Zen Ray ED....initial impressions (1 Viewer)

Steve C said:

My impression of the non standard focus direction is that the elements used in the focus operation still work in the same direction. This doesn't change. What changes is simply the direction of the cut of the gears (LH thread vs RH thread), so some need to move CW and others CCW. I have always assumed that a simple change in gears would then change focus wheel direction, but not the focus lens direction.

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Well that depends on which direction you need to get the lens to move. But it would be ore likely a change of sense of a thread on a screw or a worm gear.

Steve C said:

But I have to admit to being somewhat confused by mayoayo. It sounds like the suggestion (implication) is that there is grease inside the lens mechanism. Now I thought that the focusing was accomplished by a rod which is outside the lens assembly and that thus any lubricating grease (which would be on the rod and the gears associated with moving the rod) is therefore also outside the lens assembly and should not be able to be viewed at all. I can't imagine a decent binocular design that would let grease into the lens and prism housing.

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This seems to be quite common. There is grease (probably a synthetic low vapor pressure grease) that lubes the focuser lens mounting that slides in the machined surface of the barrel.

That grease isn't going to go anywhere else either. It's sticky and there isn't enough to run elsewhere in the system. Plus the bin is sealed so no dust should get in there to gunk it up.

I can think of other ways of doing it but they all seem to be very high tolerance mechanisms (i.e. expensive!).

Other bins put the focuser assembly in a different location (close to the SP prism) so it sort of hangs off the focuser mechanism in mid-air (well, mid-nitrogen or mid-argon) and doesn't contact the sides of the bin.

I suspect there are some other useful optical effect that leads to this sort of design like reducing aberrations perhaps with a minimum number of lenses e.g. the two objective and focuser could be different glass types or could be an sort-of-achromat followed by another lens so you get an APO effect focusing light at three wavelengths. So you you deal with a CA problem and make the bin able to focus too when you optimize the whole objective system. After all adding a larger focuser lens increases weight and cost of good so you need a good reason to put it in. Perhaps mechanical simplicity is part of the driving force too.

Tero: the lenses won't touch ... that focuser lens mount usually projects in front of the frontmost part of the focuser lens so it can't touch the objective even when forced to the end of it's travel.

Kevin Purcell said:

If they use a negative lens for the focuser it would work the other way. Optics designers choice

But that is an interesting point about focusing rotation and direction of motion of the focuser. So perhaps they all use the same sense threaded rod and cams and the focusing optics differ. I should look at my collection for a correlation in rotation direction and movement of the focuser.

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I thought all of these focusing lenses were negative. Now I wonder what the performance implications are for the two different design approaches.

I could not actually see any grease in any of my roof prisms. In some models I see a tube that moves inside the barrel. It must have some tolerance so it moves freely.The threads are lower down.

henry link said:

I thought all of these focusing lenses were negative. Now I wonder what the performance implications are for the two different design approaches.

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I hit on this before ... it seems to be the case:

... there are some other useful optical effect that leads to this sort of design like reducing aberrations perhaps with a minimum number of lenses e.g. the two objective and focuser could be different glass types or could be an sort-of-achromat followed by another lens so you get an APO effect focusing light at three wavelengths. So you you deal with a CA problem and make the bin able to focus too when you optimize the whole objective system. After all adding a larger focuser lens increases weight and cost of good so you need a good reason to put it in. Perhaps mechanical simplicity is part of the driving force too.

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I suspect a negative focuser would need a 2 element objective to deal with CA with a negative focuser.

So a positive focuser gives reduced weight by omission of a lens and reduced parts count.

Plus closer focus too ... as d goes to zero the total power goes to a higher value than you would get with a negative focussing lens which would require a higher power positive objective to get to the same power (i.e. more curved so more aberrations).

I suspect the negative lens focuser became less common when people started demanding closer focusing bins.

The negative side? I think a slightly longer bin given all of the bins I have that I can see use this technique ("Chinese ED", Promaster 7x32, Pentax HS) are longer than other bins. Perhaps that increases the overall f/number too so reducing other aberrations.

