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Hoods/A little testing ...

Discussion in 'Native Lenses' started by oldracer, May 3, 2012.

  1. oldracer

    oldracer Mu-43 All-Pro

    Oct 1, 2010
    USA
    I am a hood guy. In theory any unwanted light that gets into the lens has the potential to "fog" the photo. I've always believed that. I also like the protection that hoods give to my lenses.

    There seem to be a lot of "hood threads" here, mostly containing people's opinions. Over and over .... So I decided to set up a little test. Not highly controlled, densitometer-dominated, but hopefully enough to see the effects of a couple of lens hoods.

    Here is the setup:

    [​IMG]

    There is a piece of black construction paper against a roll of "fairly white" paper. There is a strobe about 2' from the wall to the right of the paper with the hot center of the light well outside the image field of view. I tested a Panny 14-140mm with its tulip hood and an Oly 14-42mm with a round hood verified to be at the edge of vignetting at the 14mm setting. Both lenses were set to 14mm.

    The image above is a Lightroom screen shot, showing the blocked-up areas due to off-axis, non-hot-spot light from the strobe.

    I first used the Lightroom probe to measure the pixel values at the corners of the black paper. In theory, if the image is "fogged" these pixels should be brighter for the un-hooded lenses. Lightroom gives values as 0-100%. The red area shows pixels that are 100%.

    In both cases, the unhooded lenses showed evidence of fog, but it was very slight. In the lower right, for example, the hooded 14-140mm lens showed average RGB brightness of 14.7% and the unhooded value average was 15.4%. In the left corners the difference was even less. The hood on the 14-42mm made almost no difference at all. Possibly this is because it is a round style rather than having petals.

    One place where there was a noticeable visual difference, though, was in the amount of the paper that was at 100%/the red in the photo. Measuring on my screen, the red area extended 7mm onto the paper for the hooded 14-140 and 5mm for when it was unhooded. For the 14-42mm the corresponding figures were 17mm and 15mm.

    The biggest weakness of the test, IMHO, is that I shot at f22. The hoods' benefits should be more at wide open apertures. Maybe I can figure out a way to change the setup so I can shoot at a larger aperture without changing the strobe power.

    So ... my initial/tentative conclusion is that the hoods do what they are supposed to do but the improvement is very small. Which is good, I guess, because when we zoom away from the widest setting we effectively have unhooded lenses anyway.

    As usual, YMMV. Hopefully this will inspire others to contrive their own tests and report the results.
     
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  2. phrenic

    phrenic Mu-43 All-Pro

    Sep 13, 2010
    Thanks for testing this..it seems to be one of those things that are commonly accepted, but difficult to quantify and few people have actually done comparisons. I'll leave it to the smarter folks and I'll go to the conclusion.