Question about perspective distortion in 3d printing

[Nemo_Nemo]

Hello everyone. Recently I’ve sculpted a doll head in zbrush. This was my first experience with this program, and I’ve spent half a year on sculpting. The result was really pleasing - up untiil the point when I decided to print it.

Unfortunately, I sculpted everything in orthographic mode.I didn’t know anything at all about perspective and was completely sure that the printed result would look similar to what I had on my screen. Boy I was wrong…

So this is what I have in zbrush:

And this is what it looks like after printing:

The side view looks more or less similar, but the front view is completely different. Theoretically I understood that the printed stuff won’t be an exact copy of my model, but not to that extent. Facial features are so distorted that the face feels alien to me. Now I’m wondering: is it possible to somehow make the perspective form of my model look like the ortographic form? Front view in particular. The question is probably dumb as hell, but still. I really don’t want to start everything from scratch. I’m not a professional sculptor, and even if I start a new project, this time in perspective mode, it won’t be the same. Besides, I’ve come to really like this face despite the enormous amount of mistakes done in the process.

The whole situation is stupid, I know. I should have done more preparatory work before sculpting anything, let alone printing, but here we are. Tbh I’m really upset and out of ideas.

[Spyndel]

Hello @Nemo_Nemo

Orthographic mode is very useful for establishing accurate proportions. If your proportions are mathematically correct, they will always be correct with whatever you do with your mesh, even if your way of viewing that mesh differs. If the measurements of the features are accurate, they will always be accurate.

However, it’s rare that we are able to accurately measure what the true dimensions of a subject are when it comes to faces and figures. Reference material usually has its own photographic distortion, and optical reality is a different thing altogether from camera reality. Viewing distance from the object will always be a factor. There is, unfortunately, no 1 to 1 to 1 path between digital reality, photographic reality, and optical reality. All of these are subject to misleading distortion–even your own eyes.

Turning on perspective can give you a closer approximation of how the mesh with those dimensions might look when printed, if viewed at the same distance to the mesh. In my experience, there is no magic focal length that can be trusted to simulate reality, but you can find a lot of discussion on the subject and form your own opinions. I’ve seen claims that the humans eye is similar to a camera with a focal length of 22mm, other people claim that 35mm works well for most situations, other people claiming that 55 mm is the way to go. I cannot speak with authority–you will have to come to your own conclusions.

How much you want to work in orthographic vs perspective mode is a matter of preference. You’ll find many different opinions. I personally recommend using orthographic mode when establishing proportions, and definitely if working on a mechanical hard surface object that requires precise measurements and the ability to line up symmetrical points so they fall in front /behind each other perfectly.

However at some point when sculpting organic subjects, you’ll probably want to switch to perspective mode if for no other reason than to get used to the way your model looks with perspective distortion with the proportions you have given it. Orthographic mode is a useful tool, but it is also a cheat–you shouldn’t let your eyes get too used to viewing the subject in that form.

Your best bet would probably be to make a test print of the size of your intended output, at the intended viewing distance, and match the perspective in the viewport until you feel it approximates that look. Make note of those settings, and try to work on the latter stages of your mesh under these conditions.

BTW, your printed face looks good to me–it looks more or less accurate and well proportioned.

Good luck!

[Nemo_Nemo]

Hello @Spyndel

Thanks a lot for such a detailed and professional reply! Your explanation helped me a lot. Now I at least have some primary understanding of how perspective works, and I will continue my research on the subject. I think that it was just hard for me to accept that the thing I’ve worked on for months is basically non-existent in real word, or that it looks rather different. But you know what - the printed version really feels far more realistic than the orthographic one, plus the proportions are geat! Sure it needs some tweaking (the pinted head is way too big for the body I’ve chosen for it), but at least 80% of the work is done. Thank you again for helping me see this situation in a different light.