diffrence in lens

[12sndsgood]

So I know a 35mm f1.8 lets in more light then a 35mm f3.5 but how much diffrence does it make, just looking at lenses (which I probably don't need to buy at this point. but problaby will) and im just wondering how much diffrence between the two is. wondering how much darker I can go while still getting a great shot for when its getting dark out and I maybe dont have my flash on me or can't use flash. (i'll be picking up a flash in a few months as well)

still trying to learn all I can here before i make any purchases.

 

[Johnboy2978]

A 35mm f/1.8 is 2 stops faster than a 35mm f/3.5. That means if you have a scene that has a normal 0 exposure value with the f/1.8 at a shutter speed of 1/60, the same scene would be at 1/15 shutter speed with the other f/3.5 lens.

The other difference between the lenses is construction and optical quality. Generally faster lenses like f/1.4 or f/1.8 lenses are going to have much better constuction and much better optical quality and are going to be much more (or at least noticeably) more expensive.

 

[Taylor510ce]

Your ISO represents stops also albeit with added noise. So the difference between the two stop diffeeence would be like shooting at ISO 100 verses ISO 400. Minus the noise. This is an easy way to test. Although you have DOF issues the wider you go. This may be desired or not.

 

[rpm]

there's also the play with depth of field that you can achieve with the extra stops...

edit: lol i need to remember to refresh my page when i leave it open for so long, didn't know someone already mentioned this...oh well

 

[KmH]

A 'stop' is a doubleing, or halving, of the amount of light.

A 2 stop smaller aperture, f/1.8 to f/3.5, is 2 halvings. In other words f/3.5 lets in 1/4 as much light as f/1.8.

To get the same exposure at f/3.5, as at f/1.8, you would need to slow down the shutter 2 stops, say 1/400 to 1/100, or increase the ISO 2 stops from 200 to 800. You could also get the 2 stop change by slowing down the shutter 1 stop (1/200) and bumping the ISO just 1 stop (ISO 400).

I'll mention again there are depth-of-field considerations, motion stopping considerations with the shutter speed, and possible noise issues by upping the ISO.

 

[12sndsgood]

thanks for the answers. will have to go out with the camera and just take a few shots at the diffrent settings as said above to just see the diffrence in a few pics to get a better feel for the diffrence.