Jump to content



New Members
  • Posts

  • Joined

  • Last visited

Posts posted by gremlin

  1. Hi Sorry for digging up an old thread, but I found the solution to this and thought I should share it.

    The solution is to install the north south and equatorial sections of the catalog into separate forders.  Then add each header .hdr file as a separate catalog.  If you install as pere the CdC documentation and overwrite each header file from one region with another only the last installed header file region will show.  The Cdc instructions says that its ok to overwite the header files as you unzip.  It's not ok, ypu need all three files and the only way to do that is to put the 3 regions in separate folders.

    Hope this saves someone some head scratching.


  2. Keith, in order to make a statement about your ronchigram it is necessary to know if the image was taken inside or outside if the ROC. If you knew by exactly how much, it would be possible to make even further statements on it. Looking at it as is shows you might have something going on at around the 60% zone.

  3. One of the things that can happen when pitch is too soft is that as the edge of the lap passes the edge of the mirror, the mirror sinks a bit into the lap, when the stroke reverses, the lap has to ride up on the mirror a little leading to the dreaded TDE again. All my polishing is done at around 18deg. If its gets beyond 20, I either open a few windows to cool or just leave it until its generally cooler.

  4. Keith, my advice is to hold off until it cools a bit. 32deg is way to warm to be polishing at. The pitch is just going to close up before any real work gets done anyway. It's really just asking for trouble. Yes please post the ronchigram.

  5. I have been thinking about mirror making whilst reading your guide and was wondering if it would be possible to "set" the parabolic shape back at the glass factory whilst the glass is in the furnace by somehow placing the glass in a rotating container.

    Spin casting large mirrors is actually done for some of the bigger telescopes. It works. However it doesn't froduce a perfect surface due to lots of factors. It does remove a lot of the hard work, especially when making 8-m class mirrors. But final polishing and figuring is still required.. Some of the worlds largest observatories had their mirrors made this way.


  6. Hi Keith,

    Yes if you got a TDE, you need to get on top of it before you can take it any further. Is it a classic TDE with maybe only 1mm or so turned down badly or is it more of a 'rolled outer zone' where the outer zone(s) tapers down gradually? I've heard both referred to as a TDE when they are in fact two totally separate defects. This will determine how you need to treat it. If it is the latter you can sometimes shortcut the process by deepening the zone where the rolling begins (if it's not too far from spherical). If it is the former, you could consider cheating and just mask off the outer 1mm What f/ratio is your mirror?


  7. Hi Alan,

    Yes it really is a bug. Congrats on your mirror. I love hearing about people going down this route. I'm sure it gives you immense satisfaction to view the heavens through an optic crafted by your own hand.

    My next mirror making project is to grind an exact duplicate of a 10" f/6 mirror which I was given. Then construct a pair of 10" binoculars. I suspect the mechanics of that will be a lot more complex than making the mirror!!



  8. I've always loved fast scopes. I got some amazing results from a well collimated newtonian which I owned a few years back. So earlier this year I decided I would build a custom 14" astrograph. One of the key factors I decided early on was that I was going to grind/polish/figure the mirror myself. The other design choice was a carbon fibre tube. I was consodering building this myself, but given the cost of composite materials and the possibility that I could stuff it up, I decided to just buy the tube. Well the tube is due next week and the mirror arrived back from the coating plant last week. So finally after months of hard labour, its all starting to come together.

    The mirror is very fast, f3.85. I had never made a mirror this fast before. My previous was 2 mirrors around the f/6- f/8 range. I was initially scared by the daunting task of making a large(ish) fast mirror, but the practice proved a lot less scary. Yes it is certainly a LOT more work to make a mirror this fast, figuring this baby was a real learning curve too. I also had to learn how to build and use a laser interferometer to properly test. the result was a lovely figured mirror with an RMS wavefront of 1/23 wave. More than adequate for a fast astrograph.

    Anyway I did write up an extensive article/tutorial to document a lot of the things I learned while making this mirror. The link is below and I hope some find it interesting/useful.


    Ill post some piccies etc over the next week or two as the project finally reaches a climax.

    Oh one last thing, the corrector. I am considering a high end wynne corrctor from ASA. Before that I'm going to give the baader mark III corrector a spin. If it works well, I can spend the difference on something nice for the scope.

