Arnis Hagendorfs Posted June 26, 2008 Share Posted June 26, 2008 Hi, Can anyone share exposure compensation tables for original Bolex extension tubes (5, 10, 20, 40mm). Link to comment Share on other sites More sharing options...
todd eacrett Posted June 27, 2008 Share Posted June 27, 2008 If you can't find a chart, the bellows extension formula will work. BL squared / FL squared x Time = adjusted Time or Bellows Length squared divided by Focal Length squared = Exposure Factor. Bellows Length in this case is the focal length of the lens PLUS the length of the ext tube(s). For instance, using a 25mm lens with a 10mm tube --> 35 squared (1225) divided by 25 squared (625) = an exposure factor of 1.96 or basically 2. In which case you need to double your exposure (half your frame rate or open 1 stop). Using a 25mm lens with a 25mm tube (2500/625=4) requires 4 times the exposure, or 2 stops. Rather than doing the math, an easy rule of thumb is for every 50% extension over the actual focal length you need to double your exposure (twice as long a shutter speed or open 1 stop). Link to comment Share on other sites More sharing options...
jake harris Posted August 15, 2008 Share Posted August 15, 2008 Rather than doing the math, an easy rule of thumb is for every 50% extension over the actual focal length you need to double your exposure (twice as long a shutter speed or open 1 stop). I've been trying to figure this out for a while and I eventually bought a leaflet of ebay with macro tables for d.o.f etc. Basically you open up 1/3 of a stop. Unless you extension is at the same length of the lens or over in which case its 2/3 of a stop. I'll try and scan the leaflet for you, its a photocopy though so quality might not be great. Does specify what d.o.f is with certain extensions and lens types, switar etc. Good Luck! Link to comment Share on other sites More sharing options...
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