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Astrofriend
26-11-2017, 02:01 AM
Hi,

What can you do during a rainy and boring day?

Yes, write something about about old project ideas that newer have been realized.

For many years I have been wondering how to construct a beam splitter system to make more efficient use of exposure time when doing color or narrow band imaging.

I have today written down my ideas here:
http://astrofriend.eu/astronomy/projects/project-high-efficiency-narrow-band-imaging/project-high-efficiency-narrow-band-imaging.html

There are a lot of interesting links there too to read.

/Lars

ZeroID
27-11-2017, 04:47 PM
Lars, take a look at a video projector. It uses a beam splitter cube as you describe to combine the three RGB channels to create the full colour screen picture.
I was looking at using one for guiding while imaging through one scope.

Astrofriend
27-11-2017, 08:54 PM
Hi Brent,
I have working with projectors during many years. In three panels LCD with normal "white" lamp there is both a splitter and combiner. But there is some problem, the intensity from the lamp is very intensive, the filter will not last for long time. Especially the IR cut filter. The other problems, many models have very small filters, I don't think they can be used for a APS-C sensor, but I shall take a look if I find an used LCD projector.

Very long time ago in the early 1980 there was a very special CRT Elctrohome ECP projector that had a combiner of very big size, I think it was 5", but that's way to big. It also have a big f/1 lens, but poor quality compare to the need in astronomy photos, but if you find one, take the spare parts from it and do something fun.

http://www.hcinema.de/pro/anzeigen.php?angabe=electrohomeecpg raphics

Thank Brent for the idea/information, I shall add this information on the homepage. It's much easier to find a used LCD projetor then old video cameras with this construction.

/Lars

ZeroID
28-11-2017, 09:58 AM
Hi Lars, you would not be using a lamp, just the splitter cube to provide 3 light paths to mono cameras with an appropriate filter for each.
I suspect the biggest issue would be light loss and possible refraction artefacts caused by the splitter. And of course finding a cube big enough for the purpose.
My project was a straight through path to the camera but a reflective path to a guide cam. Any star in the field was therefore a possible guide star.
The other option was to use one of the new SLT cameras, mirrorless technology to provide a lightpath to a guider but I have not got a spare camera with that technology to cannibalise to repurpose.

trent_julie
28-11-2017, 10:03 AM
Hello,
I tested this very concept about two years ago. I was able to get some good results.

Trent

ZeroID
29-11-2017, 06:34 AM
Hi Trent, are you talking about RGB splitting or guiding ?
Can you provide any more information ( on either ) ?
Always looking for new ideas....

Merlin66
29-11-2017, 11:37 AM
Brent,
The use of beamsplitters - to separate various parts of the spectrum is very common in all professional spectrographs.
I used a beamsplitter guider on the early Spectra-L200.
I also have many (!) beamsplitters and 50/50 mirror plates up to 100mm sq.
Drop me an email if you think I could help.
Ken

Astrofriend
06-12-2017, 08:29 PM
Hi Ken,
Great offer, I write to you if I start to build something like this.

I also got a link from other:
http://www.astrojac.nl/astrojac/node/66

I have not translated it, but looks more like a video camera configuration, not a narrow band deep sky camera. But same princip.

/Lars