Why have helical focusers become popular? (1 Viewer)

[tenex]

The helical focuser on my S2 works well enough most of the time, but it gets tricky at the maximum 70x of the Meopta eyepiece and worse above that, seems a bit of a reach/grope at times, and would be awkward with a stay-on case if I used one. Whereas the coarse/fine knobs on a Kowa (77?) I recently used felt very natural and had none of these issues. So what has made a single helical focuser seem so desirable, or knobs undesirable? Was the drive mechanism of the knobs prone to trouble? Does the focusing lens end up in a less advantageous position? Why have so many high-end models gone to helical that I didn't even think much about it when buying my first scope? (I do like the S2 otherwise, and got a good deal)

 

[WRL]

[...] Why have so many high-end models gone to helical [...]

My first thought is: Design. Looks cleaner and less cluttered.
My second thought is: Closer to the way photo lenses are operated which many got already used to.
However, I prefer the "old style", separate knob(s), preferably coarse/fine setup.

 

[tenex]

My second thought is: Closer to the way photo lenses are operated which many got already used to.

And yet most people come to scopes from binoculars, where they're used to finger knobs. This is why it seems odd to me.

 

[Tringa45]

The helical focuser on my S2 works well enough most of the time, but it gets tricky at the maximum 70x of the Meopta eyepiece and worse above that, seems a bit of a reach/grope at times, and would be awkward with a stay-on case if I used one. Whereas the coarse/fine knobs on a Kowa (77?) I recently used felt very natural and had none of these issues. So what has made a single helical focuser seem so desirable, or knobs undesirable? Was the drive mechanism of the knobs prone to trouble? Does the focusing lens end up in a less advantageous position? Why have so many high-end models gone to helical that I didn't even think much about it when buying my first scope? (I do like the S2 otherwise, and got a good deal)

Indeed. The depth of field of the scope at 70x is less than 1/12th of that at 20x, so even if the eyepiece were designed to be "parfocal" it's unlikely that a focussed object at 20x would still be sharp at 70x, despite the ameliorating effect of reduced exit pupil.
A helical focusser which is comfortable at the lower magnifications becomes very sensitive at the higher magnifications and even the 3:1 ratio of the focussers on the larger Kowas is not really enough and might be a problem if using an extender.
Some focussers for astronomical scopes have a 10:1 ratio, but here the magnification range could be in excess of 7:1 making the focusser about 50x more sensitive in degrees of focusser rotation/dioptre at the higher magnifications.

John

 

[Tringa45]

And yet most people come to scopes from binoculars, where they're used to finger knobs. This is why it seems odd to me.

Well, helicals on bins is IF, which is also a PITA.

 

[Binastro]

I had no trouble with focus at 600x or more.
No fine focus knob.

I also have no trouble at 145x with no focuser at all, only push pull focus.
I just minutely rotate the tube with a little pressure for fine focus.

What I do have trouble with is a normal 8x binocular looking at someone 15 metres away walking down the street, where the Minolta 8x23 autofocus binocular is pin sharp.

Regards,
B.

 

[Tringa45]

I had no trouble with focus at 600x or more.
No fine focus knob.

Except when changing eyepieces you would not need to make frequent focus adjustments on an astronomical scope. Birders are doing it all the time.
It also depends on the gearing of the focusser, which could be expressed in degrees of rotation per dioptre. I did some measurements on binoculars some years back: Focus Overtravel (compatibility for the near-sighted).
At binocular magnifications there is practically no difference in focus between 1 km and infinity.
At 600x magnification it is a difference of 360 dioptres!

Regards,
John

 

[yarrellii]

I've asked myself this question (like the OP) many times.

I'm currently using a helical focuser on my Swarovski ATS. Af first, after years of using a "traditional" double knob on an Opticron MM3ED 60 I thought that "I had to get used to the new focuser", I somehow assumed that it was my fault no to appreciate its virtues. After more than 3 years using the ATS, I can confidently say I frankly can't see the reason the industry changed from traditional to helical, really. Personally, I find it's simply worse, especially at hight mag (which is why you use a scope in the first place) or if there's some shake (like on windy days).

I concur with @WRL about his first though, the weight of "design" (in the bad sense of this word, as if there was not a ton of design on a double knob), the weight of looks and aesthetics. I would dare going a bit further and say "fashion". For me, seeing a lot of major manufacturers switching to helical focusers can only be explain by the power of fashion and the fear of being "outfashioned" and be perceived as old (and thus "worse"). A similar thing could be said about open bridge design in binoculars. The design of the first Swarovski EL was a hit, and basically everyone followed suit (Zeiss SF, Leica Noctivid, etc.)... for several years, it seemed that no producer worth its salt could produce a top-notch piece of optics and not adopt the open bridge design in the style of the EL. Now, it seems that Swarovski has made a bold move with the NL and finally even Zeiss has walked away from it with the SFL. Mind you, I have an EL as my go-to bincoular , but I think there's more to binoculars than open bridge. In a similar way, I think helical scope are perceived as "more modern", "more contemporary and thus better", but in the field this might not necessarily be the case. In fact, I applaud and admire Kowa for having the personality and keeping the traditional double knob on their much lauded scopes.

