Something's going wrong...

[Johnny666666]

Hi to everyone,

As it was such a clear night on Saturday I tried for the first time to image a DSO, namely M13. I had previously levelled the tripod and polar aligned as best I could (I'm not yet at the stage where I have had a play at drift alignment) but managed to grab a few shots. The results are disappointing to say the least because even a 5 second exposure shows what appears to be star trails. However, looking at the images in the cold light of day I'm not convinced that it's simply misalignment.

I've attached an image of crops of M13, the left hand image was 20 seconds exposure, the right hand 40 seconds. I did nothing apart from adjust the exposure duration and the shots were taken immediately one after the other. The trails show up as a weird 'S' shape and actually change direction between each image. The mount is fitted with motors and I am aware they are not the best in the world however I would've expected better performance than this.

The shutter was delayed so shutter shock shouldn't have been an issue and the set-up was on a patio so little chance of the ground moving. The camera was fired using a 5m remote cable, so again nothing was moving the mount apart from the motors. I have noticed that the mount has become quite 'stiff' and even from new balancing has always been an issue because I appear to be able to adjust the counterweights quite a fair amount in either direction before the scope swings off balance. Any thoughts or comments would be welcome as I would really like to start imaging DSO's to at least the best that my budget equipment is capable of, but I feel something is not quite right at the moment...

Regards - Johnny

[oldpink]

even unguided you wouldn't get trails like that
is it possible the motor is trying to push the scope but it doesn't want to move causing a rocking motion

[Elm0]

Looks like a focus and alignment issue to me. Maybe even a bit of wind playing with your picture. 

What PA method are you using?

You should easily get 20-30 seconds with a half descent PA. I can get 50-60 seconds with the hour angle method.

I always find that once I PA and add weights and scopes etc, the PA does go off a little so with the bits attached, i double check the alignment.

[Tinker1947]

Maybe try 10 second exposures with the tracking turned off, if there round stars it looking like the mount........

[adamphillips]

i don't know how sturdy your patio is but I would never set up on a surface like that. maybe nobody walked around on it during the exposures but I bet anyone walking would cause it to shake. I would set it up on the ground.

[datman]

Focus isn't brilliant, but that wouldn't cause the wobbles. Without some sort of guiding software which you don't mention, only the RA motor will be turning.

Looks more like a wobble to me, you can see a number of the same star in different places. What do you mean by stiff? With the clutches released the telescope should turn easily.

If it really is stiff, this would cause judder as the motor tries to overcome the resistance, then a sudden stop as the resistance bites in again, but that should be in the direction of RA

Balance is relative, it's not like a knife edge balance.  You may need to apply some motion, like a little tap/push, then see if it favours the weights or the scope

Same for balancing the scope up or down it's length with all accessories (e.g. camera) fitted. Do this with the weights/telescope at about 90 degrees from parked so the telescope

is horizontal. If you've not done it already mark the balance point with a bit of electrical tape.

Providing you are standing very still, 5 metres away, and assuming nobodies doing Double Dutch with your cable it doesn't seem likely to be the cause.

[Johnny666666]

Thanks everyone :-)

Yes I realise focus isn't brilliant - this is something else I am having issues with but I just wanted to capture something for the first time other than the moon or a planet as the exposures etc are quite different. It was more of an experimental shot to be honest to see how accurately the mount would follow the stars. I polar align using the astronomy shed technique and haven't really had any issues with it although I've noticed my videos of Saturn and Mars lately have been drifting across the camera frame over the course of a couple of minutes so again something isn't right there either.

I was expecting to see star trails of M13 to be honest but would've expected to see them as perfect straight lines, not this kind of weird wobble. Unfortunately setting up on the patio is my only option if I want to view anything south (I had been imaging Saturn earlier) but I can set up on ground at an alternative location if I want to only look at anything north, so I might try this at some time.

The mount definitely appears unevenly stiff when rotated in the RA axis. Even if the scope balance is some way off and I tap the weights to see which direction it moves, it sometimes only moves a fraction. Yesterday I put just the mount on a table with only the weights bar attached and unlocked the RA lock so that it rotated 'freely.' When I rotated the RA axis in one direction so that the weights bar was horizontal (90 degrees from 'home' position) and then released it, it freely swung back down to 'home' position. However, if I rotated the weights bar horizontal in the opposite direction (say, 270 degrees from 'home') and let go, nothing happened, it just stayed where it was. Even tapping it down resulted in it only moving a few degrees so it's definitely stiff around that area. I also use the dual motors to 'perfectly' align an object in the EP (I prefer this to using the fine controls because the motor buttons are all in my hand and I don't have to touch the scope) but when I change direction I can hear the motors change instantly but there is a delay before anything happens. I'm aware there might be some backlash in the various gears, but once this has been taken up there is usually a sudden movement and the object I am viewing darts across the EP.

