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| Diffraction on smaller aperture values |
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Message posted at 07/19/2012, 02:31:23 AM by Parkinsonsniper - member is an admin |
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I believe I can fly. Even if I can't, I will be able to jump higher in the end :))
(This is a mystery for me and I will try to solve it :) even if I can't make it, I will learn many new technics during this voyage.) |
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Message edited at 07/19/2012, 04:43:59 AM by Androniques |
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That's a very constructive point of view, which is the only way to move forward. One has to believe in something, still better to believe in yourself! :-)
Here are two nice articles relevant for this topic:
http://www.luminous-landscape.com/tutorials/understanding-series/u-diffraction.shtml
(visual inspection of diffraction effects done with medium format - note visible blurring at f22 when viewed at 100%!
- would be nice to learn/see the results of the same comparison type, if you intend to do that for your lenses)
http://www.bobatkins.com/photography/technical/digitaldof.html
(some extra info on DOF/FOV from a more theoretical point of view, comparing full-frame and cropped sensors' effects)
Flying/jumping away for the time being. ;-)
ps: don't miss out the two links at the bottom of the first webpage I gave the link to! |
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Message posted at 07/19/2012, 04:48:24 AM by Parkinsonsniper - member is an admin |
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Andrey, I will definitely check those links. Thanks for your input. I have the Tamron 17-50 and Sigma 105 macro. I will try to test them both in studio and try the post process sharpening methods, just for science! :)) |
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Message edited at 07/19/2012, 05:24:15 AM by Androniques |
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Message posted at 07/19/2012, 13:45:32 PM by Alvera |
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I will resume your first article:
- a lot of blue light in front of your lens? You can use small apertures, don't be afraid of diffraction.
- a lot of green light? Open your diaphragm as much as you can. Green is bad at small aperture. |
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Message edited at 07/19/2012, 18:01:48 PM by Androniques |
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| Originally posted by Alvera: |
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| Quoted Message: I will resume your first article: - a lot of blue light in front of your lens? You can use small apertures, don`t be afraid of diffraction. - a lot of green light? Open your diaphragm as much as you can. Green is bad at small aperture. |
You're exaggerating, of course. ;)
The wave lengths are still of the same order, the max (for red) and min (for violet) differing roughly (at most) by a factor of ~1.8. Here is the relevant quote from the article: "Typical digital SLR cameras can capture light with a wavelength of anywhere from 450 to 680 nm, so at best the airy disk would have a diameter of 80% the size shown above (for pure blue light)"
Is 80% of the shown airy disk (known as "circle of confusion") a lot of reduction? I don't think so, especially considering that we are not up to much of the visible light border colours in our pictures, but we are rather after complex combinations of wave lengths from the inner part of the spectrum. Moreover, the worst colour in terms of the diffraction spread is red, not green. Yes, I know we have two green photo-elements per pixel vs. only single ones for red and blue... But did you ever observe the coloured diffraction pattern within a photo at smaller apertures? I have not, so the colour splitting effects are negligible (much less than possible aberrations!).
Yep. to resume: a generic DSLR (cropped) sensor is good enough to resolve small details down to f16, after which the effects of diffraction become pronounced, no matter how "prime" is the lens. BTW, Nikon 1.5x crop factor appears to beat Canons' 1.6x because of Nikon's slightly larger pixel size. ;-) |
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Message edited at 07/20/2012, 00:20:30 AM by Alvera |
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"Typical digital SLR cameras can capture light with a wavelength of anywhere from 450 to 680 nm, so at best the airy disk would have a diameter of 80% the size shown above (for pure blue light)."
"This means that as the diffraction limit is approached, the first signs will be a loss of resolution in green and pixel-level luminosity. Blue light requires the smallest apertures (highest f-stop) in order to reduce its resolution due to diffraction."
I prefer to stay betwen f8 - f11 when I can.
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Message posted at 07/20/2012, 00:25:28 AM by Afagundes |
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| Originally posted by Androniques: |
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| Quoted Message: Nikon 1.5x crop factor appears to beat Canons` 1.6x because of Nikon`s slightly larger pixel size. ;-) |
No, the larger sensor need a smaller aperture to have the same DOF, so you end up with the same limitation. |
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Message posted at 07/20/2012, 00:27:55 AM by Afagundes |
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| Originally posted by Alvera: |
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| Quoted Message: I will resume your first article: - a lot of blue light in front of your lens? You can use small apertures, don`t be afraid of diffraction. - a lot of green light? Open your diaphragm as much as you can. Green is bad at small aperture. |
You are right it is more visible in the greens, but the difference is not that huge. |
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Message posted at 07/20/2012, 01:43:44 AM by Parkinsonsniper - member is an admin |
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Very interesting...this is the dark side of photography! (at least, for me it is) :)) |
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Message posted at 07/20/2012, 01:58:14 AM by Alvera |
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| Originally posted by Afagundes: |
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| Quoted Message: You are right it is more visible in the greens, but the difference is not that huge. |
Practically not, but we are scientist in this post, don't forget! :) |
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Message posted at 07/20/2012, 02:45:46 AM by Androniques |
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| Originally posted by Afagundes: |
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| Quoted Message: No, the larger sensor need a smaller aperture to have the same DOF, so you end up with the same limitation. |
sensor has nothing to do with DOF or boke (see the second link above), the lens does! ;-) although I do see you point, I was talking only about the diffraction limitations, which are more affected by the sensor pixel size than the "overall effect" you are talking about. |
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Message posted at 07/20/2012, 02:58:19 AM by Parkinsonsniper - member is an admin |
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Bokeh is effected by the quality of lens, but sensor "size" indirectly effects the depth of field. If you are using a 35mm on a APS-C sensor, your field of view is equal to 50mm, but you still get the DoF of a 35mm lens.
