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Archive 2008 · Accurate Flange to Focus distances
  
 
AlexTokyo
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p.1 #1 · p.1 #1 · Accurate Flange to Focus distances


I was looking for a list of accurate Flange to Focus distances and didn't find it anywhere (even here!). The main idea was to avoid guess work (i.e. infinity focus) and modify the adapters (or the lens) to stay as close as possible to the original Camera register. With proper distance, you get rid of CA issues etc. and maximize IQ.

Tired of searching, I downloaded a bunch of old Service Manuals. Here is a summary of the values I found with tolerance. If I missed anything or if you have some other source, please let me know.

Minolta MD: 43.73mm (+ 0.03, -0.00) from SRT Repair Manual "Body back measurement"
Nikon: 46.67mm (+/- 0.02) from N50 Service manual "Dist. between lens mount & outer film guide rail"
Canon EF: 44.14mm (+/-0.03) from EOS 1 Repair Manual "Standard to outer rail"
Olympus OM: 46.00mm (+/-0.02) from OM-1 Service Manual "Flange back standard"
Pentax: 45.46mm (+/-0.04) from Pentax-ME Serice Manual "Flange focal distance"

You will notice that these values differ quite a bit from what we usually see (Nikon at 46.5, Canon at 44 etc). This might explain some IQ issues. Also, nice to see that Minolta had the tighter tolerance of all.

OK, this is my first post here so don't jab at me too hard,
This is a great forum, couldn't have converted my Rokkor without it! (Thx Cogitech)
Alex



Jul 12, 2008 at 05:07 AM
JimBuchanan
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p.1 #2 · p.1 #2 · Accurate Flange to Focus distances


Thanks, for the accurate numbers. Wonder what the tolerance of the stated 47mm Leica R is?




Jul 12, 2008 at 05:32 AM
dirb9
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p.1 #3 · p.1 #3 · Accurate Flange to Focus distances


Here is a large list, I don't know how accurate the figures are. Some discrepancies can be accounted for by the fact that they may or may not take into account the thickness of the film (some measurements seem to be to the pressure plate), which is ~.13mm thick.


Jul 12, 2008 at 06:37 AM
 

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AlexTokyo
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p.1 #4 · p.1 #4 · Accurate Flange to Focus distances


The large list has a lot of data ... but not accurate enough (at least to me).

It lists Minolta at 43.5 and Canon at 44.00, giving a -0.5mm value to the lens modification, when the good number is actually -0.425mm. Same thing for the Nikon at 46.50 which is in reality 46.67.

So, maybe I am overkilling it, but 0.1mm shows on my caliper and could show in IQ as well. Didn't want to take a chance and decided to go for good numbers. If Minolta machined its camera +/-0.0015mm there must be a reason.;-)

Thanks for the link though, it is a good list to see if an adapter might exist or if lens
mod is required.

Oh, and I forgot, you are right about the film thickness mention. All data listed in the OP are supposed to be to the outer rail (does not include the .13mm film)

Edited on Jul 12, 2008 at 08:24 AM



Jul 12, 2008 at 08:23 AM
shirozina
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p.1 #5 · p.1 #5 · Accurate Flange to Focus distances


If Canon are still using +/-.003 as a manufacturing tollerance it would explain a lot when it comes to needing to choose or adjust adapters to work with alt glass.....


Jul 12, 2008 at 08:45 AM
AlexTokyo
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p.1 #6 · p.1 #6 · Accurate Flange to Focus distances


My experience with cheap adapters (brass chromed, AF confirm ~$25 from e-bay):
- wrong size (we knew that, to guarantee infinity focus)
- Good tolerances (+/- 0.002 mm)

So with a bit of patience grinding or few shims, it's OK to get to proper values.



Jul 12, 2008 at 09:17 AM







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