High F-Stop values: Does it affect quality?

[James Sarantis]

There are times when I want to get all of the field of view in sharp focus. I'm at work right now otherwise I'd do my own tests but rule-of-thumb, should I just go f22-32 or whatever the hightest f-value is in order to insure I get it in focus, or will this somehow affect the image quality. I have the 28-135 IS and the 50 1.4 lenses.

Thanks for your future responses.

 

[Tariq]

Most lenses perform their best(sharpest) at the middle F stops, say somewhere in the range of F8-F11.

Tariq

There are times when I want to get all of the field of view in
sharp focus. I'm at work right now otherwise I'd do my own tests
but rule-of-thumb, should I just go f22-32 or whatever the hightest
f-value is in order to insure I get it in focus, or will this
somehow affect the image quality. I have the 28-135 IS and the 50
1.4 lenses.

Thanks for your future responses.

 

[John Petter Reinertsen]

There are times when I want to get all of the field of view in
sharp focus. I'm at work right now otherwise I'd do my own tests
but rule-of-thumb, should I just go f22-32 or whatever the hightest
f-value is in order to insure I get it in focus, or will this
somehow affect the image quality. I have the 28-135 IS and the 50
1.4 lenses.

Thanks for your future responses.

Dust in front of the CMOS will show up from f16 and up. Clean the glass in front of the CMOS before you shoot.

Good luck!
-John Petter.

 

[Mikhail Bogdanov]

James,

It all depends on the specific lens (and sometimes, not often though, on the specific sample of the same lens). For example, my 28-70/L is sharp as a tack from f2.8 to f22, and when I need maximum DOF I just stop it all the way down. On the other hand, my 100-400IS at 400mm is loosing some sharpness (and also I see some light fall off)when stopped down more than f19-22 and performs the best between f8 and f16. 50/1.4 in my experience behaves the same way 28-70/L does. You probably would like to run some simple tests and see how your lenses perform.
Regards

 

[Ron Parr]

There are times when I want to get all of the field of view in
sharp focus. I'm at work right now otherwise I'd do my own tests
but rule-of-thumb, should I just go f22-32 or whatever the hightest
f-value is in order to insure I get it in focus, or will this
somehow affect the image quality. I have the 28-135 IS and the 50
1.4 lenses.

At very small apertures, diffraction effects will start softening your images some.

--
Ron Parr
FAQ: http://www.cs.duke.edu/~parr/photography/faq.html
Gallery: http://www.pbase.com/parr/

 

[Karl Guttag]

Yes image quality goes down at higher F-number. The main problem is "diffraction" which is the bending of light when going through a slit. Lenses generally peak in sharpness at F8 and start going down.

With a smaller imager of the D30/60 you gain about 1.6X in DoF for the same Field of view (ie., assuming you use a 1.6X shorter Focal length).

Rather than just cranking the F-number up, it is a good idea to know about the concept of Hyperfocal focusing. In most cases you will find that you don't have to go all the way to F22 to get the DoF you want.

The Hyperfocal distance, the focus point at which everything from that point to infinity behind the camera and from that point to 1/2 the distance to the camera will be in "acceptable focus" is pretty simple:

h = f* 2 / (A * c)

f = the focal length (real not "equivalent')
A= aperture value (f-number)

c = circle of confusion (CoC = .016mm is a good number to use for the D30/60 if you don't want to get into the details of CoC).

Note everything has to be in the same units (usually easiest to figure in millimeters and convert).

Thus lets say you have a 50mm lens at F16

h = 50* 2 / (16 * 0.016) = 2500 / 0.256 = 9765mm = 9.765M or 32 feet.

Thus if you set the focus for 32 feet, everything from 16 feet onward would be in focus.

Lets say you used F22 instead.

h = 22.66 feet and thus if you focused at 22.66, then everything from 11.33 feet onward would be in focus.

Note from the equation that h is proportional to the F-number. So if you go from F16 to F22 then h only goes down by 1.4X.

Note that what really matters is how close you want to focus and how wide an focal length (f) you use. A wide angle lens has a dramatic effect since h varies with the SQUARE of f. With a 17mm wide angle at F16, h is only 3 Feet and thus if you focus at 3 feet, everything from 1.5 feet to infinity will be in focus.

If you want to play around a bit with this, I highly recommend downloading fCalc from http://www.tangentsoft.net/ . Note you need to change the CoC to 0.016mm (or thereabouts) since the D30/60 sensor is 1.6X smaller (this value is about 1.6X smaller than fCalc defaults to for 35mm film).

There are times when I want to get all of the field of view in
sharp focus. I'm at work right now otherwise I'd do my own tests
but rule-of-thumb, should I just go f22-32 or whatever the hightest
f-value is in order to insure I get it in focus, or will this
somehow affect the image quality. I have the 28-135 IS and the 50
1.4 lenses.

