Star trailing and loss of tracking after polar alignment - Direct PC -> Mount control (no hand control)

    Dear All,


    I kindly ask ideas, guidance regarding below issue.


    My setup: SkyWatcher HEQ5 Pro EQ mount, 1500mm focal length/127mm aperture tube, no hand controller used, i.e. the mount is directly connected to PC, using stellarium and ASCOM EQ MOD for controlling the mount.

    My step-by-step protocol: 1. levelling mount, 2. balancing RA and DA of the setup, 3. Polar alignment, 4. Direct connecting of mount to PC with Stellarium (via ASCOM), 5. Slewing and synchronising selected stars using Stellarium (Ver. 23.1), 6. start imaging session.

    My issue: After star alignment described above, I could easily find and sync with my targeted deep-sky object. I started 60 sec exposures. The first 3-5 images are nice, object totally centered in field of view, no star trailing, round stars, etc. Then a small star trailing appears and it is worse and worse by each sub exposure. It looks like the tracking is simply getting worse and worse; or the tracking is simply not working, and the object falls outside after the 10th sub exposure. I checked, all clamps are tightened. The same issue occurs again if I redo the entire polar and star-alignment process. Please see some subs attached to show the issue better, and I attached my EQ MOD ASCOM settings too.


    My questions:

    1. Is it a polar / star alignment issue or rather a tracking issue?
    2. Can you please tell me what should be the protocol for polar and star alignment in case the hand-controller is not used and the mount is directly connected to PC?
    3. Can you please tell me what should be a good starting setup for tracking in Stellarium? 
    4. In the ASCOM control panel, which tracking rate should I select? Sideral tracking maybe?
    5. Is it simply more advised to keep on using the hand controller and do not connect the HEQ5 Pro mount with PC directly?

    Please advise, what could go wrong!


    Thanks a lot in advance,

    Peter

    Hi Peter,

    as you are not guiding, I would just recommend shorter exposures (10s - max. 20s/frame). Everything above that will require guiding. "Tracking only" will not be precise enough. The tracking should be set to "sideral" for deepsky-objects.


    CS, Jochen


    PS: good news: if your Goto is able to find and center objects, your setup seems to be ok - still, if your object leaves the center after some time, your polar-alignment needs to be more accurate.

    Dear Jochen,

    sincere thanks for your response. When I was connecting the mount to the PC via the SynScan Hand Controller, I could easily go up to 70 sec of single exposures without any guiding camera. I assume the precision of my polar alignment was just the same. Even my old Alt-Az GOTO mount was better in keeping the objects in center. Probably my polar alignment is worng then.

    Kind regards,

    Peter

    Hi Peter,

    you are most welcome!

    Yes, it could perhaps be a matter of proper polar-alignment but I doubt that you will really be able to capture "needle-sharp"-stars at 70s exposure without guiding.

    The reason is, that the mechanics inside a "consumer-class"-mount are just not precicse enough.

    There are mounts on the market that can do much better - but these are in a completely different price-range.

    Also, If you want to take photos I would consider using a aquisition-software like NINA or APT - these make things a lot easier and can also control a future guide-cam.


    So long, Jochen

    One more thing I noticed is that your "ASCOM Pulse Guide Setting" is set to the left minimum. I used 0.5 all the time but found somewhere in the web that it should be set to maximum.

    Last session I used this new adjustement, but with no effect I think. Maybe it's a "screw" you like to adjust next session experimentally.

    However I'm guiding with PHD2 and N.I.N.A.


    Do you use the inbuild polar - scope? It is not adjusted I'm pretty sure.


    Cheers

    Hartmut

    EQ6R-PRO | OMEGON PUSH+ | SW Allview | Unistellar eQuinox | Seestar S50 |  ASKAR FMA 135

    SW 200PDS/1000 | SVBONY 503 80/560 (448) | SkyMax 102/1300 MAK | TS 61EDPH II

    ASI 120MC-S & MM-Mini | veTEC533c / 571c | N.I.N.A.

