Hawke, Zen-Ray ED field of view (1 Viewer)

One thing struck me today.

My Zeiss Victory 8x40 always gives me the feeling of a BIG view. Wide. And easy too look through. It seems bigger than the Zen Ray and the Hawke (in my mind).

But I checked the spec and it's 135m or 405 feet or 7.7 degrees. Not as wide as I'd expected.

Weird. It really feels big. It's interesting how other perceptions drive the feeling of a large AFOV.

I suspect as I bird with glasses there is something to do with how well it works with glasses.

Kevin,

I'm still looking forward to seeing your measurements of the Promaster, Hawke and Zen-Ray fields. Your concerns about measurement error are understandable, but I'd appreciate it if you nevertheless gave the simple look-and-measure method a try. You will be surprised at how close to published specs most binoculars would come, unquantified systematic error nonwithstanding. Today, while checking the fields of the new Leica Apo-Televid 82 25-50x WW aspherical zoom (btw just under 2% wider than spec at 25x and just under 3% wider at 50x) I decided to use the setup (tripod and measuring tape tacked vertically to a wall exactly 10 meters away (exactly to the margin of less than 0.5% of the distance, measured from front lens to the center of the tape-measure) to re-measure the Hawke 8x43 as well as the Nikon 10x42 SE and Canon 10x42 IS L. The Hawke measured the exact same 134cm again, while the Nikon measured 105.5cm/10 meters and the Canon 112.5 cm/10 meters. So, the systematic error in the measurement protocol has the uncanny ability to influence the Hawke much more than the Leica scope and the two Japanese binoculars. Or, the Hawke really does have a true field significantly (about 6.5%, not taking measurement error into account) narrower than specified.

Kimmo

Ps. I use these measurements not as an accurate reading but as a reliable-enough way of assessing whether the manufacturers' published specifications are true or not, and I present the measurement results only in cases where I feel the discrepancy is large enough to be more than just normal production tolerance variation or differences in chosen measurement protocols or conversion formulae.

Kimmo

kabsetz said:

I'm still looking forward to seeing your measurements of the Promaster, Hawke and Zen-Ray fields. Your concerns about measurement error are understandable, but I'd appreciate it if you nevertheless gave the simple look-and-measure method a try. You will be surprised at how close to published specs most binoculars would come, unquantified systematic error nonwithstanding.

Click to expand...

Here is my attempt at measuring the FOV of some binoculars I have to hand.

I initially tried to do this handheld but after taking some measurements and then doing the sensitivity analysis it was clear that the results were scattered so much I couldn't trust them. So I ordered a roof prism binocular adaptor and stuck the bins on a tripod and found the measurements were much easier to make and very reproducible.

I place a tape measure calibrated in inches on the floor under a window in our apartment building. 25 feet or 300 inches away (the length of the tap measure!) I placed the tripod (Manfrotto 3011N with a 3126/128LP head and a Zen Ray roof prism binocular adaptor). The distance along the floor from the adaptor mount to the tape is 300 inches. The binocular adaptor mount was 60 inches above the floor. This makes the distance from the binocular mount point to the center of the tape measure 305.94".

This is almost exactly true for Chinese ED roof prisms (due to the geometry of the mount and the lenses ... the objectives center are about half an inch or so below the mount. For other bins the lens projected futher forward of the mount point. About an inch or so for most closed hinge roof prisms, slightly more for the Bushnell. And perhaps almost three inches for porros.

With this setup some trigonometry gave me

FOV = 2 * ATAN(305.94 * T / 2)

T is the widest width of the tape seen though the bin

Or another way of getting to the same results is by "similar triangles" to scale the measurements up to the US standard linear FOV in feet @ 1000 yards.

FOV in feet @ 1000 yards = 9.80 x inches @ 8.498 yards

Let me know if I got these wrong

A couple of comments on the sensitivity of the measurements to errors.

An error of 0.25 inches in reading the tape would give an error in FOV of 0.047 degrees (or 2.5 feet @ 1000 yards). I though I could read the tape to an accuracy of about 0.125 inches. Curiously a lot of bins have the same number ... I didn't fix that!

An error of 1 inch in distance to the tape would give an error of 0.025 degrees (or 1.3 feet @ 1000 yards). The worst case here would be the porros which might read 0.075 degrees (or 4 feet @ 1000 yards) low.

A error of 1 inch in vertical height give an error in range of 0.2". I consider this insignificant so the vertical position of the lens with respect of the mount is not an issue.

So I made the following measurements of the widest width of the tape in inches without moving the tripod or changing the setup. So the relative values of FOV should all be directly related to each other.

Make of the numbers what you will. All in my humble opinion, of course.

