Vixen Beamsplitter

[Merlin66]

I've done a write-up on the conversion of a vixen flip mirror to a 70/30 beamsplitter. Works much better that previous attempts and gives good centring and guiding for slit spectroscopes.
The file was too large to upload, so I've put it in the files area of the Astronomical Spectroscopy Yahoo group.
http://tech.groups.yahoo.com/group/astronomical_spectroscopy/

[theodog]

My beamsplitter unit is started, at least the dis-assembly. I am using an Orion Flip mirror system that has similar properties to the one Merlin66 used.

Ken, how long did you leave the mirror in acetone?

My model will have 70% transmit and 30% reflect as I want to mount the spectroscope straight through.
:)

[Merlin66]

Assuming the mirror is "stuck" with double sided tape ( like the vixen) then 20 mins should do the trick - if you can, there's no problem leaving it in solution overnight; then you're 100% sure it will just pop off.
Keep us posted on developments........
Any photos??

[theodog]

Seems the mirror is glued directly to the holder -no tape.
40 min has only softened around the edges so it may take overnight.

Photo's tonight if time allows.
:)

[theodog]

Update:
Impatience got the better of me. I took a risk to use a sharp chisel and a mallot to carefully drive the mirror from its holder.
The mirror is attached with a blob of silicon gel. Came apart easily with a small scratch on the holder. Mirror didn't break.
Now to mark and drill the hole.

[Merlin66]

Sounds good so far!
Rule #2 - when all else fails - use a bigger hammer!

[theodog]

As a builder I hated glass. I got to the point of thinking about ordering twice the quantity to allow for my breakages. Now I seem to have no trouble with it and consider myself lucky with it.

Anyway, progress has been made. But now I can't find my bloody glass cutter:(. Probably in the bush somewhere:lol:.

[Merlin66]

Whooo
I like the tilt vise! Wish I had one of those, infact wish I had a lathe and a small CNC machine, infact wish.....
You really made a hole there! I just went for the 12mm without the 45deg......

[theodog]

OK, found the glass-cutter, it was in the next cupboard -not in the bush.:rolleyes:
Image below is the completed unit, it looks the same as before, but, with the "two-way mirror fitted using 2 sided tape.
Straight through eyepiece holder not supplied with unit.

Got set up for an eyeball test (Jupiter) on the 6" with 25mm eyepieces in each outlet. Images almost aligned. Straight through gave a clear image with little percieved colour change and looked bright. The right angle was notably darker with a double image, one "pink", the other "blue". Reflections from both sides? of the glass, did you get this effect Ken? Both were bright enough to guide on and the moons could be visually seen.
Looks like a go-er.:thumbsup:
More playing to align both images.
:)

[Merlin66]

My beamsplitter is about 0.7mm thick, on a VERY bright star image ( just tested it again with the artificial star) there's a faint secondary image visible - no colour?
The straight through image has the same.......
The cost of using standard beamsplitters???
( The old 50/50 cube splitter obviously is the optical equivalent to the pellicle plates and has no secondary reflections)

[theodog]

Tonight I completed the first "rough" star test of the beam-splitter.
Scope out of collimation -due to tube shortening,
Guiding atrocious due to rushed balance,
300D image out of focus due to rush and not parfocalising both imagers
And finally no field flatener on the 300D

Having said that,
The 300D was set for straight through 70% transmission and the ST-7e as a guider in the right angle position 30%. The guide chip was used for guiding.

First image is the guide field. 2 sec exposures. (Moving up to 5pix between exp's).
Second is the 300D with white box demonstrating the guide field 572 sec unmodded.

I think this demonstrates that this system is bright enough to capture spectra on long guided exposures, with the star held on an optical fibre or slit.

Looks like a goer Ken.:thumbsup: