Mike Dworetsky wrote:
> "W. eWatson" <notval
...@sbcglobal.net> wrote in message
>
news:VmImk.7490$cn7.7118@flpi145.ffdc.sbc.com...
>> So far I haven't had much success with a RO spectroscope on our
>> museum's LDX-75 6" refractor. I'm told small refractors, f/6 to f/8,
>> may be the best for it. When I attempt to focus on the spectrum, it
>> looks like it has either diagonal or horizontal lines running through
>> it. Has anyone had experience with it that has produced good results?
>> --
>> Wayne Watson (Watson Adventures, Prop., Nevada City, CA)
>> (121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
>> Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
>> Web Page: <www.speckledwithstars.net/>
> Horizontal lines are probably due to seeing effects with a small
> telescope, with the star dancing around. We have (presumably) the same
> thing on telescopes of 8-14 inches aperture.
> Are these apochromatic refractors? We have tried this on a classical
> old achromat but the residual CA (chromatic aberration), which doesn't
> matter much for ordinary visual observing, does affect the dispersed
> spectrum focus a lot and we have to change focus for different
> wavelengths outside the range of good correction. It is best on
> reflectors, which lack CA. On apochromats this should not be a problem
> either.
> The other thing is that it works better for us with a 25-mm eyepiece
> than a 40-mm.
> I'm assuming you are using the cylinder lens supplied with the correct
> orientation, to make the lines perpendicular to dispersion.
Thanks for your response. I got carried away on related matters elsewhere.
It's just a two element AR. Part of my learning experience is that I was not
using the correct orientation. I'm now pursuing correcting that. It looks
like I need to get an O-ring or very thin and small rubber band to put on
the threads of the RO. I'll be heading for the hardware store shortly.
With some prompting and exchanges on a spectroscopy group, I've managed to
catch some spectra for Vega and Arcturus with my DSLR.
I've abandoned the 6" in favor of SCTs, because of CA problems. The SCTs are
working well, but I need to get around the orientation problem. I had
noticed an uneven bluish cast around stars with the LXD AR-6. I'm told by a
fellow who seems to know the LXD AR-6 well that I can use a Cheshire tool to
square it away; however, I have my doubts. I used one a year ago on it to
correct a bad alignment. It helped, but left me with the bluish cast.
Another source tells me the Cheshire is really only meant for reflectors. He
tells me it needs shop work. I need to work this out to understand which is
right. In favor of the Cheshire approach, the fellow mentioned other tips
that will help. Unfortunately, he has yet to reveal what they are. They are
posted somewhere where I do not yet have access.
--
Wayne Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
Web Page: <www.speckledwithstars.net/>