Zen Ray ED 8x43
40.0
392 feet @ 1000 yards or 7.48 degrees

Hawke Frontier ED 8x43
44.0
431 feet @ 1000 yards or 8.22 degrees

Promaster Infinity Elite ELX 8x42
40.0
392 feet @ 1000 yards or 7.48 degrees

Pentax DCF WP 8x32
40.0
392 feet @ 1000 yards or 7.48 degrees

Pentax DCF SP 8x32
40.0
392 feet @ 1000 yards or 7.48 degrees

Leupold Cascades 8x42 porro
33.1
326 feet @ 1000 yards or 6.19 degrees

Bushnell Elite 8x43
38.0
372.5 feet @ 1000 yards or 7.10 degrees

Bushnell Legend 8x42
33.5
328 feet @ 1000 yards or 6.26 degrees

Swift Eaglet 7x36
38.5
377 feet @ 1000 yards or 7.20 degrees

Vortex Diamondback 8x42
40.0
392 feet @ 1000 yards or 7.48 degrees

Bushnell Excursion 10x42
34.25
336 feet @ 1000 yards or 6.41 degrees

Eagle Optics Raptor 10x42 porro (Vixen Foresta 10x42 porro)
32.0
314 feet @ 1000 yards or 5.99 degrees

So of these bins my measurements match or are very close to the advertised spec

Hawke Frontier ED 8x43
Promaster Infinity Elite ELX 8x42
Pentax DCF WP 8x32
Pentax DCF SP 8x32
Bushnell Elite 8x43
Bushnell Legend 8x42
Bushnell Excursion 10x42
Swift Eaglet 7x36

which gives me some confidence in the measurement technique

This one is just a little low

Leupold Cascades 8x42 porro is advertised to have a 336 feet or 6.4 degree FOV

These seems significantly low (outside the error bars)

Zen Ray ED 8x43 is advertised to have 426 feet or 8.1 degree FOV.

Vortex Diamondback 8x42 is advertised to have 420 feet or 8.0 degree FOV

Eagle Optics Raptor 10x42 porro. I think these were advertised with a 6.5 degree FOV. IIRC.

I had access to another Zen Ray ED 8x43 so I measured that one too in the same set up. Both give the same FOV with my measurement capability (to within a 1/8th inch). So for me is a reproducible measurement.

So onto a discussion of the results:

It's curious that the only two roofs that are out are both "wide" roofs. I should have added a Bushnell 8x42 wide porro I had into the mix (I forgot about that one) to makr sure. But I get the Hawke (the widest bin) right I don't think there is a general issue with measuring wide FOVs.

I think it's fairly clear that I get the spec numbers for a lot of bins but a couple of the wider ones are different. So that seems to be a clue that I'm actually measuring the correct numbers (and manufacturers are mostly correct in their specifications too).

Of course the interesting part of these results is that they differ from Kimmo's and SteveC's measurements in some cases. One possibility with SteveC is he measures the FOV vertically but I measure it horizontally. So is the field stop actually round? It should be but I hope he checks.

The other possibility is that Kimmo's, SteveC's and my measurements are accuraate enough and there are actually differences in the binoculars e.g. the field stop is a different size than specified in some batches than others.

This could be for a few different reasons.

Perhaps the bin design has been revised to fix a problem. For example, I have a very early Hawke Frontier ED 8x43 perhaps a later revision shrunk the field stop to remove the "reflection ring" outside the field stop. I can see either an ODM doing this silently though they should inform the seller of the product so the people selling the bin don't know it's different from spec (and no you don't check every bin for FOV! Though perhaps one might check one per batch knowing this).

Or perhaps its an engineering/marketing disconnect: the engineering change is made but not communicate to marketing or marketing is slow in rolling out the new numbers to the web site. This could happen anywhere in the product design cycle (even before shipping).

Or perhaps it's a manufacturing defect where the OEM has used the wrong size of field stop for a particular bin.

Which it is I can't tell. But it is interesting that the FOV is a "round number": 7.5 degrees. So if I was betting I suspect it's a manufacturing defect by the OEM from selection of the wrong part for the field stop.

Practically for me it doesn't make a big difference as I find 7.5 degrees about as big as I need. But it is a bug.

I've sent a note to Zen Ray and they are looking into it.

I'll send a note to Vortex too. Didn't they have a account on this site too? Any direct contact email would be good (as I suspect the general email may filter out the message).

So if anyone out there has a tripod, a tape measure and some of these bins (FrankD? Surveyor?) you could verify or contradict my measurements.

I may make this as standard evaluation technique in the future. One it give a number but I found more useful is it really makes on consider the field curvature and astigmatism at teh field edge. For example, though I didn't report them because they don't have tripod adaptor sockets so I could only do the measurement handheld, the Zeiss Victory and FL bins clearly have more astigmatism at the field edge than other bins. Its quite a challenge to get a number from the tape. On the other hand bins like the Zen Ray ED actually make this easier with pretty much just field curvature and rather little astigmatism.

