Inaccurate Aperture Markings on Meike 28/2.8

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Schleiermacher Senior Member • Posts: 2,392
Inaccurate Aperture Markings on Meike 28/2.8
1

Having read a few comments online that the aperture markings on the Meike 28/2.8 are inacurrate, I got curious and did some comparison testing today. Indeed, they are off, I believe.

I metered the exact same scene without variation in illumination with my adapted Pentax M28/3.5 and the Meike 28/2.8. Here’s what I found:

The shutter speed assigned for F/22 on the Meike is actually the shutter speed for F/16 on the Pentax. It would seem that F/16 is really the smallest aperture on the Meike.

Actual F/11 on the Meike occurs when the aperture dial is set halfway between "22" and "16" on the dial.

Actual F/8 on the Meike occurs when the aperture dial is set to about 1/16" past where the missing "11" should be.

Actual F5.6 on the Meike occurs when the aperture dial is set to "8".

Actual F4 on the Meike occurs when the aperture dial is set to halfway between "4" and "5.6"

Oddly I don’t see much meaningful change in shutter speeds when the Meike aperture is set at "2.8" on the dial and when it is set to "4". The actual widest aperture of this lens seems to be F/3.5 or thereabouts.

Of course it is possible that my Pentax M28/3.5 isn’t an accurate reference lens, but I believe it is. Each click between full aperture settings yields a doubling of shutterspeed as it should. In other words a click is a true stop on the Pentax.

Now, I’m not an optical expert and don’t understand much about lens design, but in my crude test, it appears that the Meike markings are quite inaccurate.

I’m willing to be schooled and corrected by those of you who know more than me. If I’m wrong, please help me make sense of it.

Thanks,

Matt

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Schleiermacher
www.mmathews.zenfolio.com
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'At our best and most fortunate we make pictures because of what stands in front of the camera, to honor what is greater and more interesting than we are. We never accomplish this perfectly, though in return we are given something perfect -- a sense of inclusion. Our subject thus redefines us, and is part of the biography by which we want to be known.' --Robert Adams, Why People Photograph

 Schleiermacher's gear list:Schleiermacher's gear list
Panasonic Lumix DMC-LX5 Pentax K-1 Fujifilm X-T20 Pentax smc DA 70mm F2.4 AL Limited Pentax smc FA 31mm F1.8 AL Limited +11 more
kypfer Regular Member • Posts: 495
Re: Inaccurate Aperture Markings on Meike 28/2.8
2

Is it possible the Meike has a sticky or otherwise faulty aperture? Does it open and close evenly and promptly when you operate it by hand?

What mount is fitted to the Meike? If it's not the same as the Pentax lens, and you're using a different adaptor, therein could lie your problem … one or other of the adaptors could be problematic.

You talk about an "adapted Pentax M28/3.5", so presumably you're not using a Pentax camera, so there's a third variable in the mix. You'll probably need to some further testing, maybe borrowing a Pentax camera to confirm the Pentax lens would be a good starting point.

OP Schleiermacher Senior Member • Posts: 2,392
Re: Inaccurate Aperture Markings on Meike 28/2.8

Thanks for weighing in and asking for clarification.

The Meike 28/2.8 is a native x-mount lens mounted to my x-t20. It’s aperture blades open and close smoothly and responsively as I turn the ring (not sticky).

The Pentax M28/3.5 lens was also mounted to the x-t20 using a trustworthy K&F Concepts adapter that works fine for all my adapted Pentax lenses on the x-t20.

I own a Pentax body and can compare metering result with the M28/3.5 on it against results on the x-t20 to verify consistency.

But even setting aside the comparison with the Pentax, the amount of light coming through the Meike lens at each of its printed stops on the aperture ring is not a standard 1 stop of actual difference. When you move from F/8 to F/11 on the Meike dial, for example. the shutter speed only changes from 1/60s to 1/50s. You’ve got to set it nearly F/16 on the dial to achieve shutterspeed of 1/30s.

