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Canon G Cameras: Defraction at f/8 ????

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Scott Fleming

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A knowledgable and helpful individual here on the forum posted a helpful post regarding DOF on G3s or G5s. (thanks by the way) In it he explained using manual focus presets for obtaining good DOF and thus obviating autofocus lag. He mentioned something about not using f8 for fear of defraction.

Anyone sure about this? I understand defraction regarding LF gear but know nothing about it when it comes to these little whiz bang G5 lenses. Please help. Thanks

Scott Fleming
--
Too many cameras ... not nearly enough photography.
 
Also, most people say that you should use f/5.6 because it is the sweet spot of the G3/G5 lens.
 
Scott W said:
Also, most people say that you should use f/5.6 because it is the
sweet spot of the G3/G5 lens.
Click to expand...
It's a YMMV thing - personally I can't, with the naked eye see any problems with falling image quality at f8 with the G3- I don't doubt that they are there but they don't seem to show to any significant extent onscreen or on my prints. And I need f8 to get good depth of field for stuff like macro shots with close-up lenses and landscapes - so I use the full range of the apertures. Outdoors I am much more likely to avoid anything wider than f5.6 (rather than narrower) as, under Australian lighting conditions and wiht the sort of shots that I take I find purple fringing to be more of an issue than diffraction.
susan S
 
Let us pass beyond what the monitor shows. Please do not take offense but it means less than nothing to me. I shoot to print. Being lazy minded I have never even attempted to learn the math involving CoC, DOF and HFD. I just take the shortcuts. The fact that we are dealing with a zoom lens here and an itsy bitsy sensor .... well, its beyond Greek to me. I mean I know the Greek alphabet. I cannnot comprehend the math needed to prove someone's assertions regarding the complex photo-geometry involved here. So, one of you geniuses out there ( I mean that in the most respectful way ) ... Are we getting noticible refraction degradation if printing at the limits of the G5. Say 8 1/2 by 11 ?

Thank you and Good Light,

--
Too many cameras ... not nearly enough photography.
 
Scott Fleming said:
Let us pass beyond what the monitor shows. Please do not take
offense but it means less than nothing to me. I shoot to print.
Being lazy minded I have never even attempted to learn the math
involving CoC, DOF and HFD. I just take the shortcuts. The fact
that we are dealing with a zoom lens here and an itsy bitsy sensor
.... well, its beyond Greek to me. I mean I know the Greek
alphabet. I cannnot comprehend the math needed to prove someone's
assertions regarding the complex photo-geometry involved here. So,
one of you geniuses out there ( I mean that in the most respectful
way ) ... Are we getting noticible refraction degradation if
printing at the limits of the G5. Say 8 1/2 by 11 ?

Thank you and Good Light,

--
Too many cameras ... not nearly enough photography.
Click to expand...
Well to restate more precisely what I hinted at above - with my G3 I have printed out 8.5x11s which show no evidence that I can see a problem with f8 rel to f5.6 - the only difference I can detect is just a rather larger depth of field - sometimes I want it and sometimes I don't. Of course I don't have the world's greatest printer and it is possible that more fussy types with better equipment can see a difference. What I would suggest might help is conducting a test with your own equipment. Set up some well exposed shots, using various apertures of the sort of scene that you usually like to take using a tripod, correctly focussed. Then print off test strips from each shot onto one sheet of A4 highquality photopaper suitable for your printer - (I've used Elements to set up a document with strips from each image in the past) Examine wth a magnifying glass and see if one looks better than the others....that way you should be able to satisfy yourself whether there is enough of a difference, with your printer and the sort of images that you take, to worry about.

