[thegadge]

Now here's a thing....

Just purchased a second hand A 50mm 1.4 . First time I have used an actual A Prime, though have used M 50mm's and Super Takumars.
However, when I have stuck this on my KS1, I'm getting an aperture reading of 1.6, after 1.4 and before 1.8. Now, surely this is wrong. I'm assuming the aperture range would be 1.4, 1.8, 2.0 etc etc

Is this just some electrical blip and have other's experienced this?

Just wondering

Greetings from New Zealand

Steve

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Last edited by thegadge; 02-09-2016 at 09:21 PM.

[cpobuttons]

Now here's a thing....

Just purchased a second hand A 50mm 1.4 . First time I have used an actually A Prime, though have used M 50mm's and Super Takumars.
However, when I have stuck this on my KS1, I'm getting an aperture reading of 1.6, after 1.4 and before 1.8. Now, surely this is wrong. I'm assuming the aperture range would be 1.4, 1.8, 2.0 etc etc

Is this just some electrical blip and have other's experienced this?

Just wondering

Greetings from New Zealand

Steve

I would assume that if you have the lens set to A it is following your camera's aperture setting ie. 1/3 or 1/2stop increments...

[Dipsoid]

Now here's a thing....

Just purchased a second hand A 50mm 1.4 . First time I have used an actually A Prime, though have used M 50mm's and Super Takumars.
However, when I have stuck this on my KS1, I'm getting an aperture reading of 1.6, after 1.4 and before 1.8. Now, surely this is wrong. I'm assuming the aperture range would be 1.4, 1.8, 2.0 etc etc

Is this just some electrical blip and have other's experienced this?

Just wondering

Greetings from New Zealand

Steve

Surely it's not wrong, that's what my 1.4 does.

[RKKS08]

The aperture mechanism itself works stepless. Steps are just produced by the small sphere inside under the aperture ring of the lens.
If aperture is not controlled by the aperture ring, but from the body, there is no need to stick to standard values. And the value displayed may be a rounded one anyway.

This is the same with exposure time. You can manually set only a fixed set of values, but if it is controlled by the camera itself any value in between may be used.

[vonBaloney]

You will get different steps depending on whether you have it set to 1/2 or 1/3 EV increments...

[Not a Number]

A half-stop between 1.4 and 2.0 is 1.7
In 1/3 stops it is 1.4-1.6-1.8-2.0

The other thing that will confuse is with the EV steps set a 1/3rd you can't manually set the shutter speed to 1/180 but only 1/160.

[Alex645]

Much of what the other responses could be correct, but here are some other possible causes:

a) It's a used lens and the aperture is not opening completely, but sticking at f/1.6.

b) The light meter is not reading data from the lens, but rather the actual light from the lens. Due to variation in light transmission efficiency, on cinema lenses for example, the aperture is set to T/stops, not f/stops. f/stops represent the focal length of the lens divided by a number = the diameter of the aperture. And if you do the math, f/1.4 allows double the surface area of light thru the lens than f/2 (otherwise called one EV or stop). But that is theoretical and many manufacturers make approximations.

Thus my 2.4 liter engine may actually only displace 2375 cc's, but they don't call it a 2.375 liter engine. My Pentax 645 does not actually give me a 6 x 4.5 cm (60mm x 45mm) negative but a 56 mm × 41.5 mm negative. And the digital 645Z has a sensor smaller than that. And all of us shooting 35mm film are actually shooting 24mm x 36mm negatives.

So it is also very possible that they designated the lens as f/1.4, when in fact it's f/1.6 and they didn't want to confuse anyone with that 1/3 EV, yet it was a larger aperture than f/1.8, so they rounded up.

[vonBaloney]

Much of what the other responses could be correct, but here are some other possible causes:

a) It's a used lens and the aperture is not opening completely, but sticking at f/1.6.

b) The light meter is not reading data from the lens, but rather the actual light from the lens. Due to variation in light transmission efficiency, on cinema lenses for example, the aperture is set to T/stops, not f/stops. f/stops represent the focal length of the lens divided by a number = the diameter of the aperture. And if you do the math, f/1.4 allows double the surface area of light thru the lens than f/2 (otherwise called one EV or stop). But that is theoretical and many manufacturers make approximations.

