Is Full frame still the most versatile?

Started Mar 31, 2013 | Discussions thread
Leonard Migliore
Leonard Migliore Forum Pro • Posts: 15,535
Are you just digging in?

plevyadophy wrote:

Draek wrote:

plevyadophy wrote:

Well, the distortion graphs I see show the same distortion whether or not the sensor size changes.

Then the distortion graphs you're seeing are wrong, or you're reading them wrong. Care to cite a few?

A simple test would be to use a compass and draw circles from large to small, with the smaller circles sitting inside the bigger ones. Then draw a series of squares over, in the same manner, smaller squares centred inside the larger ones, with the squares sitting on top of the circles. you will see that the curve angle of those circles is pretty much the same within the large squares as it is for the smaller ones. For squares read sensors and for circles read angle of distortion.

"Curved angle"? angle of distortion? and what exactly would that prove?

You seem to be through far too many misunderstandings; I suspect you're confusing perspective distortion with optical (ie, barrel or pincushion) distortion, falling into the old mistake of thinking perspective is determined by focal length rather than position, and at least a couple other problems as well.

A 12mm lens requires more effort on the part of the lens maker to make a good lens than it does to make a 50mm, whether or not that lens is sitting in front of a small sensor or a large one. Or to put it another, make a 12mm lens with no attempt to correct distortion and do likewise with a 24mm lens; stick the 12mm on a Four Thirds sensor and the 24mm on a 35mm cam, and I think you will find that the 24mm does better.

And I know you'll find differently.

Simplified, the difficulty of designing a lens is roughly dependant on its FOV; a fast-ish normal lens is simple enough to design, whether that lens is a 80mm for a medium format camera, a 35mm for an APS-C digital, or a 18.5mm for an 1" sensor body. That's why 10mm lenses for 1/2.3" sensors are a toy, and why 120mm lenses for large format cameras aren't.

I don't get ya?

SLRs? mirror? retrofocus? ring any bells?

Yeah, I had a feeling that was what you referring to but I wasn't sure so that's why I asked.

Anyway, let me get something straight.

Are you saying that, if I have a telephoto lens that has clear signs of pincushion distortion on my 35mm, that it will worsen if I stick the lens in front of a smaller sensor and disappear (or at least be reduced) if I stick the same lens in front of a larger sensor (notwithstanding the issues of lens rear to sensor distance on the larger fromat camera)?

Where do you get that from? In response to your initial assertion that a 12mm lens has more distortion than, say, a 24mm lens, Draek noted that characteristics such as distortion are associated with the lens's field of view. I fully agree with this assertion. Retrofocus wide angle lenses tend to have barrel distortion and some degree of complexity (more elements, more $$) must be added to eliminate it. Wide range zooms almost always have distortion at the wide end and depend on post-processing to correct it.

Actually, lenses for mirrorless cameras can have less distortion than SLR lenses because there's no restriction on the back focus.

In most optical layout programs, you can scale the focal length of any design. And when you do that, the distortion remains the same; it's a geometrical property of the lens.

And likewise, am I to take it that my wide angle lens on 35mm that shows heaps of barrel distortion will produce an image displaying minimal barrel distortion if I put in front of a smaller sensor, and I guess even more distortion wil be displayed if I put that lens on a larger format?

Am I to take it that is how things work??

Are you trying to be deliberately obtuse? You would not use the same design as a wide angle lens that covers 24mm X 36mm on a smaller sensor because you don't need the field of view. And if you put that lens on a larger format sensor, you would get dark corners.

Your initial contention was wrong and indefensible; your continued attempts to support it, including denying actual graphs of distortion, are just obstinate. Lots of things affect distortion but the absolute focal length of the lens is not one of them.

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Leonard Migliore

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