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Forum: Pentax Medium Format
02-27-2019, 02:10 PM
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Handheld light meters do not have any setting for a format what complies with the statement above, and metering of incident light not only ignores format, but also field of view of the camera. I think that the question should be slightly altered: does MF need more light than 35mm frame when FOV and DOF are kept constant? Accordingly to my DOF calculator 90/4 lens on 35mm gives the same FOV and DOF as 185/9 on 6x7 (in both cases distance to subject was 3m), so the latter definitely needs more light. It may seem contradictory but it's not: the former statement is about density of exposed negative, while the latter applies to constant FOV and DOF.
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Forum: Pentax Medium Format
02-26-2019, 12:29 PM
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There are at least two approaches:)
1. 'traditional' 1/f rule - ignores format
2. 1/f rule with crop factor - this is the scenario where you could use slower shutter. Basically it means that 1/50s should be fine for every 'standard' lens regardless the format.
To shed a light on the latter: 1/50s should (on average) yield sharp images in following configurations: 35mm / APS-C, 50mm / Full Frame, and 90mm / 6x7, in short with 'standard' lens for given format. In reality, it depends on photographer and equipment used - I use option 1, but this is my personal choice, and of course YMMV. Weight of the camera may affect minimal shutter speed, but again this is matter of personal preference, albeit most people claim that heavier cameras are more stable. The weight may differ significantly even within same class of MF - for example Mamiya RB 67 is around 50% heavier than Pentax 67.
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Forum: Pentax Medium Format
02-26-2019, 10:56 AM
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I wonder which question I should answer first - let's start with amount of light. MF lenses do have longer focal lengths in order to preserve proper field of view, for instance 'standard' for 6x7 is either 90 or 127 mm. Using 1/f rule, it means slowest shutter speed of 1/90 or 1/120 s. Moreover. these lenses are slow - f/1.8 for Mamiya 645 is the fastest one, the rest for this system offers something like f/2.4 at best. Lenses for 67 are even slower, typically around 3.5 or 4. When you take bellows into account, like in Mamiya RB/RZ, additional 0.5 or 1 stop of light can be lost. Is MF practical? Well, it depends on how you are going to use it, and which MF we talk about. In general 645 SLR can be considered heavy and beefed up version of 24x36. Mamiya RB 67 is like a heavy shoebox:) but it is capable camera. 6x9 rangefinder (i.e. Fuji GSW) is large, but light. I haven't had Pentax 67 so I cannot tell anything about it.
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