Aperture ring or camera body

Hi, I'm quite confused and have some questions, hope someone can give advice. Is there now any need to use the aperture ring on a lens that has one? Is it better to use the ring or the aperture control on the body of the camera - can you get the same values using both? and lastly if using the aperture ring, I guess the dial shouldn't be set to AF?

thanks

The aperture ring on a Lens can be set to a pre-set figure or in newer (post 80s)lenses "A". If not set to "A" the camera will not change the aperture set on the Lens. If "A" is selected the camera controls the aperture of the Lens. Some modern Lenses do not have aperture rings. All of this assumes you are using compatable kit.

AF has nothing to do with aperture (in this post).

Hope this helps.

Davex.

You do not say which camera you want use with the lens. The answer will vary with the camera used. However, if you have aperture control on the camera then I would set the lens ring to A and use the body control (that is assuming the lens has an A setting). If your lens does not have an A setting then you will need to use the aperture ring. The values given F1.4, F2.8, F4, F5.6, F8, F11, F16, F22, are the same on both the aperture ring or the body control. However, the body control will give you intermediate values, eg F9.5.

If you have a Pentax digital camera and want to use a lens aperture ring, you will have to enable the function in the custom menu. You may be then restriced to manual exposure settings, depending on the lens.

The use of the aperture ring does not effect the use of auto focus, if that is what you mean by AF.

This may seem daunting at first, but once you have learnt it for you camera and lens, you will take to it.
It would help if you could describe the camera model and lens you are using.

Davex is correct. It the lens has an "A" , then use it, and use the camera wheel to select aperture. This ensures that you get the available automation in P;Av;Tv etc modes.

If the lens is an old one (like M or "K") without the electrical contacts to communicate with the camera, then use Manual exposure mode.

The AF dial ? Did you mean button/switch. My K10 has on the front of the body a switch for focus method: M = manual;AF-S = auto focus single; AF-C = auto focus continous. These settings affect only focus, nothing to do with exposure.

Oh sorry for the confusion I meant Av not AF. Its a Pentax k100d with a tamron 70-200 manual focus lens. It's an old lens without the electrics, I think K? There is n A setting, so I'll use that. Thaks for all your advice.

Just out of curiosity then, are there moving parts inside the camera that replicates the blades in the lens then?

Again thanks.

If this has an A, yes use that.

But, just in case you ever need to, you can use the aperture ring with older or non-A lenses as follows:

First you need to go into the custom settings in the menu, and set 'Using Aperture Ring' to 'Permitted'.

Then set the camera to 'M' - manual exposure mode.

Use aperture ring to set desired aperture.

Turn the DOF preview lever. The EV compesation will display -0.3 to +0.3, and you just adjust the shutter speed with the wheel until it shows 0.0.

if it has an A setting, then it does have some electrics, though not as complex as the electronics in a current generation lens.

The aperture system works like this:

If you take the lens off the camera, you will notice a couple of levers on the back. One is moved by the aperture ring, the other sticks out further and if you move it by hand it will move the aperture blades. I will call this the aperture actuator (I don't know if that's its real name but it'll do for now).

The position of the aperture ring dictates the minimum size of the aperture. In the K and M series cameras of the 70s and early 80s, all that happened was that the aperture actuator was kept depressed (to open the aperture) until you hit the shutter. When the shutter is released the actuator springs up and the lens stops down to the selected aperture.

Later on Pentax realised they needed a way to control the aperture from the camera body for Tv and Program modes to work. They therefore made A series lenses on which the aperture actuator movement is proportional to the area of the aperture. This means that if you know the maximum aperture of a lens, you can stop down to any aperture you like by moving the actuator a specific distance. That's where the electric contacts come in, allowing each lens to tell the camera it's maximum aperture so that the system can work.

That's why the A setting is off the bottom of the aperture scale, it wouldn't do any good for the camera to request F16 if the aperture ring could be set to prevent the lens stopping down past F8, so the automatic setting needs to be beyond the minimum automatically selected aperture.

thankyou all for clearing this up - it's great to know there's somewhere to come to for info and it's good to get an understanding of how things work under the hood.

Ok well I took the advice posted and tried it over the weekend. Still confused though.

I set the Aperture to 'A', when the lens is mounted on the body, the blades fully open up and the display in the eye piece simply shows 'F--' and no matter what I do I can't get this to change. When I change the Aperture ring to a different value then the blades don't move either.

The kit lens allows the apperture to change from 5.6 upwards, so it must be the lens. It's not a big issue as I'm happy with the results of the pictures, but the lack of control is annoying since I bought the thing so i could experiment with different settings and different lenses before I buy something more expensive.

I tried both options, but it won't take a picture unless it's on 'Permitted'

thanks

I've read this carefully and reading between the lines the A you refer to may not be the next click after 16 or 22 on the aperture ring? Are you referring to the A/M switch that changes from auto to manual diaphragm control for very very old screw thread lenses? Is it in fact a screw thread lens with an adapter on the back?

The fact that you need to set using aperture ring to permitted and you still get F-- in the display gives us further clues that this might be the case.

If so, the answer is to focus with the lens set to "A" to give the brightest viewfinder image, then stop down using the lever set to M and take a meter reading at this aperture by setting the camera to M or Av mode and operating the "stop down" position on the shutter release dial.

Then take your picture.

Thanks, no the 'A' is the on the Aperture ring after 22 ( at 'A' it locks and I need to press a little button to move the ring to 22, 16...4 etc.
No it doesn't have an adaptor. So it sounds like it's not doing what it's meant to do then?

Indeed so, it looks like there is a fault. It's not an expensive lens, so why not look for another one on eBay?

I will thanks, incidentally that's where I bought this one from, they're the only ones in my budget at the moment, but it's a good source when learning new things - no point buying expensive lenses when I don't know what I'm doing (yet :wink