I've often wondered how well my mobile phone would work as a digital setting circle. Has anyone tried this or similar? From what I've read there can be challenges with the scope/mount causing magnetic interference, plus the question of the accuracy of the phone's sensors in the first place. My phone is a Galaxy S3.
I'm wondering how well this might work with a small scope on an alt-az mount (even a camera tripod) for finding some of the brighter deep sky objects (or Comet Lovejoy).
Looks interesting. I've been looking at ways I can mount my phone on my collapsible dob somehow so I can use Stellarium or other programs. I've found that if I rest my phone on the scope, it doesn't work properly and sends it a bit wayward (much like a magnet does with a compass).
I've even started to play with ideas using Lego to create a phone holder but the flat surface of the lego doesn't sit on the scope very well.
I have been thinking about something like this for a few years and am glad to see it.
However, I have found in the interim, that laying my phone along the tube with bluetac, and using Skyeye in it's Mobile setting, it makes a great push-to, once you do a two star alignment with the software.
Still...... might end up with one. For $30, sheesh.
Trev
I wonder what sort of havoc the metal of the scope , mount and tripod would impart on the GPS , I know my compass in my phone wont work properly when its to close to my scopes ??? .
Great idea and if someone tries one and reports positive feedback I might grab one as well.
Brian.
My experience using an iPad 3 + several mobile apps is the pointing isn't all that great, even without any adjacent metal objects. It is frequently off enough to make it useless as a pointer.
That said, I've done design sketches to make a mount for it on my binocular paralellogram mount, sitting next to the binoculars and coupled with a parallelogram linkage to align them. If I get around to it I'll post a review in the ATM section of whether or not it was any good in practical use.
SkEye works fine using my Nexus 4 phone or Nexus 7 tablet when attached to my 90 mm Mak - the OTA is aluminium, so not too much steel to upset the compass. It works fine if I just strap the phone or tablet straight onto the OTA with rubber bands, but I also bought a cheap clone "GorillaPod" style tripod on eBay (the ones with the bendy legs) , which has the advantage of being able to mount the phone display in the most convenient orientation.
The nice thing about SkEye is that it allows you to use the pointing function with your phone / tablet mounted in any convenient orientation, not just perpendicular to the display, and this makes it a perfect app for mounting your phone as a Push-To guider.
My suggestion: download the SkEye app and try it with your phone strapped straight onto the OTA - if it looks promising for you, THEN investigate whether you need a more sophisticated mount.
Thanks for the tip with Skeye, I've installed the free version on my Galaxy phone and it seems pretty good.
Is the Pro version one of those apps that has a fluctuating price and it might be worth my while waiting a few weeks for it to go on special for $1, or is it always $6?
I glued some scraps nto the side of my dob to make a holder for my Android tablet. I have not tried it on stars yet, last night I was clamping this for strong pva joins. Will let you guys know about its pointing accuracy after tonight.
As a goto guide it was pretty lousy in practice I'm afraid. After aligning it with a number of stars and objects I tried to find some stuff with it and it was always quite off.
About the only object I was able to goto and get it in the field of my lowest power eyepiece was M42, and that was only after clearing all alignments and then re-aligning on Rigel and Betelgeuse.
My mount has very little metal at all in it. There is the focuser, the mirror cells, spider and some screws. It's otherwise all wood. I wonder if my observing chair, which has a steel frame, might have interfered, or my colourbond steel shed which was 5m away... but if it won't work in the vicinity of these then it's really not all that much use to me.
This was with an LG G Pad tablet.
I'll give my Galaxy S3 phone a go next. Hopefully its performance will be better.
It's a shame, I was pretty stoked about the possibility of having cheap goto on my old dob.
The problem is that the whole setup is limited by the low accuracy of the inclinometer of the cellphone or tablet.
Horizontal (the compass) it is dramatically inaccurate it can be serveral degrees off.
Vertically it is better but no more than 1 degree. The inclinometers used in construction are way better, to 0.1-0.2 degrees. I have such a one for using on my altazimuth scopes (8cm tabletop refractor and 40cm Dobson).
I tried Skeye on my Galaxy Note 2 but it was rather useless. Not Skyey but the hardware of the cellphone.
There is some mention in the documentation of support for Bluetooth hardware digital setting circles. Are they significantly better than this and how much do they cost?
