Quote:
Originally Posted by bmitchell82
howdie all, question for the more knowledgable.
having a big F ratio allows a narrow field view aka taking a photo you get more aparent resolution and more detail but at the expense of FOV.
having a low F ratio allows wide field shots although you can zoom in on things nothing beats Optical zoom over Digital zooming.
My question is if i where to stop down a 10" to say a 6" apart from the obvious factor that this will change the F ratio and subsiquently decrease the light capture, will this serve the same as having a high F ratio to do galaxy imaging or am i just reducing the light capturing ability with no gain.
Im just looking to confirm what CCD calc says. because the Camera FOV didnt change when the aperature decreased and F number where increased for a 40d.
Look forward to hearing what has to be said  |
FOV is not a function of f/ ratio. The FOV of a telephoto zoom lens does not change with changing aperture... it changes with change in focal length.
FOV is a function of the focal length of your scope and size of your camera chip (or characteristics of your EP). So stopping down a newt won't change FOV - but it will reduce resolution, light gathering power, etc.
Adding a focal reducer to a cassegrain type scope does change the f/ ratio, but it leaves the aperture the same... so it changes the all important focal length, and so changes the FOV while maintaining the light gathering power and resolution.
Perhaps this is where the confusion comes from?
If you want to do higher magnification imaging, increase your focal length i.e. add a barlow / Powermate.
Al.