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HDRX used to compensate for the ramp on some zoom lenses
- Thread starter Tom Lewis
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Andrew Gentle
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Surely HDRx isn't necessary, how many stops difference are we talking about, here?
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I'm not a DOP, so i'm not sure. I'll try to explain what i'm attempting & maybe that will help u assess the situation. I'm trying to do a shot set shortly after dawn with the zoom going thru the back window of a station wagon up to the rear vision mirror. So its low light, going from EXT to INT. The lense i'm thinking of using is a canon EF-S 18-200mm f/3.5-5.6 IS (I need that zoom range). Thanks
Andrew Gentle
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So you want to compensate for the difference between f/3.5 to f/5.6? Why not just shoot the shot at f/5.6?
f/3.5 to f/5.6 is 1 1/3 stops [ log(5.6/3.5)/(log(sqrt(2))) ]. I think you'll be able to compensate for that more easily and logically without HDRx but, if you really wanted to use it, you'd have to set it to +2 stops and then separate the tracks, underexpose the A track by 0.7 stops or so or overexpose the X track by 0.7 stops and switch between them over the course of the zoom. It'll look weird because the motion blur will change throughout the transition.
f/3.5 to f/5.6 is 1 1/3 stops [ log(5.6/3.5)/(log(sqrt(2))) ]. I think you'll be able to compensate for that more easily and logically without HDRx but, if you really wanted to use it, you'd have to set it to +2 stops and then separate the tracks, underexpose the A track by 0.7 stops or so or overexpose the X track by 0.7 stops and switch between them over the course of the zoom. It'll look weird because the motion blur will change throughout the transition.
Marc Wielage
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I think a better solution would be to use a faster lens.
If that's not possible, then I think any decent color-correction program out there would allow you to build in an exposure ramp to try to "massage" the change. On projects I've color-corrected in the past, the hardest thing often was trying to cover up the clumsy stop-change done by the assistant camera operator, which inevitably "bumped" even more than was necessary. So I would up having to build in 4 density changes: 1) the original shot exposure; 2) the initial change by the AC; 3) the moving difference between their setting and the correct setting; and 4) the final setting. Sometimes it took a half dozen or more dynamic changes to fix (say) a continuous walk from an interior all the way to a bright sunlight exterior.
If that's not possible, then I think any decent color-correction program out there would allow you to build in an exposure ramp to try to "massage" the change. On projects I've color-corrected in the past, the hardest thing often was trying to cover up the clumsy stop-change done by the assistant camera operator, which inevitably "bumped" even more than was necessary. So I would up having to build in 4 density changes: 1) the original shot exposure; 2) the initial change by the AC; 3) the moving difference between their setting and the correct setting; and 4) the final setting. Sometimes it took a half dozen or more dynamic changes to fix (say) a continuous walk from an interior all the way to a bright sunlight exterior.