RF accuracy chart

[ampguy]

Sure Mike!

Sure Mike!

I think you also mean @ min. distance, not infinity, right? 😉

I'll need a stationary object, a bit of light, and something with some contrast, even one of those dslr focus test charts would work. You want to up the stakes a bit?? 😀

Next meet up Ted, if you don't accurately focus the 75mm 90% of the time, the first round is on you. No drinking before the test either. We'll announce this before hand and we'll be guaranteed to have a good turn out. Free beer!

 

[ampguy]

Ok

Ok

Well I'll just state facts so as to not start unfounded rumours:

Fact 1: Erwin Puts says the German flanges are a different ligheter material than Canadian 75/1.4's.

Fact 2: Different materials can have different thicknesses.

Fact 3: Different flange thickness can affect focus accuracy.

I'll leave the technical conclusions to the engineers 😉

German, serial number beginning in the 39 range.

I think I may have caught a glimpse of your theory in another thread...

 

[ampguy]

As mentioned earlier I thought I would post my reference - on page 223 of the Osterloh Leica M Advanced book, v2 (2005), it mentions that the DOF scales of Leica M lenses, and viewfinders of the M2, and M3 are based on a coc of 1/30mm which is .033333333, making the RD1 possibly .02222222 giving a few more greens and yellows, for example, making the CL and the optional kit tele 90/4 now green (97%). I sitll think the basic premises are missing something, maybe a VF patch readability factor or inclusion of a factor for min. dist. as the low % for CL and 40/1.4 amazes me.

Still, I think it is a very useful graph that Roland, LCT, and the others have done. The curves chart (latest one) is also interesting.

 

[ampguy]

sticky please? maybe move to the lens/optical section?

 

[Kim Coxon]

Done.

Kim

sticky please? maybe move to the lens/optical section?

 

[splitimageview]

Spreadsheet is here (fixed broken link)

 

[ampguy]

Thanks, I think Roland and LCT did a great job with this tool. Answers a lot of questions on what combo is usable, although there will be exceptions with different peoples eyes, alignments, etc. I've saved a local copy and have referred to it dozens of times sometimes adding my own tweaks.

 

[johank]

Contax G1 has 41mm
G2 52mm
IIa+IIIa 72mm
II+III 92mm in base length.

 

[splitimageview]

Here is a link to the spreadsheet from a few years ago.

RF Accuracy Chart

 

[pagpow]

OK guys, very nice thank you. I get the identification of incompatible lenses or inadequate EBLs. Dumb question... how do I read the percentage entries in the cells? percentage of what?

 

[splitimageview]

<=100% indicates the lens is within the capabilities of the indicated rangefinder (camera, camera+magnifier, etc.)

 

[pagpow]

Thanks, splitimageview. That I understood.

What I don't understand is the significance, if any, of differences under 100% -- i.e. if a lens/rf cell entry reads 60%, does that mean that it is more difficult to focus than one reading 21%?

What's the numerator and denominator?

 

[splitimageview]

The numbers are just the results of the equation. It doesn't really matter what the exact percentage is as long as it is within the capabilities of the hardware (i.e., 100% or less.)

I've edited the sheet to show Red (calculation above 100%), Yellow (90%-100%), and Green (below 90%.)

 

[pagpow]

Thanks, splitimageview. So it's essentially binary -- go if less than 100%, no go if more than 100%? discounting the conversation upthread, of course.

 

[wes loder]

In addition to base and magnification, an additional factor to consider is the amount of movement of the prism that moves the RF image. Prisms such as found in the Barnack rangefinder and their copies (including the Nikon RF) have far less rotation movement than the Zeiss rotating external prisms, or the sliding prism in the Contax II, III and IIa and IIIa. In addition, one must consider whether the rangefinder uses a conincident image , or a split image, with split image effectively being more accurate. Just some thoughts. Most accurate rangefinder ever put in a 35mm camera was probably the Kodak Ektra.