View Full Version : Aperture sweet spot
cowasaki
19-07-2009, 22:42
I understand about aperture but clearly the best shots do not come from the extremes of aperture on each lens but somewhere in the middle. Is the "sweet spot" found only by experimentation of does this tend to be at a particular place in the range?
So just using my 3 current lenses
AF 50mm f/1.8
AFS 105 f/2.8 vr
AFS 18-200 vr
what are the sweet spots with these and have would say the f1.4 compare with the f1.8 for it's sweet spot.
Does the sweet spot depend on other factors such as distance from object etc.
By sweet spot, I guess you mean in terms of sharpness?
This is usually controlled by the f/number. A lens is least sharp at lowest f/number, and at the edges and corners. Central sharpness is always pretty high. As you raise the f/number, aberrations are reduced and sharpness increases, most notably at the edges. It gets higher until the effects of diffraction are greater than the increases of higher f/number, usually somewhere in the middle of the range.
The next biggest factor is focal length on a zoom. There are not any generalisations here, although I think it might be true to say that, mostly, wide zooms are better at the long end, and tele zooms are better at the short end. But I'm sure there are many exceptions to that.
Another factor is focusing distance, and all lenses except macros are optimised for relatively distant subjects. It doesn't make much difference when you get a bit closer, but when it comes to really close up, things will start to change - the image gets softer, the focus plane start to curve and distortion can get worse.
Just guessing with your three lenses, sweet spot with the 50 1.8 will be f/5.6, 105 2.8 VR will be f/5.6, and on the 18-200 VR maybe a bit higher at f/8-11. 50 1.4 will be similar to the 1.8. Another generalisation is perhaps that higher quality lenses peak closer to their lowest f/number than lower quality, or more ambitious lenses.
Edit: take a look here at the graphic for sharpness on the Nikon 18-200. http://www.dpreview.com/lensreviews/nikon_18-200_3p5-5p6_vr_afs_n15/page3.asp Move the sliders on the bottom for Focal Length and Aperture and see the colours change. Red is below average, yellow is okay, green is good and blue is excellent.
It will vary from lens to lens but the rule of thumb is 2 stops down is normally pretty good.
Flash In The Pan
19-07-2009, 23:59
It will vary from lens to lens but the rule of thumb is 2 stops down is normally pretty good.
Which always confuses newbies buying "nifty fifties" into asking "why buy a 1.8 lens then not shoot with it wide open?"
Because 2 stops down from f/1.8 is a lot better than 2 down from f/4 :lol:
Flash In The Pan
20-07-2009, 00:10
Because 2 stops down from f/1.8 is a lot better than 2 down from f/4 :lol:
<---assumes the role of newbie
Yes, but, I want it to be sharp at f/1.8 http://www.routertech.org/images/smiles/dummyspit.gif
Then buy a zeiss f/0.7 :lol:
Then you need the 50mm f/1.2L stopped down the f/1.8 - yes, that's right you need to spend lots more money :D
Flash In The Pan
20-07-2009, 00:17
Then buy a zeiss f/0.7 :lol:
Why? What's wrong with their f/0.55 one? :suspect:
It's not as sharp at f/1.8 .
Flash In The Pan
20-07-2009, 00:25
It's not as sharp at f/1.8 .
<back into newbie mode>
So should I just buy the f/1.8 then? :shrug::help:
No, cos the 50mm is no good for your crop camera, download a pattern from www.knitmealens.com and you'll be sorted :thumbs:
Oh no, now he's going to ask about crop factors, field of view, DOF and circles of confusion :exit:
this thread is men doing numbers and teknikul stuff innit? :suspect:
I was always told that for most lenses, the 'sweet spot' is always between F8 and F11, but the higher the quality of the lens, the smaller the quality fall off will be outside these apertures. Not sure how accurate this is though :shrug:
Then buy a zeiss f/0.7 :lol:
That thing was never sharp at any aperture :D
Why? What's wrong with their f/0.55 one? :suspect:
And that one was never fitted to a picture taking camera.
Flash In The Pan
20-07-2009, 02:28
That thing was never sharp at any aperture :D
And that one was never fitted to a picture taking camera.
Spoilsport :lol:
That thing was never sharp at any aperture :D
It was sharp in the studio... no, sorry, it was the moon. Yeah that's it, it was the moon not a tv studio, because people went to the moon.
KitchenGoddess
20-07-2009, 03:42
I was always told that for most lenses, the 'sweet spot' is always between F8 and F11, but the higher the quality of the lens, the smaller the quality fall off will be outside these apertures. Not sure how accurate this is though :shrug:
That's what I gathered from reading Understanding Exposure, but I could be wrong.
Speaking from experience and samples I've seen on the Internet, I would say it's 1-3 stops down from when the aperture is fully open. F1.4 and 1.8 lenses are generally sharpest between F4 and F8.
classcams
20-07-2009, 05:28
comment removed
classcams, no need for that sort of comment, you may not like the terms but perhaps you need to go and look them up, as you clearly dont know what they actually mean.
classcams
20-07-2009, 07:54
classcams, no need for that sort of comment, you may not like the terms but perhaps you need to go and look them up, as you clearly dont know what they actually mean. Oh, but I do know :lol:
Oh, but I do know :lol:
:shrug:
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