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Bushnell Rangemaster: Vintage Binocular vs. Modern Birds (1 Viewer)

henry link

Well-known member
Thanks to John Dracon, I’ve had the opportunity to play around with a monocular version of the Fuji made Rangemaster for the past couple of weeks. Reading back over this thread I see that much has already been well covered, so I’ll try not to repeat what’s already been said, except to confirm a few things. I’m afraid most of what I have to add falls into the realm of minutiae, probably only of interest to fans and collectors of this model. As always, my findings apply only to this particular specimen. It’s possible that some design details changed along the way.

First off, I didn’t find anything out of the ordinary about the design. The objective is a cemented doublet of about f/4 or a little less. I disassembled the ocular and found it to be a conventional 5 element Erfle of around 20mm focal length (see the photo below of the lens set.) One nicety is the edge blackening of the eye lens doublet visible in the photo. Overall, this is a simple, tried and true design from the 1920’s, updated only by the use of anti-reflection coatings (the optics are “fully coated” even though the prism cover reads “coated optics”).

The coating itself turned out to be very interesting to me. Most single layer coating shows blue/purple reflections, but this Rangemaster’s coating falls generally into the class of “amber” single layer coatings. I’ve seen something similar in Swift, Leitz, and Fujinon binoculars of the same period and a coating of similar appearance is still used even today by Vernonscope for Brandon telescope eyepieces.

I haven’t had much luck finding information about “amber” coating. The thread from Cloudy Nights below offers some speculation.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5714482/Main/5708023

I’m inclined to give some credence to Gordon Rayner’s idea that coating thickness is involved, but it’s also possible that the coating material is something other than magnesium fluoride. Anybody else have some information about this?

It appears to me that “amber” coating is somehow tuned for the transmission to peak at a shorter wavelength than “purple” coating and it also may have a somewhat more linear bandwidth. At any rate, what I notice about the amber coated binoculars I’ve seen is that the color bias appears to be cooler and more neutral to my eye than the usual yellow biased color transmission of MgF coated binoculars with blue/purple reflections. The left center photo below shows the Rangemaster reflection colors compared to a Nikon 8x30 E and the right center photo shows the color change in white paper after transiting the optics of the two. To my eye the Rangemaster is much more neutral and actually a pretty close match to the bias of my Zeiss 8x56 FL; that is a little cool and slightly greenish. I wonder why the amber variant of single layer coating, which looks superior to me, wasn’t used more often in the days before multi-coating.

I measured resolution using the 1951 USAF pattern and did the usual star-test (both at 57x). Resolution was around 3.55”, which is excellent and about the same as the 7x35 Nikon Action I I tested a few years ago. There’s no real surprise there, since the star-test showed no defects that would seriously reduce resolution. There are only the typical chromatic and spherical aberrations that are to be expected from a fast cemented doublet. They’re largely innocuous at 7x, especially when they‘re effectively reduced in bright light by the aperture stop imposed by the eye.

The off-axis aberrations of the Erfle eyepiece are also about as expected. I measured about 6D of astigmatism and 3D of field curvature near the field edge. On the other hand the sweet spot (loss of no more than 1 element on the USAF chart) is acceptably large at around 25-26º of apparent field, similar to my 8x56 FL, which for me is just good enough to cause no complaints, though it’s far from the best that can be done by binoculars with field flatteners.

I found that considerable pincushion distortion develops toward the field edge. It’s a bit more than is strictly required to correct angular magnification distortion, so there is slight negative AMD at the edge of the field (circular objects appear radially stretched rather than compressed). The extra pincushion has the “benefit” of boosting the AFOV above other binoculars, which have the same AFOV as the Rangemaster when mathematically calculated. For instance, the 10x35 Nikon EII with a 7º field should have the same AFOV as the Rangemaster 7x35 with a 10º field, but in fact the Rangemaster AFOV is several degrees wider than the EII, owing to the extra distortion.

I measured the true clear aperture at 34mm. Oddly enough the objective lens measured from the front (with the trim ring removed) measures 37mm. When the trim ring is in place it overlaps the objective glass edge and reduces the clear aperture to 35mm. The final reduction to 34mm comes from a slightly undersized prism shelf aperture. The prisms themselves are actually quite large (27mm on the minor axis), just not quite large enough to avoid causing a slight aperture reduction in such a wide field optical system.

