Jump to content


Photo

photometry questions

  • Please log in to reply
42 replies to this topic

#26 ASTERON

ASTERON

    Surveyor 1

  • *****
  • Posts: 1702
  • Joined: 24 Nov 2007
  • Loc: ISRAEL

Posted 16 January 2011 - 01:36 PM

Hi Jim,
Thanks for the link. looks like an interesting one ( especially as it includes the software as well). Do you know when the book was first published ? (I have some books from Willman-Bell that while being very good for their time are a little antedated because they dont cover the most recent stuff on the market.)
I am still interested in in other responses by other variable star obdservers.

#27 gavinm

gavinm

    Surveyor 1

  • -----
  • Posts: 1695
  • Joined: 26 Aug 2005
  • Loc: Auckland New Zealand

Posted 16 January 2011 - 03:27 PM

You could do exoplanets - short period, there's plenty of them, they aren't too challenging (although it is challenging to get really good data). I image from the middle of a urban environment using a range of filters. LP has not been an issue.

Try this book by Bruce Gary (exoplanet specific but v/ good)
http://brucegary.net/book_EOA/x.htm

This one is also quite good.
http://observatory.o...rccd22oct06.pdf

#28 Mirzam

Mirzam

    Skylab

  • *****
  • Posts: 4458
  • Joined: 01 Apr 2008
  • Loc: Lovettsville, VA

Posted 16 January 2011 - 04:45 PM

Hello Asteron,

I know what you mean about some of the W-B titles being out of date.

However, the Image Processing handbook is the second edition from 2005. I have the 3rd printing of the book from 2009, and the AIP4WIN software included with it is version 2.3.1, which is fairly recent (I think).

The book includes a good discussion of many basic principles of image calibration, signal-to-noise, characterizing your CCD performance, etc., that are applicable to both astrophotography and photometry. I like it but I still have a lot to learn.

JimC

#29 ASTERON

ASTERON

    Surveyor 1

  • *****
  • Posts: 1702
  • Joined: 24 Nov 2007
  • Loc: ISRAEL

Posted 16 January 2011 - 04:53 PM

Hi Gavin,
Thanks for the links.
Exoplanets are interesting - I will look into this

#30 ASTERON

ASTERON

    Surveyor 1

  • *****
  • Posts: 1702
  • Joined: 24 Nov 2007
  • Loc: ISRAEL

Posted 16 January 2011 - 04:56 PM

Jim,
Thanks. I will probably order it directly from W-B
too bad they rip you off on international shipping rates.

#31 btieman

btieman

    Viking 1

  • -----
  • Posts: 891
  • Joined: 24 Jul 2008

Posted 16 January 2011 - 06:55 PM

You might also look up Brian Warner's book "Lightcurve Photometry and Analysis" Covers most topics relating to general photometry--variables, binaries, asteroids, etc...

I got my copy direct from: http://www.minorplanetobserver.com/ but I image Amazon carries it as well.

Brian

#32 ASTERON

ASTERON

    Surveyor 1

  • *****
  • Posts: 1702
  • Joined: 24 Nov 2007
  • Loc: ISRAEL

Posted 17 January 2011 - 03:20 AM

Brian,
Thanks - looks like a very useful one I will order this soon.

#33 ASTERON

ASTERON

    Surveyor 1

  • *****
  • Posts: 1702
  • Joined: 24 Nov 2007
  • Loc: ISRAEL

Posted 17 January 2011 - 03:48 AM

Brian,
Just ordered Brian warner's book from Amazon.
Supposed to reach me only on mid February :bangbangbang:
In the meantime I will try reading the PDF books recommended by Gavin (already downloaded).
Thanks everybody for the links and recommendations :bow:
Any other intresting primers or more advanced references or books ?

#34 Hubert

Hubert

    Mariner 2

  • -----
  • Posts: 254
  • Joined: 26 Sep 2006
  • Loc: Belgium

Posted 17 January 2011 - 07:16 AM

Hi Asteron,

Have you read the AAVSO CCD manual?

http://www.aavso.org...010_revised.pdf

clear skies, Hubert
http://www.vvs.be/wg/wvs/

#35 ASTERON

ASTERON

    Surveyor 1

  • *****
  • Posts: 1702
  • Joined: 24 Nov 2007
  • Loc: ISRAEL

Posted 17 January 2011 - 07:43 AM

Hubert,
No - thanks for pointing this out. I will read it.
Incidentally I thought in order to use AAVSO website you need to be a member ?

