Digital setting circles

[FaithJ]

Does anyone here use digital setting circles? I've been considering a set of Argo Navis DSCs or similar for a while and putting off actually getting some but, after a frustrating session last night when I found only about 50% of what I set out to observe, I have decided to definitely get some, which means any observing trips before next spring are not going to happen now. I am sick of spending more time hunting for stuff than observing it, I've done that for 21 years now and it's got old.

I have a potential problem in that the clearance between my mirror box and the azimuth bolt isn't large enough, so I am going to have to make some alterations to accommodate the azimuth encoder, but I doubt that this is an insurmountable problem.

A question for those with DSCs, either Argo Navis, Sky Commander or any other make - how easy were these to install and use? Specifically the encoders going into a tight place? I am guessing that, apart from the computer itself, the fittings are pretty much the same?

[Atlas]

Hello FJ,

I have been using encoders and the Argo Navis (plus Servocat) for many years now, and I could not live without them. Installing the encoders is very easy, if you have the right hardware. You need a harness to attach the Alt encoder to your side bearing, and you need a pivot bolt with a hole in it that takes the Az encoder shaft. Astrosystems offers both items. The Argo Navis comes with a holster that you have to attach somewhere, e.g. at the UTA. The Argo Navis is a powerful system, and it is even more powerful when combined with a Goto/Tracking system.

Greetings
Johannes

[lamperti]

Faith,
Similar to what "Atlas" said earlier, I too want to spend more time observing rather than hunting, especially, as you said, after 21 years. I've had the Argo and Servocat on a 20" that was self-installed. Assistance with one other person is helpful. Read the instructions a few times before installing.
The more recent 22" UC had both 'factory-installed'. It is a very pleasurable experience to have both so as to move to various targets. Star-hopping is still used especially when the target may be a faint comet that is near an object in the database. Entering your own list into the AN is easy enough as well. I would recommend a stalk from Charlie Starks of Markless Astronomics. It keeps the wires neatly stored and you don't trip over them. Your power supply may be attached to the rocker box so that wire does not wind around the telescope too. See his web site: http://www.marklessastronomics.com/dsc%20stalk%20products.html#dscstalk
The Argo Navis also has a Yahoo Group, where one can post questions. Help is really quick, esp. from Gary Kopff, the Managing Director of Wildcard.
If you have more questions, you may contact me offline if you wish, or through this forum.

Al

Best of luck...you will not be disappointed

[Ivan Maly]

Could users of these systems please comment on their accuracy? I mean typical errors of pointing in minutes of arc. Not the resolution of the circles themselves, but the accuracy of pointing to objects, in practice.

[lamperti]

Using a cross hair high magnification eyepiece to align the 2 stars during the alignment procedure, an object will be seen near the center of a 13mm, 200x eyepiece with a 28 minute field.

Al

[Ivan Maly]

Thanks, Al. What scope are you using? I am guessing the accuracy depends on the scope as well (because of flexure etc. in the overall mechanical system).

[Ivan Maly]

Not to digress, but... interesting website, Johannes, e.g. your Cygnus project.

[lamperti]

I have a 22" Obsession U.C.

To start, I believe Argo Navis recommends using two stars that are 90 degrees apart but at different declinations.

Al

[Atlas]

Ivan,

I am glad you like my website. As for the poiting accuracy, it depends on several factors, namely the accuracy of the initial two star alignment, the tolerances built into one's scope, and the region of the sky you point to. I have used the Argo Navis first on my 18" Obsession, where it was very precise. Since three years I have been using it on my home built 25", where it is less precise, probably because of inaccuracies in the scope itself (axes may be not perfectly perpendicular to each other etc.). Often pointing is more accurate in that region of the sky where you did your initial two star alignment, getting less precise when slewing to other regions of the sky. In my 25" an object typically appears after a slew somewhere within the field of view of my 27 mm Panoptic, which gives a true field of view of ca. 40'.

There are means to improve pointing accuracy:
1) The Argo Navis has a TPAS (Telescope Pointing Analysis System) built into its firmware, which compensates for inaccuracies in the mount of your telescope. I have not bothered to put it into effect so far, because
2) I use the Argo Navis in conjunction with the Servocat, which has a spiral search function. If an object is not within the field of view of my 16mm Nagler (30' true field of vies), I just press a button and it comes to vision in a few moments. Also the Servocat has a LocalSync feature, which is extremely effective when visiting several objects in the same part of the sky. If the first object has an offset, the system stores that and factors it into the next goto. This is great when viewing galaxies in Virgo of globulars in Ophiuchus and Sagittarius.

