What is the optimal ISO setting for my camera, deep space imaging

[aljo2345]

Hi anyone, just getting started with Asrophotography. I am curious to know what the optimal ISO setting is for my DSLR Canon 400D for deep space imaging, i want to minimise the exposure/tracking time but I dont want the images to be too grainy either, my cameria is currently set at 1600 ISO.

Basic Setup: Meade LX90 8" with wedge, Canon 400D, off-axis guider, Hirsch Foal 6.3 Focal reducer (which i have not tried out yet)

best

Alex

[Meru (Michael)]

Hey Alex,

Its a really tricky question because every camera and telescope is different. With my old DSLR I used to use 30 seconds tops @ISO1600, with my new camera I can go 1 minute at ISO3200 or above! It's something you will have to judge with trial and error (It's pretty easy though, keep increasing the settings until you notice alot more noise than the DSO)

[nebulosity. (Jo)]

For minimum exposure time I think ISO 1600 would be alright, I always used 1600 with my 350D.

Cheers
Jo

[Screwdriverone (Chris)]

Hi Alex,

I used to use ISO 400 for 5 minute shots and ISO 800 for 3 minutes to minimise noise and depending on how good my guiding was. For short exposures you can push it to 1600 or more but you will introduce a lot of thermal noise, which defeats the purpose. I was using a 1000D and when I built a cooler box which dropped the sensor temp by 10 - 11 degrees, it made a LOT of difference to the result.

Not sure of the thermal or noise characteristics of the 400D, but have a play and see the difference you will get. ISO 400 was my sweet spot on long subs.

Cheers

Chris

[rmuhlack (Richard)]

I ran some experiments with my 400D (see here) at different ISO settings and temperatures and found ISO1600 gave the best signal:noise ratio at all sub exposures. Sub exposure is selected based on the ambient temperature

[rcheshire (Rowland)]

Not to introduce confusion, but light pollution may affect iso setting. My experience is similar to Chris. With a 200mm lens 3 - 3.5 mins at iso 400 produced the best dynamic range under outer suburban skies - M8 is visible, while the LMC and SMC are barely discernible, if that makes sense. Does best SNR equate to good dynamic range ?

[aljo2345]

Thanks everyone, that helpful (like your shots Richard). will have a play around with the ISO setting and exposure times with the focal reducer this time and see what i come up with.

What are peoples experience with off-axis guiders beside back and neck strain. How much drift in a guide star is permissible using a in 6mm reticle with scope set at primary focus (focal length 2000mm)


thanks again


Alex