Should I be using F2.8 as much?

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bombfrog

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Had my camera for a couple of months now and things are going well, but I'm still not understanding a few things.

For instance, I had got it into my head that larger apertures are better. More light = faster shutters = sharper pictures + shallow DOF etc.

This seemed to be working for me, my "nifty fifty" takes lovely photos and my zoom lens goes to 2.8 and is also really nice.

So, except for specialist situations (like deliberate motion blur or needing more DOF etc.) I've got it into my head that I should have it on aperture priority most of the time and keep it on 2.8 for just about every shot.

Apart from this seeming a bit too simple (hey, why not just leave it on auto?) I'm also starting to read people say things about lenses such as "it's a bit soft wide open" and getting the impression that F2.8 may not always be the right choice.

If I'm going to start using fully manual mode then I'm going to need to know a bit more about how aperture relates to sharpness. Can anyone give me a helping hand?
 
bombfrog said:
Had my camera for a couple of months now and things are going well, but I'm still not understanding a few things.

For instance, I had got it into my head that larger apertures are better. More light = slower shutters = sharper pictures + shallow DOF etc.

This seemed to be working for me, my "nifty fifty" takes lovely photos and my zoom lens goes to 2.8 and is also really nice.

So, except for specialist situations (like deliberate motion blur or needing more DOF etc.) I've got it into my head that I should have it on aperture priority most of the time and keep it on 2.8 for just about every shot.

Apart from this seeming a bit too simple (hey, why not just leave it on auto?) I'm also starting to read people say things about lenses such as "it's a bit soft wide open" and getting the impression that F2.8 may not always be the right choice.

If I'm going to start using fully manual mode then I'm going to need to know a bit more about how aperture relates to sharpness. Can anyone give me a helping hand?
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its not always the right choice, but it sometimes is. Your reasoning above is nearly correct except larger aperture means faster not slower shutter speeds.

On most modern zoom lens f2.8 there isn't a notable difference between wide open and stopped down a little in terms of sharpness - its there but you won't see it.

When you start shooting manual you'll need to understand aperture as it relates to the other exposure variables (shutter speed and iso) and the effects changing it has on your image, but really sharpness isn't a big consideration in deciding this

Hugh
 
sounds like you have a perfect grasp of what the aperture is doing, so if you're getting the shots you want at f2.8 then it's the right aperture to be using.

Your lenses will be sharper at f5.6 of f8 but how much depends on what lenses you have. It's far more noticable with the cheaper end of the market.

Of course the extra sharpness is no use at all if what you want is shallow DoF and bokeh.
 
Most lenses are at their sharpest around f8 I think however I have to say, and bear in mind I am a beginner, you should choose the aperture for one of two reasons primarily and neither is related to where the lens is sharpest... if you satisfy the below then you can think about sharpness but in most situations i would only consider the following.

1) choose a wider aperture so i can slow have a faster shutter speed or choose a narrower aperture so i can have a slower shutter speed (to create or prevent blur caused by movement of me or the subject)

2) choose a wider aperture to have a smaller depth of field resulting in my subject being isolated from the background or a narrower aperture to have a larger depth of field so i can get subjects at different distances from me all in focus at the same time.

I would recommend this book also by the way:

Understand Exposure by Bryan Peterson. It's quite thin and answers questions like the one above. Just wanted to stick my oar in before the experienced people turn up :)

Cheers,
dub
 
A very good question and I'm watching the answers with interest; not least because I have just picked up a Nikon 80-200mm f2.8. I did a recent test on my nifty fifty which is reputed to be a very sharp lens. I found that generally the sharpness looked good at f1.8 however on cropping in heavily the rendering of text on a box was significantly worse than just moving it back a stop to 2.8 where the text was lovely and sharp.

Do a test or two preferably using a tripod, all part of learning about your equipment.
 
Do you crop that heavily often? If not then does a slight sharpness difference at various apertures really make it worth basing your aperture choice on sharpness as opposed to the aperture that gives you the creative effect you are looking for as per my previous post?
 
it confuses the hell out of me too
i got a tamron 17-50mm f/2.8 and to get really sharp results have to step down to f5.6
well i already have a lens that is f/3.5-f/5.6 so i might as well have just used that in the first place or will the tamron even though stepped down produce better quality images :bonk:
 
Are you sure that below f/5.6 your pictures are not just looking blurry because the depth of field is narrow? The depths of field can be so narrow that even a focus and recompose can throw the subject out of focus because you moved the focal plane a tiny bit...
 