Greetings
Johannes

[Ivan Maly]

Thanks! The "local synch" feature is great. My LX200GPS fork-mount catadioprics with this kind of feature engaged get ridiculously precise, possibly under 1'.

[bearkite]

I have been using Sky Commander DSC's for several years (in conjunction with ServoCat). They are reasonably accurate. With a decent two-star alignment I can generally put an object somewhere in a 25' FOV (12mm Delos in 17.5" f/4.1 Dob w/ Paracorr. With a good two-star you can cut that down to 16.4' (8mm Delos w/ same scope configuration). The benefit of Sky Commander over Argo is easier initialization. Just has fewer steps to get itself aligned. The down-side... Doesn't have as many bells and whistles as the Argo.

A note about DSC accuracy... Since you're basically using your DSC computer to count encoder clicks, the speed at which you move your scope affects how much error is induced in your pointing accuracy (the faster you move the scope the more missed clicks will happen and the more error will build up). Those of you using some sort of tracking system to change where the scope is pointing (ServoCat and the like, NOT EQ PLATFORMS (scope is pointed by hand then tracks on its own)) the build-up of error is at a much slower rate than those doing it by hand (push-to users). That's because even at the fastest slew rate it's nowhere near as fast as someone moving it by hand. So... Those of you doing push-to with DSC's, either move the scope smoothly and evenly (like a tracking system) or plan a second alignment of your DSC's sometime mid-session.

Now...

Just to throw a wrench in the works. There's a new player in the DSC game that really has my interest. Nexus DSC's. See http://www.astrodevices.com/products/Nexus/Nexus.html

Long story short... I live and die using Sky Tools in the field. I use it generate observing plans on the fly. I use it to star hop to objects. I don't even carry Unranometria any more. For those of you about to ask about maintaining dark adaptation, let me just say it's a non-issue. Won't go into that now, but suffice it to say I can get plenty deep using a computer.

The point I'm getting at is that I've been wanting to drive my scope from my laptop using Sky Tools. And that's where Nexus comes in... It's a DSC with built-in WiFi capability that allows you to connect in Ad Hoc or Infrastructure mode. It will also allow you to use it as a stand-alone device (DSC and wifi) or use it as a WiFi device along with your existing DSC's to connect. A club member has bought these setting circles and is now succesfully initiating Go-To's using Sky Tools. Am going to have to see how they perform. If good, will probably make the jump.

[FaithJ]

Thanks for all the comments so far.

I was looking at Nexus but, as I've already been talking to Gary at Wildcard Innovations (the maker of Argo Navis) it would feel a bit wrong to change my mind now.

[bearkite]

It's never too late.

You're the customer and the customer's ALWAYS right.

As this is a long-term commitment, take your time and buy what fits best. Think about how/where you're going to install that head unit. How it's going to change your balance and how you'll deal with that (the Argo head is the biggest and heaviest of the bunch). Have you looked in to powering the unit? I know it'll run on internal batteries. But, if you want to take advantage of the display heater, you have to be on external 12VDC to make that happen.

Just a couple of things to think about...

[Ivan Maly]

Thanks, Lou, for the detailed write-up. I actually remember you locating that tricky NGC 1444 pretty quickly for me once in your 17.5"...

Another thing I remember is what seemed an astonishing accuracy of Star Hill Inn's retired professional 24", which was equipped with a Sky Commander. (I wonder what happened to that scope... hopefully it is being used.) I wish I could remember exactly how accurate it was, but it may serve to further illustrate the issue of the rather decisive contribution of the scope and mount mechanics to the pointing accuracy.

[FaithJ]

It's never too late.

You're the customer and the customer's ALWAYS right.

As this is a long-term commitment, take your time and buy what fits best. Think about how/where you're going to install that head unit. How it's going to change your balance and how you'll deal with that (the Argo head is the biggest and heaviest of the bunch). Have you looked in to powering the unit? I know it'll run on internal batteries. But, if you want to take advantage of the display heater, you have to be on external 12VDC to make that happen.

