Rangefinder Base Differences

[skimmel]

I'm relatively new to the rangefinder scene. I was wondering how much of a difference in the effective rangefinder baselength (ERB) is meaningful in terms of focus accuracy.

Specifically: the new Zeiss Ikon has an ERB of 55.9mm while the Leica M (0.72) has an ERB of 49 mm. (Got these off of http://www.nemeng.com/leica/031b.shtml).

How significant is the 6.9 mm difference between these 2 cameras? I realize the Zeiss isn't available yet, but can one tell, just from the difference, how much different the Zeiss may be.

Thanks.

 

[Huck Finn]

Skimmel, historically the old Zeiss Ikon AG built cameras with longer base lines than did Leica when the two were hot competitors. I think that this is the true significance of this difference, i.e. more significant to the Mareting Dept. than to anyone else. 😉

That said, a longer base line will always offer some greater precision, especially in focusing lenses that feature shallow depth of field - in particular, telephotos & normal lenses with wide apertures. For all practical purposes, however, I don't think that this is a major difference - unless in the unlikely event that you're using a 135mm lens at apertures wider than f/4. Of greater significance, I think is that for those who prefer a Leica M6 or M7 with .85x magnification for this increased focus control, they can now get something close to its effective base line on a bocy that will include 28 mm frame lines. Until now that has been the trade-off.

If you are interested in reading more on the technical side of rangefinder focus accuracy you can check the site below or better yet, pick up "Leica Lens Compendium" by Erwin Puts.

www.imx.nl/photosite/leica/technics/rfaccuracy.html

Huck 🙂

 

[skimmel]

Thanks Huck! Very useful link! Seems like it won't make a difference for me given I doubt I'll ever get a 135mm lens (and if I do, I assume using the 1.25 magnifier that I improve my ERB anyway).

I'm torn between a Leica M7 now and waiting to see what the Zeiss-Ikon looks like when it comes out in May (given its lower cost). At least the ERB doesn't seem to be a factor I should worry about.

 

[Doug]

At least the ERB doesn't seem to be a factor I should worry about.

Right, not a big deal between these two cameras I think. I agree with Huck about the extended baseline of the Z-I better allowing the lower magnification. Another issue I've found is that the longer the baseline, the more clear and obvious the correct focus becomes... The greater horizontal displacement for a given focus error leads to fast positive focus.

 

[skimmel]

Right, not a big deal between these two cameras I think. I agree with Huck about the extended baseline of the Z-I better allowing the lower magnification. Another issue I've found is that the longer the baseline, the more clear and obvious the correct focus becomes... The greater horizontal displacement for a given focus error leads to fast positive focus.

Thanks Doug. Do you think the difference between the M7 and Zeiss-Ikon would make a noticable difference in how clarity and speed of focus (say for a 50mm lens)?

Thanks.

 

[Doug]

Do you think the difference between the M7 and Zeiss-Ikon would make a noticable difference in how clarity and speed of focus (say for a 50mm lens)?

Not very much difference, but some I'd think, given both the .74x viewfinder and long baseline.

I have an M2 with .72x finder and of course the widest framelines are 35mm, easily usable at that, and it does better with the 90mm lens than my Minolta CLE with .6x and shorter baseline. The favored CLE is in the shop with sick electronics. 🙁

I've been thinking that if I were to get an M7, say, I'd choose the .58x viewfinder and look forward to usable 28mm framelines (I really like the 28mm view). And the long RF base would still do passably well for 90mm... except that the framelines will be awfully small. I'm attracted by the Zeiss Ikon, and look forward to handling one, because it appears the viewfinder is very large, has hopefully useful 28mm frames, and still has a .74x magnification for a decent view of the 90mm framelines. Its extra-long baseline is part of the equation leading to this combination of attributes. Focusing should be outstandingly fast and snappy... I doubt I'll be able to fight off the GAS attack if it turns out as good as I hope!

 

[Doug]

I guess I could add an observation I made in RFF a little while back about baseline length... I dragged out my Voigtlander Bessa-T which has quite a short baseline but high RF magnification, and compared with several other RF cameras including a Kiev 4a with very long baseline. What was immediately evident was that the long baseline means larger horizontal displacement, in proportion to the size of the object, of the doubled image for a given focus error. The Bessa-T gave a magnified view of a lesser amount of horizontal displacement, and the magnification helped the focus. But discerning that there was a focus error, and in which direction, was easier with the larger proportional displacement.

Also, of course, the larger magnification limits the field of view, as a tradeoff for its role in enhancing focus accuracy. I think this has caused some hard choices on the Bessa R3a...

 

[Huck Finn]

I agree with doug that the mechanical advantage of a long base line is always superior to increased magnification. Well put, Doug.

One note that I would add to my comments above is that a longer effective base length will be of increased value when you shoot close up. In Leica Lens Compendium Erwin Puts makes this point & presents a different chart than the one on his website, reflecting the need for increased focusing capabilities for shots that approach the minimum focus capabilities of a lens. I'm out of town for a few days, but I'll try to remember to post this next week.

