Tips On Focusing Binoculars - Does Anybody Else Find It Hard?

[willinliv]

Hi,

I've got Helios 15x70 binoculars which feature individual focussing controls on each eye piece. I also have a slight turn (lazyness) in one eye, this eye is not as sharp vision as the other, and day to day my left eye is dominant, but looking through binoculars with a very close IDP setting aligns things up nicely. However I have not settled on how best to focus these marvelous binoculars. Is there any advice or techniques that people can pass on to get really sharp focus?

At the moment, starting with my best left eye I am covering up the other side with a lens cap (not closing one eye), and adjust the (very stiff) individual focuser past the point of focus until the stars blow, and then trying to track back to the sharpest focus, but I'm having trouble determining that focus point. And I am finding that I am straining my eye to determine the in-focus point but I thought you needed to relax the eye. I'm still getting some amazing and breathtaking views (last night collinder 70 and Pleiades) but I feel the stars could be a bit tighter. I wondered if there were any techniques worth trying during day-light or something like a Bahtinov mask. With the very close IDP my eyes are a short way back from the eye pieces if this could be a cause of my trouble. 

Thanks and best wishes, Will

[BinocularSky]

You seem to be doing everything right. Bahtinovs may help but I somehow doubt it (prove me wrong! ) - the lunar terminator may be better; Go to http://astrojargon.net/maskgenerator.aspx and assume that the bino is f/4 (280mm fl); print the mask out on transparency film to save the hassle of fiddly cutting-out.

[Charic]

My 10x50 Marines have individual focuser's, and the last time I used them was to observe down over a local harbour and beyond to  the Mountains and  up  to view military aircraft during some combat manoeuvres and  it all appeared very sharp to my eyes, the depth of field is very good.  The time before was spent observing the Stars, and they too seemed sharp as they could be, so I see no reason why you cannot set them up during the Day, and they not work for you during the night?

I have also read that you should not go back and forth when adjusting, as this just brings in doubt!, screw the focuser's in or out, and then just adjust until it first appears sharp, then leave it at that, then adjust the next eye, stopping at first glimpse of sharpness.

To aid in setting up and sharpness of view, I will always rest or mount the binoculars to keep them steady.

[willinliv]

On 1/18/2016 at 14:22, BinocularSky said:

You seem to be doing everything right. Bahtinovs may help but I somehow doubt it (prove me wrong! :icon_biggrin: ) - the lunar terminator may be better; Go to http://astrojargon.net/maskgenerator.aspx and assume that the bino is f/4 (280mm fl); print the mask out on transparency film to save the hassle of fiddly cutting-out.

Thanks Steve for the encouragement! I had not thought about using the terminator line - so I shall be doing just that. Might give the mask a go too but I'll see how I get on with the first option (guessing not enough magnification for a bahtinov mask). Thanks again 

[willinliv]

On 1/20/2016 at 14:52, Charic said:

My 10x50 Marines have individual focuser's, and the last time I used them was to observe down over a local harbour and beyond to  the Mountains and  up  to view military aircraft during some combat manoeuvres and  it all appeared very sharp to my eyes, the depth of field is very good.  The time before was spent observing the Stars, and they too seemed sharp as they could be, so I see no reason why you cannot set them up during the Day, and they not work for you during the night?

I have also read that you should not go back and forth when adjusting, as this just brings in doubt!, screw the focuser's in or out, and then just adjust until it first appears sharp, then leave it at that, then adjust the next eye, stopping at first glimpse of sharpness.

To aid in setting up and sharpness of view, I will always rest or mount the binoculars to keep them steady.

Thanks very much Charic, I think doubt is definitely part of it because focus is so subjective. I will do what you suggest about focusing on a support during the day (if only Liverpool had mountains!) and stop just at the point the focus 'pops' into focus. I think doing this on landscape or the lunar terminator will be a lot easier than staring at a single star. Thanks again and I can't get over what a friendly and useful forum this is. Cheers