The Digital Picture Website give some great reviews with standard sample shots of numerous lenses at various apertures and sometimes different bodies too.

http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=105

It's a useful guide in getting the best out of a lens, but ultimately only you know the exact conditions that you're shooting in, what effect in terms of DoF you're trying to achieve and whether your present shots are sharp enough for the type of work you're doing. It all sounds a bit wishy-washy I'm afraid, but there isn't an obvious right or wrong answer to your question.
 
got a tamron 17-50mm f/2.8 and to get really sharp results have to step down to f5.6
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I am exatcly the same really sharp from f5.6 upto f8, at f2.8 not soo good although I have heard by some that my lens is a tad soft ?

Also thanks for the link excellent put my lens in and it shows that best focus at 5omm is f8 yet at 17mm f4.0-5.6.
 
terryuk said:
it confuses the hell out of me too
i got a tamron 17-50mm f/2.8 and to get really sharp results have to step down to f5.6
well i already have a lens that is f/3.5-f/5.6 so i might as well have just used that in the first place or will the tamron even though stepped down produce better quality images :bonk:
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You may find that to get the best results from your f/3.5-f/5.6 lens you still need to stop down from wide open, which could leave you shooting at f/8, so having the 17-50 f/2.8 is still valid, even if it isn't at it's best at f/2.8.
 
terryuk said:
it confuses the hell out of me too
i got a tamron 17-50mm f/2.8 and to get really sharp results have to step down to f5.6
well i already have a lens that is f/3.5-f/5.6 so i might as well have just used that in the first place or will the tamron even though stepped down produce better quality images :bonk:
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The answer is simple, Sharpness is not the defining characteristic of an image if it was some of the best photographs ever taken would be considered rubish, it is only in these digital days that we have become obsessed with pin sharp detail at 100% magnification.

The reason for having an f2.8 lens over your cheaper kit lens isn't sharpness it's that fact that it will allow you to get a shot that the slower kit lens won't like when it's dark or you want a really shallow dof!
 
boyfalldown said:
its not always the right choice, but it sometimes is. Your reasoning above is nearly correct except larger aperture means faster not slower shutter speeds.

On most modern zoom lens f2.8 there isn't a notable difference between wide open and stopped down a little in terms of sharpness - its there but you won't see it.

When you start shooting manual you'll need to understand aperture as it relates to the other exposure variables (shutter speed and iso) and the effects changing it has on your image, but really sharpness isn't a big consideration in deciding this

Hugh
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I have to disagree. You have to spend good money to get something that'll be as sharp wide open as at f/8. REALLY good money.
 
The23rdman said:
I have to disagree. You have to spend good money to get something that'll be as sharp wide open as at f/8. REALLY good money.
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I'll disagree back - I didn't say as sharp, but nearly as sharp, and generally 2.8 lenses are really good money
 
Don't forget that large max apertures aren't necessarily about image quality - you get a brighter viewfinder image, faster more accurate AF, the ability to work hand-held in low light, and that minimum DOF and nice bokeh if that's what you're after.

It's probably true that no lens gives it's sharpest performance wdie open - they all benefit from stopping down a stop or two, although with the best glass the perceivable difference in sharpness from stopping down may be quite minimal.
 
dubcat said:
Are you sure that below f/5.6 your pictures are not just looking blurry because the depth of field is narrow? The depths of field can be so narrow that even a focus and recompose can throw the subject out of focus because you moved the focal plane a tiny bit...
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I couldnt agree with you more, at wider appertures around 2.8 and below you are working with quite a thin depth of focus. Anything infront or behind the particular focus point(s) is going to be blurry/bokehy (is that a word?). I think that some people think that this is the fault of the lens and means the lens isn't sharp, its not its the way it should be. Of course any lens is going to be sharper stoped down from centre to edge but sometimes this isn't possibe or even disired.

I had an arguement on another forum, wasn't a photography one... was a very popular PC one. He got quite irrate with me when I stated to him that I thought the focus points (I rarely use focus and recompose) affected the DOF i.e. the object below the selected and the distance in front and behind it was affected by aperature and set the overall DOF. It got so bad that he actually had me questioning myself, he then went off and didnt come back. Sorry that was a bit off subject.
 
The best IQ on most f2.8 lenses is often maybe f6ish on the cheaper lenses this gets pushed up to f9ish which is getting too slow so the F2.8 lenses are still useable at their date settings in lower light. Well thats just my experience of it anyway. BUT love the 2.8 dof.
 
It's true that all lenses give their best sharpness when closed down a bit. It varies acording to lens and also the format, but generally f/5.6 to f/8 will be optimum. However, sharpness in the centre is almost always good and it's the edges that improve far more on stopping down.

In practise, you really only notice this in landscapes or other distant subjects where edge sharpness is important. At most other times with closer subjects, and certainly at f/2.8, there is not enough depth of field to cover the whole frame so any loss of sharpness away from the focused point is never going to be visible anyway.

