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in positions 2 and 7 here you have a Dobsonian mounted scopes which are not suitable for astrophotography
While planetary imaging has different needs.
Indeed.
Martin Lewis takes some absolutely superb planetary images with his Dobsonian mounted telescopes. The rings of Uranus and surface detail on each of Ganymede, Mercury, and Venus are among some of his achievements.
Do you agree with what I have written? Any additional points I have missed?
When you describe reflectors you state that one mirror is flat. This true, by and large, only for Newtonians and other folded optical path designs. My scope is a sort of Cassegrain but, to be fair, it does contain a flat just before the camera or eyepiece assembly.
I find it amusing that you have a Celestron NexStar 5 SLT which is a Schmidt-Cassegrain I believe. It also has a flat for ease of uses near the zenith.
It does OK but I wonder if a much bigger scope (how big is best?)
How much do you want to spend?
A fully kitted out 4-metre telescope will produce some very fine images but is likely beyond your budget.
Your question as phrased is essentially unanswerable.
The above was for photometry. Add another 2 magnitudes or so for usable astrometry. I’ve uploaded images to the gallery where satellites in the outer solar system are visible at mag 22 or thereabouts.
Perhaps a start could be. What are others observing. What magnitude can useful work be carried out with say C8 or say 100mm APO.
KevinHow long is your piece of string, in other words.
I have done photometry of exoplanet transits, variable stars (eruptives / cataclysmics mostly) and asteroids but exceedingly little on LPVs and eclipsing variables. Extragalactic luminous blue variables have also had a lot of attention but I accept that I am seriously weird in some respects.
Reasonably good estimates for magnitude ranges can be obtained from any one data point scaled by collecting area. Here is my data point, based on a 0.4m aperture. It has four times the collecting area of a C8 and so the limiting magnitude is likely very close to 1.5 magnitudes fainter. A 100mm APO has 1/16 of the collecting area and so will be around 3 magnitudes inferior to a 400mm. Note that essentially all cameras have effectively the same detector sensitivity these days and so the make of the camera is largely irrelevant from a performance point of view.
I can manage 0.1 mag precision at V=20 with a ~3 hour exposure.
I regularly do 0.05-0.03 mag measurements down to V=18 or so.
For exoplanets, ~2mmag precision can be done down to perhaps mag 12-13 unfiltered at a reasonable cadence — 1-2 minutes perhaps.In the words of good old Usenet: HTH, YMMV, HAND.
Kevin:
I was a newbie at CCD photometry until quite recently and I agree the learning curve can be quite steep.
Have you found https://britastro.org/section_information_/variable-stars-section-overview/baavss-mentoring yet?
I may be able to help you but this forum is not the right place to do it in my opinion. If you would like to email me at paul (a) leyland.vispa.com we can see what can be done to get you started. We can’t easily meet in person because I’m in La Palma right now and after returning to Cambridge in a couple of months we will still be a fair distance apart. Phone and/or Skype/Zoom may be helpful as well as email.
Paul
According to Sidgwick, the resolution of a properly collimated 4″ refractor should be around 1.2-1.4 arcsec though, to be fair, those values are for resolving double stars rather than extended objects. That does, of course, assume that the ocular is illuminated by the whole objective. Back in Sidgwick’s day I suspect that 2″ eyepieces were extremely unlikely to be fitted to a 4″ refractor.
I have no idea what typical seeing is like at your location but guess that it is likely to be around 2-3 arcsec. That is a typical figure at Tacande Observatory though occasionally the seeing can be as good as 1-1.5 arcsec.
Neither do I have any idea about the acuity of your vision.
Based on this analysis, I suspect you are seeing limited. The phrase “most days” also leads me to this opinion.
Perhaps the advice indicates that the brightness of the image may still be too bright. If that is the case, a ND filter should complete the task, especially as (7/6)^2 is only 1.4 and the increased IR load will be quite small.
Maybe consider a full-aperture filter over the objective? I have used aluminized mylar film with great success, admittedly with smaller apertures.
