DSLR - to long exposure

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Hi everybody!

I am abit confused at the moment and could really need som good advice.

I finally got to test my DSLR last night for the first time.

Got myself a Canon 1100D.

So after a quick and dirty photoshoot I check my results.

This is one of the images that best describes my problem.

Some stars look blown-out to me. (The pink and red ones)

Did I do something fundamentally wrong, overexpose or is it normal and fixed in processing?

This is a single, unprocessed exposure. ISO800 at about 15 sec.

RAW-format, saved as png for this forum, but the tiff looks kinda the same.

Cheers everyone and thanks for taking the time to read this far.

[steppenwolf]

The issue here is not so much overexposure but rather a case of chromatic aberration which has added a coloured halo to the brighter stars in the Double Cluster. Am I righ in assuming that you are using either a telephoto lens or an achromatic telescope?

[nightvision]

That looks OK for such a short exposure, are you tracking or guiding because it looks like the start of some trailing that is also stretching your stars.

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Steppenwolf:

Ahh I never thought of that.

Yes it is a achromatic telescope. The nexstar 102.

Explains it then. I feel much more confident now to keep practising and ignore those stars till I get a new telescope then.

1000 thanks!

Btw, I am kinda impressed that you figured it was the double cluster from that image.

Nightvision:

Thanks.

It is simple tracking. I only have a cheap setup at the moment.

Going to see if I can borrow a better setup from my local Astronomyclub this autum.

Hopefully I will be able to produce something worth showing by then.

[jgs001]

You should be able to get some results with the Nexstar... balance the scope on the mount so it's slightly tail heavy, not too much though, just a little. I'd expect, if you've got the mount setup well, you should be able to achieve 30-40 second exposures on the double.

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jgs001:

I will try that, thanks for the tip.

I was thinking about taping something "heavy-ish" on the scope (like an old ocular or something).

Think that would work aswell?

[jgs001]

If the fitted dovetail on the scope is too short, you're best bet is to buy a medium dovetail bar and a a pair of tube rings. The longer dovetail will allow you to move the scope back and forwards in the clamp.

[steppenwolf]

It wasn't too difficult to recognise the object because your image has some pretty reasonable data in it! I would definitely persevere and while you're waiting for your new telescope, just correct the issue in post processing - just a down and dirty correction but I used the 'Replace Colour' function in PhotoShop to reduce the halos in your image:-

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Cheers jgs001.

I think I am going to save that cash for a whole new setup thou. Or perhaps some DIY fixes for now.

Feels abit like "You can ducktape all you want, it still is a crappy car"

Was thinking something along these lines:

http://www.astrosweden.se/standard-nyborjare-afp03/19343-0 (It´s in swedish but I think you get the general idea)

6" reflector, f5 with CG-5 GT mount.

Either that or an OTA 80ED refractor with NEQ5 but I think I will get more (for me) satisfying results with the reflector.

But well, that is winters problem.

[jgs001]

I'd recommend starting out with Steve's book (Making Every Photon Count) as the first purchase. Something to bear in mind... even if you get an EQ6, you will at some point want to add guiding to the system, and as you already have the 102, adding a set of rings and a dovetail, would allow you to mount that scope to an imaging setup as a guide scope, and it's not an expensive option in the short term.

[Advertise]

Wow, OK that was a difference indeed.

Off to read some photoshop tutorials then.

Thanks!

jgs001

hmm, never thought of it that way really.

You sure do have your point.

Dont know why I didn´t think of that, specially since I have QHY5 camera aswell...:S

And that book sure will be ordered.

[themos]

To help troubleshoot image quality issues, shoot the Polaris neighbourhood. You know that tracking will not be an issue there and, as a bonus, it's quite high up for atmospheric effects to be small.

[dph1nm]

This was taken with a Nexstar 102 and a Canon 1000D, and a bit of judicious colour tweaking to diminish the CA.

NigelM