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

[Carole]

Spent most of the evening and early hours last night doing this.  Not the greatest image but its a start.
60 x 30secs subs unguided (see problems below), darks, flats and Bias, and CLS filter
Stacked in DSS and post-processed in photoshop.
See post number 8 for the 45 x 60 sec version



Problems, new lessons learnt and queries:
I did also do 45 x 60 sec subs (just to see what difference the longer exposure would make to the nebula), but for some strange reason DSS would only stack 1 out of 45 images saying "only 1 frame will be stacked, check/change star detection threshold to detect more stars)", I even tried stacking just a couple but got the same message, and yet it stacked the 30sec subs done on the same set up, same evening with no problems at all....why?

I could not see the Orion nebula at all on live view and had to do a 15 sec sub to identify it, only to find it was wildly out of focus, despite having sorted out a parfocal ring system albeit with an elastic band, but this was on a land object, so may be different at infinity, must get some proper parfocal rings and do this again.  

It therefore took me a further 30 images (using the Focus mask to achieve anything like focus).  

Having done that I went to start up guiding which I had set up, but could I find a flippin star!!??  Could not see one, through the SC3 camera which ever way I pointed the scope, or focussed, so thought I'd better use an eye piece.  However by that time the side by side bar was vertical (Guide camera below), cameras, and cables (and the position I had to have the table because my camera interface cable is too short and am having difficulty finding a longer one), were all in such a position that it was impossible to look through the eyepiece, unless I had the body of a serpent and could wind myself over the table and under and through the mesh of wires and cameras.  So I will have to practice all that another night and see if I can get that longer Interface cable!!!!  Might also try swapping the Guide scope to the opposite side.  

This was the first time I had used the CLS filter and could immediately see the difference.

Lastily, I have posted a small crop of the stars in this image and wonder whether you can tell me why most of the stars appear as rings.



Sorry this was so long.

Carole

[Mac]

I did also do 45 x 60 minute subs

Wow 45 hours,

The reason for the rings around the stars is that its out of focus.
Mac.

Nice image though for your first attempt at M42.

[Carole]

Hi Mac,

Yes, whoops, I realised my mistake before I read your posting, and have now amended it.  Yes I wondered whether it might be out of Focus, but as you probably read, getting focus was quite a challenge not being actually able to see what I was focussing.  But I guess you all have the same problem, so will just have to learn, there's probably no easy way of doing it.

Any ideas why DSS would not stack the 60sec subs?

Carole

[RobertM]

Did you use a focus mask Carole ? It's more accurate than just looking at the size of the stars on live view.  The only trouble is that you may need at least a magnitude 2 or 3 star and because of that it can be best to focus first then aim the telescope.  Always check the first full length frame for problems before continuing.

Don't use DSS so I'll leave that for someone else to comment on.

Hope that helps
Robert

[Carole]

Yes I did use a focus mask.  I used the one Mac told me to make, but I thought so long as you got triple stars merged into one you were in focus. 

Always check the first full length frame for problems before continuing.

, Yes I did look at the image, but didn't understand why it was like it, and having taken so long try to merge the triple stars did not want to chance unmerging them again by fiddling further with focus. 

Re DSS:  Hold your horses every-one, I have just had another go at stacking the 60sec subs on my desk top DSS and so far so good (am doing a few at a time trying to weedle out if there's a rogue file causing the problem.  So far have managed to stack 12 light subs successfully and it's already looking like an improvement on the image above.  I am wondering whether I have a different version of DSS on my laptop, will look later.

So hopefully a further M42 image to post.

Carole

[Carole]

focus first then aim the telescope

.  Yes I've done that before, I'll try to do that next time.

So many new things to think about!!!

Carole

[RobertM]

Write them down like a recipe and follow those steps; refine it further as you get proficient.

[Carole]

Write them down like a recipe and follow those steps; refine it further as you get proficient.

Good idea. 
I do have some things written down, like which USB port to plug each item into, and which settings to use on the camera, etc, and I wrote down what I did as regardings what subs, and darks I was doing, times and temperature etc, and shifted the different length ones into folders as I went along so I would not get confused afterwards.

