Hints, tips and critiques for learner wide field post processing

[dr_robot]

Hi folks,

What better to do than on a wet and awful bank Holiday Monday than re-processing some early attempts at wide field astrophotography?

A couple of weeks ago I attempted to take a wide ish shot of Cygnus using my Canon 1100d, with Canon 50mm F1.8 ii lens. This was before I learned about focusing via live view so it not perfect, I cannot be 100% Cygnus is anywhere near center of the shots. I took 59 x 19 sec exposures at ISO800 F.2.0 + 12 x dark frames at same exposure,ISO and temp etc. All using a cheap, but sturdy non tracking tripod.

DSS stacked the 28 good RAW light frames and subtracted the dark frames for me no problem.

Attached are the results after my PS CS5 attempt at processing and a version with where I think the Cygnus constellation is, below is a link for the dropbox location of the original TIFF file is anyone would like a play.

https://www.dropbox....rah2v/cygnC.TIF

So...

1) Is my constellation location correct?

2) Any other interesting objects caught in shot?

3) I cannot get nova.astrometry.net to identify my image - I have tried lots of different versions, is there anything else I can do to help it? Are there other sites that might fair better?

4) What do yo see wrong with any of the versions provided, particularly cygnC which shows my attempt at playing with levels, curves and vibrancy? (still very new to this and not entirely sure what to look out for and even what I am looking at all the time)

Thanks very much, without this site I would be very very stuck!

Gav

[Aenima]

Shame this post never became a thread :/ - dont worry it's happened to me a few times

Anyhow, the title caught my eye and hopefully this reply will allow anyone feeling generous with their know-how and hard earned experience the opportunity to add something to the subject in question.

Here's hoping,

Aenima

[autonm]

Hi Gav..

I have the same setup as you 1100d + 50mm lens.

People have advised me to set the F to 4.0 rather than F2.0... see my post

Also 19 seconds seems a little long for an untracked mount. I uses around 6 seconds with 20-25 images stacked at ISO 800.

Maybe the star trails are stopping nova.astrometry.net pick up the stars?

Also checkout my website below which is mainly of wide-field images using the same setup as you have. You will see that the majority of my posts that 'nova.astrometry' is pikcing these up.

so perhaps try a shorter exposure time?

Thanks

[JB80]

Good advice above.

Astrobin is another good site for astrometry.

[jgs001]

Gav, sorry this one got missed... 

The rule of thumb for shooting from a static tripod exposure length = 400/focal length (for crop sensor cameras), so with a 50mm, it's on the 8 second mark. You've got some trailling from the longer exposures. 

I suspect the blobiness is probably down to the trails, rather than poor focus, as you seem to have got plenty of fainter stars (with poor focus you love more of them), and DSS was able to stack 28 of them, with poor focus DSS often won't stack any.

Whilst the Nifty Fifty lets in loads of light wide open, the coma is appalling, so you really need to stop it down to at least f/4. It looks like you've also got some quite heavy vignetting showing in the stretched image.

I think, considering the length of exposures and thus trailing, you've done well. Give it another go, keep the exposures under 10 seconds though.

[jezhughes]

I've just got in to wide field! 

Like John says, stop down. In fact with any lens you can expect to stop down. I snap at mostly f4-5.

If you want some really great results, i'd suggest investing in a 10-20mm lens. You'll get much more in and can do 30s exposures with great results. Take advantage of the portable nature of it all and make your way to dark sky too, it'll pay dividends in your final images.

Good luck 

my first wide field image;

[autonm]

is that 30s WITH or WITHOUT tracking?

[jezhughes]

is that 30s WITH or WITHOUT tracking?

thats 60s with tracking. a lower ISO though