- This topic has 38 replies, 7 voices, and was last updated 3 years, 5 months ago by
.
-
Posts
-
And so you shall Grant! But firstly, herewith some responses and information from Roger on the comments in your previous post.
I will of course accept your statement that an “uncooled Lodestar” will get down to mag. 12/13. However …. you didn’t say which Lodestar you had in mind but the cheapest device with “Lodestar” in its title which Google could find me was a second-hand Starlight Xpress Lodestar Usb2 Mono St4 Guide Camera (catchy title!) on eBay for £245. Next best was £469 and then it got silly. As mentioned in connection with the similar suggestions from Jeremy, Tim & Andy, even £245 is probably a good percentage of what a beginner might have paid for their entire set-up so a device of this sort is not going to be high on their “must buy” list. The same is true for tripods of course. An EQ6 is no doubt a fine piece of kit, but with a price running potentially into 4 figures it’s not really a budget offering! When one is working with more basic, less highly specified, equipment and a desire to be more frugal, different solutions are needed.
So, to cut to the chase, of what does Roger’s finder consist? Camera first. It’s actually a ZWO ASI 034MC webcam, “bought used on eBay some years ago for £30” and obsolete now, of course. This is mounted at the eyepiece end of a basic 6×30 optical finder by use of an array of metalwork and adapters, including an internal focus tube using a webcam lens bought from China to allow the ZWO to image afocally. Total cost? Less than £50. Clearly neither practical nor desirable to make an exact copy were it to be manufactured, but Roger estimates that a “proper” version could be made for £100 all in and ready to mount & use.
Now performance. Its field of view is in excess of 6 degrees and stars down to at least mag. 8 can be clearly imaged with even field illumination and very little distortion. Just right for visual identification of direction of view when star-hopping in fact, obviating the need for potentially troublesome plate solving and therefore for an accurately adjusted and calibrated tripod.
And finally a picture. Please bear in mid that this is a test image taken when the device was undergoing development, so it is neither quite centred nor in the correct orientation (needs rotation by 105 degrees anti-clockwise for “sky equivalence”). Roger hasn’t needed to take any such images when using the finalised version for actual observations, as it works so well, so I can’t post any. But this one is an unprocessed single frame, exactly as taken – just reduced in size for ease of posting.
This image has been chosen to show that the FoV is indeed around 6 degrees – the brightest stars are Merak (left) and Dubhe (right) which are separated by 5 deg 22.43 min. It can be seen that the star images are circular right to the edge of the frame and free of false colour, and there is uniform field brightness.
A pretty useful piece of kit, I would say, and at a potentially very attractive price. Any budding entrepreneur care to change their mind as to manufacturing possibilities before it’s snapped up by the PRC?
I think I would be a bit worried by that image. Those are first and second magnitude stars! What sort of exposure are you using there? The camera allegedly has a 60% QE and is only 8 bit, but is good for exposures up to 60s apparently. I’m kind of hoping that’s a 1/25th sec exposure, as I would really expect to see more than that.
On plate solving. Its the elegant way to solve the problem. A stick on spirit level is hardly a demanding set up and you don’t need to buy a finder as you just use the main scope and also don’t need to consult charts – so its a cheaper solution too.
Sorry Grant but you do seem to be persistently mis-understanding (or mis-construing) many of the points being made here. As I clearly said in the text of my post, the image I attached was chosen mainly to prove that the “electronic finderscope” did indeed have a uniform, undistorted, FoV of around 6 degrees – twelve times greater than that of the set-up you mention and therefore of much geater use as a finder – not to illustrate that it could capture 2nd magnitude stars. In fact, by looking only a little more carefully at the image (helped perhaps by an expansion of the page in the browser), one can clearly make out very much fainter stars – down to at least 8th magnitude in fact, as claimed in the post. I admit that the need to reduce the image for convenient display in the post has made this slightly less convenient so here’s a larger view of just the bottom-left corner which has been enhanced so as to make things even easier.
As you will be able to confirm, the star visible towards the edge of the frame 45deg down and left of Merak is magnitude 8.38, that to Merak’s right (just below the cross-hair) is mag. 7.94, and there are several more stars visible of somewhat greater brightness. This number of stars of that range of magnitudes in a FoV of this size makes it very easy for an almost real-time assessment of the direction of view to be made by comparison with whatever star chart or program one is using to carry out the hopping process. This ease of “manual plate solving”, if you will, makes consulting astrometry.net entirely un-necessary.
