Jump to content

Brian Caldwell

Members
  • Posts

    153
  • Joined

  • Last visited

Everything posted by Brian Caldwell

  1. At this point, NX accessories are probably best done by NX enthusiasts like Luca. Otherwise something called "opportunity cost" rears its ugly head. What it means is that labor and financial resources are limited - especially in small companies - so you have to be very careful about choosing which products to develop.
  2. You're having a paranoid fantasy, Marco. I design the Speed Booster optics, and my colleague Wilfried designs the mechanical mount. Together we own the optical design patents and the "Speed Booster" trademark. That's it - just two people. We work with subcontractors to manufacture and QC the optical cells, and sell the those cells to Metabones, which itself is just a tiny company. Any public statement from Metabones about Speed Boosters probably comes from me, so when you say that Metabones is lying you are essentially saying that I am lying. There is no lying going on here. I doubt that Samsung - which is a truly enormous company - was even aware of Speed Boosters, much less that its presence or absence played any role at all in their decision to leave the camera business. No one from Samsung or Sony has *ever* contacted me about Speed Boosters, or anything else for that matter. Wilfried and I looked at the Samsung NX mount on several occasions, and concluded it was just too much trouble to deal with due to the metal parts surrounding the sensor. Based on our analysis, it would require several rectangular elements (similar to one of the Lens Turbo designs), which are much more difficult to make and mount accurately. It would also require a substantial re-design of the Speed Booster optics, which have a unique performance advantage at extremely large apertures (read the patents if you want to understand this). I personally had big hopes that the NX-mini mount would take off, since that was much more amenable to high quality focal reducer designs with larger reduction ratios - much like the BMCC and BMPCC from BlackMagic. But unfortunately both NX and NX-mini have both become extinct except for whatever product remains in the marketplace.
  3. In a zoom lens there is always the possibility of moving the variator during focusing to adjust the EFL and thus eliminate breathing. Its easier to do this with an electronically controlled lens, but is still possible with a mechanical design.
  4. Stacking two 1.33x anamorphic adapters will result in a 1.77x anamorphic adapter. This is close to the ideal squeeze of 1.79x that you would want to convert 4:3 to 2.39:1 . A Speed Booster will shorten the focal length.
  5. Not quite. You haven't accounted for the huge difference between front and rear anamorphics, both of which have different focal lengths in the horizontal and vertical directions. I posted the explanation here back in June:
  6. Thanks Ebrahim. As always, your contributions here are extremely helpful. What you are reporting is what I suspected, but its really nice to get confirmation like this since I don't have the camera myself. FWIW, I am doing research for a product, but its for a system of anamorphic lenses and not a fullframe Speed Booster, which may not be what you were hoping for but which I promise will be very cool.
  7. Thanks in advance if anybody can help me track down the following information. I need to know the exact dimensions of the 16x9 video frame used by the Sony A7s-II in both 4k and 2k video modes. All that I'm confident about are the following: 1) full still sensor size measures 35.8mm x 23.9mm 2) full sensor resolution in still mode is 4240 x 2832. 3) 1 and 2 together imply a pixel dimension of approximately 8.44 microns square 4) 4k video resolution is 3840 x 2160. SO: does this mean that the rectangle of sensor area used during 4k recording is 32.41mm x 18.23mm? Similarly, what would be the as-used sensor dimension when shooting 4k in "full-frame" mode?
  8. I agree for the most part, although 1.79x is a good alternative to 2x, since it is more efficient and in a good implementation actually looks more anamorphic than many 2x lenses.
  9. Is the 7D with MLRaw 4:3 or 6:5? Also, do you have any idea what the exact as-used sensor dimensions might be? Just curious since I'm developing a bunch of new lenses.
