Does your focal plane move as you stop down?

mike earussi said:

It's called "residual spherical aberration" and it just means there was a design flaw in the optics. Though very common in the past, with modern computer design it's less common, though it does still exist, in this case on the new Sigma 85 f1.4 A:

Scroll down to the bottom of the page and read the second paragraph under "Boka Fringing"

http://www.photozone.de/canon_eos_ff/1000-sigma85f14art?start=1

Click to expand...

George_pix said:

The residual spherical aberration should be quite strong to be the only source of this phenomenon.

The fact is that the DOF is not symmetric respect to nominal focusing distance:

https://petapixel.com/2015/03/09/un...ld-how-focal-distance-affects-dof-visualized/

Depending on how you evaluate the exact distance of the center of the in-focus zone, it may happen that is moves by stopping down.

Probably a combination of phenomena is at work here.

Click to expand...

George_pix said:

The residual spherical aberration should be quite strong to be the only source of this phenomenon.

The fact is that the DOF is not symmetric respect to nominal focusing distance:

https://petapixel.com/2015/03/09/un...ld-how-focal-distance-affects-dof-visualized/

Depending on how you evaluate the exact distance of the center of the in-focus zone, it may happen that it moves by stopping down.

Click to expand...

Scottelly said:

Something Tom has been mentioning over the past year or more got me thinking, "I wonder if that happens with my lenses and how much, if so." I decided to test it, and here are my results:


f2.8


f11

I shot these with my Sigma SD1 Merrill, using my 70mm f2.8 EX Macro set to manual focus (of course). I left the focus alone for both shot, and I did shoot an f5.6 shot in between these two, but it is of no consequence (doesn't add anything, so I left it out). I set the aperture and shutter speed manually, but I think I set white balance to Auto, which should explain why the colors look different between the two photos. As you can see, if you view the original size images, there is a tiny little white spot of sand on the top left portion of the upside-down, blue, L tab, which is in perfect focus in both shots. I guess this means my 70mm lens is free from the phenomenon that must plague Tom's lenses, causing the plane of focus to move, when he stops down the aperture. Can anyone else show the results of this phenomenon happening? Tom?

--
Scott Barton Kennelly
http://www.bigprintphotos.com

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Laurence Matson said:

Simply put, the focal plane is simply the distance you have focussed the lens for. Literally speaking, it is not really even a (flat) plane as one can see when using a somewhat narrow focussing distance with a standard wide-angle lens. (There are great lenses that compensate for this as well, but that is another story one can learn from Sigma's newer lenses, for instance.)

The shift you might be referring to is depth of field. It expands in two directions - closer and further - as the lens is stopped down. The video in the link posted elsewhere does a pretty good job of showing how this works and the differences at various f-stops.

Scottelly said:

Something Tom has been mentioning over the past year or more got me thinking, "I wonder if that happens with my lenses and how much, if so." I decided to test it, and here are my results:


f2.8


f11

I shot these with my Sigma SD1 Merrill, using my 70mm f2.8 EX Macro set to manual focus (of course). I left the focus alone for both shot, and I did shoot an f5.6 shot in between these two, but it is of no consequence (doesn't add anything, so I left it out). I set the aperture and shutter speed manually, but I think I set white balance to Auto, which should explain why the colors look different between the two photos. As you can see, if you view the original size images, there is a tiny little white spot of sand on the top left portion of the upside-down, blue, L tab, which is in perfect focus in both shots. I guess this means my 70mm lens is free from the phenomenon that must plague Tom's lenses, causing the plane of focus to move, when he stops down the aperture. Can anyone else show the results of this phenomenon happening? Tom?

--
Scott Barton Kennelly
http://www.bigprintphotos.com

Click to expand...

--
Laurence
laurence dot matson at gmail dot com
-----
"All of the erroneous aspects of analog or film photography are being magnified in this digital age. Images were always poorly composed and overstatements of a message. Now, we are pounding home the crappy message more easily by increasingly sharpening, saturating, contrasting, HDRing, and so on.
"The rule of thumb for each of those setting areas is: It should be done but not seen."
Laurence Matson
-----
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http://www.pbase.com/sigmadslr
http://www.howardmyerslaw.com

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Scottelly said:

Laurence Matson said:

Simply put, the focal plane is simply the distance you have focussed the lens for. Literally speaking, it is not really even a (flat) plane as one can see when using a somewhat narrow focussing distance with a standard wide-angle lens. (There are great lenses that compensate for this as well, but that is another story one can learn from Sigma's newer lenses, for instance.)

The shift you might be referring to is depth of field. It expands in two directions - closer and further - as the lens is stopped down. The video in the link posted elsewhere does a pretty good job of showing how this works and the differences at various f-stops.

