Do I have to sacrifice sharpness for large aperture?

[Langdon_Alger]

I bought a Canon EF 50mm f1.4 USM for my Canon T1i to take indoor pictures without a flash. The problem is, I can’t seem to get good results wide open at 1.4.

I understand that large aperture means very narrow DOF, but even using a tripod and remote shutter release there is not a single part of the picture that is sharp when I zoom in during PP. I’ve tried manual and auto focus, mirror lockup, with and without UV filter. The same lens at roughly f2 or higher is vastly sharper.

Is this just a known tradeoff for large aperture lenses? For this specific lens? Was this particular lens from a bad batch? Should I do anything different (different filters, or keep the subject further away?).

Thank you kindly for any help…

 

[shaunly]

Where is your ISO at? High iso will decrease sharpness.

 

[clanthar]

Hi,

A lens's performance is variable over it's aperture range. The difference can be as much as a 30% loss at either end. A lens generally performs at it's best two or three stops down from wide open.

This is a long standing dilemma -- you bought the fast lens to get that extra f/stop or two but.... It's always a compromise.

Joe

 

[tirediron]

Lenses in general are never at their best wide open. One stop down will normally make a significant difference, but the 50mm 1.4 is rumoured to be a pretty decent lens. As mentioned ISO, and exposure can have a significan impact on how sharp an image is; examples would help.

In the meantime, I suggest a home-made lens resolution test: Use a LASER printer (NOT inkjet) to completely cover a sheet of paper with 12pt upper-case 'X's. Using a tripod, level and square, position your camera such that it is within the minimum focusing distance (eg, if your lens will focus as close as 12" then use, say, 14") and ensure that the sheet of paper is exactly square to the lens axis. Use your lowest native ISO, and supplementary lighting if necessary to ensure a correct exposure.

Focus on the centre on the of sheet of paper and make an exposure wide open, followed by a series stopping down by a couple of stops each time. Then, examine the centre, and edges at 100% and compare sharpness. Even wide open, at the edges, the characters should be legible. This will give you a good idea of whether or not there is a problem with the lens (It's unlikely, but it can happen) and just how it performs at different apertures.

 

[Einstein]

I have the same lens and find it takes increadible photos. However at f 1.4 the DOF is SO narrow it is hard to get anything larger than a few millimiters of the subject in proper focus. I find shooting above F2 helps.

Also if your shooting portraits indoors its best to go with a flash and use a narrower apperture so you can get more of your subject in focus.

 

[Big Mike]

Yes, I think the first thing to investigate is whether or not you are actually getting accurate focus. At F1.4, especially at close distances, the DOF can be very, very thin.

Along with Tirediron's sharpness test, you might also try shooting a test sheet at 45 degrees to camera, so that the focus will come and go withing the frame. Find the sharpest part of the image and that should give you an idea of what sharpness the lens is capable of. This test can also help to tell you if your lens & camera are focusing accurately. It's entirely possible that either your lens or camera is not calibrated 100% accurately and thus doesn't focus exactly where you think it will.

 

[Christie Photo]

I understand that large aperture means very narrow DOF…

I often times hear DOF referred to as "narrow."

A better way to think about this is either "shallow" or "deep." This may help in your understanding of what's going on.

-Pete

 

[Langdon_Alger]

thanks for all the replies.... I did some more test shots, and I guess I would really have to call it more of a "haze" than a lack of sharpness...

I tested it using ISO 100, of a grassy slope in the sunlight (so if it was a DOF issue, there should always be at least one point along the slope thats in focus).

I went and read some reviews of this lens, and its rated very good overall, but the ones that rated it low usually complained of the "softness" at large aperture. Now I regret paying extra specifically to get a low f number that I can't use! Luckily this lens seems to have a good resale value, it will be going on ebay soon...:x

 

[Petraio Prime]

Generally speaking, with some exceptions (such as some Leica APO lenses) wide-open performance on lenses is worse than stopped down a couple stops. This is true more with high-speed lenses than with ones of moderate aperture. So, your 400mm f/5.6 lens may not be any worse at f/5.6 than it is at f/11, but your 50mm f/1.4 will often be noticeably better at f/4 or f/5.6.

There are, of course, exceptions. They are very expensive ones, needless to say.

Leica 50mm F0.95 Noctilux-M ASPH Lens 11602

 

[KmH]

So what do you replace it with? A less expensive, lower quality lens that gives less sharpness overall, not just wide open?

You didn't mention what file format you are using, nor did you mention what sharpening techniques you are using.

Do you do any capture sharpening? What about local sharpening? How are the photo's used? Online only? Print?

What are the photo's of?

How a photo will be used, and the content of the photo, has a lot to do with how it should be sharpened.

 

[Hardrock]

http://www.thephotoforum.com/forum/people-photography/200059-my-favorite-model.html
I believe #1(the shot with her sitting in the blue bonnets) is shot wide open or very close to it and I think it came out pretty well. Im at work and cant see the exif or the images. The 50mm F1.4 should work pretty well even at F1.4 and it gives a dreamy look. I think the lens works the best at F2.2 and above. Its a great lens once you figure it out. I made a post when I first got the lens and thought something was wrong with the lens but it was me. At a shallow DOF you really cant focus and recompose. Good luck!

 

[Einstein]

Example shot straight out of camera, i think this was under f2 but i cant remember. Awesome lens IMO, maybe you got a lemon?

 

[shaunly]

thanks for all the replies.... I did some more test shots, and I guess I would really have to call it more of a "haze" than a lack of sharpness...

I tested it using ISO 100, of a grassy slope in the sunlight (so if it was a DOF issue, there should always be at least one point along the slope thats in focus).

I went and read some reviews of this lens, and its rated very good overall, but the ones that rated it low usually complained of the "softness" at large aperture. Now I regret paying extra specifically to get a low f number that I can't use! Luckily this lens seems to have a good resale value, it will be going on ebay soon...:x

Make it easier on us by posting up some example pictures. :mrgreen: