Obviously it was a thing for film cameras, but now that everything is digital, something like “just make the picture darker” seems extremely easy to do with software
quick edit, I know what ND filters are for and how to use them, no need to explain. it just seems to me that it could be engineered in a way that doesn’t require them, which is what I’m asking about
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Wanted to add something here that I’m not sure was mentioned yet:
(I’ll come at this from a video perspective and not photography, but the principles are the same). So ISO on a camera does adjust the sensor’s sensitivity light, absolutely, but lowering that ISO is not always optimal. Cameras generally have a “native” ISO setting that produces the best results, and changing from that setting, either higher or lower, produces less than optimal results.
Say your camera’s native ISO is 800. Ideally, you would capture every shot at this setting. So on a very bright day, you certainly could lower the ISO, but to achieve better results it’s preferable to use ND’s to cut the light. Since generally you’ve also set the aperture to the exact setting you want, say f2.8, and shutter generally has to stay at the same setting (say 1/48), so the only variable you can play with is ND.
No you may ask WHY does lowering the ISO not produce the best results? That’s a more complicated question that I personally can’t answer very well, but I can add a few things. A digital camera sensor collects light into its pixels, which is translated into electric signal. There is a certain electric voltage passed through the sensor, and the exact voltage thay produces the least amount of digital “noise” is generally considered to be that sensor’s “native” ISO – think of it like an audio signal that is at 0 decibels if gain. Decreasing or increasing ISO is just changing the “gain” of the signal, like going to -6db or +6db. It is not making for a better quality signal, it’s just boosted.
ND filters allow you adjust the exposure triangle differently, IE longer exposer, lower aperture, etc.
There are two reasons for needing an ND filter with a digital camera. One good techinal limitation, and one that could indeed just largely be fixed in the digital realm.
First, the technical reason: Sometimes there just is way too much light (and our digital sensor doesn’t support a fast -enough minimum “shutter speed” to get the image we want). This, however, is increasingly rare with better electronic “shutters” that can support shutter speeds below 1/10,000 seconds. This used to be a major problem in the film era with cheaper cameras.
Second, a legacy reason. As the very bright scenes, or the desire for very long daytime exposures for artistic effect, are relatively rare, the camera manufacturers have not added the ultra-low ISO modes. (Where the camera would take multiple consecutive frames and instantly average them in post (average rather than sum).)
There is, however, a small technical component to this: Such stacking would need more battery power and could also cause problems with the camera overheating for very long exposures. As, now, the camera is reading the sensor hundreds of times. So, for best results in very bright light, a mild ND filter might still be optimal (when combined with the software approach to make it a heavy ND filter) as it will make each individual frame more reasonable in its duration for very bright schenes (reducing the risk for image artefacts arising from the time not actively exposing).
The complete lack of the second feature in most cameras is a shame, as the image quality of such software or hybrid ND filter would (in most situations,) be superior to a physical ND filter (which will not be perfectly neutral, but will always leave a small tint).
As a sidenote, the second approach is obviously possible manually. Just take a pile of images and average them in postprosessing. But, the manual process makes the time gaps between frames undesirably long (leading into bigger risk of motion artefacts), and obviously results in way too much a data being stored temporarily on the memory card.
It’s worth mentioning that modern video cameras such as the Sony FX6 use electronic ND filters which are (virtually) infinitely variable. Think of like an adjustable LCD filter blocking the light – rather than some tinted glass you move into the light path. So in a way they’ve already come up with a better alternative.
One thing I haven’t seen mentioned is that it is generally good to put some kind of filter on all your lenses to give you one extra layer of protection of the glass on the actual lens
You can make a photo darker in software, but software can’t change the exposure time. If you want to do something like capture the movement of water in a waterfall in broad daylight you need a relatively slow shutter speed to capture the motion of water. This would be something like 1/15s or so. You might not be able to achieve correct exposure at that shutter speed in daylight even at the narrowest aperture and lowest sensor sensitivity, so you need an external way of reducing light at the time of capture.
New sensor technology is on the horizon which will dramatically change this. Not only can photosites (think pixels) be configured have dynamic sensitivity within a single frame, they will be able to have different exposure times too!
Edit: Seems OP knows about cameras so I’ll keep my reply up because it’s in the spirit of the sub.
I’ll give a super simple answer for you.
Cameras like light. Lots of light. The more light, the better. Now if you remember the game portal with the aperture science logo, cameras have that. Even your phone does.
Now what most people don’t notice is cameras these days auto adjust the aperture based on the amount of light the camera is seeing. Bright sunny day? Tiny aperture otherwise the image will be blown out and way too bright.
Now the issue with a tiny aperture opening is that you lose some great effects, most notably depth of field blur known as bokeh.
So how do we get that awesome background blur in bright light? Well, we can’t. What’s the solution then?
Sunglasses! ND filters are literally just sunglasses for your camera that brings down the overall amount of light coming in while allowing your aperture to be completely wide open.
Cameras have a maximum brightness they can see, which you usually don’t want to hit because it makes parts of your image pure white with no details.
You can reduce the light by making the shutter speed faster or the aperture smaller, but this changes how the image looks because it affects how much background blur and motion blur there is.
If you want a certain look, like a nice blurred background and realistic motion blur (especially when shooting video) then you need to use settings on the camera than will naturally let a lot of light in, so during the day it might be too bright and you’d need another way to reduce light like an ND.
‘It could be engineered in a way’ sure, but at what cost? At some point, that *is* the engineering solution.
If I’m shooting at wide to get rid of the background in the middle of the day with strobes, and aready at the base ISO, there are three solutions:
* Faster shutter – I’m already at 1/8000.
* Hire camera assistants to carry [one of these](https://i.pinimg.com/originals/d0/8d/af/d08daf86291fb7526960c0e16cce96dd.jpg) around.
* A neutral density fiter.
Sensors at their core are not digital, they are analog devices. Their analog signal is turned into a digital one by a converter. This means that before the conversion, their signal is subject to physical constraints, and not just pure maths. If they get too much light, they will simply not provide any useful signal, and no amount of software “darkening” will help. The converter will just see the same exact maximum value for every pixel.
There are two things in the sensor that control how much light it is exposed to: ISO and exposure time. That’s it. If you have too much light, your sensor will read “pure white” and there is nothing in software that can bring back your image. That’s why we use the aperture to control light, but that has the side effect of changing the depth of field. Hence ND filters are a great way to control light without affecting depth of field.
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