Thus my 2.4 liter engine may actually only displace 2375 cc's, but they don't call it a 2.375 liter engine. My Pentax 645 does not actually give me a 6 x 4.5 cm (60mm x 45mm) negative but a 56 mm × 41.5 mm negative. And the digital 645Z has a sensor smaller than that. And all of us shooting 35mm film are actually shooting 24mm x 36mm negatives.

So it is also very possible that they designated the lens as f/1.4, when in fact it's f/1.6 and they didn't want to confuse anyone with that 1/3 EV, yet it was a larger aperture than f/1.8, so they rounded up.

Neither of these are possible simply because the pin arrangements on A lenses don't allow for that -- f/1.6 just isn't a choice (it would probably be pinned as a 1.7/1.8 in that case). It isn't reading light or the position of the lever or the opening, just the contacts arrangement on the mount tells it max aperture and range (min aperture). Everything else is a calculation based on that starting point that it is told. You can fool it into thinking it is something else with a bit of conductive (or non-conductive, depending) tape on the mount. (And so also for instance a f/1.4 lens with the aperture stuck at f/16 will still read as an f/1.4)

[Alex645]

I guess it would help if I carefully read the OP. To answer the OP's question, 1/2 EV between f/1.4 and f/1.8 IS f/1.6. The camera is correct.

[Not a Number]

The SMC-A 50mm f/1.4 has no click stop between 1.4 and 2.

If if the iris was sticking at f./1.6 with the lens in A mode the camera meters wide open. So if 1.4 is selected either by setting with the eDial in Av mode or by the camera when the appropriate shutter speed is set in Tv mode then the viewfinder and EXIF is going to show 1.4. If you take the lens of A mode the viewfinder will show F- - and nothing for the f-stop in the EXIF data.

Manual focus lenses typically have 1/2 stops between the engraved numbers, with exceptions at the extremes.

Change the setup settings for EV steps and play with the aperture settings in M or Av mode. Compare the steps with the following charts and you'll see what is going on.

https://en.wikipedia.org/wiki/F-number#Standard_full-stop_f-number_scale

With the SMC-A 50mm f/1.7 when the EV steps are set at 1/3 I can go from 2 to 1.8 to 1.7. From 1.7 it goes to 2!

[thegadge]

Thanks for the responses. I set EV steps to 1/2 and hey presto it's now 1.4, 1.7 and 2.0, You learn something every day, here! So, as there is no manual click spot for 1.7, what is the actual aperture value when set to 1.7 in A mode? Excuse my ignorance , as still relatively new to this

[vonBaloney]

Thanks for the responses. I set EV steps to 1/2 and hey presto it's now 1.4, 1.7 and 2.0, You learn something every day, here! So, as there is no manual click spot for 1.7, what is the actual aperture value when set to 1.7 in A mode? Excuse my ignorance , as still relatively new to this

When in A mode, it doesn't use click-stops -- the camera body just moves the lever a certain distance depending on the aperture setting and that's that, i.e. is it not relying on a stop or resistance from the lens to go to its setting -- it is calculating the distance to travel and goes there.

[shardulm]

The aperture mechanism itself works stepless. Steps are just produced by the small sphere inside under the aperture ring of the lens.
If aperture is not controlled by the aperture ring, but from the body, there is no need to stick to standard values. And the value displayed may be a rounded one anyway.

This is the same with exposure time. You can manually set only a fixed set of values, but if it is controlled by the camera itself any value in between may be used.

Good explanation.
Thats exactly why its even possible to get 1/2 and 1/3 stop intervals. Otherwise we will have to live with lens provided interval stops at all times.

[thegadge]

Thanks for that. Nice lens, I have to say. Here's a shot wide open and cheers for all the replies.
Steve in NZ