An interview with Gerold Dobler, leader of the SF design team (2 Viewers)

[Chosun Juan]

Lee thanks for the crumbs :t:

Details on the fixes would be nice :cat:

Perhaps the cynical cranky pants crowd could learn a thing or three if they paid attention to something other than petty sniping :storm:

Some of the optical details in this bin are very interesting :brains:


Chosun :gh:

 

[Alexis Powell]

Why speculate when you can view with the actual unit? ...

I find the discussion interesting and educational. When we finally get solid answers to what was done, this discussion gives them context and so adds appreciation. Ah, so they did it that way, rather than that way...cool!

--AP

 

[jan van daalen]

I find the discussion interesting and educational. When we finally get solid answers to what was done, this discussion gives them context and so adds appreciation. Ah, so they did it that way, rather than that way...cool!

:t::t:

Jan

 

[Vespobuteo]

Why speculate when you can view with the actual unit? Wait for the real thing, all this predictive modelling is getting oh-so-familiar here.....even with Brock somewhere off in the weeds.

Wish there were units to see,
Still no sign of any in stock, anywhere
Or any on the way,
Arrival dates are postsponed, again
Annoying,
If the sf really shines i will get one,
Otherwise swaro 8x32 sv...

 

[Chosun Juan]

.....
I am convinced that they got the aberrations well controlled - just want to know how they did that. Because the textbooks are telling us that cemented doublets are offering an insufficient number of degrees of freedom to control the aberrations. The HT is an air-spaced triplet, quite a bit more complex than the design of the SF's objective. I guess that the latter is in fact air-spaced, but if it is not, then Konrad Seil must have had some good ideas to make it work.

Cheers,
Holger

Holger,

How far away can the day be when lenses are joined by "cold fusion" ? ie. the surface finish and shape dimensions are so precise that when placed in alignment and proximity the are "welded" together. This could be further secured by evacuating any air between the space and perimeter sealing the combined unit for durability. The lens combination is then further held in place by the forces of atmospheric pressure and internal nitrogen (or whatever gas) charging.


Chosun :gh:

 

[Holger Merlitz]

Holger,

How far away can the day be when lenses are joined by "cold fusion" ? ie. the surface finish and shape dimensions are so precise that when placed in alignment and proximity the are "welded" together. This could be further secured by evacuating any air between the space and perimeter sealing the combined unit for durability. The lens combination is then further held in place by the forces of atmospheric pressure and internal nitrogen (or whatever gas) charging.


Chosun :gh:

This is possible, but not reasonable: Because the two glass elements would have different refractive indexes, light would be reflected at their contact surface. This implies that one had to coat them separately before assembly. Instead, manufacturers are using a transparent lens-cement, the index of which lies in between the indexes of both lens elements, and in this way reflections are greatly reduced and a coating of the both surfaces can either be avoided, or at least simplified.

A second aspect are thermal expansion coefficients, which differ among the jointed lens elements. Upon a change of temperature, tensions arise which lead to an image degradation or, in a worst case, to a fracture. The lens-cement has a certain elasticity which compensates for such a thermal stress between both cemented lens elements.

Cheers,
Holger

 

[Troubador]

HT Sectional Drawing

For the sake of completeness and for comparison with the SF drawing already posted, here is the equivalent drawing for HT.

Lee

 

[Vespobuteo]

This is possible, but not reasonable: Because the two glass elements would have different refractive indexes, light would be reflected at their contact surface. This implies that one had to coat them separately before assembly. Instead, manufacturers are using a transparent lens-cement, the index of which lies in between the indexes of both lens elements, and in this way reflections are greatly reduced and a coating of the both surfaces can either be avoided, or at least simplified.

A second aspect are thermal expansion coefficients, which differ among the jointed lens elements. Upon a change of temperature, tensions arise which lead to an image degradation or, in a worst case, to a fracture. The lens-cement has a certain elasticity which compensates for such a thermal stress between both cemented lens elements.

Cheers,
Holger

would be interesting to know if the new light-gray color (of the SF rubber armor) have something to do with the new lens materials. More heat sensitive?

Canon telephoto lenses are said to be white because the fluorite elements are sensitive to heat. (Nikons new fluorite lenses are black though…)

 

[henry link]

In this case, the CaF2 element is the sensitive one and should be kept inside. Now, the "flinty" (negative) element is in front, but actually it is made of a crown glass. In other words, the "ED" element replaces the crown, and a crown replaces the flint - in this way the dispersion of the entire setup is reduced (as is mentioned by R. Ceragioli somewhere in his writeup about telescope lenses).

The question is: Are these doublets actually cemented, or does there exist a tiny air space? If they are in fact cemented, I wonder how they managed to keep the aberrations sufficiently low.

Cheers,
Holger

Hi Holger,

As always with these line drawings we are left to guess how accurate the details are intended to be. This one looks like a serious effort to follow the spacings and curves of the lenses, but who knows? If it is accurate the usual practice with a cemented doublet, as you know, is to use a single line to represent a cementing as we see here. An air space, however close, should be represented by two lines. I agree that it seems odd to give up a degree of design freedom that would add nothing to the weight, but that looks like what was done.

