ISO Rating

[robindurant]

Hi

I am beginning to get to terms with astro photography using my Canon 350d. I have been taking pics of Jupiter using an extension containing a 26mm EP. The images do show faintly the cloud stripes but the image is quite fuzzy, mainly due to the bad sky I am taking them through. My Camera is set at ISO 1600 so as to use the fastest shutter speed as possible. Is my thinking wrong, should I be using a lower ISO rating, would this give me clearer images. Lots of questions but only by asking will I be able to get the answers to enjoy what must be the greatest pastime or hobby ever.

Robin

Celestron 8iSD - Canon 350D - Mad Red Setter

[Astroman]

I'd lower the ISO to something like 400 to image Jupiter. The higher ISO rating is good for long exposures of faint objects, but it introduces a lot more noise. Jupiter has plenty of light, so a lower setting may work better.

[Kaptain Klevtsov]

Higher ISO ratings inherently introduce noise and mess with your image, so the best advice is to go with the lowest ISO that you can get away with.

In oversimplified terms what the ISO does is bit-shift each pixel, so that the difference between ISO 200 and 400 is done by a binary X2. That means that the chip picked up a binary value of e.g. 0010000 and the conversion moves it to 0100000 by shifting the bits leftwards one space. You get no more information but any noise information gets magnified by the same amount as the image gets boosted.

Modern DSLRs have fancy software to cope with the noise but it can't get rid of it as the chip can't tell the software which is noise and which is signal.

It's a matter of research and / or testing to find out which ISO does it for the given situation.

Captain Chaos

[FLO]

Cranking up the camera's ISO is similar to increasing the volume on an amplifier.

On an amp - you hear hiss.

On an imaging chip - you 'see' the equivalent in the form of messy/grainy noise.

[Astroman]

Higher ISO ratings inherently introduce noise and mess with your image, so the best advice is to go with the lowest ISO that you can get away with.

Captain Chaos

Yeah, that's kinda what I said....

[Kaptain Klevtsov]

I know Astroman , but I was less eloquent and more verbose. Where are those widefield pics that we're gagging for?

Captain Chaos

[OXO]

You can use higher ISO rates so long as you collect enough frames for stacking this will improve the signal to noise ratio thus eliminate most of the noise, i had to do this a few years back as i didn't have drives on my mount thus higher iso's were needed so to stop blurring by exposure lenghs...

James

[Astroman]

I know Astroman , but I was less eloquent and more verbose. Where are those widefield pics that we're gagging for?

Captain Chaos

Yeah right, change the subject. They're coming, they're coming....

[OXO]

Going off topic a little here?