OK my package just arrived from Elec2go.
They look terrific and I think will serve this purpose well !!
The first pic is of the A3 sheet, it looks pink when it's 'off'.
The second pic is what it looks like when it's 'on' in the dark.
I then took a CWB (Custom White Balance) of the sheet and applied the CWB to this quick test flat frame using the 5D and the 24-105mm L set at 24mm f4 and ISO100 for a 1/25th sec exp.
The last shot was of the cuttable version when it's on.
I'll be using this for another purpose.
(BTW this shot was with the CWB on).
Can't wait to test it with the Tak and build up my light box now.
Hi Guys, Mine arrived today. Quickly shot a serries of flats and made a master. I didn't bother to clean the CCD of the QHY8 which needed a clean.
The info below is from one of the FITS headers. The final Master is a combination of 20 such files combined in IP3.
SIMPLE = T / file does conform to FITS standard
BITPIX = 16 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 3040 / length of data axis 1
NAXIS2 = 2016 / length of data axis 2
EXTEND = T / FITS dataset may contain extensions
COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy
COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H
BZERO = 32768 / offset data range to that of unsigned short
BSCALE = 1 / default scaling factor
CREATOR = 'Nebulosity v2.0.3' / program and version that created this file
INSTRUME = 'QHY8 ' / instrument name
DATE = '2008-11-17 01:09:16' / UTC date that FITS file was created
XPIXSZ = 7.8 / X pixel size microns
YPIXSZ = 7.8 / Y pixel size microns
EXPOSURE = 0.6 / Exposure time [s]
GAIN = 32 / Camera gain
OFFSET = 104 / Camera offset
BIN_MODE = 1 / Camera binning mode
ARRAY_TY = 1 / CCD array type
XBINNING = 1 / Camera binning mode
YBINNING = 1 / Camera binning mode
EXPTIME = 0.6 / Exposure time [s]
INPUTFMT = 'FITS ' / Format of file from which image was read
At this stage I havent been able to try it on an actual image but hopefully tonight.
Looks good Doug... Doesnt look like your camera needs a clean... Theres only really 2 spots on that (both of which look to be on the camera, although its always hard to tell) but they are small...
OK my package just arrived from Elec2go.
They look terrific and I think will serve this purpose well !!
The first pic is of the A3 sheet, it looks pink when it's 'off'.
The second pic is what it looks like when it's 'on' in the dark.
I then took a CWB (Custom White Balance) of the sheet and applied the CWB to this quick test flat frame using the 5D and the 24-105mm L set at 24mm f4 and ISO100 for a 1/25th sec exp.
The last shot was of the cuttable version when it's on.
I'll be using this for another purpose.
(BTW this shot was with the CWB on).
Can't wait to test it with the Tak and build up my light box now.
So the second one must be for that underwear fetish you have nice an customisable - - is there an anniversary coming up soon RB
Doug - a quick question, do you shoot your flats at the same gain and offset as your images?
Alex... Everything the same except the exposure duration. Trial and error seems to be the way to go with duration. Try to keep the histogram to the left of center and the readout for the center of image at about 20,000. I don't know how critical it is but I am going to explore the best or at least the theoretical best settings as posted by TerryB a while back.
This is the post. http://www.iceinspace.com.au/forum/s...ad.php?t=37175
Doug.
As for the flats, the flat needs to be in the linear part of your sensor otherwise when you divide by them they will give an incorrect result. This was discussed on one of the photometry groups as the linearity is important for photometry.
Your sensor on the QHY8 is an antiblooming sensor and is probably not particularly linear above about 1/2 the saturation level.
You could try and measure the linearity by taking a series of images of the same star field with a bright star that will saturate the sensor and some dimmer ones that don't. Expose for increasing times in ~10 sec increments. ie 10,20,30,40,50 sec etc until you have saturated the bright star. You need to start with an exposure that doesn't saturate the stars.
You then measure the flux of a few stars in the images and graph the results against time.
