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Archive 2010 · My new Zeiss ZF 100 f/2 has focus issues
  
 
Todd Adamson
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p.1 #1 · p.1 #1 · My new Zeiss ZF 100 f/2 has focus issues


I received it two days ago, and it's the first Zeiss lens I have ever used. I have been manually focusing a lot recently with old Nikkor lenses, with great success. I am using a D700 right now, and shooting from a tripod. I have the stock focusing screen and am just using the focus confirmation dot to assess focus. I have been doing this routinely with my pre-AI Nikkor 135 f/2, at f/2, and nailing focus 95% of the time. So far with the Zeiss, about 90% or more of the images shot with the same methodology are back-focused.

I know the DOF is supposed to be thinner, but I am pretty good at this (at least with several Nikkor lenses...also manually focusing the Nikkor 85/1.4 at f/1.4). Below is a real world example (I shoot portraits) of what I am talking about. The full image, then 100% crop. I used a peripheral focus point to focus right on her eye (not recomposing). I get the conformation dot firmly ON, then click. From a stable tripod, good shutter speed, etc. It's back-focused. Again and again. I can't get a person in focus dependably unless I go to f/5.6, and even then the eyes are in focus but the tip of nose isn't.

Any suggestions about what I might be doing wrong, or what my next step should be?














Aug 28, 2010 at 01:26 AM
theSuede
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p.1 #2 · p.1 #2 · My new Zeiss ZF 100 f/2 has focus issues


The Zeiss has less spherical aberration than the lenses you mentioned, which means that the plane of best focus will not move towards you as much as the other lenses (when used fully open). Try focusing exactly at the flip between focus-confirmation dot on/off in the close direction.

If the Zeiss is a ZF2 version, you can also adjust it with the menu option "AF fine tune" - a solution that actually works with this type of problem (but not with all AF-lenses and zooms...)



Aug 28, 2010 at 02:20 AM
Oasisbill
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p.1 #3 · p.1 #3 · My new Zeiss ZF 100 f/2 has focus issues


Have you used Fine tune in the D700 menu?


Aug 28, 2010 at 02:30 AM
tjny
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p.1 #4 · p.1 #4 · My new Zeiss ZF 100 f/2 has focus issues


Oasisbill wrote:
Have you used Fine tune in the D700 menu?


That was also my first impression, Nikon bodies are calibrated obviously for Nikkors. Any minor discrepency you may be able to fine tune with camera body.



Aug 28, 2010 at 02:43 AM
Todd Adamson
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p.1 #5 · p.1 #5 · My new Zeiss ZF 100 f/2 has focus issues


I did try the fine tune, to no avail. I wasn't sure if it was doing anything at all....and after reading theSuede's post, I'm thinking maybe the fine tune will not work, since it's a ZF version?

I can try the "flip" method he mentions and see if that works. Not until next week, though....this was a borrowed D700.....my D3 is at Midwest Camera Repair right now, so I have no FX body until end of nest week at the earliest.

Let me ask you this: let's say I try the flip method, and it works. Based on that and the amount of backfocus you see in the image, do you think it's likely this lens is behaving normally, and I am just too n00b to deal with it, or would you say it might have a problem that could be dealt with? Is there a Zeiss service center in the US that could assess this for a reasonable fee?



Aug 28, 2010 at 02:53 AM
ht1948
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p.1 #6 · p.1 #6 · My new Zeiss ZF 100 f/2 has focus issues


If you are shooting on a tripod, how about giving live view a shot? This is not that unusual with MF lenses when shooting with shallow DoF.


Aug 28, 2010 at 02:57 AM
Todd Adamson
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p.1 #7 · p.1 #7 · My new Zeiss ZF 100 f/2 has focus issues


ht1948 wrote:
If you are shooting on a tripod, how about giving live view a shot? This is not that unusual with MF lenses when shooting with shallow DoF.


That's something else I have not tried. But for the flow of my sessions, I think that would not be good to have to do that. Again, I have no problem focusing my MF Nikkors accurately, even at wide apertures. Is it really possible that a Zeiss lens will require that much more work? If this is the case, perhaps I am not ready for one.

If the method suggested by theSuede worked, simply using the confirmation dot as a reference, THAT is something I am sure I could adapt to....



Aug 28, 2010 at 03:06 AM
Todd Adamson
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p.1 #8 · p.1 #8 · My new Zeiss ZF 100 f/2 has focus issues


theSuede wrote:
The Zeiss has less spherical aberration than the lenses you mentioned, which means that the plane of best focus will not move towards you as much as the other lenses (when used fully open).


Would you mind elaborating on this? I'm not entirely clear on what you mean.



Aug 28, 2010 at 03:09 AM
edwardkaraa
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p.1 #9 · p.1 #9 · My new Zeiss ZF 100 f/2 has focus issues


I can't believe you're blaming a mf lens for back focusing. Have you tried focusing the lens the normal way, by checking sharpness on the focusing screen?


