DOF with transparency (and reflections for that matter...)

[Madman]

Hi Jesse,

I'm experimenting with transparency and found an issue in the beta version, that is also an issue in version 1.8 (as far as I can tell, I seem to have a knack for asking questions that you have addressed in the readme file, but in this case I don't think so...). The problem is that if you apply DOF to a transparent object and increase Z2 to beyond the "see thru" plane, no DOF will be applied to the objects beyond this plane. I guess this is because transparency is a projection on the transparent plane and not actual transparency? The same applies to reflections but it seems our brain is better capable of rejecting incorrect reflection DOF then transparent DOF.

Somehow, I feel I'm asking for a lot (hence the reason why I put it in feature request and not in bug report  ), but would it be possible to improve the DOF on reflections and transparency in some future release? That's all. Everything else is perfect in version 1.8!   

[Jesse]

Hi Madman,

you are lucky, i did not mentioned this in the readme at all 

Short answer is: no
Long one is kind of: nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnooooooooooooooo....
(ok, i am a bit lazy)
... the addional depth of objects in reflections etc. are not stored somewhere, not enough mem for it.
You would have to trace many rays for a complete DoF effect and got only one focus point.
But that would be very, very, very, very slow.

[taurus]

just to jesses relief - even some of the big renderes like advanced renderer of cinema 4d (at least the versions i got in touch with) can't do this.
i remember a project some jears ago, where i had to render several images with individual layers ,different settings and different objects visible just to "emulate" an appropriate effect. loads of (post)work and not much fun. 

[Madman]

Thanks for the quick reply, Jesse. It took me a while to read the long answer, but I think I understand it now  . I was pretty sure I was asking something impossible, but, hey, asking never hurts, does it? I guess I'll have to wait until Moore's law has caught up a bit... or start experimenting with transparent 3D printing and then take a picture of it!

[taurus]

just a bit of old school ray tracing out of c4d 11.5. btw, i'm not sure, if a blur through transparency would be realistic. even a real camera would recieve light from the transparent object, which is within the sharp zone... 

[taurus]

dunno if this prooves anything, but i can't see any additional blur in the center drip...  
or maybe i didn't even understand the initial question. didn't give a try to recent versions of m3d...

(cropped and shortened from a wikimedia image)

[Jesse]

 

Of course, there are differences on case you have plane surfaces or lenses of glass, in case of the transparent box you should receive more or less the same blurring of behind scenes.  Only light travels slower through glass, maybe this leads to a virtual more length of lightray and even a bit more blur behind??? (Really not sure about this)

You can focus the background with a lense as you can blur it with a different shape of lense...

C4d is a really good program, as far as i can judge from results of users, maybe you can tell it to render even more correct, no clue.

[Madman]

@ Taurus: I can't believe I actually went through the motions of making a picture of my bathroom mirror to prove my point, but I did... If you look at the attached picture, you will see that the edge of the mirror is unsharp all around. The reflected picture is however razor sharp. If you would try to simulate this effect in M3D, you will have a sharp edge as well as a sharp reflected image.

(BTW, I can show you a much nicer picture of a droplet on the stem of one of my orchids than the wikipedia version, but as far as I can tell, there's a difference if your transparent object acts as a lens, so it doesn't prove my point as much as this picture  )

[taurus]

nice lesson in physical optics 
the mirror image is quite convincing and your argument about planes and lenses too... thx