About Sigma 4.5mm lens

Hello everybody
I’m trying to calibrate HDRs images that I build from LDRs images. I used a Nikon D90 camera and a Sigma 4.5mm fisheye lens. However, for the calibration process to be complete, I need information about the lens’s actual angle of view. The manufacturer indicates 180º, but I believe I need to check this real angle, I know it can be a little more or a little less.
In the methodology indicated by Pierson, it is recommended to use a panoramic rotation unit and a sliding plate on which the camera is set. However, our laboratory does not have this equipment.

I would like to know if someone who used this same lens has already measured the real angle of view and if this information is applied to all lenses of the same model?
Generally speaking, can I apply the actual angle of view information from another Sigma 4.5mm lens to my Sigma 4.5mm lens?

Thank you in advance

Hello Eliana,

You do not need the panoramic rotation unit and the sliding plate to determine the real viewing angle of the lens; this can be done with a simple tripod and two sheets of paper as explained in the tutorial. However, you would need to know the no-parallax point (NPP) of your lens so that you can properly position your camera, and the tutorial indeed recommends using a panoramic rotation unit and a sliding plate to determine this NPP. This equipment, although it would make your life easier, is not absolutely necessary and there exist other techniques to determine the NPP; some of those techniques are linked at the bottom of this webpage: No-parallax point - PanoTools.org Wiki

In the paper from Cauwerts et al. (2013), they compare the difference in projection function and vignetting effect of two Sigma 4.5mm f2.8 fisheye lenses, and those appear to be very similar. Hence, I would expect the real viewing angle to be similar. However, I was not using such a lens and I can provide you with that information.

I hope that helps!

Best of luck,
Clotilde

Cauwerts, C., Bodart, M., & Deneyer, A. (2013). Comparison of the vignetting effects of two identical fisheye lenses. The Journal of the Illuminating Engineering Society, 8(3), 181–203.