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Perspective Correction (PC) And Shift-tilt Lenses  
User currently offlineTomh From United States of America, joined May 1999, 960 posts, RR: 2
Posted (11 years 11 months 2 weeks 16 hours ago) and read 1946 times:

Previous discussions http://www.airliners.net/discussions/aviation_photography/read.main/63697/ in response to Dean Allchin's 4X5 view camera work in A.net were very interesting. As Ckw pointed out, in addition to the great detail found in Dean's images, perspective control (PC) made possible with this type of camera made a huge difference in viewing quality. In 35mm photography, this capability can be obtained through the use of the "shift lens" to which Colin alluded.

Shift lenses (shift-tilt, in some cases) were produced by most of the major manufacturers in the mid-1970s. Even Minolta, the marque I use, produced a 35mm f2.8 shift lens. In the case of the Minolta Rokkor lens, it also had VFC, which was a corrective feature that you could employ when photographing curved objects, similar, I suspect, to the way that high-end slide projectors use curved-field lenses to correct for curvature of a slide in a non-glass mount.

As we have seen with recent queries about non-aviation photography, most of us do indeed press the shutter release when the lens is occasionally oriented away from the boundary fence. What I am getting at here is I know for certain now that I would have taken many more images over the years if I had purchased one of those (expensive) shift lenses a long time ago.

Among the reasons I took fewer of these other images is the distorted look of buildings through non-shift lenses. The diminishing point (remember that from art class?) appears to be about 20 meters above the building. The same is true of photography in forested areas, where the trees appear to be leaning away from the photographer at an exaggerated angle. There is an entire generation of locomotive photographers that grew up on perspective-distorted 3/4 front images of their chunky subject matter.

Photographers today are on the cusp of the digital photography age, and represent the market for future digital photography products. We are in a position to influence the manufacturers while preventing the errors of the previous generation. Digital photography manufacturers should privide products that integrate perspective correction. Electronic image manipulation in the camera is undoubtedly the way to go because all of the camera's resolution can be dovoted to a "corrected" image. I do not think a "photoshop-corrected" image is produced in this manner, and besides, it would take less time to set the camera up prior to exposure to get the desired end result than it would by sitting in front of the monitor doing it post-exposure.

I see this as a great time for the photographer, who can make his/her product requirements known now, and spend less time in the future making statements like mine that start with, "I wish I had......"

TomH



10 replies: All unread, jump to last
 
User currently offlineJeffM From United States of America, joined May 2005, 3266 posts, RR: 51
Reply 1, posted (11 years 11 months 2 weeks 14 hours ago) and read 1897 times:

Tom,

With the older equipment you mentioned, the photographer had to set the lens to achieve the proper perspective right? Set differently for each type photo based on distance, angle etc.?

With a digital camera's processor attempting the same thing, how would the camera know how to achieve this? After all, light is entering the system in the same manner as a standard camera through the lens. The only difference is how it is recorded. Some type of in camera preview would be needed. Interesting, but I think the easiest way to achieve the perspective you want is with the tilt and shift type lens. But who knows?

v/r
Jeff


User currently offlinePhotopilot From Canada, joined Jul 2002, 2821 posts, RR: 18
Reply 2, posted (11 years 11 months 2 weeks 13 hours ago) and read 1885 times:

My comments.....

A view camera offers both tilt and shift of the lens axis and plane, but also full tilt, swing, and shift of the film plane. This achieves not only perspective control, but also depth-of-focus control along a plane (not airplane).

No digital algorithm will ever be able to replace the thought and creative process of a photographer who practices good craftsmanship. This is very aptly illustrated by Dean with his large format images, some of which have been posted on A.net. It's more than equipment guys.... its also an understanding of the process of creating an image. Too many of us are coming to depend upon the "electronics" to do the thinking for us. Press the motor-drive button and hope one of the images is correct.

I dare say that give a full swing-tilt-shift lens to 95% of people and their only question would be "what are the extra buttons for?" Going digital will not remove this lack of knowledge.

So the simple answer is this. Give me more control of my images, but let me, and not some microchip, do the thinking.

thanks
Steve


User currently offlineCkw From UK - England, joined Aug 2010, 767 posts, RR: 16
Reply 3, posted (11 years 11 months 2 weeks 12 hours ago) and read 1875 times:

Not sure about this - in the final analysis, I don't think there is any inherent advantage to having the camera apply perspective correction in the field or doing it after the fact in PS.

My experiments with image sharpening in camera or after the fact in PS suggest that PS sharpening is ultimately better because

a) I have infinite control over the parameters as opposed to the handful of built in options
b) different sharpening techniques are appropriate to different subject matter - in PS I can select from a range of techniques
c) in camera choices can (if you shoot .jpg) be irreversible.
d) in PS you get to work with a large image

Similarly, I think precise perspective adjustment in the field with a tiny DSLR screen would be problematic, and undoing these adjustments later would be difficult or at best result in further losses.

And there is another factor - I really wish my D60 was simpler in some ways - get rid of the built in flash, program modes, image processing options ... I'd like something basic like my old Canon F1, and save all the clever stuff for the PC - I'm paying for a lot of stuff I never use, and could go wrong. Built in perspective control would be another complication ... and another cost factor. All in all, if the cost were applied to more pixels I think I could get better results in Photoshop.

