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Thanks Ian,
Very useful starting point for me.
Some imagers have advised to cool to only zero, but I believe that there is some advantage in going cooler with CMOS cameras, but I’m not sure about this.
Regards
KevinYou should cool to the point where the thermal noise is negligible compared with other sources of noise, such as sky background, Poisson noise, and so on.
Where that point lies depends strongly on the camera and, to some extent, on the sky background. For my present camera (a SX-814 CCD) -10C is easily cold enough and well within the reach of its Peltier cooler except in the very hottest of summer nights. Air temperatures of 25C are not unknown in La Palma and were reached this last summer on a few nights, but they are not common.
It’s easy enough to measure the thermal noise of your camera as a function of temperature. Take some (say) 60 second darks at a variety of temperatures and look at the variance of the pixel values.
Thanks Paul,
How do you calibrate defocussed images? Presumably you have to take all the flat frames at that the same defocus?Not really. All flats are completely out of focus anyway!
That is the whole point of flats: they should have no extrinsic structure whatsoever and all non-uniformity over the flat image arises from sensor sensitivity variation, dust rings, vignetting, etc, and not from anything outside the optical chain.
Richard: I have just checked again. In the text which follows I have replace square brackets with curly brackets and put a space each side of the : characters. This is to defeat any attempt by the forum software here to make my text into hyperlinks.
If one goes to the end of the page https://ukdarkskies.org.uk/dark-sky-places then down at the bottom one finds:
Planispheres (https : //britastro.org/node/12028) have rotating discs that allow you to set the date against the time and display the current night sky. See also https : //www.youtube.com/watch?v=UM8fH_NmtU4
The Youtube link is active and is clickable. The one intended to reach britastro is not clickable, for me anyway. I am using the Firefox browser.
If one examines the HTML source, the clickable version reads
{a href=”https : //www.youtube.com/watch?v=UM8fH_NmtU4″}https : //www.youtube.com/watch?v=UM8fH_NmtU4{/a}
but the other only
Planispheres (https : //britastro.org/node/12028)
There should be {a} {/{a} tags wrapped around the latter.
A small point, but on that website the link https://britastro.org/node/12028 is not active. It is correct but I had to copy and paste it into a browser.
Do you have contacts at the organization which may be able to activate the link? It seems a shame to make life harder for interested parties and to reduce the visibility of the BAA.
I’m in LP for all of February and all of August every year. How many weeks before or after those depends on what I feel like closer to the dates.
Anyone who happens to be in the district is welcome to drop by. Just let me know at least a day in advance …
(Sorry, that this is off-topic but I don’t know where else to make the offer.)
By coincidence I’m on La Palma at the moment.
What a shame. I flew out of La Palma on the 16th. We could have met up at my place and have shown you my observatory if the timing had been more convenient.
I am also on the astrometry.net mailing list and have been following your communications there with interest.
At present I’ve no real use for precision astrometry, using the plate solver only to find stars to within a few arcseconds which is plenty good enough for pointing a telescope and to enable APT to find a VS and its comparison sequence, then to do precision photometry.
On the odd occasion I do need good astrometry I use either Astrometrica, if it can be persuaded to work at all, or the IRAF tools.
Ah, yes. I remember ansvr. Its a cygwin thing isn’t it? Surprised the guy who did the conversion job has not updated it Apparently, the absence of a true Windows version is due to the way AN maps the Index files to memory.
I was forced over to WSL (or Linux on a Rpi) because the ansvr version of AN is quite old and it was failing to solve some sparsely populated fields, while the latest AN did.
Ansvr certainly worked okay most the time though.
Thanks Grant.
Perhaps I should run the latest server on a Linux box which shares the control room with the Windoze TCS. It may well be faster and more effective than ANSVR (apologies for my typo earlier) but I’ve not yet done it on the grounds that if it aint broke, don’t fix it.
Both systems use the Gaia index files so images almost always solve because there is a large number of stars in those files. The Linux local astrometry.net installations (another one lives on my laptop) are not yet configured as servers so I will need to find out how to do that.
A local astrometry.net will also run under Windoze. It is what I use on my TCS. The search term “ANSRV” will find it for you if you are interested.
Thanks to everyone for great suggestions
Seconded.
I have a rather, err, crappy Meade here which was shipped almost 5 years ago and never put into use. When the next delivery of round tuits arrive I will put it into a roll-off shed under software control
Until then, I have now decided to buy a BBQ or motorbike cover pro tem.
This may or may not be applicable for you but I use a standard small car cover (a cover for small cars, rather than a small cover for cars though there is little difference between the two concepts in practice). A motorcycle cover may be more suitable for a smaller scope.
My cover is too big but I don’t care. Rope and/or bungee cords take good care of any excess.
I’d love to attend but I have to stay in La Palma until at least mid-September.
Will the meeting be recorded for later viewing? Recording is generally much easier than live streaming over Zoom or whatever.
Grant: good luck.
My view is that storage for all that baggage is cheap and the runtime fits easily within the 1G RAM on my Pi. I have little incentive to re-invent wheels, in other words.
What sort of control do you need over and above what EKOS/INDI can’t provide?
It works fine for me on a RPi 3B
David: The Vera Rubin telescope has both an enormous aperture (8.4m) and a very low focal ratio ( f/1.23). Its field of view exceeds my 0.4m f/6.5 scope about 20-fold and its collecting area about 200-fold (call it a limiting magnitude about 5 magnitudes fainter than mine).
But this is an exceptional case and your post applies to almost all telescopes and certainly all amateur telescopes.
Once more: the question comes back to: what is your budget?
Until we get sensible answers to this question, and to the one about intended use, the original question is indeed unanswerable.
Karl: what is your budget and what do you want to image?
Robin: I agree with you almost but not quite completely.
Part of my problem is that I do not have a good definition of the term “astrophotography” other than it appears to place pretty pictures much higher than their scientific value.
Is planetary imaging “astrophotography”? I don’t know. Neither do I know whether alt-az mounted DSLRs are used for “astrophotography” but they can certainly take pretty pictures, as well as take images which when analysed yield good science.
