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Filter codes for electronic images

HUZ's picture
HUZ
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Joined: 2010-09-11

Hey - I'm trying to submit data from a ccd camera that was taken with a photographic-green filter (not a split tri-colour G), and I can't find a list of the codes anywhere.  What is the actual code for the filter for a pre-formatted file? 

 

Rick (HUZ)

I'm afraid there is no
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FRF
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I'm afraid there is no special code for such a filter. You can use either TG or CV until other option exist.
You can type in the remarks field that it was made using CCD with photographic-green filter...

Arne might correct me ig I'm wrong.

Filter codes for electronic images
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FJQ
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To:  Rick

Robert mentioned TG or CV. Just to expand on this did you check on this page under the "DATA" header:

http://www.aavso.org/aavso-extended-file-format

Here are some choices:

FILTER: The filter used for the observation. This can be one of the following letters (in bold):

  • U: Johnson U
  • B: Johnson B
  • V: Johnson V
  • R: Cousins R
  • I: Cousins I
  • J: NIR 1.2 micron
  • H: NIR 1.6 micron
  • K: NIR 2.2 micron
  • TG: Green Filter (or Tri-color green). This is commonly the "green-channel" in a DSLR or color CCD camera.
  • TB: Blue Filter (or Tri-color blue). This is commonly the "blue-channel" in a DSLR or color CCD camera.
  • TR: Red Filter (or Tri-color red). This is commonly the "red-channel" in a DSLR or color CCD camera.
  • CV: Clear (unfiltered), V-band comp star magnitudes (this is more common than CR)
  • CR: Clear (unfiltered), R-band comp star magnitudes
  • SZ: Sloan z (formerly in database as Z)
  • SU: Sloan u
  • SG: Sloan g
  • SR: Sloan r
  • SI: Sloan i
  • STU: Stromgren u
  • STV: Stromgren v
  • STB: Stromgren b
  • STY: Stromgren y
  • STHBW: Stromgren Hbw
  • STHBN: Stromgren Hbn
  • MA: Optec Wing A
  • MB: Optec Wing B
  • MI: Optec Wing C

 

 

James

photographic green
HQA's picture
HQA
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Joined: 2010-05-10

Hi Rick,

I assume that you mean a Wratten filter like a Wratten 40, and not the typical tricolor filter?  We can't have codes for the dozens of photographic filters, especially since none of them correspond to a standard Johnson/Cousins bandpass.  I'd pick something in the list that is close to what you think your filter is, and then include a comment indicating what filter was actually used.  TG is probably a good choice.

Arne

TG, TB, TR
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WBY
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Is it correct that TG, TB and TR are the correct filter designations for the normal tri-color imaging filters used in front of a B&W CCD camera as the tri-color channels from a color CCD?

One step further,  in comparing the R-G-B color imaging ("Tri-color" for short) filters, for example, the "G2E" filters from Astrodon, with the Astrodon interference type Johnson cousins filters, it seems that it should be possible to transform the tri-color G and B-G onto the Johnson cousins standard. They are different but not extremely different. However, it appears that the Tricolor R and the Rc are very different even for the Astrodon interference type that have a built in IR cutoff. Can anyone comment on the success, or lack thereof, of transforming photometry using the tri-color filters to the J-C standard? In particular, has anyone done this with FITS files from Slooh?

 

I have attached response curves of the two sets of filters for reference. 

RGB filters
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TCB168
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WBY wrote:

Is it correct that TG, TB and TR are the correct filter designations for the normal tri-color imaging filters used in front of a B&W CCD camera as the tri-color channels from a color CCD?

One step further,  in comparing the R-G-B color imaging ("Tri-color" for short) filters, for example, the "G2E" filters from Astrodon, with the Astrodon interference type Johnson cousins filters, it seems that it should be possible to transform the tri-color G and B-G onto the Johnson cousins standard. They are different but not extremely different. However, it appears that the Tricolor R and the Rc are very different even for the Astrodon interference type that have a built in IR cutoff. Can anyone comment on the success, or lack thereof, of transforming photometry using the tri-color filters to the J-C standard? In particular, has anyone done this with FITS files from Slooh?

 

I have attached response curves of the two sets of filters for reference. 

This article http://reductionism.net.seanic.net/CCD_TE/cte.html#Derivation

has a comparison using meade tricolour filters and Schuller filters. The comparison is near the end of the document.

Terry

RGB
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WBY
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Terry, Thanks for reminding me about Bruce Gary's article. I had it but had forgotten about it. It was a supplement to the 2005 version of the  AAVSO CCD photometry manual. In later years the manual was simplified, many might say "dumbed down" to make it less intimidating for beginners. I am glad to see that AAVSO has plans to reintroduce an advanced "how to" guide including more advanced calibration techniques and transformation. Although I agree that a layered approach is less daunting, in my opinion eliminating the material from the manual entirely was not a good idea. 

Looking at the article also reminded me that the shape of the star's spectrum is important in determining the amount of correction needed and the greater variations in the shape of sectra  in the U and B filter portions of the spectrum increases uncertainty in the associated transformation coefficients for shifts in these pass bands relative to V and R.   So even though the difference in filter responses curves is greater in R there may be less uncertainty in the transformation. The proof will be in the calculations. 

 

Brad Walter

photographic green
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HUZ
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Joined: 2010-09-11

Thanks Arne and everyone,

Sorry - got busy organizing a star party ... now back to photometry!

I think I will report it as CV with a note.  I do have a whole bunch (thousands) of Wratten green undergrad student frames that I am reducing.  They took these to learn about RGB imaging and colour balancing.  But luckily, each set of RBG also has V&R frames shot at the same time.  So I can do a direct comparison of the data and find the match to be amazingly good with an offset of only around 0.02V mag.  I also use lots of check stars to see if there is any fall-off and I don't see these images are particularly worse than the V frames, especially on steady nights.  When I get through some more of the data, I'll report back.

One good thing is that the students are prolific imagers, but the downside is that they are students often doing their first photometry, and they are very poor in process and consistency - often shooting in every condition , through clouds and often having poorly calibrated frames.  Good thing is that their original cal frames are available, and I can therefore recalibrate the images.  Always a challenge, but lots of fun. 

Thanks for the advice.

rick

photographic green
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HUZ
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... oh sorry ... will report as TG with a note about the Wratten filter.

 

rick

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