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Indeed the question as posed is unanswerable.
Telescopes are used to take images in two basic ways (not counting spectroscopy):
1. To image faint objects
2. To image fine detail
(3. Some combination of these)Aperture allows you to resolve detail, but focal length allows you to image the resolved detail with a detector. Aperture also allows you to image faint stars, but the imaging of faint extended objects depends inversely on focal ratio. Width of field, with a given detector, depends inversely on focal length. If you wish to image the combination of faint stars, faint extended objects, and detail, you require a large aperture at a low focal ratio. If you wish to image wide fields you need a short focal length, but unless you have a large aperture and hence a low focal ratio as well, your detection of faint objects and your resolution will be limited. But there is a limit to how low focal ratio can go without optical problems, so for the widest fields, very small telescopes are needed, which are limited in both resolution and limiting magnitude.
This is all before one gets into considerations of mounts and drives.
So what is ‘a good telescope for astrophotography’ depends on what exactly you are trying to achieve.
If the main problem is backlash in dec. you could try only guiding in RA. It is one of the options. You may be able to get long enough out of it.
If the star is wandering in RA, and the communications are all working, the possibilities are that the star is not bright enough, so the SNR is too low, or that the errors in the drive are just too large and random to allow guiding to work. I have this issue with my ancient Fullerscopes Mk.IV mount.
You haven’t actually explained what your problem is Jack. What results have you been getting from your attempts to use PhD2 so far? What is the guiding instrument? Have you succeeded in calibrating the system? Have you found suitable guide stars? What happens when you try to guide on them?
In my experience PhD2 either works or it doesn’t work with a system, and if it doesn’t, there’s some fundamental hardware problem that no changes to the default settings will make any difference to.
The first step is to enter the guiding focal length and pixel size. PhD then calculates appropriate increments for the movements. It should then be possible to do a calibration using a star. If that is successful, then it should guide.
Problems are pretty much always problems with the hardware rather than with PhD’s settings.
I would not rule out the possibility that your 1.25″ Lunt solar wedge is sub-par. I don’t have experience with this unit, but I do have experience with the Lunt 1.25″ diagonal blocking filter units for H alpha telescopes. I tried two, the B600 6mm one and the B1200 12mm one. On the same telescope, the 12mm one was clearly better. However, and this is where I get to my point, I tried a home-brew experiment (that I do not recommend to anyone who does not know what they are doing) where I pulled the 12mm blocking filter out of the 1.25″ diagonal (it was glued in) and made (on a lathe) a straight tube unit of 2″ outer diameter to house it, and a 1.25″ eyepiece tube. I was then able to use my H alpha system with a 2″ diagonal. The result was clearly better. There was therefore definitely a quality difference between the 2″ diagonal I had substituted and both Lunt 1.25″ diagonals, that was perceptible even in typical poor daytime seeing conditions. The Lunt diagonals did not seem good when one pulled them apart – well-finished outside, weighty, but just crudely glued together inside, unlikely to be precise. One experience.
Here’s a picture taken afterwards, at the doors of the National Museum of Wales: from right, Hazel Collett, Graham Collett, Graham Winstanley, Mike ?
Attachments:
The easiest type of recording of talks to make is an HDMI interception of the projector display, coupled with a recording of the speaker. We have a ‘black box’ that does this, and I am thinking of using it at the forthcoming Cardiff meeting. This does not give a video showing the speakers, but it shows their talks content. The trouble is…it’s still not so simple. The achilles heel is the sound. The integrated sound recorder in the box does not give good quality if the speaker is somewhat away from it, or wandering around. The solution to this is to use a digital sound recorder with a lapel mic. We have this equipment as well. This, however, will not capture the speaking of the meeting chair, nor of questioners. And it gives someone a big job later to marry up the video with the sound. Since none of these small gadgets have a very clear display of what they are doing, it is easy to make mistakes and fail to record one or the other of the video or sound. It is not a job the chair of the meeting (i.e. me) should be doing, as the chair has multiple other things to think about. It needs a volunteer dedicated to the task. For last year’s meeting in Elgin, a member of the local society (or possibly they were university staff) succeeded in making such a recording of most of the talks, using university equipment, for which we are very grateful. Generally, however, it does not happen. I feel the only way we could ensure videos made of each meeting outside London would be to pay contractors. When you look at the numbers of people who watch our videos, they are, by YouTube global standards, very, very low. Therefore it is a decision we have to weigh up as to whether it is worth it. The arrangement we have with the Institute of Physics in London is fantastic, because their technician, at no cost to us, records the sound, the view in the hall, the faces of the speakers, and the slides. We still have to pay our staff to edit and upload the video, but in this case it seems justifiable.