It is in close focusing capabilities that may be the true edge for the Zeiss Ikon system, if there is one. With stanadard & telephoto lenses, the longer rangefinder base line will make focusing a little more precise close up, while the camera is rangefinder coupled to focus down to 0.5 meters (19.5") with lenses that have that capability, which the new Zeiss 21, 25, & 28 mm lenses do. The closest minimum focus distance of any Leica or CV lens is 0.7m (27"). I doubt that this will make a big difference to most photographers, but the capability is there for those who are interested in using it.

You are comparing two premium cameras, both with the capabilities of taking excellent pictures. I doubt that there are many situations in which you'll find limited by an M7.

 

[Solinar]

Doug, after using the Bessa R in conjunction with some modern lenses with only 90 degrees of focus travel, I most definitely had some difficulty when trying to focus from infinity with the one of kind Duane Garrett edition of the Leica IIIf and older Leitz glass that has 180 degrees of throw in the focus lever.

I found with the IIIf it was better to zone focus by guestimation and then fine tune, especially with the 90mm Elmar.

Briefly, I just wasn't accustomed to that much movement in RF patch. Whether there is a real or perceived difference on my part, I find that IIIf, which is similar to the Bessa T in focusing, is definitely more consistent in use than the Bessa R or some of my fixed-lens RF shooters.

 

[skimmel]

Thanks everyone for the incredibly helpful, and educational, info!

 

[Huck Finn]

In Leica Lens Compendium Erwin Puts makes this point & presents a different chart than the one on his website, reflecting the need for increased focusing capabilities for shots that approach the minimum focus capabilities of a lens. I'm out of town for a few days, but I'll try to remember to post this next week.

.

Here's the Puts' chart of minimum effective base length required for rangefinder focus accuracy. The first column is for normal picture taking, the second is for slides or wehn enlargements are planned.

50/2.0 = 12.5 - 16.3
50/1.4 = 17.9 - 23.3
50/1.0 = 25.0 - 32.5
75/2.8 = 20.1 - 26.1
75/1.4 = 40.2 - 52.3
90/2.8 = 28.9 - 37.6
90/2.0 = 48.5 - 63.1
135/3.4 = 53.6 - 69.7
135/2.8 = 65.1 - 84.6

Based on this chart, the Zeiss Ikon would meet the minimum requirements for use with a 75/1.4 with slides & enlargements and for use with the 135.3.4; an M6 or M7 (.72 mag) would not but an am M 6/7 (.85) would. Neither ZI nor M would meet the requirements of the 90/2 for slides/enlargements or for the 135/2.8, but the ZI or M (.85) would get you closer to the recommended minimum ERB than M (.72). Only an M3 (62.3 ERB) would approximate the ERB required for the 90/2 in critical focus situations. For all other focal length/aperture combination, the M 6/7(.72) is superb.

 

[skimmel]

Thanks Huck! I'm keeping a copy of that info in my files!

What do you think about the 1.25x magnifier? Per Leica, it makes the 0.72 finder ERB 62.3mm (and the 0.85 73.6mm). Looks like, with a 0.72 Leica, you cover the 75/1.4 with the 1.25 magnifier for slides/enlargements and come close with the 90/2.0.

 

[skimmel]

By the way, if anyone hasn't seen this yet (it's a PDF file), here's the info on the ERB with the 1.25x magnifier:

http://www.leica-camera.com:/imperia/md/content/pdf/msystem/30.pdf

 

[andrewn]

What is less readily discernable than base length and maginification is the engineering precicion of the rangefinder mechanism. As we all know with an SLR what you see is what you get, however if there is any any inaccuracey in a rangefinder's componants, or indeed the lens cam then true focus will not be found, despite what the split image shows. This is something that you can not tell from the specifications. Whats more, a well toleranced rangefinder when new may not stay true indefinately. Some may stay in correct adjustment for longer than others. In this respect we do not know how the Zeiss will compare to the Leica.

 

[Huck Finn]

A couple of good points, Andrew. The issue of tolerances is a good argument for a longer base line - even if your lens doesn't require it. Any slack in your rangefinder will be mitigated by a longer base line, i.e. a 1 mm error in rangefinder cam precision will have double the impact on a 37 mm Bessa base line than it will on a 74 mm ZI base line that is twice as long.

I hate not knowing whether my equipment is functioning properly - whether it's Leica or anything else. Frustrating. The April article in "Shutterbug" hints that Zeiss has installed some upgrades at Cosina in quality control for the production of ZI & its lenses. I hope this is true.

With an SLR, you don't actually get what you see unless you are shooting at the maximum aperture of the lens. Since you are viewing through the lens's widest aperture & wide apertures reduce depth of field, things that look out of focus may actually be in focus in your picture. This is the opposite of an RF where everything is in focus in your viewfinder window - except for the rangefinder patch.