Can a small bino really deliver? (1 Viewer)

[lilcrazy2]

Here is an old post by Henry Link dealing primarily with DOF, but his answer in #3 certainly lends some creedence to why some might see a better view with the larger binos.

Originally posted by Henry Link

What factors affect DOF in binos?

This is a good question . It can be used to explain a number of odd things we see in bins. First of all’ different people actually don’t see the same amount of DOF in the same bin.Young people with good eyesight have greater focus accomodation than older people who need reading glasses. They will see greater DOF in any binocular (and less field curvature), so while measurements could be done ,and would be valid in comparing one bin to another they would not predict the actual DOF for an individual.

A second factor is magnification. Simply put, if every thing else is equal lower magnification bins have more DOF.

A third factor (and the most interesting one) is “effective” focal ratio which varies with different lighting conditions. The focal ratios of the objectives of most hand held binoculars fall between F:3.5 and F:4. For the moment just assume all binoculars are F:4 no matter what the objective size. An 8x25 has an F:4 objective with a focal length of 100mm, an 8x50 has an F:4 objective with a focal length of 200mm. Assume these two binoculars are being used in daylight conditions so that the pupil size of the eye is closed down to 3.125mm, exactly the same as the exit pupil of the 8x25. That means the entire 25mm of that bin’s objective is being used, but only the central 25mm of the 8x50’s objective.The “effective” focal ratio of the 8x25 in this situation remains F:4 since the entire objective diameter is being used, but the “effective” focal ratio of the 8x50 becomes F:8 (the 200mm focal length divided by the 25mm central part of the objective actually being utilized). Not only does this effectvely higher f-ratio in daylight increase DOF compared to the smaller bin, but it also reduces the visible effects of chromatic and spherical aberrations.

 

[henry link]

The ignorant guy who wrote that stuff got the DOF part completely wrong. He learned that the hard way when he constructed an experiment he thought would prove that higher focal ratio binoculars show increased DOF and found out that they don't.

He got the part about higher focal ratios lowering aberrations more or less right as a general principle, but it's still possible that a small binocular with very low aberrations at full aperture could be better than a large one with high aberrations even when it's stopped down to the same aperture.

 

[lilcrazy2]

Henry
Sorry - I had posed a question on the Zen Ray forum about the claimed better DOF of the 10x43 ED2 vs the 10x42 ZRS HD, and wondered about the "magical focus free" DOF of the 7x36 ED2. I had thought that only magnification affected DOF, whereas the answers seemed to imply that the longer binos produced a deeper DOF. In reasearching DOF, I came across your post from 2004 which seemed to support the postion that longer binos provide a greater DOF. Is this not true?

 

[pimpelmees]

yes, in the theater and opera .:-O

 

[henry link]

... In reasearching DOF, I came across your post from 2004 which seemed to support the postion that longer binos provide a greater DOF. Is this not true?

As I later discovered, it's not true. The idea seems so reasonable since the DOF in camera lenses increases with higher focal ratios, but binoculars are not like camera lenses. They're afocal devices that, strictly speaking, don't have DOF. The DOF you experience with a binocular is your own eye's DOF decreased by magnification. There are some things that can be easily mistaken for DOF, like field curvature and focus speed to name just two.

 

[james holdsworth]

As I later discovered, it's not true. The idea seems so reasonable since the DOF in camera lenses increases with higher focal ratios, but binoculars are not like camera lenses. They're afocal devices that, strictly speaking, don't have DOF. The DOF you experience with a binocular is your own eye's DOF decreased by magnification. There are some things that can be easily mistaken for DOF, like field curvature and focus speed to name just two.

This [DOF], like 'resolution' I remain unable to understand what it is or what I see in the field.

I will keep this simple. I have two 10 x 42 binoculars and look at birds at 30 feet away. With one bin., bird 1 at 30 feet away and bird 2 at 31 feet away are in focus. With the other bin., only one bird is in focus at once. I have to focus to see one or the other clearly but not both at the same time. What am I seeing if not DOF?

 

[henry link]

James,

Here are two possibilities. First, field curvature, since two birds can't occupy the same spot in the field and, second, higher aberrations in one binocular which prevents completely secure focus at any setting.

At post #6 the thread below morphs into a long discussion of DOF, one of several that have occurred here. It should tell you more than you want to know.

http://www.birdforum.net/showthread.php?t=81438

Be sure to read Ed's (elkcub) PDF attached to post #50

Henry

 

[Kevin Purcell]

This [DOF], like 'resolution' I remain unable to understand what it is or what I see in the field.

I will keep this simple. I have two 10 x 42 binoculars and look at birds at 30 feet away. With one bin., bird 1 at 30 feet away and bird 2 at 31 feet away are in focus. With the other bin., only one bird is in focus at once. I have to focus to see one or the other clearly but not both at the same time. What am I seeing if not DOF?

Depth of Field has a precise definition: it's the range of focus over which size of the circle of confusion doesn't exceed the resolution of the detector.

Read more here but understand that DOF in afocal optics like bins is not the same as in camera lenses

http://en.wikipedia.org/wiki/Circle_of_confusion
http://en.wikipedia.org/wiki/Depth_of_field
http://en.wikipedia.org/wiki/Depth_of_focus

Or in a more prosaic way the amount your can change the focus without any detectable change in the image.

