Hot pixels on Lodestar X2 C

[froxfield]

I have noticed that there seems to be a number of hot pixels on my colour Lodestar X2.

Mostly with 30 second exposures, how many would be considered usual? Is about a dozen to be expected? Here is an example from an M42 H alpha shot. I think some of it might be because of my mount alignment and 30 seconds being a bit long at that point so there is some blurring(!) I am still playing with learning how to use the Lodestar, but I am sure you get my point though...

I know that there is going to be a hot pixel removal option in the new lodestar software but until then is cloning out the way to go?

[Martin Meredith]

Hi

Yes, it is normal, and my colour Lodestar (the earlier model) has far more than this. You can get rid of them automatically by taking darks of the same exposure length as your subs.

What mount are you using?

Martin

[nytecam]

All cameras we use have hot pixels, removed with 'dark' calibration frames usually with the scope capped but once done last for the session and often much longer.   From experience they tend to increase over time [my LCx2 is 2yrs old] - if the camera were 'cooled' then hot pixels are much reduced but this brings extra expence and weight/power loads and virtually essential for AP.

Nytecam

[froxfield]

Ah, thank you Martin, that is exactly the information I was hoping for, this is my first ccd astro camera and did wonder about taking darks, but thought that was more  for general noise (of which the Lodestar seems to have little!) .

Would I need to take as many darks as stacked normal images?

With the above I was using my st80 with a MAK127 synscan ALT AZ mount.

 

[Martin Meredith]

It is definitely worth taking lots of darks since a poor estimate of the dark can result in extra noise being added in to the image at the point where the master dark is subtracted. I typically take as many as the largest number of subs I'm likely to use in the session, but I'm fairly flexible. If seeing is poor or if the session is likely to be a short one I may not bother with darks. Having said that, these days I usually use the mono Lodestar where they're not quite so distracting as with the colour! 

Martin

[DoctorD]

Hi

I usually set my Dark Frame capture up as soon as I set the scope up outside, in the time taken to polar align and do the first stars alignment with the finder I usually have between 10 and 20 30s darks which I find sufficient. 

 

With Starlight live you can save the Master Dark frame - which can be useful if Starlight live crashes (not that it does often!). 

 

My original Lodwstar-C has many more hot pixels - dark frames work well to remove them but you can be left with dark trails on the image. 

V3 with hot pixel removal should sort this out  

HTH

 

Paul

 

 

[froxfield]

Thank you all, for the tips on dark frames. I will have a go using them next time. I am really enjoying the Lodestar. Sharing the view is really good, plus another lovely bonus is that it is mostly out of the wind and cold, as I am towards the top of a hill facing  the sea with westerly winds! Sometime in the future I may get the urge to upgrade the mount, but I am about to add some weights to the tripod which I hope will improve stability a bit. 

Patrick

[Hibou]

I think the latest version of Starlight Live will use live hot pixel reduction, as Infinity already does. Otherwise, unless your stars are single pixels, many applications such as imageJ will instantly locate and replace isolated hot pixels by the mean of their surroundings. IMHO taking dark frames seems contrary to the philosophy of live capture, and you are not going to get much information from hot pixels anyway. (Just my opinion; I hope the Jedi won't zap me for it :-)

[Astrojedi]

Can't argue on that one with the wise owl.

[Hibou]

Owls are not particularly wise :-) But they see well in the dark (in monochrome) because of their big eyes; the retina (CCD) is even bigger than the cornea (aperture).