And don’t forget that this is just the image through the finder. Once the target (or the field in which the target is known to sit, for very faint objects) has been located and centred in the wide FoV of the finder, attention can turn to the greater light-gathering power and magnification (but also very narrow FoV) of the main instrument in order to make observations. This is far simpler and much faster than carrying out both the alignment and observation operations through the main instrument, especially for a beginner for whom, as I must seemingly keep on reminding everyone, this device is intended.
A 6 x 30 finder is pretty small, Astrosteve, so perhaps not surprising he was having trouble finding targets. I’d recommend a 50 mm finder as this should allow a beginner plenty of opportunities to star hop without resorting to electronic gadgets. You can pickup finders of really good quality quite cheaply these days. They have a field of ~6 degs and should easily get to mag 9.5.
A very good point Jeremy, which I put to Roger to ask for his comments. He said that when he discovered the problem with the 6×30 finder (which was simply the one supplied with his telescope rather than a deliberate purchase) he did indeed consider getting a 9×50 but, as he already had the old webcam and other “bits & pieces” from earlier projects, he decided to give the “electronic” option a go first. It was really only when he discovered that the prototype device worked so well, and that it might be able to be manufactured for a price comparable to that of a 9×50, that he began to think about whether it could be commercially produced.
While the webcam finderscope and a 9×50 will have about the same sort of performance (in terms of FoV and sensitivity), the electronic option does have a number of significant advantages over its optical cousin, which I noted in my very first post:-
1) The view seen through an electronic finder can be easily manipulated, both mechanically and by use of the driver program, to align it with that given by whatever star map or program one is using to define the hopping sequence. This includes the ability to “flip” the image in two axes as well as rotate it, something which is impossible to achieve optically without the use of additional lenses or prisms. It should be noted that, as Roger pointed out, the image in an optical finder is inherently “upside down” but the orientation changes if, for example, a diagonal prism is in use, all of which can be confusing for a beginner. The ability to easily alter the image orientation avoids these sorts of issues.
2) An electronic finder provides the observer with a much more convenient “operating environment”. Even a diagonal prism cannot always avoid the need for a most un-natural stance to be adopted in order to look through the eyepiece of a finder. Viewing the scene on a screen removes this problem.
3) Use of a camera enables the observer to take images during the hopping sequence, which can be useful for analysis after the event (particularly if the sequence went astray somewhere) and to document the sequence, perhaps to teach someone else how to carry out the same operation.
4) Driver software could enable the viewed image to be processed “on the fly” in order to improve the image quality and hence the effective sensitivity, which might permit objects at the limit of detectability to be seen.
Roger also noted that he had tried a 9×50 and found that although the performance was indeed a little better than a 6×30 it was not significantly so. While less bright stars could be seen, the difference was small and the FoV was 1 or 2 deg. less than achieved by his device. In addition, the 9×50 was much heavier which required extra weight to be added to the OTA counter-weight in order to maintain its balance.
All the above persuaded Roger that the device he has created would be of considerable benefit to a less-experienced observer, hence his request that I begin this post.
I obviously misunderstood your intent. I thought cost and convenience to the user was everything. Several members, in response to your request, suggested a variety of approaches that you felt failed on cost grounds. I suggested an alternative approach that required only the purchase of a simple camera, a stick on bubble level and a bit more effort with the software driving the camera. No engineering required. That seemed the cheapest and simplest option for supporting the cash strapped beginner.
Also, I must apologise, I had not realised that when you grabbed a chunk of the image frame you resized it using a method that so badly affected the apparent performance. The dimmer stars are pretty poorly shown. You might want to use a bicubic spline or similar next time. See attached.
Yes, the image section you now supply is much nicer and, as it happens, the image solved with astrometry.net, so you could obviate the need for charts.
I look forward to seeing Roger‘s design hit the market place, but think the commercial mark up will probably take it above the cost of a new ZWO 120mm or the systems sold by Altair, unless made in bulk.
But we’re into vanishing returns here…
The ASI 034MC was an astro camera not a webcam though and cost new similar to the current equivalent ASI120 (~£120). Cheaper domestic webcams would not go as deep. Add to that the cost of the specially adapted guidescope and you can see why a commercial equivalent to this design is going to cost ~£200
Beginners speak well of this kind of finder scope, which is quite reasonably priced compared to a digital device: https://www.firstlightoptics.com/finders/astro-essentials-9×50-right-angled-erecting-finderscope.html
It gives a correct image so the orientation is the same as seen by the eye. It has a right angled eyepiece so might be a bit more accessible to view. Astrosteve mentioned that both characteristics are important to Roger, who will also be able to ditch the power supply, computer/monitor, cables, software and other paraphernalia that beginners might struggle with.
