Jump to content

Banner.jpg.39bf5bb2e6bf87794d3e2a4b88f26f1b.jpg

Bad polar alignment, Shutter Shock/Shake or other?


Recommended Posts

Hi Danny,

I see you've got lots of good feedback on this topic already, but I just wanted to add a quick comment since those elongated stars are oh so familiar to me!!!

I have the 200PDS on an HEQ5 mount & spent hours & hours optomising this & that, fitting the rowan belt kit etc etc... About 3 min was the max exposure length I could work with & even then I'd usually be throwing away 50% of the images (which is really really frustrating).

Autoguiding solved the problem.

So just to highlight that you will almost certainly need to go down the autoguiding route, even if you upgrade the mount. It might be worth experimenting with autoguiding on your current set up to begin with, rather than spending out on a new mount & finding that while it may improve, it will not necessarily resolve the problem!

Good luck,

Rob

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

23 minutes ago, Robculm said:

Hi Danny,

I see you've got lots of good feedback on this topic already, but I just wanted to add a quick comment since those elongated stars are oh so familiar to me!!!

I have the 200PDS on an HEQ5 mount & spent hours & hours optomising this & that, fitting the rowan belt kit etc etc... About 3 min was the max exposure length I could work with & even then I'd usually be throwing away 50% of the images (which is really really frustrating).

Autoguiding solved the problem.

So just to highlight that you will almost certainly need to go down the autoguiding route, even if you upgrade the mount. It might be worth experimenting with autoguiding on your current set up to begin with, rather than spending out on a new mount & finding that while it may improve, it will not necessarily resolve the problem!

Good luck,

Rob

Certainly. Autoguiding is the life-blood of astrophotography and is remarkably easy...

Olly

  • Thanks 1
Link to comment
Share on other sites

On 12/10/2021 at 07:52, Robculm said:

Hi Danny,

I see you've got lots of good feedback on this topic already, but I just wanted to add a quick comment since those elongated stars are oh so familiar to me!!!

I have the 200PDS on an HEQ5 mount & spent hours & hours optomising this & that, fitting the rowan belt kit etc etc... About 3 min was the max exposure length I could work with & even then I'd usually be throwing away 50% of the images (which is really really frustrating).

Autoguiding solved the problem.

So just to highlight that you will almost certainly need to go down the autoguiding route, even if you upgrade the mount. It might be worth experimenting with autoguiding on your current set up to begin with, rather than spending out on a new mount & finding that while it may improve, it will not necessarily resolve the problem!

Good luck,

Rob

Hiya Rob, 

it’s good to hear my issue is solvable. guiding was on my cards, now it may be something to get sooner than planned. I’ve only been into this a few months and my collection of equipment is growing more than I initially thought lol. 
 

I had looked into a planetary cam to use for guiding too and had come up with the Altair gpcam2 290c, is this good for guiding as I read mono is better but if I can I want colour for planetary imaging. 
 

thanks

Danny

Link to comment
Share on other sites

Ha, yes, tell me about it! But I guess if it was too easy it wouldn't be so rewarding / addictive!

Sorry, will need to defer to others on the camera question. I have the https://www.firstlightoptics.com/zwo-cameras/zwo-mini-finder-guider-asi120mm-bundle.html which to be honest I randomly selected, but it seems to work OK for me & it's light (200PDS is already a heavy scope for the HEQ5 without too much additional clutter!). I believe there are mathematically optimal guide camera / scope criteria to match with specific telescope / camera configuration... Nothing is as straight forward as it first appears in this business!

  • Thanks 1
Link to comment
Share on other sites

56 minutes ago, Robculm said:

Ha, yes, tell me about it! But I guess if it was too easy it wouldn't be so rewarding / addictive!

Sorry, will need to defer to others on the camera question. I have the https://www.firstlightoptics.com/zwo-cameras/zwo-mini-finder-guider-asi120mm-bundle.html which to be honest I randomly selected, but it seems to work OK for me & it's light (200PDS is already a heavy scope for the HEQ5 without too much additional clutter!). I believe there are mathematically optimal guide camera / scope criteria to match with specific telescope / camera configuration... Nothing is as straight forward as it first appears in this business!

