the last word

Photography meets digital computer technology. Photography wins -- most of the time.

  • site home
  • blog home
  • galleries
  • contact
  • underwater
  • the bleeding edge
You are here: Home / The Last Word / Lens adapter tolerance

Lens adapter tolerance

December 15, 2013 By JimK 4 Comments

The Novoflex Nikon F to Sony E adapter that I used with the Zeiss 21mm f/2.8 is short by about the same amount as the Novoflex Leica M to Sony E adapter that I used with the 24mm f/3.8 Elmar.

I got to wondering why the focusing error caused by improper adapter spacing showed up so much more with wide angle lenses. I made a plot of the focusing error caused by a half-millimeter too short adapter as a function of focal length of the lens:

focus error

The vertical axis is logarithmic. It looks like this on a log-log plot:

focus error log log

The same too-short adapter that causes an 18mm lens focused at the 18.5 meter marked distance to actually focus at infinity will cause a 135mm lens focused at the 366 meter marked distance (if you can interpolate to that) to actually focus at infinity. The error is trivial for the long lens, and important for the short one, at least if you pay attention to the marking on the lens.

Judged on the basis of focusing error on short lenses, both my Novoflex adapters are short by about half a millimeter. In the world of machining, this is a big distance. In fact, it’s so large that I don’t see how it could happen by accident. My suspicion is that Novoflex has deliberately made the adapters short. I’m not sure why they’d do that. Maybe they’ve biased their manufacturing process so that if every possible thing adds up in the direction to make the adapter too long, it will turn out to have the right length. That would make the typical adapter short.

I can see why they wouldn’t want an adapter to be too long; the user would never be able to focus to infinity. On the other hand, half a millimeter is a big error, and the fact that I have two adapters that are off indicates that I’m not looking at an outlier.

Do you suppose that they expect that the camera the lens was originally used on could be at one end of its tolerance, and the camera that the lens is being used on with the adapter could be at the other end of the tolerance band, and that they have to apply windage to the adapter to make up for that?

I tried a Metabones adapter, and it’s even shorter than the Novoflex one.

← A little EVF trick Nikon 14mm on a7R →

Comments

  1. JCDoss says

    February 26, 2014 at 4:54 am

    It’s troubling that these expensive adapters run short. Have you checked out the $20 ones?

    Reply
    • Jim says

      December 5, 2014 at 8:19 pm

      Only one. It was also too short.

      Jim

      Reply
  2. Kelly says

    February 23, 2016 at 2:52 pm

    Allowing the adapter to be short by 0.5mm will allow the legacy lens to focus at infinity before the lens reaches the infinity stop.
    This overcomes slight tolerances in lenses and adapters that may expand with heat (or some other environmental influence.

    A 0.15mm size increase on an adapter might not allow a legacy lens to focus on distant horizons.

    Reply
    • Jim says

      February 23, 2016 at 3:26 pm

      That, IMHO, is a cure worse than the disease. See this for some numbers: http://blog.kasson.com/?p=8843

      If heat affects focus materially, it should be taken care of by the lens designer, by allowing the lens to focus beyond infinity. This is commonly done. It doesn’t need to be done twice.

      Also, see this: http://www.dpreview.com/forums/post/57309905

      Jim

      Reply

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

April 2021
S M T W T F S
 123
45678910
11121314151617
18192021222324
252627282930  
« Mar    

Articles

  • About
    • Patents and papers about color
    • Who am I?
  • How to…
    • Backing up photographic images
    • How to change email providers
  • Lens screening testing
    • Equipment and Software
    • Examples
      • Bad and OK 200-600 at 600
      • Excellent 180-400 zoom
      • Fair 14-30mm zoom
      • Good 100-200 mm MF zoom
      • Good 100-400 zoom
      • Good 100mm lens on P1 P45+
      • Good 120mm MF lens
      • Good 18mm FF lens
      • Good 24-105 mm FF lens
      • Good 24-70 FF zoom
      • Good 35 mm FF lens
      • Good 60 mm lens on IQ3-100
      • Good 63 mm MF lens
      • Good 65 mm FF lens
      • Good 85 mm FF lens
      • Good and bad 25mm FF lenses
      • Good zoom at 24 mm
      • Marginal 18mm lens
      • Marginal 35mm FF lens
      • Mildly problematic 55 mm FF lens
      • OK 16-35mm zoom
      • OK 60mm lens on P1 P45+
      • OK Sony 600mm f/4
      • Pretty good 16-35 FF zoom
      • Pretty good 90mm FF lens
      • Problematic 400 mm FF lens
      • Tilted 20 mm f/1.8 FF lens
      • Tilted 30 mm MF lens
      • Tilted 50 mm FF lens
      • Two 15mm FF lenses
    • Found a problem – now what?
    • Goals for this test
    • Minimum target distances
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Printable Siemens Star targets
    • Target size on sensor
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Test instructions — postproduction
    • Test instructions — reading the images
    • Test instructions – capture
    • Theory of the test
    • What’s wrong with conventional lens screening?
  • Previsualization heresy
  • Privacy Policy
  • Recommended photographic web sites
  • Using in-camera histograms for ETTR
    • Acknowledgments
    • Why ETTR?
    • Normal in-camera histograms
    • Image processing for in-camera histograms
    • Making the in-camera histogram closely represent the raw histogram
    • Shortcuts to UniWB
    • Preparing for monitor-based UniWB
    • A one-step UniWB procedure
    • The math behind the one-step method
    • Iteration using Newton’s Method

Category List

Recent Comments

  • JimK on Relative sensitivity of Sony a7RIV and GFX 100S
  • CarVac on Relative sensitivity of Sony a7RIV and GFX 100S
  • JimK on Relative sensitivity of Sony a7RIV and GFX 100S
  • Ilya Zakharevich on Pixel shift with the Fujifilm GFX 100S
  • Ilya Zakharevich on Relative sensitivity of Sony a7RIV and GFX 100S
  • JimK on GFX 100S sensor is a 4-shot stitch
  • John Leathwick on GFX 100S sensor is a 4-shot stitch
  • Christer Almqvist on GFX 100S sensor is a 4-shot stitch
  • JimK on Three dimensionality and sensor format
  • Tom Hegeman on Three dimensionality and sensor format

Archives

Unless otherwise noted, all images copyright Jim Kasson.