What's the Φ mean?

Tonky wrote:
Nothing!

The mark is really intended to accurately measure the amount of lens extension you're using when using extension tubes and bellows, so that you can look up the amount of exposure compensation needed to make allowance for light fall-off (due to the extension), or to accurately measure film plane to subject distance. There are exposure compensation tables available which tell you the amount of compensation required for a given amount of lens extension, too.

If you're more mathematically inclined you can work out the exposure compensation yourself using the Inverse Square Law ...

http://csep10.phys.utk​.edu …lect/light/inte​nsity.html

Thanks. Exposure compensation never entered my mind. But if that is a consideration, then Frank (PhotosGuy) did have a point about the histogram since one can use it to check exposure, too. But then, Frank likes using histograms to using a handheld light meter, too.

Fair comment there - sorry Frank!

We also tend to forget what a huge difference TTL metering has made to the ease of using extension tubes and bellows.

It has nothing to do with the film/sensor size, nor does it have anything to do with print size reproduction, but the location of the film plane/sensor plane... It's there to show exactly how far in from the front of the camera body the film/sensor is located... This is for when precise measurement from film plane to subject is needed in Macro and Micro photography where 1mm can make the difference between almost sharp and pin sharp...

Edit... Most modern cameras have TTL metering so the loss of light is usually accounted for by the camera...

My first camera was a plain F with a 28/3.5 I got for £60 while at college. The 105 was my main lens for years. Best portait lens ever! Now I use an EF 85/1.8 on a 1Dm2, and it's pretty well just as good, for my needs. Life gets better (I've turned into a digital freak)

cheers
Phil

Thanks, guys! You saved me a lot of typing!

Right! It seems like most of my stuff was shot either with that or the 20mm f/3.5! Maybe 10% with the 50 f/1.4 or the 600 f/5.6.
(Maybe I should dust the "F" off!)

>>It has nothing to do with the film/sensor size, nor does it have anything to do with print size reproduction<<

So explain why the following principle is NOT valid in this discussion of where the focal plane is positioned...
Magnification of the image is 1:1 when the subject distance from the lens is the same as the object distance to the film plane. Magnification = image dist/subject distance.
So if you wanted to have a 1cm distance on the object appear on the film at 1cm actual size, you would put extension on the lens so that the total distance from sensor to object is 4X the focal length of the lens being used. And the amount of extension to add is the same as the focal length of the lens in use. Then if you wanted a print at life size, you make a contact print. Or a print at precisely 2x, you have the enlarger magnification set accordingly. No need to measure the object on the film and measure it on the darkroom easel, too.

Because:
1) Reproduction ratio will be the same for any sensor/film size at a given image distance, object distance and focal length
2) You can achieve a given print magnification over original subject size from any original image size. Convenience in calculations isn't a requirement.

PhotosGuy wrote:
Thanks, guys! You saved me a lot of typing!
Right! It seems like most of my stuff was shot either with that or the 20mm f/3.5! Maybe 10% with the 50 f/1.4 or the 600 f/5.6.
(Maybe I should dust the "F" off!)

Your "F" looks a lot like my first SLR. It was a Nikon "Photomic F" I think. It had built-in metering, but not TTL, it was an eye on the top right of the prism housing, and there was this little metal extension tube that you screwed onto it to go from "averaging" to "spot". It more or less equated to "cropping" the metering eye to the FOV of a 135mm lens.

I learned on that baby. Spent hours in the darkroom. Even won some competitions with early stuff in B&W.

Ahh, the memories . . . .

You mean if I want a 1:1 print of Neil Armstrong's footprint on the moon I just have to use my 28-135 lens and take a snapshot of the full moon then adjust the print magnification? Do you know how big a piece of paper I will need for a 1:1 print of the Rover on Mars? (You did say any original image size.) ;<

The Photomic did come out just before the FTn. I'm told that the F pentaprism is in high demand these days since you can't get the mercury batteries for the FTn meter. Someone else also said that there is a replacement battery now.

Re: "I learned on that baby." I think this one has about 40,000 miles on it! They were great cameras.

They're still great cameras. We just expect our cameras to also be multi-mode light meters, auto-focus tracking machines and post-processing engines nowdays. If we just needed great cameras, the old Nikons would still be king.

Ours could do that! We just had to help them.

Apologies for the hijack, Dew!

Not always. The 17-40's nodal point seems to be very close to the front of the lens (certainly well in front of the middle), and I've seen mention (from very experienced pano shooters) that the 70-200 f/2.8's nodal point is *behind* the lens. That seems very strange to me, but I can't test it since I just sold the 70-200.

PhotosGuy wrote:
Thanks, guys! You saved me a lot of typing!
Right! It seems like most of my stuff was shot either with that or the 20mm f/3.5! Maybe 10% with the 50 f/1.4 or the 600 f/5.6.
(Maybe I should dust the "F" off!)

you could always get an EOS adapter for your 'F' lenses. I am very happy with the results I get with my 105 on my d-rebel

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It's one of the 1st accessories I bought!
These were taken with the 20mm: '66 Ford Shelby GT-350