    METEORCAM (RPi4) (https://globalmeteornetwork.org/weblog/DE/index.html) DE000Q

    Danke 1

    Dear Jochen and Hartmut,


    Thanks again, im very new to this forum and trully appreciate experts like you are commenting my issue already.

    Some additional response to you.


    1. Indeed, I am using APT to capture images but have a very old DSLR camera. The HEQ5Pro for sure not the best mount but was a recent invest for me and huge step forward vs. my old ALT-AZ GOTO mount from Levenhuk. :)
    2. I will reset the ASCOM Pulse guide setting, did not know, thanks.
    3. I do have a build-in polar scope in the mount.
    4. Regarding guiding, i will invest into it in the future, but let me share the photo attached, which I made with the same mount/telescope/camera few month ago. Super amateur image but it is a stack of 178x individual subs from M81, 45 sec each. The trailing appeared around 60 sec exposure only. I had the same camera/mount/scope, except that I was using the SynScan hand controller and obviously the polar alignment was different then. 

    Best Regards,

    Peter

    Zitat von Peter M.

    but let me share the photo attached,

    Hi Peter,

    I am afraid to say... but in your picture you can clearly see, that the stars a not round anymore... ;)

    Without guiding, you will get a decent result if you choose an exposure of 800x10s instead of 178x45s. The only disadvantage is that it takes longer to stack on a slow PC.

    A guidescope btw. is not expensive, PHD2 is free and if you already use APT (so do I - a superb piece of Software !) these just connect together.

    PHD btw. means "Push Here Dummy" and it is really as simple as the name promises. :)

    So - don't be afraid to guide, your picture will really improve and you will also be able to "dither" (= shift pixels after a given number of exposures) in order to get rid of "walking pattern noise" (your pictures will be much smoother).


    Regards, Jochen

    Thanks again.


    I thought the reason of the not round stars on that photo was that with slight temperature changes, i got out of focus during the session. My scope has manual focus and i did not refocus with Bathinov mask during the session after doing it at the beginning.


    Best, Peter

    I would say they would get bigger but stay round in that case. However I use a motorized focusser but never re-focussed in any session. =O :D

    EQ6R-PRO | OMEGON PUSH+ | SW Allview | Unistellar eQuinox | Seestar S50 |  ASKAR FMA 135

    SW 200PDS/1000 | SVBONY 503 80/560 (448) | SkyMax 102/1300 MAK | TS 61EDPH II

    ASI 120MC-S & MM-Mini | veTEC533c / 571c | N.I.N.A.

    METEORCAM (RPi4) (https://globalmeteornetwork.org/weblog/DE/index.html) DE000Q

    Danke 1

    If you are out of focus, the stars get blurry but stay in a round shape. Your picture shows trailing instead. Btw: refocussing can become necessary at temperature-change during a session. APT has a nice built-in autofocussing-tool. You will not need a Batinov-mask but the tool requires a motor-focusser.


    CS, Jochen

    Dear Jochen, Hartmut,


    would you have any suggestion for a guide scope and guide camera for the an imaging scope with 1500 mm focal length / 127 mm aperture and a main camera for:

    1. Canon EOS 1100D, 22.2 x 14.8 mm sensor size, resolution: 4272 x 2848, pixel pitch = 5.18 um,

    2. dedicated astrocamera, 23.48 x 15.67 mm sensor size, 6224 x 4168 resolution, pixel pitch=3.73 ?


    Many thanks again,


    Peter

    There is a guidescope calculator available https://astronomy.tools/calculators/guidescope_suitability


    Best ratio is 1:1 and up to 1:5 is good and up to 1:15 is working. I use a 60/240mm with ASI120 MC-C with 200/1000mm Newton. But monochromes are better. Have a look at cheap modells from Touptek or veTEC

    others use off axis guider which are better for a 1300mm telescope but harder to adjust…

    EQ6R-PRO | OMEGON PUSH+ | SW Allview | Unistellar eQuinox | Seestar S50 |  ASKAR FMA 135

    SW 200PDS/1000 | SVBONY 503 80/560 (448) | SkyMax 102/1300 MAK | TS 61EDPH II

    ASI 120MC-S & MM-Mini | veTEC533c / 571c | N.I.N.A.

    METEORCAM (RPi4) (https://globalmeteornetwork.org/weblog/DE/index.html) DE000Q

    Danke 1

    Dear All,


    now it gets more interesting. I tested the mount (SkyWatcher HEQ5 Pro) with its SynScan hand control, which was then connected to PC. I did first a polar alignment using the internal polar scope, continued with a 2-star alignment with the hand controller, and subsequently executed a polar alignment using the hand controller. Last step included corrections in Elevation (Mel) and Azimuth (Maz) offsets. It went well, error was reduced to 0-2 arc secs. Then I connected to Stellarium, and slewing precision was great, found many objects by hopping.


    Once I started imaging, using exposure time between 5 sec up to 30 sec, the same issue happened: the first few image seems to be fine and I see round stars. After few exposures, significant star-trailing appears, even at 5 second exposure. This is something new, did not have before, and such an EQ mount should be supporting nice 5 sec exposures.


    I am afraid, I have a hardware issue.


    Any comments, suggestions are much appreciated.


    Kind regards, Peter

    Hi Peter,


    I don't believe that you have a hardware issue (though it is not impossible) - I think that you rather have a problem with the polar-alignment.

    As Hartmut has mentioned - it is possible that the polar-scope of the mount itself is misaligned.

    Unfortunately, I can not tell you how to adjust it as I have used a PoleMaster from the beginning. :saint:


    And one more question: as you use APT - why do you use the handcontroller for a star-alignment?

    Do you first connect the controller, do the alignment and then unplug it in order to connect to the laptop?

    That sounds complicated to me. ;)


    APT can align your scope with platesolving, which is a much more convenient way and also is much more precise.

    You will just need to install a platesolving software that acts as a plug-in for APT.


    I personally use ASPS which is capable of "blindsolving". You basically take a picture of a random part of the sky which is analyzed and compared to existing star-maps.

    From that data, the scopes current position is calculated and this position will be synced. No further aligment necessary (except polar-alingment, of course...).


    Once installed, the process will be:


    1) slew to your object (by choosing a target from APT's catalogue, from Stellarium or by entering coordinates manually) with your unaligned scope (you will not be on target yet)

    2) take a short exposure (10s or so)

    3) click "Blind" in Pointcraft --> the image will be solved

    4) click "Aim" and then "Goto++" - you will be asked, if you want your scope to be synced with the position-data from the solving

    5) Vodoo-Magic happens: the scope will automatically center the target


    CS, Jochen

    Maybe this video helps if you like to adjust or just control the alignment of the polar finder:


    Externer Inhalt www.youtube.com
    Inhalte von externen Seiten werden ohne Ihre Zustimmung nicht automatisch geladen und angezeigt.
    Durch die Aktivierung der externen Inhalte erklären Sie sich damit einverstanden, dass personenbezogene Daten an Drittplattformen übermittelt werden. Mehr Informationen dazu haben wir in unserer Datenschutzerklärung zur Verfügung gestellt.


    There are a lot more videos about how to do that on youtube.


    Meanwhile I use iOptron's iPOLAR which is the easiest way to polar align. Just cover a red disk and a red cross on the PC screen and thats it.

    Unfortunately it's an expensive tool.


    CHeers

    Hartmut

    EQ6R-PRO | OMEGON PUSH+ | SW Allview | Unistellar eQuinox | Seestar S50 |  ASKAR FMA 135

    SW 200PDS/1000 | SVBONY 503 80/560 (448) | SkyMax 102/1300 MAK | TS 61EDPH II

    ASI 120MC-S & MM-Mini | veTEC533c / 571c | N.I.N.A.

