DSLR ISO setting for DSO

[zakkhogan]

Hi all,

what sort of ISO setting should i be using for DSO's.

i went out last night (1st light with new scope) took some images of The Hershel Cluster and the Ring Nebula, but wasnt till this mprning when processing my images that i realises that i took them at ISO 100.

For dso shouldnt it be much higher?

These are my 1st real attempts at DSO's, i am please with the results,

CPC800, no wedge, and exposure times are 53sec for hershel and 27sec for Ring

Many Thanks

[Pete Presland]

i would have thought around 800 would be nearer what you need

[zakkhogan]

Thanks bunny,

As im new to all this, 800 ISO means that it should allow more light into the sensor, therefore capturing more light more quickly?

[Dave Smith]

I also use 800 iso as standard but take as many subs as you can to get a nice clean image.

Dave

[dph1nm]

As im new to all this, 800 ISO means that it should allow more light into the sensor, therefore capturing more light more quickly?

No, changing ISO does not affect the amount of light detected by the sensor. This is fixed whatever the ISO. This seems to confuse a lot of people, so you are not alone. However, certainly for Canon cameras, lower ISO has higher read noise, so for short exposures low ISO not optimal.

NigelM

[beamer3.6m]

ISO 800 is common.

If you go higher your images can become noisey.

The trick is to capture as many images as possible so that overall the total imaging time is as high as possible so for example 10 x 2 minute subs = a 20 minute total exposure. For great images you really need to be in the hours which is one of the reasons why this is such a dark art.

[RAC]

This is a very interesting read.

http://www.stark-labs.com/craig/articles/assets/CanonLinearity.pdf

[earth titan]

800 here. I then adjust the exposure to suit.

[dph1nm]

This is a very interesting read.

Yes - slightly alarming if correct.

I note that in the subsequent Cloudy Nights discussion he changed his ISO recommendation to 800-1600.

NigelM

[Shibby]

Interesting reads... I think the net result is I'm good to stick with ISO-800! For narrowband, it seems ISO-1600 might offer a slight improvement at the fainter end (given that star colour is not an issue)?

No idea what to make of the histogram shift being applied pre-RAW. What are the implications?

[dph1nm]

No idea what to make of the histogram shift being applied pre-RAW. What are the implications?

The change in gain would be bad news for stacking frames with different exposure times (and potentially those with different ISOs, seeing as the shift with exposure time appears to be different at different ISOs). The removal of the dark signal may not matter, providing it just depends on exposure time.

NigelM

[zakkhogan]

so this is what happened..... went out last night... took 40 images, + darks, dead chuffed with myself.

Then.. slightly disappointed when trying stack the images, then i realized i did the whole thing at ISO100

such a rucky

[themos]

We've all been there...

[zakkhogan]

this is what i achieved at 100ISO, better luck tonight i think

[Shibby]

Unlucky, sounds like a me thing to do. I remember leaving the Bahtinov on one evening...

I think you could expect a little more out of that stack. If you can upload the stacked tiff (e.g. dropbox) then I can have a little look if you like?

[zakkhogan]

Unlucky, sounds like a me thing to do. I remember leaving the Bahtinov on one evening...

I think you could expect a little more out of that stack. If you can upload the stacked tiff (e.g. dropbox) then I can have a little look if you like?

Thanks for the offer, the problem was that deepsky stacker would register the images so i had to do it manually in photishop, nevermind.

went out last night, spent an hour out, took 26 shots + 4 darks at 800ISO and this was the result,

Each frame was 15sec, total stack size was 18 frames + darks, combined was just over 4 mins.

think im going to take some more shots tonight and see if i can build on the image.

[Shibby]

Coming along nicely... DSS has a "select stars" mode that allows you to manually enable some of the stars it was not sure of during registration. This can help you get up to the threshold needed for stacking (12 stars, I think?)

[zakkhogan]

hows this..... i took another 61 shots tonight at ISO1600, added them to the 26 i took at ISO800, run them in DSS, some slight curvs, gamma and contrast adjustments in photoshop and this is tonights results pleased with myself i am.....

DSS stacked 68 out of 91 frames (inc dark) for a total exposure of 13m 47sec

[Black Knight]

I'd say that's coming along nicely ....