onthebeam wrote:
Understood, but for those of us who have been shooting for years at focal lengths we rely on, many would argue it should be a given that 35 = 35. I'm fortunate to have a dozen lenses for Sony and held onto a select few superb Canon and Nikon lenses, too.
For my most comfortable work flow, I'll occasionally choose my 28 if I want a slightly wider prime, and frequently use my 16-35 GM if I wish to choose within the range. Depending on subject, my awesome 24mm f1.8 GM most often gets the call when wide-primin'.
It's great to have the discipline of a fixed focal length, not to mention the quality that the best primes are known for. You've got to hand it to to Batis. It's not afraid to proudly and rightfully call itself a 25!
Sorry to threadjack. Back to the show in progress!...Show more →
It's not so wide that it doesn't feel like a 35mm though. It definitely does not shoot like a 28mm where you start contending with noticeably heavy perspective distortion for portraits.
The slightly wider FOV of the 35i really only stood out once I started taking comparison shots against the Bigma 35 1.2 and the FE 35 1.8
onthebeam wrote:
Understood, but for those of us who have been shooting for years at focal lengths we rely on, many would argue it should be a given that 35 = 35. I'm fortunate to have a dozen lenses for Sony and held onto a select few superb Canon and Nikon lenses, too.
For my most comfortable work flow, I'll occasionally choose my 28 if I want a slightly wider prime, and frequently use my 16-35 GM if I wish to choose within the range. Depending on subject, my awesome 24mm f1.8 GM most often gets the call when wide-primin'.
It's great to have the discipline of a fixed focal length, not to mention the quality that the best primes are known for. You've got to hand it to to Batis. It's not afraid to proudly and rightfully call itself a 25!
Sorry to threadjack. Back to the show in progress!...Show more →
The thing is a lens labelled 35mm even if it is exactly 35mm the is typically only for infinity focus. Most lenses (for stills anyway) change focal length at least a bit depending on focus distance (in the video world they call this focus breathing). So one would not expect exactly the same angle of view for two 35mm lenses for say a 5 foot portrait even if they were exactly 35mm at infinity focus.
Any word yet on whether this lens is affected by vignetting corrections (concentric magenta bands) that get baked into Sony RAWs with some lenses, even when in-camera vignetting correction is off and when shooting uncompressed RAW?
I am loath to purchase lenses, particularly autofocus lenses, that require the contacts to be taped.
I'm frankly surprised there hasn't been more of an uproar about this. Seems like it'd be good fodder for a petition to Sony.
Steve Spencer wrote:
Most lenses (for stills anyway) change focal length at least a bit depending on focus distance (in the video world they call this focus breathing).
This conflates angle-of-view and focal length/power. A lens without focus breathing must reduce its focal length in a specific manner with close focus. A lens with fixed focal length necessarily reduces angle-of-view with close focus.
QuietOC wrote:
This conflates angle-of-view and focal length/power. A lens without focus breathing must reduce its focal length in a specific manner with close focus. A lens with fixed focal length necessarily reduces angle-of-view with close focus.
Ok, but can you explain how that matters for the general point that a 35mm lens' focal length is typically measured at infinity and doesn't necessarily have that same focal length at shorter focus distances.
Fred Miranda wrote: Rendering compared to Voigtlander 35mm f/1.2 III @f/2
The Voigtlander 35mm f/1.2 III Nokton E-mount is less corrected for spherical aberration compared to the Sigma so I was expecting even better rendering for the former. However, when comparing them side by side with same framing, I found that both lenses have smooth and pleasant rendering.
When both wide open, the Sigma 35mm f/2 DG DN is much better corrected for axial aberration and that's still the case when both are set to f/2.
The Voigtlander 35mm f/1.2's FOV is a bit narrower than 35mm at ~35.5mm while the Sigma is wider (~32.5mm). At same distance the Voigtlander would benefit from extra blur so when comparing them side by side, so I tried to frame the scene below as close as possible.
Looks really good! Sigma did a nice job with this lens and especially keeping it small. Looks like the only thing it can't do in comparison to the CV is 1.2-1.8
Steve Spencer wrote:
The thing is a lens labelled 35mm even if it is exactly 35mm the is typically only for infinity focus. Most lenses (for stills anyway) change focal length at least a bit depending on focus distance (in the video world they call this focus breathing). So one would not expect exactly the same angle of view for two 35mm lenses for say a 5 foot portrait even if they were exactly 35mm at infinity focus.
Focal length is by definition measured at infinity, what happens as you focus closer is not stricly a change of focal length, but of field of view. Very few of unusual design, such as IF actually change focal length. But with a 'normal' lens as you focus closer than infinity you move the lens further from the sensor/film and thus magnify the image.
gyoung143 wrote:
Focal length is by definition measured at infinity, what happens as you focus closer is not stricly a change of focal length, but of field of view. Very few of unusual design, such as IF actually change focal length. But with a 'normal' lens as you focus closer than infinity you move the lens further from the sensor/film and thus magnify the image.
Gerry
True, but IF has been normal, and block focus unusual, for quite a while now, as AF gets difficult with larger block focus lenses.
Steve Spencer wrote:
Ok, but can you explain how that matters for the general point that a 35mm lens' focal length is typically measured at infinity and doesn't necessarily have that same focal length at shorter focus distances.
He’s just being picky about terminology, Steve.
A unit focus 35 or any other lens doesn’t change focal length as if focuses closer, but it *does* change field of view. Of course for practical purposes (holding format fixed) photographers often use focal length and field of view interchangeably, as though they were measures of the same thing (one measured in mm and one in degrees) and this rarely is problematic.
