Second Iris to maintain desired DOF ?

[saru]

Sorry if this has been covered already but is it possible to have the second iris that digitally controls the exposure ? This works exactly same as the way we use DOF adapters out there - we control DOF with the lens in front of the adapter (eg. Nikon still lenses) and control the exposure with the iris of the camera.

Is the Red supposed to have this feature or simply this kind of thing is not possible ? Could be handy, just a thought.

 

[Andreas Fernbrant]

What would you gain from this that could not be achived with ND filters?

 

[saru]

No, not exactly..

Let's say I want DOF of f5.6 for the entire shooting of certain project (eg. documentary), where I have no control for the lighting. In that situation, by controlling the exposure with camera iris rather than lens iris, I can maintain f5.6 DOF and keep the frame in good exposure.

Cheers



EDIT:
well, hang on, yes you are right. I can do same thing with ND filters..
But you know, having the built-in camera iris is handier than having dozen of NDs.

 

[Graeme Nattress]

Can't work for RED. We don't have an intermediate image, and we have no room between back of lens and sensor. The answer is ND filters on the lens.

Graeme

 

[saru]

Hey Graeme, thanks for the clear, straight answer !
I appreciated much.

Cheers

 

[Andreas Fernbrant]

I'm by no means an expert on electonics and sensors.

I'm not saying 2 irises is a good idea, but it just crossed my mind. You don't need a intermediate image
if you could control the sensetivity of the sensor? But perhaps that can't be done?

I don't really know why I started thinking about this, because ND filters are the most logical to me.
But perhaps it's a good idea non the less.

Kind regards
Andreas

 

[Graeme Nattress]

And if you stop down too far, you get resolution loss due to diffraction....

Graeme

 

[Mark B.]

It would allow for using modern Canon lenses though, since it would bypass the need for a manual aperture control on the lens.

My physics are out of date... if an iris-like device is put in front of a lens, will it act in a similar manner to the iris typically placed behind the lens?

 

[Jim Arthurs]

And if you stop down too far, you get resolution loss due to diffraction....

Graeme

Speaking of Diffraction... With the large RED sensor, will f16/f22 be unusable, or is the size of the sensor help in this regard compared to smaller chips?

Minature or motion control work sometimes demand greater DOF than the "sweet spot" that live guys try to work in...

 

[Graeme Nattress]

Diffraction limiting of resolution is all down to pixel size. I think you're looking at f11 to be where difraction starts to get bigger than a pixel, but because we're bayer and have an anti-alias filter, you probably won't notice anything at all until beyond the f16 / f22 range. I'm not an expert on this area of optics, but I think the above is pretty reasonable.

Graeme