New lens - Diaphragm control ring?

[Justjo]

Morning
Received a Sigma 105mm F2.8 DG Macro lens for my D90 a couple of weeks ago. Was reading lens instructions last night and found that I get an error message on the camera when i follow the lens instructions regarding setting the exposure mode.

"When you use the Program exposure or Shutter speed priority auto moede, the Diaphragm contol ring must be set to the smallest Fstop. All Nikon AF/MF lenses have a safety button which should be moved to the lock position. When you use the Aperture priority auto mode or manual exposure mode, unlock the button and set the diaphragm value by turning the ring"

In shutter priority and program exposure modes, the F stop is locked at 32 and all works fine. When I unlock the lens and change the diaphrahm value to a larger aperture [smaller number], i get an error message flashing on camera 'Fee' where the aperture number normally is. Troubleshooting D90 manual states that:

Problem: Lens aperture ring is not set to minimum aperture
Solution: Set ring to minimum aperture.

Can someone explain what the diaphragm value on my new lens is and is my D90 behaving correctly. Note that once I set the diaphragm value back to 32, the error message disappears.

thanks in advance
Jo

[Tannin]

Sorry Jo, I'm having trouble working out what your problem is.

If I read your post correctly:

The lens works as expected
If you read the manual and do the opposite of what it tells you to do, it throws an error message
If you then go back to following the instructions again, it works just fine.


Maybe someone who owns a D90 and a Sigma 105 can provide confirmation and more detail, but the way I am thinking is that it is a modern camera with built-in controls for aperture and various other things. The aperture ring on the lens is just a hangover from the days of manual film cameras, and probably doesn't do anything useful at all on a modern camera like your D90.

So, unless I have completely misunderstood you, just go back to the way you were working before. That was correct. You can change you aperture by simply turning the dial on the top right of the camera body. (I am assuming you are in aperture priority mode to start with, which is generally the mode you want to be in almost all the time regardless of whether you are a beginner or an expert.)

[Justjo]

Thanks Tony
If i followed the instructions of the lens, i received an error message but i had no prior knowledge of what a diaphrahm on a lens was. I will disregard the lens diaphragm and regard it as a 'hangover' of an era i have no experience with.

thanks

[Tannin]

No worries, Jo.

That's exactly the right thing to do. But a little extra delatil, just for background information:

Technically, the "hangover" is the manual diaphragm control ring. The diaphragm remains just as vital a part of the camera system today as it ever was. I better explain:

To take a picture, you need to get the right amount of light onto the film (or digital sensor). Too little and it winds up almost black; too much and it's overexposed. There are two main ways of controlling the amount of light reaching the film:

1: the shutter - longer shutter speeds (smaller number) let in more light.
2:the diaphragm (which is what controls the aperture). By varying the size of the hole at the front of the lens, you can allow more or less light in. The diaphragm is the part of the lens that does this job. The bigger the hole (smaller number) the more light gets in.

So, your diaphragm remains important, it's just that we no longer have to set all this stuff manually by turning mechanical rings and pushing levers. Modern cameras like your D90 set the diaphragm for you, setting it either to the aperture value you yourself decided on (in aperture priority or manual modes) or to the aperture value that the camera calculates will produce the best exposure (in most of the other possible modes). The old-fashioned aperture control ring just gets in the way of this, which is why the manual says to set it as you explained, which is essentially switching the old control ring off and forgetting about it.

[bigdazzler]

Heya Jo .... Have a read of this. (http://en.wikipedia.org/wiki/Aperture) The world will make a lot more sense after :th3: