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Exposure question for my Zeiss 28-85 variosonnar

G

Guest

Hello, I am a new user of the contax system (aria + CZ 28-85 lens) and recently have bought a second hand Tamron 70-210mm/f3.5. The problem is that the exposure time of the said two lens are more different (my CZ lens always need 30-150% more exposure time than the tamron, e.g. CZ f8 / 2 sec. and tamron f8 / 1 sec.). I also used my Minolta system and a light meter for the reference and got the following exposure time result:

CZ len > light meter > minolta len > tamron len (C/Y mount)

Could anyone tell me what happened of my CZ lens and aria.

Thank you in advance

Kent
 
G

Guest

Hello Kent,

comparing cameras and light meters is quite difficult 'cause of the different measuring angles or systems (integral, matrix or center weighted).

What is with the largest aperture of each lens? Does your camera display them correctly? I also had some problems with a Tamron adapter. After adjusting ist everything was fine!

Matthias
 
G

Guest

Hello Kent,

comparing cameras and light meters is quite difficult 'cause of the different measuring angles or systems (integral, matrix or center weighted).

What is with the largest aperture of each lens? Does your camera display them correctly? I also had some problems with a Tamron adapter. After adjusting it everything was fine!

Matthias
 
G

Guest

Forgot something: the tamron has got a fixed aperture over the hole range. The Zeiss hasn't!

Matthias
 
G

Guest

Thanks Matthias,
your advise is very helpful but can you tell me how to adjust your tamron mount?
From your above-mentioned, it means that the floating aperture would affect the result (as the camera indicated the largest aperture was f3.5 when the CZ len at the 85mm focal lenght and actually it should be f4). According to the aforesaid, the exposure time maybe be all under 0.5 - 1 steps when using the hand held light meter.
Kent
 
G

Guest

Hello Kent,

> your advise is very helpful but can you tell me how to adjust your
> tamron mount?

ONLY if the maximum aperture is not shown correctly in the viewfinder of
your Aria you have to adjust the lever which I've marked in the image.

> From your above-mentioned, it means that the floating aperture would
affect
> the result (as the camera indicated the largest aperture was f3.5 when
> the CZ len at the 85mm focal lenght and actually it should be f4).

The changing aperture of a zoom lens isn't recognized in the viewfinder
display. The Contax mount doesn't support such function. Your
Vario-Sonnor is loosing half an f-stop if zoomed. So you should see the following: the maximum aperture should be shown as 3.5 in the viewfinder and does not change while zooming. The exposure time should change from, lets say, 1/125 sec to 1/90 sec.
But there is another problem. The viwefinder and the engraving on the
lens show f-stops. F-stops are calculated by the diameter of the
aperture divided by the focal length (you can simply measure and
calculate this!). But a lens like the Vario Sonnar with 16 lenses in it
has got some more light loss. Correctly the t-stop must be shown where
this light loss is regarded.

> According to the aforesaid, the exposure time maybe be all under 0.5 -
> 1 steps when using the hand held light meter.

As I already said in my last Mail. It is quite difficult to compare a
handheld meter to a build-in camera meter 'cause of the different
measuring angles. My Gossen Lunasix 3 has got an measuring angle of
about 30°. The angle of the camera depends on the focal lenght of the
lens. If you don't measure an absolutly homogeneous area, you'll get
different readings. And then comes the before written about the t-stops
in account...

Take a sharp look to your slides. If they're quite good exposed with
each of your lenses I won't make me headaches about the readings!

Matthias
 
G

Guest

>I am impressed, Matthias! In a relatively short note you explained the complex stuff very precisely! That's it. Everybody should print it out, so that the same questions do not appear every 3 months (though - it is understandable... making nodes in your brain when you do not handle such physical stuff all the time...). Regards to all Herbert
 
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