Just a couple of things to think about...

Thanks. Yes, I am giving it a lot of thought, not least about the clearance between the lowest point of the mirror box and the azimuth bolt where the az encoder will go. I think I am going to have to make some alterations because there is only 1.5 cm (0.59") clearance so an encoder won't fit unless I cut a piece from the mirror box although, looking at it, that won't take long and won't make a difference to the box itself.
It's also going to cost a lot of money to buy and fit this thing, so I want to know I'll be able to do it before committing myself.

[bearkite]

I think I am going to have to make some alterations because there is only 1.5 cm (0.59") clearance

That clearance is from the top of your azimuth bolt to the bottom of your mirror box? If so, all I have to say is wow... That's tight.

You mentioned cutting your mirror box... Before you do that reach out to your scope's builder and make sure he hasn't already built in allowances for installing encoders. I see that David offers DSC's as an option (see http://www.dobsonians.co.uk/Options.html ) and am betting he already has an Astrosystems Pivot Bolt installed (see http://www.astrosystems.biz/pivot.htm ). To be sure you don't have an issue, buy your encoders from your builder to be sure you get something that's already been tested and used. It doesn't matter which encoder you use. All DSC's work with all encoders. You just need to know the resolution of the encoders you install.

There may be a difference in cables. But am thinking even that has become standardized. That thought coming from some responses I've gotten from the Nexus folks. They've told me that my current (Sky Commander) encoder harness will plug right in to their box and work. The club member I mentioned that just installed Nexus on his scope was an Argo user. He didn't have to change cables either. So that leads me to believe they're all interchangeable.

[bearkite]

I actually remember you locating that tricky NGC 1444 pretty quickly for me once in your 17.5"...

Wow... When was that?

Was Ursa in his current configuration or was he still a sonotube dob?

It's been a while since I've looked at that cluster....

[Atlas]

Hi FJ,

the body of my Astrosystems encoders is 14 mm thick, but there is also a flat nut that takes ca. 2 mm. In addition to that you need room for the head of the pivot bolt. When I built my telescope I left 30mm clearance measured from the floor or the rocker box to the lowest point the front board of the mirror box reaches (i.e. when tilted 45°). That proved to be sufficient. If you just have to cut some wood off the mirror box, that should be no problem. It is going to be trickier if you have to alter your mirror cell.

Greetings
Johannes

[FaithJ]

The cell is fine, it's just the 'bottom' edge of the box that has the tight clearance at 45° and it will - I hope! - be relatively simple to remove a piece of it to accommodate an encoder below (the mirror box is not completely enclosed). Trouble is, when I ordered the scope, I had no plans to include DSCs at the time so David built the scope without any plans for encoders in mind; therefore I think he built it to be as short as possible. I'll try and post a photo over the weekend.

[Ivan Maly]

Lou: Three years ago in July, Cherry Springs. I think she was in the truss form already - but it was dark and it was the only time I saw her in person!

EDIT: Sorry, you call the scope "he", so above should read "he" ;)

[bearkite]

That's okay...

It's what I get for anthropomorphizing my scope.

[skyraider]

I have a Argo/Servo setup on my Obsession scope and love it. I'm an observing buddy of bearkite, and I too have been interested in the Nexus system since it showed up on one of the scopes in our club. As I spend most of my time in the PGC and MCG catalogs, the ability to slew the scope to any galaxy in the Skytools3 database could by quite tempting, BUT I'm waiting to see the accuracy of that system. Right now I swear by TPASS with my Argo. In my scope it make a huge difference. There is talk about a multi star alignment to increase the accuracy of the gotos in the Nexus system, so I'm in "wait and see" mode right now.

[Stargeezer]

I am a visual obserer 100% and recently purchased a used 15" Obsession with Argo Navis and it is great. No more hours of hunting for an object, just a lot of minutes observing it in the eye piece. Check out the yahoo group websites for Argo Navis and Obsession telescopes. There is lots of information about installing this on your scope.

[Marko]

Been using a SkyCommander for many years now. That controller is far less advanced than the Argo Navis but I'll discuss it anyway as it has been very good to me for many years. I have a current one. There was an older model from over 6 years ago so avoid that one.

