Nikon DX lenses - aperture control

[David Nardini]

I don't have any of the Nikon DX lenses, but, am I correct in assuming that they still have that small lever as shown below (back of the manual 17-35/2.8 shown) ?

When the DX lens is un-mounted, does iris close down completely ?
I hope the answer is YES.
And when one actuates the lever shown (move it with your finger / pen tip) does the aperture open ?
I hope the answer is YES.

Well ... given that there will be space between the lens mount and the RED sensor (I assume), then why not have some simple mechanism to control the aperture this way ? ie : if RED are going to offer a Nikkor mount, why not integrate this 'facility' in the mount ?
I only have two Nikkor lenses left (I moved to Canon a while back), but the position of these 'actuators' are in the same relative position.

I agree the movement is small, but hey, it could give access to quite a selection of other lenses ? No idea if Tokina, Sigma & others are the same as the Nikon DX in this regard.

Comments ... ?

PS : sadly the EOS system is sealed up ... but hopefully Birger Engineering will come to the rescue ;-)

[Dave Cooper]

Such as in this thread (http://www.reduser.net/forum/showthread.php?t=696) you can have the aperture completely open or shut on the lenses. A mickey mouse way of doing it is placing a piece of paper in the slot to keep the lever forward as much as you like. Maybe someone will develop a way to control the level as you suggest. Would be nice.

[David Nardini]

... A mickey mouse way of doing it is placing a piece of paper in the slot to keep the lever forward as much as you like ...

or indeed BLU TACK ;-)

[Evin Grant]

I recomended this to RED for their Nikon mount but the engeneering ended up being too complicated. The only problem is if the piece of paper gets dislodged and starts rattlening arond in the sensor chamber.:help:

[David Nardini]

I recomended this to RED for their Nikon mount but the engeneering ended up being too complicated. The only problem is if the piece of paper gets dislodged and starts rattlening arond in the sensor chamber.:help:

Hmmm ... I was thinking of a (can't think of a better word) screw-in-out 'plunger' to act on the lens lever. The screw action would be light proof and provide the fine control required for the actuation (care will be required when taking the lens off/on). Perhaps a simple internal 90 degree lever acting as a go between the plunger end & the lens lever will simplify usability ?

Not your normal 'aperture control', I agree, BUT worth a try ;-)
I'll try and make a drawing ...

[Evin Grant]

I know exactly what your talking about. Nikon made a C-mount adapter in the 70s that did this exact thing.

[David Nardini]

I know exactly what your talking about. Nikon made a C-mount adapter in the 70s that did this exact thing.

Ooooooooo, I see ... did a quick hunt on the net and found the following contraption.
I take it the 'plunger' in this kit acts like the old cable release ... (I'd prefer a screw thread I think ... a bit more control).

Did the RED team look to solve the problem this way ?

[Evin Grant]

I actually have that piece and gave it to them for engineering reference along with a diagram of a worm-gearded version. To their credit they considered it throughly but without accurate aperture setting they though it un-professional, which it is but it still would be nice. Birger sould have the Nikon G version of thier electronic mount out in the not too distant future so I don't really see a need for this anymore.

[Scot Olson]

... Birger sould have the Nikon G version of thier electronic mount out in the not too distant future so I don't really see a need for this anymore.

This may be a question for Birger as much as for you Evin, but are you sure an "electronic G mount" would control the iris? Or would it only allow VR and electronic control of the focus motor on AF-S lenses?

Although G mount lenses do not have an an aperture ring they also do not have an iris motor to control the iris. As far as I know they simply require the iris to be controlled by the camera via the same mechanical lever as non G lenses. This is different than a Canon Eos mount lens that I believe does allow electronic control of the iris position via electronic control.

Although I agree a worm gear or other mechanical arrangement might not be elegant, it might work pretty well.

[Erik Widding]

Although G mount lenses do not have an an aperture ring they also do not have an iris motor to control the iris. As far as I know they simply require the iris to be controlled by the camera via the same mechanical lever as non G lenses. This is different than a Canon Eos mount lens that I believe does allow electronic control of the iris position via electronic control.

Our Nikon unit will have a motor in it for control of the iris. You are correct, iris control is only mechanical. The minimum and maximum aperture are communicated to the camera body electronically.

[S. Um]

Erik,

Will your controller be able to maintain a constant aperture with lenses that change apertures over the zoom range? (Of course, assuming the lens is not set at the widest aperture).

[chuck colburn]

Erik,

Will your controller be able to maintain a constant aperture with lenses that change apertures over the zoom range? (Of course, assuming the lens is not set at the widest aperture).

You would not need that if you set the lens for the smallest stop that would work at all focal lengths.

[S. Um]

You would not need that if you set the lens for the smallest stop that would work at all focal lengths.

I'm not sure this is true. On the older manual cameras, the aperture definitely changed when you zoom in a variable aperture lens. So I think that if you hold the aperture pin in 1 place, then the aperture will change when you zoom. I think the new cameras can recognize variable aperture lenses and adjust the aperture pin accordingly to maintain a constant aperture throughout the zoom range. The Birger controller would need this capability to maintain a constant aperture.

[Erik Widding]

I'm not sure this is true. On the older manual cameras, the aperture definitely changed when you zoom in a variable aperture lens. So I think that if you hold the aperture pin in 1 place, then the aperture will change when you zoom. I think the new cameras can recognize variable aperture lenses and adjust the aperture pin accordingly to maintain a constant aperture throughout the zoom range. The Birger controller would need this capability to maintain a constant aperture.

Aperture does change when zooming a variable aperture lens, in both Canon and Nikon mounts. We need to know the current max aperture of the lens, to then calculate the mechanical position of the iris. The lenses give us, in most cases, 8 or 16 discrete values for current focal length and current max aperture. So you will see continuous variation in the amount of light the lens is capable of letting in, but at best, we will be compensating for this in discrete steps.

With the Canon mount, in a dynamic situation, we can adjust to a quarter stop, but for a number of technical reasons we are better off adjusting to only one half stop intervals. When we release the Nikon product we will announce the numbers for that mount. It is too early in the development to tell.

I think many will draw the same concusion that I do here. Variable aperture zooms are only good enough to be used as variable primes. Theoretically one could normalize the exposure across the sequence of frames in post, but I have to imagine that this is a bad idea. I will leave it for others to say just how bad.