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Nx1 16-50 2-2.8 exposure change while zooming.


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23 minutes ago, kidzrevil said:

No, I strongly believe the light transmission of a zoom lenses changes the amount of light let in as you adjust focal length even on fixed aperture zooms. I've experienced this on my sigma 18-35

Isnt the f-stop = the focal length / iris diameter? Does a fully manual zoom lens adjust the iris as it changes focal length in order to keep the same f-stop?

I have searched all over the internet for this but cannot find a direct answer.

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1 minute ago, sandro said:

Still doesn't explain why on manual the shift is for 1 second only.

Ok this is my theory and it is jut a theory at this point because I cannot find any information on the internet to confirm OR disprove it.

 

Because f-stop = focal length / diameter of the entrance pupil as you zoom the lens the lens needs to change the iris to keep the same f-stop.

Quote from the Wikipedia page on f-number https://en.wikipedia.org/wiki/F-number

Quote

A 100 mm focal length f/4 lens has an entrance pupil diameter of 25 mm. A 200 mm focal length f/4 lens has an entrance pupil diameter of 50 mm.

So assuming you have a 100-200 f4 zoom lens (fully electronic) and you were at 100mm and f/4 then you quickly zoomed to 200mm. the lens would need to detect the new focal length then calculate the diameter of the entrance pupil then adjust accordingly. The few milisec delay is just the camera calculating the then adjusting according.

 

Can someone please confirm or disprove this theory because I am starting to get frustrated with the lack of information on the internet about this. :confounded:

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33 minutes ago, MountneerMan said:

Ok this is my theory and it is jut a theory at this point because I cannot find any information on the internet to confirm OR disprove it.

 

Because f-stop = focal length / diameter of the entrance pupil as you zoom the lens the lens needs to change the iris to keep the same f-stop.

Quote from the Wikipedia page on f-number https://en.wikipedia.org/wiki/F-number

So assuming you have a 100-200 f4 zoom lens (fully electronic) and you were at 100mm and f/4 then you quickly zoomed to 200mm. the lens would need to detect the new focal length then calculate the diameter of the entrance pupil then adjust accordingly. The few milisec delay is just the camera calculating the then adjusting according.

 

Can someone please confirm or disprove this theory because I am starting to get frustrated with the lack of information on the internet about this. :confounded:

That would explain it.

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2 hours ago, sandro said:

That would explain it.

Would also explain not seeing the shift with a non-samsung zoom on the camera, if the camera - even on manual - is adjusting exposure (or adjusting the iris??) due to data it's getting from the lens. Seems odd to me, but the NX1 is a very computer-heavy camera.

This subject gets weirder by the page...

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2 hours ago, M Carter said:

Would also explain not seeing the shift with a non-samsung zoom on the camera, if the camera - even on manual - is adjusting exposure (or adjusting the iris??) due to data it's getting from the lens. Seems odd to me, but the NX1 is a very computer-heavy camera.

This subject gets weirder by the page...

I never tried zooming with a non Samsung lens since I don't have one but I don't see why it would do it...

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It happens with all variable aperture electronic lenses, doesn't matter what camera. My tamron 17-50 2.8 doesn't do this, because it has a constant aperture (physically it could be called variable opening since at 50mm opening needs to be wider than at 17mm, to be at F2.8 like MountneerMan wrote). You could think - Ok, I'll just close the aperture to F2.8 (samsung 16-50 lens) and exposure shouldn't change, but it has to adjust the aperture from fully open @ 50mm, to 1 stop closed at 16mm. It cannot adjust the aperture smoothly, that's why there are jumps in exposure at those moments when it opens or closes the aperture. Try opening the lens to 2.0 and then detach the lens (just turn a bit so it doesn't have electronic contact), you should see no exposure jumps, just a smooth 1 stop transition while zooming. Then again, zooming from 16 to 50 with the lens attached correctly and aperture set to 2.0 in the wide end, there also should be no jumps in exposur. But a quick test on my 18-200 F3.5 - F6.3 showed that there are slight jumps, but far less noticeable than if I set the aperture to F6.3 at the wide end.

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3 hours ago, ReinisK said:

It happens with all variable aperture electronic lenses, doesn't matter what camera. My tamron 17-50 2.8 doesn't do this, because it has a constant aperture (physically it could be called variable opening since at 50mm opening needs to be wider than at 17mm, to be at F2.8 like MountneerMan wrote). You could think - Ok, I'll just close the aperture to F2.8 (samsung 16-50 lens) and exposure shouldn't change, but it has to adjust the aperture from fully open @ 50mm, to 1 stop closed at 16mm. It cannot adjust the aperture smoothly, that's why there are jumps in exposure at those moments when it opens or closes the aperture. Try opening the lens to 2.0 and then detach the lens (just turn a bit so it doesn't have electronic contact), you should see no exposure jumps, just a smooth 1 stop transition while zooming. Then again, zooming from 16 to 50 with the lens attached correctly and aperture set to 2.0 in the wide end, there also should be no jumps in exposur. But a quick test on my 18-200 F3.5 - F6.3 showed that there are slight jumps, but far less noticeable than if I set the aperture to F6.3 at the wide end.

Your Tamron 17-50, is it electronic or manual?

If its manual do you see the iris move when zooming? For some weird reason I cannot find any information on the internet about this. :S

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9 hours ago, ReinisK said:

No, it does not. By manual I meant manual focus and no aperture adjustment.

 

P.S. If you need aperture blades in EF-NX adapter - https://www.fotodioxpro.com/pro-lens-mount-adapter-builtin-declicked-iris-canon-lens-to-samsung-nx-camera.html

Thank you for clarifying but this just makes me more confused.

Does the iris move when you zoom a lens in order to keep the same fstop or is there something I am missing? someone on this forum has to have the answer to this.

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