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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Abbe-Koenig vs Schmidt-Pechan? (2 Viewers)

Pinewood said:
Hello Chartwell99,

As I recall my high school physics, refraction occurs when light passes from one medium to another of a different refractive index. Light entering and leaving the prisms, must be refracted, while there are internal reflection as the light bounces off prism walls.
Does that help or confuse?

Happy bird watching,
Arthur Pinewood
Click to expand...

I'm afraid high school physics was not my strongest subject and I much appreciate Arthur and Tero's explanation. Still curious, however, as to my first question - why is Zeiss the only (that I know of) user of AK prisms?
 
chartwell99 said:
I'm afraid high school physics was not my strongest subject and I much appreciate Arthur and Tero's explanation. Still curious, however, as to my first question - why is Zeiss the only (that I know of) user of AK prisms?
Click to expand...

I think I addressed that in my post: history and development "wood behind the arrow" on prism type.

Zeiss are pretty much the only company that's put effort into the AK going all the way back. It's a kind of trademark piece that is part of their history so they keep doing it. It probably attracts people who used their previous AK products (like the Dialyt and the Classic). But Zeiss made the development effort when there was a big win in transmission for the AK over SP before multilayer AR coatings and dielectric mirror coatings narrowed the gap.

For the other manufacturers today you gain 2% to perhaps 5% at most in transmission with an AK over and SP. And get to that you make bigger bins (which customers are less keen on). For this small gain you have to develop a whole new line of AK prisms when SP prisms are essentially commodity products (though the really good ones are a little bit more special).

There is no business reason to do this: they focus on what they're good at. That's the bottom line.
 
Hmm, the physical length difference between something like the Zeiss FL 8x42 and the Leica Ultravid 8x42 is pretty obvious. Based on the comments here that difference is a result of the prism design. Interestingly this is one reason I prefered the 7x42 over the 8x42. It is noticeably shorter.
 
Could it be that maintaining the integrity of the Canada balsam(?) interface of the two AK prism components is problematical and the reason why Zeiss are exclusive users of AK prisms?
Looking at the cutaway of the 56mm Victory FL provided by Tom, the cement itself would probably be incapable of withstanding shock loads. There would be high demands on the precision of the prism housings at varying temperatures if they are not themselves to impose loads on the cemented prism interfaces.

John
 
FrankD said:
Hmm, the physical length difference between something like the Zeiss FL 8x42 and the Leica Ultravid 8x42 is pretty obvious. Based on the comments here that difference is a result of the prism design. Interestingly this is one reason I prefered the 7x42 over the 8x42. It is noticeably shorter.
Click to expand...

And yet the Zeiss FL is lighter than the Ultravid.
 
Victory 8x32FL: 550g
Ultravid 8x32HD: 535g
__________________
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Hmm, isn't that something. I had no idea the Leica was actually lighter. It definitely "felt" smaller in my hands. I wonder if the weight didn't have something to do with it.
 
I wouldn't place too much trust in manufacturer's quoted weights.
Zeiss quote 605g for the 12x45 Conquest but mine must have some hidden ballast.
Stark naked on the kitchen scales they are 670g!

John
 
John Russell said:
I wouldn't place too much trust in manufacturer's quoted weights.
Zeiss quote 605g for the 12x45 Conquest but mine must have some hidden ballast.
Stark naked on the kitchen scales they are 670g!

John
Click to expand...

When did you take your kitchen scales to the Bureau of standards to have it properly calibrated?

Very curious where the discrepancy originates,
T
 
Tom,

My digital kitchen scale has not been properly calibrated by the Bureau of standards and you therefore will immediately disregard its validity, but for what it's worth I have used it to measure the "naked weight" of the Leica Ultravid 8x32, both HD and pre-HD versions. "Naked" here refers to weight without strap or lens guards. The pre-HD measured 540g and the HD 532g. To me, not requiring German standards of precision, these readings are comfortably close to what Leica specifies. In any case, plenty light enough for a metal-bodied rubber-armored binocular.

Humor aside, I also don't trust the accuracy of old-fashioned mechanical kitchen scales, but the modern electronic ones are much better. In any case, for sufficient everyman's calibration one can buy a couple of cans of canned soup, sardines etc. and weigh them with the grocery store's produce scales as apples or oranges, then check their own kitchen scale with these same "standardized" weights. At least here in Finland, the store scales are required to be calibrated.

Kimmo

Kimmo
 
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ThoLa said:
When did you take your kitchen scales to the Bureau of standards to have it properly calibrated?
Click to expand...

After adjusting the tare for two old measuring jugs for photographic chemicals, I'm within 2% weighing 500ml and 1l of water.
I really do think Zeiss are cheating here as my Conquests were very abstemious over Christmas.

John
 
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