Forum Replies Created
-
Posts
-
My scope is indeed f8 but seeing here isnt brilliant, what with the urban heat dissipating etc…
Can you explain what you mean by ‘vignetting’ here? Do you mean the star disc spreads beyong the slit? For the stars I am looking at this is certainly the case. In this respect (star diameter vs slit width) my guide images look liek the one Andy posted above.
Kevin
Hi Robin
You are certainly right that messing with additional lamps isn’t going to help me with a basic setup! But I couldnt resist ‘looking to see’ some of the other curiosities in the spectrum…
Kevin
Hi Robin
Thanks for series of tips..!
First, yes, it is a genuinely new one (so includes all latest bells and whistles)
You will see I noted to Andy that the kind of spectrum I was getting was similar to the one he posted (bimodal cross section) so I’m not sure about the focus thing? I focus the collimator (terminology? i.e. the assembly behind the small door on the side) against the FWHM of the calibration lines.
The bimodal feature appears to come and go as I move the main mirror about its fulcrum. However, I see you recommend placing it about 1/3 way *up* (with red on right). I have it about 1/3 way *down* so maybe I’ll try swinging across the field of view (and taking some cross-sectional integrated flux measurements as I do so).
Many thanks
Kevin
Hi Andy
Thanks for full response…
Yes, your image of the spectrum looks like those I was getting before I adjusted the main mirror (i.e. a bimodal profile). I take your point about it being integrated flux rather than some peak value that is important. I will go back and have a look at that.
Your main guide star looks pretty round to me (albeit with the left hand side lobe which appears ubiquitous in these gude images). I’ll try and take some later if possible to compare. The idea of scope focusing using spectral throughput as the measure is also interesting (But I woud have thought that a correctly adjusted guide-assembly would imply otimal throughput?)
cheers
Kevin
Hi Ron
On collimation: The problem for me was that there are probably as many web pages detailing RC collimation as there are installatons…. I think I now have a collimation procedure worked out. If you get hold of the 16in RC, let me know and I can supply my notes.
The MEII looks to be a mighty beast! (I have to be able to take mine down occasionally…)
cheers
Kevin
Hi Ron
On collimation: The problem for me was that there are probably as many web pages detailing RC collimation as there are installatons…. I think I now have a collimation procedure worked out. If you get hold of the 16in RC, let me know and I can supply my notes.
The MEII looks to be a mighty beast! (I have to be able to take mine down occasionally…)
cheers
Kevin
Hi Ron
I have a humble 10in Altair Astro truss-tube RC (I think its a re-badged GSO…). So can’t help with dimensions but in general…
I am still ‘commisioning’ it properly but would say the first thing is to get a decent focuser. I now have a Starlight 3in Feathertouch with their ‘posidrive’ motorised add-on. I had hoopla with sourcing here, TS in Germany came good for me in the end. There are three moving parts in collimation which makes life ‘interesting’: focuser backplate, secondary, and primary. A Laser, Cheshire, and CCD inspector (respectively) all came in handy here.
It sits on a MESU 200 mount (friction drive). My AZEQ6 was not up to it…. I would guess a mount like the MESU or better would be required
Kevin
Hi Robin
I see its mag 16 – I struggled with 3C-273 at mag 13 (see my personal page) … Do you use an Alpy or lower res instrument?
Kevin
Is Thursday too late for this?
There is clear sky forecast here, although I have a load of teaching Thursday/Friday (so mechanics of life may preclude…)
I can see the galaxy in the DSS image overlaid in CdC but coords differ from those advertised (maybe an epoch issue?). Anyway, I’ll let you know if I am game for it later this week
Kevin
Thanks for the link Andrew – looks handy..
However, in this instance, the entry is intriguing… One catalogue gives G8III and another, G3V, but with a remark ‘type wrong’: I can vouch for that 🙂
cheers
Kevin
Thanks for all your comments. I’ve learned a lot..
I am now reworking some spectra in ISIS and am using PlotSpectra (by Tim Lester) for post-processing, measurement and plotting.
I think Robin drew attention to this as I recall?
Its well made and easy to use – albeit with a slightly opaque (at least for me!) measurement dialogue box – but I am persisting..
cheers
Kevin
Hi Robin
I reworked this one in ISIS and used their autocalibration for the Alpy.. the errors on the Balmer lines were an order of magnitude smaller (~0.23A for first 4 Balmer lines starting at Ha – it gets worse at blue end..)
Incidentally, I managed this only after reading the the thread in
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=1246&start=0
The nominal value of the Atik460 pixel size (4.54) is too big for me.. it works best with 4.45 (I wonder if there is a typo in their literature – swapping 4 and 5!?)
cheers
Kevin
Hi Robin,
dogh!
I have uploaded correct version – no idea where the other one came from – I am doing postprocessing in BASS and I find it loses the plot (literally) occasionally .. (or maybe my finger error more likely)
thanks
Kevin
Hi Robin and Andy
Thanks for comments…
Its nice to know I am up against the absolute limits here (although I understand you could, in principle, see differences in same target, over time, up to around 1.5A)
Robin – the comment on the relation between PSF, slit, and spectrum, is very interesting (although I don’t understand the physics at work here :).. My guiding is not as good as I would like (around 0.8s rms) so I think I may be getting some dither by accident than design :). I calculated heliocentric correction in BASS and it gives a blue shift of 16.8 km/s. This would seem to nearly cancel the absolute radial velocity… so it looks like my offset is definitely an artefact..
I may take a few extra calibrations over the next session just to see how stable it is..
cheers
Kevin
Hi Robin
I had several attempts at getting an instrument response with this one. To compare in the way you say, I had to load the corrected profile and the MILES spectrum into BASS – I couldn’t see an easy way of overlaying the two?
Also, my reference stars are probably not ideal so far…. I see in one of your posts here you recommend type A as reference. My criteria were that it was at roughly the same altitude, similar magnitude, and visible with my horizon (not trivial :). Next time, I’ll search a bit harder to get something closer to an A-type (the current one is F8). I guess the A-type have nice peaked shapes that lend themselves to this process.
cheers
Kevin
Hi Robin
Many thanks for all those suggestions…
Yes, I should give it a try in ISIS too..
I haven’t investigated thoroughly yet to see if its a consistent thing. I can see temperature changes could be critical, and by ‘orientation’ I presume you refer to flexure effects…
Next time, I’ll gather a few more calibrations throughout the night.
cheers
Kevin
Thanks everyone…
I’ll certainly be more confident trying guiding on the target star, and the fixed XY technique in PHD2 looks interesting…
I did look at the Maxim website, but I would rather avoid learning a whole new set of tools just now..
Unfortunately my ‘land-rights’ circumstances mitigate against a permanent set up, but I might manage something ‘semi-permanent’ in future. If so, I’ll show some pics – it might be innovative 🙂
cheers
Kevin
Hi Andy
Thanks for advice – yes, I must make sure to save guide images…
Also, can you point me to Robin’s ‘2 star’ method please?
cheers
Kevin
If the ‘seeing’ (typically 3 arc sec as you say) is thought of as comprising a uniform disc, and this covers the slit in a symmetric way, then I think the geometry gives (after a little work…) an upper bound on light loss.
I reckon that my f10, 200mm SCT (Celestron 8SE) with angular slit extent of 2.37 arc sec. incurs only 11% loss (I think Robin’s setup is a bit more at 32%). Having tried to get my 0.63 focal reducer to fit with a nominal recommended 110mm distance from reducer lens to sensor and failed (calibration module prevents this) I am therefore inclined to try without.
cheers
Kevin
