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Talking Technical on Tech Cameras

Jae_Moon

Member
Jae

The TILT/SWING axis for the TECHNO goes right through the center of the lens .
This is IMO a big advantage for focusing .
With the ALPA , the TILT/SWING axis is either at the bottom or the side of the lens mount to the camera . That makes focusing more difficult .

How do these technical differences influence your Scheimpflug calculations , if at all ?


Jürgen:

I can tell only for three Tech Cameras; ALPA, A-S RM series and Cambo. All three camera systems have the axis of lens tilt/swing through the center of the lens. I think you are mistaken (I am 99% sure) about the ALPA. As you can see from the attached photo, the axis is in the middle.


It is true that it is easier to focus with the axis in the middle of lens when you are doing by visually, either with GG or LV. My old A-S F-Metric Compact had the option called Orbix which put the tilt axis in the middle.

With the camera where the tilt axis is not located along the lens axis, you have to make an adjustment for the distance between the lens nodal point and DB sensor plane by a small a mount (= tan (alpha) x L, where alpha is lens tilt angle and L is the distance between tilt hinge and the lens center) in calculating the focus distance).


Hope it answers your question.

Jae M
 
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Jae_Moon

Member
Jae, this image was taken with 5D2 with 24mm T/S lens at about f7.1 with the camera tilted and a few degrees of lens tilt.

I used live view to get the focus at a balanced sharpness - though I did compromise a little because the camera was only about 12 inches from the back of the bike - so perspective was quite extreme. In the original image you can read all the lettering on the instrument panel including the milage. So the lens did a pretty good job from where I sit.

I never use the LV on the IQ180 back - I use the focus mask and do the shoot, check focus mask then zoom in to test for focus accuracy. Apart from the time spent to zoom and check the screen is absolutely reliable in telling me if I have nailed the focus or missed by even a small amount.

Mal

Mal:

A great shot, you proved that one can make great Tilt shots with a good LV display.

As I indicated in my earlier posts, my P45 do not have the LV and I don't have T/S lens to try with my 5D2.

So, the question is, why everyone who have IQ series DBs not use the LV of IQ display for the Tilt, or for focusing instead of focus mask? My premise was maybe the size of the display is as much important as the pixel density in usability of the built-in display.

Jae M
 

jotloob

Subscriber Member
Jürgen:

I can tell only for three Tech Cameras; ALPA, A-S RM series and Cambo. All three camera systems have the axis of lens tilt/swing through the center of the lens. I think you are mistaken (I am 99% sure) about the ALPA. As you can see from the attached photo, the axis is in the middle.


It is true that it is easier to focus with the axis in the middle of lens when you are doing by visually, either with GG or LV. My old A-S F-Metric Compact had the option called Orbix which put the tilt axis in the middle.

With the camera where the tilt axis is not located along the lens axis, you have to make an adjustment for the distance between the lens nodal point and DB sensor plane by a small a mount (= tan (alpha) x L, where alpha is lens tilt angle and L is the distance between tilt hinge and the lens center) in calculating the focus distance).


Hope it answers your question.

Jae M
I am asking this , because with my ARCA F-LINE Metric , I have an ORBIX
function , which makes focusing easy . You mentioned that as well .

Your image shows the old style of TILT/SWING adapter .
The new one is , as far as I can see , different .
ALPA OF SWITZERLAND - Hersteller herausragender Kameras - ALPA tilt/swing adapter 0° - 5°, 34 mm
Have a look to the different images of the adapter .
I am glad you see my point and that your APP calculation will take care of this .

I will give the ALPA people a call to get the correct answer .
 

AndyPtak

Member
Considering the money most of us spend on all of this stuff, i'd pay $125 in a heartbeat.

Guy does have a good point though. As usual!
 

Jae_Moon

Member
Your image shows the old style of TILT/SWING adapter .
The new one is , as far as I can see , different .
ALPA OF SWITZERLAND - Hersteller herausragender Kameras - ALPA tilt/swing adapter 0° - 5°, 34 mm
Have a look to the different images of the adapter .
I am glad you see my point and that your APP calculation will take care of this .

I will give the ALPA people a call to get the correct answer .
Jürgen:

Yes, it sure look like the hinge of tilt/swing is at the end. With this type, if we are correct with our assumptions, you have to make the adjustment for proper focus distance.

Jae M
 
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jotloob

Subscriber Member
I got an answer from ALPA .

For the T/S adapters 17mm and 34 mm , the hinge point is in the center of the adapter and therefore in the center of the lens .
The shown images on the ALPA pages do not show the hinge point . Hidden .

The same is valid for the old style T/S adapters , but here the hinge point can be seen .
 

Jae_Moon

Member
I got an answer from ALPA .

For the T/S adapters 17mm and 34 mm , the hinge point is in the center of the adapter and therefore in the center of the lens .
The shown images on the ALPA pages do not show the hinge point . Hidden .

The same is valid for the old style T/S adapters , but here the hinge point can be seen .
Jürgen:

Thank you for the clarification. I will correct my previous post.

