Close focus binoculars

[Hugh Middleton]

I see a mark 11 is out. Does anyone have any views on this and availablility?

Jack - I was fortunate to see a Scarce Tort in Lincolnshire last year

Hugh

[Jack Harrison]

Technical question about binoculars (mainly applies to the straight-through roof prism type).

When used at close distance the eye pieces (ie, the barrels) have to be adjusted closer together than when viewing a far off target. Why?
After all, the spacing between human eyes is pretty much fixed

Original query from EricY prompts me to ask: "Have you thought of these?"

Swarovski EL8.5 x 42 HD Swarovision Binoculars £1,879.00

Amazon advises only two left in stock so you'd better be quick Eric. As they are not the 6.5 x that you really want, I'm sure you could negotiate a discount

Jack

[False Apollo]

I have a pair of the Pentax 6.5 X 21 Papilios and they are brilliant. A whole new perspective on butterfly watching, seeing every detail in close up. It is like going to the cinema and watching beautiful butterflies on the big screen. They really are that good and terrific value for money. My wife has a pair of the 8.5 X 21's and I personally don't think they are as good, or bright, personal taste as she is quite happy with them. I wear glasses and lift them when using these bins, which I also do when birding with my other bins, the only drawback being butterfly or bird may have flown off in that short space of time.

Regards
Mike

[MikeOxon]

Technical question about binoculars (mainly applies to the straight-through roof prism type). When used at close distance the eye pieces (ie, the barrels) have to be adjusted closer together than when viewing a far off target. Why? After all, the spacing between human eyes is pretty much fixed

While your eyes are separated, a close-up insect is almost a point, so the eyelines to the subject converge. The special feature of the Papilios is that the objective lenses move nearer together as they focus more closely, to compensate for parallax.

Mike

[Jack Harrison]

While your eyes are separated, a close-up insect is almost a point, so the eyelines to the subject converge.

Fine. I had already understood that.

The special feature of the Papilios is that the objective lenses move nearer together as they focus more closely,...

Not just Papilios but indeed the same with all binoculars I have ever used.

... to compensate for parallax.

Now that is the bit I can’t understand. My eyes – I have a large head (!) – are 73 mms apart. When I use a typical pair of bins, eg Opticron, viewing a distant subject requires the spacing between eye pieces (and indeed also the objective lenses they being roof prism bins) to be adjusted to 73 mms apart.

However – and this is my real question – if I look at a much closer subject, to fuse the two images (ie not to get the movie-maker’s trick of a figure of eight view) I have to bring the barrels closer together. With these Opticrons focussing on minimum distance of circa 1.5 metres, the barrels and of course the eye pieces are now about 63 mms apart for the correct fused image. Yet my eyes are (of course!) still 73 mms apart. I simply cannot understand why the eye pieces of the bins have to be significantly less than that.

Over to you Mike (or anyone else)

Jack

[MikeOxon]

Papilios are 'different' in that the objective lenses move along paths that converge, as they move forwards. That's why they have the overall cover glass across the front, to enclose the mechanism. If you look at a pair face on, you can see the movement as they focus closer. In a conventional binocular, the only option is to move the whole tube, which means that only part of the lenses are used properly and they are de-centred. This won't work at all at very close distances. A diagram might help:

Mike

[JohnR]

A diagram might help:
Mike

Please don't publish such a succinct and helpful post which I understood the second I saw the diagram. You deprived me of my human right to think "wot the 'ell is he on about?"

[Jack Harrison]

Yesssss!

I had insomnia so to send me back to sleep decided ter edercate myself - like.

Thanks Mike. Back to bed!

Jack

[MikeOxon]

Glad that helped! For technical details of the mechanism in Papilios, see the US Patent at http://www.google.co.uk/patents/US7277225 The diagrams show both the 'near' and 'distant' focus positions.

It's not light reading but it does explain the essential difference between Papilios and other binoculars.

Mike

[Hugh Middleton]

Bought a pair of 6.5x21 yesterday. Despite the poor light and obviously lack of butterflies I am very impressed with them.

Thanks to all who posted with advice, comments and suggestions.

Hugh