The Recent F/stop Controversy

Started 1 month ago | Discussions thread
fferreres Senior Member • Posts: 1,510
Re: Really?

LoneTree1 wrote:

fferreres wrote:

By the way, astro folks have been doing this more-or-less since the dawn of telescopes. Telescopes are almost always sold in terms of aperture diameter rather than focal length, f-stop and format size.

The Alien Connection. And also, many telescopes don't have diaphragms. And thus it COULD make sense due to the lack of diaphragm which would ensure it's shape always be a circle.

Telescopes don't have diaphragms because the idea is that you collect as much light as possible in order to best see the object and (if the scope is diffraction-limited) the larger the aperture, the higher the resolution, which is proportional to that aperture. Camera lenses, few being diffraction-limited wide-open, usually need to be stopped-down to achieve the sharpness image with the highest contrast. Having said that, many telescopes now sold are much faster (shorter f-ratio) than in the past. This is because of imaging requirements, the need for wider fields of view and the availability of exotic glasses to control aberrations.

Most interesting fact in the thread. I suspected it but it was a guess as I haven’t had a friend or anyone introducing me to the topic.

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