I'm going to go into more detail on align. For any of these alt/az dobs you want to take care in choice of initial two cal stars. Try to choose stars that have significantly different Alt, AZ, RA and DEC where alt is greater than 20 degrees and less than 70 degrees (avoid horizon and zenith hole for different reasons). The better you do this the better your alignment. If you think about it you want many 'tics' of the alt and az encoders and you want the model of the sky to also have much space between the RA and DEC so your accuracy in the conversions is far better. You need to take care to do the cal carefully with object dead center on fairly high mag if you want good results. The SkyCommander does have a 'sync to this object' function that I use a lot if I am working a specific section of sky or am going to look for something obscure I will generally sync to something brighter and easy to center in that area to increase finding accuracy.

The device greatly increases my enjoyment as I don't have to hunt all night. I do turn it off from time to time just to stay in practice for hunting. It rarely lands the target dead center but generally hits the target if my FOV is 30' or more so I use a 'finder eyepiece' then higher mag.

My dob has tracking once aligned but that is not this topic so I will only say that for galaxy fields or careful study of objects that is priceless although expensive. (you get what you pay for).


The SkyCommander has a clumbsy membrane keyboard with only a few keys that one can get used to but it does work and I operate it's non-lite keyboard mostly from memory of it's 8 key positions and feedback from the two line LCD display. There is no argument that the Argo Navis is superior in it's input/output interfaces and dial.

The Sky Commander is small and light and as such moves between my 18" and 12" dob easily and quickly velcros in it's place. Battery life is very good but I tend to plug it into 12V so don't notice that much anymore.

SkyCommander gets 'sluggish' in very cold climate so if you are always in the ice cold I suggest avoiding this controller. It is like it's clock for the microprocessor is an 'R/C' clock and not crystal controlled. It's time of day clock of course has to be the classic 'watch crystal' so must be accurate to track but alas, I digress into geek-speak.

It has many common catalogs like NGC, IC, APN, Hickson and more but is lacking UGC and PGC (Pgc I can understand but it would be really nice to have UGC). It has a very simple low-resolution set of 99 objects that you key in RA/Dec and this I have found quite valuable to put in objects that are not in it's catalogs. The saved objects in the 99 only have room on the display for a number and no name so 'Pal 15' I have to remember or write down (and loose the paper later) or recognize the RA/DEC to know which one it is for example. I have about 20 of these used and I am very glad for this feature even though only numeric name. I often quickly put in a new one for obscure object and just leave it in there.

Never get rid of your telrad and finder of course but a device such as this makes your observing sessions more productive in general for dim and difficult targets that don't pop out in a finder (LIKE every darn thing mentioned on DSF! LOL)

[Ivan Maly]

Mark, thank you for the detailed account.

How does the pointing accuracy depend on the ground on which the scope is standing - such as gravel, grass, concrete? Or dust, for those enjoying desert skies...

[bearkite]

Mark... Nice description of life with Sky Commander.

I've been living with one for several years now and I too suffered from "sluggishness" during cold observing sessions. The problem is that if you don't run 12VDC to power the setting circles (which it sounds like you are) the display heater doesn't run and you will definitely suffer from sluggish display response in cold weather. As it turned out, my problem was that I had a poor connection to my 12V bus. It was a plug configuration that was coming loose during sessions. And when it got cold it got so bad I was putting hand warmers on the display face to make it somewhat useable. I've since permanently attached the power for the DSC to the 12V bus. I no longer have the problem with sluggish display. If it's "stupid cold" (below 10*F) it slows down a bit. But nowhere near as bad as when running on the internal 9VDC supply (no display heater running). Have had no problems in more civilized temps (below freezing into the teens). Mark... If you're suffering from a sluggish Sky Commander with 12V plugged in, you may want to check that connection.

As for the limited catalog space. This was actually an issue that got me thinking about switching. But after looking at Argo Navis I discovered they too suffered from limited catalog space. They don't have complete UGC and PGC catalogs. For that matter, sky commander gives you more flexibility in which catalogs are loaded than Argo. The problem is that you're dealing with only 512kb of space and that's not much. I played around with loading different configurations of catalogs and was never really satisfied. Have since gone back to the default catalog set and will either star hop or key in RA and Dec if feeling particularly lazy ;-) . The Nexus DSCs are probably going to be the "cure" for those of us looking to have our scopes do go-to's to really obscure stuff without star hopping or manually entering coordinates.