My test results are consistent with those of another tester on the Fred Miranda forum who came away with nearly identical results to mine when he tested with a handheld meter.

The only factor that I can think of that may be in play is the vignetting of the lens. The Meike vignettes a full stop at 2.8 and gradually improves until F/8. I’m wondering if whatever is producing thr vignetting is also altering the light hitting the meter and interfering with the standard 1-stop differential you’d expect from each full stop change on the aperture dial.

Matt

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Schleiermacher
www.mmathews.zenfolio.com
----------------------------------------------
'At our best and most fortunate we make pictures because of what stands in front of the camera, to honor what is greater and more interesting than we are. We never accomplish this perfectly, though in return we are given something perfect -- a sense of inclusion. Our subject thus redefines us, and is part of the biography by which we want to be known.' --Robert Adams, Why People Photograph

 Schleiermacher's gear list:Schleiermacher's gear list
Panasonic Lumix DMC-LX5 Pentax K-1 Fujifilm X-T20 Pentax smc DA 70mm F2.4 AL Limited Pentax smc FA 31mm F1.8 AL Limited +11 more
kypfer Regular Member • Posts: 495
Re: Inaccurate Aperture Markings on Meike 28/2.8

Schleiermacher wrote:

Thanks for weighing in and asking for clarification.

The Meike 28/2.8 is a native x-mount lens mounted to my x-t20. It’s aperture blades open and close smoothly and responsively as I turn the ring (not sticky).

The Pentax M28/3.5 lens was also mounted to the x-t20 using a trustworthy K&F Concepts adapter that works fine for all my adapted Pentax lenses on the x-t20.

I own a Pentax body and can compare metering result with the M28/3.5 on it against results on the x-t20 to verify consistency.

But even setting aside the comparison with the Pentax, the amount of light coming through the Meike lens at each of its printed stops on the aperture ring is not a standard 1 stop of actual difference. When you move from F/8 to F/11 on the Meike dial, for example. the shutter speed only changes from 1/60s to 1/50s. You’ve got to set it nearly F/16 on the dial to achieve shutterspeed of 1/30s.

My test results are consistent with those of another tester on the Fred Miranda forum who came away with nearly identical results to mine when he tested with a handheld meter.

The only factor that I can think of that may be in play is the vignetting of the lens. The Meike vignettes a full stop at 2.8 and gradually improves until F/8. I’m wondering if whatever is producing thr vignetting is also altering the light hitting the meter and interfering with the standard 1-stop differential you’d expect from each full stop change on the aperture dial.

Matt

It certainly sounds like the Meike isn't working properly. Unfortunately you're posting here on a Pentax forum and as the Meike isn't available in PK mount you're only likely to get a bit of theoretical "try this try that" response. Probably best find a user group for your camera where you're more likely to find someone with first-hand experience.

At the end of the day, does it really matter if the readings on the dial are wrong, provided the pictures are correctly exposed according to the camera's meter?

Good luck

OP Schleiermacher Senior Member • Posts: 2,392
Posted to Wrong Forum - Admin Please Delete
1

Oh my goodness! I meant this for the Fujifilm forum. My mistake. I’m going to delete the thread. Thanks for your engagement!

matt

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Schleiermacher
www.mmathews.zenfolio.com
----------------------------------------------
'At our best and most fortunate we make pictures because of what stands in front of the camera, to honor what is greater and more interesting than we are. We never accomplish this perfectly, though in return we are given something perfect -- a sense of inclusion. Our subject thus redefines us, and is part of the biography by which we want to be known.' --Robert Adams, Why People Photograph

 Schleiermacher's gear list:Schleiermacher's gear list
Panasonic Lumix DMC-LX5 Pentax K-1 Fujifilm X-T20 Pentax smc DA 70mm F2.4 AL Limited Pentax smc FA 31mm F1.8 AL Limited +11 more
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