Kevin,

You should work at Consumer Reports! Good work.

Cheers

Kevin Purcell said:

The other possibility is that Kimmo's, SteveC's and my measurements are accurate enough and there are actually differences in the binoculars e.g. the field stop is a different size than specified in some batches than others.

This could be for a few different reasons.

Perhaps the bin design has been revised to fix a problem....though one might check one per batch knowing this).

Or perhaps its an engineering/marketing disconnect: the engineering change is made but not communicate to marketing or marketing is slow in rolling out the new numbers to the web site. This could happen anywhere in the product design cycle (even before shipping).

Or perhaps it's a manufacturing defect where the OEM has used the wrong size of field stop for a particular bin.

Click to expand...

This has been an interesting discussion. I had assumed all along that the fov was one of those things that was pretty well set by the design of the binocular and that variations of fov would be pretty well in line with whatever variation existed in manufacturing tolerances of the components. Seems like the manufacture of field stops should be pretty simple, and thus simple to correct, if that is the reason for variation.

Thanks, Kevin. This is exactly the data I was hoping for. I trust your measurements as well as Steve's and, of course, my own. It'll be interesting to hear what Zen-Ray has to say, but this sounds a lot like the field stop indeed has been changed along the way. Intentionally or not, that we don't know yet. I think the small difference between your measurement of 7.5 degrees and Steve's and my 7.7 (or just under, if one doesn't round the numbers in the manufacturer's favor) probably comes from your shorter focusing distance of 25 feet versus mine of 1 km. I might try to duplicate the test at 7.5 meters to see if that brings the field down to 7.5 degrees.

Kimmo

Steve C said:

This has been an interesting discussion. I had assumed all along that the fov was one of those things that was pretty well set by the design of the binocular and that variations of fov would be pretty well in line with whatever variation existed in manufacturing tolerances of the components. Seems like the manufacture of field stops should be pretty simple, and thus simple to correct, if that is the reason for variation.

Click to expand...

I agree.

The issue might be a mis-dimensioned part (less likley I think), as I suggest a design revision, or picking the wrong part (when a design is offered in multiple FOVs). This last one could be either just one offs (wrong part in the right parts bin) or whole batch (wrong bin of parts used). Of course without being at the OEM I can't say any more.

But the opportunity for variation from, say, poor assembly is rather small and you'd probably notice this in other ways (unsharp field stop either all the way or part of the way around).

Of course the other issue might be that we might be getting our measurements wrong. The more people that make measurements on more bins the more you can see patterns. It's not that difficult (as Kimmo pointed out to me!). Go on ... try it.

Kevin,

I don't think it is likely that we are getting our measurements wrong (wrong by a meaningful margin, I mean). Both your set of measurements and my measurements both recently and before show FOV's very close to specification for most binoculars and telescopes. Secondly, when repeated, the results are consistent to an accuracy of under 1% if one takes even reasonable care with duplicating the test setup. So, if the deviation from specification we get for the few makes/models that appear to deviate were a systematic measurement/methodology error, the implication would be that all of the binoculars that now meet the spec would actually have fields much wider than specified. Having done these measurements myself, I simply cannot see how we could consistently get the wrong results with a couple of binoculars or scopes but not with the large majority of them.

Kimmo

I have now duplicated the field of view test at 7.6 meters, as an approximation for 25 feet. Focused sharp to 7.6, with my somewhat far-sighted eyes, the field was 97.5-97.7 cm. With commonly used approximations, this brings the field to about 128.5 meters at 1km, or 7.4 degrees. At this same distance, I also measured the field again with the binocular focused to 1 km (I can do this, since although the image of the measuring tape placed at 7.6 meters is now very much out of focus, I use a tape where the color changes every 10cm and, additionally, I could check the field stop limit by taping a visible marker where I thought I was reading the limit. With a couple of iterations, it is easy to get the field width established within an accuracy of couple of millimeters despite the unfocused image). Thus focused to 1 km I got a field of 102 cm, which converts to the same 134 I had measured earlier.

I suspect that the remaining difference between Kevin's and my measurement comes, in addition to my measuring setup probably being slightly less carefully measured and therefore having a bit larger random error, from my being farsighted while Kevin, if I remember correctly, is nearsighted. Since the real field of a binocular increases as it is focused towards infinity, the resultant difference in what yields a sharp focus for each of us would create a small systematic discrepancy to our readings which would tend to make his FOV readings wider than mine with an identical binocular.

In any case, I'm now confident that my sample of the Hawke 8x43 as well as Kevin's sample of the Zen-Ray 8x43 do have a real field of about 7.7 degrees, not 8.2. Unfortunately, the ones here in Finland at least don't have serial numbers. Do the Zen-Rays have serial numbers, or is the warranty just based on the model and proof of purchase?

Kimmo