Ivan... Personally haven't seen much of a difference between ground conditions. But, I haven't really been paying much attention to that variable. I do know that some nights are better than others when it comes to pointing accuracy. Am going to have to start paying attention to my ground conditions to see if that's making a difference. Could be...

[akarsh]

Hi

My earlier observing buddy, John Tatarchuk, happened to have an Argo Navis on his 25". Turns out that when looking for those faint galaxy clusters, he had to inevitably star-hop and the thing, for some reason, kept losing alignment. So it worked well for NGC, but for the Abell clusters he was really after, he almost always had to star-hop anyway.

On the question of resolution, someone on CN pointed out these capacitive encoders AMT-102 from CUI Inc. They are available from Digi-Key corporation for those in the US. These encoders seem to have better resolution than most of the commonly used rotary encoders. I'm not sure if the Argo Navis can handle these as though they were a drop-in replacement to the "usual" encoders.

Regards
Akarsh

[Don Pensack]

I use a Sky Commander on a Teeter Classic Dob.
I have some comments:
1) I enjoy the fact the database has a lot of non-NGC objects in it.
2) I enjoy putting in about 50 esoteric objects i want to find and having the DSC find them for me. You can always just move the scope until the coordinates match but since an alt-az scope doesn't move along Dec and RA lines, it can be a little frustrating.
3) I power the unit from 12V externally, not the internal 9V battery. The advantages to that are that the LCD screen is heated and never disappears, and the scope can be moved rapidly without encoder reading errors. I use 10,000 tick encoders.
4) The accuracy is greatest where small movements of the scope don't result in large positional changes. I.e., like most DSCs, the accuracy goes down a bit as you approach the zenith. Since that's "Dobson's Hole" anyway, it hasn't been an issue.
5) Inscrutably, even after using a crosshair eyepiece to align the DSC, the accuracy varies from one alignment to the next. I can align on two stars and get a poor pointing accuracy, turn the unit off and on again and align on the same two stars and get superb pointing accuracy. I have no clue what the difference is, but I've had the same problem with 3 brands of DSCs. When it's dead on, it's great--I can use a 6mm eyepiece (304X) as a finder!. When it's only pointing poorly, I have to resort to a 21mm eyepiece to find things (87X). When it's not doing well, syncing on multiple objects in a row doesn't help the accuracy. When it's pointing accurately, I don't even need to sync it because every object is near the center of the field. I've leveled the scope, even though it shouldn't be necessary, moved the scope slowly (even though it shouldn't be necessary), and hit Enter for the position within a second of centering the object. What's different from one time to the next, I have no clue. But, at a star party recently, 3 other observers noted the same thing and told me they had experienced exactly the same issues with pointing. It's my supposition that it involves momentary errors in reading the encoders, and may be encoder related, as opposed to DSC-related. I never experienced that issue with 2048 tick encoders, but I have on all higher-tick-count encoders.
6) The units available all require too much fiddling with buttons and knbs to go from object to object. I wish they had a number pad and functioned like an LX200 hand controller: hit the numbers regardless of what menu you may be on and hit enter. Instead, we have to mess with menus and up and down motion on rows of digits. DSCs are all very crude. And while the screens can be turned off, they cannot be dimmed enough for the very darkest of sites, whether Tangent or Sky Commander, or Argo Navis. The red LEDs on the Tangent boxes (JMI, Lumicon, etc.) can be dimmed the most, but still need a dimmer setting than the dimmest. They can all be dimmed with internal or external screen covers but it would be a lot easier if they simply had some dimmer settings for the screens for those of us who view under dark skies.
7) Despite all that, the ability to find objects is dramatically improved with a DSC on the scope, and I wouldn't want to not have one.

[FaithJ]

I finally got hold of an Argo Navis, while I was in Australia earlier this month. Hopefully it won't be too much of a chore installing the encoders although I need to get some extra bits for the installation.

[Don Pensack]

Faith,
You might look at JMI's website. They seem to have kits and pieces of kits to mount encoders on just about every scope that's made.

