death of bokeh?

**MossyRocks** · 08-17-2018, 11:09 AM

Originally posted by torashi

Diffraction behaves the same everywhere, every time.

I had thought that because of the substantially longer distance to the focal plane with the extension tubes that there would be an effect. I may be wrong and would welcome correction but it seems that in addition to magnifying the image we would also be magnifying the diffraction a comparable amount. So at 6:1 with my setup any diffraction would also be magnified 6x similar to using an f-stop 6x as great as the airy disk would have a diameter 6x the size on the sensor.

photoptimist · 08-17-2018, 11:40 AM - **1 Like**

Originally posted by MossyRocks

I had thought that because of the substantially longer distance to the focal plane with the extension tubes that there would be an effect. I may be wrong and would welcome correction but it seems that in addition to magnifying the image we would also be magnifying the diffraction a comparable amount. So at 6:1 with my setup any diffraction would also be magnified 6x similar to using an f-stop 6x as great as the airy disk would have a diameter 6x the size on the sensor.

Your interpretation of the effects of focal plane distances and magnification on diffraction are correct. Diffraction and the size of the airy disk are angular in nature and the further that angular cone of blurred light propagates, the wider it gets as measured in sensor pixels.

Because of geometry, that 6X magnification condition actually has the lens (1+6)X = 7X farther from the sensor than the infinity-distance setting of the lens. Thus, at 6X, a macro lens set to f/8 will show diffraction effects equivalent to f/56.

**MossyRocks** · 08-17-2018, 01:58 PM

Originally posted by photoptimist

Because of geometry, that 6X magnification condition actually has the lens (1+6)X = 7X farther from the sensor than the infinity-distance setting of the lens.

I had forgotten that part even if I had read that. It is nice to know that the rest of my understanding wasn't off base though.

torashi · 08-17-2018, 03:01 PM

Originally posted by MossyRocks

I had thought that because of the substantially longer distance to the focal plane with the extension tubes that there would be an effect. I may be wrong and would welcome correction but it seems that in addition to magnifying the image we would also be magnifying the diffraction a comparable amount. So at 6:1 with my setup any diffraction would also be magnified 6x similar to using an f-stop 6x as great as the airy disk would have a diameter 6x the size on the sensor.

Yes, that's how it works, but see that in one case you're magnifying the diffraction, whereas in the other case you're effectively adding diffraction. That's why I talk about actual aperture and effective aperture, which is just adding exposure compensation to the f number. One could also add it to shutter speed or compensate with sensor/film sensitivity.
See, f/4 is still f/4 at any focal length, but it's magnification that determines how much is in focus. Close to infinity it tends to be pretty much infinite, but as you focus closer, DoF becomes exponentially smaller. And smaller focal lenghts magnify less, so that's why everything tends to be pretty much in focus.
OTOH some designs suffer less from vignetting and light falloff while focusing than others, like rangefinder or mirrorless vs. SLR retrofocus designs for smaller focal lenghts because of the rear element to sensor/film distance and thus a different proportion between focusing travel and that distance.
It's the opposite for telephoto vs. non-telephoto designs. And it gets more complicated for front, rear or internal group focusing lenses and zooms.

pxt · 08-24-2018, 11:19 AM

Software start add bokeh like features fx. till shift blur. Some people use it in place hardware and don't understand why it can be complicated. It is bad, because it make them only for likes.

**clickclick** · 08-26-2018, 05:59 PM

Originally posted by pxt

Software start add bokeh like features fx. till shift blur. Some people use it in place hardware and don't understand why it can be complicated. It is bad, because it make them only for likes.

I really don't like this. Feel like it's cheating. Plus, in my mind, takes the fun away from feeding the LBA monster. There's a reason to have a cupboard filled with different lenses. Being able to grab a lens to suite your subject and mood can be great fun.

