Aperture on kit lenses vs smartphone

Started 2 months ago | Discussions thread
FingerPainter Senior Member • Posts: 7,810
Re: Aperture on kit lenses vs smartphone

Sam_85 wrote:

I was wondering if anyone can explain why kit lenses typically have aperture ranges of 3.5-5.6 (so not brilliant in low light) whereas my phone (samsung s9) has an aperture of 1.5 giving me much brighter, clearer and less blurry photos in low light (indoors)? I thought that with sir cameras having much bigger sensors that they would be able to let more light in and therefore produce better photos in low light but since the phone has a much better aperture for low light it's giving me much more reliable, clearer photos. My current slr (nikon d3100) in auto mode often won't even focus in low light, and I have to ramp up the iso in manual mode for it to even let me take the photo and then its blurry and un-usable! This seems crazy?! I'm looking to replace my nikon with a canon m50 soon but am concerned that as the kit lens has the same aperture range I will get the same results! Does anyone know why kit lenses don't come with bigger apertures? Seems crazy that I will have to swap to using my phone as soon as I'm in dim lighting?! Im not that clued up so sorry if this is a stupid question! I feel like I will need a bigger aperture more than I will need a smaller one so seems odd that kit lenses go for the smaller side?

Start by realizing that the aperture of your camera's lens is not 1.5, but rather f/1.5. The use of 'f' there is significant. 'f' means the actual focal length of the lens.

Your phone's camera has an actual focal length of 4.3mm. That means it has an actual aperture diameter of 4.3mm/1.5 or 2.88mm. To get the same angle of view on your D3100, you'd use your kit lens set to about 18mm, at which the maximum aperture is f/3.5, giving an actual aperture diameter of 18mm / 3.5 = 5.1mm.

The light gathered is proportional to the square of the radius, so your D3100 captures

(5.1/2)squared / (2.87/2)squared = 3.19 times as much light, about 1.6 stops.

Another way to look at it is that your phone camera has a crop factor of about 6 and your d3100 has a crop factor of about 1.5. So f/1.5 on the phone is equivalent to f/9 on a FF camera, while f/3.5 on your D3100 is equivalent to f/5.3 on a FF camera. Again about 1.6 stops apart, in favour of your Nikon.

From a pure light-gathering point of view, your Nikon gathers more light.

So why do you say your phone's pictures are better?

I suspect that there are at least two factors at play. If you are like most people who think f1.5 on their phone is bigger then f/3.5 on the dSLR, you evaluated the noisiness of each camera's images by blowing them up to 100%. The phone camera is a 12MP camera, while the dSLR is a 14MP camera, By examining both images at 100% , you are looking at only 6/7 as much of the D3100's image, A smaller portion of an image will look noisier than a larger portion, because it is made with less light.

Probably the main factor is that your phone is about 1 year old, while your dSLR is about 1 decade old. Sensor technology and computing power have come a long way since the D3100 came out. Your phone's processor will be much better at hiding noise in its images, while its's sensor will be more efficient at capturing light that falls on it and will add less noise to the noise already present in the captured light. Current sensors are more than a stop better than the D3100's sensor is. That nearly cancels out the D3100's sensor's size advantage.

If you were to compare the output of a current dSLR like the D7500 with your phone, using a properly de-noised RAW image, I doubt you'd find the phone's image better. And of course, if you used a lens like the Sigma 18-35 f/1.8 instead of the kit lens. the dSLR would clearly be ahead.

Also compare the image you get on your D3100 at 55mm with a phone's image cropped to the same field of view. You'll probably find the dSLR image better.

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