Camera Labs

Hello...

I've been hunting around trying to get my head around this...

I've been reading about low light photography and many extol the virtues of using a quality lens with small F numbers for better light sensitivity.

Sounds good but as a small F number reduces the depth of field meaning less of the picture is in focus, does this mean you simply can't afford to have everything in focus in low light photography. I know there's other variables, like using high ISO long shutter speeds etc - but the advice to look at a lens with a small F number has thrown me.

Can anybody help...

Chris

There is a tradeoff in the selection of aperture value. In short, does everything need to be in focus? Generally this is not necessary, and only the main subject or point of interest needs to be in focus. In that case, a big aperture lens may make the difference in hand holdable shots. Conversely, if you really do need more in focus than that provides, you have no choice but to compensate elsewhere, for example by using a tripod for a long exposure.

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Well first what do you want to photograph in low light, would that be low light portrait or night landscape, what kind of lens you want to use and how low light it is. About depth of field there are also some other important things than just F number.

Depth of field = focal length + F number + lens to subject distance + subject to background distance, and if u wanna go all the way then sensor size of your camera too.
Plus there is hyperfocal distance that you can calculate for any lens and F number you gonna use so you get more things in focus, and if all of this is not good for you and you have a static subject than you can do focus stacking which would give you everything in focus regardless on any above settings.

Maybe tell us what do you want to photograph in low light so we can give you better explanation

Crop sensor + F2.8 wide angle lens = Fair ammount of DOF and reasonably large aperture.


The wider the lens the more DOF.

The bigger the sensor the more DOF.

And to add on to Agun: The closer you focus, the less DOF.

Also, for low light you want a LARGE aperture lens, which is a SMALL number. F/1.8 is a large aperture, for instance

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Hello Chris, and welcome to the friendly Camera Labs forum!
To enjoy your stay here please have a look at the house-rules!
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As to your Q: There are other ways to do low-light photography! Most people use a tripod to get the absolute best image quality, others crank up their ISO, and some use a large-aperture lens. So you have to pick what you need and live with the consequences.
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Thomas (beware: Nikon-fanboy and moderator!) My Pictures, My Photography Blog
D300+assorted lenses

@agun: "The wider the lens the more DOF." is not necessarily true.
If you keep the same magnification, the dof stays the same regardless of the focal length.
But if you just stand there without moving closer to your subject, a wider lens produces less magnification and thus more dof.

So keep in mind: magnification is the key variable in influencing dof - apart from aperture and sensor-size.
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Thomas (beware: Nikon-fanboy and moderator!) My Pictures, My Photography Blog
D300+assorted lenses

I didn't know it was the magnification that did it. I'll look into it later.

Another way to achieve a large DOF with a small aperture is to do focus stacking: http://en.wikipedia.org/wiki/Focus_stacking

It's like HDR but with focus instead of exposure.

Thanks for all the great answers...

I was just thinking generally, I had been shooting at an outdoor concert and either cranking up the ISO or using flash in the pit. (I like the harsh contrast of the flash generally in certain situations).

Simply when I was reading around and people were talking about small F numbers - it threw me a bit...Can you get away with a small DOF in concert photography - well probably - yes - sometimes.

I'd imagine for concert photography a lens with a small F number is not going to do it alone anyway...

Hope you follow...

I thought a larger sensor gave less DoF...?

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Yes! Using an FX sensor vs. a DX/APS-C sensor is like using a lens of one stop larger aperture!
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Thomas (beware: Nikon-fanboy and moderator!) My Pictures, My Photography Blog
D300+assorted lenses

I thought so, but Agun stated exactly the opposite. Compact cameras with their mini sensors give way more depth of field than an APS-C camera...

Thanks for clarifying, Thomas .

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Sony α77V/VG-C77AM/α350/18-70/70-400 G SSM/NEX-5/18-55 OSS/Lowepro Pro Trekker 600 AW/CompuTrekker AW/Nova 140 AW/Street & Field gear/Toploader Pro 75 AW. And a huge wishlist...

My photos on Flickr...