RVO have said that the mount might require some adjustment and have very kindly offered to look at this for me tomorrow as I said I wasn't keen on making any adjustments myself, so hopefully that (and a revised or more accurate polar/drift alignment technique) is all that is required. Oh, and a Bahtinov mask

[datman]

I'd put my money on the stiff mount.

Although you use both motors to align the object, once you stop doing that, only the RA motor moves. It's only when a PC/Guide camera are used that the Dec motor is also used to keep track.

Don't forget the planets are following their own orbits too. The RA motor only tries to maintain tracking relative to the earth's rotation so planets will wander off.  Depending on the Declination

the speed of RA will also vary, the closer to Polaris the slower objects seem to go.

This is all extra info though, it won't cause the faults you've shown us.

Let's hope RVO fix the problem for you

[Thalestris24]

Thanks everyone :-)

Yes I realise focus isn't brilliant - this is something else I am having issues with but I just wanted to capture something for the first time other than the moon or a planet as the exposures etc are quite different. It was more of an experimental shot to be honest to see how accurately the mount would follow the stars. I polar align using the astronomy shed technique and haven't really had any issues with it although I've noticed my videos of Saturn and Mars lately have been drifting across the camera frame over the course of a couple of minutes so again something isn't right there either.

I was expecting to see star trails of M13 to be honest but would've expected to see them as perfect straight lines, not this kind of weird wobble. Unfortunately setting up on the patio is my only option if I want to view anything south (I had been imaging Saturn earlier) but I can set up on ground at an alternative location if I want to only look at anything north, so I might try this at some time.

The mount definitely appears unevenly stiff when rotated in the RA axis. Even if the scope balance is some way off and I tap the weights to see which direction it moves, it sometimes only moves a fraction. Yesterday I put just the mount on a table with only the weights bar attached and unlocked the RA lock so that it rotated 'freely.' When I rotated the RA axis in one direction so that the weights bar was horizontal (90 degrees from 'home' position) and then released it, it freely swung back down to 'home' position. However, if I rotated the weights bar horizontal in the opposite direction (say, 270 degrees from 'home') and let go, nothing happened, it just stayed where it was. Even tapping it down resulted in it only moving a few degrees so it's definitely stiff around that area. I also use the dual motors to 'perfectly' align an object in the EP (I prefer this to using the fine controls because the motor buttons are all in my hand and I don't have to touch the scope) but when I change direction I can hear the motors change instantly but there is a delay before anything happens. I'm aware there might be some backlash in the various gears, but once this has been taken up there is usually a sudden movement and the object I am viewing darts across the EP.

RVO have said that the mount might require some adjustment and have very kindly offered to look at this for me tomorrow as I said I wasn't keen on making any adjustments myself, so hopefully that (and a revised or more accurate polar/drift alignment technique) is all that is required. Oh, and a Bahtinov mask

Hiya

Looks like a vibration issue to me. Focussing too, but I'd say it's vibration causing the 'weird wobble'. Probably what you need to do is trigger the camera by remote control, if you have one, and stand well away. Computer control is the best way. If the Panasonic software includes a utility for controlling the camera via usb, that would be good

Louise

[Johnny666666]

I'd put my money on the stiff mount.

Although you use both motors to align the object, once you stop doing that, only the RA motor moves. It's only when a PC/Guide camera are used that the Dec motor is also used to keep track.

Don't forget the planets are following their own orbits too. The RA motor only tries to maintain tracking relative to the earth's rotation so planets will wander off.  Depending on the Declination

the speed of RA will also vary, the closer to Polaris the slower objects seem to go.

This is all extra info though, it won't cause the faults you've shown us.

Let's hope RVO fix the problem for you

Thank for the reminder - I often forget the planets are in their own orbit! Such is the curse of a newbie

Hiya

Looks like a vibration issue to me. Focussing too, but I'd say it's vibration causing the 'weird wobble'. Probably what you need to do is trigger the camera by remote control, if you have one, and stand well away. Computer control is the best way. If the Panasonic software includes a utility for controlling the camera via usb, that would be good

Louise

Hi Louise, Aside from the focusing issue I do trigger the camera from a 5 metre remote control, but I now realise I might not have been standing far enough away  - or at least that's something I need to be aware of next time. The camera can be controlled via WiFi with an app for a smartphone or tablet, but unfortunately I have neither and the app/program doesn't work on humble laptops as far as I know. Off to RVO in a few minutes so hopefully they can do something with the mount, if that's the issue. I'll update later

[Stargazer33]

Good luck with getting the mount checked out. I was really surprised how much my mount wobbles when I move around on my patio, but it definitely sounds like you have a sticking issue with your mount.

