Re: Wide lenses and close distances
...if the lens is a curved field lens, then the plane of focus is actually dish shaped, with the curvature keeping things in focus at the focus distance in a curved field in front of the lens. My understanding also. When you focus a lens to 1m, it means that all subjects are in focus that are in a plane positioned at 1m from the lens and perpendicular to the lens axis (the focal plane). My understanding is that if the lens is a flat field lens (macro lenses tend to such lenses), then this is the case One of the reasons I bought the bellows lens years ago. Kenneth Waller - Original Message - From: "William Robb" <[EMAIL PROTECTED]> Subject: Re: Wide lenses and close distances - Original Message - From: "Vic Mortelmans" Subject: Re: Wide lenses and close distances A thought that puzzled me lately may be related to this question. It's about the focal plane and the effective distance to the camera lens. When you focus a lens to 1m, it means that all subjects are in focus that are in a plane positioned at 1m from the lens and perpendicular to the lens axis (the focal plane). My understanding is that if the lens is a flat field lens (macro lenses tend to such lenses), then this is the case, however, if the lens is a curved field lens, then the plane of focus is actually dish shaped, with the curvature keeping things in focus at the focus distance in a curved field in front of the lens. William Robb
Re: Wide lenses and close distances
IMHO, it's only significant if you are using a camera without movements! :-) Of course, for most of us, we rely on DOF to allow us to have all of our important subject matter "sufficiently" sharp. John Coyle Brisbane, Australia - Original Message - From: "Vic Mortelmans" <[EMAIL PROTECTED]> To: Sent: Wednesday, May 03, 2006 3:19 AM Subject: Re: Wide lenses and close distances A thought that puzzled me lately may be related to this question. It's about the focal plane and the effective distance to the camera lens. When you focus a lens to 1m, it means that all subjects are in focus that are in a plane positioned at 1m from the lens and perpendicular to the lens axis (the focal plane). If a subject is at the outer edge of the field of view and in the focal plane, the distance between camera and subject will be more than 1m. In case of wide angle, the difference can be significant like 1.4m e.g., if your angle of view is 90degrees). The subject will be in focus at 1.4m 'real' distance, while the lens is set to 1m. Now, if you want to focus your lens on this outer-edge-object, you'll have to tilt your camera and point it to the subject (assuming you use the split-screen-focus at the center of the viewfinder). OOPS! You will set the lens to 1.4m! If you now tilt the camera back to it's original position (for optimal composition), the outer-edge-object will be out of focus, because it's in the 1m-focal plane and not in the 1.4m focal plane! Do you follow? Is this a 'real' problem, or only theoretically? Groeten, Vic Boris Liberman wrote: Hi! Shel recently showed us a picture and added that he wasn't quite sure about performance of his K 24/2.8... Now, having thought about it a bit, I present you a question. Is there a focal distance at which short distance performance of a wide lens is noticeably worse than at infinity? For example, I should say that I made quite a few shots with my 31 Ltd (my widest Pentax lens now) at very close distance (around 1 meter) and I really liked the results. Both shots from my photoblog that I recently posted were made with 31 Ltd. When I had K 24/2.8 I also had mixed feelings about its close range performance. But at the time I thought it was due to my poor eyesight and bad manual focusing technique... -- Boris
Re: Wide lenses and close distances
- Original Message - From: "Vic Mortelmans" Subject: Re: Wide lenses and close distances A thought that puzzled me lately may be related to this question. It's about the focal plane and the effective distance to the camera lens. When you focus a lens to 1m, it means that all subjects are in focus that are in a plane positioned at 1m from the lens and perpendicular to the lens axis (the focal plane). My understanding is that if the lens is a flat field lens (macro lenses tend to such lenses), then this is the case, however, if the lens is a curved field lens, then the plane of focus is actually dish shaped, with the curvature keeping things in focus at the focus distance in a curved field in front of the lens. William Robb
Re: Wide lenses and close distances
On Tue, 02 May 2006 19:19:34 +0200, Vic Mortelmans <[EMAIL PROTECTED]> wrote: A thought that puzzled me lately may be related to this question. It's about the focal plane and the effective distance to the camera lens. When you focus a lens to 1m, it means that all subjects are in focus that are in a plane positioned at 1m from the lens and perpendicular to the lens axis (the focal plane). At one meter from the sensor or film plane, not from 'the lens'. When talking about a meter it might not matter too much, but when you focus a 50mm marco as close as possible it starts to count: Close focussing distance of the D FA 50/2.8 is supposed to be 20cm. The lens itself is 60mm, the flange distance of K-mount is 45,46mm, so the object is only 10cm from the front of the lens... If a subject is at the outer edge of the field of view and in the focal plane, the distance between camera and subject will be