Ah, yes, quite right! It’s a big “mea culpa” from this end, I’m afraid. Apologies for this “terminological inexactitude” but when one has recently spent some time reviewing and assessing webcams for Skype & Zoom compatibility and usability as outdoor observation devices the term does eventually attain a sort of generic applicability!
However, whatever one calls them, I feel that the retail cost of a complete astrocamera unit (whether in the past with the 034 or currently with the 120) is perhaps peripheral to the issue in hand. As you yourself imply, it would clearly be uneconomic for a manufacturer wishing to duplicate Roger’s device to buy a complete unit and install it in a housing of his construction. Given the presumed ready availability of “bare” sensor modules nowadays (led by the revolution in the quality of smartphone imaging systems), a manufacturer would clearly only have to buy a module, not all the associated mounting and focus gubbins, at a wholesale price very much less than that of a complete unit. Hence Roger’s assumption that an all-in price of £100 or less is entirely feasible, given also the simplified nature of the mounting housing.
Thanks for the new information Jeremy, and the link to the Astro Essentials finder. I had in fact come across this device when I did a search for 9×50 finders after your last post but was unsure of the quality of such a device at this price point. It’s thus reassuring to hear that “beginners speak well of this kind of finder scope”.
On the downside however, one reviewer does mention the “weight” issue which Roger encountered with the 9×50 he tried. And while the erecting prism will give a corrected view, this is only true for one orientation of the optics. If the prism is removed or rotated (for “observational convenience”), the view will change in a way which might be confusing to a beginner (as I previously noted). Also, an optical device lacks the other advantages of an electronic device which I mentioned in a previous post.
In the end though, it will probably come down to a price/performance trade-off – even at this level of cost. A beginner just starting out or one not wishing to become involved with the “paraphernalia” you mention would undoubtedly find the Astro Essentials device a good fit for their needs. It is unlikely that a device such as Roger has built could be commercially constructed for a similar price to this optical finder, but a beginner wishing to take the next step in imaging might well be prepared to pay a little more for the extra advantages an electronic finder confers while still keeping things well below the price of the sort of finder/guiders mentioned at the beginning of this topic. In other words, there might well be a gap in the market which Roger’s device could fill.
Now wondering how much extra it would cost to go the whole hog and put a plate solver into the system. A Pi with a 32G SSD would have easily enough power to run it. Use a phone as a display and controller over wifi. Optics are 50mm refractor and web cam on a standard finder bracket, to which the Pi would also be attached. A pity a USB cable would still be needed but a rechargeable battery could presumably be attached to the mount somewhere, even on a Dob.
Major development cost would be writing software.
Hmm. I have a Pi-3 over in La Palma. Might have a play when I return there.
Thanks, but I already have it myself. Anyway, the Pi has a fully functional C compiler and Perl interpreter which are my languages of choice and how I implement such code on all my other Linux boxen..
On further thought, I also have the Pi IR-enabled camera so no need for a web cam, USB connection, fancy interfacing software, etc.
Have fun with that. I never got over versions 4.99, 5.00 and 5.001 all giving different answers to one script I used. 🙂
I’ve not used Perl anywhere near that ancient in a very long time and have never had significant problems in the last 20 years, despite having written at least 20k lines of Perl over that time. You got caught up in the Perl 4 / Perl 5 changeover, which was at least as big as the Python 2.x – 3.x transition. People, including myself, are still suffering from that one 18 months after 2.x EOL and several years after the writing appeared on the wall.
Although religious arguments are great fun I suggest that we should take this one elsewhere and return the thread to matters astronomical.
Not sure why I ended up with 2 copies of the Perl comment. But to clarify, it was in about 1996 when I was maintaining some astronomy code for a PPARC project called…. Starlink. Code that is still available for Linux.
Although Roger is unable to update the postings on this topic himself, he has been keeping a keen eye on the lively discussions in “read only mode”, as it were, and advising me on possible responses. However, now that things seem to have quietened down he has suggested that the topic be brought to an end.
Accordingly, he has asked me to forward his thanks to all those who took the time to suggest possible hardware solutions which embody similar functionality to his prototype device even if, in several cases, they sit at a much higher price point or, in the case of the 9×50 finder purely optical solution proposed by Jeremy, lack a number of distinctive features which can only be provided “electronically”. He remarked that he is actually encouraged by the fact that no-one has come up with an electro-optical device which has all the functionality required by a “beginner improver”, and no more (no need for focusers, replaceable eyepieces, filters, multi-element optics etc.), which might perhaps indicate that there is a gap in the market for a device such as his if it can be manufactured at a reasonable price. Proving it might be more of a problem though!
In closing, we both wish everyone “Clear Skies” and good observing.
- You must be logged in to reply to this topic.