IPD Adjustment Specs (1 Viewer)

I recall reading a few cases where the max or min limits for IPD adjustment were critical in selecting someone's binocular. Because I have an IPD of 65mm (2.5"), which is the exact center of the population distribution, I didn't think too much about it. However, I recently noticed something a bit curious, — namely that the Nikon Sport Optics chart and the Swaro Catalog chart each list their LX L and SLC products, respectively, as having the identical range of 56mm - 72mm. Somehow, that didn't seem quite right, particularly over a variety of configurations including pocket binoculars. So I set about to measure the range on a few instruments that I own.

8x32 LX L 55 - 78
10x42 SLC 54 - 75
10x25 SLC 30 - 75

Since my test/retest measurement reliability is about .5mm., in each case the measured min was below the manufacturer's spec. and the measured max was above it.

Proceeding further, I then compared the range of two other instruments I own with what prominent retailers post on their web sites.

8x32 SE 53 - 73 ( compared to 53 - 73; B&H)
7x42 BGATP 58 - 75 (compared to 57 - 75; Optics for Planet)

Essentially, my measurements and the retailers' were the same, allowing for a 1mm discrepancy with the BGATP.

Last, note that Nikon lists their new EDG models as having a range of 54/55 - 76, which is an improvement over 56 - 72, but still is 2mm narrower than what my LX L actually measures.

I'm not prone to be a conspiracy theorist folks, but this simply isn't explained by sampling variation. It seems to be self-defeating advertising, but useful for hyping new products that are said to be improving.

What do you think?

Ed :smoke:

How do you take the measurement?

Ed,

I had my Nikon 10 x 32 EDG and a steel tape handy and took these admittedly less than perfect measurements and got 54mm and 78mm. I measured from the outside edge of the left EP to the inside edge of the right EP. I had no calipers available. You would probably have to have a flat nose with no bridge if your IPD was much under 60mm as the eye cups are a bit thick. My IPD is 68 and it worked out to that when I checked it on them.

Bob

RJM,

I lay a flat steel rule over the eyecups and measure from the inside edge of one eye lens to the outside edge of the other. Works quite reliably if the eyecups are retracted or folded down.

Bob,

The Nikon table says your IPD range should be 54-76.


Ed

I put a calliper across the base of the extended eyecups (parallel sides) and subtracted the diameter of one eyecup.

Here are some measurements rounded to 0,5 mm:-

Meopta Meostar 7x42: 55,5 - 74,5 mm

Swarovski SLC 7x42: 56 - 75,5 mm

Zeiss Victory FL 10x42: 53 - 75 mm

Zeiss Jenoptem (Porro) 7x50: 45 - 75 mm

John

Ed,

I've long observed the same thing. It is true that IPD spec is of critical importance for anyone whose eye's aren't 56-72 mm apart, but everyone else is understandably oblivious to the extent that they don't know to pay attention to this spec when advising new users (who might not even be able to identify why they are having problems) on purchases, or when buying (or designing) bins for kids. The IPD spec are usually not listed, and when they are, it is common for the upper limit to be inaccurate. Rarely is the lower limit wrong. Except in pocket roofs and some old full-sized porros, the lower limit is usually 56mm which excludes many kids and a small but significant number of adults (especially women). What is irritating is that the lower limit is often determined by the hinge design, not clearance between the oculars or objectives, so it seems that the industry just doesn't care about some potential customers. Zeiss is a notable exception--their recent models (FL and Conquest) have lower minimum IPD than most others.

Astronomics/Christophers lists the IPD on all bins that they sell. I think they make the measurement themselves. You probably already saw my recent post on this, but for others, here's the link:

http://www.birdforum.net/showthread.php?p=2161358#post2161358

--AP

They have the Bushnel Legend Ultra HD's at 52mm, but both my 10x42 and 8x36 measure 56mm minimum.