Still... are these any good? Can I realistically expect to be able to align on a couple of stars and then put any object I like into at least a low power eyepiece with an otherwise blind GOTO?
Location: '34 South' Young Hilltops LGA, Australia
Posts: 1,481
Sky scout
Steel OTA's will cause problems as will the stepper motors if your mount is motorized. Stepper motorscontain very powerful permanent magnets that will throw the compass off.
The problem is that the whole setup is limited by the low accuracy of the inclinometer of the cellphone or tablet.
Horizontal (the compass) it is dramatically inaccurate it can be serveral degrees off.
Vertically it is better but no more than 1 degree. The inclinometers used in construction are way better, to 0.1-0.2 degrees. I have such a one for using on my altazimuth scopes (8cm tabletop refractor and 40cm Dobson).
I tried Skeye on my Galaxy Note 2 but it was rather useless. Not Skyey but the hardware of the cellphone.
It might vary with the device, and it may not work for everyone. It may be very tricky if the OTA is made of steel, but a lot of users get good results if you can mount the phone a 100 mm or more from the steel tube.
It certainly makes a difference if you calibrate the compass beforehand. (Turn on the compass, then wave the phone / tablet in a large figure of 8 a couple of times is the usual way.)
I regularly and repeatedly get better than 1 degree accuracy in both azimuth and Altitude with my Nexus 4 phone strapped onto my 90 mm Mak on an EQ2 mount. (I use the compass and inclinometer of my phone to first get a polar alignment of better than 1 degree, and then use SkEye to help me find my targets.) The Mak has an aluminium tube, which certainly helps, but the phone is only mounted about 200 mm from the mount which has a lot if steel, but doesn't worry the phone's compass.
One thing that I really like about SkEye is that you can realign on a nearby target star, and then you can get surprisingly good local alignment when you're chasing targets in the general vicinity of your latest alignment star.
The only decent solution is to use a mount with encoders and a Sky-Fi gadget, so you can hold a smart phone or tablet wherever it suits you, and have it show where the scope is pointing.
I tried both Sky Safari and the Theodolite app on my iPhone 4 and iPad 3 and while its a nice idea, it has a few problems.
1. To be any use as a finder you need accuracy of the order of ~ 1 degree, or better. Otherwise you're wasting your time.
2. Using the earths magnetic field to measure azimuth is not good enough for a finder. It's good enough for a compass as a crude navigation instrument, but not good enough for astronomy. The magnetic field has an offset to true north, this has to be compensated for. Unfortunately this offset is not constant, it varies according to your location and it varies with time, and it is also screwed with right royally if there is an aurora - this will cause a noticeable shift in the earths magnetic field. This variability is both unpredictable and sufficient to make software-based finders unpredictably unreliable...
3. Altitude. The iPhone/iPad sensors are good enough for altitude measurements, the resolution seems to be about 0.1 degree, however you must calibrate whatever software you're using.
4. It is extremely inconvenient, ergonomically. I attached my iPad to the front of my scope to see if it would figure out where the scope is pointing, and whether it was useable as a finder. Unfortunately it suffers from a very obvious problem - near the horizon its OK but at high elevation I rapidly got a bad crick in my neck from trying to get under the damn thing and look up at it.
In conclusion this idea doesn't work and when there is a far better solution at a reasonable cost I don't see why anyone would bother: Using a mount with encoders solves the accuracy problem - it's trivial to fit encoders that measure to 0.1 degree. Using Sky-Fi or similar to integrate the mount and encoders with a smartphone or tablet such that you can hold it anywhere you like solves the ergonomic problem as well.
Morton,
I tried both Sky Safari and the Theodolite app on my iPhone 4 and iPad 3 and while its a nice idea, it has a few problems.
1. To be any use as a finder you need accuracy of the order of ~ 1 degree, or better. Otherwise you're wasting your time.
2. Using the earths magnetic field to measure azimuth is not good enough for a finder. It's good enough for a compass as a crude navigation instrument, but not good enough for astronomy. The magnetic field has an offset to true north, this has to be compensated for. Unfortunately this offset is not constant, it varies according to your location and it varies with time, and it is also screwed with right royally if there is an aurora - this will cause a noticeable shift in the earths magnetic field. This variability is both unpredictable and sufficient to make software-based finders unpredictably unreliable...
