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Why do lenses have smaller F stops than the optimal front to back clarity F stop ...

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danfrier
danfrier  2 England
8 Feb 2012 - 9:09 PM

Why don't he manufacturers just stop at the optimal F number?

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8 Feb 2012 - 9:09 PM

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discreetphoton
discreetphoton Site Moderator 93443 forum postsdiscreetphoton vcard United Kingdom20 Constructive Critique Points
8 Feb 2012 - 9:10 PM

because sometimes a photo matters so much more than sharpness Smile

danfrier
danfrier  2 England
8 Feb 2012 - 9:14 PM

But what situation would you need a smaller F stop than the one that gives the sharpest image? I am confused Sad

Sooty_1
Sooty_1 Critique Team 41177 forum posts United Kingdom196 Constructive Critique Points
8 Feb 2012 - 9:26 PM

When you say the optimal f/ stop, I take it you mean the sharpest for the lens in question? There is no f/ stop that gives front to back sharpness in all situations.
At f/22 you might have a large depth of field, but not all the image is "in focus", only a particular zone of it, and the closer the focussing point is to the camera, the smaller the depth of field is.
Some lenses go as small as f/64!

keith selmes
8 Feb 2012 - 11:21 PM

Some of mine go to f/90

Then there are the pinholes, f stops in the hundreds

Sooty_1
Sooty_1 Critique Team 41177 forum posts United Kingdom196 Constructive Critique Points
8 Feb 2012 - 11:30 PM


Quote: Some of mine go to f/90

D'oh! A couple of mine do too!! My project pinhole 6x6 folder has an effective aperture of f/235 or so.

keith selmes
8 Feb 2012 - 11:33 PM


Quote: what situation would you need a smaller F stop than the one that gives the sharpest image?

where depth is more important than sharpness. e.g. for some macro work, there's a trade off really.

sharpness isn't everything anyway. here's one of my pinholes, some people like it, http://therationalacademy.bandcamp.com/album/pacific-rope-2

JohnParminter
8 Feb 2012 - 11:36 PM

f/2.8 to allow as much light in as possible or a fast shutter speed or shallow DOF. f/32 to achieve slowest shutter speed without using filters, for example.

You are given choice.

The combination of ISO, aperture and shutter speed produces an appropriate exposure.

The choice of aperture and shutter speed are chosen on your creative intent, sometimes outside of the sweetest apertures of the particular lens.

Last Modified By JohnParminter at 8 Feb 2012 - 11:36 PM
User_Removed
8 Feb 2012 - 11:39 PM


Quote: Why don't he manufacturers just stop at the optimal F number?

A few reasons like above, also say you wanted to do a long exposure effect like smokey water or traffic trails and your lens stopped at f11 you wouldn't be able to do as long an exposure as you would if the lens went to f22

timbo
timbo  11591 forum posts United Kingdom
9 Feb 2012 - 12:43 PM

If you shot everything at the optimal f number you would soon tire of very samey images. Photography is more art than science, which is why cameras such as pinhole, lomo and Holga are still so popular.

66tricky
66tricky  7742 forum posts Scotland
9 Feb 2012 - 4:40 PM

So the dust bunnies can become more visible..Tongue

LenShepherd
LenShepherd e2 Member 62434 forum postsLenShepherd vcard United Kingdom
9 Feb 2012 - 8:41 PM

As a rule of thumb around 80% of lenses are about 20% less sharp either wide open or at minimum aperture than at f8 or f11.
As a rule of thumb around 80% of sensors loose up to 50% of their resolution by their highest ISO setting.
As rule of thumb sensors/lens loose up to 50% of resolution in very low contrast light.
All this aside I see some first class images at f1.4, some at f16, some in low contrast light, and some at a very high ISO Wink

mikehit
mikehit  46165 forum posts United Kingdom9 Constructive Critique Points
9 Feb 2012 - 9:03 PM

As a matter of interest, how do you measure '50% resolution'?

MeanGreeny
9 Feb 2012 - 9:39 PM


Quote: As a matter of interest, how do you measure '50% resolution'?

50% resolution is 'resol' or 'ution' or 'rslto' or 'eouin' or.......... well, you get my drift..........

Last Modified By MeanGreeny at 9 Feb 2012 - 9:40 PM
mikehit
mikehit  46165 forum posts United Kingdom9 Constructive Critique Points
9 Feb 2012 - 9:57 PM

LOL. There's always one.....Smile

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