Alpa Tilt with wide lenses

[dchew]

Bernard,
That one is good but in my opinion Torger's Lumariver app is much better. I find it very helpful to play and experiment with Lumariver along with your favorite beverage. It is a very good learning tool that shows what your specific lenses do at various tilt settings.

I was far from expecting this genuine question to generate such a heated debate.

Anyway, thank you all for your inputs.

Speaking of tilt, I have discovered a great iPhone app called "Tilt calculator"! http://snapi.org/snapi/Tilt_Calculator.html

You probably already all knew about it, but I didn't.

Cheers,
Bernard

Theodoros,
Thanks for the response, but the tilt hinge is indeed farther away than Alpa's, in the face of the camera. Not out at or near the lens optics (what I would call the x axis). See the first video here:
Arca Video

My memory is bad, but I am happy to see not that bad!

Dave

[Theodoros]

The tilt mechanism is where it should be on the Arca Dave, (provided that a two cell dedicated for view camera lens is used), it is on the "x-axis" as you call it.

[Theodoros]

I was far from expecting this genuine question to generate such a heated debate.

Not a "heat" debate at all Bernard... This kind of discussions can be very beneficial to many... It's always best for one to check how accurately things work before he invests on a system... That said, I will insist on the "constant focus" method as to test a system... even if one decides on a tilt/shift lens as to use on his D810...

[Tsbphoto]

Im going to wade into this and ask a stupid question. Since both cameras require lenses to be on different length mounts to achieve infinity focus depending on the focal length and the point of rotation of each is a fixed distance from the sensor plane wouldnt the lens always not be rotated around its nodal point?

Unless the tilt of the arca is somehow built into the lens barrel?  I do not think this is the case but correct me if i am wrong...

If we look at a view camera as an example we could see how it would never be possible to have rotation around the nodal point for tech cams. Lenses for view cameras are just mounted to a lens board and mounted on the front standard which has the tilt built in.  The amount of space that would be required for the lens Barrel on the tech cam is achieved using the bellows and raking the front standard, tilt mechanism and all out. 

If we wanted to get closer to a nodal rotation on a tech cam the space needed for the lens barrel woul have to be achieved on the sensor side.  We would have to have a barrel and helical mount on the sensor so the tilt would be directly around the lens


Yes? . No?

[Theodoros]

Im going to wade into this and ask a stupid question. Since both cameras require lenses to be on different length mounts to achieve infinity focus depending on the focal length and the point of rotation of each is a fixed distance from the sensor plane wouldnt the lens always not be rotated around its nodal point?

Unless the tilt of the arca is somehow built into the lens barrel?  I do not think this is the case but correct me if i am wrong...

If we look at a view camera as an example we could see how it would never be possible to have rotation around the nodal point for tech cams. Lenses for view cameras are just mounted to a lens board and mounted on the front standard which has the tilt built in.  The amount of space that would be required for the lens Barrel on the tech cam is achieved using the bellows and raking the front standard, tilt mechanism and all out. 

If we wanted to get closer to a nodal rotation on a tech cam the space needed for the lens barrel woul have to be achieved on the sensor side.  We would have to have a barrel and helical mount on the sensor so the tilt would be directly around the lens


Yes? . No?

Not a "stupid" Q at all...

On the Alpa, the lens has a helical focusing mechanism fitted on it, so it focuses by changing distance between the lens cells, this means that the entrance pupil of it varies depending on the focusing distance... On the Arca, the lens is "fixed" and it is focused by changing its distance from the image area (like on a view camera)...

[Tsbphoto]

So the tilt on the arca is inside at the tip of its "bellows" or its huge throw helical mount? 

[Theodoros]

So the tilt on the arca is inside at the tip of its "bellows" or its huge throw helical mount?

There is a helical mechanism, but moves the "whole" lens with respect to the image area... Just like a view camera does (it replaces the bellows-yes).

[dchew]

Tsbphoto,
What Theodoros says below is not true. The helical on an Alpa moves the whole lens just like on an Arca. At least every Alpa lens I have ever used works that way: 40hr, 43xl, 60xl, 70hrw, 90hrsw, 100hrs, 150xl.

All the technical cameras that rely on a helical for focusing work essentially the same way in that regard.

Dave

Not a "stupid" Q at all...

On the Alpa, the lens has a helical focusing mechanism fitted on it, so it focuses by changing distance between the lens cells, this means that the entrance pupil of it varies depending on the focusing distance... On the Arca, the lens is "fixed" and it is focused by changing its distance from the image area (like on a view camera)...

[Theodoros]

Tsbphoto,
What Theodoros says below is not true. The helical on an Alpa moves the whole lens just like on an Arca. At least every Alpa lens I have ever used works that way: 40hr, 43xl, 60xl, 70hrw, 90hrsw, 100hrs, 150xl.

All the technical cameras that rely on a helical for focusing work essentially the same way in that regard.

Dave

Dave.... the Alpa lenses come ready with a focusing helical coil that displaces the two cells of the lens (in distance - the front cell with respect to the rear) between them... The extra ring one fits is dedicated to provide a distance scale for each different lens... https://www.youtube.com/watch?v=QLwD1_z9F98

The rear cell is always constant.

