When In Computer Perspective Controls Don't Work

[JoeKitchen]

I am in the process of scheduling an exterior documentation of three murals on a budget.  In this case, on a budget means not hiring a scaffolding team and spending the dough to have everything controlled. 

My client's client is being very picky with making sure the one-point perspective elevations are an exact replication of the physical mural. 

Although most elevation images do not need to be this precise, it is good to have a technical camera. 

[Theodoros]

I'm sorry to say Joe... that a distortionless lens is not enough... You need a distortionless camera set up to achieve this... Lens distortions can be corrected in software, distortions caused by the camera though cannot...

[Chris Barrett]

I think the wisest course is to just be up front and let the client know that they don't have the budget to be as precise as they want.  Otherwise you're doing a disservice not only to yourself but any other photographers they work with in the future.

Do the best work you can, but let them know it's they who are compromising image quality not you.  Worst case scenario, this sounds like a job you could afford to lose.

-CB

[alatreille]

Wise words Christ...very well said.

Joe, I'm interested why the scaffolding would need to be erected that precisely?
Is it so you have a consistent datum you can work from?

I think the wisest course is to just be up front and let the client know that they don't have the budget to be as precise as they want.  Otherwise you're doing a disservice not only to yourself but any other photographers they work with in the future.

Do the best work you can, but let them know it's they who are compromising image quality not you.  Worst case scenario, this sounds like a job you could afford to lose.

-CB

[Theodoros]

I think the wisest course is to just be up front and let the client know that they don't have the budget to be as precise as they want.  Otherwise you're doing a disservice not only to yourself but any other photographers they work with in the future.

Do the best work you can, but let them know it's they who are compromising image quality not you.  Worst case scenario, this sounds like a job you could afford to lose.

-CB

That's very well said, but OTOH, it's a photographer's duty (IMO) to use a distortionless set up if he is in that particular field of photography, despite if the customer requires it or not...  Using a "technical camera" doesn't mean that no errors will be involved, especially if there are so many "Technical cameras" around with so many design errors included in the design and others, that although they are well designed, they require personal involvement from the user as to be set up correctly...

Once, I required some information for a particular lens I thought of having from some members of the forum (using Lula's PM) that where using (or had past experience from) this particular lens ... I was surprised to the difference on opinion between them both on the performance of the lens and (particularly) for its distortion behavior... I ended up buying the lens and then found out that the members that where claiming of it having "tons of distortion" they where simply using it on a set up that was creating distortions! The lens was as distortionless as a lens can be!

[Bart_van_der_Wolf]

Wise words Christ...very well said.

Joe, I'm interested why the scaffolding would need to be erected that precisely?
Is it so you have a consistent datum you can work from?

While I agree on both counts, I also wonder why not solve the challenge in a simple and precise way, distortion free?

Pano stitching will automatically remove lens distortions, and allows to increase shooting resolution by using a longer focal length. Assuming the murals are flat, without protruding elements, a flat plane can be successfully stitched even when the tiles are shot from different positions (because there is no parallax error in a flat plane).

A pano-stitcher like PTGui allows the "Viewpoint" correction to be automatically optimized, alongside the optical lens distortions if enough overlap is used. The principle is explained here, with some examples, like shooting flat surfaces above eye-level, a mural, or staying out of view of a mirror, no Shift lenses required.

Because no (Tilt and) Shift lenses are require, the center of the image circle for each tile can be used, which maximizes quality and reduces the need for things like LCC corrections as remedies to counteract sensor shading and other issues. LCCs can still be used to address vignetting and light fall-off, but that's a much easier task on a centered image.

It'll save a lot of location costs, and hardly increase postprocessing cost if you get the technique set up well.

Cheers,
Bart

[JoeKitchen]

I think the wisest course is to just be up front and let the client know that they don't have the budget to be as precise as they want.  Otherwise you're doing a disservice not only to yourself but any other photographers they work with in the future.

