M64 Black Eye Galaxy

[Carole]

I started to image this after my original target disappeared behind the dome at 11pm.  This is my first attempt at this object and I didn't know how small it would be, but didn't want to waste the clear sky.  Also after the problems with the CCD cameras a few nights ago I wanted to use the DSLR to eliminate a problem with the scope itself.

35 x 300secs Modified Canon 450D CLS filter
Guided with QHY5 PHD and finder guider
Skywatcher Explorer 200PDS Newtonian
Captured in APT with dithering

With newly acquired coma corrector.  Unfortunately I wasn't able to get the spacing exact as the DSLR needed a thread adapter which was only 1mm but this put the spacing at 1mm too much.  Also focus was only just achieved at completely closed position of the focusser so it was a bit of a close thing.
The coma corrector is also a reducer so this brought the focal ratio down to F4.5

Close up


The full frame:


Link to larger file:
http://gallery.orpington-astronomy.org.uk/albums/userpics/10047/Black_eye_galaxy_35_x_5mins_DSLR_Newt_6-4-13_2nd_save.png

Carole

[Fay]

you did well Carole. change to see something we have not seen on here before. i think it would be too tiny for me to try that with my 120

[Carole]

Thanks Fay.

I don't see any problems on this image regarding the issues I had the other night with the CCD cameras, so I think this confirms that the problem is with the cameras and not the Newtonian itself.  Also am pleased to see the noise levels are better with this set up than with the DSLR and F7.5 refractors. 

Carole

[JohnP]

Looks good from Bromley Carole - also got another feint fuzzie down the bottom right hand corner... Good result will be even better once you sort out the spacings.. - John

[Carole]

There is nothing I can do about spacings John, as coma corrector plus DSLR normal distance from sensor comes to 55mm which is the exact ideal distance (but I will double check up on that).  But the coma corrector thread won't fit the DSLR T piece so I need to add the 1mm (spacing) thread adapter to make them join up.

Also any further distance and I can't get focus, and any further inwards is impossible as it is the furthest inwards the focusser will go, so I am stuck.

Going to double check all the figures to make sure though (for other cameras).

Carole

[RobertM]

That's a good attempt Carole though I agree with John that something's not quite right.  Have you checked collimation is spot on ?  Also is this the SW coma corrector or Baader - don't forget the SW CC is also a slight reducer too (0.9) so the telescope would have been operating at f/4.5 and 900mm focal length.

Fay, Carole's 200P is about the same focal length as your SW120...

Robert

[Fay]

oh ok Robert

[Carole]

Hi Robert,

Well I must confess I didn't check the collimation from the previous time I used it (a few days ago) as the scope hasn't been moved since.  But it was spot on then and a defocussed star looked fine.  But although the guide graph was good I think the guiding wasn't spot on, I am wondering whether I may have to adjust some settings in PHD now I have a different scope and am using a finder guider, but not quite sure what to do.  Therefore I did a little bit of jiggery pokery in photoshop to try to round the stars up, maybe this is confusing the issue.

I think it's a Skywatcher Coma corrector Robert, doesn't say on the box (got it second hand) but it is a focal reducer so was imaging at F4.5.

Any thoughts on what settings I should adjust in PHD for this set up, I'm afraid I don't have a clue?

Thanks for your anticipated advice.

Carole

[RobertM]

Hi Carole,

It's best to get to the source of the issue otherwise you'll be plagued by it till you sell the scope.  Regarding PHD, I don't use it but plenty here do - may be someone else will pipe up with some suggestions.

Robert

[Carole]

Actually I've been thinking about it some more, and I am not sure the guiding is the issue here.  I think it's more to do with the stars coming out ever so slightly comet shaped and this only seems to show up when zoomed in greatly.  I'll do a crop of the unadjusted image and post that up.  I will also do the same with my previous image I did of this set up without the coma corrector for comparison.  Maybe I should post this up in a technical thread. 

The thing is, I can get stuff to work if it does what it's supposed to do, but I don't have the technical ability to diagnose or fix when things go wrong unless I get advice, or unless it's something I have come accross before, so I really am at the mercy of my peers.

Carole

[Mike]

Try and get hold of a copy of CCD Inspector as it will show up collimation issues with your kit.

[RobertM]

You can also check collimation with a Cheshire; one of the best Newtonian collimating devices in my opinion.  Lasers will only give you good collimation if its nearly there anyway.

