Forum: Pentax Medium Format
01-29-2024, 10:18 AM
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I hope my comments were not misconstrued. I meant only to point out that if speeds below f/11 were going to be avoided due to some softness, then a much less expensive and weighty assembly would do.
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Forum: Pentax Medium Format
01-27-2024, 08:34 AM
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The 645Z uses P-TTL, not true TTL. My point was that true TTL -- measuring reflection from the focal plane -- might require of the TTL sensor a real-time dynamic range equal to that of the integration focal plane. Because the TTL sensor has to have high bandwidth for microsecond control of the flash, noise would be higher and dynamic range lower. S/N would improve with the square root of the TTL sensor area, but that might lead to an un-fittable photodetector.
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Forum: Pentax Medium Format
01-27-2024, 08:21 AM
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Removing all glass that rays don't pass through and reach the focal plane when operating the 600mm at f/11 would yield an f/11 lens assembly with the same performance. Note that this has to be done over the entire field. Wide angle lenses only use part of the physical aperture at any particular angle, so glass removal in that case might only be a small annulus.
Most lens assemblies are compromises over aperture, distortion, resolution, light transfer, cost, etc., so an f/5.4 that was T/8 even with the best AR coatings such that it had enough exotic glass to achieve near diffraction limited resolution at f/5.4 over the entire field might not be as desirable as one with a T/# close to 5.4, less glass, and a little degradation.
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Forum: Pentax Medium Format
01-27-2024, 07:37 AM
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The only way to do this quickly, if necessary, is with a vacuum pump and a bell jar, using only modest vacuum sufficient to get the water "steaming" at room temperature. You don't want to stress any sealed optical cells, if present in the design.
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Forum: Pentax Medium Format
01-25-2024, 08:26 AM
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So one could have a 600mm f/11 optic potentially half the diameter weighing potentially an eighth as much to produce the same quality, at least in the daytime where f/11 is practical.
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Forum: Pentax Medium Format
01-25-2024, 08:15 AM
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I suspect that the spectral/irradiance properties of the reflection off of the imaging array had "characteristics" that made it less suitable for TTL energy measurement than the reflection from film. After all, each pixel has its own spectral filter that has a reflection that is the spectral inverse of its pass band. Also, that reflection is specular, where diffuse might be preferred.
There is also the wide dynamic range of the "Z" array that the TTL sensing and control subsystem would have to be compatible with. I believe the "D" retains TTL capability, and has a narrower dynamic range. The ISO limit for TTL flash might have to be restricted.
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Forum: Pentax Medium Format
01-15-2024, 08:50 AM
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Please don't leave us hanging; would you at least clarify whether the three parts need to be fabricated from raw metal, modified from some existing parts, or can be "borrowed" from an existing lens assembly?
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Forum: Pentax Medium Format
01-13-2024, 08:55 AM
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Forum: Pentax Medium Format
01-11-2024, 08:30 AM
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I think, more precisely, the 645N and its Pentax hot-shoe flashes are not capable of wireless TTL, . Clearly, one could have a module that accepted the signal at the hot shoe that triggers the flash, and the signal that quenches the flash, and a wireless function that transmitted those two conditions to modules connected to remote Pentax (or other) TTL-capable flashes. Low latency would be necessary. To extend the control to accommodate flash zoom etc. might be more complex. Somewhere here (forum) the shoe pin-out was described some years ago.
For portraiture and other "local" tasks, cables should suffice. High speed sync for bright daylight reduction is not an available function, as I recall, at least with the '500s.'
My Cactus V6 system only does TTL pass-through at the camera shoe. There may be earlier Cactus devices that performed wireless TTL. Lately, I haven't had time to spend on the flash section of this site, but asking there may provide more information.
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Forum: Pentax Medium Format
01-10-2024, 09:28 AM
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I reported a few years ago that I could get proper TTL behavior with a set of AF-500FTZ wired together to my 645N. (Note that the connector interface and the shoe interface are in parallel.) So one 645N could quench at least four of these flashes when the TTL quench signal -- might just be a clamp -- was generated by the camera. One needs a bunch of expensive Pentax cables for this, but it works. Light balance among flashes, of course, depends on the usual suspects.
I didn't try any wireless schemes with these if wireless is even possible without a set of receiver modules providing local trigger and local quench when commanded. I have a set of wireless Cactus flashes for the 645z and I don't recall whether that system can be operated in some limited mode on the "N" as I never intended to apply it to that camera.
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Forum: Pentax Medium Format
12-10-2023, 10:21 AM
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@barondla: Is "pulled the plug" intended to be a generic complaint, or was there some specific announcement that I missed?
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Forum: Pentax Medium Format
09-28-2023, 04:29 PM
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Perhaps what is being observed is the difference between f*tan(theta) and f*theta lens assemblies. The former is what a pinhole camera naturally does with a flat focal plane; the latter is what your eye and head movement creates in your mental image of a scene. Both f-theta and f-tan-theta lens assemblies can be designed and fabricated, but I vaguely recall that f-theta is more difficult for short effective focal lengths when one can't put glass close to the focal plane because there is a prohibited space occupied by a mirror assembly.
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Forum: Pentax Medium Format
09-26-2023, 04:10 PM
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There are some Loctites that are intended to fill pores in castings. They tend to stay slightly gummy over time (at least on stainless steel) so just slightly more than finger force will loosen them, and the threads will generally allow reuse without having to dig out the Loctite again. (One outdoor table application I have has remained effective for over 30 years.) The blue and red threadlocker Loctites will require more force to remove, if that is what you prefer.
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Forum: Pentax Medium Format
09-24-2023, 08:45 AM
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Forum: Pentax Medium Format
09-10-2023, 08:21 AM
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As I understand it, the camera shutter operates as a sliding gate, where effectively a slit is moved across the focal plane such that the light received (from daylight, say) is proportional to the slit width and time over the focal plane. By this scheme very short equivalent exposure times are possible. If a single-flash flash is used, only a part of the focal plane will be exposed if the slit is narrow. If a high frequency multiple pulse flash is used, then it is possible to operate with a narrow moving slit. Otherwise, the proper approach for flash is to have to entire focal plane wide open for a period that the flash can be synced to. This value varies with camera model, but generally a MF camera will require a wider sync time than a FF 35mm camera due to the larger focal plane and higher inertia curtains used for the shutter.
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Forum: Pentax Medium Format
08-19-2023, 01:39 PM
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Maybe there is a numbering issue. I don't think 19805 has any images. But 19804 has four. ---------- Post added 19th Aug 2023 at 16:43 ----------
If NZ can censor a video throwing suspicion on the government, perhaps Australia has some reason to block Flicker.
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Forum: Pentax Medium Format
08-18-2023, 09:43 AM
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I see all of them. Firefox 116.0.2 on Linux Mint Mate 21.2.
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Forum: Pentax Medium Format
08-17-2023, 09:41 AM
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Where photography turns into art, the art of "touch up" in post gains a more extended meaning when software allows results that would have been impractical for Ansel A.
Thanks for the train views.
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Forum: Pentax Medium Format
08-11-2023, 04:41 PM
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I was hoping for photographic documentation of the man with seven wives. I guess I'll settle for the excellent shoreline images.
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Forum: Pentax Medium Format
08-09-2023, 08:58 AM
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In the case of cats, people are underpaid staff.
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Forum: Pentax Medium Format
08-04-2023, 08:20 AM
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What we don't know is the tolerance on the parameters of the filter. If we had the lens assembly design, an optics program, and someone skilled in the art, the tolerance of optical thickness at the filter position could be ascertained. It may be that non-exotic glass of the manufactured thickness will do. ("do" meaning that resolution and various spatial and chromatic distortions cannot be discerned between the replacement filter and the original. Slight changes in focus will be removed by user adjustment.)
Someone here with that lens assembly who also has a micrometer might offer to measure the thickness of his copy. Lens paper could be used as a protective means and its thickness subtracted out. Be gentle.
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Forum: Pentax Medium Format
08-03-2023, 09:06 AM
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As part of the optical design, a replacement has to have the same optical thickness, i.e., physical thickness times the index of refraction. Maybe someone here knows what those are.
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Forum: Pentax Medium Format
06-18-2023, 05:58 AM
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The HDMI port can be used as a feed to a computer monitor (display) for a larger view. I have connected in this way to an HP ZR2440w. The display will show whatever the camera's tilt-able monitor shows. I wouldn't expect that the HDMI port would operate as an image feed to a tablet, but I don't have one to test with. Two-way information flow tethering would have to be done via the USB port.
Forum member @Thorrulz has previously described use of a more compact display as illustrated below.
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Forum: Pentax Medium Format
06-16-2023, 09:32 AM
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I would vote for this source:
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Forum: Pentax Medium Format
06-15-2023, 08:15 AM
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The Union Pacific Railroad refurbished a massive one in their Cheyenne Wyoming USA yards -- the antithesis of small touristic. UP: UP No. 4014 - The Big Boy. There are some videos about it pulling tourists across the West on YouTube, etc. No images I've seen, though, achieve the level of Ed's posts.
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