Quote:
Originally Posted by Don Pensack
It's effect on back focus is that there is a specified distance at which the reducer has the 37% reduction. Farther back, the focal length of the scope shortens. For instance, with a 2" star diagonal, the f/ratio could be f/5.5 or even f/5. It doesn't change the overall amount of focus available in the scope, though.
Eye relief is not affected, as far as I know.
I used one for 11 years and never noticed that focusing became more sensitive. I did increase the focus knob diameter to 64mm, however, to slow focusing down and make fine focusing easier. That larger focus knob also made focusing at f/10 easier.
A focal reducer does NOT mean the scope has more illumination at the edge of a particular true field, though. If the scope starts displaying significant vignetting with a 1.2 degree field at f/10, it will at f/6.3 as well. So a focal reducer doesn't allow any larger a maximum possible field in the scope than the scope can have without it. it does, however, allow that maximum field with smaller, lighter, and less expensive eyepieces. You could easily spend as much for one 2" long focal length maximum field eyepiece as you would for a whole set of decent 1.25" eyepieces.
Don
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Just worked out the effect of the f/6.3 on my current eyepieces and it brings them right back to almost exactly what they were on my old scope. So I am sold. For the future I'll definitely try and shift my EPs to ones more suitable for the new scope, but for the meantime the focal reducer will be a bl**dy cheap way getting the the useful magnification range back with what I have. Especially as I've found somewhere in the US that will ship it out (new) for almost 1/3 of the cheapest price I can find in Australia. What a crazy system they have to hike stuff up that much here (the Australian site even claims it is 40% of the full price of AU$600 - vs <US$150 overseas).