Scottelly said:

Something Tom has been mentioning over the past year or more got me thinking, "I wonder if that happens with my lenses and how much, if so." I decided to test it, and here are my results:


f2.8


f11

I shot these with my Sigma SD1 Merrill, using my 70mm f2.8 EX Macro set to manual focus (of course). I left the focus alone for both shot, and I did shoot an f5.6 shot in between these two, but it is of no consequence (doesn't add anything, so I left it out). I set the aperture and shutter speed manually, but I think I set white balance to Auto, which should explain why the colors look different between the two photos. As you can see, if you view the original size images, there is a tiny little white spot of sand on the top left portion of the upside-down, blue, L tab, which is in perfect focus in both shots. I guess this means my 70mm lens is free from the phenomenon that must plague Tom's lenses, causing the plane of focus to move, when he stops down the aperture. Can anyone else show the results of this phenomenon happening? Tom?

--
Scott Barton Kennelly
http://www.bigprintphotos.com

Click to expand...

--
Laurence
laurence dot matson at gmail dot com
-----
"All of the erroneous aspects of analog or film photography are being magnified in this digital age. Images were always poorly composed and overstatements of a message. Now, we are pounding home the crappy message more easily by increasingly sharpening, saturating, contrasting, HDRing, and so on.
"The rule of thumb for each of those setting areas is: It should be done but not seen."
Laurence Matson
-----
http://www.pbase.com/lmatson
http://www.pbase.com/sigmadslr
http://www.howardmyerslaw.com

Click to expand...

The main reason I started this thread was the fact that Tom has mentioned a few times that the SD Quattro and SD Quattro H can not stop down the aperture while using magnified view to focus manually. His concern seems to be that the focal plane changes as the aperture is stopped down from f1.8 or f2.8 to f5.6 or f8 or whatever. If indeed this is the case with most lenses, I can certainly understand how that is a serious concern . . . especially for someone shooting macro shots, but even for someone shooting landscape and portraits too. I certainly wouldn't want to be shooting a 50-100mm f1.8 and finding that the model's eyes are all out of focus, because I was focusing manually on her eyes, yet when I press the shutter and the aperture closes to f5.6 the focal plane moves back an inch. Fortunately, as you can see by my posted images, it looks like I don't have that problem with my 70mm f2.8, but according to Mike's post, the 85mm Art lens does have that problem. That makes me want to get the 105mm macro instead. I wonder if anyone here had tested the 105mm f2.8 macro lenses to see if they have this focal plane shifting problem.

I'd like to see some samples Tom has produced, to see how bad the affects are with a couple of his lenses.

--
Scott Barton Kennelly
http://www.bigprintphotos.com

Click to expand...

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Scottelly said:

Laurence Matson said:

Simply put, the focal plane is simply the distance you have focussed the lens for. Literally speaking, it is not really even a (flat) plane as one can see when using a somewhat narrow focussing distance with a standard wide-angle lens. (There are great lenses that compensate for this as well, but that is another story one can learn from Sigma's newer lenses, for instance.)

The shift you might be referring to is depth of field. It expands in two directions - closer and further - as the lens is stopped down. The video in the link posted elsewhere does a pretty good job of showing how this works and the differences at various f-stops.

Scottelly said:

Something Tom has been mentioning over the past year or more got me thinking, "I wonder if that happens with my lenses and how much, if so." I decided to test it, and here are my results:


f2.8


f11

I shot these with my Sigma SD1 Merrill, using my 70mm f2.8 EX Macro set to manual focus (of course). I left the focus alone for both shot, and I did shoot an f5.6 shot in between these two, but it is of no consequence (doesn't add anything, so I left it out). I set the aperture and shutter speed manually, but I think I set white balance to Auto, which should explain why the colors look different between the two photos. As you can see, if you view the original size images, there is a tiny little white spot of sand on the top left portion of the upside-down, blue, L tab, which is in perfect focus in both shots. I guess this means my 70mm lens is free from the phenomenon that must plague Tom's lenses, causing the plane of focus to move, when he stops down the aperture. Can anyone else show the results of this phenomenon happening? Tom?

--

Click to expand...

Click to expand...

The main reason I started this thread was the fact that Tom has mentioned a few times that the SD Quattro and SD Quattro H can not stop down the aperture while using magnified view to focus manually. His concern seems to be that the focal plane changes as the aperture is stopped down from f1.8 or f2.8 to f5.6 or f8 or whatever. If indeed this is the case with most lenses, I can certainly understand how that is a serious concern . . . especially for someone shooting macro shots, but even for someone shooting landscape and portraits too. I certainly wouldn't want to be shooting a 50-100mm f1.8 and finding that the model's eyes are all out of focus, because I was focusing manually on her eyes, yet when I press the shutter and the aperture closes to f5.6 the focal plane moves back an inch. Fortunately, as you can see by my posted images, it looks like I don't have that problem with my 70mm f2.8, but according to Mike's post, the 85mm Art lens does have that problem. That makes me want to get the 105mm macro instead. I wonder if anyone here had tested the 105mm f2.8 macro lenses to see if they have this focal plane shifting problem.