[dchew]

I don't know what to say. I'd love to stop posting but I don't think we should have incorrect info out there that confuses people.

That video shows how to mount an HPF ring; I've watched it plenty of times. The helical coil does not displace two cells of the lens. It moves the whole lens in and out just like an Arca does and just like a view camera. There are different HPF rings for different lenses because the diameter of the focus grips are different, the min focus distance is different for different lenses, etc.

Dave

Dave.... the Alpa lenses come ready with a focusing helical coil that displaces the two cells of the lens (in distance - the front cell with respect to the rear) between them... The extra ring one fits is dedicated to provide a distance scale for each different lens... https://www.youtube.com/watch?v=QLwD1_z9F98

The rear cell is always constant.

[Theodoros]

Sorry... Dave is right and I'm wrong... the fitted focusing ring on the lenses do move the whole lens, it's obvious at 1:02 of the video I have provided...  The focusing ring on the ALPA also acts as a "bellows alternative"... 

[Tsbphoto]

I have alpa lenses and know that theodoros was wrong on the focusing part, i chose to ignore it to get to the bottom of where the tilt comes in.  Trying to not be argumentative. 

Since there is so little video or picture documentation on these types of cams lots of questions will have to do.

 Is the tilt at the back or front of the arca helical focus?

[yaya]

FWIW, all large format lenses, both symmetrical and retrofocus ones are designed to move as one unit, be it by a helical mount or a geared rail. Rodenstock and Schneider go to great lengths to ensure correct distance and alignment between the front and rear parts with the shutter fitted between them.

[Theodoros]

I have alpa lenses and know that theodoros was wrong on the focusing part, i chose to ignore it to get to the bottom of where the tilt comes in.  Trying to not be argumentative. 

Since there is so little video or picture documentation on these types of cams lots of questions will have to do.

 Is the tilt at the back or front of the arca helical focus?

If it "holds focus" (as people claim) its ON (at the same plane) as the helical focus... On the Alpa its certainly behind it, recessed with respect to the entrance pupil of the lens... It seems that the Alpa acts like a view camera that has the  tilt bellow shift, while Arca (correctly) the opposite...

[BernardLanguillier]

Bernard,
That one is good but in my opinion Torger's Lumariver app is much better. I find it very helpful to play and experiment with Lumariver along with your favorite beverage. It is a very good learning tool that shows what your specific lenses do at various tilt settings.

Thanks Dave, just purchased it too. I gave it a quick look and it sounds neat, but I'll have to read the tutorial to understand what it does.
 
Cheers,
Bernard

[Tsbphoto]

Theodoros..

This is not the case and really makes me wonder if you know what you are talking about.  Look at this picture of an arca with tilt...  The whole bellows is tilting thus having the the lens tilt around an arc that is not centered around the lens nodal point. The longer the bellows the bigger the arc

[Theodoros]

Theodoros..

This is not the case and really makes me wonder if you know what you are talking about.  Look at this picture of an arca with tilt...  The whole bellows is tilting thus having the the lens tilt around an arc that is not centered around the lens nodal point. The longer the bellows the bigger the arc

My answer was this "If it "holds focus" (as people claim) its ON (at the same plane) as the helical focus..." and the pictures you post show exactly that... What is you disagree with? And please avoid words like "it makes me wonder if you know what you are talking about", because you already had the answer... it makes you look "mean" than having a discussion...

EDIT: Don't think that anyone that uses a camera as to "test" it, examines its exact design as well... I've already said that my criteria is "holding focus" for what "works right"....

[voidshatter]

Despite the fact that I thought that the ALPA tilt was a base one rather than a mechanism that tilts the board by its center, if a camera looses focus when the lens is tilted, it is a proof that the lens hasn't been tilted by its entrance pupil. The focusing system of the lens (either by a helical displacement between the cells or by adjusting the distance between the image area and the lens rear cell) is totally irrelevant and can't -in either case- correct for the position of the entrance pupil. What one does by re-focusing the lens, is correcting for the entrance pupil distance from the image area, it doesn't mean (nor it is the case) that the entrance pupil is moved back to the same point where it was before (although the distance from the image area is the same) and thus, the system looses its geometry (the entrance pupil isn't positioned anymore at an axis that crosses the image area at its center, perpendicular to it).

Losing focus is not a problem for CMOS. As long as you understand what is mean by the blue overlaps the orange in my figure, you should be able to know why I'm specifically addressing your misleading statement regarding image quality.

[Theodoros]

Losing focus is not a problem for CMOS. As long as you understand what is mean by the blue overlaps the orange in my figure, you should be able to know why I'm specifically addressing your misleading statement regarding image quality.

Here we go again... Geometry has nothing to do with the kind of image area you use Yunil.... you get distortions!

[voidshatter]

Here we go again... Geometry has nothing to do with the kind of image area you use Yunil.... you get distortions!

I feel sad for the technical cameras designed by you...