14 May 2021 at 11:40 pm #574966
I have been giving some help to a former school-friend who has fairly recently taken up observational astronomy. One of his major problems has been star hopping. He prefers to locate a target manually, rather than by GOTO methods, but has been frequently thwarted by the numerous difficulties encountered. A significant one of these has been an inability to accurately determine exactly which starfield he is looking at because of the limited light-gathering capacity of his finder. This has required him to take images using a webcam with his main OTA and (hopefully!) use these to determine his viewpoint, but his ability to do so is severely constrained by the limited field-of-view of this setup.
Being a practical person, he has developed what seems to be a simple yet inventive solution, which can best be described as a Finderscope Webcam. In other words, a webcam mounted on a finder, imaging the scene afocally. This has the double advantage of greater sensitivity while retaining the wider field-of-view. Whilst currently a rather “DIY” device, it uses easily available components combined in a rather novel arrangement and so should not be difficult to replicate.
I have seen promising results from it and so feel a device such as this could be of value to other observers, as it does have a number of additional advantages over a standard “optical” finder:-
1) The device can be rotated (manually) and the image flipped (using the driver program) so that the view given by the webcam finder matches any “planetarium program” view that the observer might be using to verify that the hopping sequence is being carried out correctly
2) The “ergonomics” of the device are much superior to that of an optical finder. Specifically, because the observer does not have to look through the device there is no need to adopt uncomfortable postures at the telescope and no problems are caused for spectacle wearers
3) The observer can record both the hopping sequence taken and images of interest found during the “hop”, both for later analysis
4) By use of suitable driver software, it would seem possible to apply “dark frame correction” and live stacking to the image stream. Both of these techniques would significantly increase the image quality compared to an optical finder
I was thus wondering if any member knows whether a similar device is already available or has contacts with manufacturers of telescope accessories who might be interested in developing & marketing such a device?15 May 2021 at 9:25 am #58420615 May 2021 at 1:47 pm #584207Tim HaymesParticipant
A web-cam on the finder is a useful arrangement. Since i already have a 9×50 finder and a suitable camera, i bought one of these from FLO: https://www.firstlightoptics.com/adapters/astro-essentials-sky-watcher-9×50-finder-to-t-adapter.html.
Agreed, Its helpfull to have some form of dark frame subtraction to remove hot-pixels if the web-cam is used with longer exposure settings. False stars can be confused with real ones !15 May 2021 at 4:18 pm #584209Robin LeadbeaterParticipant
Here is my DIY version using Meccano and Jubilee clips used as an electronic finder on my remote setup. I don’t find it that sensitive though with the old webcam I am using, perhaps mag 4-5. (Maybe more modern webcams are better) Good enough to put a bright star in the main camera field to do a local sync of the goto though.
Robin16 May 2021 at 9:34 am #584213
Yes, Astrosteve: a cheap finder (likely already have, but with removable eyepiece), the adapter that Tim linked to, and a cheap detector (could be webcam or a low cost CCD/CMOS detector, depending on how much sensitivity, field of view and cost one is happy with). So, all commercially available individually or as the complete unit. Plenty of options for you.16 May 2021 at 9:41 am #584210
Thanks for those comments. However, between them they do rather illustrate the problems with “standard” solutions which my friend Roger was trying to solve. In the case of the Evoguide 50ED plus ZWO camera bundle, the most obvious objection is cost! (£319, even as a “special offer”). While I’m sure there must be a market for such a device at this price point among “professional amateurs”, I rather doubt whether many casual backgarden skywatchers would be willing to invest this amount, possibly more than their entire setup has cost them so far, in order to obtain one. This is further compounded by the fact that this device does not seem to be able to make up its mind as to what it is. For example, a “webcam finderscope” does not need the ability to accept different cameras/eyepieces nor does it need to be able to alter the focus: once the selected webcam is in the correct position it should not need to be altered or adjusted thereafter. Also, does a finder for a “moderate” telescope really need a 50mm “Ohara ED doublet objective that includes an S-FPL53 ED glass element”? All these additions can only serve to increase the price. The fact that this item does not seem to be intended purely as a finder is to some extent borne out by the reviews, which refer to its use as a astrophotography camera in its own right. Irony of ironies, one review even mentions the need for a finder to be mounted on it! Which brings me to the next disadvantage of both the Evoguide setup and adapter rings – limited field-of-view.
