F1.8 vs F3.5?

[knittinggirl]

Is an F1.8 35mm really much better than a F3.5 lens in low light. It's only a stop or two different.

[framer]

If it's a good 1.8 then its main use is to limit DOF depth of field. Blur the background. If you don't care then get the 3.5.

framer

[chipmaster]

A stop can be huge, two is even bigger. To put it in prospective each stop allows you to double your shutter speed or half your ISO.

Assuming that the IQ is the same shooting 1.8 versus 3.5 at the same ISO setting is the difference between shooting 1/60 and about 1/15th the difference between a good chance at a non blurry shot and one that is totally blurry.

Or difference between shooting at 800 ISO or 3200 ISO the difference between a grainy shot and one much less grain/noise.

Or as the other poster suggest depending on the focal length the difference between a DOF of a few inches or a few feet of stuff sharp and in focus.

What a 200F2 can get you is almost too shallow a DOF. Note the grass/nose and background

Originally Posted by knittinggirl

Is an F1.8 35mm really much better than a F3.5 lens in low light. It's only a stop or two different.

[awboater]

The other issue is that lenses are not perfect - even those costing thousands of dollars.

Generally, lenses perform better (are sharper) one or two stops down from wide open.

Therefore, a f/1.8 lens stopped down to f/3.5 will usually outperform a f/3.5 lens wide open.

[jpthomas27]

To keep the answer short...yes. The problem here is that we don't know what lenses your comparing. If I could choose between two otherwise comparable lenses then yes, I would take the 1.8. I would probably set it around 2.8-3.5 when I had the chance though because as previousely mentioned, most lenses, even the best ones will give you better pictures stopped down a little.

There are two reasons for using a lense that is this open or "fast". Either for low light or superior background blur. You asked specifically about low light and the advise that chipmaster gave you is exactly right. Each stop allows double the light and the difference between 1.8 and 3.5 is significant! The 1.8 lens will allow 4 times the amount of light to hit the mirror or sensor and it will make or break your low light pictures. If the light your worried about is truly low enough to be worried about then 2 stops can definately give you great pictures that other wise will be completely blurry and unusable.

Apature is often the most costly feature of a lens, but if you can afford it, then it's worth the investment