Robert

[Carole]

You can also check collimation with a Cheshire

That's what I've got, the collimation was spot on 3 days prior and I hadn't moved it since, except I suppose slewing might have moved it.  But as I say the defocussed star was fine.

I am not sure there are collimation problems I think it is something else. 

Gonna look at the image I did prior to the coma corrector.

Watch this space.

Carole 

[Mike]

Is the nosepiece dead centre in the focuser? Maybe it is slightly off? Perhaps you need a self-centering adaptor?

[Carole]

Actually funny you should ask that Mike, but i noticed the flats were slightly lop sided.  I do have a centering adapter, but this is adding even more distance to the already slightly too big distance, plus I won't get focus.

Anyway, For analysis this is what I have done.

First image is of the bright stars in the two DSLR images I have done with the Newtonian so far.
the left crop was done without a coma corrector and the star is as stated bottom left but not right at the edge.
The right crop was done WITH a coma corrector (Black Eye galaxy), and this star was towards the bottom left corner.  the middel vertical double spikes I wondered whether that was to do with the CC and spacing.

[Carole]

2nd image of the smaller stars near the centre of each image both with DSLR:

the left crop is BEFORE I got a coma corrector
the right crop is WITH a coma corector (Black Eye image).  I have enlarged the bottom star in the box on the left, note the comet type shaping and this is in the middle of the image.

It seems to me I got better results BEFORE the Coma corrector.



Carole

[RobertM]

It does look corrector related.  Are you sure everything is seated correctly ?

[Carole]

I'll take another look at it all Robert, but as I said before everything is right up against the focusser (no space).  Can't fit in a centring adapter as I won't get focus.

Thanks for looking.

Carole

[MarkS]

I've done an analysis using a program that analyses star elongations in nine parts of the image - corners, middle of eges and centre.  It works by taking an average of stars in each part of the image.

http://www.markshelley.co.uk/webdisk/CaroleBlackEyeAnalysis.jpg

There aren't really sufficent stars in the image and a 16 bit raw stack would work much better but the indication is a general left/right star elongation across the whole image (guiding issue maybe) combined with stars in the corners going "diagonal" (almost certainly a coma corrector with the wrong spacing to sensor).

The weird double vertical diffraction spike on that star you pointed out is definitely caused by the same issue that is causing the star elongations.

Have you re-checked what the spacing should be?

Mark

[Carole]

Thanks Mark, I could let you have the complete Tiff files if you like.

I was told by some-one I know with a similar scope that the spacer to coma distance should be 55mm, but that is exactly the distance of sensor to front of T piece of the DSLR, so I have nothing left to play with.  

On looking this up to answer your question I have realised I have made a boo boo, as I forgot to factor in the actual spacing to lens in the CC itself which is a further 17mm, so with the T to M48 adapter it is actually 18mm too large - duh!!!  (Stupid thing is I factored it in for the other cameras, how did I miss it for the DSLR?)

However I have also been googling trying to confirm the CC spacing in case for some reason my friend's kit varies in some way, though his is an F5 Skywatcher Newtonian.  But I have not been successful in finding any info, so have E Mailed Astronomia where I bought the scope, and am currently waiting for a reply.

So if 55mm is the correct spacing, it looks like I won't be able to use a coma corrector with the Newtonian and the DSLR.  

Bummer.

Carole

[Carole]

http://www.markshelley.co.uk/webdisk/CaroleBlackEyeAnalysis.jpg

That's a clever bit of software Mark.  Not that I would be able to interpret it.

Carole

[MarkS]

Carole,

Which CC is it - I'm trying to interpret what you are saying.  55mm is a standard focal spacing for such a corrector and it is measured from the rear flange of the adapter (not the lens glass) to the CCD.  This is perfect for screwing on a Canon T-mount adaptor (10mm thickness) and then the DSLR itself (45mm) - total is 55mm.

Or does the CC have a M48 thread on the back instead of the usual T-thread? 
Like the Skywatcher one:
http://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html
If so buy one of these:
http://www.firstlightoptics.com/adaptors/skywatcher-dslr-m48-ring-adapter.html

Or is the problem completely different?

Mark

[Carole]

Hi Mark

it is measured from the rear flange of the adapter (not the lens glass) to the CCD

that makes a lot of difference, as I thought it was to the rear of the glass lens.

In that case I should only be 1mm OUT which is what I thought in the first place.

That is indeed the coma corrector that I have Mark and I bought a T ring to M48 adapter to make the CC fit my current T ring but this adds 1mm to the train.  There is possibly another 1mm error because I can't screw the thread all the way and I don't want to force it.

