Re: Aperture vs Focal Ratio to determine exposure time

Bill Long

When I posted the data on this thread (I am the OP) I was just trying to show the difference between a 130mm aperture refractor at 1000mm focal length, and a 254mm aperture Newt at 1000mm focal length, on the same target with the same camera (and of course my trusty AP1100 mount, but that isnt relevant). I had no idea it would spark so much discussion about the topic, although a lot of it has been very interesting to see unfold. The idea was to show newer folks what happens when you simply change the aperture and hold all of the other values constant.

From: ap-gto@... on behalf of pnagy@... [ap-gto]
Sent: Saturday, May 12, 2018 1:17 PM
To: ap-gto@...
Subject: [ap-gto] Re: Aperture vs Focal Ratio to determine exposure time

Are you using same camera at F/10 and F/2? If you are using same camera, I find it hard to believe you get similar performance at similar exposure times at f/10 and f/2. If you are using different cameras with different pixel sizes which changes image scale, then I can believe it.

I find Stan Moore's article very misleading and poorly written.


---In ap-gto@..., wrote :


I’ve been researching this recently and found this article by Craig Stark that I also posted in the EAA section of CN.  I was interested because I found that using my C11 at f/10 versus f/2 with Hyperstar doesn’t require much more exposure for the same object and certainly not 25 times more.  Stan Moore also has an article referred to in Craig’s article that states f ratio doesn’t matter for digital cameras as long as the signal stays well above the read noise.  It’s aperture that makes the difference.  It’s different for film.  Great topic.  I’ll be interesting to see what others think.

Join to automatically receive all group messages.