Richard C writes:
Thanks to your rigorous reviews, I have now decided to buy a Nikon D800 instead of a Canon 5DmkIII, but this has raised an issue I have a serious doubts about.
I shoot a lot of time-lapse films, and had been looking forward to being able to set aperture manually using ZF.2 lenses (Nikon mount) fitted to the 5DmkIII with lens adapters, and thus eliminate any risk of aperture flicker occurring in my sequences.
However, if I buy the D800 instead, then aperture flicker becomes an issue again, as the body will set aperture electronically for every shot. The wonderful Zeiss Guide you have compiled suggests that you cannot get around this issue, but then I came across this comment on a forum (discussing hidden D800 features)...
"You can use the physical aperture ring on CPU lenses to set aperture, if you change the menu custom setting f9 > Aperture Setting to "Aperture ring" instead of "Sub-command dial"."
This is a very big deal for me and most other time-lapse shooters, and it would be great if you would (a) verify the accuracy of this suggestion and (b) note it accordingly in your guide.
DIGLLOYD: First, I admit to not understanding what “aperture flicker” is— as far as I know, first the aperture is stopped down, then the shutter is opened—always. So I don’t understand this point.
Custom setting f9 allows the aperture ring to choose the aperture. But this is simply an ergonomic alternative to specifying the aperture; it has no behavioral difference from setting it using the command dial.
However, there is one feature which does stop the aperture down prior: exposure delay mode, custom setting d4. Set to one second, the camera will stop the aperture down, mirror up, then take the image 1 second later (2 and 3 seconds are also choices).
Salim M writes:
The flicker is caused by the fact each frame of time-lapse the diaphragm is closed down to the appropriate f-stop.
The closing of the diaphragm is not 100% the same from frame to frame and causes slight variation of exposure. This variation when viewed as a time-lapse creates a flicker effect since you have a frame that is just a tad less or more exposed. The remedy is to use old manual lenses where the aperture is fixed from frame to frame.
DIGLLOYD: That makes sense. As far as I know, it takes power to stop the lens down, which might be an excuse for no option to control the behavior (e.g., leave the diaphragm stopped down).
Best solution seems to be to use a converted lens which has a fully manual aperture: Olympus, Leica and others.
I’ve noticed minor exposure variations that I couldn’t explain from time to time, maybe the tolerance is as much as 10% on stopping down? (I’ve seen up to 3/4 of a stop in the f/22 range with some Leica M lenses, even though those are manual control).
Richard C writes:
Flickering is a common problem in time-lapse footage captured using a DSLR. Frame by frame variations in lighting or in exposure lead to perceptible brightness fluctuations, i.e. flicker. In the case of aperture flicker (there are other potential sources too), exposure variations are caused by limited precision and repeatability in terms of iris actuation. For each shutter press, the camera activates a mechanical device that moves the iris to the desired aperture. The aperture cannot be exactly the same size every time because of friction and other factors, so there are differences in exposure that result in frame-to-frame luminance variations that show up as flicker when played back. Aperture flicker is less evident with smaller f-numbers (larger apertures).
Using fully manual (i.e. non CPU) lenses with manual aperture rings totally eliminates the risk of aperture flicker from occurring, because turning the ring physically opens and closes the iris, and once you choose your desired f-number the iris will not move again until you move the ring. In a sense, it is locked in position, so frame by frame variations in its size cannot occur. Now, I'm told that using ZF.2 lenses on Canon bodies has the same effect, as turning the aperture ring moves the iris and effectively sets it advance (and locks it in place until you choose to change it).
Moving on to ZF.2 use on Nikon bodies, I didn't think the same concept was possible, as you have to lock the aperture at f22 in order to allow electronic aperture control without FEE errors arising. But, if you can tell the body to allow the ring to set the iris, then full manual control should be restored. I understand the points you have made, but surely the physical action of turning the aperture ring (after setting aperture control to the ring option) changes the size of the iris there and then, and holds it in place until you turn the ring again, i.e. a behavioural difference that will prevent frame by frame luminance variations from occurring?
DIGLLOYD: yes, certainly any lens whose aperture ring stops the lens down and stays there is the dead-certain solution.
ZF.2 lenses are not “locked” at f/22 per se; this is just the setting that allows electronic aperture control, which is marked as f/22. The lens is never actually at f/22 (unless that is the chosen aperture).
One can turn the ring willy-nilly to any aperture with zero effect. The camera will not stop down the aperture until the DOF preview is used, or Live View, or the image is taken. In all those cases, the control is electronic (for Zeiss ZF.2 lenses).
With Zeiss ZF lenses and older Nikkors, there is a manual stop, and this might work, assuming turning the aperture ring has repeatable stops (mechanical lever positions).
Luc O writes:
One option is to use ZF lens instead of ZF2. As specified by Zeiss, this works on D700 body.
The mechanical control should reduce the flicker issue. At least, with a Contax/Zeiss lens 85mm/1.4, I did not observe it with a serial exposure on slides.
Although a ZF lens is not as secure as manually stopping down an adapted Lens, it is easy to get a second hand ZF lens and I expect the stop down of the diaphragm to be precise as Zeiss lenses (Contax at the time) were reported to be precise by the magazine Chasseur d’Image in the 90’s (if I recall correctly 0.1 aperture or less was the “standard”). In one sentence, it is worth a try.
DIGLLOYD: Worth a try, yes. But 1/10 stop would likely cause flicker I would think.
