Originally Posted by Yorkshiretea
OK I'll bite.
The question was does light effect it, I'm saying yes it does because there's a soft machine and another lens behind it. I'm not saying the lens changes. Diffraction changes the quality of the image, targets in dark often appear softer and targets on the horizon with the sun low will white out. Are they not examples of light effecting it?
You're a camera guy, you must have stopped down a lens to get a better image surely?
Yes. Which is why i said heat has an effect on the scope
. Light has an effect on how you percieve contrast which detemines focus
. Light doesn't affect the scope, it affects you
(or can affect you depending on how you focus)
You stop a lens down to get a deeper depth of field. Normally camera lenses are better when put down a stop or two, but beyond that there's no gains and the picture often gets worse due to diffraction when you stop it down more. But don't confuse stopping down with the light in the scope. Stopping down is the same as putting a butler creek on the front with a hole in it. But unless you do that your scope has the same aperture in the dark as it does in light. It's depth of field does not change.
A darker target doesn't have a deeper depth of field than a bright one. What happens is the darker colours means you have less contrast, less tonal range, to pick differences out with. The eye uses contrast in the same way as a digital camera to determine focus. Drop the light and it struggles to determine focus as well just like a digital camera does. That's why digital cameras use things like red lights in low light to help pre focus.