BUT I do agree with Tom that perspective control has always been a problem for the 35mm brigade!

Cheers,

Colin



Colin K. Work, Pixstel
User currently offlinePhotopilot From Canada, joined Jul 2002, 2821 posts, RR: 18
Reply 4, posted (11 years 11 months 2 weeks 11 hours ago) and read 1869 times:

One point. If you apply perspective control in PS, you are in effect "stretching" the image on a given axis. This simply distorts the available image information over a greater area.

When shot and adjusted "in camera" with a PC lens or view camera swing/tilt/shift, then you are not distorting the final image information. The film/sensor records the information as corrected by the lens manipulation. Hope this makes sense.

You can see why the lens control method is far superior to any post image manipulation by either a DSLR or PS.

Steve


User currently offlineTomh From United States of America, joined May 1999, 960 posts, RR: 2
Reply 5, posted (11 years 11 months 2 weeks 10 hours ago) and read 1868 times:

My goal in this post is to create a demand for the ability to accomplish PC in the upcoming generation of digital cameras. I'll be the first to admit that someone else will have to figure out how to do it. I see no reason why we should not try to create the demand as photographers. You've given me some interesting responses, but I also sense a willingness to make excuses for the manufacturers as to why it cannot be done. Place the demand before the designers, first. Few of them will tell us it cannot be done. It's not their job to do that, and there is SOME WAY to accomplish it-given the resources.

I'm out on a limb making assumptions again, the first of which is I don't have to be a user of a digital camera to suggest an enhancement that prevents making the same mistake that limited the average 35mm camera owner. I assume that in-camera manipulation, however accomplished, would require some preview ability. If the screens used on today's DSLR cameras won't allow viewing detailed enough to know when the PC has been accomplished, then that's a problem. So lose the screen and bring back a nice bright optical viewer. Do people use optical viewfinders on digital cameras much? Can't see doing it for telephoto work, but do some DSLR owners prefer the optical viewfinder?

I agree with Steve, "Too many of us are coming to depend upon the "electronics" to do the thinking for us. Press the motor-drive button and hope one of the images is correct." But then, I knew a guy who was functionally illiterate, but after a few years with spell and grammar checker, he could actually issue a memo that was understandable. It was really wonderful to see this catch-up education, though I doubt he could write the memo out by hand and have it make any sense. A good camera for this guy's equivalent in the digital photography field would be one that has several on screen boxes. They would be labeled "Very good", "Excellent", and the most-used, "Award-Winning." OK, that was a joke-I just couldn't help it.

You are correct, Jeff, in that the photographer with a shift lens had to set the shot up through mechanical manipulation before exposure. I would assume (there I go again) that this was pretty easy to do-real time actually-in a nice bright optical viewfinder c.1975. Which leads to my next question. Are any shift-tilt lenses in production for 35mm or digital cameras today? NO? Oh, that's too bad, I'm in the market for one.

Does ANYONE on A.net use a PC lens on a 35mm camera?






User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 6, posted (11 years 11 months 2 weeks 10 hours ago) and read 1864 times:

Canon have a few:

http://www.usa.canon.com/eflenses/lineup/tiltshift/index.html

Staffan


User currently offlineJan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 50
Reply 7, posted (11 years 11 months 2 weeks 9 hours ago) and read 1862 times:

>. If you apply perspective control in PS, you are in effect "stretching" the image on a given axis. This simply distorts the available image information over a greater area.<

That's why it is better to compress it on the other side instead. If the lines converge at the top of the pic, then squeeze the bottom.
You will have to leave some space for this when composing the shot, so don't make too tight a crop in camera when shooting this kind of photo.
/JM




AeroPresentation - Airline DVD's filmed in High Definition
User currently offlineStaffan From , joined Dec 1969, posts, RR:
Reply 8, posted (11 years 11 months 2 weeks 9 hours ago) and read 1856 times:

Will a.net accept photos manipulated like this in PS?

Staffan


User currently offlineJan Mogren From Sweden, joined Dec 2000, 2043 posts, RR: 50
Reply 9, posted (11 years 11 months 2 weeks 8 hours ago) and read 1852 times:

What does it matter if you do it with a special lens, an adjustable filmplane or in PS ??
/JM



AeroPresentation - Airline DVD's filmed in High Definition
User currently offlineCkw From UK - England, joined Aug 2010, 767 posts, RR: 16
Reply 10, posted (11 years 11 months 2 weeks 8 hours ago) and read 1849 times:

I agree with Jan - compress rather than stretch which is why I would rather have extra pixels in my DSLR above anything else.

On viewfinders - with DSLRs we ARE using an optical viewfinder for composition - the LCD is only for reviewing the shots already taken. But even when using the very best film viewfinders I think it is difficult to make absolute compositional decisions on the fly. For me a big plus of digital is the ability to de-couple certain elements of picture making between in the field and back at base - I would like to see future developments enhance this ability.

I never owned a TS lens - because they have always been very expensive and there has always been another way of dealing with the problem. Back in my darkroom days, simply tilting the paper under the enlarger work just fine!

Cheers,

Colin



Colin K. Work, Pixstel
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