One final remark. Is there someone around here with enough technical knowledge or expertise in the optical industry to comment on whether the helical focuser is lighter and whether this can be a deciding factor?

 

[tenex]

Speaking of EL, was it also Swarovski who first offered a helical focuser on ATS? "Design" then, indeed... and emulation again.

 

[Ruff-Leg]

My helical focuser birding scopes:

1985 - Celestron C90
1991 - Swaro AT-80
2004 - Nikon ED Fieldscope 82A
2020 - Nikon Monarch ED 82A

I find scopes with 'traditional' focusers to be awkward. It just depends on what you're used to.

 

[henry link]

The first Nikon Fieldscope had a helical focuser in 1981. Maybe it was the first one.

 

[tenex]

I find scopes with 'traditional' focusers to be awkward

In what way?

I wonder what the first advertisements said about helical focusers. Probably too old to be online.

 

[kabsetz]

I assume that a helical focuser is simpler to implement when the optical design features a moving lens element for focussing such as in the telephoto-type Fieldscopes and most current spotters. When focussing was done with a moving prism element, like in most Kowa scopes prior to 77x/88x series, a knob was just as easy or easier to build.

Personally, I am fine with either type of focus. My current Swaro has helical, and it works fine. Nikon Fieldscope helical focus has a very fast ratio, which makes fine focussing tricky, but I birded happily for over a decade with those as well. I also like Kowa double knob focussing, but don't find it superior to my Swaro, just different.

 

[Ruff-Leg]

In what way?

I wonder what the first advertisements said about helical focusers. Probably too old to be online.

Only awkward in that it's not what I'm used to. With helical, my hand is generally on the focus ring which helps stabilize. When I try someone's Kowa, I fumble for the focus. I'm sure I would get used to it. But, with nearly 40 years of helical use, it's just 'normal.'

 

[William Lewis]

Nikon claims the Monarch ed scopes have dual speed focusing built into one helical control. I've used one for a few months now. Its ok but not quite slow enough to be easy to use at higher, 45+ x magnifications. To be honest I haven't really noticed it's dual speed in use.

I like the helical system personally, I don't run a tripod arm so have one hand on the rubberised prism housing to point and zoom as necessary and the other on the focuser, most of the time I use the lowest mag possible for better depth of field (so less precise focusing needed) more exit pupil and a wider tfov.

 

[henry link]

The Nikon Monarch does not have separate coarse and fine adjustments that can be chosen by the user. It's a variable speed focuser that automatically speeds up at close distances to compensate for for the longer focus travel required to make each diopter change in focus a close distance compared to long distance. It works so well I don't notice it.

 

[tenex]

It's a variable speed focuser that automatically speeds up at close distances

...which is to say that it slows down at the longer distances where higher magnifications would be used. Does this make fine focusing less tricky? Is some degree of variable speed common? This would go a long way toward solving the helical problem for me. I don't think Meopta has it.

 

[William Lewis]

It does slow down at longer distances but not by enough to make focusing at 60x mag easy for me at least, it's still a case of very small movements. Overall it's much better than the amount of focus winding I used to have to do with my CTC 30/75 although I did appreciate that scopes distance markings on the focuser barrel.

 

[henry link]

...which is to say that it slows down at the longer distances where higher magnifications would be used. Does this make fine focusing less tricky? Is some degree of variable speed common? This would go a long way toward solving the helical problem for me. I don't think Meopta has it.

Yes, the mechanism that changes the speed operates on a smooth curve, so there is no sudden obvious change in speed. It's hard to know how effective it is since even at its slowest the speed it could still be faster than you want.

I don't think variable speed is common, but marketers don't seem to know how to describe its function properly, so it's sometimes just given a footnote or maybe not even mentioned at all. I've only seen it in the Nikon Monarch Fieldscope and in some members of a Kamakura made family of very similar scopes. Among those It's definitely included in the Zeiss Gavia and the old Brunton ICON, but it might also be in their siblings: the Kite KSP 80, Maven S.1 and Vortex Razor HD.

 

[Alexis Powell]

The first Nikon Fieldscope had a helical focuser in 1981. Maybe it was the first one.

How about the B&L Discoverer scope w/helical focus, when did it come out? The 15-60x60 version was quite popular in the 1980s (and maybe didn't exist until that decade? Was there an earlier version with helical focus? The older balscopes and spacemasters had knob focus).

--AP