Thanks for your future responses.

--
Karl

 

[James Sarantis]

James,
It all depends on the specific lens (and sometimes, not often
though, on the specific sample of the same lens). For example, my
28-70/L is sharp as a tack from f2.8 to f22, and when I need
maximum DOF I just stop it all the way down. On the other hand, my
100-400IS at 400mm is loosing some sharpness (and also I see some
light fall off)when stopped down more than f19-22 and performs the
best between f8 and f16. 50/1.4 in my experience behaves the same
way 28-70/L does. You probably would like to run some simple tests
and see how your lenses perform.
Regards

So from what I'm gathering here is that I'll lose sharpness and maybe get some light fall-off. I guess I'm more concerned about the sharpness factor. I'll do some tests. I plan on using my 28-135 IS lens the most. I'm sure it would be affected more than my 50 1.4 lens would be at this higher values.

Appreciate your comments

 

[James Sarantis]

Bingo! This is exactly what I was looking for. Thanks for your succinct explanation Karlg. I'll download fCalc from that site and tinker around with it. I want to get to a point where it's all second nature to me with each individual lens I have and will get.

Thanks again

With a smaller imager of the D30/60 you gain about 1.6X in DoF for
the same Field of view (ie., assuming you use a 1.6X shorter Focal
length).

Rather than just cranking the F-number up, it is a good idea to
know about the concept of Hyperfocal focusing. In most cases you
will find that you don't have to go all the way to F22 to get the
DoF you want.

The Hyperfocal distance, the focus point at which everything from
that point to infinity behind the camera and from that point to 1/2
the distance to the camera will be in "acceptable focus" is pretty
simple:

h = f* 2 / (A * c)

f = the focal length (real not "equivalent')
A= aperture value (f-number)
c = circle of confusion (CoC = .016mm is a good number to use for
the D30/60 if you don't want to get into the details of CoC).

Note everything has to be in the same units (usually easiest to
figure in millimeters and convert).

Thus lets say you have a 50mm lens at F16

h = 50* 2 / (16 * 0.016) = 2500 / 0.256 = 9765mm = 9.765M or 32 feet.

Thus if you set the focus for 32 feet, everything from 16 feet
onward would be in focus.

Lets say you used F22 instead.

h = 22.66 feet and thus if you focused at 22.66, then everything
from 11.33 feet onward would be in focus.

Note from the equation that h is proportional to the F-number. So
if you go from F16 to F22 then h only goes down by 1.4X.

Note that what really matters is how close you want to focus and
how wide an focal length (f) you use. A wide angle lens has a
dramatic effect since h varies with the SQUARE of f. With a 17mm
wide angle at F16, h is only 3 Feet and thus if you focus at 3
feet, everything from 1.5 feet to infinity will be in focus.

If you want to play around a bit with this, I highly recommend
downloading fCalc from http://www.tangentsoft.net/ . Note you need
to change the CoC to 0.016mm (or thereabouts) since the D30/60
sensor is 1.6X smaller (this value is about 1.6X smaller than fCalc
defaults to for 35mm film).

There are times when I want to get all of the field of view in
sharp focus. I'm at work right now otherwise I'd do my own tests
but rule-of-thumb, should I just go f22-32 or whatever the hightest
f-value is in order to insure I get it in focus, or will this
somehow affect the image quality. I have the 28-135 IS and the 50
1.4 lenses.

Thanks for your future responses.

--
Karl

 

[Thomas Gardner]

Ron Parr wrote:

Hi Ron. Haven't had a chance to appologize for the rancor. So here's my apology for the rancor. I'm sorry

At very small apertures, diffraction effects will start softening
your images some.

From what I've read here on DPReview's forums, the defraction effect has to do with the size of the pixels of the camera. In the case of the D30 the diffraction effect kicks in at f/22 and the D60's pixels, being half the size of the D30's pixels, diffraction for the D60 kicks in at f/11.

Hope this helps.

 

[James Sarantis]

Gee, I don't like the sound of that. I've got the D60.

At very small apertures, diffraction effects will start softening
your images some.

From what I've read here on DPReview's forums, the defraction
effect has to do with the size of the pixels of the camera. In the
case of the D30 the diffraction effect kicks in at f/22 and the
D60's pixels, being half the size of the D30's pixels, diffraction
for the D60 kicks in at f/11.

Hope this helps.

 

[Thomas Gardner]

Gee, I don't like the sound of that. I've got the D60.

I know, it leaves you feeling like you "got drawn up short":-o

I have the D30 but would like to have the D60 for all the small improvements, including the additional pixels, even if I do get shorted out of an f/stop worth of DoF. Most of my close-up images are captured in the f/8 - f/11 range.

