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Dudley Hanks 11-04-2009 07:17 AM

small aperture test
 

I've heard a lot about how the cropped sensor cameras are defraction limited
to around f/8 - f/11, so I thought I'd see what kind of an image my XSi puts
out at a small aperture.

I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22,
with a shutter speed of 1 sec.

How did it turn out?

http://www.snaps.blind-apertures.ca/...erPortrait.jpg (quick
download)

http://www.snaps.blind-apertures.ca/...raitWinter.jpg (full
size)

Take Care,
Dudley



David J Taylor 11-04-2009 07:32 AM

Re: small aperture test
 
"Dudley Hanks" <> wrote in message news:4U9Im.50459$Db2.29545@edtnps83...
>
> I've heard a lot about how the cropped sensor cameras are defraction
> limited to around f/8 - f/11, so I thought I'd see what kind of an image
> my XSi puts out at a small aperture.
>
> I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22,
> with a shutter speed of 1 sec.
>
> How did it turn out?
>
> http://www.snaps.blind-apertures.ca/...erPortrait.jpg
> (quick download)
>
> http://www.snaps.blind-apertures.ca/...raitWinter.jpg (full
> size)
>
> Take Care,
> Dudley


Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I
loathe), so there could be some diffraction visible, but I'm also not
convinced that the subject didn't move within the 1 second exposure!

Cheers,
David


Dudley Hanks 11-04-2009 07:59 AM

Re: small aperture test
 

"David J Taylor"
<david-taylor@blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in
message news:t6aIm.1501$Ym4.551@text.news.virginmedia.com. ..
> "Dudley Hanks" <> wrote in message news:4U9Im.50459$Db2.29545@edtnps83...
>>
>> I've heard a lot about how the cropped sensor cameras are defraction
>> limited to around f/8 - f/11, so I thought I'd see what kind of an image
>> my XSi puts out at a small aperture.
>>
>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22,
>> with a shutter speed of 1 sec.
>>
>> How did it turn out?
>>
>> http://www.snaps.blind-apertures.ca/...erPortrait.jpg (quick
>> download)
>>
>> http://www.snaps.blind-apertures.ca/...raitWinter.jpg (full
>> size)
>>
>> Take Care,
>> Dudley

>
> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I
> loathe), so there could be some diffraction visible, but I'm also not
> convinced that the subject didn't move within the 1 second exposure!
>
> Cheers,
> David


Thanks, David, I'll try it again with an inanimate object, or a faster
shutter speed.

I suppose, if the test is to be useful, I should also take an equivalent pic
of the subject using a wider aperture so the two images can be compared.

Take Care,
Dudley



David J Taylor 11-04-2009 08:10 AM

Re: small aperture test
 

"Dudley Hanks" <dhanks@blind-apertures.ca> wrote in message
news:DvaIm.50463$Db2.1880@edtnps83...
[]
> Thanks, David, I'll try it again with an inanimate object, or a faster
> shutter speed.
>
> I suppose, if the test is to be useful, I should also take an equivalent
> pic of the subject using a wider aperture so the two images can be
> compared.
>
> Take Care,
> Dudley


Indeed, yes. Tripod and very careful focussing come to mind. While the
degradation due to diffraction at f/22 is noticeable with careful
inspection, you probably wouldn't notice with normal use - just sharpen a
little more. Diffraction on small sensor cameras is one reason why some
of them are limited to f/8 or f/11 as the smallest aperture.

Cheers,
David


Ofnuts 11-04-2009 10:49 AM

Re: small aperture test
 
David J Taylor wrote:
>
> "Dudley Hanks" <dhanks@blind-apertures.ca> wrote in message
> news:DvaIm.50463$Db2.1880@edtnps83...
> []
>> Thanks, David, I'll try it again with an inanimate object, or a faster
>> shutter speed.
>>
>> I suppose, if the test is to be useful, I should also take an
>> equivalent pic of the subject using a wider aperture so the two images
>> can be compared.
>>
>> Take Care,
>> Dudley

>
> Indeed, yes. Tripod and very careful focussing come to mind. While the
> degradation due to diffraction at f/22 is noticeable with careful
> inspection, you probably wouldn't notice with normal use - just sharpen
> a little more. Diffraction on small sensor cameras is one reason why
> some of them are limited to f/8 or f/11 as the smallest aperture.
>


Some of them haven't even got diaphragm and the "diaphragm" is simulated
with a neutral filter.