I could get the adapter that you suggest but this will only remove 1mm and I want to make sure it's going to make that much difference before I shell yet more money out. currently I feel there is too much error that 1mm is going to make that much difference.

thanks for your continuing help Mark.

Carole

[MarkS]

So you seem to be saying that the spacing could be up to 2mm too large.  Unfortunately I don't know how critical this distance is.  However I do know that on a refractor the equivalent corrector has very critical spacing. Maybe the instructions give a clue, if there are any, which often there aren't.

I have bought a number of correctors, flatteners etc. over the years and they typically come with no instructions.  The manufacturers' collective attitude seems to be "you've bought this expensive product, now guess how to use it using trial and error and wasted nights of imaging".  It's one of the frustating things about this hobby.

Mark

[Carole]

So you seem to be saying that the spacing could be up to 2mm too large.  

that's correct Mark.  

I do have a set of instructions with the CC but all it does is tell you to use the T ring that you recommended above, then the coma corrector and attach to the DSLR so we have to assume that is the correct spacing. Says nothing about spacing otherwise.  Interestingly it doesn't mention CCD cameras except to say "You don't need to use complicated CCD cameras" (Great!)

So assuming that's all I need according to the instructions, it should be right.  But it wasn't.  
So maybe that 1 - 2mm is critical.  
As you say very frustrating that the info isn't out there.

I'll wait to hear what Astronomiser have to say.

Carole

[RobertM]

Carole I would think 2mm would make it out of spec.  I've seen 55mm +/-0.5 mm mentioned and would think you should aim for that.  As Mark mentioned there is a dedicated SW Canon m48 adaptor for this.

Regrettably, absolutely nothing is as expected in this hobby !

Robert

[mickw]

I believe Ian King sells the thin adapter

[Mike]

Try Bern at Modern Astronomy - he will be cheaper than Ian King.

[Carole]

Yes looks like I will have to get the TRing/M48 that will take 1mm out of the equation, and then see what i can do about getting the coma corrector on a bit further.  Bit of WD40 maybe.

Carole

[mickw]

If the CC is not screwing in fully, it might not be M48.
You should probably check with the suppliers of all the parts to find out if the threads match.

I can't remember what the different threads are (possibly M48 and 2") but they are very similar and seem to fit but don't properly

There is also the possibility that the anodising is slightly blocking the threads - repeated screwing and unscrewing might ease them and they will gradually clear the threads - do not overtighten in case they jam together.

[Carole]

It definitely says in the instructions M48.

I think it might be more to do with a so called tip I read about "using a bit of polish on the threads or you might never get it off again".  I did this the first time I used the coma corrector, but I think I used some old polish and I think it's just gunged it up.  I am wondering what I can use to clean it off.  Obviously I'll bunge up the barrel so I don't mess anything else up like the lens itself. 

Any ideas Mick?

Carole

[mickw]

meths or white spirit should do it

[RobertM]

If you want me to take a look then you're welcome to bring the adaptors around this evening.  I've also got meths and white spirit if you need a drink

Robert

[Carole]

meths or white spirit should do it

I thought maybe one of those two might do.  I've just looked in the shed and to my amazement my husband actually has both in there.  So which would be best?

I thought bung up the barrel of the Coma corrector with tissue and use a toothbrush to clean the threads with whichever above.  

Sorry I didn't get back before but got completely side tracked by having to sort out my mum's Home Care funding with a visit from the social worker and the Home today and having to find lots of relevant paperwork.  

If you want me to take a look then you're welcome to bring the adaptors around this evening.  I've also got meths and white spirit if you need a drink  

Thanks for the offer Robert, but I think I will be able to sort it out myself - hopefully.
However if the offer of a drink still stands it would be nice to come over but I'm not on meths!!!

Re EOS/M48 adapter
FLO are out of stock
Astronomia want an extra £4.40 or something just for posting that little thing, and only just remembered to ring Bern (who is out posting parcels) due to the distractions of the day - just caught him in time before he goes off to Kelling, so if he's got one I'll go and collect it tomorrow so I've got it for the weekend.

Thanks guys.

Carole

[Carole]

OK, I've got all the gunge off, but it seems it wasn't that that was stoping it screwing closer, seems there is a rim on the adapter stopping it go all the way, so said Adapter is obvisouly not right for the job, but it will be OK with my QHY8L which also needs the same adapter.

I have located an EOS to M48 adapter from Bern am picking it up tomorrow morning before he leaves for kelling.

Carole