DSLR F number question

[Keithp]

Hopefully, if they've got the weather right today I will be setting up tonight:hello2:

Noticed that with the standard kit lens attached I can set to manual and change the F number on the lens to whatever exposure I want.

When I go prime focus and the adapters are in use this F number is set at 0. I can understand that because the body doesn't have a lens to talk to.

Does that mean then that the chip is receiving maximum exposure?

Sounds obvious I know, but just wanted to check.

Regards

All

Keithp

[Beyond_Vision]

It will be at the F ratio of the scope.

Regards

Kevin

[jgs001]

Keith, Whilst with the camera at prime focus, the body can't determine what the focal ratio is, therefore can't display it, the focal ratio is still a key point however. It depends on the scope what the ratio is, but is that scope not an f5 ? (The f stop on the kit lens is calculated in the same way as a scope and operates in the same way, focal length/aperture). The main difference between a camera lens and a telescope, you can adjust the aperture blades in a lens to stop down the lens, reducing the aperture below maximum and a telescope is fixed (unless you want to stick bits over the objective of course ).

[Keithp]

Got ya, many thanks both.

Now it's beginning to make sense.

Regards

Keithp