--
Bertrand

Rich 11-04-2009 03:39 PM

Re: small aperture test
 
On Nov 4, 2:17*am, "Dudley Hanks" <dha...@blind-apertures.ca> wrote:
> I've heard a lot about how the cropped sensor cameras are defraction limited
> to around f/8 - f/11, so I thought I'd see what kind of an image my XSi puts
> out at a small aperture.
>
> I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22,
> with a shutter speed of 1 sec.
>
> How did it turn out?
>
> http://www.snaps.blind-apertures.ca/...erPortrait.jpg*(quick
> download)
>
> http://www.snaps.blind-apertures.ca/...raitWinter.jpg*(full
> size)
>
> Take Care,
> Dudley


With an APS-C sensor, you would lose about 1/2 your resolution
(provided the lens is good) going from f8 to f22.

Chris Malcolm 11-04-2009 05:49 PM

Re: small aperture test
 
Dudley Hanks <dhanks@blind-apertures.ca> wrote:

> "David J Taylor"
> <david-taylor@blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in
> message news:t6aIm.1501$Ym4.551@text.news.virginmedia.com. ..
>> "Dudley Hanks" <> wrote in message news:4U9Im.50459$Db2.29545@edtnps83...
>>>
>>> I've heard a lot about how the cropped sensor cameras are defraction
>>> limited to around f/8 - f/11, so I thought I'd see what kind of an image
>>> my XSi puts out at a small aperture.
>>>
>>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22,
>>> with a shutter speed of 1 sec.
>>>
>>> How did it turn out?
>>>
>>> http://www.snaps.blind-apertures.ca/...erPortrait.jpg (quick
>>> download)
>>>
>>> http://www.snaps.blind-apertures.ca/...raitWinter.jpg (full
>>> size)
>>>
>>> Take Care,
>>> Dudley

>>
>> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I
>> loathe), so there could be some diffraction visible, but I'm also not
>> convinced that the subject didn't move within the 1 second exposure!
>>
>> Cheers,
>> David


> Thanks, David, I'll try it again with an inanimate object, or a faster
> shutter speed.


> I suppose, if the test is to be useful, I should also take an equivalent pic
> of the subject using a wider aperture so the two images can be compared.


The diffraction limit of aperture is usually taken to be the last
aperture in a decreasing series of sharper apertures, i.e., stopping
down further makes the image softer because of diffraction. But that's
not a fixed aperture, it depends on such things as the exact sensor
pixel size (or crop factor) not just the nominal "1.5", on the
resolution of the lens, and whether you're looking at the centre of
the image or the edges or some compromise between the two. Why
should it depend on those? Because the point at which an extra stop's
worth of diffraction softening becomes larger than how much other
kinds of lens aberration are being improved by stopping down obviously
will depend on the size of those other errors. In other words better
lenses will have larger sharpest apertures.

I find for example on my Sony A350 that my general purpose zoom is
usually sharpest at f8, but at its soft extremes that becomes f11, and
my 50mm prime is sharpest at f5.6.

This can only be established for your camera and each of your lenses
by taking a comparative series of shots while varying the aperture. On
zooms it may change with focal length.

