ISO Settings

[gonzostar]

I was wondering is there a general rule for ISO settings?

For example star clusters lower then globular clusters, nebula.

Should then galaxys be higher at say 800 or 1600. 

Does it also depend on seeing conditions and or light pollution/

I have a canon 450d camera with a CLS filter.

Thankyou

Dean 

[spaceman_spiff]

I stick to the same ISO for all DSOs - ISO 800. I can then easily use my dark library (which is also using ISO 800).

The ISO is basically the signal gain applied to the sensor. In other words, taking the same exposure at ISO 400 and then increasing the brightness on the computer will give similar results to an ISO 800 image of the same exposure - the signal:noise ratio is the same (or very similar).

The only time I use higher ISOs is when I am using my Bahtinov mask or trying to locate a dim target on the camera sensor. I don't think seeing conditions or LP should influence the ISO settings.

At least, that is my understanding.

Dan 

[gonzostar]

As i am not guiding at the moment i am restricted to 2 min light frames. I was thinking that increasing iso would give me more stars for DSS. As i live under moderately LP skies, I was thinking ways to increase my chances of good light frames. But as they say i suppose AP = absolute patience  

[spaceman_spiff]

I think that increasing the ISO may help you see more stars on the unmodified photograph, which is useful in the field but for DSS, I think that increasing the ISO may not matter as much (although I have not tested this theory myself).

When you increase the ISO the stars do get brighter but so does all the background noise and light pollution. In terms of the detectability of the stars in DSS, there is little difference between a 2 min exposure at ISO800 and a 2min exposure at ISO1600. I guess at higher ISOs, you can see straight away  where the limit of detection is for the faintest stars which is an advantage. 

Regarding increasing the chances of light frames, guiding really does make a difference! It frees you from the shackles of a perfect polar alignment! I was in your position a year or so ago, he only step up I could see was to go for guiding. Once I got the hang of my Synguider I never looked back .

 

[gonzostar]

thanks for that Need to be more patient with synguider then, I have found it a challenge. 

[Tinker1947]

Stick with one ISO makes life a little easier with setting up and Dark Frames ect,  a simple Finder scope or ST-80 with a CCD in may be a better option as mine worked very well at the first go.........

[gonzostar]

Yes i think i should stick with iso 800 for deep sky objects.

Although i did try iso 1600 on m101, 2min subs unguided. To my shock and horror DSS stacked 28 out of 40 frames. However when processed on gimp it looked "there" however a lot of background noise and pollution.  

To embarrassed to put on SGL,  looking at how fantastic other pics are on this site