After spending time playing with CDs, cheap plastic diffraction gratings and Cokin Cosmos filter I finally ordered Star Analyser 100 from Paton Hawksley. Exchange rate is good right now and SA cost me 165$A including extension tube and postage.
I will use it mostly to obtain meteor spectra (hopefully) and variable stars spectra..
But right now I wonder if one can capture clouds spectra – I did not used scope for over six weeks. It is either cloudy, raining or too windy.
Welcome to the SA club! The SA should be ideal for Meteor spectra.
The biggest problem I see with trying to capture the spectrum of a cloud with a SA is that the cloud is a diffuse body. The resolution of the spectrum you get from the relies on the star (or meteor trail) being a point (or line) source instead of a slit in a normal spectrograph.
I look forward to seeing your meteor spectra. Sounds like to could be challenging.
Karl,
Welcome to the club!
If you haven't already, check out Ed Majden's site on Meteor spectroscopy.
Ed's been active for almost 50 years and has led the way in this field. http://members.shaw.ca/epmajden/index.htm
Hi Al and Ken, thanks for the links. I’m still waiting for SA to arrive and then it will be mechanical challenge to fit SA between the GStar camera and the lens. I’m modifying old Minolta 35mm and 50mm Rokkor lenses to T mount and somehow to fit barrel from old eyepiece so I can screw SA in optical train. I don’t know yet if it will achieve focus with SA. I will not be able to use existing CS 8mm as it will not focus with SA.
If it works out I hope to do better with CCD camera then what they were doing with photomultiplier tube and film camera.
Images of –1.4 and –2.0 mag meteors taken with Gstar and F0.95 8mm lens.
You might be better off fitting the SA in front of the lens instead of trying to shoe-horn it in between the lens and camera. See my meteor spectrum here for example. http://www.threehillsobservatory.co....spectra_20.htm
You could then use your 8mm FL lens to give you a wide field and the best chance to catch one, though the spectrum will be rather low resolution (roughly double the length of one on my website) Alternatively the 35mm lens will give better resolution but a narrower field.
You might be better off fitting the SA in front of the lens instead of trying to shoe-horn it in between the lens and camera. See my meteor spectrum here for example.
Cheers
Robin
Hi Robin, that is a good advice. After playing with old Minolta 35mm lens and various adaptors, I come to conclusion that there is no way to fit SA between lens and CCD.
Karl,
It can be done with some lenses. I tried with a Zuiko 50mm lens and an adaptor I made up from a x2 convertor body to accept a 1.25" nosepiece (similar but shorter than the Mogg type)
The problem was, that to clear the rear lens element the nosepice had to be shortened to about 15mm. This means that the SA100 would end up only 25 to 30mm infront of the CCD chip which doesn't give a very good plate scale.
As an objective grating you're obviously limited to the 25mm clear aperture of the filter.
Also if you mount the SA behind the lens you are limted to about f5 otherwise the resolution deteriorates unacceptably because of the severity of the aberations due to the steep light cone through the grating. For lenses with apertures up to 30mm (eg 35mm f1.2, 50mm f1.7 etc) mouting the lens close to the front element gives excellent sharp spectra without significant vignetting.
Here is an example of comet spectrum I took using a modified webcam and a 29mm fl lens with a 100 l/mm grating in front. (an early test of the SA concept) http://www.threehillsobservatory.co..../spectra_4.htm
near the bottom of the page
Cheers
Robin
Last edited by robin_astro; 08-10-2010 at 02:04 AM.
Reason: added link
Well, SA arrived today. And we have wall-to-wall cloud over Sydney. Never mind I have to order 28mm step down filter ring before I can try it on meteors.. Regardless of meteors, I was going to try it with my main scope – 150mm F5 Achromat and DSI II Pro camera on some bright stars.. No chance.
I got charged some 14 GBP tax – I was under impression that things exported from GB are tax-free.
Yes,
VAT is on payable on sales outside the EU. You should ask for a refund.
Fit the SA100 about 60mm infront of the DSI chip (you may need a filter extension) and align the rulings on the grating to give a horizontal spectrum within the image frame. That's it, a 3-4sec exposure will get you started.
IRIS to tilt, crop and save as a FITS/ PIC then Vspec to do the profile.
Don’t shoot me – but I had to try new Star analyser regardless of the weather. This evening hole appeared in the clouds. So I screw SA in GStar camera with focal reducer in front of it and shot this pic with 100mm F5 refractor thru dirty window glass. No tracking, no dark frame and difficult to focus.
But it works (sort of) and it looks like it is going to be interesting when I can take decent images from outside.
karl,
don't knock it....it is a spectrum!!
can you remember which star ???
Looking at the cropping the spectrum was angled across the CCD, try to get it aligned along the horizontal axis (maximum resolution).
Have you downloaded Vspec yet??? that's the next step.
Hi Ken. Yes I did download Vspec and I’m learning how to use it. For last few weeks we have awful conditions for astronomy here in Sydney. It may get clear during the daytime but as soon the darkness falls it is like if you draw a curtain over the sky.
I’m wondering if there is any advantage of using SLR lens if I’m going to fit Star Analyser in front of the lens and limit aperture to 25mm, or stick with CS lens that have aperture around 25mm anyhow and have a better F ratio. I also considering purchase of 1/3” CCTV colour camera that will give me better resolution per pixel then 1/2 “ sensor camera I’m currently using. As the meteors become visible at about 100km, 1/2 “ CCD gives me resolution of about 12m per pixel against 1/3” CCD resolution about 9m per pixel (if my calculations are correct!). The trade off is field of view..
This is for anyone that was thinking to try spectrum analysis of their astro images. Cost of Spectrum Analyser ordered from PATON HAWKSLEY EDUCATION LTD is about 72 GPB that translates to about 130A$ including postage. If you ever consider trying spectrum analysis of your astro images this may be good time to get SA.
The weather has not been very cooperative so far. I have machined an Adaptor that allows me to use M42 lens in front of SA. I have to discard Minolta 35mm lens, as it did not come to focus. Instead I’m using Pentacon 50mm F 1.8 lens. It works OK with Sigma 136mm F22.8 lens too, but trying to detect meteor with this focal length would be bit unrealistic. I was hoping to get spectra of Orionid meteor shower but couple of meteors my camera detected were too faint and did not record any spectra. Couple nights ago I recorded this, but problem is that I’m not sure if it was meteor or cosmic ray hit. My meteor capture software did not record it as video clip – only as snap shot. That usually means that the event was shorter then 160ms (capture setting of my camera for the meteor capture). In the future I will try to use mono camera because of better sensitivity and resolution.
VSpec is giving me problems on my computer because if I made mistake in selecting options from the menus it crashes.
If the strike was a cosmic ray (hitting the CCD detector) then you'd not get a spectrum, because the "light" would not have gone through the grating. If the cosmic ray hit some part of the imaging train, I don't think it would cause that kind of light ... although I don't really know this for sure.
I don’t think it could be satellite. Camera exposure was 0.16 seconds and it moved about 6 degrees in that time. I had captured three similar images over past four or so years with meteor capture camera. It is unlikely some sort of electrical discharge because it is so straight. It been suggested to me that it is cosmic ray strike parallel to CCD sensor. But – yes it should not create spectra. I just don’t know what it is.
– I did not used scope for over six weeks. It is either cloudy, raining or too windy.