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08-17-2018, 11:09 AM	#121
MossyRocks Loyal Site Supporter Join Date: Nov 2017 Location: Minnesota Photos: Gallery \| Albums Posts: 2,982	Originally posted by torashi Diffraction behaves the same everywhere, every time. I had thought that because of the substantially longer distance to the focal plane with the extension tubes that there would be an effect. I may be wrong and would welcome correction but it seems that in addition to magnifying the image we would also be magnifying the diffraction a comparable amount. So at 6:1 with my setup any diffraction would also be magnified 6x similar to using an f-stop 6x as great as the airy disk would have a diameter 6x the size on the sensor.

08-17-2018, 11:40 AM - 1 Like	#122
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,128	Originally posted by MossyRocks I had thought that because of the substantially longer distance to the focal plane with the extension tubes that there would be an effect. I may be wrong and would welcome correction but it seems that in addition to magnifying the image we would also be magnifying the diffraction a comparable amount. So at 6:1 with my setup any diffraction would also be magnified 6x similar to using an f-stop 6x as great as the airy disk would have a diameter 6x the size on the sensor. Your interpretation of the effects of focal plane distances and magnification on diffraction are correct. Diffraction and the size of the airy disk are angular in nature and the further that angular cone of blurred light propagates, the wider it gets as measured in sensor pixels. Because of geometry, that 6X magnification condition actually has the lens (1+6)X = 7X farther from the sensor than the infinity-distance setting of the lens. Thus, at 6X, a macro lens set to f/8 will show diffraction effects equivalent to f/56.

08-17-2018, 01:58 PM	#123
MossyRocks Loyal Site Supporter Join Date: Nov 2017 Location: Minnesota Photos: Gallery \| Albums Posts: 2,982	Originally posted by photoptimist Because of geometry, that 6X magnification condition actually has the lens (1+6)X = 7X farther from the sensor than the infinity-distance setting of the lens. I had forgotten that part even if I had read that. It is nice to know that the rest of my understanding wasn't off base though.

08-17-2018, 03:01 PM	#124
torashi Veteran Member Join Date: Sep 2017 Location: Medellín Posts: 1,322	Originally posted by MossyRocks I had thought that because of the substantially longer distance to the focal plane with the extension tubes that there would be an effect. I may be wrong and would welcome correction but it seems that in addition to magnifying the image we would also be magnifying the diffraction a comparable amount. So at 6:1 with my setup any diffraction would also be magnified 6x similar to using an f-stop 6x as great as the airy disk would have a diameter 6x the size on the sensor. Yes, that's how it works, but see that in one case you're magnifying the diffraction, whereas in the other case you're effectively adding diffraction. That's why I talk about actual aperture and effective aperture, which is just adding exposure compensation to the f number. One could also add it to shutter speed or compensate with sensor/film sensitivity. See, f/4 is still f/4 at any focal length, but it's magnification that determines how much is in focus. Close to infinity it tends to be pretty much infinite, but as you focus closer, DoF becomes exponentially smaller. And smaller focal lenghts magnify less, so that's why everything tends to be pretty much in focus. OTOH some designs suffer less from vignetting and light falloff while focusing than others, like rangefinder or mirrorless vs. SLR retrofocus designs for smaller focal lenghts because of the rear element to sensor/film distance and thus a different proportion between focusing travel and that distance. It's the opposite for telephoto vs. non-telephoto designs. And it gets more complicated for front, rear or internal group focusing lenses and zooms.

08-24-2018, 11:19 AM	#125
pxt Senior Member Join Date: Jul 2018 Posts: 290	Software start add bokeh like features fx. till shift blur. Some people use it in place hardware and don't understand why it can be complicated. It is bad, because it make them only for likes.

08-26-2018, 05:59 PM	#126
clickclick Loyal Site Supporter Join Date: May 2016 Location: East Coast Posts: 2,904	Originally posted by pxt Software start add bokeh like features fx. till shift blur. Some people use it in place hardware and don't understand why it can be complicated. It is bad, because it make them only for likes. I really don't like this. Feel like it's cheating. Plus, in my mind, takes the fun away from feeding the LBA monster. There's a reason to have a cupboard filled with different lenses. Being able to grab a lens to suite your subject and mood can be great fun.