I just picked mine up today and while I am pleased with the first test shots, I noticed that when I focused at 24mm but zoomed in to 70mm, the image on the viewfinder was noticeably out of focus. Is this lens a parfocal lens then? Not a big deal by any means really but I am just curious.
After I posted the thread, I realized I should have made it clearer. I should have said that I thought this was a parfocal lens. Yes, the focusing distance changes at any distance. I remembered during the MF days, it was really a pain but now by a push of a button, it will focus instantly; well, almost . Again, no big deal, I just didn't realize that.
Yes, its parfocal. I've seen a couple of reviews that say the focus accuracy at 24mm is not perfect (on some samples, perhaps) and the corresponding recommendation is to zoom in to 70mm, focus, then zoom back out to 24mm. What you may be seeing is this innacuracy at the 24mm setting. I wonder if you focus at 70 and zoom to 24, is it still in focus?
Your post made me curious, too. Pulled mine out and found the same thing you did.
Ironically, I'd not noticed this in actual shooting. I guess this is because, with a mid-range zoom, I usually set the focal length, then compose, and then focus--rarely zooming after making the initial choice of focal length for a given composition. For someone who has a different way of using zooms, I could see it making a bigger difference.
Well, that still doesn't quite count, but that's my fault for not phrasing the question clearly. Does focus vary when you zoom while focused outside close range, so say beyond 6' or better, at infinity? If it does, then this is a full-range varifocal lens which really does surprise me. Focus variation at close range is pretty common and the fact that this lens has a different MFDs at different focal lengths is a good indicator that some CRC is used to increase magnification, which again is a pretty common design.
I've read some reports that the 24-70 tends to misfocus at 24mm. That could be another reason there's a focus variation -- between good focus and misfocus. So I'm curious if this behavior is still there between 30-70mm
Elan, I just tried mine with an object about 25 feet away--it's night time here, so infinity isn't an option. The effect is definitely there at a 25-foot distance.
Also, the need to refocus is apparent between 70mm and 35mm, and, to a lesser degree, between 35mm and 24mm.
Not that any of this matters to me--as I said earlier, I hadn't actually noticed the effect in the couple of months I've owned it.
Elan II wrote:
Well, that still doesn't quite count, but that's my fault for not phrasing the question clearly. Does focus vary when you zoom while focused outside close range, so say beyond 6' or better, at infinity? If it does, then this is a full-range varifocal lens which really does surprise me. Focus variation at close range is pretty common and the fact that this lens has a different MFDs at different focal lengths is a good indicator that some CRC is used to increase magnification, which again is a pretty common design.
I've read some reports that the 24-70 tends to misfocus at 24mm. That could be another reason there's a focus variation -- between good focus and misfocus. So I'm curious if this behavior is still there between 30-70mm ...Show more →
It shows varifocal characteristics even at 6-7 feet. And yes, the behavior is there as well if focused at 30mm and zoomed in to 70mm, but not as much as from 24mm. As others have mentioned, it is definitely not a parfocal lens.
Well, Chris posted the same conclusion and beat me to it .
It is my understanding that this lens is parfocal. There can be some loss in focus, but it still is parfocal. I've pulled mine out, set A5 to Off and shot numerous test shots. They all were in focus. I believe Nikon calls this Internal Focus (IF), but don't quote me.
Varifocal lenses do not keep focus, at least that is my understanding.
Thanks for the info guys. Very interesting. I don't know if there's such a thing as a 'mild' varifocal, but if there was, it sounds like this lens would fit the description. I have several varifocal MF zoom lenses and with those, the change in focus while zooming is pretty drastic. Although the quality of some of them can be quite stunning. The Tokina 35-105/3.5 especially.
I would think that any Nikon 24-70 that doesn't reasonably hold focus would be defective. I've had varifocal lenses and you had to refocus after zooming--the 24-70 definitely isn't varifocal.
john s. wrote:
Yes, its parfocal. I've seen a couple of reviews that say the focus accuracy at 24mm is not perfect (on some samples, perhaps) and the corresponding recommendation is to zoom in to 70mm, focus, then zoom back out to 24mm. What you may be seeing is this innacuracy at the 24mm setting. I wonder if you focus at 70 and zoom to 24, is it still in focus?
Joshua,
This is exactly what I noticed what John s. said that the focus accuracy is not perfect at 24mm however when you focus at 24mm and take a picture it is sharp even wide open which is most likely due to the larger depth of field at 24mm.
So myself also got into the habit to focus at 70mm (I never use the shutter release for focus) then zoom to frame and take the picture.
To be honest with you I found the same thing with my Canon 24-70L lens also and used the same practice.
James,
Based on your description, there are quite a few of defective 24-70mm out there, mine included. However, I am not quite convinced that this is the case. I will contact Nikon and try to get a confirmation one way or the other.
Julius,
So yours has the same varifocal characteristics as well, huh? I sold my Canon 24-70mm already but my 24-105 seems to be parfocal, at least on the viewfinder while the Nikkor definitely seems to be more varifocal than the Canon. We have not confirmed this though. Like I mentioned in the original post, it doesn't bother me if it is indeed varifocal, since I tend to refocus again before I press the shutter button anyway.
This thread made me interested but confused. I personally don't have a 24-70 but planning to buy one so there are a few questions that I want to make them clear before my purchase.
Are parfocal lenses by all means good lenses? From my experience every lenses I've used need to refocus if I readjust the zoom length. Is 24-70 meant to be that way as well?
Is 24-70 a parfocal lens?
Is AGeoJO's lens needed to send back to Nikon for recalibrate?
Should I test the lens before buying?
AFAIK, parfocal lenses are rare. I own several pro nikkors and I think that the only one that is parfocal is the 70-180 micro. Not sure about that.....
. Again, no big deal, I just didn't realize that.