• REMINDER - COVID-19

    Any content, information, or advice found on social media platforms and the wider Internet, including forums such as YBW, should NOT be acted upon unless checked against a reliable, authoritative source, and re-checked, particularly where personal health and liberty is at stake. Seek professional advice/confirmation before acting on such at all times.

    Users who are found to promulgate FAKE NEWS on the forum in regard to this issue, intentional or otherwise, may find their access terminated. It is your responsibility to provide references to bona fide sources.

    FAKE NEWS, in this regard, is that which is posited by organisations, media, etc., that is repeated on the forum, or used to support personal opinion/hypothesis posted by users - FAKE NEWS is not necessarily the personal opinion/hypothesis being posted in itself, any issues with such should be challenged respectfully.

binoculars auto focus - how work

jamesgrant

New member
Joined
4 Aug 2007
Messages
246
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?
 

misterg

Active member
Joined
31 Oct 2003
Messages
2,884
Location
N. Wales
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
 

FWB

Active member
Joined
29 Feb 2004
Messages
4,361
Location
Kernow
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.
 
Joined
11 Jun 2002
Messages
64,559
Location
Tesla in Space
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

New member
Joined
4 Aug 2007
Messages
246
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

Well-known member
Joined
13 Jul 2002
Messages
45,327
Location
Home: Kent. Boat: Chichester
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

Active member
Joined
23 Sep 2007
Messages
1,995
Location
Bulcote
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.
 

jamesgrant

New member
Joined
4 Aug 2007
Messages
246
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

New member
Joined
4 Aug 2007
Messages
246
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

Well-known member
Joined
13 Mar 2004
Messages
6,357
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

New member
Joined
23 May 2005
Messages
2,136
Location
West Cornwall
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

Member
Joined
8 Sep 2004
Messages
46
Location
West Mids/ North West
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

New member
Joined
23 May 2005
Messages
2,136
Location
West Cornwall
[ 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.
 

Gladys

Well-known member
Joined
29 Aug 2003
Messages
4,917
Location
Colchester, Essex
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.
 

Gunfleet

New member
Joined
1 Jan 2002
Messages
4,524
Location
Orwell
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.
 
Top