M42 first attempt (and all the warts) 10.12.09 Back garden

[Fay]

You will need a lot longer subs Carole, also a better focus. You are en route though!!

[The Thing]

Well done Carol!

I know how hard it is especially with light pollution fighting you all the way not to mention the dew, laptop and all the other gubbins. Keep trying, we can only improve.

[Carole]

Thanks Duncan, I now know what Fay meant when she started imaging about it being a nightmare.  

You just start to think you're getting somewhere and then something else comes along to trip you up.  

Currently it's guiding.  I tried to tackle guiding on it's own last night, but I think the cheap Guidescope I bought from Mark (which he cleverly manages to use) is proving to be impossible for me as focus is on the body of the tube under the adjustment screws (in the picture it is the patterned ring around the OTA between the guide rings) which means it moves forwards or backwards inside the guide rings and I am finding it impossible to manage, or even find focus when I've got a star.  So I think I'm going to have to get myself a normal guidescope.  



You will also note that the guide ring adjustment screws do not have knobs on them which I wasn't very pleased about when they arrived.  I complained about it but was told that's how they come, you're supposed to adjust them with an Alun key (yeah right, easy peasy in the dark with freezing hands).  So need to find a way to fix a knob on them.

Carole

[MarkS]

Carole,

For that guidescope lens you only have to focus it once - ever.   That's assuming your guide camera always sits at the same distance.  Focus it on something bright to begin with, then verify it on a small star then mark the position of the focusing ring (so if you accidently move it you can put it back). 

It's really that simple and you never have to do it again!

Good luck

Mark

[Carole]

Does it reach focus with an eyepiece, as I could not get it to do so last night?

Carole

[The Thing]

I now have a 200mm lens as a guide scope, it does need focusing as its very easy to inadvertently jog the wide focuser barrel.

I am using a ring arrangement from one of my long Minolta lenses which clamps around the lens body behind the focuser barrel bit. I have used some hard plastic strip as shims to tighten the fit. Thus I can still use the focus barrel. I have no trouble finding guide stars as I can pivot the lens in RA, which is the preferred axis of movement for offset guiding I believe.

This is the clamp on the Sigma lens. The knob has an off centre cam arrangement so as you turn it tightens the clamp. SRB-Griturn can make you a similar arrangement to fit your lens. http://www.srb-griturn.com/tripod-lens-mounts-27-c.asp

[Carole]

as I can pivot the lens in RA

Trying to imagine how you can do that!!

Carole

[The Thing]

Just twist a bit. Since the clamp has a single tripod bush and I put a wide washer between the mounting plate and the clamp base...

[Carole]

I used to have a clamp like that on mine, but was worried it would shift during guiding so took it off and replaced with the Guide rings.  I was also told that I might need the flexibility of the adjustment screws to find a guide star.

Can only be guided by others (pun!)

Carole

[MarkS]

I began guiding exactly like Duncan, but soon discovered I needed the flexibility of guide rings for 2 reasons:
1) I could not always find a sufficiently close guide star when searching only "left" and "right"
2) I've found the optimum guide stars to be diagonally outside the imaging frame (not left and right) - then any slight rotation of the frame around the guide star (almost unavoidable on a portable setup) will cause "happy drift" which averages out any banding, both horizontal and vertical,  on your CCD.

I had a 4 hours of M31 data ruined at Riberac only last month because I accidentally chose a guide star to the right of the imaging frame.  So the rotation was vertical in the frame centre and this did not average out the vertical banding. It was not "happy drift".

If you don't use "happy drift" you'll have to use guiding software that dithers.
 
Mark

[Carole]

Hmmm, trying to get my head around that.  I understand about rotation of frames, (from a frame stacking point of view) so what you are saying is every rotates around the guide star which makes sense.  However I am trying to understand why choosing a star to the right of the of the imaging frame makes a difference.    Might need to see this in a diagram Mark. 

Incidentally I have ordered that Skywatcher guidescope I showed you, (Xmas present) as I really think after 2 evenings of messing about with the current one, it's just going to make my life too difficult.  So if any-one wants to buy the one I got off you for the price I paid for it £15, they are welcome.

Carole

[Carole]

Do you mean the USB lead?  They are far too short - I use a USB extension cable with mine to give another few metres.

Mark

Bought a USB extension cable, and it works - brilliant - thanks Mark.  Will check the extension cable out on the guide camera too and if that works will think about buying longer cables for that too, so once I've set up the scope I can trail my longer leads through into the conservatory and sit in there with the laptop instead of freezing outside.

Carole

[Daniel]

Great to see your imaging coming on Carole, focus needs a little tweaking, but your getting longer and longer subs now so you'll start to see all that detail coming through.

Do you use the on computer Live view to focus your stars Carole? I find this is great for getting focus bang on, lately I've been taking 1 second exposures too to check the focus, but almost always find I had it just right with the live view (though I wouldn't trust the live view on the back of the camera, the screen is just too small)

Ineteresting what Mark was saying about guiding, I shaall have to ensure im guiding on stars out at a diaganol from the frame from now on.


Daniel
:O)

[Mac]

though I wouldn't trust the live view on the back of the camera, the screen is just too small)

i thought most live views allow you to zoom in to assist with focus.

M ac.

[Carole]

Hi Daniel, I am using Live view when imaging, but I was unable to see M42 on live view.  The only way I could see it was there, was after I did a short image, and had to keep tweeking an invisible target and then take another image and compare them.  I did about 30 in all, very frustrating not being able to see it. I used the focus mask and that helped a lot, but again I was not focussing something live.  Even tried to zoom in but still could not see it.  

Mac said something about using a different ISO for focussing which I was wondering about myself, but not sure which way to go.  Currently imaging using 800 ISO, next one up is 1600 next one down is 400, Mac Said the highest setting, so I am assuming that means 1600. 

I think I'll also try to focus on something bright next time before I go for the fainter object to be imaged, which Robert previously suggested, and that is what I did for Andromeda and it worked OK.

Carole