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Why would you invest in an eyepiece combo that gives an 8.0-8.5mm exit pupil? It will reduce the effective aperture of your scopes by perhaps 20% - 30%. Yeh, I know, it gives a widest fov. BUT, it makes a 15" scope a 11-12" scope. It'll turn your 10" scope into a 7" scope.

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That's why I prefer a short focal length refractor as the next step up from binoculars in terms of fov and magnification.

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Well yes, but ...

Why not just use shorter focal-length eyepieces on your BT-100 to achieve the same effect? My experiments hint that at identical magnification, binoculars are pretty nearly equivalent in how much you can see (though of course not in subjective experience) to a telescope of identical light-gathering ability. In other words, when used at not-very-wide exit pupils, 100-mm binoculars are more or less equivalent to a 140-mm telescope running at the same magnification.

True, the 13-mm Ethos is physically too big to use in a binocular telescope, so you'd have to settle for the 82-degree AFOV of the Nagler rather than the 100-degree AFOV of the Ethos. But is that such a greivous loss?

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It seems that a refractor and binos complement each other very well.

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Odd! I would say that they complement each other particularly poorly. Put another way, of all conventional telescopes, short-focus refractors are the instruments that most nearly overlap the capabilities of binoculars. Not surprising, considering that binoculars are simply pairs of short-focus refractors.

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Hi Tony

In another thread, I pointed out that my BT100s with 1 1/4 inch eyepieces have two limiting factors....they are f/6 and limited to a 27mm field stop due to the 1 1/4inch format.

This, in effect limits the apparent fov/magnification/eye relief possiblities....my 24 Pans are about as good as you are going to get. This also means a 2.7 degree fov and only 4mm exit pupil.

With the 140mm Petzvel (800mm) and the 2 inch 40mm UO MK70, I can reach lower magnification (20x) and fov (3 1/2 degrees) and 7mm exit pupil. This allows my to view large extended low contrast objects like the Veil in its entirety.

So, in fact, a short focal length refractor and large aperture binoculars do complement each other quite well.

Again, I have the 10 or 15 inch reflectors equipped with a Paracorr to cover the high magnification, high resolution duties.

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10x50 Fujinon FMT-SX binos
15x70 AP binos + Paragon p-mount
Oberwerk 100BT 45 degree + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/6.5 Antares achromat
150mm f/8 homemade achromat....EE Barnard MW Sweeper
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery split tube
35mm Pan, 26mm Nagler, 17mm Nagler, 13mm Ethos, 8mm Ethos

Member IDA

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