ZS testing, problems, flare etc - critique and discussion

[Michael R 1974]

DELETED

[Bill Burk]

ORIGINAL POST DELETED - EDITED THIS POST TO MAKE SENSE WITHOUT IT

Flare curve is expected to taper, in the first experiment the curve didn't do what would be expected so to avoid misleading the discussion is edited.

[Michael R 1974]

Exactly, Bill. This was a sort of "step 1" - ie see what kind of flare factor I can generate. Because it is not a single exposure with different subject brightness levels (or reflectance values), the curves should be parallel (as you and Stephen have shown me in the past ). I was trying to prove that here. This does not show the effect on an actual scene where flare affects the lower values more.

That would be "step 2" where multiple reflectance values are in one exposure.

[kbrede]

How was the camera lens "masked?"

Could you give a frame of reference for "3 density points," in stops perhaps?

So to counteract the flare, would you reduce exposure to make the exposure match the first test subject?

Interesting test.

[Michael R 1974]

Now I'm having second thoughts about posting this curve first. It might be confusing on its own since it does not show the effect of flare on an exposure of a full scale subject. This test only shows the effect of flare on a single tone. Showing the effect of flare on a full scale subject would illustrate that you cannot "counteract" subject flare, and reducing exposure does not help (in fact it can be detrimental). This was the point I was trying to make in the other thread but now I may have confused things for people.

Regarding lens masking, I made an attachment for the front of the lens that reduces the image circle to a rectangle the size of the 35mm frame. This prevents most of the flare that might be caused by extraneous light bouncing around inside the camera.

[Bill Burk]

EDITED FOR CONTINUITY

The original (deleted) test shows the beginning of a valid flare test.



The first points to the right of the origin show a possible "flare factor". The displacement on the x-axis... it's how much light (if you can deduce the mcs) the flare added. Taper would start there and within a few steps to the right it would re-join the Non-Flare curve.

A good test to determine flare could be to shoot a variety of gray patches that meter says differ by one-stop each, surrounded by a white background.

[Michael R 1974]

Yes exactly. I should not have shown a "curve" for flare in this way because it is misleading. The different exposures just add more data points to the sample, but it doesn't add any value to show a curve of multiple exposures of a uniform target for this purpose, and it is confusing.

I prepared a set of grey cards that measure one stop (metered) apart for the second part of the test (single exposure of grey scale) but should have posted that part first so that one could see the displaced curve that then merges with the "non-flare" curve.

Sorry about this, people. Wish there was a way to delete the thread at this point. The last thing we need is a thread that confuses people.

[Bill Burk]

Now I'm having second thoughts about posting this curve first.

EDITED FOR CONTINUITY

The original post showed good scientific method, but Michael decided to delete it for clarity.

[Michael R 1974]

Still, I don't like that this can confuse people into thinking the effect is a parallel shift of the curve.

I'm going to delete the original post for now.

[Stephen Benskin]

Michael, can you post the testing procedure?