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isd May 20, 2006 8:39 AM

hello, im looking for solution of something i just realise because i dont used my camera much at night be4, here go:
i observe colored pixel points in image (dark sky) i was searching for similar observations in internet but no results, the question is:
is something wrong with camera and i should take it to the service?
i dont know how to shot over night? (most of the time im using manual mode)

i very apreciate your opinion of this please

in this web site i find it sample picture taken over night and also with described problem here is please have look at the full image there are colored points visible

and in this picture for example i cant see itany

why im thinking this could be something with camera? because those marks stays in the same place in other shots justlike dust

i can provide more examples of my picturesif any body need it

thank you igor

JimC May 20, 2006 9:42 AM

When you see pixels that are brighter than they should be, they are referred to as hot.

Hot pixels on longer exposures are normal.

Most modern digital cameras, including your E-300 have a Dark Frame Noise Reduction System built in to map them out on longer exposure.

What happens, is when Noise Reduction is turned on, the camera is actually taking two photos (one of your subject, and another with the shutter closed). That's why long exposures take twice as long with Noise Reduction turned on.

It then looks for hot pixels in the dark frameexposure (these are the only pixels that will be bright because the shutter was closed),and mapsout pixels in the same locations in the actual exposure of your subject (it replaces them with values interpolated from adjacent pixels). This is know as "dark frame subtraction"

But, the longer the exposure, the less accurate this type of system is. It's relying on hot pixels to be in the same place in both the actual and dark frame exposure, since the exposures are being taken at approximately the same time, with the sensor at approximately the same temperature, using the same exposure settings. But, when you get into very long exposures, you sometimes end up with pixels that are hot in the actual exposure, that didn't show up hot in the dark frame exposure. So, the system misses these.

Not too long ago, digital cameras did not have this type of system (you had to take your own dark frame exposure with the lens cap on, and map hot hot pixels yourself using software).

Make sure to turn on Noise Reduction if you want the camera to map out hot pixels on long exposures. That's what it's there for.

If you are getting hot pixels in the same locations, regardless of shutter speed, then they are considered to be stuck (always bright).

In that case, your camera has a feature that is designed to detect them and map them out by replacing them with values interpolated from adjacent pixels, regardless of your shutter speed.

To use this feature, select the Pixel Mapping menu choice under your Setup menu. The camera will locate any bad pixels and update a table in EEPROM so that they will no longer be visible.

isd May 20, 2006 10:28 AM

ah thank you so much:D JimCfor a nice explanation i was all ready woried if anything goes wrong with my camera, could you please just confirm what are you see in picture taken by my camera is hot pixel you are talking about? so i start my research to understand beter this issue please.

and just to be sure in one word iunderstud: for long exposure i should use noise reduction on?

yes i remember to press few times Pixel Mapping when i get the camera but i tough nothing hapens so i just forgot about it and did not touched again

thanks a lot JimC i will never finded another way (im unable to read any instruction)

thank you igor

JimC May 20, 2006 10:36 AM

Yes, you have a number of hot pixels in that image. Again, they are normal on longer exposures. Pixel Mapping won't help these (because they will probably not show up on anything except long exposures).

Turn on Noise Reduction and your camera will try to map them out on long exposures. That's the entire purpose of this feature.

isd May 20, 2006 11:35 AM

many thanks JimC, after all i losted just one storm,:| hope i have another ocassion to take some lightnigs, thanks a lot i will remeber to switch on noise reduction on the night time

laters igor

zoegy73 Jun 2, 2006 10:31 AM

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First time I tried long exposure (14s @ ISO 100), I got many nasty hot pixels and the NR was on. I run pixel mapping once and this is a result, a 125.93" bulb shoot :

isd Jun 4, 2006 8:33 AM

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hello zoegy73 from the time that JimC told me about existence of NR i have no more problems:blah:with pixels. but still have problems withreading instructions...

ps. it is cool picture of yours, where is taken? for me seams like a london town?

laters igor

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