clarification of LCC

[craigrudlin]

I am initiating the move from 35 mm to MF.  Since one of my main interest is landscape, I have been advised to
consider tech cameras for their movements.  I do not fully understand all the aspects of view or tech cameras, but
am reading and studying.  I just read that while a LCC image is required for wide angle lenses, it is NOT required if
the lens has "rear focus", and that some newer lenses for tech cameras therefore do not require a LCC.  Is this
true, please advance my knowledge.

As a separate, but related question, since landscape is not my only genre of photography, and I may not be able
to afford both a "general" MF body and a tech camera,  how does a tilt/shift lens such as the Schneider "compare"
to a real tech camera? 

Thank you, and I appreciate your tolerance of my ignorance in my new endeavor.

craig

[theguywitha645d]

Lens color cast is a result of vignetting--light striking the edge of the sensor at an angle. It results not only in darker corners, but also a radial green/magenta shift. When working with a the camera, you would shoot one frame through a opaque plate to make an image of the cast. That image is then used to subtract the cast during post processing. The wider the lens and/or the greater the camera movements, the greater the need to shoot an LCC frame. I have had to correct for color casts with 55mm and 90mm lenses, so it is not just a problem with wides.

Some lens designs can mitigate the problems of lens cast (telecentric and reverse telephoto (or retro focus) designs, but from my experience and for what others do, it helps, but does not alway eliminate a color cast.

Yes, a tilt/shift lens can do the same thing as a tech camera. The advantage of the tech camera is you have all the movements for every lens.

Ask questions. It is a really good way to learn. BTW, have you ever thought of renting some of this equipment so you can get a better idea about how they work and the pros and cons. I have used view cameras and technical cameras for a very long time. They are very powerful tools. But for my own personal work, I have found I prefer not to worry about movements. Sometimes the tool can get in the way.

[siebel]

Shift is not the only reason to choose a technical camera. Tech cam lenses are optically superior to reflex lenses in many, many ways. This superiority is especially pronounced in the shorter focal-lengths, though in my observation, holds true all the way up to the 120mm focal lengths. It may go further in some cases but I have little personal experience of these, so I choose not to comment. In particular, you will find edge sharpness of tech cams leaves reflex lenses for dead.
I have heard some people claim that the semi-retrofocus design of the Rodenstock HR Digarons makes it unnecessary to do the LCC correction. This is simply not true. I have shot with the 23, 28, 32, 40 and 60 and they all require LCC. It is true that the amount of cast reduces as pixel size increases, hence a P25, with 9micron pixels, will show less lenscast than an IQ180 with 5.2micron pixels. However the cast is still there and quite clearly so.
As far as I know, the only Schneider TS for medium format is the 120mm focal length. This is a pretty limited choice for landscape, though the lens is superb. My understanding of it is that it is optically identical to the 120mm SK  tech lens, though nobody at Phase seems willing to officially confirm this. The absence of a wide solution limits this path for landscape shooters.
Shift is not the only reason for choosing tech cams. For me, the optical superiority is paramount.The existence of non-shifting tech cams such as the Alpa TC is an indication of the superiority of tech cam optics.

Cheers,

[theguywitha645d]

I few things about tech camera lenses. They cannot be used wide open--that is just for focusing. A reflex 35mm is going to be better at f/4.5 than the tech equivalent--LCC will not help. So you are limited when wanting a narrow DoF with a tech camera. When shooting wide tech lenses, you will need a center filter to get the quality out of them, LCC won't be enough--reflex camera lens don't need center filters. Reflex lenses don't need LCCs. I shoot with a technical camera with a Phase back and with Pentax 645D. The quality difference is not significant, none of your viewers will be able to see what camera produced what beyond the use of movements.

[TH_Alpa]

I do disagree, with all due respect.

Rodenstock lenses can and are usually used full open and give remarkable, some focal lengths even outstanding results.

Thierry

I few things about tech camera lenses. They cannot be used wide open--that is just for focusing.

[TH_Alpa]

+1

Shift is not the only reason to choose a technical camera. Tech cam lenses are optically superior to reflex lenses in many, many ways. This superiority is especially pronounced in the shorter focal-lengths, though in my observation, holds true all the way up to the 120mm focal lengths. It may go further in some cases but I have little personal experience of these, so I choose not to comment. In particular, you will find edge sharpness of tech cams leaves reflex lenses for dead.
I have heard some people claim that the semi-retrofocus design of the Rodenstock HR Digarons makes it unnecessary to do the LCC correction. This is simply not true. I have shot with the 23, 28, 32, 40 and 60 and they all require LCC. It is true that the amount of cast reduces as pixel size increases, hence a P25, with 9micron pixels, will show less lenscast than an IQ180 with 5.2micron pixels. However the cast is still there and quite clearly so.
As far as I know, the only Schneider TS for medium format is the 120mm focal length. This is a pretty limited choice for landscape, though the lens is superb. My understanding of it is that it is optically identical to the 120mm SK  tech lens, though nobody at Phase seems willing to officially confirm this. The absence of a wide solution limits this path for landscape shooters.
Shift is not the only reason for choosing tech cams. For me, the optical superiority is paramount.The existence of non-shifting tech cams such as the Alpa TC is an indication of the superiority of tech cam optics.

