I made a quick spectroheliograph scan today to follow-up on the previous initial thermal test viewtopic.php?t=36508. I was able to do a full-disk scan using my 106mm, 700mm FL APO refractor. This telescope has typically performed very well for solar imaging in white light, CaK and H-alpha. The set-up is essentially the same as my previous SHG experiments and is shown in the photo below.
The spectrum looked very clean and fairly sharp. Most importantly, there was little to no "transversallium" running perpendicular to the spectral lines. Below is a screen shot of an SER video file taken near H-alpha.
I was able to capture a full-disk image at 700mm focal length, with plenty of room to spare on the slit and a little room to spare on the camera sensor. I had some problems with focusing all the various optics since the image scale was very different from my previous setup. Given quite a few clouds today, I didn't have time to sort out all the focus problems so the images did not come out very sharp.
Below is a "raw" output from our in-house SHG software. It does not have any noise reduction, geometric correction or contrast enhancement. Despite not being quite in focus, the noise level is seen to be quite good (no significant "transversallium"). The new 9 micron by 12 mm chrome-on-quartz slit will likely give good quality images once the system is better tuned. This image was scanned in DEC so the correct orientation would be rotated 90 degrees counter-clockwise.
On the topic of heating: the "blue" absorbing oxide on the quartz/chrome interface (see viewtopic.php?t=36508) does result in heating of the slit assembly with long-term exposure, such as a 1-hour imaging session. I took out the Thorlabs 1-inch optical tube for examination it and it felt quite warm, almost hot. The good thing is the copper disk, on which the quartz chip is mounted, seems to act as a good thermal conductor and dissipates the heat away. I may look for a way to even better heat sink this in the future. The chrome/quartz chip showed absolutely no damage; it seems to be almost indestructible. The cyanoacrylate glue also did not show any degradation.
Some experimental details: a 2400 l/mm holographic grating, 30mmx30mm from Edmund Optics, was used; both the collimator and camera lenses were 100mm f4 old-fashioned SLR lenses; the camera was a ZWO 178MM. Due to the high light intensity, I could use a 1ms exposure at a gain of 24 (4%). For some reason, the frame rate was lower than expected (I think a USB interface computer problem) so the FPS was only 200, which meant the scanning was done at 8X sidereal rate (normally I would be able to do about twice that).
First full-disk SHG image at 700mm FL with new chrome-on-quartz slit
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First full-disk SHG image at 700mm FL with new chrome-on-quartz slit
Last edited by thesmiths on Thu Jun 16, 2022 5:56 pm, edited 2 times in total.
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Re: First full-disk SHG image at 700mm FL with new chrome-on-quartz slit
Woaw, that sounds really promising
spectro-coronographe ,Bresser 127/1200 ; Bresser 102/1350 , ASI 178MM
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Re: First full-disk SHG image at 700mm FL with new chrome-on-quartz slit
Well done a great start and I am sure will only get better
Alexandra
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