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There is a simple fix, which is to provide you with two observer codes and logins.
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This would not be as neat a solution, as it would split your observations into two observers.This approach has worked well for me in a different context.
In the past I have been engaged in significant collaborative projects where credit was due to two or more people. Hence, for example, THL which is short for Team-Hills-Leyland. Kevin Hills took all the images and performed the astrometry. I did the photometry and uploaded the results.
AAVSO does not understand the value of team-work 😉 so all the joint results were uploaded to their database under my name — with the prior agreement of my cow-orkers of course. So, Ian, when your results wend their way over he Atlantic I am pretty sure that all will be attributed to you.
Andrew: could you post more detail please? This is the first time I’ve heard of “PixelSkies” and I am sure that many others have not done so either.
I don’t feel confident to publicise it more widely with so little to to on.
Paul
AlanM – There is a place in space where you could observe a Sun/Earth eclipse
[pedantry]Apart from points within the antarctic/arctic circles, don’t we see one of these every 24 hours throughout the year?[/pedantry]
Ian: it’s hard to tell.
Perhaps a longer series of measurements at a very wide range of magnitudes (from 7 to 17 perhaps) of a standard field (likely a Landolt field) may be mre informative.
A plot of differences between the two filter sets against magnitude may be informative too, as it will give a much larger y scale and accentuate the readings.
Paul
And what have the Romans ever done for us?
Romanes eunt domus!
Grant: 2TB drives are pretty cheap thes days. I just replaced two of them (one was soft-failing) with 4TB units, for a total cost of around £175. The 3-disk array of which they were part already had a 4TB drive to which replaced an earlier dodgy unit. Once all three were 4TB the array could be grown to provide an effective 10.5TB filesystem.
The extended array (actually a ZFS pool) is already 22% full because it holds all the archives & backup of all the systems on the home network.
Another 4TB unit is inside a portable USB-3 drive. Very useful for ferrying material between the UK and LP.
And thanks also to you, Robin, for drawing it to my attention. Already downloaded for later study.
Paul
Paul: Almost entirely agree. Where we may differ is in the level of understanding required. One needs to know what those words mean but one does not need to be able to conduct original research in those fields. What is required lies somewhere in between. In my opinion, anyway.
That’s a major reason why I recommend MTW. It not only defines those words, it gives a relatively gentle introduction to what they mean and how to use the concepts in practice. Though, to be fair, Lagrangian dynamics is (IIRC) treated in the advanced track and can be skipped on initial study. An STEM undergraduate level of group theory is undoubtedly very useful but may not be strictly necessary. Again, IMO.
It is not unusual for pedagogues to disagree on details. What is unusual is for them to agree on all the details.
A few minutes ago I learned of the death of Jim Hartle.
Hartle’s book on GR, Gravity: an Introduction to Einstein’s General Relativity, also has an extensive fan club. I happen to prefer MTW but please take a look at Hartle to see if it is more to your taste.
In my view, by far the best book on GR is known as MTW amongst those who study the subject. For everyone else it is “Gravitation” by Misner, Thorne and Wheeler. A web search on “MTW Gravitation” will turn up plenty of useful links.
It is now 50 years old so misses recent developments such as gravitational wave astronomy (though it does cover gravitational waves themselves), chunks of modern observational cosmology, more treatment of alternative theories to GR than would be taught these days, and so on. However, for a thorough grounding in GR it still can’t be beaten in my opinion.
Beware, though, that this is not a book for the faint-hearted dilettante. It’s roughly 1300 pages long, can do double-duty as a door stop, and assumes a background knowledge appropriate to a physics graduate. (That said, I don’t have a physics degree but Oxford chemistry appears to have been sufficiently rigorous.) Some sections are clearly marked as being at a significantly higher level of difficulty; all of these can be skipped without missing anything important for those who want a more gentle introduction.
Ken: sounds like you have the physics background to cope with this work. I’m pretty sure that you have a better grasp of classical electrodynamics than I, for example, based on what you write above.
