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It’s also worth noting that when I connect my DSLR to my (dumb) Mewlon 180mm F12 ‘scope, the effective viewing aperture is F12 at prime focus and F19.6 with the Tak x1.6 extender.
With a DSLR lens, light throughput to the viewfinder is at the maximum aperture of the lens, as the camera meters the scene wide open and only stops down at the moment of exposure.
So, if you fit an F2.8 lens, then you are essentially viewing at 4 to 5 stops wider than my F12 ‘scope, even if you have set the aperture to F22.
Cheers
Dennis
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