em_dee_aitch
Senior Member
I encourage anyone who actually owns and uses a 24/1.4G to learn how to recognize and exploit the following behavior that I'm about to describe here.
As premise for this thread, you need to know the difference between optical infinity an the infinity hard stop . Optical infinity is the spot on the focus ring at which a very distant subject, such as the moon, is at its best focus. The hard stop is the place at which the focus ring will turn no further. These two spots are often not the same. On some lenses (most likely high dollar cinema lenses) the optical infinity may be closely aligned with the hard stop. On other lenses, the focus ring will move well past actual infinity focus, such that the image becomes blurry again. As a user of a lens, you need to learn how to recognize, by simply looking at the focus indicator window on the lens, when the camera has focused in the zone that falls between sharply focused optical infinity and the hard stop that is where it is for other reasons .
There are good reasons for this extra mechanical play on some lenses, such as to accommodate heat expansion (as noted by Erwin Puts of some Leica designs), but only the designer of a given lens can tell you why it's there on a particular model. I can't speak with blanket knowledge of whether going past optical infinity and the infinity hard stop will result in a worse picture on all lenses, but in the case of the Nikon 24mm 1.4G it most certainly does. That being said, I'll get to the point.
The Nikon 24mm/1.4G is a lens on which the focus ring will keep turning well past a sharply focused optical infinity to a hard stop at which your image will be quite blurry. Therefore this is not a lens for which, during manual focus, you should ever just turn the ring until it stops, as doing so would result in bad picture (due to the design of the default focus screen in most Nikon cameras, it is extremely difficult to see this with the naked eye in the viewfinder). Rather, if you are forced to guess at infinity focus (and don't have time to go to Live View), you should turn the ring until it stops then turn it back by a learned amount.
I believe at this point that I have what qualifies as a properly functioning and optically excellent copy of the 24/1.4G, i.e. this is not a "broken" behavior, or does not appear to be based on my experience with 2 prior copies of this lens. That being said, its behaviors are not perfect. At close distances it cannot focus on as many different types of textures as the 14-24mm/2.8G, for example; and, in what I believe is a related behavior, it often misperceives focus on distant objects. This is easily observable by using the focus indicator window on the lens. For example, this picture shows the correct optical infinity for an object that is about a quarter mile away:
(Please excuse the cell phone quality pic of my camera.)
This picture shows a re-focus on the same object which resulted in an incorrect setting beyond actual focus and closer to the hard stop:
The actual infinity hard stop on my copy of the lens is a bit beyond the left edge of the infinity mark on the dial. Because this is a short-throw lens, the small movements of the ring make very large differences in focus as you approach optical infinity. So the focus pictured immediately above is quite a bit off, though it could get worse by going all the way to the stop.
An important aspect of "mastering" or "dealing with" this behavior is to learn when it's likely to do it, then use the focus window to periodically check the focus results as you shoot subjects that are likely to invoke this behavior. So far I have learned not to trust focus on any landscape that lacks ultra-high-contrast detail.
But, barring that Nikon improve this behavior with a firmware update, the real solution for slow-paced landscape shooting it to make increased use of Live View. I recommend setting the multi-controller center button to Zoom during Live View (this is function f1 on the D3s, for example). Because Live View seems to be immune to this particular error, working in Live View ensures an optimal result on difficult focus targets. Once that custom function is set, you can drop into Live View, zoom in quickly, set your focus manually, then either stay in Live View to take the pic or go back out to compose in the VF. Of course if you do the latter, be sure you either turn off AF when leaving Live View or configure your focus not to be on the shutter release.
My lens has an AF Fine Tune value of +4 on this particular camera body. To eliminate AF Fine Tune as possible source of this focus error, I turned off AF Fine Tune. The result is that the focus error is the same amount either way.
--
David Hill
http://www.bayareaweddingphotographer.com
San Francisco & San Jose, CA | Austin, TX
Wedding Photographer and Apparent Gearhead
As premise for this thread, you need to know the difference between optical infinity an the infinity hard stop . Optical infinity is the spot on the focus ring at which a very distant subject, such as the moon, is at its best focus. The hard stop is the place at which the focus ring will turn no further. These two spots are often not the same. On some lenses (most likely high dollar cinema lenses) the optical infinity may be closely aligned with the hard stop. On other lenses, the focus ring will move well past actual infinity focus, such that the image becomes blurry again. As a user of a lens, you need to learn how to recognize, by simply looking at the focus indicator window on the lens, when the camera has focused in the zone that falls between sharply focused optical infinity and the hard stop that is where it is for other reasons .
There are good reasons for this extra mechanical play on some lenses, such as to accommodate heat expansion (as noted by Erwin Puts of some Leica designs), but only the designer of a given lens can tell you why it's there on a particular model. I can't speak with blanket knowledge of whether going past optical infinity and the infinity hard stop will result in a worse picture on all lenses, but in the case of the Nikon 24mm 1.4G it most certainly does. That being said, I'll get to the point.
The Nikon 24mm/1.4G is a lens on which the focus ring will keep turning well past a sharply focused optical infinity to a hard stop at which your image will be quite blurry. Therefore this is not a lens for which, during manual focus, you should ever just turn the ring until it stops, as doing so would result in bad picture (due to the design of the default focus screen in most Nikon cameras, it is extremely difficult to see this with the naked eye in the viewfinder). Rather, if you are forced to guess at infinity focus (and don't have time to go to Live View), you should turn the ring until it stops then turn it back by a learned amount.
I believe at this point that I have what qualifies as a properly functioning and optically excellent copy of the 24/1.4G, i.e. this is not a "broken" behavior, or does not appear to be based on my experience with 2 prior copies of this lens. That being said, its behaviors are not perfect. At close distances it cannot focus on as many different types of textures as the 14-24mm/2.8G, for example; and, in what I believe is a related behavior, it often misperceives focus on distant objects. This is easily observable by using the focus indicator window on the lens. For example, this picture shows the correct optical infinity for an object that is about a quarter mile away:
(Please excuse the cell phone quality pic of my camera.)
This picture shows a re-focus on the same object which resulted in an incorrect setting beyond actual focus and closer to the hard stop:
The actual infinity hard stop on my copy of the lens is a bit beyond the left edge of the infinity mark on the dial. Because this is a short-throw lens, the small movements of the ring make very large differences in focus as you approach optical infinity. So the focus pictured immediately above is quite a bit off, though it could get worse by going all the way to the stop.
An important aspect of "mastering" or "dealing with" this behavior is to learn when it's likely to do it, then use the focus window to periodically check the focus results as you shoot subjects that are likely to invoke this behavior. So far I have learned not to trust focus on any landscape that lacks ultra-high-contrast detail.
But, barring that Nikon improve this behavior with a firmware update, the real solution for slow-paced landscape shooting it to make increased use of Live View. I recommend setting the multi-controller center button to Zoom during Live View (this is function f1 on the D3s, for example). Because Live View seems to be immune to this particular error, working in Live View ensures an optimal result on difficult focus targets. Once that custom function is set, you can drop into Live View, zoom in quickly, set your focus manually, then either stay in Live View to take the pic or go back out to compose in the VF. Of course if you do the latter, be sure you either turn off AF when leaving Live View or configure your focus not to be on the shutter release.
My lens has an AF Fine Tune value of +4 on this particular camera body. To eliminate AF Fine Tune as possible source of this focus error, I turned off AF Fine Tune. The result is that the focus error is the same amount either way.
--
David Hill
http://www.bayareaweddingphotographer.com
San Francisco & San Jose, CA | Austin, TX
Wedding Photographer and Apparent Gearhead
