Aperture question

[anda]

Hello,

I was wondering how does aperture work in term of "infinity". I know that when I am shooting close up and using for e.g 2.8 I get everything blurred in the background, but what happens if I am shooting at 2.8 but say a landscape which is far away, how does the quality differ from F11 to F2.8. Because there will be no OOF and DOF would be large no?

This is abit confusing still for me.

Also when I shoot portraits with Sigma 50mm F1.4 at a distance of 1-2 meters its amazing. If I try to shoot a landscape shot with it it look soft and not really nice. Why is that? can someone explain please.

 

[String]

The smaller the f number you use, the less depth of field you get. Also, a lens performs at it's best in the "sweet zone" which is probably going to be in the range of f5.6 to f11. A lens will not perform to it's best at extremes of aperture, such as f1.8 or f22, depending what you maximum and minimum apertures are.

For landscapes, try to stick at f8 or f11. Try to have a read of articles on here regarding hyperfocal focussing

Also shallow depth of field is more apparent at short range. So, if you shoot a flower with a 50mm lens at f1.8 from a range of two feet, the background will blur more dramatically than shooting the same flower with the same lens at a range of 20 feet.

 

[Moski]

I'd agree - if shooting landscapes, I tend to prefer being up at f8 and beyond (of course if the light is such that you're leaning towards the wider aperture for your exposure, far better to get the camera on to a tripod and go for narrow aperture + slower shutter speed).

+1 for researching Hyperfocal Distances too - caught a thread on here over the weekend which really opened my eyes

 

[anda]

Thanks for the explanation guys, I will try to find the articles on Hyperfocal Distances...

Also is it possible that a lens at 1.4 is backfocusing and when you step it down to 2.8 the focus becomes corect? If thats possible do you knwo if sigma calibrates lenses under warranty?

 

[String]

Thanks for the explanation guys, I will try to find the articles on Hyperfocal Distances...

Also is it possible that a lens at 1.4 is backfocusing and when you step it down to 2.8 the focus becomes corect? If thats possible do you knwo if sigma calibrates lenses under warranty?

I think it's more likely that as you stop down to f2.8 the depth of field increases and you see more of you subject in focus. If it's a portrait, focus on the eyes. Or at least the eye nearest to you if the DOF is so shallow you can't get both..

 

[anda]

I tested on 3 cigarete packs, focus on the middle one but the one closest to me seems to be most in focus :/ I tryed micro adjustment but doesnt seem to be doing anything

 

[String]

Maybe it's too close and the lens won't focus that close.....

 

[DaveKing]

There is also the possibility it is your technique. At F1.4 the slightest move forwards or backwards will change the area in focus as the depth of field is tiny! Put your camera on a tripod and use this focus test chart:

http://focustestchart.com/focus10.pdf

 

[dentonkarl]

With reference to original poster I would like to know the answer too. I was looking at a wide angle 11-16mm lens for landscapes but it has a fixed aperture of 2.8. My guess would be that it would all be in focus unless you specifically focused on a tree of something and then the background behind it would be blurred.

 

[DaveKing]

With the 11-16mm at f2.8 the area in focus will still be large, as the wider the lens the larger the depth of field. You can see this if you have a zoom - compare the bokeh from 18mm and 50mm at the same aperture, its much less defined.

 

[gad-westy]

With reference to original poster I would like to know the answer too. I was looking at a wide angle 11-16mm lens for landscapes but it has a fixed aperture of 2.8. My guess would be that it would all be in focus unless you specifically focused on a tree of something and then the background behind it would be blurred.

It doesn't have a fixed aperture as such. What the constant F2.8 refers to is the fact that a F2.8 aperture is available throughout the zoom range. Many (some would say inferior) lenses may be say F3.5 at the widest end but only F5.6 at the long end.

You could still crank that 11-16 down to F11 say if you were taking a landscape.

In the OP's question about using F2.8 using F2.8 for a landcaspe and setting the focal point quite far away. Yes, this could give you a large depth of field (though F11 will always give larger for the same focal point) but there will likely be an area in the foreground that is OOF.

This website explain this wonderfully. Try some numbers and see for yourself.

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