Maxxum 50/1.7 actually 1.4 !

[Golem]

I put a Minolta Maxxum 50/1.7 Nex-7 via an

LA-E2. The readouts were showing an f/stop

range of f/1.4 thru f/22 .... for a lens marked

on its barrel as an f/1.7.

 

Considering that this might be just a minor

weirdness in the control interface, I did not

immediately assume that this f/1.7 lens was

really an f/1.4, so I ran a practical check.

 

Shooting out-of-focus images thru the whole

[indicated] f/stop range, the shutter time was

always adjusted for a constant exposure, the

shrinking size of the defocused highlights

showed that the indicated f/stops, from 1.4

thru 22, were the real f/stops. The 50/1.7 is

actually a 50/1.4.

 

Somehow Maxxum bodies cannot access the

extra lens speed, but the Nex-7 body can :-)

 

`

[OldNoob]

Crop factor might be cutting out a bit of the "fall off" that would normally be associated with the lens on a full frame. With the falloff, on a full frame sensor, it would no doubt read f1.7. 

Not to mention that on the APS sized sensor, the DOF of the f1.7 may actually be closer to that of the DOF of a f1.4 when mounted on a full sized senor.

 On the other hand,, the LA-Ea2 metering process is a bit different than the LA-EA1

If i recall the LA-EA2 uses a translucent mirror for focus. The camera may be trying to compensate for this loss by exchanging exposure settings and end up givng a reading of f1.4.

Have you checked the raw data?

[Golem]

There is no raw data.

 

Jpegs show the constantly changing size of

the intentionally way-out-of-focus highlights.

Thaz the test I had in mind, so I didn't shoot

raw files.

 

The "weirdness" is in the control interface. If

you put the lens on a Maxxum the only f/stops

you can dial up are 1.7, 2.0, ..... 22. In half

stops that would be:

1.7 2.0 2.5 2.8 3.5 4.0

4.7 5.6 6.3 8.0 9.0 11.0

13.0 16.0 19.0 22.0

.... thaz 16 settable stops.

 

Put the very same lens on a Nex-7 and you get

one more settable stop, specifically f/1.4, and it

still ranges in half stops down to f/22, which

means 17 settable stops rather than only the

16 stops available from a Maxxum body.

 

If it were simply compensating for the SLT loss,

I could see a different set of stops, but not the

increased number of available stops. There's

no SLT body involved anyway. This lens was

built for a film era SLR, and is then, years later,

tested on a post-SLR, post-SLT, mirrorless,

live-view Nex-7 body.

 

------------------------------------------

 

I wanna be clear about the test procedure. The

only reason for adjusting the shutter speed to

maintain constant exposure was a convenience

for viewing the test results. IOW, I was in no

way judging uniformity of exposures results to

test the f/stop range, nor to confirm whether all

17 of the indicated stops were indeed different

stops. I did NOT run an exposure test ... the

only changes I was watching for were the sizes

of the out of focus highlights [the focus setting

was never changed]. That alone tells me what I

need to know ... that every indicated stop was

indeed a different aperture size.

 

Before seeing the results, my intuition predicted

that the indicated f/1.4 would show an aperture

size no larger than the indicated f/1.7. Finding

the larger aperture size for the indicated f/1.4

was a complete surprise.

 

`

[OldNoob]

when you take a photo in 1.4 what does the EXIF record? and What is the picture quality like in 1.4? you might find it somewhat artistic.

[favol84]

It's an Electronic "feature"... A real 1.4 lens would be brighter than an electronic pumped 1,7 . Stop dreaming.

The Minolta 50/1,7 it's a truly great lens, but it's not an f1,4 one .

[Golem]

It's an Electronic "feature"... A real 1.4 lens

would be brighter than an electronic pumped 1,7 .

Stop dreaming.

The Minolta 50/1,7 it's a truly great lens, but

it's not an f1,4 one .

An explanation of "electronic pumped"

f/stops would be quite interesting. I'm

toadally unfamiliar with such phenomena,

at least by that name or any jargon even

halfway similar to that ...

 

? ? ?

 

`

[Golem]

when you take a photo in 1.4 what does the EXIF record?

and What is the picture quality like in 1.4? you might

find it somewhat artistic.

Good point about image quality. Just cuz defocused

blobs show proof of a physically larger aperture, it

doesn't necessarily follow that the IQ at that extra

aperture would be decent if it were in focus !

 

When I get back to home base I'll wanna look into

that, and check the exif as well.

 

`

[OldNoob]

Good point about image quality. Just cuz defocused

blobs show proof of a physically larger aperture, it

doesn't necessarily follow that the IQ at that extra

aperture would be decent if it were in focus !

 

When I get back to home base I'll wanna look into

that, and check the exif as well.

 

`

My point being 1.4 on a 50mm lens has a quite narrow DOF. You might find some artistically pleasing "Bloom" effects in the images.

It's something to think about..

If i recall correctly, there were 3 AF 50mm f/1.7 versions released by Minolta ( all claiming to have the same lens configuration with slight variances in coatings and assembly features)

   Lets say , for the moment, that, hypothetically, one of the Minolta AF 50mm f1.7 versions actually had a hidden ability to open the aperture past the IRIS limit of f1.7

Then apparently Minolta felt that the image quality of that setting must have not been good enough to incorporate into the official capabilities of that lens.

In such a hypothetical situation the opening of the iris would of been limited, ether physically, mechanically or electronically, within the lens itself.

Hypothetically you could of stumbled upon one of those lenses in which that limitation may have been removed. In such a case the actual amount of light coming in would be the same at f/1.4 as it is at f1/1.7

 

But... i am almost 90% sure that is not the case here.

Note the actual Physical diameter of the aperture opening is quite different between the AF f/1.4 50mm and the AF f/1.7 50mm lens