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Brian Caldwell

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Everything posted by Brian Caldwell

  1. Well, the combination of an 80mm lens and a 0.7x focal reducer does have a focal length of 56mm. After all, focal reducers really do reduce focal length. You could prove this to yourself by measuring the separation of photographed stars or I could prove it to you in my lab using the nodal slide on my optical bench. And if you use that 56mm lens on FF (24x36mm) format, then *it is* a FF 56mm lens. In this case, the use of a focal reducer together with an 80mm lens is a perfectly valid way of designing and creating a true 56mm lens. As I mentioned in my earlier post, the only possible reason it will look different from any other 56mm lens will be due to lens/reducer aberrations and other flaws.
  2. Let me get this straight - are you denying that the combination of an 80mm lens with a 0.7x focal reducer is a 56mm lens?
  3. Character/rendering are entirely separate issues from photographic basics like DOF and perspective. Certainly, if you like the character then there's nothing wrong with that. Heck, if you find that using an 80mm lens with both a 1.4x teleconverter and 0.7x focal reducer (in series!) to get back to 80mm but with some funky aberrations gives you the results you want then you should certainly do it. My only real objection is with pseudo-explanations - basically "fake physics" - that cross the line into mysticism. Mini correction: techically, aberrations can and do influence DOF.
  4. You are expecting a level of precision in this comparison that is entirely unreasonable. Little things like changes in distortion and entrance pupil position during zooming make it impractical to make a blink comparator test completely perfect. What the comparison does show - with more than sufficient precision - is that you can optically reproduce all aspects of an image shot on a large format with one shot on a smaller format - or vice versa. The notion that, say, an 80mm medium format lens has some inherent "80mm-ness" or "medium formatishness" that somehow stays with that lens after you attach a focal reducer is just silliness. The combination of a 0.7x focal reducer and an 80mm lens is a 56mm lens. Period. Put that 56mm lens on a 24x36mm format camera and it will behave just like any other 56mm lens attached to that camera, the only caveats being related to aberrations and other flaws in the lens and focal reducer.
  5. The bokeh that I saw in this movie was definitely Zeiss Master Anamorphic, which is to say it has an aspect ratio of ~1.64:1 rather than 2:1. The Zeiss anamorphics are famous for requiring add-on junk to create flare - available from Zeiss themselves, but I would be surprised if anyone would knowingly copy the 1.64x bokeh with an aperture disk.
  6. You should be aware that this is a religious discussion. Comparisons, and discussions about comparisons, should be avoided and only discussed in private!
  7. 40mm on a 1.33x gives the same horizontal FOV as 60mm on a 2x.
  8. All of the original m43 Speed Boosters were replaced by the Ultra model a couple of years ago. The OM version of the Ultra is a current product: http://www.metabones.com/products/details/MB_SPOM-m43-BM3
  9. And a 1925 Model T was only $260 new . . . .
  10. I haven't tried that particular combination, but the 0.64x BMCC Speed Booster has a full millimeter *less* clearance on the camera side than the 0.64x XL. The XL also has a larger image circle that is compatible with the fill size m43 format, and it is also optimized for the standard m43 filter stack rather than the non-standard Blackmagic stack. Odds are you can probably get the BMCC version to work, but you'll probably be pressing on the flexible shutter cover and you won't get optimal image quality.
  11. The 0.64x Speed Booster XL and 0.71x Ultra are both designed to cover fullframe 4:3 format (21.6mm diagonal). As long as you use a master lens with a sufficiently large image circle you wont have vignetting. 24x36mm format lenses will always work. I expect some issues with certain APS-C lenses. Well, you would be slightly hampered by 4:3 if shooting with 2x anamorphics. But with 1.79x anamorphics on the other hand . . . . .
  12. Can you elaborate on how the double-focusing on the Mesmerizer is not as hard as with other adapters?
  13. Hi Hans: Using a good diopter will definitely improve the closeup image performance of a single-focus attachment, since it allows the attachment itself to be used closer to its "zero aberration" infinity setting. I'm not entirely sure what you are describing about the highlight blob ghosting effect. Most single focus attachments use a plano-concave moving front element followed by a convex-plano stationary element. The concave surface of the front element is normally very close in radius to the convex surface of the stationary element, and this could set up a pair of reflections that might cause the effect you are seeing. Its also possible that a reflection from the sensor followed by a reflection from either or both of the plano surfaces can cause noticeable ghosting, although in this case I would expect sharply focused mirror-image type ghosts. Regardless of the root cause of the ghosting, its appearance can be reduced, but not completely eliminated, by using better AR coatings.
