Focusing Issues with Nikkor T-ED 360/500/720 lens?

[LFLarry]

I am in the process of buying a Nikkor T-ED 360/500/720 lens and I was reading about its nodal point and the impact on focusing with axis tilt cameras. The way I understand this issue is that the image on the ground glass will move as I apply tilts and/or swings. My 4x5 camera has axis tilts, so I thought I would get some input from the group here so I can be prepared when the lens arrives.

I am wondering how much of an issue this is in reality and based on experience, do you have any suggestions or tips to pass along?

Thanks!

[Huub]

I have the same set and tilting and swinging the front standard is a pain as the nodal point is way in front of the lens. It makes that even small amounts of tilts and swings lead to massive movemens on your ground glass, often in combination with loosing your point of focus. When using this set i limit myself to shifts on the front standard and use my back standard for tilts and swings. Not ideal because of the impact on the shape of objects, but when doing landscapes it is often acceptable.

[Pere Casals]

In fact all long focals rise a lot the image circle when doing a front tilt, a tele rises it less than a regular lens !!!!


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I wanted to know, and... with the 720mm T nikon, a 10º tilt provocates a circle rise that is 42mm smaller that the one that would provocate a regular non Tele lens,

So a Tele lens is more suitable than a regular lens for field cameras that have limitations in the movements, not only for the commanded extension, but also (usually) it would be benefical that you have a lower rise provocated by a front tilt.


It was a urban legend, the reality is that having the nodal point in front of the (long focal) lens is benefical because it decreases the rise effect of a front tilt, compared to a regular lens having the nodal near aperture.


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With long focals, use first the rear tilt, after reaching rear tilt limit you have to use the front tilt, but with a Tele lens you will be able to tilt more degrees, as a regular lens exhausts sooner the rise margin you have for compensating.


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Note that while the T system has clear advantages for the field... also a Tele lens has optical drawbacks. It is true that in many situations you'll have other limiting factors. But in particular it's not clear to me if the 720 is necessary, as we may get mostly the same quality if shooting with the 500 and later taking the crop of the equivalent framing, specially if we use a sharp film like (say) TMX or Velvia.

[Pere Casals]

I have the same set and tilting and swinging the front standard is a pain as the nodal point is way in front of the lens. It makes that even small amounts of tilts and swings lead to massive movemens on your ground glass, often in combination with loosing your point of focus.

It is exactly the counter, a regular (non Tele) lens of the same focal has more that nasty effect you say than a Tele lens.

[LFLarry]

Good info, thanks for the tip on using the rear starndard for the tilts.

For my landscapes, I generally use the front standar for rise and fall to control the horizon and with this lens, I will just try and use the back standard for my tilts to get everything sharp.

I have the same set and tilting and swinging the front standard is a pain as the nodal point is way in front of the lens. It makes that even small amounts of tilts and swings lead to massive movemens on your ground glass, often in combination with loosing your point of focus. When using this set i limit myself to shifts on the front standard and use my back standard for tilts and swings. Not ideal because of the impact on the shape of objects, but when doing landscapes it is often acceptable.

[LFLarry]

In fact all long focals rise a lot the image circle when doing a front tilt, a tele rises it less than a regular lens !!!!


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Hi Pere, thanks for that detailed reply. You have a good point about the 500 vs 720. I will have to try both focal lengths in the field and see over time if I can in fact just use the 500 and crop.

Thanks!





I wanted to know, and... with the 720mm T nikon, a 10º tilt provocates a circle rise that is 42mm smaller that the one that would provocate a regular non Tele lens,

So a Tele lens is more suitable than a regular lens for field cameras that have limitations in the movements, not only for the commanded extension, but also (usually) it would be benefical that you have a lower rise provocated by a front tilt.


It was a urban legend, the reality is that having the nodal point in front of the (long focal) lens is benefical because it decreases the rise effect of a front tilt, compared to a regular lens having the nodal near aperture.


______________


With long focals, use first the rear tilt, after reaching rear tilt limit you have to use the front tilt, but with a Tele lens you will be able to tilt more degrees, as a regular lens exhausts sooner the rise margin you have for compensating.


______________


Note that while the T system has clear advantages for the field... also a Tele lens has optical drawbacks. It is true that in many situations you'll have other limiting factors. But in particular it's not clear to me if the 720 is necessary, as we may get mostly the same quality if shooting with the 500 and later taking the crop of the equivalent framing, specially if we use a sharp film like (say) TMX or Velvia.

[Eric Leppanen]

There are a couple tricks you can try. If you are concerned about the distortion caused by rear movements, you can use back tilt to determine the total amount of tilt needed, then re-zero the rear standard and apply the same amount of tilt to the front standard, then adjust the entire camera to re-center the composition.

Another technique is to apply front tilt, then re-center the composition by applying front rise, assuming your lens has enough usable image circle for this. This is the quickest way to get the shot. The Nikon T 360/500/720 has a moderate amount of image circle for this, I don't know if it has any additional wiggle room beyond its rated circle (the 500 and 720 focal lengths may have additional room based on my experience with the Nikon T 600/800/1200).

Fortunately rear movement distortion is usually minimal with longer focal length lenses like the Nikon T, so rear movements are usually fine.

[Pere Casals]

There are a couple tricks you can try. If you are concerned about the distortion caused by rear movements, you can use back tilt to determine the total amount of tilt needed, then re-zero the rear standard and apply the same amount of tilt to the front standard, then adjust the entire camera to re-center the composition.

Eric, "distortion" provocated by a rear tilt it's the same than "distortion" provocated by the equivalent front tilt, if the same framing and circle placement.

[Corran]

I am wondering how much of an issue this is in reality and based on experience, do you have any suggestions or tips to pass along?

It's a non-issue. Just use a bit of front rise to correct the change in composition, or use rear movements. The amount of perspective distortion from the angle of the camera on a long tele lens is basically nil - and using the rear standard is the same as the front standard once you tilt the camera to return the back to level. But then you need rise to correct the composition...just like the front movement.

[reddesert]

In fact all long focals rise a lot the image circle when doing a front tilt, a tele rises it less than a regular lens !!!!

...

It was a urban legend, the reality is that having the nodal point in front of the (long focal) lens is benefical because it decreases the rise effect of a front tilt, compared to a regular lens having the nodal near aperture.

The amount of motion of the circle of coverage is not the same as the motion of the focused image on the groundglass. The former is caused by the angle of the lens. The latter is caused by the displacement between the camera tilt axis and the lens nodal point.

This can be seen if you think about tilting a simple 1-element thin lens about its axis. The ray that passes through the lens center will pass straight through whether the lens is tilted or not, so the image it forms on the groundglass will not move. However, the circle of good definition does move when the lens is tilted.