I am about to post the 45 x 60sec image which has processed this time on DSS (no idea what the problem was before).

Carole

[Carole]

OK.  Here is the 45 x 60 sec version.  Unguided (for reasons previously explained).
Lights, darks, flats, Bias, . 10.12.09 back garden Bromley
Canon DSLR 450D unmodified + CLS Filter


Carole

[Ian]

I reckon there's more faint detail there that could be brought out in the processing. Try a simple histogram stretch to start with.

BTW, focussing is the biggest P.I.T.A. in imaging. I read a website once that went into the maths of focussing and the incredibly small tolerances we have to work with when moving the focusser.

[Mac]

That is very good, you can start to see the faint nebulosity.

As for the focus, hmmmm, as Ian said, PITA.

Use the live view on the camera with the focus mask, and zoom into a brightish star using the live view. use the mask to assist the focus,
once thats done remove the mask. and then start taking the images.

set the iso to the highest setting on the camera whilst focusing.
and dont forget to reset it when you've finished focusing.

Mac.

[MarkS]

Carole,

It's a real shame about the focusing because, otherwise, that is an excellent attempt.  It shows that you have got everything else right.

There may well be more detail there waiting to be stretched out.

As you said, the CLS filter has made a lot of difference.  Once you begin guiding - that will make even more difference.

Mark

[Carole]

Thanks every-one for your advice and comments.

Try a simple histogram stretch to start with.

Now histograms are something I am not sure about.  Would this be the histogram in DSS or a histogram in Photoshop, if so where do I find it and what's it supposed to look like? How do I stretch it?  I did try using curves in PS but that did not make any satisfactory improvement.  I mostly used levels and brightness and contrast, and colour adustments to bring out the red and keep the sky dark. 

Does any-one who owns a Canon 450D use the interface cable, and if so how long is theirs?  Any thoughts on getting a longer one?  I have found the cable on the internet, but it's trying to actually obtain it as it seems to be currently out of stock with no expected date of delivery. 

I'll keep trying in case I can find some-one with one still in stock.

Carole

[MarkS]

Colour stretching in IRIS is the same thing.  You might be able to simulate it using multiple applications of PS curves as long as your black point is set correctly.  You might find that DSS has set it too high and already lost your faint stuff.

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

[Carole]

One more question:

The image is very grainy especially if I try to enlarge the image any more.  Can you tell me, is it longer subs or more of them (or both) I need to do to get a smoother image.  

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

It is the cable that plugs into the DSLR camera and then into the USB on the laptop.  Would you mind bringing it to the Xmas meeting (I'll bring my DSLR and Laptop) so I can try it out.  Or I could pop over. 

Thanks

Carole

[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

[MarkS]

Better than a diagram is the actual data - here is a raw stack of 38 five minute subs.  The guidestar was just off the right of the picture - the other stars rotate around it:



The image below (again from the raw stack) shows the vertical striations (an artifact of the CCD/camera electronics).  In the areas of the raw stack where the smears align with the striation, the striation will never be averaged away during the registering and stacking process.



I have now created a processing sequence that removes these striations but it is not at all easy.  It involves "reverse engineering" a frame containing the striations only and then subtracting it from each sub.

Mark

[Rocket Pooch]

I'm getting an OAG to stop this from happening, after I prove the current batch of flatteners etc, I'm fed up with flexture etc....

[MarkS]

How would an Off Axis Guider help?  The rotation in that image took place over a 3 hour period - it was due to polar alignment being slightly off.  Each individual sub was fine and, after alignment, they stacked together fine EXCEPT there was no dithering to get rid of the vertical striations in the CCD pattern (due to a bug in that particular version of Nebulosity).

The point I was making is that in the image areas where (vertical) smears align with the (vertical) striation, the striation will never be averaged away during the registering and stacking process.

Mark

[Carole]

Very interesting Mark, thanks for that. 

Carole