more than 1m. In case of wide angle, the difference can be significant like 1.4m e.g., if your angle of view is 90degrees). The subject will be in focus at 1.4m 'real' distance, while the lens is set to 1m. Now, if you want to focus your lens on this outer-edge-object, you'll have to tilt your camera and point it to the subject (assuming you use the split-screen-focus at the center of the viewfinder). OOPS! You will set the lens to 1.4m! If you now tilt the camera back to it's original position (for optimal composition), the outer-edge-object will be out of focus, because it's in the 1m-focal plane and not in the 1.4m focal plane! Do you follow? Is this a 'real' problem, or only theoretically? Just tested this: I took a macro lens on an MX, focussed as close as possible (that's 1:2, focus distance 0,39m) and focussed on my PC screen using a matte gridscreen by moving the camera. Tilted to the edge (trying to tilt around a vertical axis running though the film plane) refocussed (to 0,395m), tilted back. The screen is now distinctly out of focus. So, yes, focus-recompose introduces real errors. My guess would be that ninety-five percent of the time it is not noticable. Extreme wideangle and/or extreme close focussing could be the exceptions... -- Regards, Lucas
Re: Wide lenses and close distances
I do not know that answer, but I have thought about that myself, and your line of thought does make sense... at least theoretically. :) Russell
Re: Wide lenses and close distances
A thought that puzzled me lately may be related to this question. It's about the focal plane and the effective distance to the camera lens. When you focus a lens to 1m, it means that all subjects are in focus that are in a plane positioned at 1m from the lens and perpendicular to the lens axis (the focal plane). If a subject is at the outer edge of the field of view and in the focal plane, the distance between camera and subject will be more than 1m. In case of wide angle, the difference can be significant like 1.4m e.g., if your angle of view is 90degrees). The subject will be in focus at 1.4m 'real' distance, while the lens is set to 1m. Now, if you want to focus your lens on this outer-edge-object, you'll have to tilt your camera and point it to the subject (assuming you use the split-screen-focus at the center of the viewfinder). OOPS! You will set the lens to 1.4m! If you now tilt the camera back to it's original position (for optimal composition), the outer-edge-object will be out of focus, because it's in the 1m-focal plane and not in the 1.4m focal plane! Do you follow? Is this a 'real' problem, or only theoretically? Groeten, Vic Boris Liberman wrote: Hi! Shel recently showed us a picture and added that he wasn't quite sure about performance of his K 24/2.8... Now, having thought about it a bit, I present you a question. Is there a focal distance at which short distance performance of a wide lens is noticeably worse than at infinity? For example, I should say that I made quite a few shots with my 31 Ltd (my widest Pentax lens now) at very close distance (around 1 meter) and I really liked the results. Both shots from my photoblog that I recently posted were made with 31 Ltd. When I had K 24/2.8 I also had mixed feelings about its close range performance. But at the time I thought it was due to my poor eyesight and bad manual focusing technique... -- Boris
Re: Wide lenses and close distances
Hi! I didn't say I was dissatisfied with close distance performance of the K24/2.8. Hmmm, guess I misinterpreted what you wrote... Anyway, what you wrote led me to some thinking which eventually produced the question I asked. I guess next time I should spend even less time writing the preamble and get straight to the "amble" ;-). I hereby stand corrected. -- Boris
RE: Wide lenses and close distances
Hello Boris ... I didn't say I was dissatisfied with close distance performance of the K24/2.8. Shel > [Original Message] > From: Boris Liberman > Shel recently showed us a picture and added that he wasn't quite sure > about performance of his K 24/2.8... > > Now, having thought about it a bit, I present you a question. Is there > a focal distance at which short distance performance of a wide lens is > noticeably worse than at infinity? > > For example, I should say that I made quite a few shots with my 31 Ltd > (my widest Pentax lens now) at very close distance (around 1 meter) > and I really liked the results. Both shots from my photoblog that I > recently posted were made with 31 Ltd. > > When I had K 24/2.8 I also had mixed feelings about its close range > performance. But at the time I thought it was due to my poor eyesight > and bad manual focusing technique... > > -- > Boris
Wide lenses and close distances
Hi! Shel recently showed us a picture and added that he wasn't quite sure about performance of his K 24/2.8... Now, having thought about it a bit, I present you a question. Is there a focal distance at which short distance performance of a wide lens is noticeably worse than at infinity? For example, I should say that I made quite a few shots with my 31 Ltd (my widest Pentax lens now) at very close distance (around 1 meter) and I really liked the results. Both shots from my photoblog that I recently posted were made with 31 Ltd. When I had K 24/2.8 I also had mixed feelings about its close range performance. But at the time I thought it was due to my poor eyesight and bad manual focusing technique... -- Boris
