Do I need a full-frame camera for low-light photography?

Question

I primarily shoot low-light photos, and I upgraded from a point-and-shoot to the Sony NEX-5R (which has an APS-C sensor) a few months back.

However, I find that the low-light performance of the NEX-5R is not as good as I'd like. I find myself shooting at ISO 400 or lower, with a tripod, even at f/2.8 (I do have an f/1.8 lens, too).

I was wondering if I should upgrade to a full-frame camera. I'm told that there's only a one-stop difference between a full-frame and an APS-C sensor, which doesn't seem like much. For example, this is a 13-second exposure on my NEX (at ISO 100):

With a one-stop advantage on a full-frame sensor, I'd still need a 6.5-second exposure at ISO 200, to maintain the same quality. Even if it were a .65-second exposure, I'd still need a tripod, in which case I might as well use an APS-C sensor and give it a few more seconds.

Am I correct in understanding that for me, full-frame provides a negligible advantage at a high price? Thanks.

Answer 1

Short answer: some full-frame cameras will offer a distinct advantage in noise levels if you must freeze action with high shutter speeds at high ISO settings (above, say 1600). So, unless you are shooting sports or other fast moving subjects in marginal light, there's little practical advantage with a full-frame sensor. Stressing "practical."

Longer answer: Resolution is irrelevant. 20 MPs, for example, record the same amount of detail, regardless of the sensor size. Full-frame sensors are not inherently sharper than sub-full frame sensors. 20 MPs are 20 MPs. Each records the same amount of detail and displays the same amount of sharpness.

Of course, you can squeeze more pixels onto a larger sensor. There are plenty of reasons to want or need that kind of resolution, but there are always a trade-offs. Operating speed (Even the best camera technology can't process a 40MP image as fast as it can a 20MP image). You need more computing power to efficiently process image files at that size, both at capture and in post-processing. You need more storage. While pros often have clients who want these large files, most practical uses are going to require massive downsizing. It's great to have all that information, but most of it is going to be thrown away 99% of the time because most forms of display don't require it.

It's true that full-frame sensors can record a broader dynamic and tonal range, and more color depth, if you are shooting RAW files. However, the human eye can only discern about 10 million different colors. While RAW files offer more flexibility for tweaking images in post processing to avoid posterization, images – ultimately – need to be crunched down to 8-bits for display. So saving an image in any more than 8 bits is excessive if the only intended purpose is for viewing. Also remember that file bit-depth and display bit-depth are expressed differently. An 8-bit image file is actually displayed at 24 bpp (8-bits per pixel/channel, for RGB).

So, in the end, unless you shoot action in low light, or you need the ability to finely control which colors and tones will ultimately be expressed in the final 8-bit image for display, there is little-to-no advantage to a full frame sensor over AP-C (all other things – like resolution, the camera's image processor, lenses, exposure settings, etc. – being equal).

Answer 2

Essentially, your argument is correct as long as you understand that negligible and high-price are relative terms.

You are correct that you get one or at most two stops advantage between a full-frame and an APS-C sensor of the same generation. More importantly so, the advantage is lower at low ISO sensitivities with modern cameras which are essentially noise-free until ISO 400 at least.

Shooting from a tripod and keeping ISO low is key to having nice clean results in low- light which is why I am satisfied with using an APS-C sensor camera for night photography. Shooting hand-held or in extremely low-light imagery is another story where full-frame shows a more significant advantage but for general night photography, the price of full-frame, including matching lenses is of high cost compared to the benefit.

Answer 3

Do you need a Full Frame camera for low light work? Not necessarily.

Will a Full Frame camera give you better results and make low light photography easier? Most likely. The primary question is, "How much more are you willing to spend for an incremental increase in camera performance?"

Ultimately the FF sensor is less noisy at base ISO than the APS-C sensor. To get the one-stop advantage of the FF sensor you would still have to expose for 13 seconds at ISO 100. If you only expose for 6.5 seconds with the larger sensor you are reducing the Signal to Noise Ratio to the same as shooting at ISO 200 with the larger sensor and ISO 100 with the smaller one, regardless of what the ISO is actually set at. This is because you are collecting half as much light. Since the FF sensor is roughly twice the size of the APS-C, the SNR of the larger sensor at 6.5 seconds will be roughly the same as the smaller sensor at 13 seconds. In terms of low light performance, the advantages of Full Frame over APS-C sensors are greatest at higher ISO settings necessitated by shutter speed limitations.

The advantages of a Full Frame sensor go beyond low light noise performance to things such as Dynamic Range, Tonal Range, and Color Sensitivity. Additionally, most cameras with larger sensors also have more powerful internal processing units that do better at things such as Auto White balance. At the very top end, some cameras even meter in RGB instead of monochrome as most cameras do! But the increased cost for that miniscule increase in performance is rather disproportionate unless your livelihood depends on being just that much better than the next shooter.

Especially for tripod mounted long exposure work, there are a multitude of ways to deal with noise. Shooting at a lower ISO for a longer exposure is only one of them. Shooting multiple images, whether at varying exposures (HDR, Exposure Fusion, etc.) or at the same exposure (Image Stacking, Median Blending, etc.), and then combining those images is another way to approach the problem. So is using lenses that have better light transmission that increases contrast, color accuracy, and resolution.