    METEORCAM (RPi4) (https://globalmeteornetwork.org/weblog/DE/index.html) DE000Q

    Danke 1

    Dear Hartmut and Jochen,


    many thanks again, you gave me new ideas and learnings. Few comments on your suggestions:


    1. Which is better, using SynScan hand controller or direct PC - mount connection? -> to be honest, i am confused whether it is better to use hand controller or not. There are quite some videos out there how to polar align and star align with HC before imaging sessions (e.g.: https://www.youtube.com/watch?v=adKut0KPgHw
    2. So far I used the HC only for star alignment and did not use the combo of APT + Plate solving, simply because APT was crashing when activating "live view". Now i got the latest release full version, and it seems to be OK. Regarding Plate solving, I  found this video, seems to be straight forward AND it is using the hand controller: https://www.youtube.com/watch?v=K8R0X-B6M7Y&t=29s    What is your opinion about this plate solving approach?
    3. @ Jochen regarding question "Do you first connect the controller, do the alignment and then unplug it in order to connect to the laptop?". Well I used two techniques:
      1. With HC: I first did Polar alignment, then 2 star alignment, and then connected the mount via the HC to the laptop, and used Stellarium to slew. APT was used for photography only.
      2. Without HC:  I first did polar alignment, then I connected to PC directly (cable btw mount and PC), and used Stellarium and ASCOM EQ MOD to slew. I did star jumping, corrected the offset via using the "sync" option of Stellarium. APT again was used only for photography.

    Although I do not use iOptron (thx for the idea, nice kit), I believe my polar alignment is good enough, as polaris remains in the target circle of the in-build polar scope when moving the RA. I totally agree that plate solving will help a lot more.


    Can you please advise me if you suggest to do all the polar alignment, star alignment, plate solving WITH or WITHOUT Hand Controller (Skywatcher HEQ5 Pro mount) ?


    thanks and best,

    Peter

    Hi again!


    Zitat von Peter M.

    Which is better, using SynScan hand controller or direct PC - mount connection? -> to be honest, i am confused whether it is better to use hand controller or not.

    You don't actually need the handcontroller - I haven't seen mine for a while and don't even remember in which of the many drawers I had put it. ;)

    Everything can be done with APT. Using EQMOD (which you already do...) is IMHO the best choice for Skywatcher EQ-mounts. The Synscan-ASCOM-driver causes a lot of trouble (at least with my setup).


    Zitat von Peter M.

    simply because APT was crashing when activating "live view".

    You do not need to switch to "live view" for platesolving. To be honest, I have never used live view.


    Zitat von Peter M.

    Regarding Plate solving, I found this video, seems to be straight forward AND it is using the hand controller:

    Externer Inhalt www.youtube.com
    Inhalte von externen Seiten werden ohne Ihre Zustimmung nicht automatisch geladen und angezeigt.
    Durch die Aktivierung der externen Inhalte erklären Sie sich damit einverstanden, dass personenbezogene Daten an Drittplattformen übermittelt werden. Mehr Informationen dazu haben wir in unserer Datenschutzerklärung zur Verfügung gestellt.
    What is your opinion about this plate solving approach?

    I am a huge fan of Dylan, but there are a lot of different approaches to platesolving (he uses "Sequence Generator Pro"). If you want to try to stick to my instructions with ASPC, you will be able to platesolve in no time. On top, the software is free. Just give it a try! ;)


    Zitat von Peter M.

    With HC: I first did Polar alignment, then 2 star alignment, and then connected the mount via the HC to the laptop, and used Stellarium to slew. APT was used for photography only.

    Ah, ok - so you switch the HC to "PC direct mode" ? You can do so, but In most cases it will be better to connect to the mount directly (you might need a special cable if your mount does not have a USB-connector). I would recommend sticking to your "version 2" without the HC. You may use Stellarium to select an object (which has a nice graphical interface), but you can also just select an object from APT catalogue or enter its celestial coordinates manually.

    Zitat von Peter M.

    Can you please advise me if you suggest to do all the polar alignment, star alignment, plate solving WITH or WITHOUT Hand Controller (Skywatcher HEQ5 Pro mount) ?

    My opinion: as you work with the laptop anyway - throw the HC away! ^^


    CS, Jochen

Jetzt mitmachen!

Sie haben noch kein Benutzerkonto auf unserer Seite? Registrieren Sie sich kostenlos und nehmen Sie an unserer Community teil!

Benutzerkonto erstellen Anmelden