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Walking on the Moon

Orion Starshoot - bad pixels


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Hi all.

Was just tinkering with PHD2 and I noticed the option to build a bad pixel map, rather than use darks. So I went through the process, and even with hot pixel agressiveness set low at 25, I'm getting about  3000 hot pixels. This seem an awful lot!! That said, the example in the guide notes for PHD2 here show >2000 bad pixels.

Does this seem right?

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That sounds like a lot, but a camera usually has milions of pixels, so 2 - 3000 is acceptable. Not all of these pixels are necessarily dead (hot or cold). In an imaging camera, bad pixels are compensated for by calibration. DSLRs usually have an internal bad pixel cancelation procedure.

As long as guiding works ok, I wouldn't worry about this

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Hi Wim.

Maybe percentage wise it isn't so much - but it looks a lot on the pixel map! I think if I was buying a new 1.3MP camera and the dealer said that 3000 pixels wouldnt work I'd be none too happy!

But as you say it probably doesn't affect performance too much and the fact that the number of dud pixels can be altered by using the aggresiveness  slider suggests some of the dodgy pixels are warm rather than hot and can be mapped accordingly. (The cold pixel count isnt so bad)

My guiding has always been so-so... I'd love to blame the camera, but maybe I'll have to look for something else!

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If you can get some guiding, but not great, I would suspect common causes such as polar alignment, balance, flexure, and possibly guiding settings in the guiding software, before hot pixels in the camera.

But if you suspect that your guide camera has more than a normal number of defect pixels, and it's still under warranty, you can always contact the supplier and ask for advice. I'm sure they can answer your question and assess the situation.


Good luck

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