Do the best work you can, but let them know it's they who are compromising image quality not you.  Worst case scenario, this sounds like a job you could afford to lose.

-CB

To be honest, this came up in conversation.  The City does not have the budget to have this done correctly with highly precise equipment and the time involved. 

Plus the buildings are scheduled to be demoed soon.  The developer who owns them really wants to move on and start building something new. 

Their is just not enough time or money. 

Documentation using a tech camera is the only feasible way right now. 

Anyway, I had to spend two hours looking though my library trying to find one-points of the flattest facades I have shot to demonstrate what can be expected. 

[JoeKitchen]

While I agree on both counts, I also wonder why not solve the challenge in a simple and precise way, distortion free?

Pano stitching will automatically remove lens distortions, and allows to increase shooting resolution by using a longer focal length. Assuming the murals are flat, without protruding elements, a flat plane can be successfully stitched even when the tiles are shot from different positions (because there is no parallax error in a flat plane).

A pano-stitcher like PTGui allows the "Viewpoint" correction to be automatically optimized, alongside the optical lens distortions if enough overlap is used. The principle is explained here, with some examples, like shooting flat surfaces above eye-level, a mural, or staying out of view of a mirror, no Shift lenses required.

Because no (Tilt and) Shift lenses are require, the center of the image circle for each tile can be used, which maximizes quality and reduces the need for things like LCC corrections as remedies to counteract sensor shading and other issues. LCCs can still be used to address vignetting and light fall-off, but that's a much easier task on a centered image.

It'll save a lot of location costs, and hardly increase postprocessing cost if you get the technique set up well.

Cheers,
Bart

We will probably do something like that, but with shift. 

One particular mural has a couple of trees in front of it, so we have to shoot it from an off center perspective. 

On top of that, one mural faces the street, so longer lenses are the only choice for that one. We will need to deal with traffic as well. 

My client, the architect, knows the budget for this is low compared to a true archival setup. 

My game plan is to use my Rodie 90mm for each and stitch. 

[Theodoros]

Bart is right... simple stitching will do... The distortion problems involved with many cameras are all due to their tilt and swing mechanism design with respect to the entrance pupil of the lens and then with the positioning of these mechanisms with respect to side and vertical sifts when combined movements are applied... Using side and vertical shifts only should do just fine with any camera and then stitching could remove all lens distortion...

[JoeKitchen]

Bart is right... simple stitching will do... The distortion problems involved with many cameras are all due to their tilt and swing mechanism design with respect to the entrance pupil of the lens and then with the positioning of these mechanisms with respect to side and vertical sifts when combined movements are applied... Using side and vertical shifts only should do just fine with any camera and then stitching could remove all lens distortion...

Yes, I felt the yaw from the tilt/swing would certainly effect the distortion. 

My plan was to not use any tilt/swing. 

We also will be doing a site visit before and making measurements and markings as precise as we can to position the properly.  I will also capture an overall wide view that gets the entire mural in one shot for reference. 

[Bart_van_der_Wolf]

We will probably be something like that, but with shift. 

One particular mural has a couple of trees in front of it, so we have to shoot it from an off center perspective.

Using shift will need to be compensated for in the parameters used for the (automatic) stitch. When shooting from 2 sides, the trees can often be easily masked out of the stitch, if they are not too close to the wall. Again, flat planes are relatively easy to stitch.

On top of that, one mural faces the street, so longer lenses are the only choice for that one. We will need to deal with traffic as well.

Different focal lengths can be combined in one stitch, PTGui can vary the focal length parameter for each tile.

Cheers,
Bart

[DanielStone]

If you cannot use any scaffolding, can you use a tall ladder with a tripod/tripod head attached?

What about a rented man lift(the self powered hydraulic ones)?

My other thought is shooting from the 2nd or 3rd floor of a building from across the street(if such is actually there). Especially if you can open the windows necessary, that'll be more stable than any gantry/cherry locker/man lift, etc...