The FirstLightOptics page for just the guider has an “applet” for determining the FoV of various setups, which shows that the Evo plus ZWO camera bundle can span from M32 to M110 – barely 1 degree. This again would tend to confirm that it is not really suitable purely as a finder for a moderate OTA. Adapter rings tend to have the same problem: Roger’s setup can achieve an FoV of over 6 degrees, which is much more usable for star hopping. Finally, although Robin’s setup is much nearer to Roger’s, he himself says that the webcam he used is not sufficiently sensitive, thus emphasising the need for careful selection of components.
In summary then, although there are products out there which address the same “operational space”, there does not seem to be anything currently on the market which combines high sensitivity, very wide fov, and modest cost – unless someone knows differently, that is!16 May 2021 at 10:48 am #584215
Yes, the “assemble available components” route is the one Roger hoped he could go down. As I suspect Robin also found though, given his use of Meccano & Jubilee clips, the solution to the problem turned out not to be that simple, particularly in the case of obtaining a wide FoV. He thus had to engage in some creative engineering metalwork (and a crash course in silver soldering!) in order to make everything (literally!) come together.
Given the lack of immediate responses saying “oh yes, I got one of those ages ago”, it would seem there is indeed no commercially available unit of this specification available, which answers the first part of Roger’s query which I posed in my original post. As to the second part, while he is sure that such a unit would be of great benefit to the beginner, the fact that constructing one is not straightforward leads him to suspect that, now he has (he believes) come up with a workable solution, it is only really a commercial manufacturing process which would be able to build them to a reasonable standard in reasonable numbers. Hence his appeal to members who might have contacts with such an enterprise (or possibly a hot line to BBC’s “Dragons’ Den”!). Anyone able to help?16 May 2021 at 11:55 am #584217Andy WilsonKeymaster
A few years ago I got the equivalent 50mm guide scope and camera, currently selling for £235 on this page. I think it was more expensive when I bought it and prices have come down. They do various options, including the telescope guider body with a non-rotating helical focuser on which you could put your own camera of choice for £109.
Of course the main purpose of this setup is as a guide camera rather than a digital finder, but I found it worked perfectly for my purpose. A GoTo mount that wasn’t quite good enough to always put the target in the small field of view of the guide camera on a spectrograph.
Andy16 May 2021 at 11:56 am #584218
Dragon’s Den? “I’m out”16 May 2021 at 12:04 pm #584219Andy WilsonKeymaster
There are also the Celestron Starsense and Meade Starlock. The drawback is that I think these only work with their products, but sound a lot like what you describe.16 May 2021 at 1:02 pm #584220
Thanks for your input Andy. The item you mention is pretty close to Roger’s idea but in fact the “Altair MG32 Mini Guide Polar Alignment Scope + QRB Rings + GPCAM Guide Camera” (phew!) seems to be a closer match – no (un-necessary) focuser and a sensible size objective lens. However, the cameras on both of these are only mono (presumably a colour one would cost rather more) and there’s no mention of FoV – but as they are specified to be mainly for guiding purposes one must assume that this could be quite narrow. And then there’s the price of course (£275 for the Altair!) when a basic, beginner level, optical finder can be bought for £35 (Rother Valley). Note that I’m not suggesting that the build quality of these two would be anything close to the same, simply that there doesn’t seem to be anything available for a beginner.
The Celestron and Meade devices do indeed seem to work only with their own products – and pretty beefy ones at that, judging by the Meade pictures! I suspect that in these cases if one has to ask the price then one can’t afford it!
Sorry about the apparent emphasis on price, but this is a factor which should not be overlooked if beginners are to be encouraged to move onto slightly more complicated observations than simply looking at the larger planets. Finding Uranus, Neptune and the brighter galaxies (for example) with only an optical finder on a standard “consumer” 150mm reflector, for example, can be very difficult – particularly for someone with little experience. Adding an “electronic finder”, a bit of technology and a star-hopping plan makes things so much easier! Not everyone has large aperture OTAs on motorised, permanently mounted, perfectly adjusted GOTO drives, I’m afraid.
