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Note though, that time and location are both important. You need a good position and good times. So, to get accurate pointing:
1, Set the computer system clock using its “Change date and time” setting.
…Remember to activate your NTP client (operating system dependent) and configure it to use reliable low-stratum servers.
My Win10 TCS is rarely more than 20ms from reality and my Linux boxen are usually under 5ms — the one I am using now claims to be 0.214ms away from GPS time..
I use Google maps. At full zoom a position can be located to within 10m in most parts of the civilized world and in most of the US for that matter.
Right now I am sitting at 52.143392N,0.117095E and my car is parked at 52.143390 0.117336E.
The difference in latitude is .000002 degrees and at 60 nautical miles per degree, or 111.12 km, that is 22cm. The difference in longitude is 0.000241 degrees but that must be divided by cos(latitude) to convert to an angular separation. The conversion factor is 0.613254320 according to my good old Chambers 7-figure log tables. Performing the division and multiplication yields a linear separation of 44m. In reality the car is about 1m north of me but the east-west distance is actually about 18m.
Good enough for me. Note that one arcsecond is 112120 / 3600 = 31m so my co-ordinates are good to an arcsecond or better.
Hi Jack,
Do you want to use the mount to do any deep sky imaging? Both links are to Alt-Az mounts which will not be suitable for astrophotography as they will introduce field rotation, unless you use a very short exposure. Alt-Az mounts are fine for visual observing.Peter
Or fit a field rotator before the camera. Not exactly a low-cost option.
The Seestar uses 10s exposures to keep field rotation within its acceptable limits.
Incidentally, I was brung up in Long Eaton, near Nottingham, and a younger bother lives nearby. I could in principle pay a visit to your observatory and explain things in more detail.
Paul
Mel, thanks. We want something which will hold it whenever someone takes their hand off the crank handle; if they let go it runs away as described above. The U bolt idea is good though for holding it; we use a rope at present which does something similar. But thank you.
Paul, that is a good idea. Our shutter is pretty heavy so it may need to be a chunky battery. How do you go about charging up that battery? We’d need someone to remember to connect it to the charging circuit unless we always parked the dome in azimuth in the same position and set up a positive and negative contacts at specific locations on the dome and the on the rim of the supporting wall. But an interesting idea.
James
The battery charges automatically from the solar panel. No human intervention required and there are no electrical contacts between the wall and the dome. All of the slit motor, battery and solar panel are attached to the rotating part of the dome so nothing moves relatively to anything else. The purpose of controlling them all through a small computer such as a Raspberry Pi, which is itself fixed in position relatively to the UPS and takes its power from it, is that WiFi works regardless of the position of the computer as it rotates with the dome.
As for the chunkiness of the battery, it only needs to be able to open and close the slit once or twice before it is recharged from the solar panel. The power drain of a Raspberry Pi is tiny and any reasonable UPS could keep it running for weeks if not days. For a reason which I hope is obvious, the panel should be on the south side of the dome when the latter is in its parked position. If the azimuth of the dome is also automated, as is the case with my dome, it can be parked automagically in the correct position. Assuming that the azimuth motor is fixed to the wall, powering and controlling it should be straightforward.
The size of the panel and the capacity of the UPS will need to be calculated from power of the motor used and for how long it needs power applying.
Of course, with all that in place the dome can be fully controlled over the interweb thingy given an connection to the TCS, which is the rationale behind my plans. It’s all I need to make my observatory fully automatic and available whenever the sky is clear, wherever I happen to be located at the time.
I think it would be too slow Bill unless we motorised it but getting power to the dome at any position in its 360 degree rotation would be difficult.
I have been considering the same problem for my dome.
Front-runner idea at the moment is a UPS (i.e. a controllable and rechargeable battery) attached to the inside of the dome. Attached to it, also on the inside is a Raspberry Pi which switches power from the UPS to the dome motors – slit and dome azimuth – as required, the Pi being controlled from the main TCS over WiFi. Attached to the UPS on the outside of the dome is a solar panel which keeps the UPS fully charged.
In my case the dome azimuth is already motorized and controllable by the TCS so I need only the slit control but you may need both degrees of freedom to be upgraded.
Perhaps the same idea may work for you.
Paul
Thank you, very interesting.
Where I am here near Cambridge and the observatory in La Palma were both rated Bortle 4 in 2015. However the former is near the top of the scale and has a sky brightness of 20.58 mag / arcsec^2 and the latter 21.58. I suspect the difference may be more marked now. Certainly the sky looks much darker in LP and the Milky Way is spectacular on a clear night at new moon. M31 is obvious from there but difficult from here in the UK. So many stars are visible that I have difficulty recognizing constellations!