(For me wide apertures are the problem - the effect of purple fringing at f2.8 or even f4 at wide angle if there is even a hint of overexposure of light areas next to dark contrast shows up very clearly on both screen and print with a lot of my outdoor shots. Too much bright sunshine and contrast here in Aus, even in winter! )
Susan S
 
Rybber said:
This is where it all comes from. It's called hyperfocal technique.

http://www.marcjutras.com/ehyperfocal.html

--
... Greets, Rybber
http://www.pbase.com/rybber
Click to expand...
Dont know if this interests you as its done using a canona70, but I setup my camera on a tripod, and went through every fstop from 5.6---> 8 from memory, each fstop has 1 photo set at infinity focus, and 1 photo letting the camera do it automatically.

the photos are all untouched except for cropping in photoshop so I could get the multiple shots on one picture, and are here if ur interested

http://danielsa70.instantlogic.com/itemDetail.ilx?idContainer= {988C0BF4-3E0B-45CD-870F-6048B51DFD1E}&page=37
 
The original question was about diffraction and why digital cameras are limited to about f/8

Diffraction means that an image can never be perfectly sharp. That would mean that a light ray is brought to a spot focus. In fact, the diffraction spot size is 2.44*lambDA*f/# (in the absence of optical abberations). For green wavelength = 550nm, then the diffraction spot size is 10.7µm at f/8. The G3 has pixel size of 3.1µm and G5 has 2.8µm. Clearly, the "single pixel" resolution will be affected by diffraction at this end.

In reality, things are a little more complicated by the RGB interpolation used to define an image pixel. In effect, the interpolated pixel size is bigger than a single CCD pixel and there is overlap between them.

MarkS
--
http://www.pbase.com/mark_ds
 
Scott Fleming said:
A knowledgable and helpful individual here on the forum posted a
helpful post regarding DOF on G3s or G5s. (thanks by the way) In
it he explained using manual focus presets for obtaining good DOF
and thus obviating autofocus lag. He mentioned something about not
using f8 for fear of defraction.

Anyone sure about this? I understand defraction regarding LF gear
but know nothing about it when it comes to these little whiz bang
G5 lenses. Please help. Thanks

Scott Fleming
--
Too many cameras ... not nearly enough photography.
Click to expand...
 
Mark,

Is the defraction size depndent on focal length? The equations make it look like it doesn't .... Then 35mm DSLR ought to have the same limits, but with pixels that are 6 times larger in area, and 2.5x in linear dimensions, F8 for a Point & Shoot is equivent to F24 for a DSLR.

And at F8, the G3 is 4x over the limit. Because of the interpolation, 2x larger than the pixel size should be fine. So, perhaps F4 would be a better targert FStop for a small sensor, and F10 for a DSLR????
  • Shel
just curious
MarkS said:
The original question was about diffraction and why digital cameras
are limited to about f/8

Diffraction means that an image can never be perfectly sharp. That
would mean that a light ray is brought to a spot focus. In fact,
the diffraction spot size is 2.44*lambDA*f/# (in the absence of
optical abberations). For green wavelength = 550nm, then the
diffraction spot size is 10.7µm at f/8. The G3 has pixel size of
3.1µm and G5 has 2.8µm. Clearly, the "single pixel" resolution will
be affected by diffraction at this end.

In reality, things are a little more complicated by the RGB
interpolation used to define an image pixel. In effect, the
interpolated pixel size is bigger than a single CCD pixel and there
is overlap between them.

MarkS
--
http://www.pbase.com/mark_ds
Click to expand...
 
Scott Fleming said:
A knowledgable and helpful individual here on the forum posted a
helpful post regarding DOF on G3s or G5s. (thanks by the way) In
it he explained using manual focus presets for obtaining good DOF
and thus obviating autofocus lag. He mentioned something about not
using f8 for fear of defraction.

Anyone sure about this? I understand defraction regarding LF gear
but know nothing about it when it comes to these little whiz bang
G5 lenses. Please help. Thanks
Click to expand...
By the way, it's DIFFRACTION not defraction.. and yes it can be a factor at f8 with these tiny digicam lenses.

Having said that, I have never noticed any ill effects from using f8 on my A70 (or either of my Casios for that matter). I do see 'star' effects at small apertures like that on bright lights at night due to the six bladed iris diaphragm though.