Aug 28, 2010 at 03:37 AM
Justin Huffman
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p.1 #10 · p.1 #10 · My new Zeiss ZF 100 f/2 has focus issues


edwardkaraa wrote:
I can't believe you're blaming a mf lens for back focusing.



Hu He's not. He's asking for advice based on his technique and hardware... neither of which placed blame on any one factor. read the original post... sheeesh...



Aug 28, 2010 at 03:42 AM
 

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theSuede
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p.1 #11 · p.1 #11 · My new Zeiss ZF 100 f/2 has focus issues


Spherical aberration is quite hard to visualize, but imagine that you could separate the light passing through the lens like an onion, in several concentric layers. The middle would be very high F-no's, the outer layers would be the lowest F-no's (largest apertures).

Light comes from one POINT in the scene, passes through the DISC of the aperture, and is concentrated to a POINT on the sensor again (if the point in front of the lens is "in focus"). Spherical aberration means that light passing through the aperture closer to the rim is not focused at the same plane as light passing through the middle of the aperture.

Most lenses have a positive SA, meaning that you get "focus shift" as you stop down, the plane of best focus moves backwards as you increase F-no. This is also what gives "smooth bokeh".

Your camera MEASURES focus at roughly F/5.6, meaning that it measures the light passing through the lens at an ANGLE of F/5.6. Light passing through the lens closer to the middle of the aperture (F/11?) and further out towards the edge of the aperture (F/2.0?) is ignored, blocked out by the optics in the AF-module.

Now, if a lens has less SA, the focal distance difference between the F/5.6 "layer" and the F/2.0 "sum" of light will be smaller. And if the lens has more SA, the difference will be bigger.

The D700 is quite probably slightly back-focusing, a behavior that fits perfectly to most fast lenses, like the 50/1.4, 85/1.4 and 135/2. The back-focus perfectly offsets the amount of focus shift from F/5.6 to F/1.4-F/2. But since the 100F/2 macro has less SA, you get less focus-shift, ending up with a system total @F/2 of a slight back-focus.

And no, I don't think the AF-adjustment works if the camera doesn't receive a lens ID - which you don't get from the ZF-lenses before the ZF.2 update. But the "front on/off limit" dot trick should do the trick, if your sample picture is about the "average" error you get.



Aug 28, 2010 at 03:49 AM
Keith B.
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p.1 #12 · p.1 #12 · My new Zeiss ZF 100 f/2 has focus issues


There may be optical design differences between the Nikon lenses you've been using and the Zeiss 100 which may subtly contribute to your focusing error using the D700, such as the LACK of a focus shift between viewing wide open and stopping down to expose, or vice-versa(though I'd bet on the former, except in the case of the ZF 85). I have the Nikon 135/2, and the ZF100, and I'm using the D3 camera which has a noticeably contrastier finder. I'm able to successfully focus either lens by eye. Assuming your eyesight is decent(mine is, with glasses), couldn't you use your eyes to focus instead of relying on the green dot? Maybe reset the diopter adjustment more often(several times in a day if necessary), or try the Nikon focusing magnifier(DK-17A, I think) for this camera. All pro-level cameras need to have a internal, flip-in 6X magnifier built-in, but it would increase the size by 1.5 cubic inches or so and raise the cost by $40, so the profit-addled manufacturers won't do it.


Aug 28, 2010 at 03:54 AM
magiclight
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p.1 #13 · p.1 #13 · My new Zeiss ZF 100 f/2 has focus issues


I shoot Canon 1DS Mr3 and all my Zeiss lenses are way out using the 'green dot'. All three lenses required a good deal of Microadjustment dialed in.

I calibrated all lenses at the point were the green dot first comes on when focusing in from infinity.

My focus hit rate now is very good when shooting wide open.



Aug 28, 2010 at 04:15 AM
edwardkaraa
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p.1 #14 · p.1 #14 · My new Zeiss ZF 100 f/2 has focus issues


Justin Huffman wrote:
Hu He's not. He's asking for advice based on his technique and hardware... neither of which placed blame on any one factor. read the original post... sheeesh...

What an idiotic post. Are you his lawyer or his brother? He clearly says his lens has focusing issues. Sheeesh



Aug 28, 2010 at 04:38 AM
philber
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p.1 #15 · p.1 #15 · My new Zeiss ZF 100 f/2 has focus issues


Todd, an MF lens cannot have focusing issues unless it is mechanically broken. What you are experiencing is a discrepancy between your AF (confirm), which is body-dependent and your lens. You are confident that this is not a camera issue becuse you don't experience this problem with MF Nikkor lenses. As The Sude points out, this is not necessarily true. It could also be a slight calibration issue of the AF device, which is why Canon and Nikon offer micro-adjust in their high-end cameras.
On top of which, fact is, if you are shooting portrait at the distance of your sample, and, based on the background blur, wide open or close, you will have a ridiculously thin DOF. Plus, as was explained by Makten on another thread, because of the very short throw of this part of the range of this macro lens, nailing focus is going to be mechanically very challenging.
The only way to find out if indeed your lens is "off" in some mysterious way is to use liveview, because, then you are not using the AF system or the viewfinder, two potential causes of your issue. I understand that you may not want to work this way, but at least you should use it as a troubleshooting method, and report back.
Hope this helps.



