The past few months have seen some changes to my equipment – unfortunately the biggest (or most expensive) change was due to my original Gemini 1 controller dying. The mount is back in action after I upgraded to a Gemini 2 from Losmandy via an existing owner trade-in. Good news is that the mount appears to be working well, though still needs PEC sorting and full building of pointing models.
I’ve also got a 0.8x reducer/flattener for the William Optics FLT110 (this is the latest model of the William Optics FLAT4 reducer), allowing me a larger field of view on the SBIG ST2000X, a flatter, faster field, and also the ability to mount a recently acquired, astro-modded Canon 350d on there as well – I look forward to trying to image the Pleiades and the Orion Nebula using a sensitive, wide field arrangement this winter… I also have started to use Pixinsight for processing images; while it’s been a learning curve for me, I feel I’m starting to get somewhere in using it, and think it could be a very powerful tool.
I have managed to put the new kit to use already: after tuning the spacing for the CCD camera, I managed to take a lot of sub-frames of the Bubble Nebula (NGC 7635) and M52. The image shown is in H-Alpha (using the Astrodon 5nm filter) and consists of 7hrs total in 20min subframes (at -20C).
The Bubble itself is a large (~7 light year) void formed by the action of the fierce stellar wind from a hot, highly luminous Wolf-Rayet star. This star also causes excitation of the surrounding nebula, giving us the H-Alpha light we image here. M52 is the open cluster to the bottom right, with Czernik 43 the slightly looser open cluster to the right of the image. The nebulosity to the bottom left is part of the larger region SH2-158, and the smaller areas of nebulosity to the top centre-left of the frame is the not often referenced planetary nebula KjPn8 (though this is quite faint here and needs a bit more magnification, and a lot more data to pull out well!)
Field is centred at: RA: 23h 22m 29.0s Dec: +61° 19′ 07.7″ Up is 0.71 degrees E of N (plate-solve from nova.astrometry.net)
I’ve recently completed the first stage of modifying the mirror cell to convert it to use 6 point supports instead of 3 points.
By modelling deformations of the 350mm mirror in PLOP, I get the following figures for the current 3 points:
Support radius = 123mm
P-V: 1.65 x 10-4mm (~1/5λ at 500nm)
RMS: 3.81 x 10-5mm (~1/13λ)
For a mirror with a zygo report of 1/12λ P-V, this is less than impressive!
By using equally spaced 6 point supports, these figures are:
Support radius = 110mm
P-V: 1.07 x 10-5mm (~1/46λ)
RMS: 2.37 x 10-6mm (~1/210λ!)
So it can be shown that the deformations are potentially over an order of magnitude better using 6 points. Interestingly, allowing PLOP to run for a 9-point cell for the same mirror gives a slightly worse result than the 6 point, and though the 9 point is much better than a 3 point it’s harder to adapt this cell into.
My modification adds three “U” shaped supports that attach to the existing cell parts (being attached loosely via an M8 bolt to allow them to rock a little). There are two nylon mushroom head bolts that screw into these parts which the mirror will sit upon (these are the black cross heads in the image).
I think I’ll most likely need some mechanism to stop the bars rotating (but this might just be a bit of tape), and I’ll need new lateral nylon grub screws as 2 of the three current ones are well and truly stuck!
I’ve been working recently towards finally completing the observatory dome in my back garden (that I bought almost 4 years ago now…) – with flooring done and power connected, I need just some steps, finish security and I can start to setup.
Attention has turned towards the Orion Optics SPX350 that’s been languishing in my garage awaiting use. I’ve known that the current secondary mirror doesn’t offer anywhere near enough completely illuminated field – and so I’ve finally measured the location of the focal plane and using the excellent “Newt” software (now available as a web based app) and determined the size of a new secondary mirror for it. Yesterday I ordered a new 89mm secondary from Galvoptics that I plan to mount in a new secondary holder from Protostar (and hoping I won’t need a new spider :-/ ). This should give me a 100% illuminated diameter approaching 20mm – more than enough to cover the KAI2020 CCD chip I use, and good enough (with flats) should I decide to try upgrading to a KAF-8300 based camera in the future.
More importantly, the primary is going to need some work to bring it back to its full potential (the original zygo report says it is ~1/12 wave P-V) as even after washing off the dead moth remains (!) and flies, the coatings look to be past it, and there’s a load of spider poo stuck to the surface as well. Here’s hoping that they will clean off well and it’ll recoat fine – and so once I have the new secondary installed, a trip to Newcastle-under-Lyme will be needed in due course to look to get the whole thing serviced.
So the weekend just gone has had fabulous weather here in the UK – sunny, warm (for February!) days, and cold clear nights – and so I thought I’d try to setup my imaging kit to have a go at some astronomy for the first time since April 2007, and also as a bit of a dry run before the Kelling Heath star party in April. I even managed an image of the moon – 30 images using the ST2000XM on the FLT110, processed in Registax – click the image above to view it!