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Focusing


Claire

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Hey everyone. I've just been out for the first time with my new Celestron 15x70's.

I've read the instructions on focusing them, and followed it. But when I view through both eyes, the image isn't as sharp as it is viewed through just one eye.

Could this be something I'm doing wrong? I am having to lean on the car roof to view as I haven't got a tripod yet.

I first focused it using the moon, which did look amazing (though I wasn't expecting it to be so bright. Maybe not the 'brightest' of idea's on a full moon!)

I went to Jupiter and the Pleides to see if I could get it better, but still, one eye was sharper than two.

Is this me focusing them incorrectly? Or a limitation in my own vision? I don't wear glasses at all and as far as I know I have pretty much perfect vision.

Thanks for any help :)

Claire

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As said, it is likely to be related to adjusting the separate focus on the right eye piece. The process I use is to close my right eye, focus with the centre focus, then close the left eye and focus with the adjustment on the right eyepiece. This should get you there, maybe repeat a couple of times to get it exact, then remember where the adjustment is so you can easily set it again.

The other possibility is that the collimation is out on the binoculars which may mean sending them back if they are new. When you look at a star, do the images coincide exactly or are they misaligned at all?

Stu

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I followed the 'close right eye focus with centre' then 'close left eye and focus with right eye focuser thing' :)

but when i use both eyes they are not sharp. Should I then be further focusing? I've read that you shouldn't have to but I must do?

I don't see a double image. I can get the moon looking perfect I think, though it is hard to tell exact because of the wobble of me holding it.

Thanks for all help btw :)

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You need just to think through the separate focus thing logically. First you focus the main knob which moves both eyepieces but you only look through the side which doesn't have its own focuser. Then you go to the side which does have its own focuser and look only through that, focusing it separately.

Now you need to get both eyes behind the eyepieces so try pull the two tubes apart and squeeze them together till they are sending light nicely into both eyes.

And if, at this point and with a bit of trying, you don't get a clean single image then they are not right. Could you find a more experienced user to try them? Local astronomical society? There are several SGLers in Preston.

Olly

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Hi Olly - thanks for that. I think I'll get myself a chair next time and have a proper go at focusing like you say. I didn't actually alter the tubes as you say, so they were just as they were in the box. Maybe that is my problem!

Thank you :)

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The view through binoculars isn't like they show in the movies (i.e. binocular shaped), it is circular, like the view through a telescope. By adjusting the 'inter-ocular' distance of the binoculars to suit your own 'inter-ocular' distance, the view may be improved...

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One problem with all cheap centre focusing binoculars is that there is a fair amount of wobble in the focuser. The procedure described by Olly and others is correct, but it is very easy to lose focus in the left eye, when setting the dioptre of the right eye. Once you have found focus, it very easy to lose it again, just by bumping into the EPs. This is why individual focusing is ideal in astronomy.

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There's also a hell of a lot of wobble on the bridge of those Celestron 15x70s. Any pressure of the eye sockets on the eyepieces, and focus goes. Also, you tend to get better focus if, instead of closing your eyes alternately, you cap the objective of the side you are not focusing: Cap right objective, centre-focus; cap left objective, focus right dioptre.

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I have just picked up a bargain pair of 10x50.s at a local charity shop and cannot keep focus. As Steve said, there is a lot of movement on the bridge. it seems a lot of binos may suffer the same problem.

The view through the left eye is good though. :tongue:

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It's also a physical fact that using one eye puts a small strain on the unused eye. Although the procedure described is correct, you can arrive at a situation where each individual eye view is correctly focused but the relatively relaxed view of both eyes at once goes slightly out of focus and might want a further centre focus tweak. Having said that, the most common problem is the play at the centre bridge as already mentioned. :smiley:

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It's also a physical fact that using one eye puts a small strain on the unused eye.
Small, but significant! This is why I prefer to cap the objectives, rather than close my eyes: easier to relax. I find it to be the only way I can focus with independent focus binoculars (no CF to compensate for the "unrelaxed" focus shift).

(On the batphone with Tapatalk)

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But during day light it's fine...
It may well appear so in daylight. Astronomical use is a far more stringent test of visual optical systems and it highlights issues that are not apparent in daylight use. One thing you could try during the day is using those coloured 3-D spectacles (or, say, a red and blue cellophane sweet wrapper over each eyepiece). That can (but doesn't always) make poor collimation more apparent.

Poor focus tends to make stars blurred, not double.

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