  10. Apologies in advance if this is widely known. Personally, I've never found a really good explanation of why front anamorphs produce oval bokeh and rear anamorphs don't, despite reading my fair share of patents, technical papers, internet gossip and the like. Feeling that my own understanding needed some firming up I finally set up some paraxial models and went through the math in gory detail. It all boils down to how front and rear converters alter (or don't alter) the f/#, and basic DOF type circle of confusion calculations. It has nothing to do with higher order aberrations, or the shape of the front lens, or various mechanical aspects of the lens. Briefly: 1) A front anamorph is just a special case of a front afocal attachment, and as a result it preserves the f/# of the lens its attached to. With an anamorphic front lens the focal length is shorter in the powered axis than in the non-powered axis. For example, consider a 2:1 anamorph attached to a 100mm f/2 spherical lens. In this case the net focal length is 50mm in the powered axis and 100mm in the non-powered axis, but in both cases the aperture remains f/2. If you venture into the weeds to do circle of confusion calculations for a given object-space defocus you discover that a de-focused point source evaluated at the image plane is an ellipse with an aspect ratio of 4:1. However, you only need to de-squeeze the image by 2x to correct the in-focus geometry, so you are left with de-focused ellipses with an aspect ratio of 2:1. 2) A rear anamorph is just a special case of a rear-mounted teleconverter, and as a result it *does not* preserve the f/# of the lens its attached to. In particular, in the powered axis the aperture becomes slower. For example, consider an 50mm f/2 spherical lens with a 2x rear anamorph. Here the net focal length is 100mm in the powered axis, but the aperture has dropped to f/4, and is still 50mm f/2 in the non-powered axis. When you do the circle of confusion calculations with object-space defocus you find the on-sensor defocused image to be an ellipse with a 2:1 aspect ratio. When you desqueeze by 2x this defocus ellipse becomes a perfect circle. Bottom Line: Rear anamorphs have circular bokeh because they *don't* preserve the f/# of the spherical lens in both axes, while front anamorphs have elliptical bokeh because they *do* preserve the f/# of the spherical lens in both axes.
  11. Just something to keep in mind: aberrations in the cylindrical optics and/or front focusing group will almost certainly dominate the overall lens performance, not the rear spherical group.
  12. "DOF falloff" seems like a really poor term. How about simply "defocus", or perhaps "MTF as a function of defocus" - which I think is what people actually mean. In optics this is referred to as "through-focus MTF", and its a standard and useful way to characterize a design. It will vary from design to design because it is strongly aberration dependent, but it has nothing to do with sensor size. One advantage that larger formats have is that you can use a smaller relative aperture to achieve a given DOF. Since aberration correction tends to be very non-linear with respect to f/# you often wind up with better correction on a larger format. For instance, I used to shoot 11x14" film a fair amount, and aside from an advantage in film grain it allowed me to shoot at f/16 instead of the ~f/1.4 I would have had to use on 24x36 format to achieve an equivalent picture. Focal lengths scaled accordingly, naturally. At f/16 the ultra large format lens was nearly diffraction-limited, whereas a small format lens at f/1.4 is nowhere near that limit. Of course, as you depart from such extremes in aperture any potential optical differences between large and small formats begin to disappear, and these differences are further minimized by improved sensor quality. So that ridiculously huge view camera stays on the shelf these days! Regarding the argument about whether a long lens on a large format has less perspective distortion than a proportionally scaled lens on a smaller format, the answer is "no". In terms of perspective and geometry, all lenses mimic the behavior of simple pinhole cameras - with the possible exception of rectilinear distortion which is generally a non-issue. One other thing to be aware of is that larger formats require a larger magnification, which essentially means you are using a longer lens than you may think you are for close-ups. For example, when shooting close portraits on 11x14" I was typically shooting at around -1x magnification, which effectively doubles the length of the lens. However, when you take this effect into account any potential discrepancies go away, and you are left with the stark reality that larger formats really don't offer any special "magic".
