Aperture on kit lenses vs smartphone

Started 2 months ago | Discussions thread
Tom_N Forum Pro • Posts: 15,735
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)?

The f-stops shown on lenses actually mean an entrance pupil of the focal length divided by the f-stop number.

As sensors get bigger, they require longer focal lengths to maintain the same framing or field of view. The Galaxy S9 cameras have 1/2.55" and 1/3.6" type sensors. An APS-C sensor is more than 16x bigger, requiring focal lengths more than 4x longer.


To match the same framing and maximum f-stop, a lens on the D3100 has to be longer, has to project enough light to cover a larger sensor, and has to have a larger entrance pupil. A manufacturer looking to cut costs can reduce the entrance pupil requirement by reducing the lens' maximum aperture.

This is exactly what manufacturers of kit lenses (and many affordable zooms) do.

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.

They can. But total light collected depends on:

  • How much light is available to be collected
  • How long the shutter is open
  • How much light the aperture hole lets through to the sensor
  • How large the sensor is

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?

Price seems the most likely reason.

When I bought my DSLR, the kit zoom was effectively $100 if purchased as part of the kit. Nikon's constant f/2.8 version cost $1000 or more. Third-party constant f/2.8 ones went for maybe $400 or $500. That Nikon lens is now up to $1500: enough to buy almost four D3500 kits.

Canon's version for their DSLRs is closer to $900 (less on sale), but still not cheap enough to be a kit lens.

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