Mar 07, 2021 at 05:33 PM
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DavidBM wrote:
He’s just being picky about terminology, Steve.
A unit focus 35 or any other lens doesn’t change focal length as if focuses closer, but it *does* change field of view. Of course for practical purposes (holding format fixed) photographers often use focal length and field of view interchangeably, as though they were measures of the same thing (one measured in mm and one in degrees) and this rarely is problematic.
Ok, I got what he was saying, but I don't think it changes the general point I was making that even if a 35mm lens is measured precisely and accurately as a 35mm lens as measured at infinity, it may not measure precisely as a 35mm lens at, for example, a 5ft portrait. Simply put for many lenses focal length varies a bit by focus distance, so getting too hung up on a lens being precisely 35mm at infinity doesn't make much sense, IMO.
DavidBM wrote:
He’s just being picky about terminology, Steve.
A unit focus 35 or any other lens doesn’t change focal length as if focuses closer, but it *does* change field of view. Of course for practical purposes (holding format fixed) photographers often use focal length and field of view interchangeably, as though they were measures of the same thing (one measured in mm and one in degrees) and this rarely is problematic.
I think the terminology may be confusing. As I understand it (to a very limited degree), the focal length of a lens is defined as the distance from the rear nodal point of a lens to the plane of focus. Lenses are notionally identified and named by what this distance is when an object at infinity is brought into focus (e.g., 50mm). However, the focal length does change when an object closer than infinity is focused because in order to bring the closer object into focus the nodal point may be moved further away from the plane of focus and thus the actual non-notional focal length becomes a bit longer. This change is largest when the object is closest.
You can benefit from knowing the focal length at infinity and a fixed useable close focus distance, say 2m - for each lens. When you start seeing infinity FL ranging from 32mm to 37mm, calling them all 35mm is just gaslighting your customers.
CZ used to provide actual focal lengths but not any more, now they give 'angular view' or some such. Smart move to produce a 32mm if you have also a 24mm and a 45mm in the range. It's useful to know this, particularly in a rich lens environment like E mount, with a lot of choice.
Steve Spencer wrote:
Ok, I got what he was saying, but I don't think it changes the general point I was making that even if a 35mm lens is measured precisely and accurately as a 35mm lens as measured at infinity, it may not measure precisely as a 35mm lens at, for example, a 5ft portrait. Simply put for many lenses focal length varies a bit by focus distance, so getting too hung up on a lens being precisely 35mm at infinity doesn't make much sense, IMO.
Sure, the angle of view will be different, and you shouldn’t obsess about infinity AOV we all agree, as lenses that agree at infinity may disagreee at other lengths (though if they agree at infinity, they ought agree at close distance if they are unit focus, even thigh what they agree on may be different from what they agree on at infinity) if they agree at infinity, and disagree at the same closer distance, at least one must be IF or have a floating group.
chiron wrote:
I think the terminology may be confusing. As I understand it (to a very limited degree), the focal length of a lens is defined as the distance from the rear nodal point of a lens to the plane of focus. Lenses are notionally identified and named by what this distance is when an object at infinity is brought into focus (e.g., 50mm). However, the focal length does change when an object closer than infinity is focused because in order to bring the closer object into focus the nodal point may be moved further away from the plane of focus and thus the actual non-notional focal length becomes a bit longer. This change is largest when the object is closest....Show more →
Maybe it is confusing, I was taught that the focal length is defined as the distance from rear nodal point to pane of focus when focussed at infinity. From which it follows that it doesn’t change if it’s unit focus as you focus closer.
So why does it change if there’s IF or FE? Because if you focus close, and the elements move relative to each other *and then refocus without changing the arrangement of the elements* (which of course you can’t in practice do) the focal length as defined would be different.
But of course nine of this matters much in practice (except perhaps to encourage us to think in terms of AOV rather than FL)
DavidBM wrote:
Maybe it is confusing, I was taught that the focal length is defined as the distance from rear nodal point to pane of focus when focussed at infinity. From which it follows that it doesn’t change if it’s unit focus as you focus closer.
So why does it change if there’s IF or FE? Because if you focus close, and the elements move relative to each other *and then refocus without changing the arrangement of the elements* (which of course you can’t in practice do) the focal length as defined would be different.
But of course nine of this matters much in practice (except perhaps to encourage us to think in terms of AOV rather than FL)
Yes, confusing terminology. I think it is the notional focal length of the lens that is the distance from nodal point to the plane of focus when the lens is focused at infinity. But the actual or empirical focal length may vary a bit as the nodal point moves further away from the plane of focus when focusing on a close object, and with the change in focal length comes (I think) a change in magnification and angle of view.
chiron wrote:
Yes, confusing terminology. I think it is the notional focal length of the lens that is the distance from nodal point to the plane of focus when the lens is focused at infinity. But the actual or empirical focal length may vary a bit as the nodal point moves further away from the plane of focus when focusing on a close object, and with the change in focal length comes (I think) a change in magnification and angle of view.
I don’t think it’s merely notional (although the definition in terms of plane of focus, infinity and nodal point is not quite precise)
Here’s why
Strictly speaking, focal length is the reciprocal of optical power. And optical power is an angular measure...it the degree to which the lens converges or diverges light. That is something which is an intrinsic property of the lens regardless of how it’s focussed, even if focussing closer will change magnification and hence AOV. So focal length should not change with focus, even if AOV does, unless the elements move relatively as in IF or CRC lenses, where the intrinsic shape of the lens changes.