The problem with low f/numbers is almost always mis-focusing, or too shallow depth of field, rather than any shortcoming in the lens.
 
boyfalldown said:
I'll disagree back - I didn't say as sharp, but nearly as sharp, and generally 2.8 lenses are really good money
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I'll see your disagreement and raise you a question: What lenses are you talking about and what is nearly as sharp?
 
HoppyUK said:
It's true that all lenses give their best sharpness when closed down a bit. It varies acording to lens and also the format, but generally f/5.6 to f/8 will be optimum. However, sharpness in the centre is almost always good and it's the edges that improve far more on stopping down.

In practise, you really only notice this in landscapes or other distant subjects where edge sharpness is important. At most other times with closer subjects, and certainly at f/2.8, there is not enough depth of field to cover the whole frame so any loss of sharpness away from the focused point is never going to be visible anyway.

The problem with low f/numbers is almost always mis-focusing, or too shallow depth of field, rather than any shortcoming in the lens.
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I've found that lack of center sharpness is just as big a problem with portrait work as landscape. I mean, who sticks their subject bang on the center of the frame?
 
The23rdman said:
I've found that lack of center sharpness is just as big a problem with portrait work as landscape. I mean, who sticks their subject bang on the center of the frame?
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Not just bang in the centre! Generally speaking, a good level of central sharpness at low f/numbers extends across 30-50% of the frame width, which means central subjects or those positioned off centre according to the rule of thirds will still be adequately covered.

It's unusual to have the key point of focus outside that zone. And the level of sharpness doesn't suddenly fall off a cliff, it's a gradual effect so less noticeable in that respect. The overall scheme of things, it's not usually lens performance that is the limiting factor. Unless you shoot brick walls a lot ;)
 
dubcat said:
Do you crop that heavily often? If not then does a slight sharpness difference at various apertures really make it worth basing your aperture choice on sharpness as opposed to the aperture that gives you the creative effect you are looking for as per my previous post?
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I agree, but it's worth knowing what you sacrifice.

It seems to me the general maxim is - stop a lens back by 1 stop from full unless you can't for light or artistic reasons.


Have a look here for some f2.8 vs f5.6 shots on the Nikon 80-200mm AFD
http://www.bythom.com/nikkor-80-200-lens.htm
 
Dazzler said:
I agree, but it's worth knowing what you sacrifice.

It seems to me the general maxim is - stop a lens back by 1 stop from full unless you can't for light or artistic reasons.


Have a look here for some f2.8 vs f5.6 shots on the Nikon 80-200mm AFD
http://www.bythom.com/nikkor-80-200-lens.htm
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That link shows what happens, but what is not clear is how small a section of the image that actually is, or the degree of enlargement. All I know is that it's a tiny section and a very big enlargement!

It is also very hard to make a realistic assessment from a test taget image of what a real picture looks like, and I think he's got his captions wrong (bottom pic is corner at f/5.6, I think, not centre).
 
This is the problem with the digital age and the ability to zoom in to 100% or more. When displayed on a website or printed, f2.8 lenses will produce a sharp result to the human eye at 2.8. Pixel peeping is way over hyped. Also a lot of "my lens at 2.8 isn't sharp" is due to depth of field and focussing issues, not lens issues.

If I need to use a lens at 2.8 to get the shot I want, who cares if at 200% the corner is softer than if I used 5.6. I don't and you will find most people don't. You buy the best glass you can afford and use it however you need to.

What do you shoot most? If it is people then 2.8 is a nice aperture to make them pop from the background, and can achieve flattering effects. If you're shooting landscapes the deeper depth of field is more useful. There is no right and wrong aperture, it depends on the situation and what you want from the pic.
 
The23rdman said:
I'll see your disagreement and raise you a question: What lenses are you talking about and what is nearly as sharp?
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Fair enough - I'll raise my reference as the current generation of f2.8 zooms from Nikon. So the 24-70 and 70-200 current generation,
 
Most lenses are sharpest about two stops down from wide open - unless specifically (and expensively) designed to be sharper wide open.

On a modern, high resolution, 1.5x or 1.6x crop sensor, images become softer due to diffraction somewhere between f/8 and f/11 onwards.

So, a lens which is wide open at f/5.6 may perform best at f/11, but on a body like a Canon 550D, anything narrower than f/8 will start to become soft.

Basically, general advice tends to:
f/8 and be there for photojournalism/general photography
Whatever you want if you're going for a specific look.

In real life, off a tripod, with you moving, your subject moving, interesting things happening, does it matter? Probably not.

For reproduction, macro, landscape, studio and other work where attention to detail is key, then yes, it's important.
 
Bang on for me Blapto. Overall why wprry about shooting at 2.8 if you like the results. That`s your preference, your style, your way - go with it. But when you want that perfect landscape change your ways
 
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