I will wait for advice as don’t want to jump in again with my own decisions and be wrong. I did see that bundle too and cheaper than the Astro Essentials 50mm f4 guide scope and GPcam2 I was planning on but if it works I can dual use the camera for planetary and guiding. 
 

thanks 

danny

Link to comment
Share on other sites

On 09/10/2021 at 18:10, DannyST said:

If I think sensibly, I should get the 600d for little actual cost and use it to learn more before diving in with a more expensive camera be it dslr or dedicated.

Thats the approach I took and it turned out that the ASI224mc was less expensive than DSLR, so thats where I began to learn (and still learning) :) My journey is in the link on my signature. BTW, I can get around 60s unguided, so havent purchased guider etc. and managing with short subs of 30-60secs

Edited by AstroMuni
  • Like 1
  • Thanks 1
Link to comment
Share on other sites

On 13/10/2021 at 16:31, AstroMuni said:

Thats the approach I took and it turned out that the ASI224mc was less expensive than DSLR, so thats where I began to learn (and still learning) :) My journey is in the link on my signature. BTW, I can get around 60s unguided, so havent purchased guider etc. and managing with short subs of 30-60secs

Hiya Astromuni, 

How did the asi224 effect your FOV? I was looking to keep to APS-C sized camera as my current camera and the 150pds only just frames some DSO objects. I used astronomy tools to see what I would expect so was skepical about even dropping to a 4/3rd sensor. So I was planning to stick with DSLR for the time being while I figure things out. A 600d is pretty much free with trade in, then it’s just mod cost while I learn the ropes. 

Maybe the plan could be to keep the 600d for larger brighter objects and a 4/3rds dedicated for other objects. 
 

thanks 

Danny

Edited by DannyST
Link to comment
Share on other sites

17 hours ago, DannyST said:

Maybe the plan could be to keep the 600d for larger brighter objects and a 4/3rds dedicated for other objects. 
 

If your 600d is effectively at zero cost then your plan above gets you best of both worlds. 👍

With the asi224 a few of the larger DSOs wont fit in (m31, veil, pelican etc) but on the plus side it lets through IR so images are more detailed than an unmodded DSLR. I have setup the fov for the asi on Kstars, so can easily see if my potential target will fit in. You can always do mosaics but that will be next stage for me 🙂 .
 

PS: Like I mentioned before you can see some of the images I captured with asi here

 

Edited by AstroMuni
  • Thanks 1
Link to comment
Share on other sites

With the weather being the typical uk weather I have been doing A lot of reading, in between making a storage box and case for my telescope and gear. I also made a diy dew heater controller and now trying out my own diy heater pads.
 

After much spiralling and going round in circles saying if I just go a bit more I can get…… getting way out of control.  I have settled on the following. 
 

ASI462mc with a ZWO 850 ir pass filter

Astro Essentials 50mm guide scope. 
 

 

the hope is that although an ASI120mm mini is cheaper and more than capable the ASI462 has very high QE ( I admit I had to google what this meant) at close to 100% in IR making it almost the same as a mono cam is used with IR pass and guiding with only IR light. Then I can also use it as a planetary cam with its fast frame rate( a lot faster than the gpcam 2 I was originally looking at) and also as a dedicated Astro cam for small targets with its high sensitivity. 
 

I will then get the M3 swapped for a 600d and send that for its mod to use on the large objects, lastly I’ll keep an eye out for a cheap second hand ASI 120mm just to guide my ASI462 when I use it for planetary and dso imaging. 
 

thanks for all the info everyone. 
Danny

Link to comment
Share on other sites

  • 1 month later...

Hello all, I thought I would come back with some updates. 

On 09/10/2021 at 16:52, rickwayne said:

Oh,  and the drift alignment stuff sounds correct. One thing, though, change the slewing speed on your mount so you can run longer exposures. It actually doesn't matter if you go off the edge of the frame so long as you get the timing right.

Perfect advice, I was able to do 3 minutes and the V was less than half my frame. 

On 09/10/2021 at 16:19, Ohgodwherediditgo said:

I think the HEQ5 has a worm period of about 8 mins, so that would rule out periodic error if you had a half hour with good tracking. The camera causing shake would cause it consistently ( i really doubt it's that ). Maybe a cable snag ? Or rough running RA bearing ?

Although I assumed out the box it would be nice and smooth, it turned out I had tight spots and backlash in the Dec axis and tight spots in RA. I stripped, cleaned and re-greased the ring gears and worms(wasn’t much grease there). The Dec axis some bad backlash and has a tight spots in the ring gear and the worm as it was getting tight every 360 degrees of the slow motion knob and about 120 degrees of the axis is tighter. In RA luckily it’s just the ring gear that got tight about 180 degrees was stiff and no backlash at any point. 
 

now RA has no tight spots and little to no backlash in the looser areas. But Dec has bad backlash and very sloppy in the looser areas, I may readjust to minimise in the loose areas and try and avoid the tight spots. The result? After a quick alignment and test exposure I have doubled my length from 45 secs to 1.5 mins. 
444B17B9-11CD-4A25-823A-375F8E23BD40.thumb.jpeg.f9a41cc1ffb3c64588f2b0ea158457f5.jpeg

it’s over exposed even at iso 400 as the near full moon was high and bright. 

 

 

 

Edited by Enceladus Dan
Link to comment
Share on other sites

On 12/10/2021 at 07:52, Robculm said:

Hi Danny,

I see you've got lots of good feedback on this topic already, but I just wanted to add a quick comment since those elongated stars are oh so familiar to me!!!

I have the 200PDS on an HEQ5 mount & spent hours & hours optomising this & that, fitting the rowan belt kit etc etc... About 3 min was the max exposure length I could work with & even then I'd usually be throwing away 50% of the images (which is really really frustrating).

Autoguiding solved the problem.

I picked up a 50/200mm guide scope and an asi462mc, while testing my smoother RA I added them to my setup for a quick test. A bit finicky but I got there and the result was. Let’s say magical. 
345873E6-3976-411A-886A-E308794F53EF.thumb.jpeg.fbb0716f6d05feb93b1c929b95dff0e5.jpeg

I aimed for 5 mins but due to only setting up camera and IR remote not Wi-Fi to app on phone it was 5.5 mins. 
D5C6BF10-5401-4A90-A435-1520A16A3DBB.thumb.jpeg.22fb4f8c48818b212a6ecc65abbd794a.jpeg

this one was 5 mins, happy as Larry. Now I can’t wait for a clear night without the moon. My biggest issue it seems is work life+ home life +British weather all playing ball at the same time. I do need to test some new balance now too as guide scope and cam made it rear heavy. 

  • Like 1
Link to comment
Share on other sites

On 09/10/2021 at 15:51, ONIKKINEN said:

Are you autoguiding?

All mounts experience something called periodic error in RA where the tracking speed oscillates a bit above and under the ideal rate. Unguided exposures are limited by your RA drift rate, which varies quite a lot between different mounts.

 

Below is an example i just found online, the red line is your DEC, which in this case was spot on as it hardly moves in the long term while the blue line is the RA which is constantly in use. The steep drops and cliffs of the graph are where you experience bad subexposures, but just by pure chance you could have your exposure at the relatively even top section and not notice trailing as much. I don't know what mount (or even if it was a mount) this image is from but it gets the point across. My EQM35-PRO experiences somewhere around 8 arcseconds RMS of periodic error during one worm cycle, which is 8minutes on my model. In theory that would limit a 1 as/pixel resolution image to just 30 seconds, but in reality there are these same steep cliffs and drops in the graph, making unguided exposures not worth the effort.

How much you can get away with will depend on your mounts periodic error and the resolution you're imaging in.

2074132964_Periodicerrorexample.thumb.png.7806984cd1dc02d6ea2bb8ab5437f72d.png

My chart definitely wasn’t like this lol. It looked like my mount was having a heart attack. But even so it did guide 5 mins. I can only get better at the setup and get my error lower. My Dec was more like the RA in this pic, possibly the bad backlash in Dec. It doesn’t help the worm having a tight spot as well as the ring gear. 
 

thanks everyone I am over the moon now and eagerly awaiting clear dark skies. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.