--
Chris Malcolm

Dudley Hanks 11-04-2009 07:20 PM

Re: small aperture test
 

"Chris Malcolm" <cam@holyrood.ed.ac.uk> wrote in message
news:7ldt5gF3cimtaU1@mid.individual.net...
> Dudley Hanks <dhanks@blind-apertures.ca> wrote:
>
>> "David J Taylor"
>> <david-taylor@blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in
>> message news:t6aIm.1501$Ym4.551@text.news.virginmedia.com. ..
>>> "Dudley Hanks" <> wrote in message
>>> news:4U9Im.50459$Db2.29545@edtnps83...
>>>>
>>>> I've heard a lot about how the cropped sensor cameras are defraction
>>>> limited to around f/8 - f/11, so I thought I'd see what kind of an
>>>> image
>>>> my XSi puts out at a small aperture.
>>>>
>>>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at
>>>> f/22,
>>>> with a shutter speed of 1 sec.
>>>>
>>>> How did it turn out?
>>>>
>>>> http://www.snaps.blind-apertures.ca/...erPortrait.jpg
>>>> (quick
>>>> download)
>>>>
>>>> http://www.snaps.blind-apertures.ca/...raitWinter.jpg
>>>> (full
>>>> size)
>>>>
>>>> Take Care,
>>>> Dudley
>>>
>>> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I
>>> loathe), so there could be some diffraction visible, but I'm also not
>>> convinced that the subject didn't move within the 1 second exposure!
>>>
>>> Cheers,
>>> David

>
>> Thanks, David, I'll try it again with an inanimate object, or a faster
>> shutter speed.

>
>> I suppose, if the test is to be useful, I should also take an equivalent
>> pic
>> of the subject using a wider aperture so the two images can be compared.

>
> The diffraction limit of aperture is usually taken to be the last
> aperture in a decreasing series of sharper apertures, i.e., stopping
> down further makes the image softer because of diffraction. But that's
> not a fixed aperture, it depends on such things as the exact sensor
> pixel size (or crop factor) not just the nominal "1.5", on the
> resolution of the lens, and whether you're looking at the centre of
> the image or the edges or some compromise between the two. Why
> should it depend on those? Because the point at which an extra stop's
> worth of diffraction softening becomes larger than how much other
> kinds of lens aberration are being improved by stopping down obviously
> will depend on the size of those other errors. In other words better
> lenses will have larger sharpest apertures.
>
> I find for example on my Sony A350 that my general purpose zoom is
> usually sharpest at f8, but at its soft extremes that becomes f11, and
> my 50mm prime is sharpest at f5.6.
>
> This can only be established for your camera and each of your lenses
> by taking a comparative series of shots while varying the aperture. On
> zooms it may change with focal length.
>
> --
> Chris Malcolm


Thanks, Chris, that's good info to have.

This is a pretty cheap lens, and I think its a bit soft to begin with.

I've always been a fan of mildly soft portraits, and this lens has worked
well for that purpose. But its also given me a few nice and sharp pics as
well.

It'll be interesting to see how it performs across its full range...

Take Care,
Dudley



Better Info 11-04-2009 10:47 PM

Re: small aperture test
 
On 4 Nov 2009 17:49:36 GMT, Chris Malcolm <cam@holyrood.ed.ac.uk> wrote:

>Dudley Hanks <dhanks@blind-apertures.ca> wrote:
>
>> "David J Taylor"
>> <david-taylor@blueyonder.not-this-bit.nor-this.co.uk.invalid> wrote in
>> message news:t6aIm.1501$Ym4.551@text.news.virginmedia.com. ..
>>> "Dudley Hanks" <> wrote in message news:4U9Im.50459$Db2.29545@edtnps83...
>>>>
>>>> I've heard a lot about how the cropped sensor cameras are defraction
>>>> limited to around f/8 - f/11, so I thought I'd see what kind of an image
>>>> my XSi puts out at a small aperture.
>>>>
>>>> I snapped on my 50mm f/1.8 lens and set it up to take a picture at f/22,
>>>> with a shutter speed of 1 sec.
>>>>
>>>> How did it turn out?
>>>>
>>>> http://www.snaps.blind-apertures.ca/...erPortrait.jpg (quick
>>>> download)
>>>>
>>>> http://www.snaps.blind-apertures.ca/...raitWinter.jpg (full
>>>> size)
>>>>
>>>> Take Care,
>>>> Dudley
>>>
>>> Difficult to say, Dudley. Yes, the image isn't "tack sharp" (a term I
>>> loathe), so there could be some diffraction visible, but I'm also not
>>> convinced that the subject didn't move within the 1 second exposure!
>>>
>>> Cheers,
>>> David

>
>> Thanks, David, I'll try it again with an inanimate object, or a faster
>> shutter speed.