This is a tiny range in bins and cameras (what you see when focusing the bin ... do you notice a big dead band there? Me neither) and certainly not what most people mean by "perceived depthoffield" (even in camera lenses) where they're talking more about the characteristics of the bokeh

As Henry says what most people call "perceived depthoffield" is acutally something else. And has been discussed quite a lot here. Some say threads about DoF in bins are an example of a different sort of circle of confusion

 

[spyglass]

So after all this, did we decide that small binos can deliver?.....or not.

 

[[email protected]]

So after all this, did we decide that small binos can deliver?.....or not.

I would say what they deliver is not as satisfying as what a big aperture binocular delivers. Not good at all at twilight, more finicky to use because of ER and exit pupil issues, most agree the resolution is not as good and they just don't deliver the relaxing view of a good 32mm or larger binocular. But if you really need something that is pocketable and extremely compact and can put up with their shortcomings then stick with the alpha compacts if you can afford them. Me, I've given up on them. Just not worth the drop in optical performance from a full size for the increase in convenience. Too others having a binocular that is with them at all times proves to be better than nothing at all and I can understand that. I will stick with 30mm apertures and above for birding.

 

[Sancho]

So after all this, did we decide that small binos can deliver?.....or not.

The bottom line is - the binos you have with you most often are the ones with which you´ll see most birds. On this basis, a good pair of pocket binos, if you carry them generally, will "deliver" more, although they won´t perform as well, in certain situations, as regular-sized binos.

 

[Kevin Purcell]

The bottom line is - the binos you have with you most often are the ones with which you´ll see most birds. On this basis, a good pair of pocket binos, if you carry them generally, will "deliver" more, although they won´t perform as well, in certain situations, as regular-sized binos.

A perfect summation. I agree totally with this.

I don't think the compact bins are as far off as some other comment would say but they are bested in comfort by larger bins.

 

[KorHaan]

You can't argue with the fact, that the best bins are the ones you actually carry on any outdoor activity. Small ones are more discrete, and therefore much more convenient to have in non-birding situations. Compacts are supposedly great to carry in a pocket, but I am not willing to buy an alpha compact when I can take my Dialyts 10x40 BT*'s with me.
I have put a dog-leash strap on them, and I can instantly adjust the length of the strap, from very short to very long, which allows for bandoleer-style carrying of the bins, just by sliding the buckle along the strap.
It's a matter of perspective, though, when I go out birding I always take my Canon 18x50 IS's, which are so much bigger that I honestly consider my Dialyts 10x40 as compacts.
Owning these, I've no interest in going smaller still and compromise on viewing comfort.
My greatest concern is, what big aperture owling bins to acquire next; these will be filling a niche that is vacant at the moment.

Best regards,

Ronald

 

[Cleme]

Same difference with the filters. Astronomers use filters to increase contrast on telescopes so binoculars could do the same thing. I think some binoculars used to have screw on filters that you could change and we discussed it on a thread here on Bird Forum. Could be a nifty idea really. Change your filter depending on what kind of a view you want or what kind of conditions you are viewing under.

Yes, as someone who used to have film SLR cameras in the early 1980s it seems very odd to me that a newish budget design scope like the Opticron MM2 doesn't have a thread for a screw-on filter while the old Classic 1F 60mm scope does...

Do the manufacturers want to deny us a choice here or are they just saving a small amount on production costs?

 

[[email protected]]

Yes, as someone who used to have film SLR cameras in the early 1980s it seems very odd to me that a newish budget design scope like the Opticron MM2 doesn't have a thread for a screw-on filter while the old Classic 1F 60mm scope does...

Do the manufacturers want to deny us a choice here or are they just saving a small amount on production costs?

I would guess production costs. It costs a little bit of money to put those threads on the scope.

 

[[email protected]]

A perfect summation. I agree totally with this.

I don't think the compact bins are as far off as some other comment would say but they are bested in comfort by larger bins.

Yes, a $250.00 Nikon 8x42 Monarch which is pretty compact will definitely give you a better easier view than a $500.00 Leica 8x20 Ultravid. Food for thought!

 

[Hermann]

Yes, a $250.00 Nikon 8x42 Monarch which is pretty compact will definitely give you a better easier view than a $500.00 Leica 8x20 Ultravid. Food for thought!

Sure. But the Ultravid (or one of the other compacts) will fit into a shirt pocket. The Monarch won't.

Hermann

 

[Sancho]

Sure. But the Ultravid (or one of the other compacts) will fit into a shirt pocket. The Monarch won't.

Hermann

By Gum, I have it!!! Bigger Pockets!!!

 

[ceasar]

By Gum, I have it!!! Bigger Pockets!!!

Good idea! Now we just have to talk the companies into including them as an accessory!:-O

Bob

 

[Graham Osborne]

Bought my wife a pair of Zeiss Victory 8x20s for Christmas (and a pair for myself also!).

My wife thinks they are great (she is used to Nikon HG 8x32s so is accustomed to high quality optics) and was happy to use them to watch our first Waxwings of the year today.

For the the weight and size I reckon they provide a very good image, and whilst I agree that for all the reasons stated in previous posts, they are significantly less 'comfortable' to use than full size binoculars, I cannot see any discernible difference in resolution of detail in comparison with my Zeiss FL 8x32s.

As to whether they will deliver for me, only time will tell, but at present I am optimistic.

Happy New Year
Graham