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02-28-2012, 10:38 PM   #1
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Register Distance and Lens Types

I've been thinking that the K-mount's longer flange distance doesn't make a huge difference on lens designs, except for the smallest types.

The attached diagram shows 5 different designs. A traditional SLR/DLSR can only support "Long" and "Telephoto A". In contrast, an average MILC can support all of these lens types.

I think that the K-01 can support 4 of these 5, which covers a lot of ground. The only type not covered would be "Short". Which eliminates the possibility of pancakes falling somewhere between 16-30mm. But other than that, I don't think many lenses fall into "Short".

My post isn't a dissertation on the topic. Some problems need addressing. First, in some cases focus motors would have to fit or drive recessed optics. Second, the mirror box is rectangular, which doesn't lend itself to housing recessed optics without accounting for the rotational bayonet attachment.

What I'm trying to say is that certain lenses can house elements inside the mirror box to open up possibilities.

And on a somewhat unrelated note, I think that fast telephoto design always looks like "Telephoto A" or "Telephoto B", which is probably why neither 4/3 nor E-Mount have fast telephoto zooms: they would look embarrassingly large, just like a DA 50-135mm stuck on the end of a NEX body. In this case, the K-01 looks better, too, because it has a reasonably large body to attach reasonably large lenses.

PS I'm just throwing ideas around, if some optics professor wants to school me then please do. I'm not saying that other systems are advantageous or crippled. I'm just thinking aloud.

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02-28-2012, 11:09 PM   #2
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Some more lens stuff

I'll throw my little knowledge in the ring too. I once worked for a guy that had several optical patents when I was in a duplication house. He had everything custom made, it was quite impressive. He explained some things in a way that has stuck with me. The big limitation when you are dealing with a mirror box is that you have to use a retrofocus design for wide angles. Otherwise, the rear element will go too far into the mirror box. The retrofocus design places the optical center of the lens behind the rear element so that it can be used on an SLR. A true telephoto lens is actually a reverse retrofocus lens. It places the optical center of the lens in front of the front element. The advantage there is something that makes the lens physically shorter and smaller. I'm not sure what the lenses that are not retro focus or telephoto are actually called, maybe normal? These show up with the crazy symmetrical wide angles like the Biogon that get real close to the sensor. I'm pretty sure the uber large and expensive long lenses are also not reverse retrofocus, but I don't really know. If those are lighter weight versions, I'd hate to see what the regular lens would look like!

For most photographers the optical center of a lens is trivia but of no real importance. It suddenly becomes important when trying to do panoramic shots or when doing movements on a view camera. For panoramic shots, it is important to rotate around the optical center of the lens in order to avoid perspective distortion.

My question is why benefit is there to lenses that get closer to the sensor in a digital camera? With film, it was true for many years that retrofocus lenses simply weren't as good as the symmetrical ones. The Biogon was king of wide angles and it never lost its cache. Hasselblad had a dedicated wide angle camera for it, the last iteration of ALPA used one that was originally designed for Linhof I believe. They were always expensive, but actual Biogons were always great performers. Film didn't care how close the lens was to it when it made the exposure. Other than some vignetting, there really weren't very many optical issues with them. Digital sensors are completely different so far. If you get too close to them, the angle of the light hitting them gives rise to all sorts of color weirdness.

So, I think it's cool and all that the K-01 can take lenses that have deeper lens elements, but it isn't clear to me what it accomplishes. I guess there are designs that involve the rear elements to be slightly further back but not to the extent of the Biogon. I think that's what a lot of the current Leica wide angles do. Of course, Pentax's lens designers are just a tad smarter than I am, so we'll see. I am still obsessed with the prototype lens they showed. I want to know what it is! I'm really hoping they have made a 28mm or thereabouts that will blow us away!
02-29-2012, 05:46 AM   #3
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QuoteOriginally posted by isaacc7 Quote
So, I think it's cool and all that the K-01 can take lenses that have deeper lens elements, but it isn't clear to me what it accomplishes.
What I have in mind is basically an Olympus 45mm or 12mm, or Panasonic 25/1.4 adapted for K mount without a mirror box. The rear elements recess in the body. When attached to a body, the lens appears to be a pancake. (yes, APS-C and 4/3 require different image circles. this is an example).
02-29-2012, 12:39 PM   #4
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QuoteOriginally posted by Aegon Quote
What I have in mind is basically an Olympus 45mm or 12mm, or Panasonic 25/1.4 adapted for K mount without a mirror box. The rear elements recess in the body. When attached to a body, the lens appears to be a pancake. (yes, APS-C and 4/3 require different image circles. this is an example).
Wouldn't that make them rather hard to focus? It's an interesting idea although I think that it would be much easier to do lens swaps with a thinner camera like the NEX or NX series.

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