A Context/Zeiss lens would be full manual control AFAIK; turning the ring would stop down the lens no matter what. Of course that would work. I don’t understand the D700 comment.
A Zeiss ZF lens (or older Nikkor) uses mechanical stops, not electronic control. As noted above, this might be a solution if those mechanical diaphragm stops have no variation (e.g., choosing f/8 always puts the mechanical stop in exactly the same place, thus making the aperture exactly the same size). I’m skeptical, because the aperture blades could stick just a little, or maybe those stops aren’t 100% repeateable. Compared to a lens that stays put forever once the aperture is set, it’s a “worth a try” solution that might work— I don’t know.
Miguel B writes:
I think he might be able to get around this fully if (god forbid!) he unlatches the lens from the fully locked position, enough to have the aperture lever not open up the diaphragm. Obviously there would be no AF or aperture readout, but there's no AF in the Zeiss lenses anyway and I presume he's using manual exposure anyway.
It takes a slight turn to undo the lever effect, the lens feels pretty tight still. Give it a try: stop the lens to the smallest aperture (highest f number), unlatch, and turn slightly until the diaphragm fully closes.
Only issue is to be careful not to loosen it too much or the lens might get loose and wobbly. I just tried it on my D700 and it works like a charm.
DIGLLOYD: This won’t work at all for Nikon “G” lenses, which have no aperture ring.
It makes me nervous for the obvious reason: the lens falling off (time lapse and wind for example). Duct tape?
Other concerns would be focusing (might be hard to do exactly if the lens is loose) and also planarity (lens to sensor alignment).
With all due respect why is there discussion about flicker with a professed stills (not video) shooter such as yourself.
I would think these folks need to look at the Zeiss lenses designed for video to see how they set aperture, certainly their requirements are quite exacting for those multi-million dollar budget movies.
DIGLLOYD: the writer thinks that I am unfit to discuss still photography if stills are used for a video sequence. The first four weasel words speak for themselves. Yuck.
The Zeiss CP.2 lenses are stated as having “Stable exposure due to manual operated aperture”, which presumably means the aperture is not electronically controlled and will stay where set (diaphragm stopped down). I don’t know if this is true or not, but I’ve inquired with Zeiss.
Assuming a shooter is willing to invest in new lenses at 2X - 3X the price of Zeiss ZF.2 lenses, and deal with the larger and heavier form factor, this might be a solution. But a video rig that supports the lens might be needed, since the CP.2 lenses are quite heavy, and might place undue stress on the lens mount.
Richard C writes:
I must admit that all of the above has left me even more perplexed than before! Tackling several of the points in turn...
What Miguel describes is already a well known cheat in Canon circles, and is commonly termed the 'lens twist method'. You set the shutter and aperture for your scene, press the depth of field preview button (which stops down the iris) and, whilst continuing to hold it in, then press the lens release button and undo the lens by about 5-10 degrees. This decouples the lens from the body with the iris locked in place, meaning that you can now shoot as many frames as you like with no change whatsoever in the size of the iris... and thus no flicker. Yes it's risky to a degree, but it is how I currently shoot time-lapse with my 60D and EF lenses, with no accidents to date. However from what I have read some Nikon bodies and lenses are not as tolerant of this trick.
To answer Daryl's poorly put point; I want to buy ZF.2 rather than CP.2 lenses because I am also a stills shooter. The CP.2 lenses, whilst outstanding for rolling video use, are too bulky and heavy for my needs, and don't feature essential stills accessories such as hoods (they use matte boxes instead). Time-lapse requires more the skills of a photographer than a cinematographer, so there is no question that Lloyd is well placed to oversee and moderate this discussion!
Returning to the nub of the issue; today I telephoned the official Zeiss distributor over here in the UK (who also happens to be a Nikon specialist) and discussed the topic with them. Hats of to you Lloyd, everything you said about the way aperture control works when ZF.2 lenses are attached to Nikon bodies is correct, save for one thing.
It turns out that it is a straightforward job to remove the electronically actuated aperture lever from within the lens, making the lens fully manual with regard to iris movement. Furthermore, this low cost modification does not invalidate the warranty (as long as it is performed by an official Zeiss trained technician) and can easily be reversed for resale purposes in the future. Bingo, issue resolved!
Thanks for your help and comments, and please keep up the great work.
DIGLLOYD: great tip on the electronic-defeat!
Zeiss CP.2 aperture
Richard Schleuning of Zeiss USA explains how the Zeiss CP2. cine lenses control the aperture (lens diaphragm):
The CP.2 lenses feature a continuous, manual aperture using 14-blades.
The aperture is controlled manually, which allows the lens to be mounted to a variety of camera platforms without the dependency of an electronic interface. From a functional standpoint, it also allows the filmmaker to continuously 'pull' the iris as they are filming, to account for changes in light as the camera is panned across the scene.
All of the CP.2 mounts designed for still cameras (EF, F, MFT and E) feature a support bracket. This bracket allows the use of a support post to the camera rig and isolates the lens from the camera body. This will prevent the shifting of the lens in the mount during focusing, which is especially important when manual or motorized follow-focus systems are used. The PL mount version of the CP.2 lenses does not need the support bracket due to the robust nature of this mount type.
Heavier lenses, such as the new CZ.2 70-200 zoom, will use both the support bracket as well as a mounting bracket to support the lens' weight. The latter is used across all of the mount types, as no mount is completely free from the stresses of using a long, heavy lens.