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Field of view and other attributes (1 Viewer)

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ewsjr

Active member
There was another chance for me to use a Kowa 8X42 BD binocular over this past weekend. It has a rather narrow field of view (331' at 1000 yards). This binocular also shows a good depth of field and impressive resolution. In the construction of a binocular, what tradeoffs exist with the field of view vs other viewing attributes such as resolution and depth of field?

I am truly impressed by the Kowa BD and will likely be buying one soon.

Thank you in advance for sharing your knowledge.
 
Most mid price 8x42 binoculars will fall in the 330-340ish fov. There are a few exceptions, most notably the Promaster and Hawke. I have always felt like 330' was enough, but just barely. My Monarch (330' fov) which I used for a number of years never bothered me in that regard. So I would say that if you are more than satisfied with the other aspects of the Kowa, such as the edge distortion (it covers a larger % of the view in a smaller field), center field resolution, and ergonomics, I would say there would seem to be no reason not to buy it. It seems you like it and is a known to you item, of which the importance can't be denied.

Another thing is that you may develop superior use technique with the smaller fov. You can't rely on fov for peripheral use. But that is the advantage of the nearly 100' extra view of the Promaster/Hawke.
 
Steve C said:
Most mid price 8x42 binoculars will fall in the 330-340ish fov. There are a few exceptions, most notably the Promaster and Hawke. I have always felt like 330' was enough, but just barely. My Monarch (330' fov) which I used for a number of years never bothered me in that regard. So I would say that if you are more than satisfied with the other aspects of the Kowa, such as the edge distortion (it covers a larger % of the view in a smaller field), center field resolution, and ergonomics, I would say there would seem to be no reason not to buy it. It seems you like it and is a known to you item, of which the importance can't be denied.

Another thing is that you may develop superior use technique with the smaller fov. You can't rely on fov for peripheral use. But that is the advantage of the nearly 100' extra view of the Promaster/Hawke.
Click to expand...

As much as I can be seen as a Promaster and Hawke fanboy I do have reservations about the "bigger at any cost" FOV approach.

The Promaster is said to have a 7.5 degree field and better stray light control than the 8.1 degree field of the Hawke (which has some stray light issues even admitted by our tame Chinese bin designer). I suspect there is a correlation e.g. the Diamondback might be better stray light controlled if it wasn't so wide.

But I can see the marketing people demanding it: it is a WOW feature especially for those who haven't seen a big field before. Stray light is the subtle feature that very slowly annoys you (or if you are lucky annoys you quickly so you can return the bins!).

That said even my Bushnell Discoverer (7x and 8 degree field) does rather better with stray light (but it's not "Zeiss 7x42" perfect -- you can push it into stray light issue but it takes a more extreme light problem that I can't quite reproduce yet).

I'm starting to lean to a "just enough FOV" is perhaps the best approach. I suspect about 7 degrees is it for me (367 feet @ 1000 yds) though I suspect people can adapt quite well but below 6.5 degree (my two 10x bins have this field width) is perhaps my lower limit. More is nice (and the "Zeiss 7x42" shows that you perhaps can have your cake and eat it if you really work on the design). No offense on the other Alpha's this is just using one well known example.

That said I've often wondered if the narrow design style of Pentax, Nikon and Kowa is based around "flatter" fields and better stray light control. Though I do note that the only Pentax bin I own (the $50) Pentax WP 8x32 does have a 7.5 degree FOV.

It's all swings and roundabouts ....
 
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Kevin

I agree with you on the FOV at all costs. However, I have found it to be a waste of time to argue over. There are folks that want all they can get and will argue ceaslessly fo it. Fine, to each his own. I think that the Kowa fov referenced in the OP is fine. I personally am OK with the 330' minimum (6.3*). The fov of the Promaster is such @7.5*, I need seek no further improvement to satisfy my tastes. I have always been a centerfield resolution first, low edge distortion next, other stuff in between, and fov last, (at least down to 6.3*) sort of user.

It is really amazing how well trained marketing people are in psychology. If a good team decides to convince a target group they certainly know how to go about the task.

I always assumed that the reason most 8x mid price binoculars are in the 330-340' range was simply because the necessities in a binocular view other than wide fov were easier to come by, so the got what they could with resolution etc, and settled on what was left for fov at the price level, which is 330-340'.

I don't think I want to know what we'd have to pay for 9* fov with adequate eye relief with minimal edge distortion in a really decent binocular. I tend to think there is a reason why 8x fov doesn't often get to 410-420'.
 
Agreed, Steve.

I just think some (including myself ... the lure of 8 degrees FOV is very powerful!) occasionally forget the trade-offs that have to be made to make an optical design.

Of course a major problem with the trade-offs is there isn't a table out there we can consult. It's in the head of a small number of optics designers who have a feel for design. I think perhaps with that info people could refine their choices.

For example, for me, stray light control is the single biggest issue with mid range and below bins. If I could trade FOV for stray light then I'd do it. But I wouldn't want to trade say FOV for just a flatter field. Though I can see that on there forum there are people who'd make a different mix of choices.
 
to OP, 330ft for 8x might be too narrow if you were to take it into the woods. But it is adequate for other general use. I echo some of the comments from SteveC and Kevin. A good compromise for FOV is some where around 60 AFOV. There are two types of wide angle going from there to 65 degree: (1) high quality ones (like Hawke/Promaster, I haven't seen one, but trust the reviews from Kevin/Steve and frank), or (2) mediocre ones (like diamondback). Don't get me wrong, diamonback is a decent entry level binoculars. But the edge of wide angle just cannot stand deliberate scrutiny.
 