If you wish to loose some weight after drinking that beer there’s a Moberley Sports Centre (one b) in Kensal Rise, NW London. I’m not sure if it should be pronounced Mobberley or Mowberley.
On Alex and Paul’s point, I think it is quite understandable that so many people get the terms astrology/astrologer and astronomy/astronomer confused. Other scientific disciplines have the ‘ology’ suffix – think of geology, meteorology, physiology, biology etc. ‘Astronomy’ is a peculiarity, linguistically. It means, literally, the naming of the stars. It would be more logical for the science of the stars to be called astrology.
I’ve been looking into this event, and, for the record, there seems to be an error in Bill Barton’s original post.
On 24 March the figures that were being given by news outlets for this close approach were that the asteroid would pass the Moon at 515,000km and Earth at 168,000km (not 68,000km). In fact this prediction was quite accurate, the miss distance being 175,000km. The object was measured at 70m diameter.
The BBC news article Bill linked to was revised on 25 March, but see, for example, the Guardian article:
https://www.theguardian.com/science/2023/mar/24/city-killer-asteroid-to-pass-harmlessly-between-earth-and-moonI wonder if what we need, in view of recent discoveries by the JWST of massive galaxies only 500 million years after the Big Bang, is a revival of the Steady State theory of cosmology, or some version of it. The detection of evolved galaxies further and further back in time through advancing telescope technology (that actually was going on for some time before JWST) does not fit with the standard model, and was not predicted.
The main discovery that caused the Steady State Theory to loose out against the Big Bang Theory in the 1960s was the discovery of the cosmic microwave background. But could there be some other explanation for that than the Big Bang, I wonder?
Allow me to formally welcome to the Association again 😀
I see this question exactly was asked on Cloudy nights forum in 2009. No-one seemed to have a good answer.
https://www.cloudynights.com/topic/231104-field-flattener-for-megrez-110/I’ve tried flatteners on telescopes they were not designed for, and they always improve the results over a non-flatted setup, though not necessarily as much as should be possible when using exactly the right thing for the job.
It might be best to find one or other of the lenses suggested in that thread second-hand and just try it out. It might not be fantastic but might be good enough to be getting on with without large expenditure.
Others may have other suggestions.
I think it would mainly cost an enormous amount of time to convert it into a telescope, but if the glass is suitable (and I really don’t know whether it is), it should be possible; after all, Andrew Common in the 19th century managed to build an even bigger telescope on an amateur basis, with little prior experience of mirror-making. The mechanics would perhaps be more challenging than the optics.
As for a remote BAA telescope, I have to say, without saying too much, that Council has not been very keen on going down that route, feeling it is a service well-covered by commercial suppliers, and not wanting to risk a ‘stranded asset’ that could be difficult to manage. But we may discuss it again.
The widow of John Wall has also offered me a 36″ mirror blank! I know nothing more about it (thickness, type of glass). Any interest in the BAA?
I mentioned and illustrated the occultation of Mars on the night of its opposition, December 8, in my Sky Notes at the end of the AGM (which is now on YouTube). This is between 5:00 and 6:00 exactly from London.
I was aware of the occultation of Uranus, but did not mention it as it is not visible from the UK.
I look forward to an in-depth account of the work at the observatory James. It sounds like the capstan needs high friction in the hoizontal direction but low in the vertical, so maybe it should be grooved.
Thanks for your comments Daryl. I’d say if you spend much time looking at the Moon and planets, or double stars, an ED refractor is a very worthwhile upgrade from a standard doublet. The resolution and colour perception are both substantially enhanced by the almost total lack of chromatic fringing. The other advantage is an ED can be made shorter for its aperture and still give good images. The standard 100ED refractor is f/9, but its performance is better probably than a normal 100mm doublet at f/13.
She has been a BAA member, but is lapsed. Still, it’s potentially good that she is interested in the subject.
Seems it’s only possible to post one image per thread in this forum system. Even when I tried to post again with another image it din’t allow it. I’ll have to ask the webmasters about that.
