Do current Nikon DSLR's boost ISO at wide apertures?

[Ian Rance]

<p>A few years ago I read an article that sensors were not able to gather all the light offered by wide aperture lenses (f/1.2, f/1.4) so boosted the ISO to look like you were getting the benefit of more light gathering...when in fact you weren't. So is this still the case or have the D750, D810, D4 sensors improved on sensors from 5 years ago with respect to this? It was the micro lenses limiting the light I recall.</p>

<p>I have some VERY low light photography planned (a midnight walk) and have a 50mm f/1.2 lens so hoping that I can make the most of the speed.</p>

<p>I don't see it mentioned here so hoping that it is a thing of the past!</p>

[Wouter Willemse]

<p>Ian, on my D700, I can notice no such thing happening. Opening up my AiS 50mm f/1.2 from f/2 to f/1.4 usually doesn't add a full stop of shutterspeed, and f/1.4 to f/1.2 again, not the 1/2 stop expected. Same with a AiS 35mm f/1.4, from f/2 to f/1.4, metering tends to indicate about 2/3rds of a stop difference.<br /> I always contributed it to the more severe vignetting, and the increasing difference between F-stops and T-stops with these high-speed lenses, but it could be something else - I never cared to dive deeper into it. Either way, I'm not seeing clear full stops difference; if they'd be manipulating the ISO in the background, I'd expect to see full stops.<br>

No experience with the newer DSLRs and these lenses, so maybe they "fixed" it later, but I doubt it, considering that these lenses do not have any electronic interface with the camera. So apart from setting the lens as a f/1.2 lens in the menu, the camera has no way of knowing the actual real aperture of the lens.</p>

[Peter_in_PA]

<p>Never heard of that. I think you might be remembering something else.<br /><br />Because what I HAVE heard of is that viewfinders (focusing screens, really) of modern DSLRs can't resolve above a certain aperture (I think at one point it was f2.8). So, if you were at f2.8 on your f1.4 lens, looked through the viewfinder while using DoF preview, you'd see no difference. However, there IS a difference when you actually take a picture, it's only the viewfinder that is limited (another reason that modern DSLR viewfinders are difficult for very wide aperture manual focusing).<br /><br />Could that be what you're remembering?</p>

[Andrew Garrard]

<p>Boosting the ISO would surprise me, not least because I'd be surprised if the camera knew enough to do this. You do get this effect if you turn on vignetting control in the camera, but the same would apply if you were doing the same thing in post. I could absolutely believe that cameras are a little less sensitive than they used to be when it comes to the telecentricity of the light leaving the rear element (Leica supposedly go to great lengths to compensate for this), and I could also believe that light drop-off from light entering from wide apertures is less bad than it once was - but I would expect film to be better still, since it doesn't have sites that are vertically divided (with the downside that light is crossing the finitely-thick film medium in a wider cone).<br />

<br />

Whether you - or the AF sensor - can see to focus in light that low is another matter. Live view may be your friend. Unless you're under street lighting, in which case I suspect you'll be fine. Good luck!</p>

[michael_bradtke]

<p>My D4 does it with my 50 f/1.2. So yes it is still a thing but it is not as much of a thing. There was a thread a while back that talked about this and that was when I tested my D4 using the 50 f/1.2 and RAW Digger to read the data. I know that the person who I was talking to about this on the thread was impressed at how little the D4 had to boost the ISO.<br>

But honestly in real world shooting I have not found it to be a problem.</p>

[5711]

<p>i can remember beeing really annoyed by the difference in exposure between the d3 and d3x due to something like this.<br /> but this was during the day.</p>

<p>never had any issues with that at night.</p>

[rodeo_joe1]

<p>Ian, I think the article you read was talking rubbish. Was it sponsored by Leica by any chance?<br /> A wider aperture lens will always let in more light than one with a smaller aperture, and so more light <em>has</em> to hit the sensor - at least in the middle. There is an issue with the microlenses used on digital sensors having a narrow acceptance angle and so causing vignetting at the edges and corners of the image, but aperture vignetting in the lens itself is usually far more significant. Besides, by careful design of microlens geometry the loss of light can be minimised - by slightly offsetting the lenses from the sensor sites for example.</p>

