Question about Lens Speed.

T

taybo20

Member
Excuse the amateur question. I just haven't found a clear answer anywhere.

For example, if a lens is a f/5.6 lens, even if you open the iris on the camera to wide open does it not matter?

I guess I am confused on the iris of a camera (such as the HVX-200) being able to go through differing f stops and a lens that has a maximum f stop.

Can anyone help me understand better?
 
If a lens is called a F/5.6, that means it cannot open any wider than that. When I say I own a 50mm F/2.8 lens, it means the maximum aperture (the widest it can open) is F/2.8.

Having a f/5.6 lens wide open will be an F/5.6.


If what you are referring to is a lens 'set' at F/5.6 then depending on the lens it could very well open to a wider stop. (F/4, F/2.8, F/2, F/1.4)
 
taybo20, perhaps you're thinking that the lens has an iris, and the camera has an iris? If so, that's not correct. The only iris is in the lens. Whatever the limit is on the lens, is the limit, totally.

So the HVX's lens has an iris range from f/1.6 to f/11. The limit on the HVX's lens is 1.6 (at wide angle; like almost all zoom lenses the more you zoom in, the smaller the maximum iris is). When at full telephoto, the maximum you can open it up to is f/2.8.
 
Okay Ryan and Barry. I think I have it now.

If I set the aperture to Open or f/2.8 and the lens is a f/5.6 is there any effect? Or will I have to go to f/8.0 to see any effect?

I appreciate both your responses. Thanks!
 
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I'm planning on using a Canon T2i. Of course I haven't actually handled it, so that could be part of the reason I'm not making much sense.

I just remember using a HVX-200 and being able to rotate the iris dial from open to f/11. Maybe I was doing something wrong.
 
Barry_Green said:
taybo20, perhaps you're thinking that the lens has an iris, and the camera has an iris? If so, that's not correct. The only iris is in the lens. Whatever the limit is on the lens, is the limit, totally.

So the HVX's lens has an iris range from f/1.6 to f/11. The limit on the HVX's lens is 1.6 (at wide angle; like almost all zoom lenses the more you zoom in, the smaller the maximum iris is). When at full telephoto, the maximum you can open it up to is f/2.8.
Click to expand...

I now see that this is what he was thinking.

To the OP: Aperture (or the iris) is only found on the lens. There is only one. Depending on the lens, the maximum f-stop (or 'wide open') will vary.

taybo20 said:
I'm planning on using a Canon T2i. Of course I haven't actually handled it, so that could be part of the reason I'm not making much sense.

I just remember using a HVX-200 and being able to rotate the iris dial from open to f/11. Maybe I was doing something wrong.
Click to expand...

Camera's such as the HVX, which have a built in lens, controls the lens iris/aperture via the body. As Barry said, there are not two. The camera simply controls the lens... notice there isn't an additional iris ring on the lens.

Then again, if you are using a lens adapter such as an HVX200 and Redrock, there are two lenses thus two apertures. That can make things difficult at times.
 
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taybo20 said:
I'm planning on using a Canon T2i. Of course I haven't actually handled it, so that could be part of the reason I'm not making much sense.

I just remember using a HVX-200 and being able to rotate the iris dial from open to f/11. Maybe I was doing something wrong.
Click to expand...

No, it's exactly the same.

The lens on the camera will have a dial (assuming you buy an older lens that actually HAS one) that you will turn just like you did on the HVX. It works exactly the same way. The maximum OPEN on the HVX may be F1.8. You cannot turn it past this point. The lenses that you put on a T2i will also have a maximum open, but they won't necessarily be the same numerically as the HVX. If the lens you have is a F5.6, then when you open it to that number, it's OPEN.
 
taybo20 said:
I'm planning on using a Canon T2i. Of course I haven't actually handled it, so that could be part of the reason I'm not making much sense.

I just remember using a HVX-200 and being able to rotate the iris dial from open to f/11. Maybe I was doing something wrong.
Click to expand...

Sort of mixing up the situation. In the case of the HVX-200, you have a 'fixed' lens on the camera, and there is an adjustment setting/dial/control that allows you to control
the iris.

This is equivalent to a camera like the T2i, which may have an compatible Automatic capability, and you use the control/dial/wheel on the camera body to control the iris.

But however the control is performed, dial on the camera body, or whatever, the ultimate element that is controlled is in the lens, and the lens sets the maximum. So, for
a lens with a maximum of f/5.6, a pretty 'slow' lens, that's it, no amount of camera body thumbwheel fiddling will change that maximum.

Here is another situation. If you put a 35mm lens on an adapter on the HVX-200, then yes, you would have 2 iris controls... but the standard operating setup is that
the 'fixed' lens on the HVX-200 would be set to 'wide open', and only the 35mm lens iris would be adjusted for the f-stop.

If you get different readings from the camera's viewfinder status indicaitons, like it says the lens is at 2.8, and you know the maximum for the lens is 5.6, then
something is broken, and the camera body and lens are not 'talking' with each other...

On the T2i, you can use non automatic lenses, and so you would set the f-stop on the lens barrel using the f-stop ring. The camera would have no knowledge of
the lens, if it an 'old' lens with no electronics.
 
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