Why is a lens soft wide open?

[paigew]

It's just my opinion but this is a little soft. Personally when I shot that lens I had to stop it down more than that to get it tack sharp.

It isn't soft
100% crop


I shoot my 24-70 wide open every day. (2.8) it is pretty dang sharp imo...and that is even after I dropped it in the mud

 

[71M]

So i'm wondering why the area that is within the dof softer for example: on my 50mm at f1.4 than say f2? Why does stopping down to f2 make the dof sharper?

It reduces the amount of vagabond rays reaching the focal plane. Optical coatings (e.g Zeiss's T - 'Transparency' coatings) are also to reduce these reflections at wide aperture.

 

[TCampbell]

It's just my opinion but this is a little soft. Personally when I shot that lens I had to stop it down more than that to get it tack sharp.

It isn't soft
100% crop
View attachment 75766

I shoot my 24-70 wide open every day. (2.8) it is pretty dang sharp imo...and that is even after I dropped it in the mud

(a) you're using an crop section from near the center axis of the image. That's the area most likely to be sharp even in a situation that generates a soft image. If you want to test it... try to get sharp focus in the corner of a frame.
(b) this image actually does look a little soft to me... even in the center. The contrast on the eyelashes isn't very high.

 

[jkzo]

Its magic.
Natures mysteries.

it's not only nature's mistery but perfected by man

 

[W.Fovall]

my 70-105 f/4L is soft at f/4 and only sharpens up at f/5.6

 

[Derrel]

I do not think this has been mentioned yet, but there area still a good number of lenses in use that were designed and computed back in the film era, and which are ,"Not that hot" when used on digital sensors. FIlm, being lots on tiny little bits of sensitized silver suspended in an emulsion was more or less fairly adept at picking up and forming images with light rays that came in to the edges of the frame at pretty steep angles; PIXELS, or pixel wells, are not quite as receptive to light that "glances in" at steep angles. Telephoto lenses do not have near the same issue, as the light leaving even old-style teles is exiting and hitting the sensor at fairly straight-on angles.

Most manufacturers of lenses now have taken into account the "digital capture" need for light rays that are not doing "deep knee bends" as the light comes out of the rear of their wide-angle lenses...and they've redesigned most NEW wides and wide zooms for greater, as Nikon calls it "telecentricity". Stopping down most lenses a bit seems to help sharpen up their image a bit; but not too far down, as today's higher megapixel sensors and smaller sized sensors are more prone to being limited by diffraction at smallish f/stops.

 

[minicoop1985]

I dunno, this 65 year old Ektar's pretty sharp wide open. 80mm f2.8. f2.8 looks a hell of a lot like f8 in terms of IQ. This was Ektar 100, 2.8, 1/1600

Steampunk R2 unit by longm1985, on Flickr

My Tamron 17-50 f2.8 is kinda soft at 17mm f2.8, but back out and zoom in a bit and it gets a little sharper (odd). Still, it's not the sharpest down there.

 

[paigew]

It's just my opinion but this is a little soft. Personally when I shot that lens I had to stop it down more than that to get it tack sharp.

It isn't soft
100% crop
View attachment 75766

I shoot my 24-70 wide open every day. (2.8) it is pretty dang sharp imo...and that is even after I dropped it in the mud

(a) you're using an crop section from near the center axis of the image. That's the area most likely to be sharp even in a situation that generates a soft image. If you want to test it... try to get sharp focus in the corner of a frame.
(b) this image actually does look a little soft to me... even in the center. The contrast on the eyelashes isn't very high.

A) Yes, this is a 100% crop to the sharpest area...her eyes. I shot it wide open so the DOF is very very thin. I don't understand this argument that lenses are soft...at all. I mean, at 1.4 or 1.8 there should be something sharp. Period. I chose to use the center focus point for this because it was the most accurate point on my camera. You are correct in that I might not have been able to get such a sharp shot at another focus point...but that isn't the point is it? The point is to prove you CAN get a sharp shot wide open. I have better luck shooting wide open on my center fp.
B) You are crazy 😜...that is tack sharp. Do you want me to zoom in farther? I am shocked you can't see the clarity on the 100% There may be a little noise (iso 1000) as this was shot on my rebel.

A lot comes into play when shooting wide open that is for certain. But a lens can certainly be shot wide open with sharp results. It takes good light, and practice with dof.

 

[robbins.photo]

This would be easier to explain with a picture.

Ok, so what you're saying here is you adjust the thingymajigger and look thru the deallybob and push the little button and blamo! Magic.

Got it. Lol

Sent from my LG-LG730 using Tapatalk