Spectroscopy - Page 15

Merlin66 (Ken) · #**281** 22-04-2009, 12:42 AM

It was raised way back...
Maurice has been active with spectroscopes for over 20 years!
He lives about 10 miles from me, in SW London!!
Been over to visit a couple of times......

theodog (Jeff) · #**282** 22-04-2009, 07:29 AM

Sorry, the thread is so big I missed it.
Nice info 'though.

Merlin66 (Ken) · #**283** 22-04-2009, 04:56 PM

Not much to report from this end!
The weather seems to be improving and there should be some clear weather later this week.
Re camera calibration - I'd just use the "best" we can find from the standard library curves... I don't think the calibration varies over the CCD frame unless there's some optical effects ( vignetting??)
You could try some exposures with various filters and see if there are any differences?
I'll set up the Littrow for Solar and check out the resolution....

theodog (Jeff) · #**284** 22-04-2009, 05:56 PM

Been quiet here too observation wise.

I have however, spent some time constructing my BAA style spectroscope. All seems to be going well so far, mirrors arrived today. Lenses are from a cheap 10x25mm binocculars.

Modifications from the BAA plans I have seen include a flip mirror for alligning and a movable camera mount to assist focusing the spectra.
Just a trial and I've had the time.

If it works I'll look for larger Binoc lenses and build a bigger one.

Merlin66 (Ken) · #**285** 22-04-2009, 06:07 PM

Looking good!!
Will you use a razor blade slit or go for a Surplus Shed adjustable??

Terry B · #**286** 22-04-2009, 08:42 PM

Great start.
Too much cloud here for anything.

sheeny (Al) · #**287** 22-04-2009, 09:04 PM

Yeah... 2 weeks holidays (3/4 over) and all I've had is cloud and drizzle...

Al.

theodog (Jeff) · #**288** 23-04-2009, 08:12 PM

Quote:

Originally Posted by Merlin66

Looking good!!
Will you use a razor blade slit or go for a Surplus Shed adjustable??

I have started with a fixed slit (ground by myself) -not razors.
The mirrors and lenses have been fitted and an image of the slit can be formed ( and moved by the movable mirror -right top) on a piece of paper held about 30mm above the hole at the top.

Off fishing for the weekend

so no further progress until next week.

sheeny (Al) · #**289** 23-04-2009, 10:42 PM

Well, didn't the blue sky surprise me this arvo!

I got about an hour of play tonight... fog brought the innings to an end. Everything is so damp and cool you have to expect that

.

But I managed to do a little experiment.

I'm aware of the theory that a shorter focal length will improve the purity of the spectra from the SA, but in the past my attempts with the focal reducer have been less than encouraging. So tonight, I set down to do the experiment. I captured spectra of both gamcru and etacar at f/10. Then I put the f/6.3 focal reducer in and took them again.

The results of the Eta Carinae spectra are attached. I haven't processed the Gamma Crucis sectra yet, as VSpec has been testing me out with funny errors and not saving SPC files correctly

. But from this test, the focal reducer is a clear winner

.

Al.

Merlin66 (Ken) · #**290** 23-04-2009, 10:49 PM

If you look at the shape of the zero order image you see the improved (!!??) image size profile.
Smaller star images, with a no slit configuration will give you better resolution; what you can do to improve things even further is to move the grating away from the chip to give a higher dispersion; then you get the best of both worlds... smaller stars and larger spectrum spread!!!???

sheeny (Al) · #**291** 23-04-2009, 11:07 PM

Yep.

Here's a corrected spectrum.

Al.

theodog (Jeff) · #**292** 23-04-2009, 11:11 PM

Nice one Al.
Good to see some observing being done.
I must admit I've been a bit lazy.

sheeny (Al) · #**293** 24-04-2009, 09:15 AM

Here's part 2 of my focal length experiment. The subject was Gamma Crucis this time. I found the camera response curve was a bit screwy below 4000A with the focal reducer, so that's cropped out. Not sure what's going on there, the response curve took a jump up

. Makes no sense at all... I could understand it blocking frequencies...

The depth of the absorption lines is improved with the FR and you can see some detail starting to emerge. Definite

.

I found out the problem I was having last night with VSpec. I was saving the SPC files with the header applied. When I go to reload the spectra afterwards I get an "Input after end of file" error.

Any ideas on how to fix/work around that?

Al.

sheeny (Al) · #**294** 24-04-2009, 09:41 AM

Oh yeah... after thinking about the wrestling I was doing in my last session with the black point in the spectra, this time I made a point of making sure the brightness setting for the DMK was always on 0... it greatly simplifies the processing of the spectrum

cause there's no offset to remove before doing the divisions for camera response.

Al.

Terry B · #**295** 24-04-2009, 10:13 AM

Well done Al.
I spent the clear night

doing time series of the nova in the LMC so no spectra. Interesting result with the focal reducer.

Merlin66 (Ken) · #**296** 24-04-2009, 05:17 PM

Some good results there Al!!!
The reducer certainly pulls out a bit more detail; what do you think you'd get with a bit greater distance to the chip??
With the small DMK chip can you still get the whole spectrum or will you have to go to "sections"???

sheeny (Al) · #**297** 24-04-2009, 05:29 PM

Quote:

Originally Posted by Merlin66

Some good results there Al!!!
The reducer certainly pulls out a bit more detail; what do you think you'd get with a bit greater distance to the chip??
With the small DMK chip can you still get the whole spectrum or will you have to go to "sections"???

At the moment I have to do 2 sections to get the zero order image and the spectrum. When I first put my SA in the filter wheel, I could find the star image but not the spectrum. Eventually I found it... well over one frame width away... I had the diagonal between the camera and the filter wheel. I could try to stretch it a bit more with a short barlow body, but ATM I only have the 1/3 of the spectrum on the zero order image frame, so going much more will make it difficult to stitch the frames together accurately. Wouldn't a DMK 41 be nice? (I'd still be doing spectra in sections no doubt!) Al.

Merlin66 (Ken) · #**298** 24-04-2009, 06:14 PM

Al,
There's a couple of options:
Now that you have a calibrated spectra you don't need the zero order..just use the Ha and Hb lines...
Alternatively add a 4 degree prism ( Edmunds) and turn it into a Grism; this will then bring the first order spectra back close to the optical axis.
I made one up for the P-H gratings I have and it worked as advertised.

bojan · #**299** 25-04-2009, 06:41 AM

Just in case some of us did not know about this (I didn't), here is this link:
http://www.astrosurf.com/vdesnoux/
Christian Buil is a legend :-)

sheeny (Al) · #**300** 25-04-2009, 10:35 AM

Quote:

Originally Posted by Merlin66

Al,
There's a couple of options:
Now that you have a calibrated spectra you don't need the zero order..just use the Ha and Hb lines...

I may progress to that as I gain experience. Not all stars have Ha or Hb lines though, so I still have some learning to do.

Quote:

Originally Posted by Merlin66

Alternatively add a 4 degree prism ( Edmunds) and turn it into a Grism; this will then bring the first order spectra back close to the optical axis.
I made one up for the P-H gratings I have and it worked as advertised.

That would make the SA a "Grism-ism" wouldn't it?

The 4° prism would move the spectra back towards the axis of the scope, but wouldn't it also move the zero order image?

Quote:

Originally Posted by bojan

Just in case some of us did not know about this (I didn't), here is this link:
http://www.astrosurf.com/vdesnoux/
Christian Buil is a legend :-)

Thanks Bojan. Good site. There's a lot of people in the astronomy field that provide excellent information and software to amateurs for free! Good on 'em!

Al.