Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_2019_sp_banner.thumb.jpg.a0ff260c05b90dead5c594e9b4ee9fd0.jpg

Gerhard

problems tracking / collimation?

Recommended Posts

Hi all!

Yesterday I was out taking a few pics of M56 and M71 (no nebulas or galaxies, because the moon is still quite full).

This was the first time I tried my new coma corrector, which I think works fine. One RAW sub:

post-39678-0-34981600-1443601551_thumb.j

A few problems, though. As you can see from the above RAW example, there is no coma anymore, but all stars are kind of triangular in shape.

Is this due to collimation error, ie warping the primary by tightening too much?

I tracked (unguided) using also PEC...

Second problem. On RAW sub that wasn't so good...:

post-39678-0-55884800-1443601703_thumb.j

These subs are frequent, one in every 4, on average... I'm guessing my HEQ5 is old and not too precise anymore... Or could it be something else still?

Here is the stack of the good subs (no post production), to show the beneficial effect of the coma corrector again:

post-39678-0-63102400-1443601001_thumb.j

Ideas?

Gerhard.

Share this post


Link to post
Share on other sites

Just taking the second light frame you posted this is representative of backlash in one of your axes. Before a session I ascertain the orientation of my chip relative to the mount axes by taking a single sub and moving the mount in each of RA and DEC. Then I can easily diagnose any issues relative to the mount axes. I would put a pack of Jaffa cakes on your mount showing backlash in RA. There are lots of reasons for your finding. How good is your polar alignment?

Share this post


Link to post
Share on other sites

Just taking the second light frame you posted this is representative of backlash in one of your axes. Before a session I ascertain the orientation of my chip relative to the mount axes by taking a single sub and moving the mount in each of RA and DEC. Then I can easily diagnose any issues relative to the mount axes. I would put a pack of Jaffa cakes on your mount showing backlash in RA. There are lots of reasons for your finding. How good is your polar alignment?

hmmm... I saw this option in the Synscan menu. I'll have to look into it... So you're saying that while you're taking the sub you move the mount in RA and then in DEC?

And then how does one see if there's backlash? I'll study about this.... @work now, so cannot get distracted too much...

I think (hope) my polar alignment is quite good: I always perform drift alignment as well after aligning with the polar scope... I don't wait half an hour to see if the star drifts, but at least 5 minutes for both RA and DEC... And yesterday they seemed quite stable....

Share this post


Link to post
Share on other sites

Regarding the triangular stars...I had a similar problem and it turned out to be pinched optics. I cleaned the mirror and I think I tightened the clamps too much when I reassembled it. It was easy to rectify, just loosen the mirror clamps a little.  Tim. 

  • Like 1

Share this post


Link to post
Share on other sites

Regarding the triangular stars...I had a similar problem and it turned out to be pinched optics. I cleaned the mirror and I think I tightened the clamps too much when I reassembled it. It was easy to rectify, just loosen the mirror clamps a little.  Tim. 

will do! :-)

Share this post


Link to post
Share on other sites

hmmm... I saw this option in the Synscan menu. I'll have to look into it... So you're saying that while you're taking the sub you move the mount in RA and then in DEC?

And then how does one see if there's backlash? I'll study about this.... @work now, so cannot get distracted too much...

I think (hope) my polar alignment is quite good: I always perform drift alignment as well after aligning with the polar scope... I don't wait half an hour to see if the star drifts, but at least 5 minutes for both RA and DEC... And yesterday they seemed quite stable....

I read somewhere (couldn't resist googling backlash problems... :-) ) that backlash is seen when the slew movement is not responding well to the controls on the keypad.

This I have seen A LOT with my mount. So next time I'm out, I will look at this definitely, and adjust my backlash settings accordingly...

Next time will be a while, though... clearoutside shows bad weather all the way up to next tuesday....

Share this post


Link to post
Share on other sites

the backlash compensation on your mount is good for observing, but not so good for imaging.