All offers to manufacture gratefully received!16 May 2021 at 1:19 pm #584221
Silly question, but why stay with a small refractor when a Meade 85mm reflector (or similar) could be used instead?
I’ve tried CCDs on cheap small aperture refractors and the star images are distinctly blobby because the different colours come to different focuses.
I’ve used a reflector as my autoguider/finder for years – run by my own code – and found using a small reflector, with its less blobby stars, more sensitive than when I used the refractor(s).
Would also say, avoid colour cameras as far as possible, the Bayer matrix reduces sensitivity a lot.
Intrigued by “Star hopping plan”. I just used a copy of Uranometria…16 May 2021 at 2:23 pm #584222
I’ve just realised I missed something in this.
Why not put the camera straight on to the main telescope, display the image it generates, platesolve via a cygwin installation of Astrometry.net and have the software tell you how far to move in RA and Dec to get to the right place. Most Astrometry.net solutions only take 10secs on my 5 year old laptop, so you could point at the rough location and be there 2-3 minutes later.
If you are not autoguiding why have the finder guidescope at all? Eyeballing along the tube would give a good start point.17 May 2021 at 4:33 pm #584229
A really great bit of lateral thinking there Grant, but I feel it doesn’t really move us forward. I’m sure that an 85mm reflector would indeed give a better image than a small refractor finder but the practical difficulties of mounting, and probably counter-weighting, such an item on the OTA of the sort of slightly up-market but still essentially “consumer” reflector a keen beginner is likely to be using (something like a Skywatcher 150?) hardly bear thinking about. Then of course, as the 85mm will almost certainly have been intended to be used as a “proper” (if small!) telescope rather than a finder, there is the question of FoV to consider. One might even have to mount a finder on it!! (and round we go again). As for “blobby coloured images”, I can assure you that those produced by Roger’s device are nicely round and white, right to the edge of the field. [P.S. I sincerely hope you didn’t mean “85mm refractor“, by the way – available, but not exactly at the budget end of the market!]
We did consider using Uranometria as a guide to star hopping, but I’m afraid the Bodleian didn’t seem keen to lend out their copy ….
Moving on to your second post Grant, I knew that Roger had mentioned “plate solving” so I checked back with him and he confirmed that, to put it succinctly, “been there, done that, didn’t get the T-shirt”. There were two basic problems. Firstly, astrometry.net rarely came up with a solution, even “after the event” let alone “live”, probably due to having captured an insufficient number of stars. Then, even if it had found a solution, the instruction to move X in RA and Y in Dec. does rather assume that these axes are correctly aligned and that the relevant setting circles are accurately calibrated and with a fine enough resolution and lack of back-lash to permit an accurate move. With a beginner’s telescope which has to be heaved outside and set up each time an observation is attempted, neither of these constraints is likely to be true. If they were, one could of course simply use the setting circles to point directly at the target of interest without having to go through the star-hopping process. As mentioned earlier, not such a problem with permanent installations but a frequent problem with beginners’ set-ups.
In Roger’s case, the reason he was needing to visually identify exactly where he had got to in the sky after each “slew” between target stars was precisely because he was aware that, although he had taken care to ensure that his equatorial was set up as accurately as possible and that he had turned the dials as precisely as he could, he was aware that the setup was usually just slightly “out” which meant that the end-point was often not quite where it was intended to be. This error could easily be corrected if only he could see sufficient stars to get a “fix” – not possible due to the small FoV of the main instrument and not possible through the optical finder due to low sensitivity. Hence the need for a wide FoV, high sensitivity, “electronic” finder.
And yes, “eyeballing” will certainly give a good starting point but what then? Looking along the tube will give an approximate aiming point but, assuming the target is invisible both to the naked eye and to the (optical) finder, this could be some distance away from the intended aiming point. Even if it’s fairly close, unless you know exactly where the telescope is pointing there is no way to know in which direction to move, let alone how far. As above, relying on the RA & Dec. circles may not be helpful, and “random search” (taking images each time through the main instrument) is unlikely to be effective for faint objects.