  13. Perhaps I could call such a product "The Naked Emperor Focal Reducer"? At least then I could sleep at night. I thought Kipon announced one of these, but it still seems to be vaporware. To be clear, adding a focal reducer to a medium format lens to convert it to a 24x36 format lens will only result in a slowish FF lens. That's because medium format lenses tend to have very conservative designs and are very slow to begin with. I can't think of a single MF lens + focal reducer combination that would be a compelling new addition to the FF optical repertoire. As you have correctly implied, there is no magic to be found here.
  14. I think a lot depends on how much you need lens speed, and how important the speed vs. size/weight tradeoff is to you. The new Panasonic 12/1.4 is no doubt a nice lens, and it looks pretty compact, but a Speed Booster XL on an 18-35 Sigma will give you an 11.5-22.4mm f/1.1 with excellent wide-open sharpness. In this case the native lens would make more sense if size/weight is more important than speed, and if you don't plan to use a Speed Booster on other lenses. On the other hand, a truly sharp f/1.1 zoom can come in pretty handy!
  15. Two afocal attachments in series should have significantly better image quality than a single shorter one with the same total squeeze ratio.
  16. Vladimir: Very cool idea, and although it may lead to some very physically long lenses (!!) it should work pretty well. Richard: Your suggestion of an Iscorama 54 on the front is a good one since the rear diameter of the front anamorphic section will likely determine how much vignetting there is. The rear anamorphic section won't be stressed too much since the objective lens will be longer than usual, and will be in a normal location. Too bad Isco54's don't grow on trees! Although Vladimir rightfully likes wide aspect ratios I think that a near-16x9 output could be very useful for lots of applications.
  17. The attached PDF file contains some of the data I've measured and collected for various lenses. EFL is the paraxial focal length, EXPP is the exit pupil distance measured from the image plane in air (positive value means pupil is towards the object from the image), ENPP is the entrance pupil distance measured from the first glass surface (positive value means the entrance pupil is towards the image plane from the first surface), and BFL is the distance from the rear glass surface to the image plane measured in air. All measurements are in millimeters.LensData.pdfLensData.pdf
  18. Its the angle of view that counts, not the physical size of the screen. So, a 5" screen plus a pair of cheap reading glasses can easily match a 7" screen (or a 12" screen, or a 24" screen, etc.) so long as all of the screens have the same resolution.
  19. What exactly don't you like about the 1.33/50 with your 85/2.8? I would expect any attempt to focus-through with the rear lens to fail pretty miserably due to astigmatism, but if you set everything to infinity and use a single-focus variable diopter front attachment it should be OK unless you're focusing really close.
  20. Any afocal anamorphic attachment should be compatible with fullframe, so long as the focal length of the spherical component is large enough. You may be restricted in terms of maximum aperture, however, depending on the exit pupil diameter of the attachment and how much aberration you are willing to put up with. Take an extreme example: An Iscorama-36 should work just fine on 8x10" format with, say, a 600mm lens, but you would be limited to about f/16. BTW, in your mind, what counts as fullframe? 24x36mm, or a 16x9 crop (20.25x36mm), or a 4x3 crop (24x,32mm), or ??????
  21. The Buhler Isomet is a nice low-speed saw that takes ultra-thin kerf diamond blades, but its very expensive. I used one of these a lot when I was working on gradient index glass. You might have some luck with a lapidary saw or a tile saw, and you might find a used one cheap. The trick will be holding the lens properly, and make sure you put plenty of paint on it for protection during cutting.
  22. http://www.4kshooters.net/2016/04/15/nab-2016-slr-magic-anamorphot-1-33x-40-is-a-new-anamorphic-adapter-for-mft-and-super-35aps-c/ The 4kshooters article suggests that this single-focus unit is compatible with only two SLR Magic backer lenses, and not with any third party lenses. I assume this is just a misunderstanding, since I would assume you could use the attachment with any lens that fits, as with any Iscorama-type device.
  23. My apologies. My last post got repeated 4 times, and I have no idea what happened.
  24. I've been curious about this project, and then read this today: http://www.4kshooters.net/2016/04/18/nab-2016-veydra-19mm-t2-2-mini-prime-for-sony-e-mount-2x-mini-anamorphic-and-wide-project-discontinued/
×
×
  • Create New...