GRAS FITS files problem

[Craig_L]

Hi,

Thought I would try the GRAS scopes out and while the imaging went fine I'm having trouble with their FITS images. When I open them in Nebulousity or PS through the Liberator plugin, they are very, very dark with very little nebulousity showing, even with stretching.

Shots looked fine viewing them on the GRAS site as I took them through their window, but once downloaded from the site, problems.

I also use Nebulousity sometimes to capture through my DSLR and these are stored as FITS files but I have no problem processing these, just the GRASS ones. I'm use to using DSLR and RAW, TIFF files, not FITS.

Anyone have any any tips?

Cheers,

Craig

[Terry B]

Try opening them in something like Iris (http://www.astrosurf.com/buil/us/iris/iris.htm) that is very easy to move the dynamic range of a fits file. The other simple option is FITSview (http://www.nrao.edu/software/fitsview/).

[Craig_L]

Thanks Terry, will give both a go. Craig

[Bassnut]

Gras FITs are 16 bit unstreched uncalibrated, raw out of the camera, just like the FITs out of any Astrocam. The signal level is relative to exposure time. I always use the log stretch function in Liberator with (calibrated and stacked) FITs, otherwise, as you have found, they are very dark and need lots of stretching in PS.

Stacking/calibration programs screen stretch whilst processing, so this is all not obvious with them. I may misunderstand what your tying to do, but I guess you are 1st useing a stacking/calibration program on the GAS FITs, which also can stretch before loading into PS if you wish.

You cant just load GRAS FITs into PS as is, they at least need calibration which cant be done in PS. Calibration files are avaiable on the GRAS FTP site for the camera you used.

[Craig_L]

Ah, thanks Fred. Have the GRAS calibration files. Just looking into it all now. Not as easy as I thought. Craig

[dugnsuz]

Will Images Plus handle FITS/Calibration files?

[jase]

Yes. Image Plus will handle FITS and calibration files.

So does DeepSkyStacker...however, if you need to scale the dark frames, DSS has problems. It assumes that the dark frames are the same exposure as the lights. If you've got a 30min dark frame and need to scale it to match a 10min light frame - it will not work. CCDStack, MaximDL, Image Plus and others support dark frame scaling.