I suppose a summary of many of the points I have made in all the posts is “Welcome to the world of the beginner”! Everyone has to start somewhere, and that somewhere can be well down the scale of instrument sophistication. Beginners often have problems which “professional amateurs” don’t even think of, which can lead to blindness as to reasonable ways to solve those problems.17 May 2021 at 4:59 pm #584230Dr Paul LeylandParticipant
We did consider using Uranometria as a guide to star hopping, but I’m afraid the Bodleian didn’t seem keen to lend out their copy ….
How faint do you need to go? Freely available charts reach mag 7. Here is one of Orion, for example, and another around the NCP.17 May 2021 at 10:23 pm #584231
I think you will find that the people on here were all beginners once and most did star hopping and remember it well. Some still go that way by choice. I myself didn’t use a GOTO in anger until about 2008 – 37 years since I first had a telescope. While I wanted an LX200 from their introduction onward, mortgages got in the way… An EQ6 eventually proved affordable and is still what I lug outside at night.
My experience suggests that Astrometry.net will generally solve any image with more than 10 stars on with an SNR > 5. I’ve seen lots of frames solve with 8 stars – but it may take longer. So, what size webcam sensor are you thinking of then? In a 1sec exposure with a 100mm aperture (£60 from a car boot sale) with an uncooled Lodestar I would expect to image stars down to 12-13th mag which with the 100mm gave an ~30 arc minute field. So what field of view are we thinking for the webcam? Could you post one of his pictures?
Also, the idea of using the main scope was mainly for simplification ie no need for finder scope and the camera used could be used for object imaging.
If you had an alt-az mount set up roughly level or a German equatorial aligned by eye to the pole star, by recursively taking images and adjusting the scope slow motions (as indicated by software) either in alt/azimuth or RA/Dec – you would move toward the correct position even if the scope was not properly aligned. The better aligned the quicker it would succeed, but it would still work in a few iterations (unless your alignments were hugely out – a spirit level for alt/az and the pole star would avoid that).
The lack of blobbiness might be explained by the colour webcam having an integral IR blocker (quite common) but the cost of that is lower camera sensitivity and fewer stars.
Re: eyeballing. You don’t need to know where the telescope is pointing. If you plate solve, the software will know where its pointing from the plate solution for the middle pixel of the image. Thus it can tell you in which direction to move the slow motions. You just need to move in roughly the right direction.
From where I’m standing – beyond using a guide camera instead of a normal Zoom/Skype webcam – the issue isn’t so much the equipment as the software to use it. Its fairly simple though.18 May 2021 at 11:13 am #584234
Sorry Xilman – my comment about using Uranometria was just a joke! (replying to the mention of same by Grant Privett in his earlier post). Thanks for offering the info. on star charts though.18 May 2021 at 6:59 pm #584237Robin LeadbeaterParticipant
Just come across this on “Cloudy Nights”. I’ve not tried it but it looks like you strap the phone to your scope, centre a nearby bright star in the main scope and then use the phone as a “virtual sky” to hop to your target18 May 2021 at 11:40 pm #584238
Certainly an interesting take on the theme, but it seems to require one to have a smartphone of some sort (which not everyone has, you might be surprised to hear!) but maybe a tablet would work as well? Also, there would appear to be some problems with it yet so maybe not something to take up immediately.
It is, however, encouraging to hear someone else saying that beginners often have problems with star-hopping! Not sure this is the solution, but at least the problem is recognised. Not so sure about the excursion into “plate solving” in the later posts though, as this again fails to recognise that, as the original poster says, the fundamental problem here is obtaining good enough images with basic hardware for plate solving to find a solution – exactly the issue Roger was trying to address.18 May 2021 at 11:44 pm #584239
Thanks for your further contribution Grant, and apologies for not responding sooner. I had to communicate with Roger again to find some of the information you requested, and unfortunately he has not been feeling well today so things have been delayed. I’ll get back to you as soon as I can.
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