[Thalestris24]

Thank for the reminder - I often forget the planets are in their own orbit! Such is the curse of a newbie

Hi Louise, Aside from the focusing issue I do trigger the camera from a 5 metre remote control, but I now realise I might not have been standing far enough away  - or at least that's something I need to be aware of next time. The camera can be controlled via WiFi with an app for a smartphone or tablet, but unfortunately I have neither and the app/program doesn't work on humble laptops as far as I know. Off to RVO in a few minutes so hopefully they can do something with the mount, if that's the issue. I'll update later

Oh ok - 5m should be fine I use my setup indoors and although I sit about 3m away I still have to stay perfectly still during exposures! There's obviously something causing movement in your case. As said, it could be a problem with your mount/motors. Hope you can sort it.

Cheers

Louise

[Owmuchonomy]

I'd take a look at your bearings. From the symptoms you describe the RA bearing axis is sticking probably due to the bearings being too tight or even off square. I had the same issue and now adjust the bearings back off tight by 1/4 of a turn. Been fine since.

[Johnny666666]

Hi and thanks for the replies

Well, the mount seems to check out OK and any perceived stickiness is apparently nothing untoward (it's my first scope so I have nothing to reference it to!) We did notice that there was some play in the backlash of the Dec gearing which has now been dealt with although the RA motor seems fine. The RA lock has also been slightly adjusted to disengage more. I've said I'll go through a series of checks the next opportunity I have - such as any backlash or stickiness when operating either the Dec or RA motors and changing direction, and also see how smoothly the mount rotates when it is fully loaded. RVO have kindly said if I'm still concerned I can take the whole set-up to them and they'll check everything for me

One thing I need to check when I'm observing is the small thumb screw that locks the hour setting scale on the RA axis. I never use this (or rather it is always slack) when following the astronomy shed polar alignment routine. However, when looking at the mount tonight I noticed it has inadvertently tightened up due to handling in transit, and this definitely makes the RA rotation less smooth.

I'm also going to have a look at the video footage of Mars and Saturn I took on Saturday from the same location, because I remember walking away from the mount and back to it again, so this might show up any wobbles on the patio!

[datman]

Well that's one thing off the list.

I used to have my setup on wooden decking, and that's even worse than concrete.

It's amazing how a small movement translates into a big wobble.

As Louise says the best method by far is to use a computer to control the mount/camera.

If you have the motor hand controller I think you have, it can be modified so it can be used with EQMOD.

Not quite as good as a full blown GOTO but certainly better than what you have.

You'd need an interface, RVO do one for about £45 but I'm not 100% sure if that's the right one. I'd have to check.

I'm not sure if this is a possible self build.

If you don't what to risk modifying your handset, I have a spare one.

I also built an alternative version. I'd have to check it out but I'm pretty sure my version would give better speed control, it could also be made/programmed to have more choices.

There is a story to this, but it's too long for here.

Not particularly expensive to make, just takes time. It uses 2 x microcontrollers one for each motor, so can be programmed for different speeds.

Have a think about what you want to, if you want to go down that route, let me know and I'll do a bit of research.

I've just checked the interface at RVO, it would work.

I live in Worksop so we are fairly close.

David

[Johnny666666]

Thank you so much for your kind offer, David - I'll certainly keep it in mind

I have a few simple mods I want to try at basically 'low cost' but in the meantime I'll have another bash at the existing set-up and see how I get on. I'm sure I'm doing something wrong somewhere and if I'm setting up on the patio again (I have very little choice) then I'll ensure I'm not moving anywhere when exposing. To be honest, I wanted a set-up that was 'intermediate' and capable of good results to see if the bug bit, then in a couple of years if I still feel the same way then I would like something far better. The GH3 is 'uncontrollable' from a laptop (unless I download some distinctly unstable dodgy looking 3rd party coding) or I have a tablet or smart phone, which I don't. So I would be looking at a camera or imager upgrade as well.

It's a lot of expense and upgrades are hard to make future-proof - with the exception of my ability to now use 2" filters throughout my telescope and camera system, something else I need to look at because I do have a spare dovetail and camera lenses from a nifty-fifty up to 600mm.

I'm just waiting for clear skies...!