A second aperture question

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simonmoran

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So I was out this morning shooting the quayside (essentially a landscape) and I realised I wasn't exactly sure how high an f number I should be using to keep the whole scene sharp.

In general I was using anything above f10 but is there an optimum or should I just shoot with as high an f number as possible (depending on the correct iso and shutter speed needed for correct exposure)
 
simonmoran said:
So I was out this morning shooting the quayside (essentially a landscape) and I realised I wasn't exactly sure how high an f number I should be using to keep the whole scene sharp.

In general I was using anything above f10 but is there an optimum or should I just shoot with as high an f number as possible (depending on the correct iso and shutter speed needed for correct exposure)
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No, because above about f/11 you start to get diffraction which actually looses sharpness.

F/11 is suitable for most scenarios, especially if you use hyper focal distance focusing, or variants thereof.
 
TCR4x4 said:
No, because above about f/11 you start to get diffraction which actually looses sharpness.

F/11 is suitable for most scenarios, especially if you use hyper focal distance focusing, or variants thereof.
Click to expand...

Well I was using f22 today (to allow for slower shutter speed to get a smooth water effect) and when I reviewed the photos later they definitely didn't seem that sharp so this makes absolute sense.

I really need to get an nd filter so I can use the slower shutter speeds without having to use super high f numbers to balance the exposure.

Can I ask what hyper focal distance focusing is?
 
simonmoran said:
Well I was using f22 today (to allow for slower shutter speed to get a smooth water effect) and when I reviewed the photos later they definitely didn't seem that sharp so this makes absolute sense.

I really need to get an nd filter so I can use the slower shutter speeds without having to use super high f numbers to balance the exposure.

Can I ask what hyper focal distance focusing is?
Click to expand...

A polariser will add a stop or so to exposure times which may be enough to smooth water. Harbour quays tend to be fairly well protected against waves, so smoothing may not be better looking than faster exposures with clearer reflections.

http://www.talkphotography.co.uk/gallery/showgallery.php?cat=7202 Has a few examples of exposures up to 10s but only of a stream, waterfall and surf, no harbours. They were shot either at dawn or dusk to get the longer exposures apart from the waterfall shots which were in a deep glen (St Nectan's near Tintagel) with a pol as a makeshift ND filter.
 
I use a software product called Focal in order to assist in the AF calibration of my lenses with my bodies. One feature it offers (at least in the higher end version(s) of the product) is an analysis of lens sharpness vs aperture. It is quite scary how badly IQ suffers at smaller apertures. There is a plot of sharpness vs aperture value shown on this page....

http://www.reikan.co.uk/focalweb/index.php/tests/aperture-sharpness/

Good quality primes would probably turn in their best results at values closer to f/4-f/5.6

The effect of stopping down is more severe when shooting with crop sensors. The amount of diffraction softening is actually the same, regardless of sensor size, but the smaller image from the smaller sensor requires greater enlargement for any given final picture size and this magnifies the diffraction softening more than with full frame.

My rule of thumb of achieving large DOF is to shoot at an aperture equivalent to focal length divided by 2, but I try to avoid going smaller than f/11 on crop bodies and smaller than f/16 (f/22 max) on full frame. If you are stopping down to achieve longer shutter speeds rather than massive DOF then filters might be the better way to go.

EDIT : The Focal software has been collecting/collating data for various bodies and lenses (with end user permission) and this has been pulled together into an online reference so you can see how sharpness varies with aperture for a range of cameras and lenses....

http://www.reikan.co.uk/focalweb/index.php/online-tools/lenscamera-information/
 
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tdodd said:
If you are stopping down to achieve longer shutter speeds rather than massive DOF then filters might be the better way to go.
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Summerstar said:
Why filters? Why not just drop the ISO?
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Please not the context for my suggestion. The suggestion was in relation to desiring longer shutter speeds specifically.

If your intention is to achieve a longer shutter speed, for milky water for example, you would already be at 100 ISO so that would be a dead end. Your only options are to mess with the aperture, wait for the light levels to fall or...... add filtration. So if your DOF needs are fully satisfied at f/8, for example, and you need f/22 to get the sort of shutter speeds you desire then instead of stopping down well into diffraction softening territory you could instead add a 3 stop ND filter and keep the aperture at a much more IQ friendly value.
 
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