binoculars auto focus - how work

[jamesgrant]

How do auto focus binos work? What if you want to look at a distant object and then a near object?

Are they any good for people who wear specs with different prescriptions in each eye?

 

[jamesgrant]

And if binos are advertised as centre focus, does that mean they won't have dioptric correction?
For example these from marinestore:
http://marinestore.co.uk/Merchant2/merch...;Category_Code=

 

[misterg]

Do you mean "auto focus" or just "Focus free" ?

In the latter case, the binoculars are just stopped down to give a reasonable depth of field with a fixed focus. Far better (I think) with a cheapish pair of 'focussable' 7x50s. I have found 'Helios' brand OK, but Jessops' own very poor: (Try looking at the night sky through them - the image is severely vignetted).

Andy

 

[oldsaltoz]

http://www.monkoptics.co.uk/General/about-binoculars.html

 

[jamesgrant]

Well, these are described as auto focus,
but I suspect focus free is what htey really are:
http://marinestore.co.uk/Merchant2/merch...;Category_Code=
I will go and have a look at your links thanks.

 

[FWB]

Most 'autofocus' binocs are in fact not that at all but Focus Free. They work like a telescopic rifle sight,using your own eye to focus. The range is about 40ft or so to infinity. Almost all binocs have individual eyepiece correction.
I use focus free binocs but I do find it best to remove my specs.
A disadvantage is the inability to focus below about 40 ft but have not found it a prob for marine use.

 

[BrendanS]

milltech doesn't post here much any more, but he had a very good guide to buying bino's for use at sea, do a search on his posts, and you may find his guide

 

[jamesgrant]

Nice sight, thanks.
Would you know at all, the yellow plastimo binos in my first link are advertised as centre focus, but what about dioptic adjustment - do you know / think all binos have them - otherwise wouldn't they be limiting their products to 20:20 eyesight people?

 

[VicS]

I think you will find Auto focus does mean fixed focus. Centre focusing should have individual adjustment of one eyepiece (usually the right)

I prefer not to keep my specs on when using a binocular. I cannot as a result focus on close objects (birds closer than the far end of the lawn for example) but i have slightly modified one to focus more closely.

I asked a similar question a while back and came to the conclusion that for me a fixed focus binocular was unlikely to be satisfactory.

Worth doing a Google search just for binoculars. Some of the websites have a lot of useful info about binoculars and how to choose one.

 

[mikehibb]

Does any one know what make of Binocs the RN use?
I have used many sets of binocs, but none have ever been as good as the ones that I used 20 years ago on a RN MFV when I was a cadet.

They were big , rubberised, drop proof, quite heavy but bally good optics. Just picked them up and looked through them, perfect focus.

 

[VicS]

[ QUOTE ]
milltech doesn't post here much any more, but he had a very good guide to buying bino's for use at sea,

[/ QUOTE ] Well remembered Brendan (always thought you had a hard drive where others have a brain)

'Tis here http://www.allgadgets.co.uk/about-binoculars.htm but does not seem to mention auto focus or fixed focus

 

[jamesgrant]

Thanks to all responders.

I have now just purchased a set of waterproof, nitro filled, centre wheel focus (and I am assuming there will be a dioptic focus - as all the advice and links seem to suggest most binos have it) binoculars.

 

[jamesgrant]

That's the RN for you.

I was on a sub some months back and had a peek through the periscope.

The optics were absolutely superb - a pleasure to look through.

 

[simonfraser]

most spec prescriptions are similar in power for r & l eye, with the diference rarely being over a few diopters.
as long as you can adjust for the diference between the two eyes you are in business.
the first number on your prescription tells you about your near / far sightedness.
so, say R = + 2.50 / + 1.00 x 50
the + 2.50 means you are + 2.50 units long sighted. ( minus number & you're nearsighted )
if the left says + 3.50 / + 1.50 x 130, you'd need to be able to set eye eye piece one unit different from the other.
you then use the central focusing power of the bino's to focus on what your are viewing.

astigmatism, that is the second number, for the right eye = + 1.00 & is not catered for in the bino's at all.
if it is less than one unit of power you are likely to see well without your spex on.

clear ?

 

[shmoo]

Focus-free with glasses is fine if you have progressive lenses. You move the eyepiece of the binos up and down over the glasses lenses to get "course focus" then allow your eye to accommodate the rest.

 

[mapron]

I had a pair of Plastimo focus free but couldn't get on with them. I read that if you are over 40 ish you are likely to have difficulty with this type, as your eyes age. I sold them and bought a pair of 7x50 by Bushnell. Very pleased.

 

[shmoo]

[ QUOTE ]

40 ish you are likely to have difficulty with this type, as your eyes age.


[/ QUOTE ]
I am 60 and have the same ones and found there were two tricks to getting them to work for me. One was what I outlined in the post above and the other was to stop trying to figure out how they worked and just look. Mine were given me as a present and at that time I was unaware of the concept and spent a couple of days puzzling how they might be focusing and looking for the battery compartment! Once I gave up all that and just trusted them to work, they worked.

One big advantage of the focus-free ones is that they are robust. Its not unknown for binos to be sat or even stood on aboard our boat and because they have no moving parts they take that in their stride.

 

[ex-Gladys]

I bought the Plastimo for the boat and am delighted with them. Cheap as chips, so no worries about bouncing them around, and both my wife and I with totally differnet eyesight get on with them fine.

 

[pbeard]

You obviously haven't tried Monk's then, as bright and clear an image as you will need.

 

[Gunfleet]

I have a pair of crow's foot marked binoculars which are falling apart in terms of the rubber perishing but, as you say, stunning in terms of 'just pick them up and use them.' They looked very similar to the Monk's own brand Artemis and at under £150 I think I may just buy myself a pair.

ps what I'd really like to do is get the original ones repaired, but where and at what cost? It seems a crime to write them off.