iso and exposure question?

[jonnydreads]

to photograph something as distant as m42 nebula, would you set the iso low or high?

if your taking a photograph and object is very faint and very distant then I would have assumed that the iso would be set high because it would need as much light as it could get hitting the sensor?  am I right in thinking this? 

would setting the iso low but make the exposure time long compensate for the lack of light getting to the sensor?

ive been trying to get information to stick to my tiny brain but it just seems to want to learn about football transfers 

[Whistlin Bob]

@jonnydreads setting the iso high doesn't cause more light to hit the sensor it just causes the sensor to react more to the light that's hitting it. That may sound like a good thing, but it actually decreases the accuracy with which the camera captures the colour of that light and increases the noise.

Most camera's have a sweet spot which balances the ISO with the time taken to capture and noise generated. I've got a Canon 600d and that sweet spot is ISO800.

[jonnydreads]

I bought a canon 300d, basically because it was quite cheap, I know nothing about photography but would like too...

yes sorry I understand that I think, I'm thinking about distances and brightness, because obviously we are talking about vast differences in distances for different objects in the sky, would say taking a photograph of the horse head have a different iso to say Saturn? because of the distance and brightness, or are they all so far away it doesn't really matter...... I think I'm not typing this out so well with what I actually need to ask but oh well.... ?

[jonnydreads]

I've got so many questions I need answering about astronomy and telescopes I actually don't know where to begin ??

I see forum conversations on this website and I literally think If I would have discovered the rosetta stone I would have deciphered that quicker.....

I've made a decision to learn 2 things a day about it ?

[wxsatuser]

The general rule is low ISO for bright objects and high ISO for dim objects.
For most Canon cameras this equates 400 bright and 800 dim, more modern Canon's can do 800 bright 1600 dim.
I started with a Canon 60Da and that easily did 1600 ISO on faint nebulae.

Of course there are other things to take into consideration, read noise at these ISO's and the QE of the sensor.

[MartinB]

It can get a bit complicated with ISOs.  At it's simplest iso relates to the amount a light signal is amplified, it's like turning up the brightness.  The downside of this is that something called the  dynamic range is reduced, your ability to manipulate the image with processing is much reduced.  Astro images typically need a fair bit of processing, brightening dimmer areas of a image whilst avoiding saturation of brighter parts such as stars.  It is a good idea to pick the lowest ISO you can that doesn't need excessive manipulation in the processing stage.  Some chips are "iso equivalent" which means that you can shoot at 100 iso and brighten it up to the same image that would have resulted from iso 1600.  However most Canon chips aren't iso equivalent and brightening from 100 to 1600 can lead to some unpleasant effects in darker parts of the image.

So go for the longer exposures at lower iso if you can whilst making sure you don't have to brighten your image excessively when it comes to processing.  This will involve trial and error!

[Rush]

Well, EOS 300 D in particular has a DIGIC sensor with maximum light sensitivity  at ISO 800. U cant  hike it further than ISO 800. 

But its  sufficient to Image bright objects like M 42 , M31. etc..

Surface brighness of the object plays a role (Dim & Bright Story). With 300 D unmodded or modded , its advisable to start with ISO 400 @ 300 s to presrve the core and eventually for the nebulosity  ISO 800.

 It is easy to strech unblown frames , gives u room  to strech further without danger of clipping. So keep the ISO low and increase the exposure time. If the Frames come out noisy reduce the exposure time. 

Some old sensors are less noisy and  rich in  colour. Shoot as  many as you can , 30, 60, 120 Frames. Slowly u will get the feel for ISO Settings.  DIGIC,DIGIC III,DIGIC 4,DIGIC 5+ all  show different light sensitivity.

Canon EOS sweet spot is somewhere in between ISO 800 /ISO1600 for APS-C sensors. Hope this helps.

CS

Rush

 

[jonnydreads]

I've been messing around with it today shooting pictures of birds just to get some sort of experience... i cant find how to lengthen the exposure time... I've seen on YouTube videos of people showing you how to change exposure time but i havent been able to change that yet in manual settings... ? I just gonna keep clicking buttons and reading up...its like anything, I've just gotta do it and have a go. ?

[wxsatuser]

Manual should go to 30seconds, if you want more you will need bulb mode and a shutter release/intervalometer.

[Alien 13]

This link gives a good indication of the best ISO range for Canon cameras for AP but does not include the 300D although I would expect the 350D which is listed to be similar.

http://dslr-astrophotography.com/iso-values-canon-cameras/

The only Canon camera that breaks the rules is the 80D which is a Nikon in disguise 

Alan

[dannybgoode]

Look at @vlaiv excellent response to a similar question here. There’s more to it than just high or low. 

https://stargazerslounge.com/topic/329518-what-iso/?do=findComment&comment=3589330

[Rush]

Page 80 of I. manuel describes bulb settings ( check on internet )

Similar topic :  SGL

300D Bulb Setting, EOS Utilty, and Timed Exposure Sequences

By michael8554,  May 25, 2015 in Discussions - Software