is it a problem to have more lights at raking level?

[René van Gageldonk]

I have a project with evenly distributed lights, 15 degrees apart. At raking level I've added at 7,5 degrees an extra series of lights, because of the importance and quickly changing details at that level. That makes it not evenly distributed anymore. Can I trust the results?

Thanks,

René van Gageldonk

[Dave Martin]

René, every use case will be different, but I would suggest it may not be ideal to have illumination so low, especially when using the highlight method.

The software uses the spot of light on the surface of your reflective sphere to work out the exact position of the light. As the light gets lower, the spot becomes more and more on the increasingly vertical equator of the sphere. Geometrically, that is OK for azimuth but it becomes increasing inaccurate for elevation.  So, I guess it won't 'break' things but the edge face results won't be as accurate as if you had stopped at the recommended 15 degrees lower limit, and having both 15 degree and 7.5 degree might be worse than just 15 degree - think of it as 'blurring' due to inclusion of inaccurate data.

If you were using the dome method, with precisely known light positions (from measurement, not from a highlight run), then it might be better.

Dave

EDIT: I think that the only way you can tell if there is an improvement, or no better, or worse, would be set of tests on an artefact with low, distinctive, clear relief - Shoot it with conventional set from 65 degrees down to your 7.5 degrees and make two projects - process one with photos just down to the recommended 15 degrees (i.e. omit the 7.5 degree photos) and then process again with all i.e. including the 7.5 degree ones; then compare a range suitably sensitive areas of the lowest possible relief. My suspicion is that you'll see negligible improvement if you look across a range of relief features/orientations, and I suspect it be worse. Depending on scale, a suitable object might be a coin or medallion with raised text, preferably not too worn from circulation or pockets.

Edited February 15, 2023 by Dave Martin

[René van Gageldonk]

Thanks Dave, I'll try your suggestion of making two projects.

regards,

René

[Dave Martin]

Thanks René, let us know how you get on - ideally some side-by-side screen grabs of the same area to show the impact. That would be a great service to the community too!
cheers
Dave

[René van Gageldonk]

Hi Dave,

My project is somewhat different than most. I’m using a setting that is repeatable. So the lights are in same place every time. Still I’m using the highlight method, using a .lp file and dome PTM setup in Builder.

 In your answer I understand you think there is a blurry part of a scan when using low light positions: so I guess what you are saying is: it is better to have no information than to have the wrong (blurry) information.

I don’t see much difference between the two versions, but that might be my inexperience in reading te files.

My actual question is answered I think. Lighting distribution doesn’t have to be completely even. You came up with a new problem that needs to be taken into account; the possible blurry result with raking lights. Thanks for mentioning this.   Finding out what I don’t know is a fundamental step in the learning process.

I hereby added the test results.

The next post is with the specular.

I did as you suggested; did my original setup with lots of lights at a almost raking level and a setup with less lights at that level.

I can’t go into more detail right now, I’m affraid. I will share more information as soon as my circumstances allow.

regards,

René van Gageldonk

[René van Gageldonk]

 

[René van Gageldonk]