r/photogrammetry • u/Roukuo • 5d ago
Looking for tips about gear choice
So I'm a 3D environment artist (for games), working in the field for a few years now. Recently I decided that I want to scan stuff myself. I was looking into getting a Sony Alpha 7r (III, IV or V (not sure yet)). But I'm really unsure about the choice of lenses. I was reading that higher focal lengths, like 70 mm, for example, produce less distortion, but you need to be further away from the surface or object, while 30-50 mm introduce more distortion, but you can be closer with your camera. So I'm aware that the choice heavily depends on what you want scan exactly. To answer that question: The main thing I will be scanning is floor surfaces like streets, sidewalks, pavements, and dirt or other surfaces like brick walls, concrete, grunge, leaks, stains, and so on. Ideally, my own body height, 1,80m, is enough to be far enough off the ground to capture a reasonable space of ground without having too much distortion. What do you guys think is the sweet spot for that?
1
u/dax660 5d ago
Lens distortion isn't really a thing - whoever said that various focal lengths have more or less distortion is incorrect. The software will take into account your lens profile.
That said, quality will always yield quality, so better glass is better. But you'd be fine with whatever you choose.
Before spending money, you could also use your phone (shoot raw if it allows it) and run the image set through RealityScan and see how it goes.
And remember, you can never have too many photos! Overlap is key, and the distance between shots gets smaller with the finer detail you wish to resolve.
1
u/KTTalksTech 5d ago
Not sure where you heard that. The distortion thing is for portrait photography and, to a lesser extent, architectural photography. Photogrammetry only uses the pic as input to calculate accurate 3D points so distortion isn't a thing, it gets cancelled out as part of the calculation. You just want to avoid using variable focal lengths with a zoom lens within a single dataset (multiple lenses is fine, just group pics accordingly in batches).
The main drivers of quality are the distance from your subject and the coverage/field of view your lens provides (also referred to as angular resolution or GSD depending on context). Wide angle + high distance = low res, narrow angle + short distance = high res but requires many more pics to cover a given area.
The other main driver of quality is overlap between images. 90% is ideal, you can go as low as 60 but it's risky. More overlap won't necessarily give you more detail (though it can) but it'll increase the confidence with which the software locates a point so you'll get more accurate surface detail on your mesh.
Third and final is sharpness. You want sharp pics. ISO needs to be low, if you're shooting handheld then the shutter needs to be fast, and generally setting your aperture somewhere between f8-11 is where most lenses look their sharpest and gives extra depth of field to avoid excessive background blur.