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


JS
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Kidzrevil mentioned seeing similar things with his Sigma zoom, which presumably would not be operated electronically.

I think it is just a function of the rapid change in the field of view (with consequent exposure change) and the time it takes for metering to adjust to gain to a different level to compensate.

IMO you will see it with any camera if gain correction is not instantaneous.

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3 minutes ago, tugela said:

Kidzrevil mentioned seeing similar things with his Sigma zoom, which presumably would not be operated electronically.

I think it is just a function of the rapid change in the field of view (with consequent exposure change) and the time it takes for metering to adjust to gain to a different level to compensate.

IMO you will see it with any camera if gain correction is not instantaneous.

how can it be if it happens even when everything is all manual? If doesn't have to adjust to anything. 

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48 minutes ago, sandro said:

I believe it's a design of these electronically controlled lenses. It's disappointing it happens with a S lens...

Electronic aperture is not the cause, optical design is. Try EF lenses with constant aperture.

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So I have wondered about this quite a bit myself and have not found anything on the internet about it.

So aperture is calculated as the focal length / diameter of the iris correct? so wouldn't that mean the lens needs to open the iris when you zoom a lens in order to keep the same f-number?

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It's inherent to the design of the lens. Like you said, use it as a series of primes, not for crash zooms. The only exception is at wide open, where this does not occur and the exposure change is smooth. 50-150 thankfully does not have this issue.

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39 minutes ago, JS said:

I like the theory that nx1 does this thing with variable aperture lenses(50-150 is fine) but why is this happening with sigma 18-35 also? 

I really think its the design of zoom lenses period. Maybe there is a delay in light passing through the lens when you change the focal length ? Idk but I am seeing it with my 18-35. Doesn't matter to me because I lock down my exposure before I hit record after I seen the same issue with my sigma

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7 hours ago, MountneerMan said:

So I have wondered about this quite a bit myself and have not found anything on the internet about it.

So aperture is calculated as the focal length / diameter of the iris correct? so wouldn't that mean the lens needs to open the iris when you zoom a lens in order to keep the same f-number?

That's correct. Years ago I had the EF 17-40L lens, the aperture was coupled with a mechanical slider, and I can see the aperture change by itself when I zoom, even without power, and there was no change of exposure of the camera while zooming. Nowadays the constant aperture could be fully controlled by electronic, I'm not sure about this though.

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7 hours ago, gsenroc said:

That's correct. Years ago I had the EF 17-40L lens, the aperture was coupled with a mechanical slider, and I can see the aperture change by itself when I zoom, even without power, and there was no change of exposure of the camera while zooming. Nowadays the constant aperture could be fully controlled by electronic, I'm not sure about this though.

Well then there is your answer. The camera just take a few seconds after you zoom to figure out what focal lenght it was zoomed to then calculate and adjust the irus accordingly.

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On ‎5‎/‎13‎/‎2016 at 2:03 PM, sandro said:

how can it be if it happens even when everything is all manual? If doesn't have to adjust to anything. 

If everything is on manual, including gain, then zooming out will increase the amount of light on the sensor and increase overall exposure. Converse for zooming in. The video clip apparently has gain on auto, but the response to changes in exposure is not instantaneous, which is why the exposure changes like that. If he zoomed more slowly then you would not notice it.

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"zooming out will increase the amount of light on the sensor" - I think that's only a function of the setting and what's in the frame. Have you tested against a white wall that's evenly lit?

I'd assume zooming out - or dollying out quickly, while shooting, say a small window in a dark room - that as the frame fills more and more with the dark wall and the bright window gets smaller, you'll perceive an exposure shift since the frame is getting larger and displaying a higher ratio of dark-to-light. It would be easy to test a zoom vs. a move - for instance stick a gray card on a large black card - and eye dropper the center at various focal lengths and distances. The center **should** stay the same RGB value.

I've seen this happen on variable-aperture zooms, just the nature of the beast; and though I haven't tested specifically for it, I haven't noticed it using a constant aperture Nikkor zoom on the NX1. (and that Samsung S is a variable aperture zoom..., just not at the cheap level).

I had expected that when using a variable lens - say a 3.5 - 5.6 18-35 Nikkor - that if I stopped down to 5.6, the lens would stay 5.6 for the entire zoom range. But that wasn't the case with a variable aperture Nikkor for me - I saw very visible exposure changes. Not seeing them with, say, the 28-70 2.8, but again, haven't really tested it.

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It's probably because there's a difference between f-stop and t-stop. Just like a f/1.4 lens might actually be t/2 because of emission loss of light, just that with a zoom it will be depending on focal length setting. I think the Canon EF 24-105 f/4 L IS is the same, when you zoom in the image gets darker even though the f-stop is consistent. So kidzrevil is right, it's one of the reasons why photography lenses are cheaper than cinema lenses (plus stuff like focus breathing, etc.)

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18 hours ago, tugela said:

If everything is on manual, including gain, then zooming out will increase the amount of light on the sensor and increase overall exposure. Converse for zooming in. The video clip apparently has gain on auto, but the response to changes in exposure is not instantaneous, which is why the exposure changes like that. If he zoomed more slowly then you would not notice it.

But shouldn't that increase stay the same? Instead with the Samsung lens I used it goes back to "normal" after a moment. 

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6 hours ago, Phil A said:

It's probably because there's a difference between f-stop and t-stop. Just like a f/1.4 lens might actually be t/2 because of emission loss of light, just that with a zoom it will be depending on focal length setting. I think the Canon EF 24-105 f/4 L IS is the same, when you zoom in the image gets darker even though the f-stop is consistent. So kidzrevil is right, it's one of the reasons why photography lenses are cheaper than cinema lenses (plus stuff like focus breathing, etc.)

Exactly. This is the answer to all your questions @sandro, you are welcome :-)

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5 minutes ago, kidzrevil said:

Exactly. This is the answer to all your questions @sandro, you are welcome :-)

I am confused... So it is because when you zoom in/out the camera needs to readjust the iris to keep the same f-stop witch might be a different t-stop as well?

eg f/2.0 at 16mm might = t/2.8 and f/2.0 at 50mm = t/3.0

 

Unrelated side note. Does anyone have an NX1 w/ 16-50 S and a T rated lens do determine the exact T rating of the 16-50 S?

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36 minutes ago, MountneerMan said:

I am confused... So it is because when you zoom in/out the camera needs to readjust the iris to keep the same f-stop witch might be a different t-stop as well?

eg f/2.0 at 16mm might = t/2.8 and f/2.0 at 50mm = t/3.0

 

Unrelated side note. Does anyone have an NX1 w/ 16-50 S and a T rated lens do determine the exact T rating of the 16-50 S?

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

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