>
>> I suppose, if the test is to be useful, I should also take an equivalent pic
>> of the subject using a wider aperture so the two images can be compared.

>
>The diffraction limit of aperture is usually taken to be the last
>aperture in a decreasing series of sharper apertures, i.e., stopping
>down further makes the image softer because of diffraction. But that's
>not a fixed aperture, it depends on such things as the exact sensor
>pixel size (or crop factor) not just the nominal "1.5", on the
>resolution of the lens, and whether you're looking at the centre of
>the image or the edges or some compromise between the two. Why
>should it depend on those? Because the point at which an extra stop's
>worth of diffraction softening becomes larger than how much other
>kinds of lens aberration are being improved by stopping down obviously
>will depend on the size of those other errors. In other words better
>lenses will have larger sharpest apertures.
>
>I find for example on my Sony A350 that my general purpose zoom is
>usually sharpest at f8, but at its soft extremes that becomes f11, and
>my 50mm prime is sharpest at f5.6.
>
>This can only be established for your camera and each of your lenses
>by taking a comparative series of shots while varying the aperture. On
>zooms it may change with focal length.


Your test won't work. Unless the widest aperture of your lens is the very
sharpest, that means that the lens is not of diffraction-limited quality,
the very best there is. If you lose detail at any time that you open up the
lens, then that means the lens is not diffraction-limited. If it's not
diffraction limited you can't tell when diffraction is what is causing the
softening. As in all DSLR glass, the softening you see is due to lenses not
being of diffraction-limited quality, poor lens manufacturing. Usually only
one stop is adequate because the defects are overridden by that particular
aperture stop. Anything above and below it is showing lens-figure defects,
not diffraction problems.


Chris Malcolm 11-05-2009 02:02 AM

Re: small aperture test
 
Better Info <binfo@address.info> wrote:
> On 4 Nov 2009 17:49:36 GMT, Chris Malcolm <cam@holyrood.ed.ac.uk> wrote:


>>The diffraction limit of aperture is usually taken to be the last
>>aperture in a decreasing series of sharper apertures, i.e., stopping
>>down further makes the image softer because of diffraction. But that's
>>not a fixed aperture, it depends on such things as the exact sensor
>>pixel size (or crop factor) not just the nominal "1.5", on the
>>resolution of the lens, and whether you're looking at the centre of
>>the image or the edges or some compromise between the two. Why
>>should it depend on those? Because the point at which an extra stop's
>>worth of diffraction softening becomes larger than how much other
>>kinds of lens aberration are being improved by stopping down obviously
>>will depend on the size of those other errors. In other words better
>>lenses will have larger sharpest apertures.
>>
>>I find for example on my Sony A350 that my general purpose zoom is
>>usually sharpest at f8, but at its soft extremes that becomes f11, and
>>my 50mm prime is sharpest at f5.6.
>>
>>This can only be established for your camera and each of your lenses
>>by taking a comparative series of shots while varying the aperture. On
>>zooms it may change with focal length.


> Your test won't work. Unless the widest aperture of your lens is the very
> sharpest, that means that the lens is not of diffraction-limited quality,
> the very best there is. If you lose detail at any time that you open up the
> lens, then that means the lens is not diffraction-limited.


You've got it back to front. Since diffraction increases as the lens
is stopped because because of the change of proportion of lens area to
lens circumference, the test works for all cases EXCEPT when the
widest aperture is sharpest.

> If it's not
> diffraction limited you can't tell when diffraction is what is causing the
> softening. As in all DSLR glass, the softening you see is due to lenses not
> being of diffraction-limited quality, poor lens manufacturing.


That's true when the aperture is wider than the diffraction limited
aperture, and false when it's smaller. The point you're missing is
that lens aberrations reduce as the lens stops down, because a higher
proportion of the image is coming from less refracted parts of the
lens, but as you stop down the proportion of diffraction increases,
because the diffraction proportion is related to the
area/circumference proportion of the aperture. So in any
non-diffraction-limited lens there will be an aperture where the
improving of lens defects by stopping down is overtaken by the
worsening of diffraction effects.

--
Chris Malcolm


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