brian

Lives in United States Petersburg, VA, United States
Works as a lens designer, photographer, entrepreneur
Joined on Oct 2, 2000

brian's recent activity

  • 0.5x is possible, but only in special circumstances unless you're willing to give up on image quality.  For example, I designed a general-purpose 0.5x reducer for the Pentax-Q system, and it ...
  • Exactly correct. Non-linear, e.g. mechanically-compensated zooms have been around since at least the early 1950's, and possibly earlier. An example is Harold Hopkins' lens, see U.S.P. 2,663,223. ...

  • Hi Alan: I've seen Speed Boosters produce faint greenish ghost images when a super bright object like the sun is in the field of view.  However, I haven't seen the sort of glare you are showing - ...
  • Replied in It Depends . . .
    In many cases a FF lens plus Speed Booster is significantly sharper than an equivalent native lens.  Case in point are the Voigtlander f/0.95 lenses, which are very weak wide open and can't match ...
  • The lenses I was working on had multilayer coatings that were harder than the underlying glass substrate.  Not sure what would happen with old style soft coatings.  But I wouldn't use Q-tips in ...
  • Replied in Fungus
    I've recently had surprisingly good results clearing fungus from glass surfaces with hydrogen peroxide.
  • Not quite.  You're measuring the distance between the *image* of the iris blades (as viewed from the rear of the lens) and the image plane. When you look through the back of the lens at the iris ...
  • The exit pupil is the image of the aperture stop as seen from the rear of the lens.  The exit pupil distance is the distance from the exit pupil to the image plane.  To measure the exit pupil ...
  • Hi: I have a sample of the Canon 17-55mm lens, but have not measured its exit pupil distance(s).  Bear with me because I'm currently a little busy, but will try to do the measurements relatively ...
  • The 0.64x XL Speed Booster was designed to fully cover the m43 sensor.  Vignetting issues can occur when the master lens has an insufficient image circle diameter.  For m43 using the XL the master ...
  • I think it comes down mostly to a tradeoff of lens speed and size.  The native lens is compact but slow at f/2.8.  The Sigma+Speed Booster is large but 2-1/3 stops faster at f/1.2.  Its a little ...
  • Replied in Diffraction
    Its true that small scale lenses will reach the diffraction limit quicker as they are stopped down because they have smaller geometrical aberrations.  However, diffraction is mostly irrelevant in ...
  • I agree that tolerances are looser for larger scaled-up lenses, but part of my point was that smaller scaled-down lenses can still be made well despite tighter tolerances because the smaller parts ...
  • Hi Roger: I was actually speaking to both lens design *and* manufacture.  For example, about fifteen years ago I was the only optical engineer at a large OEM camera maker with a factory in China. ...
  • I have not read through this entire thread, or the earlier one alluded to, so my apologies if I am re-stating something that someone else has said.  Imagine you have a lens design for 24x36mm. ...
  • T-stops only measure transmission of the lens relative to the f-number.  The 800-lb gorilla in the room is the angular sensitivity of the sensor, which causes a drop in signal starting about f/2. ...
  • You're right, a 135mm f/1.8 + 0.71x Speed Booster does not become a 90mm f/1.2.  It becomes a 96mm f/1.2.  The combination really is a completely different lens, with a shorter focal length and ...
  • Ye of little faith!!
  • I'm not nearly that expensive.  Canon might be surprised by how reasonable I could be!
  • Hi Tom: I've got a few 0.5x m43 reducer designs, but they only work with a few selected lenses with a large working distance. In the past I've encouraged Metabones to build an EF to EF-M adapter ...
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