BabaJ
Just to re-iterate, changing the aperature(hole opening size in this case) does not change the ‘cropping’ or ‘zoom’ or final ‘size’ of the image.

Which aperture are you referring to - lens aperture or horizontal/vertical aperture? The later totally does change the cropping/zoom. That's for example why digital SLR sensors are often referred to as “full” and “cropped”.

https://www.slrlounge.com/workshop/crop-vs-full-frame-cameras/ [www.slrlounge.com]

antc
Which aperture are you referring to - lens aperture or horizontal/vertical aperture? The later totally does change the cropping/zoom. That's for example why digital SLR sensors are often referred to as “full” and “cropped”.

Since we're talking about USD attributes/houdini parameters, aperture refers to the image plane size, not the lens aperture (fstop).

Which aperture are you referring to - lens aperture or horizontal/vertical aperture?

? I already qualified which ‘aperature’ I was referring too - Lens. And the distinction between the two.

The only reason I can think of as to why you would ask which one I am talking about is that when I said:

the aperature(hole opening size in this case)

You still think that an aperatures(lens) hole(whether a large hole or small hole), somehow still affects the size of the final cropped image?

A lens aperature typically ‘sits’ immediately at/behind a lens, ‘up’ and away from the film plane.

This position of the shutter(lens aperature, shutter, iris, etc.) is fixed in its' distance from the film plane.

It(lens aperature) does not lie at/close to the film plane to function as a cropping mechanism.

It (lens aperature), whether the hole is set to be wide open, or very small - does not affect or change the final cropped size of the image.

Ok I was just asking for clarification. Like jsmack said already, in the context of this LOPs thread, aperture should not mean lens aperture. But it has been used in this thread numerous times meaning lens aperture So at this point for the sake of typing one more word it makes the most sense to me to be clear and prefix it, but whatever.

In any case … no, of course you're correct that lens aperture makes no difference to the zoom/crop of the image. But the LOPs aperture does, which is what I was saying a couple of posts back.

Hi. I do wish common render engines could give you the options for real photography. I would love to “expose” my render like the real world. I think maxwell render may be able to do this. One day I would love to match cg to photography as a test in maxwell. Best mark

Mark Wallman
Hi. I do wish common render engines could give you the options for real photography. I would love to “expose” my render like the real world. I think maxwell render may be able to do this. One day I would love to match cg to photography as a test in maxwell. Best mark

I agree, it would be ‘nice’.

However, I believe the algorithm to take into account Focal compression would be crazy difficult.

As much as I like to tinker with coding algorithms, that is one I wouldn't touch.(Don't think I could pull it off if I wanted to either).

Like I was saying before as in the images below, all are ‘cropped’ the same, but the distortion makes for an altogother different result.

BabaJ
Like I was saying before as in the images below, all are ‘cropped’ the same, but the distortion makes for an altogother different result.

“focal compression” as you describe it is not a property of a camera, and it's easy to reproduce in CG
those photos are simply not taken from the same distance to the subject
different FOV, different distance to compensate

in Houdini this would be same aperture (sensor size), different focal length, different distance from the subject in world space just to keep the screen space size of the subject more or less the same

(again use of aperture word here has no relation to the physical lens aperture (hole opening))

EDIT: also it seems like this thread is more about semantics than anything else, not only aperture but for example you also seem to be using crop and not relating to the crop factor of the sensor
so without fixating on a single specific meaning of any specific word I'll assume we are all on the same page

“focal compression” as you describe it is not a property of a camera, and it's easy to reproduce in CG
those photos are simply not taken from the same distance to the subject
different FOV, different distance to compensate

No focal ‘compression’ is a property of a real lens, which I explained in earlier posts in this thread.

And yes the objects were not not taken at the same distance and that was part of my point earlier:

You cannot crop an image ( like with Houdini ‘aperature’ or any other software ‘zooming’ or crop like Photoshop ) and get the same result other than cropping, like in the photos I supplied, with a different image that was taken at another focal length. Two different focal lengths always have inherently different compression/distortions.

What Mark means and I was agreeing would be nice if there was a ‘CG’ camera, where all the ‘controls’ were present so that one could get a one to one correspondance(with a real camera) and in turn the same image as if it were taken with a real camera.

At the moment all one can do to get the same resulting image is guessing through the current available settings as an iterative process.

you also seem to be using crop and not relating to the crop factor of the sensor

Not sure what you mean by this or why you would say that.

