Sigma v Pentax lens exposure meter difference

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left eye
left eye Senior Member • Posts: 2,523
Sigma v Pentax lens exposure meter difference

When I got the Sigma lens I instantly noticed it was over exposing by about 0.7 to 1.0 stop, compared to my Pentax lenses.

Of all the cameras I own (and have owned) I've never mixed brands of lenses, so I'm not sure if this is a known phenomena, but it is perplexing me.

With my Pentax lenses (on a KP) I'm regularly needing about +0.7 EV comp on the camera to achieve what I think is a normal exposure (it does depend on the subject, but that's the norm).

With the Sigma, I was getting over-exposed shots, so I dialled the EV comp on the camera back to 0.0, that did the trick, it exposures normally to my eye.

Looking at the exposure times between the two brands of lens, with the above change in EV comp between them, the exposures were identical. In other words to achieve the same exposure between brands I need to adjust the EV comp by 0.7 to 1 stop.

What is going on??

Why do I have to dial in an EV comp differently for the two lens brands to achieve the same exposure. Doesn't make sense.

If the meter is reading through the lens why doesn't it provide the same exposure value, why do I have to compensate to get the same exposure value?

The only explanation is either Sigma or Pentax are not being honest about the max f-stop of their lenses (through which the meter reads then calculates thereon).

You might not think 0.7 stop is a lot (actually I think it's between 0.7 and 1.0), but 1 stop is double the light - and that looks really over-exposed!

As an example...

Pentax lens, needing in-camera +0.7 EV-comp (without this the results are nearly stop too dark)...

f5.6, 1/25th sec (same exposure as Sigma, but Sigma having 0 EV comp)...

Sigma 0 EV comp,

f5.6, 1/25th sec (so the same exposure as Pentax, but Pentax needing +0.7 EV comp)...

/

Of course the it's same story if we stop down...

Pentax lens with +0.7 EV-comp

f8, 1/13th sec (same exposure as Sigma, but Sigma having 0 EV comp)...

Sigma 0 EV comp,

f8, 1/13th sec (so the same exposure as Pentax, but Pentax needing +0.7 EV comp)...

 left eye's gear list:left eye's gear list
Fujifilm X100V Olympus E-300 Fujifilm GFX 50S Panasonic GH5 Pentax KP +11 more
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