Reflective slit with optical fiber is excellent (no transversaliums).. but a bit dark, so aluminization should be in order. Also I wander if ghost lines are visible (left, internal reflections in fiber?)
On image below I captured green line (577.7 nm) from spiral lamp.
The whole thing is too fiddly for solar spectrum.. so I need to do some more of mechanical work.
Based on slit image (first pic from previous post) and measured fiber diameter (0.12 mm, 40 pixels), effective slit width is ~6 pixels, ~18 um.
Please note, this measurement is done without any optics.. and the scope I intend to use will be Rubinar 8/500 or Samyang 500/ f6.3.
And, if higher f/number for colimator (Industar 50) is used (currently 3.5, wide open), the effective slit width could be reduced to <5 um.
Not bad for the price I paid for it :-)
I've not been following the thread. Let me know if you need more/various fibers/glass rods (or mirrors but then post to/from nz may be a pain) aluminized. I have a working aluminizing chamber.
aluminizing a fiber may require at least 2 passes if a full coverage is desired in order to avoid the need to care about which side of the fiber you have facing your light source. The aluminium atoms fly in a straight line inside the chamber.
Hi Hamish,
My apologies for late response and thank you for your offer...
At the moment I have all the help I need from Stefan :-)
After quite some time I had a chance to have a brief look (visual, no camera yet) through my spectrometer, mounted on Rubinar 8/500.
I tried with camera, but there is too much stray light, so I need some sort of a black cloth enclosure to be able to take usable images.
Contrast and resolution are quite decent (there was no NF, still waiting for it)).
I managed to rotate the fiber in right direction, but still there are a lots of transversals.. so I wonder if we will be able at all to solve this problem with fiber.. Of course the standard slit approach is still the viable and tested option.
Anyway, this is a progress.. small and slow but still a progress..
Since my ø76 mm NF8 arrived couple of days ago, today I attempted another approach - with Hartridge spectrometer.
I already had necessary adapters ready, so it was just a matter of putting the system together in 10 minutes and try..
Spectrum looked OK, but Sun's image focus on slit was way off..
Then the clouds rolled in.
I suppose the challenge will be to control the camera exposure (I was using Free2X Webcam capture app, it seems it was set to Auto - I have to fugure how to adjust that yet).
Sun's image diameter may need to be scaled properly (at the moment, it was ~5mm in diameter (scope is Rubinar 500mm f/8, without Barlow).
Also, I should increase the spectrum scale, secondary band is not necessary and may confuse Sol'ex software.
Bojan,
The INTI software for the reconstruction of the solar image from your SHG relies on selecting an ROI which just shows the target spectral line.
With my camera, ASI 178 this means processing an SER video file of 3000 x 100 pixel. The SER file is usually about 2000 frames to give good coverage of the solar disk.
Ken
Bojan,
I don’t see any frame rate control.
To get a usable SER file you need to be able to run at a high frame rate.
When you’re ready just drop me a PM or email.
Frame rate can be set to 30 f/sec max.
Once I sort out the electronics f/w for my tracker (I will set it to 10x faster than tracking), I will have ~18 sec for Sun disk scan (540 frames.. should be enough for the proof of concept).
Also, I have two cameras - Logitech 4000 Pro (640x480) and IMX291 (1920x1080).
The latter one has IR filter glued to the sensor cover glass, so I have to figure out how to remove it without damaging the sensor. Maybe with hot air soldering iron and scalpel to lift the filter.
I managed to obtain sensible video scan this morning in IR part (starts as narrow transversal line, gets wider and wider, then after a while starts to shrink until it disappears as Sun disk is traveling over the spectrometer slit), but apparently the focus is still not quite OK.
The mount I was using for this experiment (EQ3-2) has limited controls (only tracking), and unfortunately my LXD75 in at Mount Pleasant.. so the adjustment of the whole setup was fiddly, and sunlight glare on the lap screen didn't help either.
Anyway, now I have first-hand experience about what else needs to be done to make this procedure more comfortable (proper mount under full remote control, sun shade for lap, comfortable chair etc..).
The fat line on the spectrum below is at ~750 nm (according to dial on the spectrometer - I am not sure how accurate it is in IR since it is calibrated for visual), most likely O2 band (760 nm)
Yes, I was going for the most prominent feature in the spectrum.
Dial is actually quite accurate, even in IR.
This photo was taken with modified Logitech 4000 Pro, and "blue" is not blue, is is IR.
I may try again H-alpha later today or tomorrow.
Bojan,
Using an ROI to isolate the immediate area around the target line will minimise the size of the capture file. They can get pretty large!!
Many SHG users use FireCapture (freeware) or SharpCap (pay ware) to control the camera and ROI
I use FireCapture.
When the solar disk is in focus, the top and bottom edges of the spectrum should be clean and tight.
The next step then then to get best focus WITHIN the target line - that’s where the data lies to for the SHG image.
You’ll start to see wiggles bright and dark spots within the line as you get close to usable focus.
Ken
Thank for the tips..This was roughly what I was doing...
Focus of the Solar disk is not easy to achieve, the focus ring on that Rubinar (8/500) is quite tight.
I think I will try to come up with some sort of focusing screen, to get it close enough for the start. F/8 will be forgiving for couple of 1/10 of mm difference in slit distance from lens focal plane (I hope..)..
The capture software (Free2X Webcam) is quite easy to use, and camera driver allows for adjusting exposure time (minimum is 1/10,000, just fast enough. Slit is also close to minimum width, I can't go much lower in order to avoid transversals).
I tried couple of codecs, MP4 results in lowest compression artifacts. Maybe video camera without compression is the way to go (that will be in the future).
Attached is one frame from AVI file, southern (or is is northern?) solar limb is nicely visible. Obviously, 5 mm solar image diameter is too large for Hartridge slit, so I will have to do couple of scans to capture the whole disk.
Anyway.. slowly getting there.