Jae M
 

jotloob

Subscriber Member
I have just ordered 2 adapters , one T/S17 and one MULTI USE 17 .
I still need my HR DIGARON 4,5/40mm get adapted for SB17 and then
. . . . . I can tilt like mad with my 40 and 90 mm DIGARONS .
 

Jae_Moon

Member
The challenges of using Tilt do not stop at finding a proper lens tilt angle and the required focus distance. The conventional concept of DOFs, two parallel planes perpendicular to lens axis, does not hold once a lens tilt is made, Instead we have 'Wedges of Near and Far Focus' which are tilted up (for Near Wedge) and tilted down (for Far Wedge) from the Plane of Sharp Focus.

In the example shown, I defined the surface of water as Near Object and the middle of building as Far Object, and resulting Plane of Sharp Focus tilted up from the reference plane (water surface). Please note the 'line diagram' is 'exaggerated view' to show the concept.

While composing the image, I like to know how far up and down from the 'far object' would be in focus, or will the steeple in focus, or will the surface below the dam be in focus, etc. The advantage of using the 'mathematics' is all those information are readily available for any specific settings for lens tilt.

Lens was tilted 1.5 degree and the Plane of Sharp Focus was 8 degree tilted up from the reference. A quick check indicated that the Near Wedge at the distance of Far Object was 5.7 meter above the reference plane while the Far Wedge was at 1.8 meter below the reference plane (ensuring that both water level below the dam and the top of tree are within the wedges). Then, I checked the wedges boundary at the distance where the steeple is located, and the results show that the Near Wedge at the distance was 12.5 meter above the reference plane while the Far Wedge was at 2.8 meter below the reference plane (ensuring that the steeple is within the wedges).

Too much math instead of image making? It is not, at least in my case since I have a tool, and the whole 'math' process took me less than 5 minutes, and it allowed me to have more 'image making' time.

Jae M


 
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Jae_Moon

Member
at which aperture did you get this wedge?
and at which distance did you focus?
Aperture was 8.0, the camera was 1 meter above the reference level (water) and I picked the near object at the ref. level and 4 meter (approximate) away and the far object at 2.1 meter above the ref. and 21 meter away.

By tilting lens, I could put entire objects; from the water just below the tripod to the top of steeple, within the wedges of Sharp Focus.

Disto does not work well on reflective surface so I picked a nearby branch sticking out and made an estimate from it.

Jae M
 
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jotloob

Subscriber Member
Jae

You can Not set the distance to two different values .:)
Did you focus to the average of 21m + 4m = 12,5m ? ? ?
 

Jae_Moon

Member
Jae

You can Not set the distance to two different values .:)
Did you focus to the average of 21m + 4m = 12,5m ? ? ?
Jürgen:

Sorry, the calculated focus distance was 10.5 meter. Another benefit is I could take the 'screen grap' of iPhone for records..

Jae M
 

Jae_Moon

Member
Jae

You can Not set the distance to two different values .:)
Did you focus to the average of 21m + 4m = 12,5m ? ? ?
To clarify, just in case. Near and Far Objects defines the Plane of Sharp Focus, lens tilt angle and the Wedges of Sharp Focus, but the tilted lens will aim at a point somewhere between those two points that is located on the PSF. The calculated focus distance is the distance between that point and the DB image plane.


Jae M
 
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tjv

Active member
This thread has fried my brain... And I've got a full day ahead of me! Will have to come back and read properly after work.
In all seriousness, I've been in need of a hard core technical explanation of tilt / swing for some time. I use a Linhof Techno and use the GG the set tilt angles referencing the iPhone app Tilt Calculator, but often end up scratching my head wondering what the hell I'm doing and why!
 

f8orbust

Active member
For the T/S adapters 17mm and 34 mm , the hinge point is in the center of the adapter and therefore in the center of the lens...
For shorter focal length lenses any displacement when tilting is probably very small using such a system. However, as the lens gets progressively further away from the axis of tilt, focus shift is unavoidable. For instance:

 

Jae_Moon

Member
For shorter focal length lenses any displacement when tilting is probably very small using such a system. However, as the lens gets progressively further away from the axis of tilt, focus shift is unavoidable. For instance:


I think Jürgen had a discussion with ALPA and was told that all ALPA tilt adapters have the tilt hinge along the lens axis. I think the hinge is hidden but still located along the lens axis for the picture you attached.

In these cases, there are NO Lens shift due from the lens tilt. If the tilt hinge is located at the bottom, a simple adjustment is made to compensate the added distance between the lens nodal point and the DB image sensor (see previous post).


Jae Moon
 

Jae_Moon

Member
This thread has fried my brain... And I've got a full day ahead of me! Will have to come back and read properly after work.
In all seriousness, I've been in need of a hard core technical explanation of tilt / swing for some time. I use a Linhof Techno and use the GG the set tilt angles referencing the iPhone app Tilt Calculator, but often end up scratching my head wondering what the hell I'm doing and why!


I agree it is not a simple subject.

I cannot remember the link now, but I saw a photo of a very large camera setup that a German (?) company built which had computer controlled and electro-mechanically actuated system for all camera movements; tilt, swing, focus, etc.

