Maurice
Thanks for that.
However, I think the observation that I can image a nice sharp slit (when
illuminated with a collimated fibre) *or* a reasonable 'spot' when using a
raw fibre possibly exonerates any path lengths issues. Incidently, my
earlier comments about Optics Lab confirming the problem were probably a red
herring (poor definition of source in the model) .
I'll repost this question to the Yahoo spectroscopy group that Robin L
mentioned and possibly the optics ng and see if any one there has come up
against the issue.
Since my posting I've been also looking at a few more devices on the web
and the vast majority seem to use a raw fibre (no slit) but this really
canes the resolution. The one exception that I've seen is the commercial
Ocean Optics USB device - I have a couple of them here - which uses both
slit and a fibre feed so it clearly *can* be done, but doesn't for some
reason seem very popular (maybe I'm finding out why...).
Iain
"nytecam" wrote in message
...
Wrote:
Maurice
I have in mind some planetary spectroscopy (hence the resolution),
possibly
Titan If I can coax my old C14 back into life.
As a start, just to see how the device performs, I'll probably do the
old
rotational velocity experiment using the D lines on the E-W solar
limbs.
Further down the line I may have a look at the Mid IR (my day job
involves
working in that region of the spectrum, so a sensor may be available).
Have
to look at new gratings though.
I'll post a photo / link once I've sorted out these last bugs with the
feed.
***************************
That sound good Iain - the beauty slit/ fibreoptic feed spectroscopy
aligned in RA, small scope miss tracks still record data.
***************************
Incidentally, did you ever pursue commercializing your own compact hi
res
spectroscope - you mentioned the possibility a few years ago when we
last
spoke?
*******************************
Maybe three years back Starlight Xpress were talking of say 100 units
which I said was wholly unrealistic for the amateur market. Terry
Platt raised it again with me as London Astrofest. His image-shift
system [rocking glass plate] has a pickoff prism for the autoguider
essentially identical to my WPO Littrow spectrograph and he will
reinvestigate the possibilities and maybe make a mockup. Essentially
he has all the components to hand except off-the-shelf grating and
imaging [camera] lens.
*******************************
All the best Iain
Been rethinking your defocus problem. If I recall the SBIG SGS CzT is
an Ebert arrangement http://home.freeuk.com/m.gavin/ebert.htm with two
extra flats to align the input-output beams to a common axis. The slit
is imaged full size onto the detector [just like the Littrow]. Are you
confident these two beams are of equal length? If not light projected
onto the grating will not be parallel and the image scale at slit and
detector will be of dissimilar scale.
I have a Sivo fibreoptic feed spectrograph
http://www.astroman.fsnet.co.uk/sivo.htm and frankly the throughput and
resolution was initially very poor where the 30[?] stacked fibres form a
virtual slit and where the collimator and image [camera] lens were of
similar focal length the result was gross oversampling. I suggested
incorporating a barlow between virtual slit and collimator [eg doubling
its focal length] so slit image onto detector half size and so much
sharper - see footnote to about 'review'. Reimaging may be the route
with fibreoptics to improve resolution but does little to help
throughput with those horrendous numeric[?] apertures.
best regards
Nytecam
--
nytecam