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Fits headers



Good morning Guylain - well for me in France it is already 10 O'clock and I'm having a second cup of coffee.

I have a little question about Headers. When opening CR raw pictures, taken with my Canon EOS 60Da by BYE, in for instance Pixinsight the header shows very limited information. Strangely enough the field FOCALLEN (focal length) by default shows 50 mm, which is very annoying as some functionalities make use of this info (Plate solving_ ImageSolver in PI) and one has to change this manually for every picture taken (to 950 mm in my case).

Is there perhaps a way to enter such data so that it becomes a default value?

Additionally, it wouldn't be bad if also RA and Dec data could be added (using Astrotortilla).

I don't know if all this is can be done inside BYE or maybe perhaps not at all.

Bien à toi/ Magnus


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Canon CR2, as well as Nikon NEF, File Formats store most of the sort of information that you reference in the EXIF Data embedded in the File.


EXIF Data has a pseudo-standard, but it is VERY Extensible.  And Apps like PixInsight use this to do just that - fields like "RA" or "DEC" wouldn't be applicable to the the original Canon or Nikon Cameras.


Do remember that when attached to a Scope, and not a Lens, the Camera has no knowledge of the Focal Length or other Parameters often communicated between the Lens and Camera.

So, yes, the EXIF field FOCALLEN would be left to be populated with a Default Value.


(Can we assume that while you reference "FITS Header" in your Thread Title, that you don't actually perform a RAW-to-FITS Conversion before feeding the Images into PixInxight??)

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My guess is that the FocalLength parameter in the EXIF data is intended to show the focal length of a lens, not a telescope. For my T5i, the value is 0.0 mm with no lens attached.


If you have the Premium version of BYE and you have a telescope connected via BYE's ASCOM telescope functionality BYE does add the RA and DEC, along with the Altitude and Azimuth, to the EXIF data.  The following were copied from an image that I captured with BYE 3.1.6 while the ASCOM Telescope Simulator was connected.


BackyardTelescopeALT          : 47.518304
BackyardTelescopeAZ           : 78.498915
BackyardTelescopeDEC          : 30.000000
BackyardTelescopeRA           : 1.443376


While on the Imaging screen you can view the EXIF data in the currently displayed image. The User Manual describes how to do that.


It would seem to be trivial to add the telescope focal length to the EXIF data, as well. You should create a post in the Feature Suggestion Box forum for this request.


BYE does not have access to plate solutions from AstroTortilla. In any case, the images captured by BYE for AT are JPG images that are used only for plate solving and do not have BYE's EXIF data added into them.

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Bonjour Magnus,


As Rick said, the FOCALLEN value as a default of 50mm when no lens is attached.  This value is populated by the camera firmware.  Additionally, the RA/DEC can be added in the EXIF header with the Premium version if a telescope is connected to BYE; make sure you do not skip the EXIF WRITE in the advance settings otherwise BYE will not write these additional data fields.


However, there is no option to actually add your telescope focal length directly but there is an alternative.  You can use the filter field in BYE capture plan; this field is a free text field and you can put anything and even have this value added to your file name.  This value is also added to the EXIF data, though not in the FOCALLEN field.


Hope this helps,



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