 

[Ron Parr]

Hi Thomas,

Hi Ron. Haven't had a chance to appologize for the rancor. So
here's my apology for the rancor. I'm sorry

I'm happy to put it behind us. There are better ways for us to use our time than to be fighting with each other.

At very small apertures, diffraction effects will start softening
your images some.

From what I've read here on DPReview's forums, the defraction
effect has to do with the size of the pixels of the camera. In the
case of the D30 the diffraction effect kicks in at f/22 and the
D60's pixels, being half the size of the D30's pixels, diffraction
for the D60 kicks in at f/11.

The size of the the pixels will affect your ability to pick up the diffraction effects, but it's fundamentally an optical effect. You'll notice diffraction effects with film too. Think of it this way: If you got tighter grain film, you'd be better able to notice tiny optical effects too, but this isn't a reason to avoid better film.

The multiplier of the D30/D60's sensor size means that you'll notice diffraction effects 1.6X sooner than you would with film. So, if you notice diffraction effects with film at 8x10 for a particular f-stop, you'll noticed it at 4x6 - 5x7 with the D60. The only reasons this wasn't more of an issue for the D30 is that the resolution was low enough that it couldn't detect minor softening from diffraction. The very worst thing that can happen with small apertures on the D60 is that things might soften up to the point where the resolution is no better than what the D30 would get on the same shot.

--
Ron Parr
FAQ: http://www.cs.duke.edu/~parr/photography/faq.html
Gallery: http://www.pbase.com/parr/

 

[Karl Guttag]

James,

Below is a table of hyperfocal distance for a D30/DF60. The first table is in Meters and the second is in feet. Remember, you focus at the Hyperfocal distance and then you get "acceptable focus" to about way to half way to the camera from the focus point.

http://www.fototime.com/ {A957EC38-20A8-4AF4-A888-751DBE6A2035} picture.JPG

Another interesting fact is that DoF is largely a function of the FoV at the focus point and the F-number, INDEPENDENT (to a large degree) of the Focal Length. The Following table I find very handy for getting an estimate of the DoF. All you have to do is get a reasonable estimate of the height at the focus point and read off the F-number for the desired DoF. This approximation falls apart near the Hyperfocal distance and the Gray areas of the chart are where the table gets pretty inaccurate with a change in focal length.

http://www.fototime.com/ {D6DE395C-A0C9-4E3F-B2A6-CF0AD316A0AE} picture.JPG

Thanks again

With a smaller imager of the D30/60 you gain about 1.6X in DoF for
the same Field of view (ie., assuming you use a 1.6X shorter Focal
length).

Rather than just cranking the F-number up, it is a good idea to
know about the concept of Hyperfocal focusing. In most cases you
will find that you don't have to go all the way to F22 to get the
DoF you want.

The Hyperfocal distance, the focus point at which everything from
that point to infinity behind the camera and from that point to 1/2
the distance to the camera will be in "acceptable focus" is pretty
simple:

h = f* 2 / (A * c)

f = the focal length (real not "equivalent')
A= aperture value (f-number)
c = circle of confusion (CoC = .016mm is a good number to use for
the D30/60 if you don't want to get into the details of CoC).

Note everything has to be in the same units (usually easiest to
figure in millimeters and convert).

Thus lets say you have a 50mm lens at F16

h = 50* 2 / (16 * 0.016) = 2500 / 0.256 = 9765mm = 9.765M or 32 feet.

Thus if you set the focus for 32 feet, everything from 16 feet
onward would be in focus.

Lets say you used F22 instead.

h = 22.66 feet and thus if you focused at 22.66, then everything
from 11.33 feet onward would be in focus.

Note from the equation that h is proportional to the F-number. So
if you go from F16 to F22 then h only goes down by 1.4X.

Note that what really matters is how close you want to focus and
how wide an focal length (f) you use. A wide angle lens has a
dramatic effect since h varies with the SQUARE of f. With a 17mm
wide angle at F16, h is only 3 Feet and thus if you focus at 3
feet, everything from 1.5 feet to infinity will be in focus.

If you want to play around a bit with this, I highly recommend
downloading fCalc from http://www.tangentsoft.net/ . Note you need
to change the CoC to 0.016mm (or thereabouts) since the D30/60
sensor is 1.6X smaller (this value is about 1.6X smaller than fCalc
defaults to for 35mm film).

There are times when I want to get all of the field of view in
sharp focus. I'm at work right now otherwise I'd do my own tests
but rule-of-thumb, should I just go f22-32 or whatever the hightest
f-value is in order to insure I get it in focus, or will this
somehow affect the image quality. I have the 28-135 IS and the 50
1.4 lenses.

Thanks for your future responses.

--
Karl

--
Karl