur and 6.218 + 4.235 - 7.141 = 3.312 compared with "62".
Actually I apply corrections for differential atmospheric correction before doing these sums. The actual arithmetic is done for my convenience in a small computer program which reads the AIP4WIN log file & processes it automatically.
I take 25 frames at a time, average & compute the expected average of the mean, and end up with something like
Epsilon Aur Oct 17.96 3.415V +/- 0.007 ref 000-BFS-941 = 3.172V
Epsilon Aur Oct 17.96 3.330V +/- 0.011 ref 000-BFS-939 = 4.705V
Epsilon Aur Oct 17.96 3.319V +/- 0.016 ref 000-BIP-386 = 6.218V
Zeta Aur Oct 17.96 3.887V +/- 0.008 ref 000-BFS-941 = 3.172V
Zeta Aur Oct 17.96 3.802V +/- 0.010 ref 000-BFS-939 = 4.705V
I'm using a Canon 40D, EF 50mm f/1.4 lens, the settings are 8 sec at f/2.0, ISO 400 with a ND8 (density 0.9) neutral density filter. Using a ND filter looks strange but it helps keep the random variations due to scintillation to a minimum, in fact scintillation is the limiting factor for the accuracy of my measures when the sky is reasonably clear.
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Hubert
super member
Reged: 09/26/06
Posts: 122
Loc: Belgium
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Hi Brian,
thanks for the very good info. I will get AIP4Win and follow your description.
clears vkies, Hubert
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walt r
Post Laureate
Reged: 02/13/07
Posts: 3458
Loc: Doylestown, PA
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Hubert,
I also have used API4WIN and it's a nice program. The book that comes with it is excellent on describing all aspects of imaging, calibrations etc. Be sure to read most of it even if you are using a DSLR instead of a CCD. There is a chapter on photometry that will walk you through the methods.
Good luck, have fun and keep us posted with your results.
--------------------
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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Hubert
super member
Reged: 09/26/06
Posts: 122
Loc: Belgium
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Walt, thanks for the advice. I'm going to buy AIP4WIN next week.
clear skies, Hubert
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phxbird
super member
Reged: 12/24/07
Posts: 116
Loc: New Mexico, USA
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I think IRIS will also do photometry but since I also use AIP4Win I can't say for sure. Iris is freeware.
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Celestron 6" Refractor
Celestron AS-GT Mount
"The Bargain Bucket" 8" Dob
Meade ETX 90 EC
Orion ST 80mm
SAC-7b Imager
SBIG ST-7E Imager
Temple Research Observatory
AAVSO Member
Society of Astronomical Sciences Member
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Hubert
super member
Reged: 09/26/06
Posts: 122
Loc: Belgium
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I've tried IRIS but it's really difficult. I'll wait for my version of AIP4WIN.
regards, Hubert
http://www.vvs.be/wg/wvs/
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