<p>Most modern DSLRs, and certainly all of Nikon's DSLRs (AFAIK) have the option to automatically correct for vignetting, but only in JPEG file format. This is done as part of the image processing, in the same way as noise reduction and the like. RAW files aren't affected, as they would be if the ISO speed was being manipulated. You can also disprove the article's nonsense by fitting a non-CPU lens of wide aperture - like your f/1.2 50mm Nikkor for instance - and "lying" to the camera about what lens is fitted. If the microlenses really did limit light gathering, then opening the lens up and increasing the shutter speed would result in underexposure; since the camera knows nothing of what aperture the lens is actually using. That doesn't happen, and therefore there can be no raising of sensor sensitivity to compensate. QED.</p>

<p>A related but separate issue with Nikon DSLRs and film SLRs is that the viewfinder system doesn't show an increase in brightness or shallowing of depth-of-field with any lens brighter than f/2. In other words, lenses of f/1.4 and f/1.2 will look just as dim(!) as a lens of f/2, and the DoF as seen on the screen will look the same as an f/2 lens. You can see this for yourself by using the camera's preview button with any lens wider than f/2. Pressing the button will show no perceptible difference in screen brightness until the lens is stopped down beyond f/2. The issue appears to be with a combination of exit pupil vignetting by the mirror, and the acceptance angle of the Fresnel condenser system in the screen. Really, though, it's not a problem as long as you realise that buying a wide-aperture lens isn't going to make viewing any brighter or manual focusing any easier.</p>

<p>Good luck with the low-light project!</p>

<p>Edit: This may not be particularly relevant, but it's an interesting observation. Aperture vignetting in a lens causes the edges of the image circle to be dimmer than the centre - that much is obvious. However the "brightening" of the edges as the lens is stopped down is a false perception. What's actually happening is that the centre brightness is being dimmed down while the outer part of the image stays at much the same brightness. This continues until the whole of the image circle is fairly evenly illuminated. Only then do the edges keep pace with the central brightness.</p>

[rodeo_joe1]

<p>One more thought on the subject, but too late to edit into the above post.<br>

If there was vignetting of a lens's exit pupil by microlens restriction, then we would see no difference in depth-of-field above a certain aperture. That doesn't happen and we can clearly see a difference in DoF in the captured image as we stop a lens down from f/1.2 or f/1.4 to a smaller aperture. QED again!</p>

[songtsen]

Ian, perhaps it was <a href="https://luminous-

landscape.com/an-open-

letter-to-the-major-

camera-manufacturers/">this article</a> on Luminous Landscape a few years ago.

[jose_angel]

<p>Very interesting. The very same info on dxomark site: <a href="http://www.dxomark.com/Reviews/F-stop-blues">link</a>.<br /> If the ISO is pushed as much as 1/3 or 1/2, I don`t see a big problem here. With current sensors, noise should not be an issue at all.</p>

[kari_oinonen]

<p>My F-100 had only 2x 1/3 stops from f/1.4 to f/2, with the af-s 50mm f/1.4 lens. This was measured with the camera meter, the camera in A mode and the aperture was changed. No fault with the lens function - all apertures available.<br>

My D-700 has 3x 1/3 stops from f/1.4 to f/2, with the same lens.<br>

At least something is different even the lens is the same.</p>

<p>In practise, this OP's question is nothing to worry about. Maybe we are not allways just getting f/1.4 lens even we have paid for one. I remember that there may be several factors behind this behaviour.</p>

[jose_angel]

<p>Kari, according to dxomark, *our* D700 loose 0.35EV @ f1.4. I suppose it will depend on the lens, too.<br /> So if the meter reads correctly, it means the camera is actually boosting the ISO... this is what I understand (I may be missing something).<br /> The article mentions that it start to happen from not that wide apertures. I assume the loose is minimal there.</p>