    Clear Skies,


    • Like 4
  9. Hi Spectronuts!

    I thought I'd share and article which I just finished on the design and construction of by latest spectroscope. The "G300" as I'm calling it is a full slit based instrument with a slightly modified classical design. Anyway rather than go on at length here, I refer you to the article on my website.

    The G300 Spectroscope

    Hopefully might provide a some ideas for a budding DIY'er.



  10. I have to confess to posting in a hurry last night and I really didn't give the above spectrum a more meaningful explanation. I'm afraid I just re-used text from an e-mail which I had e-mailed to some other spectroscopy enthusiasts, so I apologise for the lack of explanation in my original post.

    The really interesting thing here is the previously mentioned -"P-Cygni" profile. This is labelled in the spectrum as Ha. What were looking at here specifically is hydrogen rushing both toward and away from us. The huge velocities involved means the H which is coming toward us is being 'blue-shifted' to the left (represented by the dip) and the material going away is red-shifted (to the right and represented by the peak). Normally (in P-Cygni profiles) of non-exploding stars, the P-Cyngi profile would be no where near this wide, however the incredibile velocities here means that the profile is widened dramatically.

    The H gamma and h delta lines marked are also interesting. These are known as part of the Hydrogen-Balmer series lines. Only type II events have these. So given the obvious p-cygni profile we can see from this that that a:) there is lots of hydrogen and b:) there is material rushing away from the event at collossal speeds. Therefore we can see that this is a type II supernova. Professionals would use larger scopes and higher res spectra to further sub-categorise.

    Here's the cool bit. The massively expensive and horribly complex spectrograph used to capture the above is simply a £100 'Star-Analyser'. I did add a small wedge prism to the front of the SA to give me a 'grism' arrangement grism = grating + prism. I do own a higher res instrument, and hope to get a close up of that p-cygni profile soon. With this higher-res it may be possible to measure the speed of the outflow and perhaps put a size on the progenitor star. I think that would be really cool.

    Scope is a C14.

    If anyone has any questions, I'd be only too happy to answer (if I know the answer!)



  11. This evening I managed to capture some spectral data of supernova 2012aw covering the range from 4000angstroms to 8500 angstroms. The attached image is just a first output and is not corrected for instrument response. However it shows quite clearly a couple of interesting features. There is a clear P-Cygni profile developing around the H-Alpha line. Evidence too of classic H-balmer series lines emerging from the continuum. I also see evidence of Sodium absorption which when compared to SNe 1992H (A.V.Fillipenko) seems a little early (with 1992H Sodium absorption became prominent at T+73days) . Ca II absorption is also prominent.

    I will of course follow up with an response corrected profile, but for now I thought this was worth sharing.

    Equipment: C14, Star Analyser+Prism, SBIG-ST8 27x120sec stacked


  12. Hi, I see you're learning that none of this is easy. I'd suggest the biggest single thing to get sorted is some sort of autoguiding. Without that you'll always be limited to the 30secs or so and as a result you'll wont get the data you need. You got the focus and framing well sorted. Flats etc wont really add an awful lot until the guiding is sorted.

  13. Hi SGL'ers,

    As Imostly do science stuff nowadays, I don't get to take as many images as I would like. Always another asteroid etc to work on, however a friend loaned me his lovely WO 110 FLT and Atik 4000 so I decided it was time to make use of them. Here's an image from Sunday night. Messier 106. I do like this galaxy but never got to shoot it before.


    LRGB 120:60:60:60 L Binning 1, RGB Binning 2

    Processed Images Plus v3.5 and Photoshop CS2.

    Equipment, William Optics 110 FLT APO, Atik 4000, AP1200 mount, Astronomik LRGB filters.

    Click here


    for full sized image

    Best Wishes,



  14. Hi my name is Dave Grennan I live and observe in Dublin. This is my first post on SGL. I had the opportunity to capture the following image of M51 - The Whirlpool Galaxy in Canes Venatici over the past two nights.

    Image attached.

    [edit] I notice SGL sizes down attached images, you can see the full res image here;



    C14 @ f/5.3, Ap1200 mount, SBIG ST8 XME CCD, Astronomik LRGB filters.

    L(90)R(30)G(30)B(30) all in 5 min subs binned 1x1

    Processing in Images Plusv3.5, Neat Image Pro and Photoshop



  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.