binoculars auto focus - how work

[macd]

Ah, auto-suffocation.

/forums/images/graemlins/smirk.gif

Hope you're recovered.

 

[davies]

There is always the same compromise with any optical instrument, be it binoculars, a camera or a microscope. Stopping down the numerical aperture increases depth of focus and contrast at the expense of brightness and resolution of detail. For birding I wouldn't consider focus-free, but for the lesser demands of general boat use they are fine if you like them.

 

[snowleopard]

I have a pair of top-of-the-range Steiners. They are proudly labelled 'auto focus' and at £600 so they should be. The truth is that they have a very good depth of focus but are actually fixed focus. They are set up for one individual but can be altered for others by rotating both eyepieces.

'Centre focus' means being able to focus both eyes simultaneously by turning a wheel in the centre. This type are rarely waterproof.

p.s. I didn't pay for them!

 

[macd]

You're right, of course (I'm a photographer, so I'd know). On a moving yacht utmost clarity of detail is less important in practice than ease of use. I've used expensive Karl Zeiss bins which are an utter delight, but overkill on a boat. But I'd still love a pair if money were no object.

 

[actionoptics]

You could get "Auto focus " binoculars from Minolta which had the same electronics as auto focus cameras and they did have an individually focusing dioptre eyepiece to correct for anyone with less than 20/20 vision. You can also get "Sports Focus" especially on Steiners which are individual focus eyepieces which when set to suit your eyesight and focused on the hyperfocal distance, allow quite good focus from infinity to about 25 feet. You can also get fixed focus models or focus free which are just that - both eyepieces fixed at the hyperfocal distance and they don't have an adjustable dioptre on one side. You can also get models which have a conventional centre focus but which you can lock once you have set the focus to suit your eyesight ( Bresser Riva )and they can have one adjustable eyepiece or one front lens adjustable. Another model ( Bushnell Spectator Plus ) has two quick adjustment settings on each fixed focus eyepiece - one for about 25 feet to infinity and the other for much closer focus range. The last time I spoke to miltech he had semi retired to Wales. My web site has quite a lot of information and an explanation of hyper focal distance but it is a point about 3/5ths of the way from you to infinity so that objects a bit in front of that and objects quite a lot beyond that point, appear to be acceptably sharp to either a cameras film or our eyes.

 

[actionoptics]

Snowleopard - I agree - centre focus are not usually water proof but they can be - the Bresser Nautic was and one or two others are but the bino must have "Water proof" written on it - centre focus or not . Rubber armouring is also not a guarantee of water proofing. Buyers beware.

 

[actionoptics]

Misterg - an interesting idea 'stopping down' a bino to get focus free but whilst that principle is used in cameras, it would defeat the object in a bino. There are no internal 'stops' in a focus free bino. The manufacturers try to get every last ray of light that hits the front lens, all the way through to your eyes.

 

[actionoptics]

mikehibb - I have been buying the old Barr & Stroud CF 41 7x50 from the Navy as they decommission them but the ones you remember sound like C Zeiss Jena 7x50. The latest Military bino was made by Avimo in Taunton and is a 7x42. Lovely optics but a swine to collimate and very weak centre bodywork that breaks in half too easily. Water proof and fixed focus with no dioptre adjustment

 

[Lakesailor]

[pedant] You are referring to Depth of Field, which refers to the subject side of the lens. Depth of Focus refers to the image-forming side of the lens describing the latitude allowable for the film plane or in the case of binos, the placement of the user's eye.[/pedant]

 

[jamesgrant]

I wish I'd known about your website sooner.

Maybe next time.

You have some nice binos there at attractive prices.

 

[misterg]

[ QUOTE ]
Misterg - an interesting idea 'stopping down' a bino to get focus free but whilst that principle is used in cameras, it would defeat the object in a bino. There are no internal 'stops' in a focus free bino. The manufacturers try to get every last ray of light that hits the front lens, all the way through to your eyes.

[/ QUOTE ]

Sorry, I stand corrected - I thought that this was how they achieved a greater depth of field. (I can understand why it would be a bad thing.)

Interesting comments, thanks.

Andy

 

[alan_d]

[ QUOTE ]
... a point about 3/5ths of the way from you to infinity.

[/ QUOTE ]

Umm ... Isn't that infinity too?

Alan