Henry

 

[henry link]

For the sake of completeness and for comparison with the SF drawing already posted, here is the equivalent drawing for HT.

Lee

Thanks Lee. This diagram is better than an earlier one that only showed lens edges. In this one we can see the curves and cementings. If it's accurate it shows exactly the same optics as the 42mm FLs installed in a different housing. It looks like the optical improvements were confined to glass transparency, coatings and baffling.

Henry

 

[james holdsworth]

Thanks Lee. This diagram is better than an earlier one that only showed lens edges. In this one we can see the curves and cementings. If it's accurate it shows exactly the same optics as the 42mm FLs installed in a different housing. It looks like the optical improvements were confined to glass transparency, coatings and baffling.

Henry

There are other differences - most notably the size and shape of the so-called sweetspot - something I would think has something to do with physical differences.

Although a very personal matter, and few seem to find consensus, I find the ''sweetspot'' to be quite different between the two. The FL has a much smaller zone of best sharpness and the sweetspot tends to be mostly central. In the HT, this zone of sharpness is noticeably larger and the sweetspot extends nearly top to bottom and forms a much more ''oval'' shape. Actual edge sharpness [side-to-side] seems about the same but I have trouble with this as I get flickers and black-outs if I try to look too far off axis.

 

[Troubador]

Thanks Lee. This diagram is better than an earlier one that only showed lens edges. In this one we can see the curves and cementings. If it's accurate it shows exactly the same optics as the 42mm FLs installed in a different housing. It looks like the optical improvements were confined to glass transparency, coatings and baffling.

Henry

Henry

Looks that way doesn't it.

Regarding the SF objective doublet, I will try to find out whether it is air-spaced or cemented.

Lee

 

[Troubador]

Holger and Henry

Another little snippet of info: SF's focusing lens is also in CaF2.


Lee

 

[Troubador]

Hi Holger,

As always with these line drawings we are left to guess how accurate the details are intended to be. This one looks like a serious effort to follow the spacings and curves of the lenses, but who knows? If it is accurate the usual practice with a cemented doublet, as you know, is to use a single line to represent a cementing as we see here. An air space, however close, should be represented by two lines. I agree that it seems odd to give up a degree of design freedom that would add nothing to the weight, but that looks like what was done.

Henry

Henry and Holger

The objective doublet is indeed cemented, not air-spaced.

Lee

 

[ticl2184]

Lee

Great interview and great questions....
Good to know that Gerry confirmed the presence of image softness in the 10x, which I obseved at Birdfair.

Good to know I don't need my eyes tested as suggested by some...


Cheers Tim

 

[Troubador]

Lee

Great interview and great questions....
Good to know that Gerry confirmed the presence of image softness in the 10x, which I obseved at Birdfair.

Good to know I don't need my eyes tested as suggested by some...


Cheers Tim

Hi Tim

Thanks for your kind words.

Gerold did confirm the effect you mention in the 10x but to be clear the 'softness' he described is relative to the rest of SF field of view. Taken in isolation this area, in his opinion, would still be considered competitive with other models with respect to sharpness, and in normal circumstances would not detract from the enjoyment of the view.

Lee

 

[ticl2184]

Lee

Yes I would agree with most of that.... I use my 10x42 SV's for Astronomy.... So any softness in any part of the fov is really noticable and annoying.
This is why I want tack sharp images across the field...Gladly my SV's offer this and do what is says on the tin....
Sadly, because I a 10x42 man,,,, I may have to pass on the 42 SF this time due to the softness.

Additionally I think posts of this nature, where by key people are asked specific questions concerning their product, provide a really useful and transparent medium to help explain issues concerning the SF...
Dr Doblers honesty is quite refreshing and welcome....

Thanks to you and Dr Dobler


Cheers Tim

 

[Troubador]

Hi Tim

We were on the Isle of Islay recently and in the dark skies they have there the Milky Way was stunningly dense. We could barely make out familiar shapes due to the density of the visible stars.

They looked pretty good through my HT 8x42s even though 42s aren't supposed to be up for the job, but as I say we had the benefit of no light pollution.

Lee

 

[bh46118]

Am I reading this right, the designer of the SF confirms that it has a soft view ? If this is the case, then how is it the new state of the art ?

Hi Tim

Thanks for your kind words.

Gerold did confirm the effect you mention in the 10x but to be clear the 'softness' he described is relative to the rest of SF field of view. Taken in isolation this area, in his opinion, would still be considered competitive with other models with respect to sharpness, and in normal circumstances would not detract from the enjoyment of the view.

Lee

 

[NDhunter]

Am I reading this right, the designer of the SF confirms that it has a soft view ? If this is the case, then how is it the new state of the art ?

That means the new King has not yet earned the crown.

Until the new Zeiss production models get out, we should not get
too excited.

Jerry