f-stops - f/1.4 versus f/1.8

[bucketman]

Hi all
was looking at adding to my stuff now that i am using GIMP and havent bought PS. So was looking a 50mm lenses. So is a f1.4 much different than a f1.8 the first one is twice the price. Cant wait to start my evening class then I would know the difference.
rob

[carregwen]

I presume you mean the Canon? I have the 1.8 which is outstanding for the money (I paid £69) Sharper than a Samurai sword, and a lot cheaper. The 1.4 will give you a stop more and is very well-built, but it's three times the price.

http://www.warehouseexpress.com/cate...=3077&brand=37 This gives the prices.

[bucketman]

Thanks
But its for a d90 and what I am asking ( thanks for you help again) is one stop? worth the extra cash
In my little world I thought it was .4 of a stop? .4 .8 ?
Roll on my course the teacher will send me out of class with a hat with D on it.
rob

[carregwen]

It's actually 2/3 of a stop. f/1.8 x 40% =f/2 which is a whole stop. 2/3 of that will give you f/1.8. http://www.uscoles.com/fstop.htm

[bucketman]

Thanks again
I have so much to learn its unreal. Dont know what they will make of me on my course. But i know where to ask when i get stuck. Will read the link you sent latter. Got eye ache watching meet the gimp.
rob

[carregwen]

Rob



It's worth getting your head around this. It took me ages to grasp it.

1. An f-stop is just a convenient way of stating different exposures. Each f-stop is just a doubling or halving of light going through the lens.
2. In order to double/halve it you have to reduce or increase the total surface area of the lens.
3, Although your sensor is oblong, the lens area is, of course, round. Due to the way 'Pi' works and the area of a circle means to double/halve the area is not actually double/half the circle diameter. If you look at the table above you can see in the right column that the area halves/doubles, but on the diameter and radius columns it doesn't. The difference, going up, is 40%. So, for example, it goes from 35.7 to 50 on diameter which is an increase of 40%. Which means that f/1 has to increase by 40% to f/1.4. That is why the f-stop numbers, which are so puzzling to many people, jump up in weird amounts. They are just 40% increases to allow for a halving surface area.

I think I got that right.

[Joy]

thanks carregwen for this info.

[eNo]

I see you are talking about Nikon equipment. The difference between f/1.4 and f/1.8 is 2/3 stops, and in some rare cases, that extra aperture may be useful. However, both my f/1.8 35mm and 50mm lenses are fantastic, and I don't see what I would gain with the extra aperture. In fact, I have a Sigma 30mm f/1.4, and my 35mm beats it at f/1.8. The Nikon AF and AFS 50mm f/1.4 have very good reputations, depending on who you ask, of course. I actually have an AIS (MF) 50mm f/1.4, and I must say it is an amazing lens, but can I see a difference when I compare images against my 50mm f/1.8? Not really. I think the f/1.8 lenses are great values (note also the "lesser" plastic build, if that matters to you, though the 35 and 50 both have metal mounts), and you won't go wrong with them.

I'm rambling on and on here, so one more coment regarding wide apertures: for the most part, you want as wide an aperture as possible so that you can stop down and get sharp results at smaller apertures. IOW, f/1.4 is handy because by f/2.8, things are getting really sharp. If you are 2/3 stop down from f/1.4, then it will be something more like f/3.5 by the time you get similar results... now, that's as a general rule of thumb. For the Nikkor 50mm lenses, many people claim that at f/2.8 and above, both lenses perform pretty much the same.

[bucketman]

Well thats as clear as mud
I think for now I will get the f1.8 will order it on Fri. unless you say NO stop. Buy the other one. The clock is ticking
Thanks all
rob

[bmpress]

Rob



It's worth getting your head around this. It took me ages to grasp it.

1. An f-stop is just a convenient way of stating different exposures. Each f-stop is just a doubling or halving of light going through the lens.
2. In order to double/halve it you have to reduce or increase the total surface area of the lens.
3, Although your sensor is oblong, the lens area is, of course, round. Due to the way 'Pi' works and the area of a circle means to double/halve the area is not actually double/half the circle diameter. If you look at the table above you can see in the right column that the area halves/doubles, but on the diameter and radius columns it doesn't. The difference, going up, is 40%. So, for example, it goes from 35.7 to 50 on diameter which is an increase of 40%. Which means that f/1 has to increase by 40% to f/1.4. That is why the f-stop numbers, which are so puzzling to many people, jump up in weird amounts. They are just 40% increases to allow for a halving surface area.

I think I got that right.

Almost right (LOL) The diameter and radii actually need to go up by the square root of 2, which is about 1.414. ...... Who says that I am a perfectionist????

[carregwen]

Almost right (LOL) The diameter and radii actually need to go up by the square root of 2, which is about 1.414. ...... Who says that I am a perfectionist????

Yeah, they don't run exactly, as you say. I'm sure there must be a better way of expressing f-stops. Perhaps we should think of one and unleash it upon the unsuspecting, but long-suffering world

[Colin Southern]

I'm sure there must be a better way of expressing f-stops. Perhaps we should think of one and unleash it upon the unsuspecting, but long-suffering world

I think that after a while we just tend to remember them anyway, but the easiest way I found was just to consider two lists - where each one doubled - and then they get interleaved (sounds complicated!).

eg one "F-Stop List" F1, F2, F4, F8, F16, F32, F64, F128 etc

The other F1.4, F2.8, F5.6, F11 (rounding), F22, F44, F88

Put em together ...

F1, F1.4, F2, F2.8, F4, F5.6, F8, F11, F16, F22, F32, F44, F64, F88, F128

So to move something by 2 stops, just double or 1/2 it.