There is a series of reflections at the edge of the exit pupil which compromises glare resistance. The first one is “external” and comes from the inside of the trim ring. The next one comes from the objective lens cell and the third one from the prism shelf aperture. The prism shelf reflection is the only one that does any real damage, because its undersized aperture blocks the other two from reaching the eye when the eye pupil is well centered (see exit pupil photo). Looking into the binocular from the front you can see a reassuring looking ribbed baffling cone, which, as unfortunately is often the case, is largely ineffective because the front of it is too large to block the trim ring/objective cell reflections and its back aperture is too large to shield the prism shelf aperture. I don’t want to exaggerate the veiling glare “problem” the Rangemaster exhibits. It’s easy enough to see in the very difficult test set-up I use, but in the field it’s only likely to show up under very unfavorable back light conditions and, even then, it’s far from the worst I’ve seen.

Finally, I measured the eye relief at 14mm from the glass, which others have mentioned as the official spec. With the hard eyecup in place the eye relief is perfectly comfortable for me without eyeglasses.

I can easily understand the enthusiasm this model has generated. It’s built very much like WWII military binoculars, which is to say very very well. Even the monocular version is impressively immersive and comfortable to look through. However, there is no secret sauce that I can find in the optical design. I think this is just what you get from a simple, old-fashioned Porro with a cemented doublet objective and an Erfle eyepiece, when that venerable 90 year old design is well executed.

I haven’t returned the monocular to John yet, so if there is anything else anybody wants me to check out while I have it, please let me know.

Henry Link
 

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OPTIC_NUT

Well-known member
I was down on amber coating for quite a while. Among other things, it seems to
haze up more easily. I finally took a chance cleaning Sears Discoverer pair. The
contrast became huge, and the brightness only came up a little. With old blue or
the violet "UV" coatings, both come up a bit. I am speculating that amber coating has a
very high off-axis absorbance, and that was very valuable for extra-wide FOV
binoculars. There are old ads saying that "amber is better", but it might be that
amber was great for wides and then was over-generalized for use on ordinary
field width binoculars.

It would be interesting to see light pass through an amber-coated lens and a regular
one into a meter, to see how the transmission changes with angle of incidence.
 

henry link

Well-known member
OPTIC_NUT,

That's an easy enough supposition to test. I'll substitute a smaller eyepiece field stop and convert the Rangemaster's field to an "ordinary" width. I doubt that it will matter since the very same rays will go into forming the image in the central part of the field as now.

Henry
 
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OPTIC_NUT

Well-known member
I'm not sure the increase in absorbtion is in the intended range.
I think it's unintended rays, stray light. If there are many coatings,
the angular absorbtion would have a flattish rippled top, like a bandpass
filter, and steep sides (vs angular rotation of the lens).

We used such a coating in NIR and IR material ID equipment.
It wasn't 'amber', of course. Different wavelengths. The same
angular filtration is possible.

If you reduce the Rangemaster's field width you will get an improvement
in contrast anyway.

I would really need to directly look at the amber coating's rotational attenuation.

Also, amber coatings up front would do most of the attenuation.
Isn't it on every lens?
 

John Dracon

John Dracon
Many thanks to Henry for his analysis of the Fuji 7x35 monocular. For the relatively few persons out in BF land interested in the Rangemasters, (my assumption), I need to caution them that one cannot analogize from his examination of one sample to the CF Fuji 7x35, particularly the silver ring version. The objectivity and expertise Henry brings to his analysis, makes his comments worth noting.

While the bodies appear to be identical, the coatings differ in hue, and the view colors differ. Both show excellent 3-D effect, and the resolution appears to be the same, but that is only my perception. I carefully measured the close focus of both. The IF Fuji focuses down to approximately 24 feet - the CF down to about 14.5 feet.

At the risk of repeating myself, the only advantage of the silver ring version lies with the dedicated eye glass wearer once the eye cup is removed since the top piece of the ocular stays put. As Henry mentioned the ER is 14 mm, but with the CF eye cup removed it is greater, depending of course on the individual eye glasses. I can see at least 85% of that 525 foot field with my spectacles on.

For reasons I cannot explain, I find the view from both Fujis to be very "comfortable" and my eyes seem to relax using them. I realize I am introducing a very subjective sense into this discussion by saying that.

In my separate communications with other Fuji users, they articulate much of what I say and tend to use superlatives when describing their experiences with their Rangemasters. One person with a good size collection wrote that the Fuji would be the last binocular he would keep if put into a forced choice situation. I'm almost there.

