Originally Posted by Conspiracy
we got an expert over here guys.
let me go ahead and just say for everyone else here. unless your primary subject is focus test charts comparing lenses using those is pretty much worthless. while you can examine which lens holds sharpness throughout the frame on test charts actually saying that the 50 1.8 is better is only useful if you plan on exclusively shoot using a tripod with a primary subject that is inanimate. if you are doing product photography and want the image to be sharp throughout the frame then you want the 50 1.4. the 50 1.8 is hands down the best bang for your buck lens but its by no means better. it is better in terms of price and quality if you are shooting and do not need the image to be perfect every time.
also where are you getting that specifically at f2.5 is where these lenses shine? a focus test chart? the true test of a lens is how it performs when you are shooting in the real world with whatever your main subject is such as portraits. and unless you are using a lens with just the worst quality and design ever created then pretty much every lens on the market today will "shine" when you stop it down from wide open on a focus test chart. but when you pixel peep a lens on a focus test chart after stopping down they will all look the same in terms of how much is in focus. its when you examine all the other factors that makes one lens stand out from the rest in terms of image quality and how it renders your subject.
just to let you know the difference in your depth of field from shooting a f1.4 and f1.8 is not that significant unless you are sitting right at the minimum focus distance in which case you will need a tripod because you will take more shots that miss focus simply because of you not being able to hold the camera perfectly steady. but if you are shooting from 3-4feet away and taking a portrait of a person with these lenses wide open the difference in depth of field is less noticeable. but the true difference will be in the quality of the image in terms of the glass in the lens and the lens construction. the 50 1.4 will produce a much more visually pleasing image with slightly better colors and hands down much better bokeh. the bokeh on the 50 1.8 wide open if shooting a portrait is honestly ugly.
No need to be rude, I wish you the best and well being.
As for your claims of charts and what not, it has been shown that even when pixel peeping the 1.8 is sharper than the 1.4 because it uses newer optical technology. If you zoom in 100% with a kit lens vs a L lens and both shots were in focus don't you think the L lens would be sharper? Well of course it would, this is one of the areas where the 1.8 shines, it is indeed sharper than the 1.4. So no, all lenses do not look the same when you pixel peep them on a chart as some lenses are sharper than others. All glass is not equal or else why would people put out the money for L lenses???
Also, the images are sharp throughout the frame on my 1.8. There are no soft corners as due to the 1.6x crop factor you're seeing the sharp part of the lens and there are no soft points unless you use it on full frame but even than I have yet to hear anyone say that the 1.8 has soft corners.
The difference between 1.4 and 1.8 is also bigger than you might think, at 1.8 your focal plane is already extremely small, you have to be dead still with the camera and your subject can't move or else your picture will be out of focus unless you use an af tracking mode. How do I know this you might ask, experience.
Also, I have yet to see any proof of the 1.4 having better contrast and a sharper image than the 1.8 (that's what you mean by better colors and more pleasing images). I'd like to see some proof to back those claims up. I have proof right here that the 1.8 is capable of producing beautiful bokeh while shooting portraits. Let's please try to be honest with ourselves and others on here as nobody likes to be lied to.
Here are some portraits that were taken yesterday with a simple 50mm f 1.8 and $75 speedlite and umbrella/lightstand. For the money, you can not do much if any better as the speedlite is $75 and is fully manual but has as much power and power settings as the $500 Canon 580 ii and the 50mm f1.8 is only $100. So instead of paying $350 for the f1.4 and blowing it all on a lens why not spend $225 and have an awesome portrait setup???
Also, how can you tell me that the f1.8 has ugly background blur or does not have good contrast? For $100 it can not be beaten.
Also, if you zoom in you'll notice that they're all 100% tack sharp.Edited by Mwarren - 9/25/12 at 10:45am