  14. Awhile back I spent many weeks designing variable diopter systems, including simple 2-element designs using singlets, 4-element designs with achromatic doublets, and a few complex 5 and 6 element designs. What I discovered was that the limiting aberration in every case was spherical aberration at close focus. Surprisingly, using more complex designs has very little impact on that spherical aberration, and they have numerous drawbacks including excess cost, and larger size and weight. It turns out that a simple 2-element variable diopter, such as the ones used in all of the Iscoramas is not such a bad solution at all. They give fantastic results for distant objects, and only gradually reveal weakness as you focus close. As an aside, the only thing that I found to reliably eliminate close focus spherical was to allow the elements to get very weak, but this is completely impractical because the elements get huge and the front element motion becomes BIG. BTW, it doesn't make much sense to talk about f/#'s when evaluating single focus units because absolute pupil size is what really matters. For example, you might get a terrible result when attaching the unit to a 200mm prime at f/4 because the pupil diameter is 50mm, and yet get a really nice result with a 24mm f/1.4 because the pupil diameter is only 17mm.
  15. The main reason for shooting 1.33x (actually, 1.344x would be best) is to get 2.39:1 output with no waste of a 16:9 sensor. Shooting 2x on 16:9 and cropping throws away resolution. Aside from these considerations, there is the aesthetic look that different squeeze ratios provide. Many people dislike 1.33x because it doesn't look very anamorphic. However, even 2x anamorphics don't always share the same look. Rear anamorphics don't look anamorphic at all. Zeiss 2x Master Anamorphics actually look more like 1.64x true front anamorphics due to their mixed front/rear design.
  16. Its a little complicated due to the fact that the outer surface of the Speed Booster is concave. But you should have at least 1mm of clearance with this particular combination. Note for anyone else reading this post that the Speed Booster XL for m43 has more clearance than a Speed Booster Ultra for APS-C.
  17. It depends a lot on the lens. For some lenses, such as the 50/1.2 Nikkor, there is almost no space between the rear element of the lens and the front element of most Speed Boosters. I would hate for you to crush your filter between two lens elements!
  18. A Zeiss Otus plus Speed Booster XL has pretty amazing IQ wide-open at f/0.90 on m43.
  19. The optics between the front surface and the iris are what determines the location of the entrance pupil. "Quality of the pairing" is only indirectly related to entrance pupil distance, but the amount of vignetting is directly related to it. To minimize vignetting you want the entrance pupil as far forward as possible, and the air gap between an anamorphic adapter and the prime lens to be as small as possible.
  20. Best done on an optical bench with a low-power microscope. But a macro lens will work OK as long as you focus by moving the whole camera. 1) stop lens under test (LUT) all the way down; 2) Focus on the iris diaphragm; 3) move microscope or camera away from the LUT until the front lens surface is in focus - you may have to apply some dust or some Scotch tape in order to see the front surface. The distance that the microscope or camera moves is the entrance pupil distance, e.g., the distance from the front surface of the LUT to the image of the iris diaphragm.
  21. I'm thinking about manufacturing some 114mm clamp-on (fast on-and-off) achromatic diopters for the wide-angle anamorphic attachment I'm developing. Similar to the now-extinct Zeiss Master Diopters. Also similar to the Leica Macrolux, except larger and less expensive. Aside from being useful accessories for my anamorphic attachment, would these be of more general interest to readers here? Thinking about +0.4D, +1.0D and +2.0D .
  22. Its definitely a factor, and it certainly helps to be aware of what is actually the limiting aperture in the system. Even the Iscorama-54 isn't large enough to avoid stopping down an 85mm f/1.2. Although I don't have the Iscorama-54 design prescription and can't accurately evaluate its performpance, I do expect that it has plenty of aberrations on its own, especially at full aperture. A good test of the 36 vs 54 would be to use a prime lens with great performance that has an entrance pupil larger than 54mm. The 85mm Zeiss Otus comes to mind . . .
  23. Bear in mind that in your case with an 85mm lens the rear of the adapter limits the aperture, so you are shooting at f/2.4 and not f/2. You would need an Iscorama 42 to shoot at f/2 with an 85mm lens.
  24. Has anyone heard anything about whether the automatic anamorphic crop mode of the GH4 has been retained/improved? Or will it require manual post-processing?
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