BabaJ
What Mark means and I was agreeing would be nice if there was a ‘CG’ camera, where all the ‘controls’ were present so that one could get a one to one correspondance(with a real camera) and in turn the same image as if it were taken with a real camera.

I don't think anyone was arguing with the need of physical camera, physical camera for Mantra and now Karma has been requested for years, some renderers have it though

BabaJ
No focal ‘compression’ is a property of a real lens, which I explained in earlier posts in this thread.
And yes the objects were not not taken at the same distance and that was part of my point earlier:
You cannot crop an image ( like with Houdini ‘aperature’ or any other software ‘zooming’ or crop like Photoshop ) and get the same result other than cropping, like in the photos I supplied, with a different image that was taken at another focal length. Two different focal lengths always have inherently different compression/distortions.

if the distance was not the same, how can you say that the “compression/distortion” is a result of focal length change?
as I tried to point out with my image the resulting effect needs the distance to change, otherwise (if we disregard lens distortion) focal length change just changes the FOV the same way as having different sensor size, or cropping in photoshop
no parallax distortions will happen with just focal length change (as your article also points out)

BabaJ

you also seem to be using crop and not relating to the crop factor of the sensor

Not sure what you mean by this or why you would say that.

just to illustrate that this thread is more play on words than anything else
you constantly bring the fact that aperture in houdini doesn't behave like aperture in real camera while being told that they are not describing the same thing
then you mention crop/cropping to describe what clearly is caused by dolly (moving camera towards/away from the subject) instead of what actually can be a cropping (camera crop factor, houdini crop settings, 2d post image crop)

but regardless, it's true that houdini doesn't have physical camera, or lights or even terminology of the properties that relate to many real world names in the same way as one may expect from specific point of view, so a bit of willingness to understand the how CG camera relates to real one can help easily achieving what you want instead of it being an “iterative process” as you describe

BabaJ
Two different focal lengths always have inherently different compression/distortions.

Babaj ^ this is where you keep losing me.

I'm going to avoid too much terminology but here is a scene at least showing Focal Length and Aperture are related in a simple linear fashion. Here there are four cameras with focal lengths of 35, 70, 200 and 800. The horizontal/vertical aperture is adjusted in each case such that the resulting projection math comes out identical and all four cameras produce the same image exactly. The distance to the subject is obviously not changing.

With real lenses it is true however that lens distortion would be a little different in each case. That can also be simulated in a renderer that supports lens shaders though.

if the distance was not the same, how can you say that the “compression/distortion” is a result of focal length change?

Because your not looking at it from the context I was explaining.

The thread started off on the topic of aperature, then it started to include the element of ‘zooming’ in my converstaion with jsmack when he said:

No that's exactly what it is. Zoom is changing the size of the projection. It is equivalent to changing the size of the imaging device. It is expressed in Houdini in terms of focal length and aperture, since these are the values that correspond to the real world. A zoom value would be just as valid, however since it is unitless, it would make relation to physical camera and lens sizes impossible.

I'm not going to re-post my response to that, but I should at some point take some time and put together an image example to illustrate the point which I believe is not being understood.

…just to illustrate that this thread is more play on words than anything else
you constantly bring the fact that aperture in houdini doesn't behave like aperture in real camera while being told that they are not describing the same thing…

Well, I've already acknowledged that there is a difference with respect to what the term ‘aperature’ means, having different contexts, a number of posts ago and have been carefull since to annotate when I am using the term aperature as to which one I am referring too; When discussing the additional topics under discussion.

…then you mention crop/cropping to describe what clearly is caused by dolly (moving camera towards/away from the subject) instead of what actually can be a cropping (camera crop factor, houdini crop settings, 2d post image crop)…

What did I say that you think is clearly a dolly movement? affecting the context of the point I was making?

so a bit of willingness to understand the how CG camera relates to real one can help easily achieving what you want instead of it being an “iterative process” as you describe

Well, in this long thread the only thing I am certain of being wrong(other than being misunderstood) is just what you said.

Just doing a quick review of all the cameras parameters and the ‘offloaded’ separated from fstop Depth of Field factor to mantra/karma node;

If the algorithms are ‘correct’ there is no reason why I don't see I could not get the same one to one correspondace of a real life camera results. Aside from expecting f-stop to contribute towards exposure which is a non-issue, not needed.