Manual Focus Lenses Forum

BurstMox · Expire: 2016-08-02

Hello,

I came across a soviet triplet lens on which the focus is done by moving the front element only (not the full optical block like all the other soviet lenses I met).

I was wondering if it was common thing in the west, especialy in Germany at this time, and if you know other lenses that are operating this way (war or pre-war time).

Note the diaphragme located behind the front lens also, like Leitz tessar 50/3.5 if I remember right.

#1

danfromm · Joined: 04 Sep 2011 Posts: 600

stevemark · Joined: 29 Apr 2011 Posts: 5507 Location: Switzerland

BurstMox · Expire: 2016-08-02

Thanks a lot for your quick answers!

I checked the Kodak Tourist, it's a medium format folding, right? Do you know compact cheap 35mm camera using this at this period?

alex ph · Joined: 16 Mar 2013 Posts: 1802

I guess, almost any Zeiss Ikon folder, with triplets and tessars.

titrisol70 · Joined: 14 Dec 2021 Posts: 211 Location: State of Denial

jamaeolus · Expire: 2015-08-20

Consider a folding camera. If you mount the shutter in a fixed spot and ony screw in/out the front element (which will be screwed in place to begin with) your camera is dramatically less complex. A screw in lug to provide minimum and maximum and you are done. By contrast moving the front apparatus, shutter, shutter bracket and lenses as a single unit while keeping everything parallel to the film plane is a much more daunting task. Optically it will generally be inferior though, as you are changing the spacing of the elements as you focus. With a solid frame, focal plane camera it is less of a challenge, since you can easily add a helicoid between the optical section and the camera frame.

calvin83 · Joined: 12 Apr 2009 Posts: 7740 Location: Hong Kong

Front focusing is much more common than rear focusing in the old days...

RokkorDoctor · Expire: 2025-05-01

Fairly common; it cuts down on machining cost for the focus helicoid, and for (post-war) auto-aperture cameras it also (very marginally) reduces the complexity of the aperture actuator mechanism.

Where this focus arrangement is employed the first element is usually of relatively high power compared to the overall power of the optics, which means only a small amount of movement is required to cover a usable focus range. This in turn means a less expensive single-start simple screw thread can be machined for the focus instead of a more expensive conventional long multi-start helicoid thread.

The compromise is that the maker needs to decide at which focus distance the aberrations are best corrected; for other focus distances the aberrations will become progressively more noticeable compared to unit-focus designs.

paulhofseth · Expire: 2018-06-28

sirs,

the VoigtlÃ¤nder color skopar was front element focussing on some cameras. I seem to recall that someone investigated how that changed results and concluded that setting at 20meters gave the best results. Not certain whether it was at taunusreiter.de who nevertheless described that tessar clone as very laudable.

p.

kymarto · Mon Aug 21, 2023 11:17 am

Certainly most if not all German folders and turret cameras without rangefinders used front element focusing. I have a number of the faster f2.9 lenses from these cameras (Balda Baltar, Isco Westar and Isco Westar C, Enna Correlar). If one takes these lenses off and mounts them on a focusing helicoid for mirrorless, such that focusing can be done by moving the whole lens after changing the front focus, some interesting things result. Focusing with the front element changes the spherical aberration correction. It appears that most manufacturers set optimum correction at middle focusing distances, and let close focusing and infinity do what they might. Many of these lenses do not exhibit a great difference, but the Enna Correlar is an exception to the rule. At infinity the bokeh is reminiscent of the Trioplan, however with heavier and less bright outlining of the bokeh circles. At minimum focal distance it turns into a soft lens, with severe undercorrection of spherical aberration. The Westars exhibit some slight change, but nothing like the Correlar.

#1 - infinity

#2 - infinity

#3 - closest

#4 - mid

Ernst Dinkla · Joined: 30 Nov 2016 Posts: 498

calvin83 · Joined: 12 Apr 2009 Posts: 7740 Location: Hong Kong

eggplant · Joined: 27 May 2020 Posts: 517

stevemark · Joined: 29 Apr 2011 Posts: 5507 Location: Switzerland

Jozef_AV · Joined: 24 Sep 2015 Posts: 39

Interesting thread.
I have a 35mm film lens that also uses front element for focusing and the results are similar.
Its a triplet, Steinheil Auto-cassaron 50mm f2.8.

When at infinity, with only focusing helicoid used for getting closer, it does nice bubbles like trioplan, domiplan etc...
If you use the lens focusing mechanism to get you to MFD 0,8m +helicoid for a bit of extra reach, bokeh is way smoother, bubbles are nearly gone.
Not that I am in need of 50mm/f2.8 bokeh, especially if it can do bubbles, but its nice to have the option, 2 in 1.

Also not all lenses on medium format folders had focusing done by front element, the older ones relied on extending the bellows, getting the lens further away from film.
For example D.Rodenstock Trinar 10,5cm f4.5.
But even there I found out that if you unscrew the front element by 1 turn the results are actually sharper than in its original "correct" state.