Saturn Thursday Night

[Greg]

Took this quickly Thursday night with the 5" Refractor and the Cannon, more of an experiment than for anything else ....

Question is have a captured a moon or is a hot pixel...I think it's a pixel???

[Greg]

PS. it's not shopped, it's as nature intended

[OXO]

Looks like a Hot Pixel to me Greg, you have got one moon though :shock:

James

[Greg]

James,

The brown smudge at 10 o'clock is a hot pixel??

The dot at 1 o'clock is a moon??

[OXO]

Brown Sauce poss a moon?

White Sauce a hot pixel

[FLO]

James is right Greg 8)

[lunator]

Greg

The brown smudge looks like it's Titan.

I have checked the Position of Titan in S&T and it is shown as North West of Saturn.

Onw way to spot hot pixels is to take a single image with the lens cap on, this will show you any hot pixels.

Cheers

Ian

[OXO]

On the Subject of Hot pixels these can sometimes be removed from the Camera using software i wonder is there some on the net of the Camera Greg? Also some photographic retails offer this as a service too but of course theres a charge for this Steve maybe able to shed light on this more?

James

[FLO]

.. Steve maybe able to shed light on this more?

First a definition (from Olympus):

What are "Stuck Pixels", "Dead Pixels", "Hot Pixels" and "Noise"? How do you deal with these issues, and what additional solutions does Olympus offer?

Dead Pixels: a pixel that reads zero or is always off on all exposures. This state produces a black pixel in the final image.

Stuck Pixels: a pixel that always reads high or is always on to maximum on all exposures. This produces a white pixel in the final image.

Hot Pixel: a pixel that reads high on longer exposures, and can produce white, red (orange) or green (yellow green) pixels in longer exposures. The longer the exposure the more visible the hot pixels.

Noise: the state with fixed pattern and random patterns created as the CCD heats up, in extended use or longer exposures. If you have a long enough exposure you can find hot pixels and noise in any digital photo. Along with heat, higher equivalent ISO's result in increased noise in the digital photographs.

A common misrepresentation of dead and stuck pixels is to set the camera to a low ISO (such as ISO 100), and put the lens cap on the camera or cover the lens, resulting in a long exposure. When you look at the image you will see misrepresented pixels, some red or greenish in color, some white. This is a normal state and should not be confused with dead or stuck pixels. It is noise, and the red or greenish coloration is called Christmas tree artifacting in slang terms. The color is caused by the RGB and CMY colored filters of the CCD.

At the time of manufacture, imaging chips are put thru a software routine called 'Pixel Mapping' which detects faulty pixels and essentially excludes them from the cameras image processing algorithms. As a camera ages, other pixels will fail and if that troubles the user the camera can (usually) be returned to the manufacturer to have the Pixels re-mapped - there is a charge for this service. (Olympus have included the Pixel Mapping routine into the firmware of several of their cameras so that the user can activate it when necessary).

Personally, 2 or 3 dead pixels don't bother me - I simply remove them in Photoshop.

[OXO]

Dark frame subtraction is a good way too, the only bug bear with hot pixels is if you have an image full of stars it can be a pain to work out which is hot and which is not, but the Dark Frame Sbtraction always sorts this out..

Thanks Steve

James

[daz]

DFS - This is taking an exposure as the same length as the original exposure so identify the hot pixels. Simply putting the dust cover back on the scope and taking the image is the way to do it. Is my understanding correct???

[Greg]

I've done some reserch on this and - You can take a dark frame to identify the hot pixel or pixels then take your normal frames and subtract the dark frame in Photoshop....

I just have to learn how to do it..

[OXO]

Thats correct, when you take a Dark Frame it is best to do as soon as possiable after you have taken your image, this will give you nr perfect results for the Dark Frame Subtraction because the DF will match the cameras status ie:Temp.

James