[rmollise]

The Argo Navis is fine...but for me all its features are an annoyance more than a help when I am using DSCs. Best damn unit I have ever used in every respect? Sky Commander. ;-)

[Don Pensack]

The Sky Commander has some problems (though I own and use one):
--it fades out in the cold. The answer is to power it from a 12V power supply, which heats the screen, but that isn't necessary with the other DSCs.
--the screen is too bright at minimum setting. I fixed it with some dark cellophane between the screen and the window, but that isn't necessary with other DSCs, which can be turned down to lower brightness settings.
--if you hit the wrong button, there is no easy "back" or "Escape" button, and since the buttons are not illuminated at night, it's all too easy to hit the wrong button when wearing gloves.
--the database is a little too small for any scope over 10". Or, to put it another way, thousands of objects visible in small scopes are NOT in the database, while thousands of objects that are NOT visible in small scopes ARE. This is an issue with other DSCs, and computerized scopes, too, so this complaint is not unique to the Sky Commander.

That's about it. Otherwise, I like it, and it works.

[rmollise]

--Must be a lot colder where you live. I have never, ever had to exercise the 12volt option. Not once.

--At the lower setting I find brightness just right.

--I do wish the keypad were illuminated, I get tired of having to point a red light at the keypad. But I've never got myself into something I couldn't back out of.

--If I want more, I'll hook up a computer. Most of the time the good old NGC/IC is enough, however.

;-)

[Don Pensack]

Rod,
At my high-altitude site (2550m, 8350'), it can be 0C (32F) in August. Last month was a warm 4C(~38F) near dawn. Without the 12V connection, the SC is not usable after 10pm.
I also must observe under darker skies. At low setting, I can see the screen from 200' across the parking lot. I tape over all my red LED operating lights because they hurt my eyes at night.
The problem with the NGC/IC (and the database in the SC isn't complete) is that there are literally thousands of open clusters without NGC numbers. And a ton of globulars, small bright nebulae, dark nebulae, etc. If I were doing the database for a DSC, I would start with the items visible in smaller scopes and then fill in fainter and fainter until I reached a reasonable limit (say, magnitude 17) instead of including some at that fainter limit and ignoring a lot of Mag. 5 objects.
Hooking up a computer is a guaranteed way to ruin your night vision, so I eschew the use of anything with a screen larger than the SC. As a general rule, if you can see it and read it in twilight, it's too bright for night use.

[Jim Chandler]

Hooking up a computer is a guaranteed way to ruin your night vision, so I eschew the use of anything with a screen larger than the SC. As a general rule, if you can see it and read it in twilight, it's too bright for night use.

Enter the eyepatch. At the eyepiece, cover your non-observing eye to allow it to be fully relaxed. At the laptop, shift it to cover the observing eye. After looking at a deeply red-filtered, very dim laptop for a minute or two, a blink comparison between the covered and uncovered eyes shows the obvious degradation in dark adaptation to which Don refers. The patch allows the use of the laptop without sacrificing dark adaptation.

The benefits of covering the off eye while at the eyepiece should not be ignored either. Having the off eye completely relaxed aids in concentration and ultimately allows you to see deeper. Having tracking, using a hood, using an eyepatch; each one eliminates a small but noticeable demand on your attention. Getting rid of each of these distractions incrementally improves your concentration.

Walgreen's house brand eyepatches have a nice, stiff eyecup and reasonable life expectancy for the elastic band.


Rod, is it just me, or does anyone else detect eerie overtones of the circa 2000 discussions about "real astronomers don't use DSC's" in your the-SC-is-good-enough-for-me comments? <g>

[rmollise]

SkyCommander gets 'sluggish' in very cold climate so if you are always in the ice cold I suggest avoiding this controller. It is like it's clock for the microprocessor is an 'R/C' clock and not crystal controlled. It's time of day clock of course has to be the classic 'watch crystal' so must be accurate to track but alas, I digress into geek-speak.

I've never worried about anything but azimuth and that star two isn't too low. Polaris is my Star One, always, and Procyon and Fomalhaut take up the slack the rest of the year. Polaris and a star 90-degrees plus away in azimuth and I am ready to go. As I mentioned earlier, my Sky Commander has never gotten sluggish enough in the cold to worry about, but if it does, as was also mentioned earlier, power it with 12volts and an internal heater kicks in as needed. :-)