Finally! my first guided image :)

[Daniel]

Ok, i know it's still a bit on the grainy and blurry side (I really need to collimate again) but this is my first fully guided image of M51, have to say since moving to the DSI for guiding the accuracy has been great (well apart from a few teething troubles which are now sorted)

This image is 10x 300s at ISO 800 on the Canon 40D, as soon as I get some more time I'll go out and get some more subs and hopefully start to see a little more colouring too.

Anyway, here it is

[JohnP]

Great Daniel - Looks like you are making progress fast. Guiding looks great for 5min subs...

John

[Daniel]

Hi John, thanks for the encouragement, Im definetly chuffed the guiding is working now, there's a little drift still, but compared to what I was getting even with 1 min subs unguided, It's much better.

M51 was a nice acid test too, since it's almost straight up and my mount has all sorts of problems when it's at that angle.

One thing I do wonder though is that my subs are coming out very blue-ish with the CLS filter, I know the CLS tends to tint a little blue, but Im unable to go much beyond 5 min subs at ISO 800 without it getting over exposed, would dropping down to ISO 400 collect more photons over 10 minutes and enable me to collect more colour information?

[Fay]

Well done Daniel, was you out last night?

[Daniel]

Yes, I head out last night, suprised we had a good patch in between all this rain.

I realised I lost sight of the image a little while i was processing it, got so bothered about not buring out the middle I lost a lot of detail, So here's another re-processed version, i think this ones a lot better though could do with some more subs

[MarkS]

Daniel,

You've done well - you must be really pleased with that.  Guiding makes a such huge difference - I've just got into it myself.  Your M51 definitely needs more data - but you can collect that over a few evenings and add the data together.

I agree entirely with your comments about the CLS filter - I use one myself and things do come out very turquoise.
As an illustration, take a look at my website http://homepage.ntlworld.com/the_shelleys/Astronomy/ Near the bottom, there are two versions of M51 both taken with a Canon EOS 300D on my Celestron C11:
1) One is 5 hours of data with a CLS filter from Sidcup
2) The second is only 2 hours of data from dark skies
I think you'll agree that the second one is vastly superior and the colour rendition is better balanced. 

I have to be honest, I think the CLS gives strange colouring on galaxies but for emission nebulae it is great.  I wonder if there are other light pollution filters that are more balanced?

Take a look at this thread http://forum.orpington-astronomy.org.uk/index.php?topic=3026.0  - it demonstrates what gets removed from the spectrum.

Mark

[Daniel]

Hi Mark, thanks for the input, Love the work on the website the progression you can see from the start to the end is incredible, agree with you about the 2 images, that lovely Mauve colour is what I want to get out of my M51 eventually.

I have a UHC-S filter here which i may try, I haven't used it for a while now because the CLS filter has been pretty good for everything else, But I do remember it not looking so blue tinted so I might give that a shot, another thing I'd like to try is a Ha filter to pull out as much of the red channel as I can then mix it in.

hopefully this weather will lift and I'll  be able to get out and take a few more subs soon

Daniel
:O)

[MarkS]

If you try out the UHC-S filter on M51 I would be very interested in the results.

As for the Ha filter, I don't think it will go too well with the Canon - they have an appalling lack of Ha sensitivity (Nikon is the same).  Christian Buil has some very useful technical stuff on Canons including response curves (do you speak French?) - he loves the 40D from an astrophotography point of view (except for the Ha insensitivity):
http://www.astrosurf.com/buil/eos40d/test.htm
http://www.astrosurf.com/buil/20d/20dvs10d.htm
http://astrosurf.com/buil/350d/350d.htm
The third link has some great IR shots of a soldering iron at various temperatures!

[Daniel]

I shall try out the UHC-S and post the results next time im out, I was thinking if I took very long exposures using Ha, even with the poor Ha sensitivity of the canon camera's I might be able to pad out the red to even the balance up, that said, the Ha filters are massively expensive, might get the EOS clip in version from astronimik, which is slightly cheaper than the 2" and still has very little vignetting, Im using the clip in CLS right now which is very good.

[RobertM]

Hi Daniel,

Very nice results.  I can't comment on DSLR's as I haven't got one but you will need to take dark and flatfield frames to bring the best out of your images.  It's especially so as the weather warms up and the noise increases.  The flat fields will remove the vignetting that seems to be there - notice the centre is brighter than the periphery.

Hope that helps and keep up the good work !

Robert

[Daniel]

Hi Robert, yes I wanted to take some flats and darks, but since I had to be in work the following day had to pack up and leave it at that, just wondering, I know with flats and darks it's best to take them right there and then after or before your imaging, If i set up the scope pretty much identically as I had it, could I still take them on another night?

[RobertM]

You should really take them with the image train in exactly the same position but it shouldn't matter if you put them back more or less the same.  You might want to mark the positions with sticky tape or something in future so you can put them back repeatably and that should do the trick.  Flat fielding makes an enormous difference where there is vignetting or dust shadows.  Some people manage to get away without flat fielding but that requires a smaller sensor than the fully illuminated imaging circle - something I'm grappling with at the moment.

Don't forget you can take flatfields during daylight to !

 

[Mike]

....If i set up the scope pretty much identically as I had it, could I still take them on another night?....

This will not work at all unless you are able to put everything back exactly as it was with sub-millimetre accuracy.

[Daniel]

Damn, i could probably get it back to how it was almost exactly, but i doubt with quite that level of accuracy