Hi Axel, About the filter, actually it was attached with tape to the back of the FC-E8 adapter (and in front of the camera lens). So it was in the middle of the optics. I think this may have helped. The back lens of the adapter does not protrude, so it was easy to fix it parallel to the other lenses.
The problems with the nd filters were mostly with colour shifting. The cheaper darker filters get everything too green (and these were the best I could get from a photography shop, not that cheap). The calibration was done with the filters in place and compensated with measurements. If I remember correctly, the stated tolerance for the transmissivity was about 5% (for an ND3, that's 1/20 000th?), but I didn't verify whether the real one was within this. Cheers, Santiago ________________________________________ From: Axel Jacobs [[email protected]] Sent: Tuesday, February 21, 2012 1:38 AM To: High Dynamic Range Imaging Subject: Re: [HDRI] HDRI capture of LED Hi Santiago, good to hear from you. May I ask you to elaborate this: > Flare from the sun was quite a problem, especially as I was using a filter > behind the fish-eye. I'm still not sure if the filter in front would reduce > it, as the less flare would be compensated by the need of a longer > exposure... Still, the flare affects the lower end of the dynamic range, so > it shouldn't be an issue for the measurement of the LED itself. How did you attach the filter behind the fisheye lens? Did you simply stick it there with some glue or silicone? Or onto the sensor? > A note about ND filters, I've had very bad experiences with photography > filters, especially at high ND values. It really needs to be an optical > filter (I ended up using a combination of filters from Edmund Optics). Do you mean that the light attenuation was not what was written on the box? Or were there other issues? I assume you calibrated even the EO filter, or did you just take it at face value? Thanks for sharing your insights. Cheers Axel _______________________________________________ HDRI mailing list [email protected] http://www.radiance-online.org/mailman/listinfo/hdri ____________________________________________________________ Electronic mail messages entering and leaving Arup business systems are scanned for acceptability of content and viruses _______________________________________________ HDRI mailing list [email protected] http://www.radiance-online.org/mailman/listinfo/hdri
