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Nikon 50mm F1.2 Hard to focus
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PostPosted: Fri Dec 04, 2009 7:59 am    Post subject: Nikon 50mm F1.2 Hard to focus Reply with quote
I am using D90 with default focusing screen, try using 50mm/1.2 but very difficult to get good focus, when using Nikon 35-135mm and 200mm/f4 I can get perfect focus.

Is this the character of 50mm/f1.2 lens or there is something wrong with my lens ? I feel the focussing ring is too loose.

Thanks

Last edited by sky1174 on Fri Dec 04, 2009 8:18 am; edited 1 time in total


PostPosted: Fri Dec 04, 2009 8:06 am    Post subject: Reply with quote
The DOF of a 50mm f/1.2 lens is super thin, so no wonder that it's hard to focus. But at least one small plane in the picture should be in focus. Also, most focusing screens are not really suitable for the bright f/1.2 lenses. So use Live View if you have that function or get more experience focusing Smile


PostPosted: Fri Dec 04, 2009 8:21 am    Post subject: Reply with quote
Spotmatic wrote:
The DOF of a 50mm f/1.2 lens is super thin, so no wonder that it's hard to focus. But at least one small plane in the picture should be in focus. Also, most focusing screens are not really suitable for the bright f/1.2 lenses. So use Live View if you have that function or get more experience focusing Smile


May be should I use modified focusing to get a good focus? Does the 50mm/f1.4 also have the same character ?

Thanks


PostPosted: Fri Dec 04, 2009 8:58 am    Post subject: Reply with quote
Most DSLR viewfinders (With stock focusing screens) present a depth of field as if the lens was set around f4. Anything faster than that won't be reflected in the viewfinder, so you really can't nail focus no matter how good an eye you have.

You can appreciate this effect pretty easily with a fast lens. Focus on something close so you can easily see the focus transition and take a shot. Then compare the shot to what you see in the viewfinder, and hey where'd all that depth of field that was in the viewfinder go?

Focusing screens intended for MF, chipped adapters for focus confirm, and Live View can all improve on this. Lacking any of those aids, you'll have to bracket focus.


PostPosted: Fri Dec 04, 2009 11:06 am    Post subject: Re: Nikon 50mm F1.2 Hard to focus Reply with quote
sky1174 wrote:
Is this the character of 50mm/f1.2 lens or there is something wrong with my lens ? I feel the focussing ring is too loose.


The focusing feel of my 50/1.2 is firm but not stiff, it is certainly not "loose" as in almost travels by itself.

http://www.dofmaster.com/dofjs.html

On a D90, the 50/1.2 at minimum focusing distance and f/1.2 will give you total depth of field of 4mm. For critical focusing, I also recommend a tripod and live-view or focus bracketing when hand-held.


PostPosted: Fri Dec 04, 2009 1:54 pm    Post subject: Reply with quote
Mike Deep wrote:

Focusing screens intended for MF, chipped adapters for focus confirm, and Live View can all improve on this. Lacking any of those aids, you'll have to bracket focus.


The D90 is only lacking the first of those aids (and the focus screen can be changed for a better one). "Chipped adapters" are needed for Canon, but not for Nikon, to get focus confirm. And the D90 has liveview.


PostPosted: Fri Dec 04, 2009 1:55 pm    Post subject: Re: Nikon 50mm F1.2 Hard to focus Reply with quote
sky1174 wrote:
I am using D90 with default focusing screen, try using 50mm/1.2 but very difficult to get good focus, when using Nikon 35-135mm and 200mm/f4 I can get perfect focus.

Is this the character of 50mm/f1.2 lens or there is something wrong with my lens ? I feel the focussing ring is too loose.


Is this just at f/1.2, or at all apertures, with that lens?


PostPosted: Fri Dec 04, 2009 2:11 pm    Post subject: Reply with quote
I use MF with my Nikkor 85mm f/1.4 and the focus confirmation on my D700 (and previously D300) was pretty accurate, so you should be able to "nail it".

As pointed out, the DOF is very narrow, so the difference between good and bad as very thin.

If you stop down the lens, you should get much wider DOF so that you can do zone focusing; I do that when shooting in brighter light and with 50, 35 or 25mm lenses (unless I want the narrow DOF, of course).

Shoot at a ruler or similar to make shure that you can actually get focus.


PostPosted: Sat Dec 05, 2009 12:53 am    Post subject: Reply with quote
@Chris : At all Aperture not only F1.2

Thanks all for the info, I think I have to explore more to get better result and compare with other 50mm/f1.2 if i can find a friend that have the same lens


PostPosted: Mon Dec 07, 2009 12:00 am    Post subject: Reply with quote
It's probably worthwhile doing a few tests to make sure the focusing screen is properly aligned so the camera is focusing where it looks like it is. A small error in the alignment of the screen might be hidden at f4, but very noticeable at 1.2. If you have live view, use it when you can. I recently had the chance to use live view for a first time, and it's amazing how good my MF lenses are now.

--Geoff


PostPosted: Mon Dec 07, 2009 12:02 am    Post subject: Reply with quote
sky1174 wrote:
@Chris : At all Aperture not only F1.2

Thanks all for the info, I think I have to explore more to get better result and compare with other 50mm/f1.2 if i can find a friend that have the same lens



At all aperture ? Something wrong , yes.


PostPosted: Mon Dec 07, 2009 3:45 am    Post subject: Re: Nikon 50mm F1.2 Hard to focus Reply with quote
sky1174 wrote:
I am using D90 with default focusing screen, try using 50mm/1.2 but very difficult to get good focus, when using Nikon 35-135mm and 200mm/f4 I can get perfect focus.

Is this the character of 50mm/f1.2 lens or there is something wrong with my lens ?


Well, after reading the responses I'm not so sure about the relevance of my comment anymore, but I'lll make it anyway.

I bought a couple of 1.2 lenses a couple of months ago: a Canon FL 55mm f/1.2 and a Canon FD 85mm f/1.2. Using them first on a Canon AE-1 Program and then an F-1 -- both with standard focusing screens that consist of the split-image circle with microprism collar -- I found both lenses very difficult to focus. And this was with the standard focusing aids. I replaced the focusing screen in my F-1 with a plain ground glass screen and now I can focus with these two lenses much better.

I'm not familiar with the D90, but I own a Canon crop body camera -- 1.6x compared to the D90's 1.5x. And I find manual focusing with my Canon to be a real chore, mostly because of its rather tiny and squinty viewfinder. Live View helps immensely in that regard. I've mounted both my 1.2s to my Canon via an FD-EOS adapter, and looking through the viewfinder, I can't focus with those two lenses worth a darn. No problem with Live View, but not with that viewfinder.

Stopping down doesn't help either with my DSLR because the more I stop down, the dimmer the view is (because the iris is operating manually), and the harder it is to clearly see the object I'm trying to focus on.

So I'm thinking that it's not the lens and it's not you -- it's mostly that you're trying to manual focus with lenses that have very shallow depths of field with a crop-body camera.

Incidentally, Mike Deep's comment about focusing screens being designed to show an image as if the lens is stopped down to f/4 intrigued me, so I mounted my 85/1.2 to my F-1 and had a look. Nope. The out-of-focus areas are completely blown when I look through the viewfinder. And if I set the lens to f/4, then hit the stop-down lever, I'm looking at an image that looks as if the lens was stopped down to f/4. So, this is not the case with all focusing screens.
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