The image you provided as an example has the potential to be a very nice photograph. Expecting the results you desire to come straight out of camera that way, if that is indeed the case, is more than just a little unrealistic. Correcting for the 2700K sodium vapor lamps that light most of the foreground is something most cameras don't do well at all on their own. But it is something most skilled users can deal with fairly well with image processing applications such as Aperture, Lightroom/Photoshop, or even the open source application known as GIMP. The same is also the case with various Noise Reduction tools.

Answer 4

Do I need a full-frame camera for low-light photography?

No. It's not essential, but usually helps, all else being equal.
The ongoing improvement in sensors means that the latest APSC sensors are about as good in low light situations as a full-frame sensor from a few years ago.

The DxO Sports/low light ISO ratings listed below purport to allow comparison between various sensors. Some care is needed. I own a Nikon D700 and a Sony A77. As a picture acquiring system the A77 utterly trounces the D700. As a low light photo taker the Nikon, with a notional 1.5 stops better performance, in practice is utterly superior to the A77. So, te results below may be what the measurements show - but the differences may well appear larger in practice.

As a useful comparison aid, DXO's "Sports" / Low light ISO sensor figures lists sensor achievable ISO sensitivity for a given set of test conditions for a wide range of cameras.

The APSC Nikon D5300 scores 1338 ISO, whereas the full frame Sony A900 scores 1431 ISO and a Canon EOS 5D scores 1368 ISO. The 2009 Phase One P40 with a larger than full frame sensor scored 1307 ISO. The 5300 is arguably the best low light performing APSC camera ever sold - but it's superiority relative to your NEX-5R is minimal. The 5R has a DXO low-light ISO rating of 910 ISO. In stops this is log_base_2(1338/910) = 0.56 stops.

The best ever performing full frame camera is the aging 12 MP Nikon D3s with a DXO rating of 3253 ISO (!). Compared to your 5R that's log_base_2(3253/910)~= 1.8 stops.
At $US2500 on up used on ebay, that's a lot to pay for the gain, even though it would be nice to have.

A 12 MP Nikon D700 / DxO ISO 2303 / 1.3 stops, can be had for under $US1500.

Note that these results are normalised to 12 MP. Scaling factor is sqrt(Sensor_MP/12) so if eg you have a 24 MP sensor then the actual result will be sqrt (24/12) - sqrt 2 = 1.1 x worse than shown if the full 24 MP image is used. eg if the DXO sensor high ISO figure was 2800 ISO that is for the image scaled to 12 MP. The ISO value that gives the same noise result when the 24 MP image is used ~= 2800/1.4 = 2000 ISO.

Warning !!!
Do NOT look at the top right of the table or your life will be ruined :-).
Only owning a Sony A7R will restore it.

The difference between your NEX and the A7R is about 3:1 or about 1.5 stops.
The difference is useful, but the large $ difference would make such a radical change very hard to justify.

Answer 5

If the issue is long exposure and high ISO for night sky landscapes, like Milky Way, and time lapse. The DX cameras are fully capable for high res images. It all depends on the techniques and lenses used. Nikon's modern DX cameras have incredible dynamic range, which captures a lot of shadow detail when underexposing. And with techniques like multi shot panorama, the resoulution becomes huge, thus reducing any problems with noise. If you ever shot a multi shot 2 row panorama 150+mb, 10000x6000pix, you can zoom in 300%+ and still have super sharp images from corner to corner. And with some auto stitch programs, they do the focus stack and do some kind of overlapping that reduces noise. Bring that image back into light room, and do another run of NR, and you have a superior quaity image for any print or billboard. But this is really not needed, as a lot of print shops have software that upscale any photo to create huge high quality prints. Anyway, That's my take on the DX for long exposure, High ISO.

Answer 6

There are two other advantages that full frame will give you besides better low light performance. A full frame image is 50 to 60% wider depending on the crop factor on your camera platform. On Nikon, it is 50% wider. This is crucial for landscape photography and makes it a far more compelling case for me. The other important factor is that full frame creates a more shallow depth of field so you're able to blur the background more thus creating a more interesting portrait. Your subject is much more eye popping and the background bokeh is more interesting on full frame.

So if I had consider only low light advantages, it would not have been worth it for me who is just an photographic enthusiast. But with all three combine, it was well worth it. For me personally I would say the 50% wider angle is the one single most important advantage. So far, I've only shot a handful of nightscape handheld with my Nikon D750 and a 35mm f1.8 and the quality looks good but not great. I plan on hauling my tripod on my next trip for night cityscape and I expect much better results.

And as for cost, I am able to use my Nikon 35mm and 50mm f1.8 on my FX camera. The only issue that I see is that on my 35mm, there is some vignetting starting at f8 or higher. And my 50mm lens works flawlessly on my FX camera at all aperture. This really helps to lower my switching cost to full frame on Nikon. I know this is not an option for Canon users but I don't know about Sony.