Aug 28, 2010 at 07:22 AM
Andi Dietrich
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p.1 #16 · p.1 #16 · My new Zeiss ZF 100 f/2 has focus issues


Feel free to correct me here, I just try to remember what I have read about it...

The camera uses phase detection and not contrast detection for autofocus. In the process the best focus is calculated and not measured.

I understand that the lens is part of the focus system in the way that it has to interpret the signals from the camera. If that so, then it doesnt matter if it is a MF or AF lens, both can misinterpret the readings.

maybe the fools hat can be given around



Aug 28, 2010 at 09:16 AM
Jonas B
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p.1 #17 · p.1 #17 · My new Zeiss ZF 100 f/2 has focus issues


Andi Dietrich wrote:
Feel free to correct me here, I just try to remember what I have read about it...

The camera uses phase detection and not contrast detection for autofocus. In the process the best focus is calculated and not measured.

I understand that the lens is part of the focus system in the way that it has to interpret the signals from the camera. If that so, then it doesnt matter if it is a MF or AF lens, both can misinterpret the readings.

maybe the fools hat can be given around


To my understanding the PDAF system measures the phase shift and then calculates how many steps the lens focusing motor should move to achieve no phase shift. There are open loops systems and closed loop systems, in theory making for faster focusing but accepting more errors or slower focusing process but more correct as the result from the focusing action is checked and sometimes adjusted again. So, both measuring and calculating.

When manually focusing a lens waiting for the green signal all we can do is turn the focusing ring until the camera measures the phase shift to be close to zero. The lens never interprets any signals from the camera. So, in the end there is measuring only - resulting in green light or not.

Well. Anyone knowing better, feel free to correct me as well.



Aug 28, 2010 at 09:39 AM
Todd Adamson
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p.1 #18 · p.1 #18 · My new Zeiss ZF 100 f/2 has focus issues


edwardkaraa wrote:
What an idiotic post. Are you his lawyer or his brother? He clearly says his lens has focusing issues. Sheeesh


Simmer down, Sparky. I'm just looking for help, and I'm happy that some people are willing to provide it. There are only so many characters in a thread title, and I want people to read and reply. You may not have read my first post. The main question, clearly, is "What am I doing wrong?"

THANK YOU everyone for the posts, and the very detailed info. I haven't had time to digest it all yet, but later this morning I will. I have the Diglloyd membership, so I need to read up on things like Focus Shift, etc, and I will. I'll also do some testing with Live View, but as I said I can't do this until next week.

Makten said in another thread: "The Makro-Planar is better than you, and every flaw is because of you." I am going on the theory that he is probably right, and I'm simply trying to bring my skills up to the level of this lens.

The seller of the lens has immediately and very kindly offered to take it back, but again, I hope I am just not living up to the lens yet, and that with practice and a little help from everyone here, I can change that. I shall be reporting back with results, and no doubt further questions. Thanks again.



Aug 28, 2010 at 12:18 PM
theSuede
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p.1 #19 · p.1 #19 · My new Zeiss ZF 100 f/2 has focus issues


You can at least count on the focus confirmation dot to behave CONSISTENTLY, which really is the main criteria for "learning" to manually focus a lens with it. That's why using the front on/off, middle or back on/off of the dot can help a lot. Wait for the return of your own D3, and do some controlled testing - it only takes a few minutes. Static subject, normal daylight, take three pictures - first on the front on/off, then middle, then back on/off. To ensure that no freak mistakes affects the test too much - Change angle a bit, do over. Move the tripod again, do over. From just those nine pics you will be able to see where your focus "aim" with the 100/2 and your D3 ideally should be.

Jonas;
No need to correct anything there, except - be careful when quoting "closed loop" systems, some people get really edgy about the absolute definition of "closed loop systems".... :-)



Aug 28, 2010 at 01:43 PM
Jonas B
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p.1 #20 · p.1 #20 · My new Zeiss ZF 100 f/2 has focus issues


theSuede wrote:
(...)
No need to correct anything there, except - be careful when quoting "closed loop" systems, some people get really edgy about the absolute definition of "closed loop systems".... :-)


Thank you.
Ah, well... there are always some very touchy lurkers/posters out there. The closed loop thing was taken from memory and discussions in Pentax forums... several years ago. I won't mention it again.



Aug 28, 2010 at 03:05 PM
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