Cheers,

[theguywitha645d]

I do disagree, with all due respect.

Rodenstock lenses can and are usually used full open and give remarkable, some focal lengths even outstanding results.

Thierry

No offense taken. I am just replying with my experience with the Rodenstock digital lenses I have used. So you don't think Schneider lenses work well wide open? A brand thing?

[john milich]

as a point of clarification, as i understand it:
vignetting is light falloff at the edges and corners due to a longer distance to the sensor compared to the center
color cast at the edges is due to the angle of incidence to the sensor

[Jack Flesher]

John's got it right. Lens cast is caused by angle of incidence and pixel pitch diffracting the light beam as it enters the pixel well.  Therefore as a general rule, lenses with shorter flange focal lengths and sensors with small pixels present the worst cases for lens cast. The corollary is choose your tech lenses wisely if you shoot with a 60 or 80 MP back .   On the upside, Lens Cast Correction (LCC) is relatively easy with today's software.

[rainer_v]

No offense taken. I am just replying with my experience with the Rodenstock digital lenses I have used. So you don't think Schneider lenses work well wide open? A brand thing?

its not a brand thing but a lens design result.
its true that the rodenstocks are shark wide open and the schneider wides not, but this is only true for the rodenstock HR line. the HR lenses are wide open sharp, even very sharp. this results from their slightly retrofocal design. the schneiders usually are symmetric design, as most large format wides have been also. therefor the HR lenses show less color cast than the schneider wides too, because resulting from their design their flange distance is larger than symmetrical lenses with same focal length.
symmetric lenses usually wants to be stoppd down two or even three stops for sharp results till the corners.

the price the retrofocal design have to pay is more distortion, so in this respect the schneider wides are better than the rodenstocks. although the 1% or 1,5% distortion the 23, 28 and 35mm rodenstock HRs are showing is moderate, and in critical cases this can be corrected using the alpa plugin.

[Doug Peterson]

the price the retrofocal design have to pay is more distortion, so in this respect the schneider wides are better than the rodenstocks. although the 1% or 1,5% distortion the 23, 28 and 35mm rodenstock HRs are showing is moderate, and in critical cases this can be corrected using the alpa plugin.

Typically the other costs of retrofocal designs are larger, heavier lenses and often (but not always) a larger thread size for filters and higher price tag.

This is of course a simplification - each lens should really be judged on it's own merit.

[theguywitha645d]

Just for clarification for the OP. There are two types of vignetting, mechanical and natural. As John and Jack have pointed out, natural vignetting is a product of the angle light strikes a plane. Center filters and LCC are good at correcting for that.

Mechanical vignetting is when the physical barrel of the lens cuts off the aperture for off axis light. This is usually apparent at wide/large apertures. The light fall off from this compounds the natural vignetting and fall off can be severe. Mechanical vignetting does not only effect edge exposure, but it also changes the shape of the aperture from circular to oval or cats-eye shaped. This can have a large influence on the resolving power at the corners/edges. I have yet to find a lens that does not have mechanical vignetting to some degree at maximum aperture and usually is eliminated closed down about two stops from maximum--some view cameras had cut-out corners in the ground glass so you could check for that.

[rhsu]

John's got it right. Lens cast is caused by angle of incidence and pixel pitch diffracting the light beam as it enters the pixel well.  Therefore as a general rule, lenses with shorter flange focal lengths and sensors with small pixels present the worst cases for lens cast. The corollary is choose your tech lenses wisely if you shoot with a 60 or 80 MP back .   

The "Achilles' heel"...

[MNG]

On the subject of LCC, specifically with a Leaf Aptus 2-12 on an Alpa and C1Pro.

I have made a set of LCC reference photos. I left these LCC files on the card and shots some wide angle shots and downloaded the photos and LCC files. I made a set of LCC and I could apply the LCC to these photos in C1Pro.

When I formatted the card and shot another set of photos C1Pro can't see the LCC file I made in the earlier folder? I'm on location and cant make another set of LCC files. I have tried copying the LCC file from the original folder into the 2nd folder but C1Pro does not see them???

Does anyone know if these LCC captures can be save onto the cf card, so that every time you format the card you dont loose this info?

Thanks
Michael