You really have to try the binoculars in hand. Some will just make you puke at the loss of focus and distrortion toward the edge, some have worsening image, but not to such an extent that is unpleasant. Most 8x32s are that way. I have two, one is slightly better. Mine is not sold anymore but the Pentax 8x32 SP is an example of the fairly pleasant view to the edges.
 
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Of my 8x bins, and because I use them for woods, etc., I like wide FOV. The 8x32 EL at 8 degrees is fine, the Nikon EII 8x30 is superb at 8.8 degrees. But for open-country birding, I find this almost distracting...too wide, too much going on in the FOV....and I´m easily distracted. (This is why I´ve come to prefer EII 10x35 with a 7 degree FOV, or Canon IS 12x36 with 6.5 or thereabouts).
 
ewsjr said:
what tradeoffs exist with the field of view vs other viewing attributes such as resolution and depth of field?
Click to expand...

One of the most direct trade-off is between field of view and eye relief. I think there has been a trend in recent decades towards providing binoculars suitable for glasses wearers, and this has led to increased eye relief. But increased eye relief also decreases field of view as a general matter. So I would be wary of binoculars advertising quite wide fields of view if you wear glasses -- be sure to try before you commit to buying (I think this would include the Hawke). Incidentally, at the very high end of binoculars, I believe there are complex eyepiece designs that permit both wide field of view and decent eye relief.

Best,
Jim
 
The ER vs FOV is not an issue today with the current design of longer focal length eyepiece lens. The bins I mention with 7 to 8 degrees all have eye relief of > 15mm with most in the 18-20mm range. Important to me as an eyeglass wearer.

But one should always check the parameters of interest to user.
 
J. Moore said:
One of the most direct trade-off is between field of view and eye relief.
Click to expand...

Er, that certainly isn't a given. The Discoverers had both large FOV and large eye relief. Those were the two most important aspects for me when I went shopping.

However, I would suggest not taking the FOV numbers for granted and test the binoculars side-by-side. I didn't find that the FOV spec always matched what I actually saw when I looked through different binoculars. The FOV you get out of them will depend somewhat on how far your eyes are from the eyepeice, and changed for me depending on whether I was wearing my glasses or which pair of glasses I was wearing at the time. Some of them really open up a lot without my glasses.
 
Kevin Purcell said:
The ER vs FOV is not an issue today with the current design of longer focal length eyepiece lens. The bins I mention with 7 to 8 degrees all have eye relief of > 15mm with most in the 18-20mm range. Important to me as an eyeglass wearer.

But one should always check the parameters of interest to user.
Click to expand...

Not convinced of that Kevin. I doubt binocular manufacturers are restricting themselves to 350 feet fields of view or less at the 8 x 42 level without some kind of technical restriction. Moreover, within the same binocular class (some of the binoculars you mention are seven power binoculars -- of course you can get away with more there), the relationship seems to be pretty constant. I do not know of any sub $1000 8 x 42 binoculars that have 20 mm or more of eye relief and more than a 400 foot field of view. (And the only one I know of that even comes close is the vortex razor -- 410/18 mm, and it is fairly expensive and somewhat heavy).

bkrownd said:
Er, that certainly isn't a given. The Discoverers had both large FOV and large eye relief. Those were the two most important aspects for me when I went shopping.
Click to expand...

Your discoverers are seven power, that enables them to have greater field of view and eye relief than the eight power binoculars the original poster mentioned.

Best,
Jim
 
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J. Moore said:
Your discoverers are seven power, that enables them to have greater field of view and eye relief than the eight power binoculars the original poster mentioned.
Click to expand...

My point was that FOV and ER are not always at odds with each other like you implied, which is true for any magnification.
 
I concur with bkrownd. The current design trade off isn't ER versus FOV. It's those parameteres and something else.

And my original point which was ER > 15mm and below 20mm I can find a handful of 8x42 bins at Eagle Optics that have 7.5 degree (almost 400 feet) and larger FOV with FOV in that range (Diamondback, Excursion, Zeiss ). In fact that's pretty all the 8x42 with that wide a FOV.

Of course most of the bins have an FOV less than 400 feet and a few of those do exceed 20mm. But for me that's of no consequence. I find even the Yosemite 8x30 14mm ER works for me.
 
bkrownd said:
My point was that FOV and ER are not always at odds with each other like you implied, which is true for any magnification.
Click to expand...

I do not see that the example of the discoverers proves any such thing. I was speaking about 8x binoculars, because that is what most birders prefer and that is what the original poster mentioned. But even at 7x, there is going to be an inverse relationship between field of view and eye relief generally speaking. It is just that at that low magnification the constraints are not as tight, so you get what for an 8x binocular would be considered a wide field of view together with good eye relief. If you go down to 4x you can get a 900 foot field of view with some binoculars for sport events. So you could argue that your discoverers have a puny field of view (to get their good eye relief) if you start comparing binoculars from different magnification/objective classes, as you are doing.

Best,
Jim
 
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J. Moore said:
if you start comparing binoculars from different magnification/objective classes, as you are doing.
Click to expand...

No, I did not. That's the way you'd like to read it, but it's not what I said. Anyhow, the numbers are out there for all to see, for whatever they're worth. Draw your own conclusions as you please.
 
bkrownd said:
No, I did not. That's the way you'd like to read it, but it's not what I said. Anyhow, the numbers are out there for all to see, for whatever they're worth. Draw your own conclusions as you please.
Click to expand...

I think we were probably talking about somewhat different issues. In any event, I agree that the Discoverer offers an unusually nice combination of field of view and eye relief.

Best,
Jim
 
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