correct verticals with a wide angle !

[btaylor]

Curious how you deal with the fact that lighting of the image will not be equal through the picture?

Hmmm, I have never tried the trick ic-racer is illustrating-- read about it, but never had much of a reason to try it. I do the perspective correction in camera. When doing this there is no problem with the evenness of light. I suspect the distances are too small for the inverse square law to make much of a difference, and the same holds true on the enlarger side for the most part, though it would be easy to burn the less exposed (furthest away) area a little to make up the difference.

 

[ic-racer]

With a wide angle lens at the limit of coverage, the edges of the frame are dark. So that would be a dark sky. During the printing process the dark sky is projected farther away from the enlarger lens and therefore prints lighter; this corrects the falloff of the camera's wide angle lens.
This is the print from the enlarger pictured in post #21:

 

[ic-racer]

So that negative was exposed on 8x10 film with the common compact Symmar-S 210mm. A lens most people would insist does not even cover 8x10, let alone provide for a massive front rise on the camera. Of course I had no front rise; I pointed the 8x10 camera upward to make negative and corrected it in the darkroom. That negative was made with my old Century, years before I got the Shen-Hao and massive coverage Angulon 210.

 

[Dan Fromm]

ic, about y'r 210/5.6 Symmar-S. On 8x10 shot straight ahead it has to cover 72 degrees. Cos^4 will put the corners ~1.2 stops down from the center. That really isn't much.

 

[jim10219]

Curious how you deal with the fact that lighting of the image will not be equal through the picture?

With a tilted easel like that, you can just take a piece of cardstock, hold it halfway between the image and lens, and pull it back, exposing the far side first, and the near side last. This, of course, is assuming you're actually running into a noticable problem of uneven exposure. Often if the exposure differential is gradual, you may not notice it.

"Normal" is supposed to mean a lens that isn't a telefocal or retrofocal design. Since most SLR's lens mounting flanges sits about 45ish mm away from the film pane/sensor, lenses around 45-55mm will be a normal design. You can technically have a 300mm normal lens, but it might be 600mm long in order to do it (focal length plus length of elements). Of course, common parlance doesn't necessarily follow technical terminology.

Prime lenses tend to be more rectilinear than zoom lenses. So the reputation of wide angles producing distortion (at least barrel distortion) comes more from the use of zooms at their widest settings. Most primes that aren't fisheye lenses, tend to be pretty rectilinear.

 

[Dan Fromm]

"Normal" is supposed to mean a lens that isn't a telefocal or retrofocal design. Since most SLR's lens mounting flanges sits about 45ish mm away from the film pane/sensor, lenses around 45-55mm will be a normal design. You can technically have a 300mm normal lens, but it might be 600mm long in order to do it (focal length plus length of elements). Of course, common parlance doesn't necessarily follow technical terminology.

Oh, dear, another term with several meanings. A lens of normal construction is, as you wrote, neither telephoto nor retrofocus. A lens that is normal for a format has a focal length that is equal to the format's diagonal. Two unrelated concepts, more or less one term.

The normal focal length for 35 mm still is 43 mm. This has nothing at all to do with 35 mm SLR's registers. Your concept fails completely for 35 mm rangefinder cameras, which typically have registers much shorter than ~ 45 mm.

 

[RalphLambrecht]

Hi,

I was assisting an interior photographer the other day and he said that whilst doing interiors you had to get the verticals correct. Which I thought was fair enough but then when I went home I realized he was using a wide angle approx. 50mm (medium format), and as wide angles distort verticals, how does one get them correct using a wide angle ??. He was using a mamiya 67 medium format with a 50mm...

ta ader

I correct perspective disttion while enlarging; t does ,however, require a capable enlar5ger and some exposure corrections.

 

[tezzasmall]

Curious how you deal with the fact that lighting of the image will not be equal through the picture?

Not all the final replies came up whilst I was writing my reply, so I'm probably repeating advice from others but here goes anyway...

I'm presuming you mean during the enlarging stage and not the actual taking stage?

I've never done it in the darkroom, but from what I recall from reading a few times, it's the basic technique of dodging / burning to even out the exposure over the whole print during exposure under the enlarger lens. I don't know though, how accurate one has to be before it becomes noticeable on the final print that one end is lighter / darker than the other...?

Terry S

 

[jim10219]

Oh, dear, another term with several meanings. A lens of normal construction is, as you wrote, neither telephoto nor retrofocus. A lens that is normal for a format has a focal length that is equal to the format's diagonal. Two unrelated concepts, more or less one term.

The normal focal length for 35 mm still is 43 mm. This has nothing at all to do with 35 mm SLR's registers. Your concept fails completely for 35 mm rangefinder cameras, which typically have registers much shorter than ~ 45 mm.

Not necessarily. A 50mm lens may still be of a normal design when mounted on a rangefinder. Just because the register is shorter, doesn't mean the focal length of the lens has to be compressed or extended to maintain infinity focus. You can simply push the lens elements forward in the lens body by a few centimeters.

Besides, none of that was my point. My point was that photographers, just like most lay people, use terms they don't understand and give them new meanings based on what they're heard. And this habit isn't limited to photography. There are lots of commonly used names that are misapplied due to gross public ignorance. For example, what most Americans call cantaloupes are actually muskmelons. Cantaloupes are something different. Same thing with buffalos (which are actually bison). We tend to think peppers, cucumbers, and squash are vegetables (they're fruits). And thanks to Leo Fender, guitarists often call tremolo vibrato, and vibrato tremolo. The list goes on and on. Everything thinks that because that's what everyone else says, that it must be right. But "everyone" can be wrong.

And I'm not trying to say that everyone is stupid or anything for calling something by the wrong term or not understanding the terms they're using. We all do that. I was just pointing out what the term technically means. I agree that most people who use the term "normal focal length" are probably either referring to it's relationship with the format's diagonal or what they believe is it's relationship to the normal human viewing angle (which is a whole other can of worms). Neither is not correct, but both are common misconceptions that are more common than the truth. So in light of the two competing and prevailing inaccurate definitions, I think it's important to understand what the term actually means, while still acknowledging that what it actually means, may not be what someone who uses it actually means. A little education isn't a bad thing, is it?