So I've got a D700 and recently picked up a 55mm f2.8 Micro Nikkor AI-S along with a 135mm f2.8 ai-s. The kicker is that I've left the 'non-cpu lens data' section set to the previous lens a fair few times so far. The one thing I don't understand is, what difference does it actually make? Does it affect the focus indicator? Does it just affect the metering? I've noticed that with the 135mm set to the 55mm Micro Nikkor, the image was slightly underexposed. I haven't done any proper testing, but there doesn't seem to be a HUGE difference. On another note, why couldn't they have just had the camera recognise automatically what lens was attached? Hang on, no cpu Argh!

I believe the lens data is ONLY for the exif data, you dont have to change it if you dont care since it makes no difference in exposure and metering.

dgcrane

The lens data is useful to display/select the right aperture and to record the "right" exif data...

Guy

If you are using 3D colour matrix metering, the lens focal length and max aperture are taken into account. It will in fact resort to centre weighted if non-CPU lens data are not entered (p115 D3 manual). Therefore you could get different results by having the wrong non-CPU lens selected, depending on the composition and lighting.

In practise I wouldn't stress too much about it. It is a nice feature that you even have the option to enter the non-CPU lens data, so the the aperture and focal length is in the EXIF. Canon doesn't have this feature.

I don't think it's anything to stress about, although I like having the data when searching for photo's.

Something that hasn't been mentioned hwoever is that the camera would use this data to confirm flash, and flash focal length for the zoom. I beleive that it would be useful for correct exposure, but nothing earth shattering.


Gilles

Gilligan wrote:
I don't think it's anything to stress about, although I like having the data when searching for photo's.

Something that hasn't been mentioned hwoever is that the camera would use this data to confirm flash, and flash focal length for the zoom. I beleive that it would be useful for correct exposure, but nothing earth shattering.


Gilles

I would of thought the chip that designated the lens as a "D" type or any "G" lens which I assumed had the same type of chip would have done that..... and not the EXIF

Darren

Yes, the CPU chip does that, not the exif. But...

Setting the non-cpu lens data also provides information to the processor so that matrix metering works close enough to correct to call it "correct". Focal length shouldn't come into play with matrix as it is metering TTL on the actual scene and exif data is going to be moot at that point.

What I'm curious about is that we're talking about an old AI-s macro. Now I'm not sure about that particular lens but the diaphragm in a lot of macro lenses stops down with focus distance when working at macro distances and non-cpu macro lenses won't be able to share the true working f-stop with the body. This could potentially cause the metering to be a bit off, but we're more than likely talking a negligible amount.

Short answer with my limited knowledge, exif data is going to be the only truly noticeable difference. I'm assuming any fluctuations in exposure would have more to do with the macro lens aperture and working focus distance than the non-cpu lens settings.

It shouldn't affect the focus indicator at all and so long as the lenses in question have the same max aperture the metering should work correctly even with the wrong focal length dialed into to body.

Sorry Guys, Andrews correct. There's a lot more going on with the metering than it first suggests. As Greg pointed out in his initial observation, the focal length and aperture will effect what the camera will do with the exposure.

Put on a 28mm manual lens and then a 135mm lens and you will see to VERY differently exposed images.

So to answer the post, not annoying or frustrating at all.

We talked about this before recently in another thread. Shorter focal length lenses bring in more light than longer ones in laymans terms.