andrew s

All kit assembled and seems to be working. Polar alignment done and now doing a large Tpoint model. Then I need check the spectrograph alignment and should be ready of a real data run tomorrow if it is clear again. Rain forecast here while I am travelling back 😱. Regards Andrew

Each obs roof opens independently but in one piece per obs. The scope is set so the roof cannot hit the scope or mount in any position. It is a spectrograph see my thread "Simple transmission spectrograph " Just got the mount slewing😀 Regards Andrew

just bolting it to the floor

General view of observatories and the moon in a sky that has been clear all night. Regards Andrew

Arrived but not got set up yet. The sky here is amazing. The threads of the Milky way are clear from horizon to horizon. The stars are as I remember them a a child under rural unlit skies . Nirvana for astronomers. More to follow with pictures tomorrow. Regards Andrew

Yes spectrophotometry is exactly what I what to do! Not sure I can crack it but I will do the sums and experiment. The only other option I can think of is to use a photometric slit and rotate the instrument to suit! Something new to build... ...no stop it use what you have got. Regards Andrew

Yesterday I set off for the south of France with broken cloud and some sunshine. As I approached the centre of France the storm clouds gathered and as I reached the A75 "sunshine route" it was doing an impression of the M62 on a wet bank holiday weekend but with less traffic. Had I made a big mistake? Today again started cloudy with some spits and spots of rain. However, as the A9 became the AP-7 at the Spanish boarder the clouds broke first into cotton balls, then buds and finally evaporated into a powder blue sky that has remained so all day. Relief. I have done the trip through France a dozen times but Spain was new and for the most part the traffic was light so I could enjoy the view . Quite stunning at times but green enough to show it must rain sometimes. Tomorrow I get to meet Colin and see the facilities. I am as excited as a 67 yr old cynic can be but with a touch of "I hope nothing important got damaged on the trip and did I forget anything". Hope to have more interesting content tomorrow. Regards Andrew

For what it's worth I was going to experiment with various "flat" options once my new set up is up and running. I will report back in due course if I get anything worth sharing. Regards Andrew

You can make a PRNU (pixel response non uniformity) "flat" as described by C Buil which can then be use. Don't have the reference to hand as access difficult on the road. When looking at IRAF examples they tended to apply different types of flat for different reasons. Low frequency for vignetting, higher for dust doughnuts, PRNU etc. Not saying you should do the especially for Star Analyser for the reasons Robin gave. Regards Andrew

"I hope you got some nice CV measurements under your belt Jeremy" said he through gritted teeth. Regards Andrew

Set off at 04:30 UCT and arrived at the Logis on the south of Chartres at 16:00 UCT. Traveling on Sunday was a good choice with even the M25 approximating a motorway rather than a car park. The only excitement was when a wild boar ran across the motorway near Evreux. It showed considerable skill in avoiding the light traffic but well beyond the skill of a domestic pig. The Cheshire permacloud extends all the way to Chartres but I hope to get out from under it as I head for the south of France tomorrow. Just had two beers with steak and chips at the local buffalo grill followed by a coffee with a petite au praline which was a close approximation to a Malteser. Now for some well deserved sleep. Regards Andrew

Not much room to spare. All packed and ready for the off tomorrow morning. Regards Andrew

@vlaiv practically focusing on the spectrum is difficult at the best of times. You could step through with a very accurate automated focuser. I am not sure how you would identify the good bits and stich the spectrum together. It might be practically simpler to use a grism or go fof a parallel beam arrangement. Do you have a specific project in mind or just enjoying seeing what can be done? Regards Andrew

@vlaiv you can mitigate the spectral curvature by tilting the sensor with respect to the optic axis but then it makes the rest of the field defocused. Also you need to keep the first order on the image to allow calibration of star without obvious sharp lines. This limits the grating chip distance you can have although vignetting will also be an issue if you go too far. Good luck with the project. Regards Andrew

Yes it will F8. If you are seeing limited then it does not matter if it's a compound telescope or not apart from the light loss due to the obstruction. In your SA200 calcs just use 200mm F8. If I remember correctly he main aberration is chromatic coma which along with the star size due to seeing limits the resolution in a slitless converging beam configuration. Regards Andrew

For SA200 calcs just use the output focal ratio znd main mirror diameter as this is what counts. With my ODK I just used F6.8 and 400mm diameter What I mean is that you can start from the focal point and project back to the secondary mirror usi g the output focal ratio. The diameter there will be less than the secondary mirror diameter. Using this and the main mirror diameter you can estimate the main mirrors F ratio and focal length. This assumes it is not oversized. Regards Andrew

Posts crossed see my PS

Tbe same basic geometric optics applies but you can't use the approximations commonly used in manual ray tracing. This is particularly true when one element compensates for the aberrations of the other. Ray tracing programs are the way to go. However, I am sure to first order, simple geometric optics should get close to give the basic layout. Not totally clear on your question but I would calculate the diameter of the beam the primary makes at the secondary using the spacing and the primary mirror diameter and focal length. Then use this with the net F ratio to find output beam dimensions. Regards Andrew PS or you can work back the other way if you don't have the main mirror details.

Sounds familiar car slightly more and I made a ramp that bolted to the dovetail plate to get it on the mount. Still a two man job. Regards Andrew

Both atoms and molecules can emit and absorb radiation. These can be electronic transitions and in addition for molecules rotational and vibrational modes. An example is a microwave oven where microwave excite water molecules. In the interior of a star radiation scatters off ions and electrons exhanging energy and momentum. What starts as gamma rays from nuclear reactions emerge after a long random walk due to scattering to emerge from our sun as visible light with roughly thermal distribution (modified by the photosphere). Regards Andrew

I am coming back just the kit is staying. Regards Andrew

@DaveS mentioned the cost of hosting in my other recent thread on moving my kit to Spain. It is expensive for an individual but I do wonder if there is a future in sharing a set of kit. If say 5 to 7 people shares a rig the running cost start to look reasonable and you save on 4 to 6 sets of kit (sorry FLO). In addition they should get more clear nights a year. The obstacle I found when looking at this is varing expectations of potential partners and how to do it so as to protect everyone's interests . However, once a model is established it could prove the way forward. I know you can hire time on existing telescopes but it can be expensive so a shared arrangement might be cheaper in the long run. Just thinking allowed and I am not looking to share at the moment. Regards Andrew

I am going to the new Ian King/Colin Cooper site. Regards Andrew

Don't see an issue. The host will still look after it and I traveled to Europe before we joined and am sure I will be able to afterwards just like to any other non EU country. Regards Andrew

You need to go to AAA (astronomical accessories annonoms) while it is good of you to keep the market buoyant it can't be good for you health. 🤣 Regards Andrew