Canon ISO

[michael8554]

I usually use 800 on my 500D but have been trying 1600 at half the exposure time.

It's just a bit too noisey, so is there a way of getting an in-between value, say 1200, or should I just expose at 1600 for say a third of the time?

Michael

[Alien 13]

There might be a menu setting somewhere that lets you change the ISO increment from 1/2 stop to 1/3 stop this should give you the extra range you need.

Alan

[alacant]

6 hours ago, michael8554 said:

1600 at half the exposure time

On my 700d, 800 gives the lowest noise. 1600 will collect the same amount of light as 800 so perhaps you should keep the exposure similar to make a fair comparison (?). HTH.

[StuartJPP]

Always a contentious area.

Twice as noisy at ISO1600 vs. ISO800 but at half the exposure, to be expected since only half the number of photons hit the sensor. As mentioned above you'd need to stack 2 of your frames at ISO1600 (at half the exposure time for each frame) for a fair comparison of noise.

Total exposure time is what counts, there's probably not much difference between ISO800 and ISO1600 to be honest as long as the exposure/histogram is optimal (i.e. don't clip the highlights/stars in the ISO1600 mode) and are well away from the left side of the graph.

There are texts on the web that say that 1/2 or 1/3 stops on ISO should be avoided so I'd stick to either full stops of 800 or 1600.

[Alien 13]

18 minutes ago, StuartJPP said:

There are texts on the web that say that 1/2 or 1/3 stops on ISO should be avoided so I'd stick to either full stops of 800 or 1600.

Thats interesting to know, must do some digging on this.

Re the OP noise vs ISO it is never a straight line so it can be camera specific coupled to sky quality as to what value will give the best results.

Alan

P.S. initial searches on the avoidance of 1/2 or 1/3 stops seem to show only old topics so not sure if they are still applicable especially with "ISO less" type cameras like the very new Canons and most Nikon's.

[michael8554]

Thanks all for the replies.

Hadn't thought of exposure comp, I will give that a go.

Michael

[Adam J]

On 18/06/2017 at 01:57, michael8554 said:

I usually use 800 on my 500D but have been trying 1600 at half the exposure time.

It's just a bit too noisey, so is there a way of getting an in-between value, say 1200, or should I just expose at 1600 for say a third of the time?

Michael

Never use intermediate ISO settings as these are not true native settings of the amplifier and as a result are simply software extrapolations of the setting below. There is no benefit to applying what is effectively a firmware stretch of the RAW file prior to stacking the image and in fact its is likely to reduce image quality. 

[StargeezerTim]

I'm sure someone will put me right, but you will have more noise if you half the exposure time. Try upping the iso and using the same exposure (taking care to see the histo is not too far too the right). Personally, i find there is not much difference in noise between 800 and 1600 on my 100D and 1200D.

[michael8554]

6 hours ago, StargeezerTim said:

I'm sure someone will put me right, but you will have more noise if you half the exposure time. 

My understanding is that noise generated by the camera increases with exposure time, but not necessarily in a linear fashion.

Similarly the noise from increased ISO.

So half exposure same ISO should be less noise, not more ( signal to noise ratio is another subject....)

I've had good results at ISO 1600 and 3 min exposures since opening this thread.

In this cloudy weather spoiled 3 min exposures are less of a disaster than spoiled 10min exposures, and stars are tighter due to less cumulative guide errors.

Of course there is time lost due to more dithers and guiding recoveries.

Michael

[StargeezerTim]

6 hours ago, michael8554 said:

 

I've had good results at ISO 1600 and 3 min exposures since opening this thread.

In this cloudy weather spoiled 3 min exposures are less of a disaster than spoiled 10min exposures.

Michael

Agreed! 

[Robd]

I use a Canon 1000d, hence a friend passed me the following links regarding best iso to use

http://dslr-astrophotography.com

There's an interesting article on the techy side of how setting the ISO affects astrophotography images...
http://dslr-astrophotography.com/iso-dslr-astrophotography

but if you just want the bottom line you can look up your Canon DSLR model and find the optimum ISO setting for astrophotography...
http://dslr-astrophotography.com/iso-values-canon-cameras
I hope that they are of some help.

Rob

[Alien 13]

28 minutes ago, Robd said:

I use a Canon 1000d, hence a friend passed me the following links regarding best iso to use

http://dslr-astrophotography.com

There's an interesting article on the techy side of how setting the ISO affects astrophotography images...
http://dslr-astrophotography.com/iso-dslr-astrophotography

but if you just want the bottom line you can look up your Canon DSLR model and find the optimum ISO setting for astrophotography...
http://dslr-astrophotography.com/iso-values-canon-cameras
I hope that they are of some help.

Rob

I have looked at these before but my 80D doesn't seem to fit the standard Canon pattern regarding best ISO.

Alan

[michael8554]

Thanks for the links Rob

Interesting that the figure for my 500D is ISO1600 - which is the setting I came up with at the start of this thread.

And also interesting was ISO400 for the 450D I had before - I always ran that at ISO800 as I believed that was the perceived wisdom.

Michael

 

[dph1nm]

13 hours ago, michael8554 said:

And also interesting was ISO400 for the 450D I had before - I always ran that at ISO800 as I believed that was the perceived wisdom.

I think some of the numbers suggested are just odd. ISO200 for a 1000D? - no thank you, the read noise is huge.

NigelM

[tooth_dr]

1 minute ago, dph1nm said:

I think some of the numbers suggested are just odd. ISO200 for a 1000D? - no thank you, the read noise is huge.

NigelM

I too have a 1000d,and it does say 200 or 800 though.  Have you tried it at 200?

[Alien 13]

The canon 80D is quoted best at ISO 200 or even 100 and some quick tests suggest they might be right.

Alan

[Adam J]

2 hours ago, tooth_dr said:

I too have a 1000d,and it does say 200 or 800 though.  Have you tried it at 200?

Problem is that the 1000D is only a 12bit camera so if you use a very low ISO (less than unity gain) you will end up occluding colour information in dim targets as there will be no fidelity between the channels. You will have the same issue with High ISO trashing colour in bright targets. Overall the 1000D is not great at color come to think of it (having owned one)..but sticking around ISO800 seemed to work well for me with the exception of some targets like M45 when I dropped it to ISO400. Its not all about pure signal to noise ratio.