richardabeattie
Well-Known Member
My old but excellent Plastimos are fixed focus. They seem to work at all useful ranges and to suit all my crew members - even my steward is impressed. So what is the downside of fixed focus?
Fixed focus Binos
- Thread starter richardabeattie
- Start date
savageseadog
Well-Known Member
You can't have a closer look at the topless girl in the boat next door.
Drascomber
Well-Known Member
Haven't found a down side yet
vyv_cox
Well-Known Member
They are not great for bird-watching (not the topless-next-door variety) I don't think it's a consequence of old age creeping on, but I find that fixed focus bins cannot cope with going from very close range, a few metres, to infinity. I use variable focus on shore, fixed focus at sea, although I also have a variable focus pair on board (for topless use) /forums/images/graemlins/smile.gif
FlorealIII
Well-Known Member
They have a great field depth .
Fascadale
Well-Known Member
I've used an old Russian pair of fixed focus bins for 45 years. Love them.
I've also got a pair of medium quality variable bins. They're okay, but I prefer the fixed.
I've also got a pair of medium quality variable bins. They're okay, but I prefer the fixed.
roly_voya
Well-Known Member
Top quality veriable focus will give a slightly sharper image but at the cheaper end spend the money on the lenses not the focusing mech' I have plasimo fixed set at £50 and posh variables at £350, they are better but would not have got the if they hadn't been at 75% dicount fron LIDL!
RestlessL
Well-Known Member
I too find the Plastimos excellent. I can out them down and the crew cannot adjust the focus, so they are always right for me.
I am perhaps fortunate that they suit my eyes, and can use them both with and without my glasses.
John
I am perhaps fortunate that they suit my eyes, and can use them both with and without my glasses.
John
shmoo
Well-Known Member
The downside is I don't understand how they work. I have a pair and they work very well but still think there must be some sort of black magic at work. I don't like not knowing how things work...
geoffatstanpit
Well-Known Member
You'll get to find out why bins need to focus when you approach the three score and ten! The only ways to increase depth of field are to reduce magnification or aperture - there's no free lunch in optics!
charles_reed
Well-Known Member
To answer your question
rather than re-affirm my prejudices.
Fixed-focus (a misnomer as they'll have individual eyepiece adjustment) binoculars obtain their depth of focus by a much reduced aperture.
This means that light-gathering is, of necessity, reduced and they can be less effective in low-light conditions.
However, you'll not find genuinely waterproof binoculars with central focus.
Light-transmission is probably more influenced by quality of optics than by size of aperture. Porro-prism binoculars tend to give better results than roof-prism binoculars of similar quality.
Another criterion of quality is whether or not their mil-spec - which are always heavier than their "ordinary" brethren because of die-cast construction.
In fact ABS moulding can be even more precise than diecasting and far less fragile.
Final price determinant is whether or not they're assembled in China.
The Plastimo binoculars (IMHO) are definitely in one of the lower quartiles in optical and construction terms.
If you're looking for a price/quality benchmark have a look at the ABS, Chinese-assembled Fujinon Mariner range.
rather than re-affirm my prejudices.
Fixed-focus (a misnomer as they'll have individual eyepiece adjustment) binoculars obtain their depth of focus by a much reduced aperture.
This means that light-gathering is, of necessity, reduced and they can be less effective in low-light conditions.
However, you'll not find genuinely waterproof binoculars with central focus.
Light-transmission is probably more influenced by quality of optics than by size of aperture. Porro-prism binoculars tend to give better results than roof-prism binoculars of similar quality.
Another criterion of quality is whether or not their mil-spec - which are always heavier than their "ordinary" brethren because of die-cast construction.
In fact ABS moulding can be even more precise than diecasting and far less fragile.
Final price determinant is whether or not they're assembled in China.
The Plastimo binoculars (IMHO) are definitely in one of the lower quartiles in optical and construction terms.
If you're looking for a price/quality benchmark have a look at the ABS, Chinese-assembled Fujinon Mariner range.
jimbaerselman
Well-Known Member
Re: To answer your question
Great post, Charles. Thanks.
Great post, Charles. Thanks.
actionoptics
Well-Known Member
Apologies for coming in a bit late to this post but there are a few errors in the replies.
Fixed focus works by setting the focus to the hyperfocal distance which is when a lens is focused at a given distance and the depth behind the focused point becomes infinite.
The depth of focus also allows closer objects to be acceptably sharp. The aperture is NOT reduced - a 7x50 fixed focus bino is as bright as one with either individual focusing eyepieces or centre focus. Individual eyepieces are not called fixed focus and fully water proof binos can and do have centre focus and usually an ability to adjust the right eye focus to suit those of us whose eyes are not the same prescription.
A down side of fixed focus is if you don't have the same eyesight - left and right - so have to wear spectacles to see clearly with both eyes. Also if you are short sighted, the whole range of focus will be shortened. Vive versa if long sighted.
Fixed focus are a compromise. They cannot give a really sharp image across the whole focus range but they are much quicker to use.
Porro prism models have an advantage over cheap roof prism models with regard to image quality until you pay enough to get phase corrected roof prisms which are then no different from porro. If you want to know the technical reason, pm me.
Fixed focus works by setting the focus to the hyperfocal distance which is when a lens is focused at a given distance and the depth behind the focused point becomes infinite.
The depth of focus also allows closer objects to be acceptably sharp. The aperture is NOT reduced - a 7x50 fixed focus bino is as bright as one with either individual focusing eyepieces or centre focus. Individual eyepieces are not called fixed focus and fully water proof binos can and do have centre focus and usually an ability to adjust the right eye focus to suit those of us whose eyes are not the same prescription.
A down side of fixed focus is if you don't have the same eyesight - left and right - so have to wear spectacles to see clearly with both eyes. Also if you are short sighted, the whole range of focus will be shortened. Vive versa if long sighted.
Fixed focus are a compromise. They cannot give a really sharp image across the whole focus range but they are much quicker to use.
Porro prism models have an advantage over cheap roof prism models with regard to image quality until you pay enough to get phase corrected roof prisms which are then no different from porro. If you want to know the technical reason, pm me.
jimbaerselman
Well-Known Member
Better still! Thanks again. I do love it when experts talk dirty and explain things clearly . . . off to Google hyperfocus and porro prisms . . .
actionoptics
Well-Known Member
jimbaerselman
Well-Known Member
Thanks. Gone ito my favourites under the 'Sailing Techical' heading. Together with API oil specs, Battery FAQs etc etc.
richardabeattie
Well-Known Member
All very helpful but (Charles) my fixed focus binos are fixed focus - no central and no individual eypiece adjustment.
The connclusion I draw from all this is that for ordinary use at sea - not hitting the Isel of Widget - cheap fixed focus are fine.
The connclusion I draw from all this is that for ordinary use at sea - not hitting the Isel of Widget - cheap fixed focus are fine.