The Pentax HS is a good example of this style of design with a 2 element objective (i.e. one fixed planoconvex lens (easy to clean on the outside) and one "close" positive focusing lens, I suspect made of different index glass) and a simple (Kellner? RKE?) 3 element EP give a surprisingly good bin for a very low parts count (and low manufacturing cost).

I think the Big 4 may still use the negative focuser given the cutaway diagrams I've seen. That would lead to more compact bins.

Somehow I am not getting the message. Can you just list your guesses as to + and - focusers and models, like Monarch and Pentax DCF series.

Kevin Purcell said:

I hit on this before ... it seems to be the case:



I suspect a negative focuser would need a 2 element objective to deal with CA with a negative focuser.

So a positive focuser gives reduced weight by omission of a lens and reduced parts count.

Plus closer focus too ... as d goes to zero the total power goes to a higher value than you would get with a negative focussing lens which would require a higher power positive objective to get to the same power (i.e. more curved so more aberrations).

I suspect the negative lens focuser became less common when people started demanding closer focusing bins.

The negative side? I think a slightly longer bin given all of the bins I have that I can see use this technique ("Chinese ED", Promaster 7x32, Pentax HS) are longer than other bins. Perhaps that increases the overall f/number too so reducing other aberrations.

The Pentax HS is a good example of this style of design with a 2 element objective (i.e. one fixed planoconvex lens (easy to clean on the outside) and one "close" positive focusing lens, I suspect made of different index glass) and a simple (Kellner? RKE?) 3 element EP give a surprisingly good bin for a very low parts count (and low manufacturing cost).

I think the Big 4 may still use the negative focuser given the cutaway diagrams I've seen. That would lead to more compact bins.

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Interesting speculations, Kevin. Now I'm depending on you to do some web research and come up with plenty of hard supporting information. ;-))

Are you sure about the objective design and focusing method of the Pentax HS? I haven't seen that binocular but Pentax information says the objective is 2 elements/1 group. Wouldn't that have to be a cemented doublet? If so, the focusing would have to be a moving objective with a flat glass protective plate in front of it.

Henry

henry link said:

Interesting speculations, Kevin. Now I'm depending on you to do some web research and come up with plenty of hard supporting information. ;-))

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A combination of optics and an email from a certain optics designer telling me I got this right makes me think I know what I'm talking about.

henry link said:

Are you sure about the objective design and focusing method of the Pentax HS? I haven't seen that binocular but Pentax information says the objective is 2 elements/1 group. Wouldn't that have to be a cemented doublet? If so, the focusing would have to be a moving objective with a flat glass protective plate in front of it.

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Quite sure.

I thought that initially but tracking the reflections off the back surface of the the "flat plate" shows it has a curved back (as I said ... it's planoconvex). It's a lens.

The two elements/1 group is the objective + focuser and no it doesn't have to be a cemented doublet otherwise you'd be an element short for the focuser as Pentax doesn't mention any other optical components. You can see the focuser lens with this same sort of close to the objective large lens sliding tube assembly. It's a common design pattern at the low end. And the Chinese EDs show that the pattern can be used to make optically very good bins.

The HS is a designed to a price bin. And it's rather well done for that.

They really do make bins this way, Henry

Kevin,

Maybe you could encourage this designer to occasionally post here. It would be very useful to have some input from a real pro to keep us from veering too far out of line.

I'm afraid I'm still doubtful about the Pentax focusing method. As you know "groups" are cemented multiple elements or single elements separated by air spaces, thus 2 elements/1 group should only refer to a cemented (or oiled) doublet. An objective with one fixed element and one moving element would be 2 elements/2 groups. The objectives of the 80 and 100mm Pentax scopes, for instance, are described as 3 elements/3 groups, and consist of an air spaced doublet up front and a small singlet close to the prism. Also the specs Pentax give for their other internal focusing binoculars conform to the usual industry practice and include the focusing lens as an objective element. Most are listed as 4 elements/3 groups, which is a common arrangement with a fixed triplet in 2 groups (cemented doublet and singlet) and a moving focusing singlet for the third group. The only other binoculars Pentax describe as having 2 element/1 group objectives are eyepiece focusing Porros with cemented doublet objectives.

Henry