improving quality on shooting time + questions

[lecaramel]

Hi,

I have several technical questions in relation to the shooting. I'll have to shoot people with just one DSLR (5D MkIII) and doing head scan and body scan. Of course I know that doing a scan with just one DSLR won't produce the best scan ever, but i already have good results, then for that, it's ok.

1 - In the documentation, it's mentioned that fixed focal lenses are advised. Is using a zoom lens (24-70mm) fixed at 50mm will be problematic? Even if it have some micro variations of zooming while shooting, between two photos?

2 - What is the best focal lens to provide good quality? 50mm 85mm? (on a full frame camera).

3 - What is the best compromise in terms of scan quality: increasing the ISO to increase the depth of field or lowering as much as possible the ISO even if it reduce the depth of field? Because I'll shoot outside, I won't be able to use studio lights. Of course, I would like to have a decent shutter speed.

4 - To improve the alignment of the photos, then the dense cloud generation (and reduce as much as possible the noise) in the final model, is it better to do a set of photos which will include the whole model in each photo for a first pass, then in a second pass, doing close up, or only close up are enough? Having these photos taken far from the model may introduce some extra noise?
I'm considering doing my scans in several pass in fact, like the full body in low quality, then shooting separately the face/head, the hands, parts of the body, then when doing, processing the scans separately, then at the end, recombining everything in one mesh in ZBrush. It may be a longer process, but perhaps can increase the quality of scans taken in not very good conditions?

5 - in addition to above, is it better to do in several chunks a scan by far and a scan with closeup photos and then combining them or just having all the photos, far and close, in the same chunk?

6. The Ultra high quality of dense cloud worth the extra waiting time in terms of quality (at least for a face/head) or high is far enough? I mean if adding 10 extra hours of computing versus 10 hours (or less) of 3D retouching in ZBrush.

7. no problems on shooting photos with two different focal lens? (35mm for photos by far and 85mm for closeup)

Thank you for your help!

[David Cockey]

I've used zoom lenses for boats and ship models with good results. I use a piece of tape (blue painters tape) to keep the zoom ring from moving. If you want to use a single focal length lens Canon has two suitable lenses which are low cost; 50mm F1.8 and 40mm F2.8. I use the 40mm F2.8 with a Canon 500D/T1i and it is very sharp.

50mm lens with full frame 35mm sensor (such as the 5D MkIII) may give better alignment than the 85mm lens. If both are available then why don't your try both. Or experiment with different focal lengths with a zoom lens.

Going from ISO 100 to ISO 200 or even ISO 400 shouldn't have noticeable effect with a 5D MIII. Higher ISO can result in noise in dark areas but if depth field is a major problem at lower ISO then the noise my be a good tradeoff. Experiment.

Absolute no problems with shooting photos with different focal lengths, even with the photos in the same chunk. PhotoScan sorts the photos in each chunk into groups depending on focal length. And if photos are taken at different focus distances then it can help to further group the photos by focus distance.

You can align photos together, then duplicate the chunks to split them. Or turn off photos for dense point cloud generation.

[lecaramel]

Thank you David for these informations.

I mentionned the 85mm because I have a prime lens which is very sharp at f/10. I'm also using Lightroom to edit my raw and then eventually denoising them, but of course, avoiding noise is I guess, a top priority!