Miscellaneous A70 pics
http://mywebpages.comcast.net/bdolson/a70/a70.html
Sincerely, Bob the Printer
 
Scott Fleming said:
Let us pass beyond what the monitor shows. Please do not take
offense but it means less than nothing to me. I shoot to print.
Being lazy minded I have never even attempted to learn the math
Click to expand...
There is nothing to be seen on a print that can't be seen on a monitor at 1:1 pixel ratio though.. No math needed! You make it sound a lot more complex than it really is....

Miscellaneous A70 pics
http://mywebpages.comcast.net/bdolson/a70/a70.html
Sincerely, Bob the Printer
 
The tiny leses used on these cameras are more prone to diffraction so for the best possible image you might want to avoid the smallest apertures when possible. Personally I use f8 all the time when I need the depth of field, and I haven't noticed difrraction efects - certainly none that would discourage me from using the setting when necessary.
Scott Fleming said:
A knowledgable and helpful individual here on the forum posted a
helpful post regarding DOF on G3s or G5s. (thanks by the way) In
it he explained using manual focus presets for obtaining good DOF
and thus obviating autofocus lag. He mentioned something about not
using f8 for fear of defraction.

Anyone sure about this? I understand defraction regarding LF gear
but know nothing about it when it comes to these little whiz bang
G5 lenses. Please help. Thanks

Scott Fleming
--
Too many cameras ... not nearly enough photography.
Click to expand...
 
The diffraction effect depends on focal length and lens diameter. However, both of these already enter into the f/# definition so they don't have to be considered again.

If you compare G3 to DSLR, on a 10D the pixel size is about 8.2µm so f/21 would give about the same diffraction effect as f/8 on G3.

Diffraction effects don't give rise to "star" images as far as I know, simply to some blurring at the pixel level. I imagine it would be very hard to see on a G3 at f/8 although someone pointed out that the lens sharpness is best at f/5.6.

--
http://www.pbase.com/mark_ds
 
I will never spell diffraction defraction again. I will never spell diffraction defraction again. I will never spell diffraction defraction again. I will never spell diffraction defraction again. I will never spell diffraction defraction again. I will never spell diffraction defraction again. I will never spell diffraction defraction again. ............
(I should do this with pen and paper. Cutting and pasting is cheating.)
 
You might see it as a very slight loss of resolution on a resolution test chart or in the MTF curves for the lens, but, practically, the effect in everyday pictures should be minimal. At f/11 or f/16 it would become more pronounced, hence f/8 or occasionally f/11 being the smallest aperature offered, vs. f/16 to f/32 often seen on moderately wide to moderately telephoto 35mm SLR optics, and even smaller f/numbers on longer F.L. medium and large format optics. All else being equal (which it rarely ever is) you would be better to shoot at perhaps f/4 to f/5.6, but I wouldn't loose any sleep over it if wider or smaller was needed.
Bob Dolson said:
Scott Fleming said:
A knowledgable and helpful individual here on the forum posted a
helpful post regarding DOF on G3s or G5s. (thanks by the way) In
it he explained using manual focus presets for obtaining good DOF
and thus obviating autofocus lag. He mentioned something about not
using f8 for fear of defraction.

Anyone sure about this? I understand defraction regarding LF gear
but know nothing about it when it comes to these little whiz bang
G5 lenses. Please help. Thanks
Click to expand...
By the way, it's DIFFRACTION not defraction.. and yes it can be a
factor at f8 with these tiny digicam lenses.

Having said that, I have never noticed any ill effects from using
f8 on my A70 (or either of my Casios for that matter). I do see
'star' effects at small apertures like that on bright lights at
night due to the six bladed iris diaphragm though.

Miscellaneous A70 pics
http://mywebpages.comcast.net/bdolson/a70/a70.html
Sincerely, Bob the Printer
Click to expand...
 
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