Newbie lens question - Difference between lenses wrt aperture ?

phigmov · #1 September 23rd, 2011, 12:37 AM

Hi all,

Quick (I hope) newbie query regarding lens quality with regard to aperture.

I understand what lens focal length will do to a picture.

I understand what aperture does to a picture.

What I'm interested in is what the difference is between an f1.4, 1.8 on image quality if the aperture were similar.

eg if I had a 50mm f1.4 or f1.8 and shot them both at f2.8 or a 50mm f1.8 and f2 and shot them both at f8

Is it purely down to lens positioning and cost in a family of optics or longevity of mount (over time it just happens) ?

eg Nikon have a 50mm f1.8 and a 50mm f2, why?

Thanks in advance !

Markb · #2 September 23rd, 2011, 01:05 AM

Fast lenses use bigger lens elements and need far more correction than slower lenses. This is why they are boh bigger and more expensive. In theory an f1.4 lens would be better than an f2 (I prefer to ignore 1/2 stops for this kind of discussion) at f2.8 because it's stopped down further into its range. In practice there's often not a lot in it. At f8 the playing field should be pretty level for most well designed lenses. My feeling is if you're going to shoot mostly at "daylight apertures" like f5.6 or f8 why carry a huge lens with performance issues if you don't need to. That's why I kept a Leica Elmar (f2.8) and sold my CV Nokton 50/1.5.

In the 60s and 70s manufacturers got into a bit of a speed contest for standard lenses. If you sold your slr body with a 50/1.7 it would get a few more marks in reviews than the competition's f1.8 offering. Hence the f2 and f1.8 Nikkor. Pure marketing really, and not an issue in real life. there is a difference in performance because usually the slower lens is an earlier design. The extreme case was Pentax offered who f1.4, f1.7 and f2 50s as kit lenses with the M bodies at different price points (and an indifferent 40/2.8 pancake). The 1.7 is the sweet spot here. Not much bigger than the f2 and only 1/2 a stop shy of the 1.4 while being much cheaper but at the time there was a great deal of cachet in having a huge front glass (ooh err).

Grant · #3 September 23rd, 2011, 06:57 AM

I have both of the f/1.4 and the f/1.8 Nikkors. In theory the f/1.4 is shaper and has better contrast up to and including f/2.8 but after that they are identical. In practice I can see no difference and I challenge anyone to see the difference in my images. The build on both lenses is first class and they just last and last.

I suspect the difference in cost is due to four things. The larger the glass the harder and more costly it is to produce. They make far more f/1.8 lenses therefor the unit price can drop. The f/1.8 is made in China and the f/1.4 is made in Japan. Finally even if the markup percentage is the same the markup price for the more costly lens would be greater.

I have both because I have two SLR bodies, I bought the f/1.8 when I was on a budget and at that time it didn’t have the “D” option. I bought the 1.4 exclusively for the “D” option (Distance transfer between lens and flash).

The f/1.4 is really good in attracting gear head chicks if that is a concern but at my age I don’t need to attract chick as much as when I was 20.

avidone · #4 September 23rd, 2011, 03:49 PM

[QUOTE="The extreme case was Pentax offered who f1.4, f1.7 and f2 50s as kit lenses with the M bodies at different price points (and an indifferent 40/2.8 pancake). The 1.7 is the sweet spot here. Not much bigger than the f2 and only 1/2 a stop shy of the 1.4 while being much cheaper but at the time there was a great deal of cachet in having a huge front glass (ooh err).[/QUOTE]

Hey! I has that 1.7 on the black Pentax MX I got when I was a freshman at university, back in the Paleozoic era. It was good and I was able to afford it

Sent from my iPad using Mu-43 App

~tc~ · #5 September 23rd, 2011, 04:01 PM

There is one more factor, here - marketing.

The faster lenses are usually marketed to the higher end, more discerning user, and therefore have a higher level of design and quality control than just the difference in aperture would explain.

You know the car saying "no replacement for displacement"? The same thing with aperture. IMHO, you should buy the fastest lenses you can afford.

flash · #6 September 23rd, 2011, 04:35 PM

At mid range apertures (say f8). It would be difficult or impossible to tell most lenses apart from the same family except that the more expensive one will most likely, have better bokeh. A faster lens is larger, heavier, more difficult to manufacturer and more expensive. But they will also often be built better, use special glass or glass designs, have faster autofocus and they will have more aperture blades for a nicer bokeh and lens fall off. Additionally most normal lenses reach peak performance around 2.5 stops from wide open. A faster lens is going to get there sooner. And this is for most lenses, not all. Some very fast lenses are not as good as a slower lens from the same family due to the compromises made to make that lens really, really fast. Usually this is for lenses faster than 1.2. In the same family a 1.4 version is almost always sharper than the 1.0/1.1/1.2 version. The super fast lenses are often softer, have CA issues, more flare and ghosting wide open. But if you need f1.0 then a 1.4 isn't going to help you. I have a CV 1.5 and 1.1 for my Leica. That's a difference of only one stop. The 1.5 is always the better lens (optically better, half the size, weight and cost), except when I need 1.1, so I carry both.

Lenses are a bit like cars. You can get very good performance for modest money but for outstanding performance (an extra 10%) it takes a lot more resources and cost. A Bugatti Veyron uses half it's available horsepower to achieve the last 5% increase in speed. Lenses are like that.

Gordon