Basically when you're observing, and change direction on the direction pad, there's a dead zone when you press it and nothing happens, until eventually it catches (and invariably overshoots).  While it's not moving, that's the backlash being taken up.  You can program the mount with a backlash compensation setting that you have to find by trial and error, so that when you change direction, the first few presses act faster than normal, so it takes up the backlash quicker.

The PHD guys recommend that you don't use backlash compensation for guiding though as that can result in unpredictable behaviour.  Try the following:

- if the guiding errors are occurring in the RA direction, moves the weights slightly so that the set-up is 'east heavy'.  ie if the scope is on the west of the mount, move the weights further out, but if the scope is on the east of the mount, move the weights further in.  That will mean that the RA tracking is always pushing the mount against the slight imbalance, and it doesn't wobble in RA backlash.

- if the guiding errors are in Dec (and they often are), it's trickier.  Try the 'resist switch' algorithm in PHD which tries to avoid changing direction and entering the backlash unless it has to.  Also if you find you have a clear drift one way or the other in Dec, then you can try setting the dec guiding to 'north only' or 'south only' instead of 'auto' - try both and find which one is trying to adjust the drift.  That will mean the mount will never voluntarily enter the Dec backlash.  You can also try making the scope slightly tail-heavy to counter Dec backlash to keep it on one side of the gears, but that has limited effect (eg will have no effect if pointing straight up)

Share this post


Link to post
Share on other sites

the problem is, I don't guide... maybe it was not clear, but the problems I have are with tracking with the mount only... So I have no PHD on which to rely...

I wish... :-)

in fact, I think if I started guiding, I would get better subs... I'd sincerely hope so, since that is the whole point of guiding... :-D

Share this post


Link to post
Share on other sites

I used the handset to do a 2 star align, the use the polar align option for the PA, run through it twice on different stars and while i didn't extend the sub time to find the limit a 3 minute sub had no trailing just points of light, Balance and PA are crucial...

Share this post


Link to post
Share on other sites

I will be redoing the PEC training as well, as precise as possible...

That is unlikely to reduce your backlash. Unguided, the best I ever reached was 90 second subs unguided at 715mm focal length. The best thing I did to my mount's hardware was this:

post-35542-0-70410900-1443630035_thumb.j

Share this post


Link to post
Share on other sites

if it's unguided, it's unlikely to be backlash isn't it ?  PHD won't be pushing the mount around, so will just be the RA drive constantly pushing, and the Dec doing nothing.  More likely periodic error unfortunately

Share this post


Link to post
Share on other sites

if it's unguided, it's unlikely to be backlash isn't it ?  PHD won't be pushing the mount around, so will just be the RA drive constantly pushing, and the Dec doing nothing.  More likely periodic error unfortunately

I'm just now coming to understand what backlash is, so if you say so! ;-)

if it's periodic error, which I also suspected, could a good PEC training maybe have some positive effect? eliminate at least those errors?

This periodic error would disappear if one starting guiding, no? But maybe THEN I would have backlash problems... :D

it's a mess.... :-)

Share this post


Link to post
Share on other sites

yes, PEC training will help, but you'll need to be very good !  Make sure that the correction speeds are low, something like 0.125x tracking speed, and you'll need s steady hand and eye and a reticule eyepiece to keep it centered.

Guiding will make an awful lot of difference, and doesn't cost too much to get started - I use a Celestron T70 travelscope got off of ebay for £40, and started with a simple webcam (a meade LPI also off ebay)

  • Like 1

Share this post


Link to post
Share on other sites

yes, PEC training will help, but you'll need to be very good !  Make sure that the correction speeds are low, something like 0.125x tracking speed, and you'll need s steady hand and eye and a reticule eyepiece to keep it centered.

Guiding will make an awful lot of difference, and doesn't cost too much to get started - I use a Celestron T70 travelscope got off of ebay for £40, and started with a simple webcam (a meade LPI also off ebay)

for PEC training I will be in fact VERY still, not moving the position of my eye relative to the eyepiece, and with slow speed. I have a reticule eyepiece, 12,5 mm, with 2x barlow to do this job as precise as possible...

for guiding the biggest part will be getting a laptop... I only have a desktop at home (just bought it new a year ago, when I didn't have my scope yet... of course now I would have taken a laptop...), and my work laptop I cannot use... The guide scope is already ready for me: the president of my club, who sold me the newt, also has a guide scope especially for my OTA. 