The app and firmware updated nicely this evening.
I have also downloaded seestar_alp (https://github.com/smart-underworld/seestar_alp) which works remarkably well and is much more controllable than the Seestar app. It can send the S50 to a specified position in RA/Dec (either Jnow or J2000 epochs), those data can be typed in, pasted from the clipboard or transferred from Stellarium. It also has a scheduler for fully unattended usage. Very highly recommended and I hope that the official ZWO app takes some of the features on board. The app has finally caught up with seestar_alp in that it now does mosaic mode.
Of course, just as I was getting the hang of seestar_alp this evening the sky clouded over completely and I didn’t get a single image.
Thanks. It looks like a generic problem as your image also shows rings around the brighter stars.
Not a deal breaker as photometry is very tolerant of slightly blurred and/or trailed images and I want to do science and not artwork.
Anyway, such artefacts can often be cleaned up in post-processing.
It appears that my image is not properly focused. It should be obvious, but wasn’t, that auto-focus should be run every time before taking images. One day I will print a Bahtinov mask to see how well AF works. Reports are that it is pretty good.
Thanks. It looks like a generic problem as your image also shows rings around the brighter stars.
Not a deal breaker as photometry is very tolerant of slightly blurred and/or trailed images and I want to do science and not artwork.
Anyway, such artefacts can often be cleaned up in post-processing.
Now that I seem to have control over most of the needed functionality, I turn to image quality.
Only one object has been imaged so far, Albireo or β Cyg. It was taken on a poor night but during the only clear spell so far available. Bear in mind that thin haze may have been present. The image shown is the green channel of the 40s stacked image. β Cyg B shows a very obvious ring around it, measured at a radius of 14 arcsec from the center of the stellar image. Other fainter stars show similar rings at 11-14 arcseconds radius. The radius Airy disk of a 50mm aperture in green light is 2.4 arcsec (and pretty much the same for FWHM) and the first bright diffraction ring should be at 5.4 arcsec assuming I calculated correctly. Much less than 14 arcsec anyway. The image scale is 2.37 arcsec/pix according to astronomy.net; this is a good match to the Airy disk size.
Any ideas what may be causing this? Stray reflections is one possibility that comes to mind, as is rather bad spherical aberration.
I will take more images on properly clear nights to see whether the effect is reproducible but I would be interested to learn whether other Seestar users experience the same effects. If not, perhaps it should be fixed / or exchanged under warranty.
Here’s the image which shows the ring.
Attachments:
Thanks Diane. Turns out that I had already done that without noticing. Once station mode was started properly a file browser on the Linux box could also see the internal storage and was able to copy the individual frames.
Also: wrt Bluetooth I found that giving the app permission to chane system setting was necessary. Not at all sure that is wise from a security point of view so may disable it again and rely on station mode for access within range of the wifi and USB cable when I am on the road.
Thanks Steve.
I found that connecting the USB cable to a Windows PC makes the FITS files available as an external storage device. It doesn’t (yet) work on a Linux box.
Initial experiments with station mode were not very productive but as I don’t really know what I am doing, perhaps that may be expected.
TFM is woefully inadequate and saving individual frames is presently beyond my ability. That will almost certainly change fairly soon.
Paul
OK, so far, so good. A brief gap in the clouds allowed an image of Albireo to be taken. Only four images were successful, it seems, out of an imaging session which lasted two or three minutes, but lets let that go for a moment.
The only way I could find to get them off the phone was to connect a USB cable and use the file browser to copy them to the local disk. Again, lets let that go for a moment.
There were 5 files, corresponding to four 10-second subs and a stack of four. All the files are in JPEG format and the stack is included here.
Next question: I would like to do precision photometry, so how can raw FITS files be created by the Seestar app in a place which is generally accessible? The JPEG shows clear artifacts which I would prefer not to have imposed. AIUI, the raw images can be saved and transferred.
Thanks,
PaulAttachments:
Thanks both.
I have a series of questions but will deal with them one at a time to help reduce confusion. Further, please note that I know very little about this system, in part because of the woefully limited documentation that ZWO provides, so may have some completely false assumptions and preconceptions.
First concerns set-up. I thought that the S50 would use Bluetooth to communicate with an Android phone. At initialization time the S50 states “Need bluetooth access to search Seestar nearby” and it is necessary to set the phone’s Wifi connection to the 10.0.0.0/8 local network created by the S50. Connection then proceeds satisfactorily but, of course, the phone no longer has access to the internet — seriously crippling other important features.
I have tried everything I can think of to configure the phone to allow the use of Bluetooth, without success. The phone will happily pair with other devices, such as a laptop so much is clearly working.
Any suggestions? If it helps, the Seestar firmware is V2.95
