CPU LENS DATA

DSLRventurer

Hi folks,

First post on here.

Wondered if you can help:

If I have a 28-50mm f3.5 AI-s lens, what do I set the focal length at on my CPU Lens Data menu selection? 50mm f3.5 or 28mm f3.5?

And...

If I were to use a variable aperture 70-210mm f4.5 - f5.6 AI-s for example, what would my numbers be inputting onto my DSLR (D750)?

Many thanks in advance.

PB_PM

Non-CPU lens data is a great tool, but it really only works well with fixed aperture lenses. For the lenses in question you'd need to make different sets for each aperture setting and focal length you intend to use. The camera will not know that the aperture is changing as it zooms, since there is no direct link to the lens.

DSLRventurer

Non-CPU lens data is a great tool, but it really only works well with fixed aperture lenses. For the lenses in question you'd need to make differient sets for each aperture setting and focal length you intend to use. The camera will not know that the aperture is changing as it zooms, since there is no direct link to the lens.

Thanks. Is this more for EXIF data or does it actually mislead the camera in terms of the lens's ability to be sharp at a specific focal length if it isn't in sync with the CPU Data it was originally input for?

WestEndFoto

It will have no effect on sharpness. What the camera interprets is irrelevant for that.

PB_PM

Thanks. Is this more for EXIF data or does it actually mislead the camera in terms of the lens's ability to be sharp at a specific focal length if it isn't in sync with the CPU Data it was originally input for?

As noted by @WestEndFoto non-CPU lens data has nothing to do with sharpness. It tells the camera two things, 1) Focal length and aperture, which it uses for calculating exposures and 2) EXIF Data.

NSXTypeR

What you could do is set multiple "focal lengths" into the camera and switch them as you go. It's not ideal, but I guess it's the only way for you to get proper exif files.

spraynpray

Why would you want 'proper EXIF files' if you have a dumb lens?

WestEndFoto

Otherwise there is no way to know focal length, aperture etc. When you have 4 dumb lenses between 20 and 50 like I do, it is pretty handy.

Nikoniser

28-50mm f3.5 AI-s lens is a horrible, horrible lens. You would be way better off putting the 35mm f2 which is cheap, sharp, free from flare/ghosts and CA on and cropping to get a 50mm.

DSLRventurer

I think the reality is that over the last year, all of my variable aperture / fixed aperture AI-s zoom lenses are essentially not going to expose properly unless I keep tweaking with the lens data. How about my 80-200mm f4 AI-s? Same deal? If I am at 80 or 100 or 150 or 200 I am going to have to set the lens data each time I zoom in or out? If so...I suddenly feel like I have 'wasted' my monies...

PB_PM

As long as the maximum aperture is fixed throughout the zoom range you won't have a problem. The EXIF data might be wrong for focal length, but otherwise it will be fine.

DSLRventurer

As long as the maximum aperture is fixed throughout the zoom range you won't have a problem. The EXIF data might be wrong for focal length, but otherwise it will be fine.

Thank you

Ironheart

The CPU thing is really a misnomer. @PB_PM is correct, all it does is read out the position of the aperture ring. The focal length isn't used. As far as metering goes, it is looking through the lens just like you are. I use some really old non-cpu lenses and all I do is take a test shot and look at the histogram. Way more accurate than anything else. Actually I've been doing this so long, I pretty much know what ballpark aperture and speed I need just by looking at the scene, and going +/- on the sunny-16 rule.
Meters are for wimps really ) (just kidding of course)