Newbie tracking issues

[spiraleye]

Hi SGL!

After hankering for a telescope for some years and spending about a week with an awful AZ mounted Bird-Jones reflector I decided to bite the bullet and get myself a 130PDS on an EQ3 Pro Goto mount mainly for learning and visual observations but also would like to get involved in a bit of photography to whatever extent the mount will allow. I know it's not the EQ5-6 that most reccommend but unfortunately I couldn't stretch to that and also a prime concern for me is the potability for which the EQ3 Pro seemed just right. First impressions of the scope are way better than I had imagined especially compared to the awful 114LCM I had for a short while. I am still getting to grips with the EQ mount and practicing getting my polar alignment dialed in correctly. After a first light observing session I stuck the camera on a took some conservative 15s exposures to play with and things went ok and stacked ok. After trying some 30s exposures I was getting very few hits due either the image beginning to trail (I suspect this is my polar alignment accuracy - I have not learned how to drift align yet) to a doubling of the star image which I assume is to do with some sort if issue in the gear meshing? The latter is not like star trails it's more like it hopped to a different spot half way through the exposure giving all the stars a small double next to them. I did wonder if this might be a correction coming from the DEC axis but I didn't think it made adjustments to this. Focusing seems fine. I think really at this stage I would love to hear whatever tips people can put forward to help me get the best out of this mount whatever that best might be, I know it's not the ideal long exposure astrophotography setup but I have a feeling there might be some things I am missing with regard to my setup or balance. Despite the initial tuning trouble I have had the most wonderful few nights looking at the stars. I didn't realise how much I didn't know about the night sky and can't wait to learn more!  Any tips much appreciated!  Thanks!

[sagramore]

Just to rule out one really obvious question - are you controlling the camera with a laptop or intervalometer or are you manually pressing the shutter to begin exposures? If you knock the camera it might lead to the kind of double-star you mention and pressing the shutter would easily do this.

The other thing to just check is that your scope is collimated well as this might lead to some issues with the shapes of stars.

I have the same scope and it's a joy so I'm glad you like it!

[Cornelius Varley]

Hello and welcome to SGL. Can you upload a photo in either jpg or png format which might help us to identify the problem.

[spiraleye]

Hi and thanks for the welcome! I am currently using Magic Lantern intervalometer and getting well out the way before it starts snapping so I'm pretty confident I am avoiding any serious mechanical jitter. It also keeps the shutter open I think between frames as it only makes a very quite snip sound as it takes each pic.   Just trying to upload pics but have a max of 1024kb....what format do you usually upload in here? These are raws currently and a jpg seems too large.... Just looking at png....

[spiraleye]

It's ok. Firing up gimp now. Just want to make sure you get the detail in the picture you need to see whats going on

[spiraleye]

I know I need a coma corrector and light pollution filter but here are some examples of the unprocessed images This first one is I assume trailing from a lack of proper alignment.

[spiraleye]

And here is the double star affect. It seems to be quite a defined jump.

[spiraleye]

I know I can't ask too much from the mount, it just seems there are some things going on here I don't understand yet and may well be able to improve on with the knowledge here

[sagramore]

Firstly the trailing certainly isn't awful but I would imagine improvements in the polar alignment can only help there! I was also going to ask if you use a focusing mask like a Bahtinov? It might just be the effect of the slight trailing but I think you could get sharper stars with a mask if you aren't already using one.

That double exposure does indeed look strange! I'm afraid I might have to defer to those with more knowledge there though but perhaps you are indeed seeing a slight jitter in one motor - especially as the double exposures look to be offset in the same direction as the trails - is that the east-west axis?

[spiraleye]

Yes I was tracking from east to west and it does seem to run in the same direction as the trailing. The main issue with the trailing was that it meant DSS wouldn't even register the stars and would only offer to stack one of the images after registering. I did slightly bias the balance towards the weights which seemed to create less of the doubles but I don't think I have taken enough shots yet to really establish how much that is helping. I don't currently have a Bahtinov mask but will pick one up for sure! Up to now I have just been mega zooming and tuning the focus like that on the DSLR live view. I think polar alignment definitely needs work but I will need to pick up a reticle eyepiece as I do not have one yet. All very early days I know there are lots of little bits that will improve the shots but I'm just trying to work my way through step by step dealing with issues as they arise  

[dph1nm]

Orion is pretty near the equator, so if the trailing is in the RA direction it is almost certainly not polar alignment (which will cause trailing in declination) - much more likely to be periodic error in the mount. The double stars are quite a common feature of these mounts. My HEQ5 shows them all the time - it has even been known to get quadruple stars!

NigelM

[spiraleye]

Excellent that is good to know thanks, Nigel. I like to know what I'm seeing and good to know it isn't so out of PA as to cause trails from that. The double stars were probably only 10 out of the 75 pictures with most just showing the beginnings of trailing along the RA axis it just struck me as odd. Do you think the periodic error correction setting might help with getting some better subs? Or should I just cut back to 15s again and go from there? I know it has this setting somewhere but I have not delved that deep as yet. Any tips on how to set up the PEC or generally get as accurate as possible would be much appreciated. Can't wait for another clear night now.....even after spending four and a half hours taking completely useless subs it's amazing I was still left with the level of satisfaction I was from the visual performance of the scope and the accuracy of the goto system  I just want to squeeze all the performance out of it I can in time. What would be the maximum exposure you would look to use for a mount and scope like this unguided?