f1.4 portraits

[joel222]

I've just purchased a sigma 30mm 1.4 and tried some portraits today at different f stops to see how it performs. It seems sharp down to f2 but any wider seems to be slightly blurry, I also tried shooting apples with the camera on the table and got the same result. It's not a problem as f2 is wide enough for me but just wondered why this is, and how far would others usually stop down for a good shallow dof portrait. I know that the distance from camera to subject to background makes a difference but would like bit of a general answer.

 

[woof woof]

The obvious answer is that DoF is thin at close distance and wide aperture and any camera or subject movement matters, but if you've shot with the camera on a table that should rule out movement.

When I had a 20D my 30mm f1.4 was pretty sharp at f1.4. Here's a whole image test shot and a 100% crop. I was trying to focus between Cartman's eyes.





That shot was a RAW processed in CS5, sharpened and with a slight boost to contrast, saturation and vibrancy.

Something in the image should be as sharp as it can be but away from the point of focus/focal plane things will drop off quite quickly at f1.4.

PS. Gotta also give the camera and lens the best chance of achieving focus by pointing it at something that gives the best chance of achieving a lock.

 

[Steve]

I don't have the lens in question, but I never shoot my portraits at f1.8 (largest aperture I have), as DoF is just too small.

 

[Throttle]

I have never owned the lens but it could be a few things possibly a slightly poor build and just needs stopping down to give sharp images or is the focus out and it needs micro adjusting if the camera supports it ?
Your better trying focusing on a non moving subject and if possible use a tripod, remote wireless or a wired shutter.. or make just sure the camera is held steady by leaning against something,
If your focusing at something quite close and happen too move back or forth the movement would give you a out of focus capture due too the thin dof

I have quite regularly used the f1.8 and f1.4 aperture on portrait photos using a 50mm and 85mm equivalent and focusing on the eyes, the further you are from a subject the more dof you get and as you get closer it goes thinner making there more of a chance on a out of focus capture.

 

[mark1616]

I've just purchased a sigma 30mm 1.4 and tried some portraits today at different f stops to see how it performs. It seems sharp down to f2 but any wider seems to be slightly blurry.

Is it that they are blurry, or that the focus is not quite spot on and being so narrow it looks soft?

Have a bash again with a portrait and use liveview to focus on the eyes and see what you think.

 

[4wd]

Using liveview and manual focus you will realise how paper thin focus is when wide open.
I suspect in the model focus is just in front of his face.
It all gets much easier around F2 and you still get the desirable defocused background.

 

[Lyonspride]

http://www.dofmaster.com/dofjs.html

You can't just open up to f/1.4 without some idea of your depth of field @ distance.

Close up you can literally get a nose in focus and lose the rest completely.

 

[TheTimeChamber]

I don't have the lens in question, but I never shoot my portraits at f1.8 (largest aperture I have), as DoF is just too small.

f/2.8 - f/4 is my preferred range for portraits/peoples (when I rarely take them).

 

[shaylou]

I was told that no lens will be at there best wide open and found that to be true. With my 70-200 2.8 markII I found the widest I should shoot it is 3.5 if I want really sharp shots. Don't get me wrong it usable wide open but its soft.