Aperture vs ISO in astrophotography/ astro-landscape

Started 2 months ago | Discussions thread
JimH123 Veteran Member • Posts: 3,136
Re: Aperture vs ISO in astrophotography/ astro-landscape

Kai West wrote:

Hello there,

I couldn't find a proper answer to this question so maybe people with more experience can help. I own the Samyang 18mm F2.8 and have done a few decent astro-landscape shots but was wondering about upgrading to either a wide angle zoom or a wide angle prime and this is were my question comes from.

Given the amazing ISO performance of modern cameras what gets you better results (better in this case means more contrast in the milky way for example)

1. A F1.8 wide angle lens shot at let's say ISO 4000 with an "old" Sony A7


2. A F2.8 wide angle lens shot at ISO 10000 or higher with a "new" Sony A7III

I am asking about two different cameras in this case as I plan to retire my Sony A7 in the next 2 years (still going strong) but the lens will be something I don't plan to retire ever. Therefore the price for the lens in this case is irrelevant. The prime lens disadvantage is that it requires an additional filter holder and I like to pack light.


First - Aperture. Ideally you want as wide open as possible. But wide open may show various kinds of distortion such as CA, coma and astigmatism. Prime lenses usually out perform zooms. If you are happy with your current lens, you risk not being happy with another lens.

ISO - As you raise ISO, you see more stars. But, stars saturate sooner and you lose color. You have to decide what is more important to you.

Camera - The A7iii has a real advantage in ISO and lower noise. Some noise can be reduced with stacking and noise removal software such as Topaz Denoise AI. Or DxO DeepPrime. Or the new ON1 No Noise.

The A7iii certainly will outperform the A7. You can keep using the lens. And then find out how high to raise the ISO that produces what you are happy with.

As for going to f1.8, many lenses just aren't sharp at f1.8 and you end up backing off a stop or two.

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