iris f-stop

T

Ty Fancher

Active member
What's the difference between adjusting f-stops and adjusting the iris? this may be a stupid question. i'm new to all the film terminology.
 
The Iris is the 'diaphragm' which adjusts to create different apertures.
Apertures are F stops, sometimes refered to as T stops.

Are you referring to adjusting a film camera or digital video?

If it's film camera , then it's the same thing.
"F stops" or "T stops" or "Aperture" or "Iris".

If it's a video camera, then I assume "the iris" is {controlled by} the 'exposure' {button} which usually refers to this, but {sometimes on consumer cameras, with limited manual controls, adjusting the exposure MIGHT} increase/decrease gain when at max aperture (eg: F1.8).
 
Last edited:
Charles Lowthian said:
If it's a video camera, then I assume "the iris" is the 'exposure' which usually refers to this, but also increases/decreases gain when at max aperture (eg: F1.8).
Click to expand...

Whoa, opening and closing the iris in camera will not affect the gain! Sharpness yes, noise, no.

F-stop is defined as the focal length over the diameter of the iris. When you increase the f-stop, you're telling the camera to close the iris (decrease the diameter). That's why a larger f-number results in less light coming in through the lens. "Exposure" is not quite the same thing. Adjusting f-stop certainly affects exposure, but there are other ways to control exposure, including adjusting the shutterspeed, raising the gain or use ND filters.
 
Thankyou Huy Vu.

This is why I asked what camera the question is referring to.
Eg: a very consumer camera = there is often only one 'exposure' control. Which controls every element, hence pointing out it may affect gain, and not just the actual 'exposure'.

But yes, on fully manual cameras, there are individual dials for each element of control.
 
True Charles but that still doesn't change the fact of how the F-Stop / Iris works. Your response was a bit off, at least in content. I'm sure you understand it but if I were to read what you wrote it didn't make much sense... :-)

Exposure is a result, not a think on the camera. The camera only has two main parts that you can adjust, each resulting in different exposures depending on how you set them. No camera anywhere that I've ever seen would relate exposure only to the Irus, FStop like you just did..

Also, on All cameras you have Aperture, not only on Pro cameras. The fact that the camera is set to automatic only because its cheap has no bearing on the original question...

glenn
 
You must log in or register to reply here.
Back
Top