Inspired by Ken's implementation of Christian Buil's design some time ago, this is what I have done so far... No images yet, just ideas on how to put together SHG with what I have on my junk yard...
The biggest challenge is slit (image of 1/2 blade through optical train is attached), considering it has to be very narrow (10 um as per Christian Buil), but I think I solved it - at least in principle, using Gillette razor blades and simple sliding mechanism to adjust the slit width. Hopefully it will work. I even have miniature stepper with linear actuator, I may use it at some stage in the future if I am happy with operation of this instrument.
Optical elements are: old Industar 50 lens as colimator, foil grating (1000 l/mm) and old Kyocera M400R camera with it's 10x zoom lens.
Everything is mounted on improvised frame made from cut-offs of "L" 50x50x3 mm extrusions (with machined holes for optics), assembled and tightened with screws...
Pencil sharpener blades, with the single bevel work better than razor blades.
It’s more usual to work with higher resolution reflection gratings.
For the SHG the minimum seems to be around 1800 l/mm with the standard at 2400 l/mm
The Camera really needs to be fast frame, capable of >60 fps and a typical solar scan will take up to 3 Gb depending on the chip.
The INTI program to convert the AVI to a quality image has undergone some significant improvements in the last few months and the latest V3.5 is very capable.
Onwards and Upwards.
Thank you for the comments..
This is just my attempt to re-purpose what I have, and by no means the last one.. If I find observation with this instrument interesting (for me), I will invest in more capable camera and better optics.. This camera has 30 f/sec, and supports AVI format.
This arrangement of the slit width semi-adjustable block is better, I believe...
The left side (with 1/2 of the blade) is screwed to the bottom of the adapter, the right block (with second half of the blade) can be moved up-down to adjust the slit width.
It is easy to add screw for manual/motorized adjustment as well.
I will add the springy shim to hold the right-hand block (with other blade) down to the base plate (using two holes for screws on the left).
This arrangement has been used on other spectroscopes.
Just check the wedge angle vs closure.
Pencil sharpener blades are still better.
Yep.. I can still use pencil sharpeners down the track, the same principle applies...
Angle I will use (hopefully) will be 1°, this will give me fine enough adjustment.
First spectrum.. Energy saving lamp.
I will definitely need better grating (more l/mm) and more narrow slit (this one is made from 2 razor blade halfs.
After watching this video, I decided to try this approach, using pencil sharpener blades.
My implementation should look something like in the attached sketch.
Also, it occurred to me I could try to use here my Hartridge spectrometer..
There will be some limitations (very narrow FOV), now waiting for neutral filter for my Rubinar 8/500 (to avoid possible thermal damage to parts close to focal point).
Solar spectrum from hand... Magnesium triplet is clearly visible.
Needle (reflective slit) has some issues, (not polished properly.. I need to find a better one) but generally resolution is decent.
Also there is a lot of stray light.. I need to think of some sort of enclosure for the contraption.
Bojan/ Hamish,
I spent some time with Maurice when I stayed in Cobham. He used to visit me and I'd go over to his observatory (12" Meade).
We did discuss, among other things, various slit designs, including reflective needles.
The generally poor surface accuracy gives lots of Transversalium and the reflected beam spreads out over a wide arc - very inefficient. High speed rotation of the needle seemed to give slightly better results.
(See p142 "Astronomical Spectroscopy for Amateurs.)
I used a needle reflection to show the solar results which can be obtained with a grating and telelens.
I wonder if glass fiber (ø0.12 mm) could be used? The surface appears to be much better, compared to the needles I have at the moment.
Since there is a lot (too much actually) of light from Sun, losses are actually welcome.
Bojan,
There a guy in the US spray painting his large mirrors rather than aluminium vacuum coating. The details must be somewhere.....cheaper solution to test?
There's Angel Gilding spray silvering that's not really spray painting. It uses spray bottles but is really a chemical deposition.
Have a look in the ATM section and see if anyone is silver coating their own mirrors.
The optical fibre sounds like a good idea, even without a coating. It will certainly be smooth and it's designed to be as reflective as possible within the fibre so it would seem reasonable that the outside would be too.
Guys, thank you for the tips.
If all goes as I hope it would, I could try this spray (prohibitively expensive!!), or better still, I could ask someone to put my fiber with their mirror in their aluminizing chamber...
Holman 25 mm PVC plain Tee is perfect for the purpose.. machined (with holes for precise positioning of the reflective slit) and ready for spray of black paint.
The tee-shape will also help keeping the stray light away from camera (to further improve attenuation, I may add some more black painted tubing at the end)
