Clear skies 27/01/12

Tzetze

There was a window of clear skies in between the heavy showers last night and I intended to make the most of it.

First up was M33.
20 subs @ 180s
20 subs @ 120s
30 flats and about 25 or 30 darks for each sub length (dark library)
Canon 450D
SW ED80 DS Pro unguided on a cg5-gt
Stacked in DSS
Tweaked in Photoshop




I've been itching to try a capture of M42 and it was due to come into view past the gable end of the house at about 10:30. I took care of the flats before then so as I could spend a little time framing. It took some time to get the image framed just how I wanted and was working against the clock. Only managed to get 20 subs before having to call it a night.

20 subs @ 120s
30 flats and about 25 darks
Canon 450D
SW ED80 DS Pro unguided on a cg5-gt
Stacked in DSS
Tweaked in Photoshop

NUTZZ

Awesome pictures man, well done!

Kersh

Nice one, love the M33 pic, beautiful.

ThatDrGuy

Tzetze,
Those are absolutely fantastic. How did you get such a wide field ?

Tzetze

Cheers ThatDrGuy
Field of View (FOV) is a function of focal length and sensor size. Basically, for any given camera a long focal length scope will give a smaller FOV than a short focal length scope.

The scope I used for the above shots has a focal length of 600mm. Using the 450D with this scope gives me a FOV of 2°7' x 1°24', Resolving 1.79"/Pixel, Magnification 23x (Calculated by APT).

The 450D with my 1200mm focal length Newt gives a FOV of 1°3' x 0°42', Resolving 0.89"/Pixel, Magnification 45x.

pixbyjohn

Superb shots, would love to try this, thanks for sharing.

"20 subs @ 120s
30 flats and about 25 darks"

Can someone explain these terms to me please.

Tzetze

Thanks pixbyjohn.

To explain the terms.
A subexposure (sub) is one of a number of exposures of a particular object.
20x subs @ 120s means there were 20 subexposures each of 120 seconds duration. Total exposure time on the object is 40 minutes.
Many subs are taken and subsequently stacked in software to increase the signal to noise ratio.

Darks and flats are calibration images.

During long exposures thermal noise is generated on the camera's sensor chip. Dark exposures are taken of the same duration as the sub and ideally at or close to the same temperature. They are taken with no light getting to the sensor, ie the scopes cover is left on. The darks are also stacked together to create a masterdark image. This masterdark will contain the average thermal noise also present in all of the light subs. This masterdark is subtracted from each light sub before they are stacked - this removes the thermal noise.

Flats are used to correct imperfections in the optical path. They can remove issues caused by dust motes on the lens/camera sensor, vignetting and gradients.