Short of having that kind of gears, I think there are three approaches one can take with Lens Tilt (my personal opinion) with present technology:

1. Do a simple rule of thumb (or at least develop a simple look-up table)
This option should be limited to the lens tilt only (no camera tilt) and to the objects that are on the horizontal level; ground or tabletop, street below, etc.
The mathematical formulae for this method is rather simple to use with the spreadsheet. They are listed on the previous post (#4). You will have very accurate tilt angle and the focus distance setting that you do not need a visual confirmation.

2. Do with Visual Confirmation using GG, tethered or built-in Display.
The mathematical formulae are rather complex if you want either to tilt the camera or to focus on a tilted plane or to do combined, and you should rely on visual feedback. The challenge in this case is that you have two variables; tilt angle and focus distance (you have to guess the tilt angle first then focus, then repeat until both are correct). There are many articles available online how to tilt and to focus using visual feedback.

3. Do with mathematical formulae. This is my approach and it has been working for me. I am considering a way to make the formulae available to others, and evaluating if there are 'real needs' by users.


Jae Moon


ps

4. Be an 'Outlier' as in Malcolm Gladwell's book 'Outliers'. Gladwell told stories of 10,000 hours of practice required to be Bill Gates, Midori, star hockey players, and Wall Street Super Lawyers, etc. Develop your own way by repeated practices until you are happy with the methods and the results.
 

f8orbust

Active member
In these cases, there are NO Lens shift due from the lens tilt...
Assume all camera adjustments are neutral. If we tilt the lens about it's centre, the distance between it and the sensor remains the same on cameras such as the A/S ML-2, Techno etc. (all cameras that have an 'orbix' style tilt). On pancake cameras like Alpa and RM3D/i, long lenses in particular are 'hung out' on long lensboards, with the axis of tilt displaced (obvious in my previous picture). So, when you tilt the lens, the distance between its centre and the film plane changes - it gets less.
 
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Jae_Moon

Member
Assume all camera adjustments are neutral. If we tilt the lens about it's centre, the distance between it and the sensor remains the same on cameras such as the A/S ML-2, Techno etc. (all cameras that have an 'orbix' style tilt). On pancake cameras like Alpa and RM3D/i, long lenses in particular are 'hung out' on long lensboards, with the axis of tilt displaced (obvious in my previous picture). So, when you tilt the lens, the distance between its centre and the film plane changes - it gets less.

See attachment: b = b1 + b2 and f < b1 + b2 so f < b. Also, you can see that because e and g are different, a non-orbix style tilt will change the shape of the subject compared to an orbix style tilt (where a = c, even when the lens is tilted).

N.B. This is a simplified diagram assuming a simple symmetrical lens design where it's 'centre' is simply defined - obviously with retrofocus lens designs the 'centre' can be displaced quite significantly from where we imagine it might be.

I think you are half right and I am half wrong (or the other way around :))

It is a little difficult to explain by writing but I will try.

1. All three Tech Cameras have the lens tilt hinge along the lens axis (but not at the lens nodal point). I agree Orbix (also Cambo T/S lenses) would have the hinge closer to the nodal point.
2. Your depiction for 'Orbix Style Tilt' is not correct. The light path does not refract and it should look like to your 'Tilt about a displaced axis'.
3. 'Focus Shift' occurs with ALPA and A-S RM due to the horizontal distance between the DB sensor plane and the Tilt hinge location.The length of lens focal lens does not have any effects.


With a set focus setting, the focus distance (=Xf) is the distance between the lens nodal point and the DB sensor plane along the lens axis. And Xf can be expressed as the sum of two distances; distance from lens nodal point to lens tilt hinge and the distance from lens tilt hinge to DB sensor plane. The first distance, between lens nodal point and the lens tilt hinge along the lens axis does not change whether the lens is tilted or not, but the second distance, between the lens tilt hinge and the DB sensor plane along the lens axis changes when the the lens is tilted. This change (Focus Shift) is the function of the lens tilt angle and the second distance (between the lens tilt hinge and the DB sensor plane), not the function of lens focal length.

At a given lens tilt angle, the error will be proportionally larger as the distance between the lens tilt hinge and the DB plane increases (which is fixed for AS RM camera at approximately 12 mm and is much larger for ALPA with its thicker adapter plates in addition to camera body depth).

For example, AS RM can tilts up to 5 degree and would results in the focus error of 0.046 mm or 0.6 in helical focus ring setting. At more common tilt with wide angle lens, 2 degree, the error is 0.007 mm or 0.1 in helical focus ring setting.

I can only speculate for ALPA that the error would be a bit larger since the distance between the lens tilt hinge and the DB sensor plane is much larger than 12 mm.

However, it should be noted that this 'Focus Shift' is only relevant to the application where the Tilt Angle and the Focus Distance is mathematically calculated. Both ALPA and AS RM cameras will function just like any view cameras with Orbix like feature to focus using the Visual Confirmation since the lens tilt hinge is located along the lens axis.

I hope this makes sense.

Jae Moon
 
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