Quote:
Originally Posted by Brycepj
Following on from the below post can anyone tell me "what happens when you push the mag. Up beyond a scopes capability". ? Am I correct in the assumption that you won't be able to obtain a clear focus? Or unable to focus at all?
Let's say using the sw 80/400 f5 and I use a 6mm Ep in a 3x Barlow.would that work.?
Peter
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Very good question Peter
For any given scope, there is a limit to which the magnification can be pushed before the image deteriorates. Often that is given as 50x per inch of aperture. But that is a theoretical limit, meaning that it assumes perfect optics, perfect collimation, perfect seeing. Given all those factors it may be possible to push a 3" scope like yours to 150x, but the combo your are suggesting gives a power of 200x (400/6x3).
Essentially, the more magnification you use the more you are also magnifying the atmospheric distortions. Also as you magnify you reach a point where you make the image larger but the resolution limits of the scope (which is mainly a function of size) means you reveal no more details. This is known as "empty magnification".
Experience tells us that 10x or 20x per inch is more useful. So the 67x revealed by your 6mm EP is more likely to give satisfying results.
Cheers
Malcolm