I suspect that part of that with me is a bias that comes when struggling with some level of internalized xenophobia. The Japanese binocular craftsmen over fifty years ago were world class. Their products give testimony to that.

John
 

Grimnir

Well-known member
Henry,

Excellent report - very interesting reading - thank you.

In your view, how does the Rangemaster's quality compare to other wide-angle binoculars of the same vintage?

Graham
 

OPTIC_NUT

Well-known member
It's been amazing watching the analysis of the Rangemaster and
all the permutations. Reminds me a lot of the aircraft model histories
I used to read. It's neat watching the lenses and mechanics drift
through different models as they tweaked. There's a lot of Japanese binocular
history that seems gone so these forensics are key.
The laying out of the erfle is awesome.


I found a small clue, but a clue, on the amber coating:
---------------------------
Nice coatings chapter:
http://photonics.intec.ugent.be/education/ivpv/res_handbook/v1ch42.pdf

Reference 74 of the paper refers to amber coating.
The context of the paper reference is: color applications,
(ie, photography at first) and using "particularly achromatic coatings"
in the layering. so, while the reflected light has a brownish cast,
maybe the reflected+transmission losses are low and very color-neutral.
-----------------------------

I formed the theory about knocking down reflections off-axis after cleaning
nicotine off the prisms and lenses. Nicotine on amber coating is amazingly
'haze-making', and that disappears with cleaning. I should leave it at that.
Somehow the tar molecules cause more havoc on amber. Looks clear
from outside, but transmission adds up foggy.

If it's just a matter of a very achromatic coating that happens to look
pale amber, I'll shift to that. The inner walls were so incredibly flat black then.
A good coating puts the job back on the walls and irises.
The irises were so meticulous. I think modern binoculars could get a boost from that.
 

Highway Dog

Well-known member
End note is as follows:
"V . V . Obodovskiy , V . N . Rozhdestvenskiy , and I . Chernyy , ‘‘ ‘Amber Coating’ and Colour Photographic Objectives , ’’
So y . J . Opt . Technol . 34 : 324 – 330 (1967) ."

That paper would have significance in your learning. I wonder how to get that Journal reference. I have no connection with a University.
Rob.
 

OPTIC_NUT

Well-known member
Yes....that's the big one! I smuggled myself into the MIT/Barker Library once
but I don't look like a grad student anymore. Maybe my town has a cooperative deal
with UMass.
 

henry link

Well-known member
Henry,

Excellent report - very interesting reading - thank you.

In your view, how does the Rangemaster's quality compare to other wide-angle binoculars of the same vintage?

Graham

Thanks Graham. I'm afraid I don't know the answer to your question because I haven't recently seen, much less tested, any other wide-angle binoculars of the same vintage. I did test a Nikon Action I wide-field 7x35 from about 1985 a couple of years ago. The Nikon is a very nice binocular, but I would prefer the Rangemaster, mainly because of the superior build quality and more neutral color bias.

Henry
 
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Grimnir

Well-known member
Henry,

Ok - I have several vintage 7x35s and will write a short comparative report on their various merits etc when I have time later this year.

How is the cement in the objectives and oculars holding up?

Thank you again for the clarity and comprehensive nature of your report.

Graham
 

Steve C

Well-known member
Henry,

Thanks for the evaluation. As always I learned something from that.

As to the question of how the Rangemaster compares to other contemporary wide angle porros, I'll take a shot at that. I have some wide angle 7x35's in addition to the two Rangemasters.

Those include:
Jason Venture 4000 12.0* 631' Bak-4
Wards 11.8* 624' Bak-4
Tasco International 400 11.5* 604'
Tasco International 400 11.0*
Tasco with no model # 11.0* 578'
Binolux with no model 11.0
Jason Clipper 11.0
Tasco 116 10.5
Holiday no model # 10.0

They are all more similar than they are different, except the Jason Clipper which is no great shakes.

Build quality wise they don't compare to the Rangemaster,except the Jason Venture, which is quite close. The Venture would match the Rangemaster optically, but like its close cousin, the Bushnell Custom, it has identical, small prisms, which are sort of pointed when looking at them from above. The Venture and the Wards both have Bak-4 prisms. The Wards is possessed of better color rendition than the others, but it falls off pretty fast toward the edges, as do the others.

The Holiday, which is of the German body style is a nice compact binocular. It was actually the surprise of the bunch of non Rangemasters.