[rodeo_joe1]

<p> A one third stop discrepancy is absolutely nothing compared to the vignetting of the average f/1.4 lens - anywhere from 1.5 to 2 stops from centre to corner of the full-frame image. It's also comparable to the difference between marked aperture and T-stop transmission of such lenses.</p>

<p>I just ran the test I suggested on my D800 and D7200 - i.e. set the exposure to manual and then "fool" the camera by using a non-CPU lens and tell the camera it has a different maximum aperture.<br>

I could detect no difference in exposure between telling the camera the true aperture of f/1.2, and telling it that the lens was f/2 or f/2.8. The exposure tracked perfectly over a series of stops as well, no matter what aperture the camera was told. So there's no apparent raising of ISO by the camera's software to compensate for wide aperture lenses. However the flaky Matrix metering gave about a stop different reading between the lens's true aperture and the fake one. Using the meter readings the faked aperture shots were overexposed by some degree. The conclusion I draw from this is that Nikon's matrix metering is too "smart" for its own good, and should stick to actually measuring the light that's coming into the camera, rather than second-guessing it.</p>

[pete_s.]

<p>http://www.photo.net/nikon-camera-forum/00cBUG</p>

 

[michael_bradtke]

<p>Pete S.<br>

That's the thread I was thinking about.</p>

[5711]

<p>i reported this issue to nikon.<br>

i had a forum post here aswell.</p>

<p>i cannot find the reply of the technician as he wrote me perosnally not from the nikon adress.</p>

<p>every camera does have a different exposure system</p>

<p>check the exif files.<br>

you will see the iso is something like..lets say 105 instead of 100 and so on.<br>

the nikon guys told me that is perfectly normal.</p>

<p>however it is annyoing if you are photographing with..as i did..a d3 alongside a d3 and get two different exposures.<br>

this also effects high iso.<br>

doesnt do anything, really.<br>

it, well, as far as ive been told, is working as intented.</p>

[Matthew Currie]

<p>I have no fast lenses that meter with my camera anyway, but for future reference, do I take it that any ISO boost is reflected in the EXIF file? In other words, the true ISO is shown?</p>

[pete_s.]

 

<blockquote>

<p>I have no fast lenses that meter with my camera anyway, but for future reference, do I take it that any ISO boost is reflected in the EXIF file? In other words, the true ISO is shown?</p>

</blockquote>

<p>Nope. It happens behind the scenes before the raw file is written to the card. Regular users wouldn't have a clue about it.</p>

<p>It's just that when the camera knows what lens it is it will use a higher iso than what it tells you to compensate for the light loss at large apertures. Precooked rawfiles is what it's called. There are also cameras that have been known to do noise reduction on the raw files as well to make the raws look better.</p>

<p> </p>

 

[pete_s.]

<p>Just to clarify further, it has <strong>nothing</strong> to do with metering.</p>

<p>You can set the ISO, the aperture and the shutter speed manually and the camera still uses another higher ISO setting to compensate for the light loss.</p>

<p>While the FX cameras increase iso about 1/3rd of a stop at f1.4, my guess is that cameras like the D7200 are around 2/3rd of a stop.</p>

<p>The in summary it means that if you are buying larger aperture lenses to get more light into the camera so you can shoot at a lower iso or using faster shutter speeds while maintaining the ISO, you are not getting the full benefit of your investment.</p>

<p>For instance going from f2.8 lens to f1.4, you expect a 2 stop increase, at least in the center. But if you have a high megapixel DX you are probably only getting 1 1/3rd of stop more light and 2/3rd of a stop ISO increase. So you might as well just buy the f1.8 lens and you'll probably get 1 stop more light into the lens and you can do one stop of ISO increase yourself.</p>

[Matthew Currie]

<p>So if there is nothing shown in the EXIF, how are people figuring it out? Just extrapolating?</p>

[Matthew Currie]

<p>I just answered my own question, I think. It appears that the change is not shown in exif or anywhere else, and is deduced from very detailed study.</p>