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Brian Caldwell

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Everything posted by Brian Caldwell

  1. Hi Andrew: I'm very interested in understanding the differences you are seeing between s35 (with a focal reducer) and 24x36mm.
  2. From my point of view, the NX1 is a terrible design because the deep "canyon" in which the sensor is located prevents development of a Speed Booster for it. However, with a little re-sculpting of the mechanical area near the sensor . . . . . .
  3. 3 scenarios here: 1) Your zoom lens is perfectly parfocal, meaning the two endpoints and all points in-between focus to the same plane. Adding a properly adjusted Speed Booster to such a lens will have no effect on its parfocality. If the Speed Booster has a small adjustment error you can loosen the set-screw on the side of the lens mount and then thread the optical cell in or out to achieve perfect parfocality. 2) Your zoom lens is parfocal at the end points (wide and tele), but drifts in-between. This is a non-linear condition that is normally cured by re-machining the cam in really expensive cine zooms. If your lens cost less than ~$20k then this non-linear error is ignored. A Speed Booster has no effect on it. 3) Your zoom is not quite parfocal at the end points. The Speed Booster can be used just like a set of precision shims to fix this condition. However, the Speed Booster will likely not be properly adjusted for your other lenses. So either you need a dedicated Speed Booster for this particular lens, or else consider the parfocality adjustment to be temporary.
  4. In this example, the quality of the Speed Booster is really degraded by the Canon 85/1.2, which isn't a very good lens. Try putting a 55mm Zeiss Otus on a m43 Speed Booster Ultra if you want to see the state of the art in large aperture lens sharpness.
  5. With a Speed Booster XL you would get 18mm x 0.64 = 11.5mm.
  6. The front element diameter doesn't have any direct affect on sharpness in the sense that you can always conjure up a counter example. For instance, I could add a foot diameter filter to the front of any taking lens and the sharpness would hardly be effected at all. Again, what really matters a lot is the entrance pupil diameter, which is the diameter of the image of aperture stop as viewed from the front of the lens. Of course, there are limits to the sharpening effect of using a shorter focal length taking lens. If you go too short then you'll encounter aberrations and/or vignetting in the outer parts of the image.
  7. Front focusing attachments are more sensitive to entrance pupil diameter than they are to f/#. So, if it is soft at f/2.8 with an 85mm prime, then it might be just fine at f/1.4 with a 28mm prime since the pupil diameter is actually less for a 28/1.4 than it is for an 85/2.8. So, my question is what focal length(s) give you soft images at sub-f/2.8, and are you able to get sharper results by using a shorter focal length?
  8. The m43 ULTRA version is for all intents and purposes optically perfect over the entire m43 format. It's intended as a general-purpose Speed Booster for both stills and video shooters, and it replaces the original m43 Speed Booster. As a general-purpose Speed Booster, the ULTRA can be mounted and used with all m43 cameras. The XL version is more specialized, and gives the maximum possible focal length reduction for video shooters using the GH4 and a limited set of additional m43 cameras. Performance is extremely good, but is not as good in the extreme corners of fullframe m43 as the ULTRA.
  9. Hi Julian: The 0.71x SB ULTRA is intended as a true general-purpose Speed Booster for m43. The 0.64x XL is a more specialized item tailored for the GH4 and a few other cameras, particularly for the higher crop factor in 4k. The ULTRA has incredible optical performance all the way across the field, as you can see from the MTF curves. BTW, the Speed Booster XL and all other m43 Speed Boosters for the Canon-EF lens mount can be upgraded to autofocus by means of a firmware download. So if you like the XL and want autofocus you can have it. Brian
  10. ​I'm almost certain they are. Metabones always has a stock available for direct website sales before they announce a new item. However, it may take a little time before retailers like B&H list it.
  11. ​My mistake, here is a link to the full press release: http://www.metabones.com/assets/a/stories/Metabones_Speed_Booster_XL_0.64x_Press_Release_5Jun2015.pdf
  12. ​Your're correct: the Speed Booster XL is really a dedicated GH4 focal reducer. The design is very similar to the BMCC version, but I squeezed out a bit more than a millimeter of extra space to clear the GH4 shutter, and, as you surmised, optimized for the thicker filter stack. In addition, the coverage was enlarged to encompass the entire m43 image area compared to the smaller BMCC sensor. However, I tuned the performance to be really good over the reduced area Cinema-4k mode of the GH4. High optical performance at extreme apertures are what this new Speed Booster is all about. Metabones seems to be having technical difficulties getting the full press release up on their website, so I'll show the data here. As you can see from the MTF curves, even at f/0.8 the contrast and resolution are extremely high out to an image height of 8,7mm, which corresponds to the Cinema-4k mode image circle diameter of 17.4mm. Beyond that point the performance drops gradually to the corners of fullframe m4/3, but is still pretty good.
  13. ​Phone-sized image circles are typically a lot less than 2/3" these days! Four things limit the ability to arbitrarily lower the reduction ratio of a focal reducer: 1) Inability to get really close to the sensor due to shutter, filter pack, mechanical junk, etc.. 2) limited space on the master lens side due to a short working distance of the master lens 3) Image quality requirement 4) f/0.5 ultimate speed limit for any well-corrected lens In practice, its possible to go down to 0.5x for certain special applications, with an aperture as large as f/0.66 or even f/0.63. In the case of the Blackmagic Pocket, the extra space and smaller sensor permitted 0.57x with great quality even at f/0.74, but all my attempts to get a smaller ratio resulted in unacceptable aberrations. In your example of a FF-2/3" reducer the magnification would need to be ~0.25x. So, an f/2 lens would be reduced to f/0.5, which is the fastest speed allowed by physics. For various reasons a focal reducer capable of 0.25x at f/0.5 is an unattainable goal. You might be able to get 0.25x at a slower speed, so long as the attached lens has a very large working distance (e.g., telescope objective etc.)
  14. ​Hi Ebrahim: It's certainly possible to do a 1-stop reducer from medium format to 24x36mm mirrorless, and likely a bit more than 1-stop. However, the real question is "why"? After all, if you offered a device that could convert an 80mm f/2.8 lens to a 56mm f/2.0 lens I think most people would not get very excited. Simply put, medium format optics are too conservative in their specs, and IMO you're better off purchasing native or adapted 35mm SLR optics for the A7.
  15. I designed the ULTRA Speed Booster optics, and work with partners to manufacture the optical subassembly. Currently our only customer for ULTRA optics is Metabones. I expect that Kinefinity is sourcing cheaper glass from another company.
  16. 1.45x squeeze is an interesting choice given that they are aiming for 16x9 sensors. Almost identical to the old Iscorama, and will still require significant cropping to get from the resulting 2.6:1 down to 2.4:1 . Also interesting is the 2-meter minimum focus. Perhaps they will be developing a large diameter diopter as an accessory?
  17. ​Patents pertaining to these lenses would have expired when Richard Nixon was still in office, and are now in the public domain. The Auto-Panatars date back to 1958, but Panavision switched from selling stuff to its current rental model back in the mid-1960's. That means that there should be quite a few of these in private non-Panavision hands.
  18. BMPCC-specific Speed Boosters have a magnification of 0.58x, and are only available in Canon-EF, Nikon-F, and Leica-R lens mounts. You could mount Yashica lenses to the Canon-EF BMPCC Speed Booster via a EF-C/Y adapter ring. Another possibility is to use the normal 0.71x m4/3 Speed Booster, which is available in a C/Y mount. However, you lose the extra speed increase and focal length reduction you get with the BMPCC-specific version. Also, the BMPCC version is optimized to work with the non-standard filter thickness of the BMPCC camera, which makes a difference if you are shooting with fast optics (e.g. f/1.4).
  19. Central hotspots are a ghost image of the aperture stop. They are caused by a pair of reflections between two surfaces located between the aperture stop and the image plane. Often this is a first reflection from the sensor followed by a reflection from one of the lens surfaces on the image-side of the aperture stop. However, it can also be caused by pair of lens surface reflections. Because its a ghost image of the aperture stop it gets smaller as you stop down. If the ghost image is well focused and has low aberrations then it is possible to clearly make out the individual iris blades in the ghost image. The surface brightness of the spot remains constant during stop-down, only the size changes. But of course, as you stop down the overall image gets dimmer, so the relative brightness of the ghost image increases. So, hotspots are much more problematic at small apertures because they are smaller and better-defined and also because they are bright relative to the image content. Hotspots are typically blue because the anti-reflective coatings of the lens are less efficient in the blue portion of the spectrum. Hotspots are also prominent in IR photography because coating performance is generally very poor in the IR. Improving the lens coatings can minimize hotspotting, but can't eliminate it. The best approach to avoiding hotspots is to design the lens in such a way that the pupil ghosts are very large and diffuse, and also to use the best possible lens coatings. Hotspots were well known years before the Speed Booster first went on sale in 2013, and many lenses are well known to have hotspot problems.
  20. The fundamental problem is that the Speed Booster shrinks the vertex length of the lens (the distance from the front glass surface to the image plane). So even if you could mount the SB optics inside the C300 EF mount you wouldn't be able to focus to infinity because the EF mount protrudes too far. Even if you could design a focal reducer that maintained the vertex distance you would then have the problem of mounting the optics since an adapter approach wouldn't work (zero flange-to-flange distance).
  21.   Yes, that's me.  I really appreciate your extensive review, and the unexpected behavior with the original version of the Sigma 30/1.4 is certainly something I need to look into.  The new version of the 30/1.4 is a really nice lens, BTW, and even though I only bought it for Speed Booster testing I'll definitely keep it since 21mm f/1.0 is really nice on m4/3.
  22.   I co-authored that Metabones document, so I'm familiar with the figure :)   It makes no sense at all to me that your Sigma lens could vignette for video.  That is, assuming that the width of the sensor's active area remains 17.3mm when in 16:9 mode.  The Sigma has to cover a 28.4mm image circle for DX format, meaning that its image circle with the Speed Booster will be at least 28.4 x 0.71 = 20.16mm.  A 16:9 rectangle that is 17.3mm wide has a diagonal of only 19.85, so something is definitely odd here.  Does your m4/3 body have a variable active sensor width depending on the aspect ratio?   DX lenses we have tried on full micro four thirds format (21.6mm diagonal) with the Speed Booster without any obvious vignetting (at any aperture) include: 1) Sigma 30mm f/1.4 version II 2) Tokina 11- 16 f/2.8 3) Nikon 35mm f/1.8 4) Nikon 10-24mm f/3.5-4.5   The Sigma 8-16mm does have vignetting due primarily to its fixed lens hood shaped for 3:2 instead of 4:3.   I've also heard that the Nikon 17-55/2.8 works fine with no vignetting, although I haven't tried it myself
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