3. Altitude. The iPhone/iPad sensors are good enough for altitude measurements, the resolution seems to be about 0.1 degree, however you must calibrate whatever software you're using.
4. It is extremely inconvenient, ergonomically. I attached my iPad to the front of my scope to see if it would figure out where the scope is pointing, and whether it was useable as a finder. Unfortunately it suffers from a very obvious problem - near the horizon its OK but at high elevation I rapidly got a bad crick in my neck from trying to get under the damn thing and look up at it.
SkEye is an Android-only app, so won't work for you, but for Android users, it is vastly superior as a telescope-mounted finder tool compared to SkySafari etc, because of how it works. I am not aware of any comparable iOS app. (But SkySafari is my pick of the "planetarium apps" for all other functions - and is available on both iOS and Android.)
1. I get better than 1 degree accuracy on both axes with SkEye. It has the ability to do a local "re-calibrate", so that you use SkEye to navigate to an easily identifiable target star in the general vicinity of where you are planning to observe, then "align" it to that star, and then you get better than 1-degree precision over that whole field of sky (60-degree range, say). When you swing to a new quadrant of the sky, if the alignment isn't good enough (it generally is!), just realign it to a new local star and carry on.
2. SkEye includes the local magnetic deviation to automatically know True North from Magnetic North, based on your location. (In fact, any decent smartphone compass should be able to do this. Compass deviation variation with time occurs over a scale of years , not minutes or hours, so a simple look-up table is all that is required to get better than 1-degree precision.)
3. Calibrate the compass by waving the smartphone in a figure-of-8 a couple of times before relying on it for accurate Azimuth control, but then it works just fine.
4. Ergonomics - this is where SkEye is really clever. Most "planetarium" apps in "compass" mode show you the sky view "straight through" the smartphone, perpendicular to the back of the phone. This means that to use the smartphone as a finder, you need to mount it EXACTLY perpendicular to the OTA. With SkEye, you mount the phone / tablet firmly onto your telescope in any convenient position / orientation - e.g. strapped straight onto the tube (as long as it isn't made of steel), or mount it at a convenient offset using a bracket of some sort. Then you tell SkEye what you are actually looking at through the telescope, and it works out the offset angles between the phone's orientation and the telescope's orientation. When you swing the telescope in azimuth and / or altitude, you swing the phone through the same differential angles, so SkEye can work out how much you have moved on both axes, and what you are now pointed out. Simple, but very clever, and as I said, I think it is still a unique feature.
Is the Pro version one of those apps that has a fluctuating price and it might be worth my while waiting a few weeks for it to go on special for $1, or is it always $6?
Sorry, I don't know whether it is ever on special - like all Android Apps, once you have purchased it, the Play Store shows it as "Already Owned" and doesn't display the purchase price any more.
I paid for the Pro version not so much because I "need" the extra features, but because I think the app is good enough that the developer deserves to be paid for his efforts. (I'm one of those strange people who is actually happy to pay a reasonable price for useful software - I have even been known to donate to "Beer-ware" and "Postcard-ware" app developers!)
The only decent solution is to use a mount with encoders and a Sky-Fi gadget, so you can hold a smart phone or tablet wherever it suits you, and have it show where the scope is pointing.
I have two telescope mounts - an EQ-2 with a motor-drive, and a Celestron SLT computerised Go-To mount, with a Bluetooth controller plugged into the handset.
I can control the SLT mount with SkySafari 4 Plus on my handheld phone or tablet, and this is certainly my preferred mounting, but using SkEye on my phone on my 90 mm Mak mounted on the EQ-2, I have both a computerised GoTo telescope and a computerised Push-To telescope. (Being a motorised EQ mount, once I have aligned the mount and found a target using SkEye, the motor-drive will easily hold it in view for 30 minutes or more.) This lets me use both telescopes at once - and the Mak / EQ-2 combo is a really handy grab'n'go portable telescope. (And SkEye will even work if all I have is a really basic light-weight Alt-Az tripod.)
SkEye is a free app if you have an Android phone (or about $6 for the Pro version), and I can mount my phone to the telescope with nothing more complex than a rubber band - but I lashed out and spent $5 to get a cheap "gorilla-pod" type flexible tripod which lets me mount the phone at a more convenient viewing angle:
I wonder what sort of havoc the metal of the scope , mount and tripod would impart on the GPS , I know my compass in my phone wont work properly when its to close to my scopes ??? .