What about this one, using a APS-C oriented lens (like my Tamron 17-50, it's unusabla on a full frame camera) and using a full-frame lens (like my Sigma 105mm macro) might effect the diffraction limitations? What do you think, my King and my scientist friends? |
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Message edited at 07/20/2012, 04:50:25 AM by Androniques |
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| Originally posted by Parkinsonsniper: |
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| Quoted Message: What about this one, using a APS-C oriented lens (like my Tamron 17-50, it`s unusabla on a full frame camera) and using a full-frame lens (like my Sigma 105mm macro) might effect the diffraction limitations? What do you think, my King and my scientist friends? |
I thought of this too, because it would seem reasonable to assume less diffraction at the same aperture from a bigger lens than from a smaller one (as the actual aperture diameter is bigger for the same f-number). However, I can't say for sure... and here is why.
In a simple schematics for the light rays passing through an aperture and widening before being captured by the sensor, the in-plane spread depends on the distance from the hole itself. That's where the good and bad effects might cancel out in real life. I mean, if you have a larger lens, with the correspondingly larger aperture sizes (for same f-numbers) it will have its inversion point/plane further away from the image plane, and the aperture will be proportionally further away too (when comparing with the "equivalent" cropped lens). Then the angular spread of light rays due to diffraction will produce just the same effect on the image. This simple scaling property of camera optics is probably the reason for the above article not bothering about lens types and such. Note that their calculators allow you to vary the sensor type (and aperture f-number) only.
Sorry if I brought a bad news for you, I hope someone proves me wrong. :) |
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Message posted at 07/20/2012, 05:03:13 AM by Alvera |
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I had never a image refused for diffraction:)) |
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Message posted at 07/20/2012, 05:11:50 AM by Afagundes |
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| Originally posted by Alvera: |
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| Quoted Message: I had never a image refused for diffraction:)) |
No, they cant tell its diffraction by looking, they will probably use this one
" - Image is out of focus or too much of the subject is out of focus (DOF too shallow or DOF not justified) / Image is shaken. Use a faster speed or a tripod. Please check the files at 100% zoom before submitting them" |
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Message posted at 07/20/2012, 05:19:55 AM by Parkinsonsniper - member is an admin |
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It will take some time to translate this! :)) |
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Message posted at 07/20/2012, 05:21:31 AM by Afagundes |
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| Originally posted by Androniques: |
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| Quoted Message: sensor has nothing to do with DOF. |
Yes it does, a larger sensor needs a smaller aperture to get the same Depth of Field as a smaller one.
A tiny sensor on a point and shoot might have the same DOF as a DSLR with an aperture 8 times wider, but you have the consider they are using the same 50mm equivalent focal lenght.
Now the interesting thing is that difraction ends up limiting the DOF in the same way for any type of sensor, so, say, you get 3meters DOF in a certain condition with a point and shoot f2, you will get the same DOF with a DSLR APS-c f11, it keeps the same with a full frame f13, and still the same with a 4x3" at f64, the diference is that the larger the sensor, the higher resolution you can get at the limit of difraction.
This is pure optics, no lens can change that, in fact, bad lenses can make things worse, but not better than that. |
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Message posted at 07/20/2012, 05:22:15 AM by Androniques |
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| Originally posted by Afagundes: |
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| Quoted Message: No, they cant tell its diffraction by looking, they will probably use this one" - Image is out of focus or too much of the subject is out of focus (DOF too shallow or DOF not justified) / Image is shaken. Use a faster speed or a tripod. Please check the files at 100% zoom before submitting them" |
hmmm, they could look at the f-number in the EXIF and suggest to reduce it ;-))) |
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Message posted at 07/20/2012, 05:30:43 AM by Androniques |
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| Originally posted by Afagundes: |
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| Quoted Message: Yes it does, a larger sensor needs a smaller aperture to get the same Depth of Field as a smaller one.A tiny sensor on a point and shoot might have the same DOF as a DSLR with an aperture 8 times wider, but you have the consider they are using the same 50mm equivalent focal lenght.Now the interesting thing is that difraction ends up limiting the DOF in the same way for any type of sensor, so, say, you get 3meters DOF in a certain condition with a point and shoot f2, you will get the same DOF with a DSLR APS-c f11, it keeps the same with a full frame f13, and still the same with a 4x3" at f64, the diference is that the larger the sensor, the higher resolution you can get at the limit of difraction.This is pure optics, no lens can change that, in fact, bad lenses can make things worse, but not better than that. |
Alexandre, I told you "I see your point", so I knew what you meant... however, you can still use a "full-frame" lens on a cropped DSLR and get just the same DOF as you would have on the full-frame (but cropped). So, it is the lens size (shorter or longer pathways for the light) which determine the DOF for a particular f-number. Smaller lenses for smaller sensors is a compromise between the optical quality and the usability/needs etc. Still, it is the lens that controls the DOF and FOV, not the sensor. :) |
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