#36 Hubert

Hubert

    Mariner 2

  • -----
  • Posts: 254
  • Joined: 26 Sep 2006
  • Loc: Belgium

Posted 17 January 2011 - 07:57 AM

No, you don't have to be a member.

clear skies, Hubert

#37 zvaragabor

zvaragabor

    Sputnik

  • -----
  • Posts: 35
  • Joined: 25 Jan 2011

Posted 21 December 2013 - 06:16 PM

My question is, can I use a color webcamera for photometry?

#38 Ed Wiley

Ed Wiley

    Apollo

  • -----
  • Posts: 1049
  • Joined: 18 May 2005
  • Loc: Texas, USA

Posted 21 December 2013 - 09:03 PM

I used to think that one needed a mono ccd and filters. Not so. Google "webcam photometry." Here is one paper I found, there are others.

http://adsabs.harvar...SASS...28..117T

Ed

#39 jgraham

jgraham

    Voyager 1

  • *****
  • Posts: 13908
  • Joined: 02 Dec 2004
  • Loc: Miami Valley Astronomical Society

Posted 21 December 2013 - 09:56 PM

I don't see why not. I would use the green channel and the V photometric reference data. The usual guidelines apply in that you either need to operate within the linear range of the camera or determine the transfer function to linearize the data. One possible challenge in that a webcam might be limited to 8 bit data. Whenever I start using a new camera for photometry I'll take some time to compare my results with data reported on the AAVSO web site.

Give it a try, what could possibly go wrong?

#40 zvaragabor

zvaragabor

    Sputnik

  • -----
  • Posts: 35
  • Joined: 25 Jan 2011

Posted 26 December 2013 - 01:45 PM

Can I convert G (RGB) to V (UBVR)?

#41 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 26 December 2013 - 06:25 PM

No, the V filter is specific. There are some thAt don't care.

#42 Ed Wiley

Ed Wiley

    Apollo

  • -----
  • Posts: 1049
  • Joined: 18 May 2005
  • Loc: Texas, USA

Posted 26 December 2013 - 08:27 PM

I think you need to start digging into this if you want to do photometry with a color camera. A good place to start is

http://www.citizensk...out-citizen-sky

and

http://www.citizensk...n-and-reduction

I think that if you nose around the Citizen Sky site, sign up, do a bit of reading and research you will find most of your answers. I say this not because I am withholding information but because I don't have authoritative answers; but the folks at Citizen Sky probably do.

Ed

#43 NJScope

NJScope

    Ranger 4

  • *****
  • Posts: 382
  • Joined: 08 Mar 2004
  • Loc: NJ

Posted 29 December 2013 - 04:46 PM

zvaragabor:

In principle, yes you could convert "G" from the RGB system to "V" from UBVRcIc typically used for photometry. For example VT from the Tycho-2 catalog is not exactly equal to V from the Johnson-Cousins system. Nonetheless, when VT values collected with the Hipparcos satellite are compared to reference V values determined elsewhere, within reason a relationship can be established between the two magnitude systems [ie. VT - 0.090 * (BT - VT)]. Note however, that in this case BT values are also required. The formulae are actually much more complicated and depend upon the range of (BT-VT). This should in no way discourage you from using the G channel from a color camera to produce lightcurves from a number of targets including asteroids, variable stars, stars with potential exo-planets, or even some extended star-like objects (eg quasars). This is particularly true for anyone who is simply trying out photometry as an alternate to visual observing or astrophotography. Indubitably if you intend to regularly publish your data, you should consider purchasing a purpose-built, temperature-controlled, non-antiblooming ccd camera equipped with photometric filters. That does not, however, preclude the use of a mono- or color-webcam, dslr or single-shot color ccd camera which can produce publishable lightcurves from minor planets or prove the existence of a new variable star.






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics