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> Bellows extension compensation |
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#1
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Bellows extension compensation
I assume that if I use a 300mm lens with bellows extension of 450mm, then I have a bellows exposure factor of 450/300 = 1.5?
That means that I have to multiply the exposure by that amount in addition to any other factors? |
#2
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the bellows extension and focal length each have to be squared before the division
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An old dog learning new tricks |
#3
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Quote:
I should have realised that because that's the same formula that I use for print enlargement size changes based on the inverse square law. So for my example it will be 450x450/300/300 = 2.25. So 3 seconds meter reading will become 7 in exposure time. |
#4
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You can calculate it as (450/300)^2 which may be easier to do without a calculator i.e. 450/300 = 1.5^2
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An old dog learning new tricks |
#5
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The bellows extensoin should be measured from the rear nodal point of the lens which on a view camera is usually close enough to the lensboard that measuring from the lens board to the film plane is good enough. On your mamiya with your 140 lens, things may be different so you need to know where the rear nodal point is located to do the measurement unless it is marked and tells you how much extension there is.
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An old dog learning new tricks |
#6
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#8
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Need some clarification please. Just reading up about bellows extension compensation. How do I know what is the 'normal' bellows length of my camera before I have to apply any compensation? I have this 310mm lens on my 13x18 camera and their are no markings. Does this mean I measure 310mm from the lens to the film plane and anything beyond that is compensated for?
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regards, Tony |
#9
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I knew there was a quick and dirty method of calculating the bellows extension factor and I've just looked it up to make sure I wasn't giving you false information, and here it is;
For every 25% more bellows extension than lens focal length Increase Exposure time by 1/2 stop OR Multiply Exposure time by a factor of 1.5 And measurement is normally between the film plane and the centre of the lens. And yes there are some wierd and wonderful mathmatics out there if you want to be absolute.
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MartyNL “Reaching a creative state of mind thru positive action is considered preferable to waiting for inspiration.” - Minor White, 1950 |
#10
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The quick'n'dirty method I use (found on one of the large format sites) - Using the focal length and extension expressed as inches, convert to f-stops. the difference between the two is the number of stops to add to the exposure.
For the example in question: 300/25.4 = 11.8 (11 1/4 stops) 450/25.4 = 17.71 (16 1/3 stops) ...difference (as near as damit) one stop. |
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