I'd like to see some samples Tom has produced, to see how bad the affects are with a couple of his lenses.

Click to expand...

TN Args said:

Scottelly said:

Laurence Matson said:

Simply put, the focal plane is simply the distance you have focussed the lens for. Literally speaking, it is not really even a (flat) plane as one can see when using a somewhat narrow focussing distance with a standard wide-angle lens. (There are great lenses that compensate for this as well, but that is another story one can learn from Sigma's newer lenses, for instance.)

The shift you might be referring to is depth of field. It expands in two directions - closer and further - as the lens is stopped down. The video in the link posted elsewhere does a pretty good job of showing how this works and the differences at various f-stops.

Scottelly said:

Something Tom has been mentioning over the past year or more got me thinking, "I wonder if that happens with my lenses and how much, if so." I decided to test it, and here are my results:


f2.8


f11

I shot these with my Sigma SD1 Merrill, using my 70mm f2.8 EX Macro set to manual focus (of course). I left the focus alone for both shot, and I did shoot an f5.6 shot in between these two, but it is of no consequence (doesn't add anything, so I left it out). I set the aperture and shutter speed manually, but I think I set white balance to Auto, which should explain why the colors look different between the two photos. As you can see, if you view the original size images, there is a tiny little white spot of sand on the top left portion of the upside-down, blue, L tab, which is in perfect focus in both shots. I guess this means my 70mm lens is free from the phenomenon that must plague Tom's lenses, causing the plane of focus to move, when he stops down the aperture. Can anyone else show the results of this phenomenon happening? Tom?

--

Click to expand...

Click to expand...

The main reason I started this thread was the fact that Tom has mentioned a few times that the SD Quattro and SD Quattro H can not stop down the aperture while using magnified view to focus manually. His concern seems to be that the focal plane changes as the aperture is stopped down from f1.8 or f2.8 to f5.6 or f8 or whatever. If indeed this is the case with most lenses, I can certainly understand how that is a serious concern . . . especially for someone shooting macro shots, but even for someone shooting landscape and portraits too. I certainly wouldn't want to be shooting a 50-100mm f1.8 and finding that the model's eyes are all out of focus, because I was focusing manually on her eyes, yet when I press the shutter and the aperture closes to f5.6 the focal plane moves back an inch. Fortunately, as you can see by my posted images, it looks like I don't have that problem with my 70mm f2.8, but according to Mike's post, the 85mm Art lens does have that problem. That makes me want to get the 105mm macro instead. I wonder if anyone here had tested the 105mm f2.8 macro lenses to see if they have this focal plane shifting problem.

I'd like to see some samples Tom has produced, to see how bad the affects are with a couple of his lenses.

Click to expand...

I have seen it referred to as focus shift.

Click to expand...

TN Args said:

Not sure about mike earussi's implication that it is a problem from the past on 'flawed by design' optics. After all, the very expensive brand new Nikon 105/1.4 has been measured to exhibit 2.5cm of focus shift at 10 feet.

Click to expand...

TN Args said:

The good news is that if your lens does AF, then the camera should stop down to focus when using AF. And if using a non-AF lens, you should be able to stop down manually and focus. The 'issue' arises when focusing manually with an AF lens for shots being taken at a stopped-down aperture.

Click to expand...

TN Args said:

I am not sure about your method in your example above with the blue 'L' tab. I think the correct method would be to photograph a ruler or scale placed longitudinally in the image, and calculate the focus point from the near and far distances that are equally out of focus in both images. (and remember, it won't be the average of the near and far distances)

cheers

Click to expand...

TN Args said:

Scottelly said:

Laurence Matson said:

Simply put, the focal plane is simply the distance you have focussed the lens for. Literally speaking, it is not really even a (flat) plane as one can see when using a somewhat narrow focussing distance with a standard wide-angle lens. (There are great lenses that compensate for this as well, but that is another story one can learn from Sigma's newer lenses, for instance.)

The shift you might be referring to is depth of field. It expands in two directions - closer and further - as the lens is stopped down. The video in the link posted elsewhere does a pretty good job of showing how this works and the differences at various f-stops.

