alanr0

alanr0

Lives in United Kingdom Harlow, United Kingdom
Joined on May 13, 2005

alanr0's recent activity

  • Jim, Your measurements suggest that the effect on read noise is small, but there could be a larger self-heating effect at shutter speeds slower than 1/2000. One mechanism for temperature-dependent ...
  • I should wait until they actually put it on glass before you get rid of your current lenses.  It's on silicon at the moment, and only works at infra-red wavelengths. "No CA" is arguable something ...
  • Thanks for the link , but I couldn't find a direct answer the OP's original question "why is it called four thirds". There is a rather oblique reference to size here : From context "4/3 type" ...
  • Bearing in mind your comments about selective quoting If we quote more of the very same text ( my italics ): From the beginning of the same Wikipedia section : And below, complementing rather than ...
  • Also reported in this thread Paper: http://arxiv.org/ftp/arxiv/papers/1411/1411.3966.pdf Focal length varies strongly between the 3 design wavelengths with a significant level of scatter, even at ...
  • From the same Wikipedia article: Cheers
  • Leonard is correct.  Magnesium fluoride is an inorganic material and unlikely to dissolve in acetone.  However acetone  will dissolve certain plastics and paints.  According to wikipedia magnesium ...
  • Replied in Hmmm... Still?
    My reading is that Zemax image space f/# is for infinite object side distance.  I thought this was clear from the wording above, but the the user guide adds. " Note that infinite conjugates are ...
  • Posted in News & Rumours but didn't garner much intelligent comment 2 months ago. It is a way of manufacturing pure silica glass at the relatively low temperature of 1100 C, compared with 2000 C ...
  • Replied in Hmmm... Still?
    Agreed. I don't know where you are coming from here. I made no mention of "relative" or "corrected" focal length. "Working f-number" is defined irrespective of the magnification and image quality.  ...
  • OK, I (finally) see more of where you are coming from. For a well-corrected photographic lens the second (rear) principal surface is a sphere of radius f , centred on the focal point. Whatever the ...
  • No argument about the physics.  I am poking a stick into the definition of f-number, aware that there may be attempts to bite my arm off. I don't believe there any ambiguity if we use working f-number
  • This is getting to the root of the problem. What are the limits on usablility? My concern is that an unqualified "f-number" does not not appear to have a universally accepted definition. If one ...
  • Hi Jack, Agreed. Reading between the lines of both the Focal Encyclopedia and the Wikipedia entries, I would not be surprised to find "standard" definitions of f-number which reflect traditional ...
  • Most folk posting here would accept that 1/(2 NA) is a "sensible" definition of f-number.  I am curious to know when (or if) it became the formal or "official" definition of f-number? The Focal ...
  • The manual I linked is for the Brownie 2 and 2a.  Page 2 of the manual shows the lens (E) on the same face as as the two viewfinders (F), with the shutter release (C) adjacent. The back of the ...
  • It is a window so that the user can see the frame numbers printed on the film's backing paper.  After each exposure the film must be wound on until the next consecutive number is visible in the ...
  • RichRMA wrote: BBC News : "It doesn't look very exciting - a cardboard box about 5in (13cm) tall, covered in leatherette, with a small round opening at the front." The text describes a box. The ...
  • Replied in Binary prefixes
    Binary prefixes : a note for pedants (readers with a life may wish to move on): G (giga) prefix is defined by the International System of Quantities (ISQ) as 10^9: 1000,000,000. Gi (gibi) prefix is ...
  • Agreed - there is no problem for real-world imaging, or even for solar concentrators where the heated element has an opaque surface. In both cases each point on the detector or collector surface ...
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