Miha, I believe you are trying to photograph the stress lines in transparent plastic by "cross polarization (aka bi-refringence)".
The sheet polarizer you are using on the light box will be, almost certainly, a linear type. This can cause incorrect meter readings (mainly underexposure). However, the effect that you are after (rainbow colours against a black background) can not be achieved using two circular polarizers as it is impossible to totally eliminate the light source, even when fully crossed. Sometimes reversing one of the circular polarizers helps. I first tried cross polarization many years ago and had no exposure problems using two linear polarizers and good old fashioned centre weighted metering. Probably best to regard the pictures you have as a test and give the next lot a bit more light. Regards, Craig Z ----- Original Message ----- From: "Miha Valencic" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Monday, February 04, 2002 1:38 PM Subject: RE: EOS Exposure factors for extension tubes > :)) Gerard, I know about the problems with linear ones. I think that the > problems mainly relate to focusing, not to metering. I do have circular > polarizer though and have used them a lot. > > > -----Original Message----- > > Miha, > > > > Did you mention the word... 'polarizer'?!? > > > > Did you use the recommended circular pol or did you go for the > > linear? The > > light sensors inside the camera can be fooled by a linear > > polarizer and the > > metering will go bananas. (actually I've used linear pol's without much > > troubles but they *CAN* be the cause of them) > > > > Also, the black-out vs light portions of the image could have caused your > > exposure problems. Does the 300 have partial metering? If it does > > it's best to > > use it and lock the reading on a color & hue that you know it's 'like' the > > famous shade of gray. > > Again, I think that is _the_ only possibility. I will test again and let you > know of the results. The set up could be the problem. Let me illustrate: > > Camera > Extension Tube > Lens+polarizer (CIRCULAR) > > > plastic subject > polarizer > light box > > All those items in vertical position, as I tried to illustrate.. > > rgds, > ivi. * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