This assumes that the stars you are imaging are not variable in the short term and that no clouds etc have stuffed up some of the images.
The results you get will look like the attached charts.
After doing this you can pick what intensity is linear for your CCD and keep the flats within that range.
Does this mean that you still need to build a box to hold it? Or am I missing something?
Pete
I was thinking of building something simple so I can have the EL sheet in a tidy frame, but I suppose I can just lay the sheet directly on the dew shield of the scope as a bare minimum.
I have just built a lightbox (very dodgy construction but it does the job) - I am in danger of being seduced by the prospect of a simple illuminated screen.
I have just built a lightbox (very dodgy construction but it does the job) - I am in danger of being seduced by the prospect of a simple illuminated screen.
Looking forward to updates on how it goes
Pete
Will keep you updated Pete.
Quote:
Originally Posted by AlexN
I'll just build a small frame similar to what people make for full aperture film solar filters... Seems simple enough, and will do the trick
I'm thinking similar, something simple will suffice.
I have just stuck mine on a suitably sized sheet of plywood with double sided mounting tape (Cloth type). I will eventually get some clear perspex to go over the top and edge it with plastic C section. Should do the job. I may even get rash and make a fabric protective bag to keep it in.
I have finally done a few tests on the light panel. The test images consist of 2 X 10 minute images of NGC253 Calibrated with flat frames only. The flats were 5 images combined in IP3 with a median combine. IP3 was used for the full calibration and stacking process.
It is obvious that these still require a bit of work to sort out the best settings with the QHY8. I think I will have to experiment a lot more to get things correct but the panel does show promise.
The images were stretched in PS CS3 way more than normal to show the extent of the correction.
The shots in order are calibrated using the following calibration files.
Thanks for the feedback Alex. I have a bit more work to do and I an investigating the best settings for taking Flats with the EL Panel. I will post the results when I work it out.
"One way to test the quality of the flat field frame light source is to create a master flat field frame and create a second master flat field frame with the telescope or light
source rotated 90 degrees. The first master flat field frame is used as the test image
which is calibrated by the second rotated master flat field.
A good flat field calibrated test image is a uniform noisy image with no dark or light areas. A good test image histogram is a normal probability distribu
tion. The normal probability distribution is caused by at least three types of noise that are in the master flat field frame and the test image. The noise sources are photon noise, dark current noise and readout noise. A nonuniform light source causes dark or light areas in the test image."
"One way to test the quality of the flat field frame light source is to create a master flat field frame and create a second master flat field frame with the telescope or light
source rotated 90 degrees. The first master flat field frame is used as the test image
which is calibrated by the second rotated master flat field.
A good flat field calibrated test image is a uniform noisy image with no dark or light areas. A good test image histogram is a normal probability distribu
tion. The normal probability distribution is caused by at least three types of noise that are in the master flat field frame and the test image. The noise sources are photon noise, dark current noise and readout noise. A nonuniform light source causes dark or light areas in the test image."
Thanks for the comments John. I don't think the light source quality is the issue. I think the intensity of the flat frames is the item in question. The length or duration of the exposure is the hard thing to get right. Once this has been scoped for my camera I think the panel will produce excelent frames which correct abberations in the light frames and don't tend to add a few from an over exposed or under exposed flat frame.
I'll keep at it when the weather clears and I can find the linear exposure for this camera.
Thanks John I will look it up and see what they have to say. Interestingly the internet is full of information on flat frames but some directly opposes other information. Looks like trial and error is going to be the best method. At least for me.
Hughy bought his electroluminiscent sheets round, heres 2 pics I took of the sheet, it gives an even bluish white glow. The histogram on the camera shows that there is plenty of red light present as well, so it would be good for flatfielding in any colour band. As a guide to its brightness the full frame view was with the camera lens slmost touching the sheet, F5.6, 1/60sec ISO400, with unmodded 400D, on Auto.
Scott
nice an customisable - - is there an anniversary coming up soon RB