Where the Rangemasters shine against the others is obvious superior build quality, contrast, wider sweet spot, neutral color representation, better colors, and better edges, closer focus, and in detail at distance.
 
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Grimnir

Well-known member
Steve,

Have you measured the TFoV of your wide angle 7x35s?

My experience is that the actual TFoV is typically 0.5* - 1.00* less than that claimed on the prism plates.

Graham
 

Steve C

Well-known member
Steve,

Have you measured the TFoV of your wide angle 7x35s?

My experience is that the actual TFoV is typically 0.5* - 1.00* less than that claimed on the prism plates.

Graham


Yes, I have measured the fov's. After looking back through notes, It seems that the one Tasco 400 that claims 578' in the prism plate is actually the same 604 feet as the other one.

As to the Rangemasters, I make the Fuji to be just a little over its stated 10*, actually 10.3*. The Tamron seems spot on its claimed 11*.

I do this by placing the objective of a tripod mounted binocular as, close as I can measure, 30' from an 8' cloth measuring tape tacked to the wall. I determine the distance seen on the tape, and it's simple math to convert. It may not be scientifically precise, but it seems to be pretty close. They may be within a few feet one way or the other, but my experience is it is as likely to be a bit larger than a bit smaller. As a bit of a ground truth check, we have a fence with steel posts every 10 feet that I have measured with a laser rangefinder to be 800 yards from a handy spot to set up the tripod. It is a pretty simple matter to count up the posts that span the fov, which (obviously) at that distance is 80% of the fov distance. The two methods always seem to be pretty much in in agreement. The next handy fence is almost a mile away (1,700 yards) too many posts to count.
 
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Grimnir

Well-known member
Steve,

Of the binoculars in your list I only have the Tasco 400 and a Bk7 FPO Rangemaster but I should receive a Cory Suddarth reconditioned Bak4 FPO CF Rangemaster within a few days, apparently this particular glass is a very good example of its type.

I'll measure their TFoV using the angle measurement tool in Stellarium and suitable pairings of stars. This should be quite exact.

I'll report my findings here when I'm done.

Graham
 

Steve C

Well-known member
Interesting. I'd never heard of Stellarium, so I just downloaded it. I'll see if I can figure it out later. I'll be interested to see what FOV data you get.

I shall be quite surprised :eek!: if you are not impressed with that FPO Rangemaster.
 
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brentwood

Well-known member
A few months ago, I can remember reading something, can't remember where, about the fields of view of the various Rangemaster models. Two of the stars of the bowl of the Big Dipper are 10 deg apart and two are 11 degrees.
I checked this with my three different models and I had the same results as indicated on the hinge or prism cover.
 

brentwood

Well-known member
This was the posting I found on another thread.

" I think Phecda to Dubhe is about 11°, and from Megrez to Merak is just slightly less than that. So of you can frame the entire bowl inside your FOV then you have an TFOV of something in excess of 11°.
Alpha to gamma UMa is 10°26' and the entire bowl should just fit inside a 11° FOV."

I was intrigued by this test, so last night, I tried this with some of my binoculars. Two of my Rangemasters succeeded, with all four stars of the 'bowl' fitting in. The 11* early Tamron was a tight fit, while the 11* Tamron Custom (the ugly one) did so easily. The 10* FPO could clearly not get all the stars in. I also tried a 11* Marksman 7x35, that I have. They all fit and I was surprised at how good the star images were.
Interesting test!
 

Steve C

Well-known member
OK, I just did the big dipper test. All of my 11* marked binoculars will frame all four stars of the bowl. The FPO Rangemaster 10* will not quite frame them all. Either Dhube or Phecda is left just outside the fov, but it will frame the other three.

The Tasco 116, listed as 10.5* frames about the same space as the FPO Rangemaster, three out of the four stars in the bowl.

The Jason Venture 4000, listed at 12* frames the same space as do the 11* binoculars. The 11.8* Wards easily frames the entire bowl, obviously the widest of my lot.

The Holiday, listed at 10* and a new Nikon Aculon, listed at 9.3* seem to frame an identical amount, but less than the 10* Rangemaster.
 
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Grimnir

Well-known member
I make the Fuji to be just a little over its stated 10*, actually 10.3*.

Steve,

I measured the TFoV of my FPO Bk7 Rangemaster yesterday evening at 10.3* to 10.4*. So it would appear that the FPO Bk7 and BaK4 Rangemasters have the same TFoV.

Graham
 

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