So, laptop and CCD... plus I don't know what I'll have to pay for the guide scope...

maybe some extras, like an adapter to put the laptop on my battery... I don't see all this happening before new year's....

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By gerardsheldon
      I tested the tracer polymer battery over a six hour period and although the red light on the HEQ5 flashed most of the time, and more rapidly as time went on, the mount moved so that the time on setting circles changed by six hours, suggesting the mount will track OK.  (the test was carried out during the day).  I did not try to get the telescope to point in a different direction using the handset.
      1) Should I be bothered by the flashing lights on the HEQ5 mount?
      2) Is tracer misleading people by saying their batteries are 12 volts?  (they say that their discharge curves are flat)
      I found that the battery's voltage falls.  Below is from the Tracer datasheet.
      ---------------------------------------------------------- 
      Built-in Fuel Gauge - 5 colour LED fuel gauge mounted externally to show charge level. LED Status:
      3 green & 2 red: Battery fully charged 11.7V
      2 green & 2 red: Over 50% capacity 11.4V
      1 green & 2 red: Over 20% capacity 11.1V
      2 red: Less than 20% capacity 10.7V 1 red:
      Less than 10% capacity 10.3V No lights: Battery empty 8.25V 
      ----------------------------------------------------
      Thanks
      Gerard
       
    • By Oslet
      Sooo...I'm getting quote frustrated here. This spring I tested my HEQ5 with guiding. The synscan controller was connected to the computer trough the USB plug on the hand controller. This worked like a charm in my living room. On the new controllers you dont need the rs cable. But when I tried the whole thing with guide cameara for some live shooting, it just did not work. I get something wrong with the com port in decice manager, driver not working. I have tried 3 different drivers. The whole thing responded, connected and was guiding when i did a dummy test before the summer. So setup is pc-synscan via usb for pulse guiding. Can it be a problem with windows 10? What t h.... just happened? Where can I find a driver that works? And believe me it worked 5 months ago, argh. Thanks for any respons and support
    • By Michele Scotti
      Hi everybody,
      i'd like to share with you the design, making and progress of a project my astro club endeavoring to. I'll post here relevant info in a run-up  to where we got to so far.
       
      Here is the mission: 800mm in diameter. That's it. A lot of inspiration out there but it needs to be able to do science. So it's a relatively fast Newtonian capable of tracking for tens of minutes.
      So we realized that we were facing 2 projects in one. The mirror on one side and the mount on the other. Shall we start with the mount? What's the best compromise in terms of ease to build and cheap components and the chance to have a stiff yet light structure. An alt-az, like the biggest telescope! - or rather a glorified dobsonian in this case.
       
      Ambitious? Definitely
      Any comment/suggestion is welcome!

    • By Rza
      As title. Not the best to look at cosmetically but in good working order.
      Mount has upgraded latitude bolts.
      Will throw in the following:
      Sky-Watcher power supply
      HiteCastro DC focus controller
      EQDIR cable to control mount from laptop
      Long UK plug mains power cable
      USB hub
      Lovely Lords Cricket bag
      £375 ONO
      Based in Kent near Maidstone.
      Collection only.
      Cheers

    • By Vroobel
      Hi, 
      As my GoTo is successfully finished (some cosmetic issues remain) I shoud focus my attention on planets' positions. I have proper source of information: fantastic book "Astronomical Algorithms" by Jean Meeus, thus I will sort the planets soon. But planets are not a challenge for me at this moment, they are just something obvious to do in my list. 
      I have another idea and ambitious plan for next project within the year: locating and tracking the ISS to be able to make a video of its fly, not only transition. 
      Similarly to other objects, I need some equations. I'm pretty sure they are available somewhere, because plenty websites or apps offer showing current position of the ISS. 
      I will use this topic for sharing a progress ot the project. 
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.