Collimated?

[Neeken]

Hello again

Basic beginner question I take it.. But when I photgraph with my dSLR i noticed that some of the stars have a blured spot to one side on them. Not next to them with a gap in between, but on them to one side.

Is this cause of bad collimation, or something else? I still don't own a laser, so it might be a bit off if that's the case.

[cantab]

If they're towards the edge of the field and the direction "radiates" from the middle that just sounds like coma, proper collimation will get the star images good on-axis but there'll still be coma away from it. If they're the same direction everywhere in the field that's bad tracking or guiding.

[Neeken]

Ok, sounds like coma then. I do have a coma corrector, but maybe it doesn't fix it completely.

[Steve Ward]

Could you post an example , it will be easier to help if we can actually see the problem ,

[Neeken]

Yes, of course.

Here are 2 zoomed in stars.

[Moonshane]

can you also show the whole field? I think it's coma but hard to say from a small section.

[earth titan]

What type of set up do you have? Makes a difference if you have reflector, refractor etc.

Typed by me on my fone, using fumms... Excuse eny speling errurs.

[Neeken]

Sorry for the lack of information given here, hehe. I'm using a TS 6" (150 / 750mm) reflector.

Here's my first ever image, one attempt of M42. You should be able to see the effect at this scale. Everything has this "upwards" motion. I mean, it could be that my 0.8s shutter is a little bit too long without a tracker. It just didn't look like the same effect to me.

[Neeken]

By the way, how do I use the thumbnail images in my posts

[Moonshane]

I cannot see the pic but from your description it sounds like your assumption is correct.

[Neeken]

Oh.. Maybe if I post the link http://i48.tinypic.com/jqibmg.jpg

[Peter Drew]

Looks like collimation error to me.

[Neeken]

Hmm, I see. As I don't have any tools for the job yet, and I'm a total beginner, I might not be doing it the best way. I should read some more about it, even though it's a bit hard to understand at times. Although a laser would be nice to have..

[Jannis]

I was about to say the same, yes. Doesn't look like koma. I haven't seen anything likle that before, but i guess if collimation is off it could maybe result in a pic like that. Think it'd have to be way off though, as i know my scope is currently off, but still doesn't give anything like that as a result.

It could also be cuased if the camera wasn't completly attached to the scope i think (if it was slightly off on one side)?

[Neeken]

Well, it shouldn't be that much off as far as I know. The donut it pretty well centered as far as I can tell. And the reflection of the focuser tube is pretty much circular, I don't see more of the inner parts of the tube on any of the sides. Maybe there's a step I'm missing here..

[Jannis]

Just thinkig though, you used 0,8s exposure there, with no trackinjg, correct? Did you use mirror lockup? Is it possible, if you didn't use that, that it's just the scope shaking from the mirror? I'd try again tonight, but use the 2 or 10 sec delay on the camera and see if it helps any.

I know that on my scope, without mirror lockup, the mirror shakes the scope enough to cause the stars not to be pinpoint anymore.

[Neeken]

No, I did not use mirror lock up. Didn't even know that was a thing. After reading about it now though, it seems like a good idea to use. If I can find the settings for it. I do use a remote IR trigger though, so I'm not touching any of the equipment when shooting.

[Neeken]

And yes, 0.8s without tracking.

[Neeken]

I also noticed some ghosting of sorts when looking at the moon through the camera. It doesn't stay sharp in the image. It goes in and out of focus all the time kind of.. Not sure what causes that.

[Neeken]

If it's the Shutter/AE lock settings, it's set to AF/AE lock as default. Is that what I need it to be?

[Jannis]

I think that would be turbulense in the atmosphere, causing the focus to jump in and out a bit. It's also cause if the camera and/or scope have not cooled down to surrounding temperature. Usually i let my scope cool down at least 30 min before starting to take pics.

The mirror lockup, you have 2 options here, or 3, in a way:

1. where you select shooting mode, single picture, burst, 2s delay or 10s delay with burst. When you select 2 or 10 sec here, the mirror will flip up when you push the shutter, and wait 2 or 10 sec before actually taking the pic. This is good if you only need a couppel of pics to check focus, framing and so.

2. you also usually have this 2s delay option on the IR remote, it works the same way as abow.

3. in the cameras CF menue (same as where you also turn off high ISO noise reduction and long exposure noise reduction), you have the settings called mirror lockup. When you have this set to enable, it works like this: push teh shutter once, and it flips up teh mirror and is ready to take the pic. It takes the pic when you push teh shutter the next time.

This si very simple and recommended to remove all camera vibrations before yo utake the pic. For astro use, where we have such long focal lenghts, it's pretty much essential to use.

I have to admit that normally it won't look as in your case though, but i've never tries such short exposures with the scope and without mirror lockup though, so it shuoldn't be excluded as a possible cause at least.

[Jannis]

If it's the Shutter/AE lock settings, it's set to AF/AE lock as default. Is that what I need it to be?

It's not that setting, no, it's one that's called "mirror lockup". It's in the custom functions menu.

[Neeken]

Oh, I see. Found it. Yea, I can't use the particular remote I have without a 2sec delay, so that's pretty much fine. So does enabling mirror lockup help then, as I already use the 2 sec delay?

Also, are there any other settings I should change? Like "High ISO speed noise reduction" etc.

[Neeken]

Oh never mind, I just noticed that without the mirror lockup it didn't do it before the 2second delay. Silly me

[Peter Drew]

If, as you say, the general collimation looks OK then I would check that the camera is properly squared on. Coma in a well collimated telscope is radial, the effects your photo show are unidirectional suggesting collimation or out of square components.