# Using Fuji lenses for astrophotography

Started 2 months ago | Discussions thread
Re: Using Fuji lenses for astrophotography
1

TOMMMMMM wrote:

getochkn wrote:

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Nice photo! But that doesn't really answer the question...

I think the reasoning is that a longer focal length at a similar f stop as a wide angle will have a larger area open to receiving light.

F-stop = focal length/aperture diameter. As the focal length increases, the aperture diameter must also increase to keep the f-stop the same. Since the area for aperture diameter is calculated as (pi*diameter_aperture^2)/4, you can see that a focal length twice as long lets in 4 times the amount of light (aperture area is 4 times larger).

This is true, but I feel the need to add an important correction here:
The bigger physical aperture gathers more light per light source in the frame (for example a single star). A 35mm f/2 still gathers just as much total light as a 200mm f/2, though, because the wider field of view takes in light from many more sources, compensating the smaller aperture diameter.

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