Hi AP,

Many/most of my binoculars can actually do somewhat better than 56 at the lower end. So, it boggles the mind why hi-end manufacturers would undersell this feature. In the case of the Swaro 10x25, even if I open one side to the limit and fold in the other, it still produces a comfortable range of 52—75. (Both sides folded in, of course, produces 30—75 as mentioned above).

Nikon's is another strange case. First they make a huge and unnecessary effort to "correct" the conventional way of estimating AFOV, but then systematically provide inaccurate IPD numbers that mislead potential buyers.

Frankly, it's not even logical.

Ed

elkcub said:

RJM,

I lay a flat steel rule over the eyecups and measure from the inside edge of one eye lens to the outside edge of the other. Works quite reliably if the eyecups are retracted or folded down.

Bob,

The Nikon table says your IPD range should be 54-76.


Ed

Click to expand...

I double checked it yesterday AM using a steel ruler. It came out to 54-78 again.

Bob

elkcub said:

Many/most of my binoculars can actually do somewhat better than 56 at the lower end...

Click to expand...

Really? Many old full-sized porros and pocket roofs can do this, but if you have any reverse-porro compacts or any roof prisms in 8/10x32, or 8/10x42 that do better than 56 mm, please list them and the spec you measure. I know of a few older (out of production) models that go to 54 mm, the Zeiss FL which go to 52 mm in x32 and 54 mm in x42, and I think that the Leica x32 HD models do something better than 56 mm. I was really excited to see 52 mm for the Bushnell Legend Ultra HD 8x42 on the Astronomics/Christophers site, but when I asked about it in the Bushnell subforum, I was told that it actually measures 56 mm.

--AP

AP,

Except for 8x30 and 8x20 SLCs under repair at SONA, I listed my working roofs and the SE in post #1. I believe the two SLCs under repair will probably measure under 56. The Swift 804 HR/5 Porros and HHS roof all actually measure 56.

So, other than the two Swaro compacts I don't own any binoculars that scrunch down to 52. Even my reverse Porro Bushnell Custom Compact 7x26 measures 58—80.

Although these anthropometry data are somewhat dated, the 5th to 95th percentiles of the male-female population are 51 and 70 respectively. So, the advertised ranges of 56—72 (by Swaro and Nikon) omit a surprisingly large percentage of the population at the lower end of the distribution (my guesstimate is > 10%), to say nothing about children.

It does give one pause for thought...
Ed

My wife is in the camp of those with a narrow IPD -- measured at 56mm by an optician (for fitment of progressive lens glasses). The fitment and performance of her progressive lens glasses is good, suggesting that the measurement was accurate. (if anyone has tried to put progressive lenses on a small lens appropriate for a small face, you know this measurement must be spot on!)

Anyway, being "on the hairy edge", as it were, we have had an interesting time finding a pair of good quality optics in a waterproof package that she can use. We've tried every sub-$600 pair we can find locally, all with 56mm minimum specified IPD, and only the Nikon Monarch's work for her.

I find that the published IPD specification simply cannot be used to help determine candidates that will fit those who's measured IPD is at or close to the published lower limit. There is just too much uncertainty in that number as it relates to how they actually work on a real face. The variability may lie with the optician, or with the eye relief and eye cup designs of the bins (for those who wear glasses), or in the IPD specification itself but in the end it doesn't really matter who is accurate and who is not -- comparing two numbers in an effort to determine fitness for use just doesn't work if one's own IPD is near the bino spec limit. Especially for those who wear glasses, which I suspect is an additional variable in the equation.

I just ordered a pair of 10x43 Zen-rays for my wife, hoping that she will be able to take advantage of the fine optical performance of these bins. keeping fingers crossed!

Just noticed that the Vortex Razor HD 8x42 and 10x42 are spec'd with a minimum IPD of 54mm:

http://www.vortexoptics.com/product/vortex-razor-hd-8x42-binocular

Over $1,000, but still nice to have another option out there for those with IPD's below 56 (assuming that the specs are correct).