First test with star traker - advices welcomed

[aster94]

Hello,

 

I finally bought an astro tracker (the star adventurer 2i) and a few nights ago I shoot my really first session during a bad night (I just wanted to test the equipment): I shoot almost against the full moon and I took only 30 lights.

 

So the result is quite good considering the conditions:

Stacked with siril with 20 darks, 80 flats and 80 bias, then little corrections in darktable

 

This is one of the lights that I used for the final image above:

120s, ISO 100

IMG_5440.CR2

 

And I took a few 60s, ISO 100

IMG_5439.CR2

 

So I would like to ask advices mainly to the RAW lights files

1) Do you think the 60s would have been better?

2) How do you understand when it's the "perfect" settings (ISO, exposure, ecc) for your sessions?

 

Best

[KP82]

Nice shot!

The shape of the stars shows a little bit of trailing, so shorter exposure to minimise tracking errors would be a good idea.

The optimal ISO (ie the one that yields the best dynamic range for that particular sensor in your DSLR) depends on which camera you have. Here is the link for Canon: http://dslr-astrophotography.com/iso-values-canon-cameras/ . You can find links for Nikon and Sony on the page.

As for optimal exposure you want the peak of the luminance histogram to be about 1/3 from the left. If you're using a camera lens, you can adjust the aperture to achieve this since your choice of exposure time is limited in order to minimise tracking error. If you're actually using a scope (fixed aperture), you might not be able to achieve it until you add guiding into your setup.

80 flats are kind of excessive. 20-ish would be enough. Also since you're using pretty short exposures, I'd recommend you take more darks to minimise the noise in the master dark frame.

 

Edited December 5, 2020 by KP82

[Scooot]

This is a useful calculator to compare settings. https://rechneronline.de/exposure/

If I were to take a 300 second exposure with my canon at ISO400 and baby tak, which is f6.2 with my flattener, the exposure value is -5. Roughly the same as using my 135mm lens at f2.8 for 60 seconds. However your local conditions will affect what you can reasonably achieve so as @KP82 above says, most try to get the histogram about 1/3 from the left.