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One eye good - two eyes much better


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When focusing my Celestron 15x70s I adjust the main focus wheel looking through my left eye with lens cap on right lens or right eye closed. Then I vary diopter adjustment on right side with left eye closed or lens cap on. From my most recent eye test, my left eye distant vision is pretty close to perfect, my right eye needs +0.25 diopter spherical and +0.75 cylindrical (for astigmatism) correction. I have a very stable tripod/trigger-grip ball-head mount and I allow time for vibrations to damp down. When I subsequently view my target (planet or cluster) my (subjective) judgement is that I see more than twice as much with two eyes than with one alone. Am I likely to be disappointed therefore when eventually I get a telescope?

Ed

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It's different but not disappointing - depends on a lot of stuff though including: which scope, which eyepiece, and what the see'ing is doing. But if you enjoy using two eyes then you might be well advised to research use of bino viewers with refractors and cassegraine scopes. It's a very immersive experience with the right combination of gear. :)

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When I subsequently view my target (planet or cluster) my (subjective) judgement is that I see more than twice as much with two eyes than with one alone. Am I likely to be disappointed therefore when eventually I get a telescope?
In terms of what you can see, a telescope needs an aperture of about 1.4x that of an equivalent quality binocular to show you as much. Your Celestron 15x70 has an effective aperture of about 63mm (it is stopped down internally), so a telescope with a true aperture of approximately 90mm should show you as much.

Whether you like the monocular view as much as the binocular one is a matter of personal taste: only you can know that. If you want to use a binoviewer with your telescope to reintroduce the binocular experience, remember that you will need to double up on your eyepieces and that many binoviewers will limit your true width of field to significantly less than that of the equivalent binocular.

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Thanks for the encouragement brantuk and the technical update tetenterre! Presumably the 1.4 factor comes from a simple doubling of the light gathering area of objective lenses, but is there also some psycho-visual 'gain' from using two sets of retinal sensors summed through two areas of brain (visual cortex)? Sorry I'm a bit out of my depth here (as an engineer not a neuro-scientist)!

Sent from my iPad using Tapatalk HD

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I do not quite agree with Steve on the aperture issue. I think my 80mm APM shows a touch more than the 15x70 Helios Apollo, but that might be down to the higher magnification I was using, which darkens the background. I should test that with the 31T5 in the APM, which will give 15.5x. A short-tube refractor with 2" EPs will also show a wider field of view (5.3 deg @ 15.5x for the APM 80mm vs 4.4 @15x for the Helios Apollo). A really big scope shows a lot more in a very much smaller part of the sky.

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When fully dark adapted, my Celestron 15x70s give me about the same light grasp (eg on easy galaxies like Bode's and M33) as my 4" frac.

Interestingly though, my left eye (non-dominant) takes quite a long time to fully adapt - until then it has the effect of making the combined image through the binos apparently fainter than just looking through the right eyepiece with my dominant eye. Could be an old-age thing though....

Chris

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I do not quite agree with Steve on the aperture issue. I think my 80mm APM shows a touch more than the 15x70 Helios Apollo, but that might be down to the higher magnification I was using, which darkens the background. I should test that with the 31T5 in the APM, which will give 15.5x.

You are correct, Michael; I should have noted that the aperture equivalence is for approximately equal magnifications (and, obviously I hope, equivalent optical quality and transmission coefficient)
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You are correct, Michael; I should have noted that the aperture equivalence is for approximately equal magnifications (and, obviously I hope, equivalent optical quality and transmission coefficient)

I will do a comparison as soon as I can, hopefully before we enter the grey summer nights (not looking good, given the forecasts). I will take most of the kit with me to Tuscany this summer (staying on a farm south of a village, so it should be good). The Scorpius Sagittarius region should be great to perform such a test.

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