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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):

13-second exposure

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.

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You'd also get a notable sharper image with FF, and that might be worth the cost for night and day landscape photography. –  Michael Nielsen Nov 27 '13 at 10:25
    
Thanks, Michael. Do you mind posting a comparison of the same scene on ASP-C vs FF, with similar lenses and exposure? That is, not a f/1.4 vs an f/8 :) paragraph break Isn't this an incremental improvement at a totally un-incremental price difference? –  Kartick Vaddadi Nov 27 '13 at 11:51
    
1  
Thanks, from the petapixel comparison, it seems that the difference in quality is indeed incremental while the price increase is disproportionate. There's another useful tip for me from that article: it's better to use a great lens on an APS-C sensor rather than an average lens on a full-frame sensor. –  Kartick Vaddadi Nov 28 '13 at 1:47
    
Buy a good used D700 :-). (They can see things in the dark that my eyes cannot at useful shutter speeds. ) –  Russell McMahon Nov 28 '13 at 8:27

3 Answers 3

up vote 10 down vote accepted

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.

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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.

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Thanks, Michael. Let me rephrase my comment -- you seem to be saying that a 13-second exposure at ISO 100 with an APS-C sensor is roughly equivalent to a 6.5-second at ISO 200 with a full-frame sensor. Taking a step back and forgetting about ISO, the point seems to be that a full-frame requires half the exposure time to produce roughly the same output (leaving aside other stuff like depth of field, and assuming you are using the same aperture on both). That seems to be a minor advantage -- I still need a tripod, and if I'm using one, I might as well expose for a few more seconds. –  Kartick Vaddadi Nov 26 '13 at 9:11
    
In other words, shaving off a few seconds of exposure is in my book worth $200, not $2000. I guess full-frame is not for me. Thanks for helping me see that. –  Kartick Vaddadi Nov 26 '13 at 9:12
    
Last comment from me for now: To answer your question, that photo was shot in RAW and exported to JPEG in Lightroom. I didn't do any editing but toning down the highlights a bit (the street lights were too bright because of the long exposure). –  Kartick Vaddadi Nov 26 '13 at 9:26
    
When shooting RAW the difference between ISO 100 and ISO 200 is negligible. The amount of noise in an image is only indirectly related to the ISO selected. What determines the SNR is the amount of light collected in the exposure compared to the fairly constant amount of noise generated with each shot. All other things being equal, a sensor twice as large collects twice as much light over the same exposure time, or collects the same amount of light over half the exposure time when compared to a sensor that is half as large. –  Michael Clark Nov 26 '13 at 11:14
    
The point was that a full frame camera may marginally improve the color accuracy straight out of camera due to better in camera processing ability. But to get the kind of results you seem to be looking for, you are going to have to significantly post-process the results of either camera when shooting a scene such as that. And if you did no editing other than toning down the highlights, the in-camera results quite possibly would be better than the results using LR, depending on what type of profile LR is set to use to open images by default. –  Michael Clark Nov 26 '13 at 11:18

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.

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Sorry, both your first and last sentences were vague. Were you saying that a full-frame camera provides a marginally better performance (1.5 stops) at a high price and is therefore unjustifiable for me? –  Kartick Vaddadi Nov 28 '13 at 9:24
    
@KartickVaddadi Answer expanded. The initial "No" fully addressed the question in your subject line :-). –  Russell McMahon Nov 28 '13 at 13:32

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