Scottelly said:

Something Tom has been mentioning over the past year or more got me thinking, "I wonder if that happens with my lenses and how much, if so." I decided to test it, and here are my results:


f2.8


f11

I shot these with my Sigma SD1 Merrill, using my 70mm f2.8 EX Macro set to manual focus (of course). I left the focus alone for both shot, and I did shoot an f5.6 shot in between these two, but it is of no consequence (doesn't add anything, so I left it out). I set the aperture and shutter speed manually, but I think I set white balance to Auto, which should explain why the colors look different between the two photos. As you can see, if you view the original size images, there is a tiny little white spot of sand on the top left portion of the upside-down, blue, L tab, which is in perfect focus in both shots. I guess this means my 70mm lens is free from the phenomenon that must plague Tom's lenses, causing the plane of focus to move, when he stops down the aperture. Can anyone else show the results of this phenomenon happening? Tom?

--

Click to expand...

Click to expand...

The main reason I started this thread was the fact that Tom has mentioned a few times that the SD Quattro and SD Quattro H can not stop down the aperture while using magnified view to focus manually. His concern seems to be that the focal plane changes as the aperture is stopped down from f1.8 or f2.8 to f5.6 or f8 or whatever. If indeed this is the case with most lenses, I can certainly understand how that is a serious concern . . . especially for someone shooting macro shots, but even for someone shooting landscape and portraits too. I certainly wouldn't want to be shooting a 50-100mm f1.8 and finding that the model's eyes are all out of focus, because I was focusing manually on her eyes, yet when I press the shutter and the aperture closes to f5.6 the focal plane moves back an inch. Fortunately, as you can see by my posted images, it looks like I don't have that problem with my 70mm f2.8, but according to Mike's post, the 85mm Art lens does have that problem. That makes me want to get the 105mm macro instead. I wonder if anyone here had tested the 105mm f2.8 macro lenses to see if they have this focal plane shifting problem.

I'd like to see some samples Tom has produced, to see how bad the affects are with a couple of his lenses.

Click to expand...

I have seen it referred to as focus shift. Not sure about mike earussi's implication that it is a problem from the past on 'flawed by design' optics. After all, the very expensive brand new Nikon 105/1.4 has been measured to exhibit 2.5cm of focus shift at 10 feet between f/1.4 and f/4, link.

The good news is that if your lens does AF, then the camera should stop down to focus when using AF. And if using a non-AF lens, you should be able to stop down manually and focus. The 'issue' arises when focusing manually with an AF lens for shots being taken at a stopped-down aperture.

I am not sure about your method in your example above with the blue 'L' tab. I think the correct method would be to photograph a ruler or scale placed longitudinally in the image, and calculate the focus point from the near and far distances that are equally out of focus in both images. (and remember, it won't be the average of the near and far distances)

cheers

Click to expand...

Scottelly said:

TN Args said:

I am not sure about your method in your example above with the blue 'L' tab. I think the correct method would be to photograph a ruler or scale placed longitudinally in the image, and calculate the focus point from the near and far distances that are equally out of focus in both images. (and remember, it won't be the average of the near and far distances)

cheers

Click to expand...

O.K. I used a ruler.



You can tell by these two ruler photos that the focal plane did not move more than 1/16 of an inch, when I stopped down from f2.8 to f8.


f2.8


f8

Again, I used my SD1 Merrill to shoot raw photos with all manual settings (manual aperture, manual shutter speed, manual white balance, and manual focus). I did not touch the focus from one shot to the next.

Click to expand...

AiryDiscus said:

Every lens you buy has focus shift, none are corrected for it.

Click to expand...

mike earussi said:

AiryDiscus said:

Every lens you buy has focus shift, none are corrected for it.

Click to expand...

What evidence do you have for that?

Click to expand...

AiryDiscus said:

mike earussi said:

AiryDiscus said:

Every lens you buy has focus shift, none are corrected for it.

Click to expand...

What evidence do you have for that?

Click to expand...

There is no amount of spherical aberration, of any singular order or balance of orders, which has no difference between paraxial and minimum RMS wavefront error focus, or any other focus criteria.

No lens you can buy is diffraction limited at its full aperture, QED all lenses have focus shift.

Click to expand...

mike earussi said:

AiryDiscus said:

mike earussi said:

AiryDiscus said:

Every lens you buy has focus shift, none are corrected for it.

Click to expand...

What evidence do you have for that?

Click to expand...

There is no amount of spherical aberration, of any singular order or balance of orders, which has no difference between paraxial and minimum RMS wavefront error focus, or any other focus criteria.

No lens you can buy is diffraction limited at its full aperture, QED all lenses have focus shift.

Click to expand...

Would you care to explain then how on stopping down most lenses the focus point doesn't shift?

Click to expand...