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08-23-2010, 05:38 PM   #16
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QuoteOriginally posted by Damian Quote
... I'd love to use wider glass if I could afford it. The whole point was to not have to buy wider glass, when I have wide glass. My DA L 18-55 is plenty wide, and so WAS my Pentax-A 28 f2.8 until now. ...
Get yourseld a film body and instant full frame: you can use all your "heritage" lenses as they were designed!

08-23-2010, 07:22 PM   #17
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OK, back to the point of this thread, I guess I'm going to wrap this up as STUPID QUESTION and definitely not a Brilliant idea.
08-23-2010, 09:00 PM   #18
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one way to get a wider field of view (in your print) out of a lens is to use photomerge in photoshop, and merge 4 tiled shots. Just leave room for cropping and distortion correction. It works best off of a tripod with stationary objects, but I have used the technique hand held quite often with satisfactory results. It is a good way to get around having to buy a wide angle assuming you dont shoot with wide angles that often.
08-24-2010, 05:16 AM   #19
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I've only seen wide angle adapters that screw in at the front of the lens, not the back. They also give you a nasty fisheye perspective
I have one (Idating from the Canon S2's days) and it does NOT create a fisheye effect. Then again, it's a high-quality converter (costs more than the kit lens).

08-24-2010, 07:22 AM   #20
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"I have one (Idating from the Canon S2's days) and it does NOT create a fisheye effect. Then again, it's a high-quality converter (costs more than the kit lens)."

I'm glad I'm not the only one who owns a 'good' wide angle converter. I picked mine up for a bargain price but brand new they cost more then my kit lens would have. And again I will restate what I said earlier, it does not add any nasty fisheye perspective or any detectable optical distortion.
08-24-2010, 09:08 AM   #21
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You could always stitch & crop shots done it portrait mode to get the width you want. The trick would be finding the proper camera-to-subject distance for the effort to work correctly. And that would depend on whether subject size or field of view was more important to you.

Good luck in your quest.
08-24-2010, 06:36 PM   #22
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Does fov change when you reverse mount or only minimum focus distance get closer?
08-24-2010, 08:59 PM   #23
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QuoteOriginally posted by troglodyte Quote
Does fov change when you reverse mount or only minimum focus distance get closer?
I think this a question about macros, not widening angles.

First part: I *think* (but I'm not sure) the FOV remains the same -- that's a function of the sensor/frame size and the lens' focal length. Is there an optics designer here who can answer that?

Second part: it's not so simple. Any lens that is NOT reversed cannot be focused closer than its focal length. Put a 50mm lens on tubes or bellows, with 50mm or 100mm or 150mm or whatever of extension -- and the closest focus is still 50mm. AFAIK the only way to focus closer is to change the lens' focal length.

When a lens is reversed, it's working distance is the register of that lens type -- with Pentax, Nikon, Sony, that's about 45mm. Think about it: an un-reversed lens gathers in light from a distant view and focuses it onto the frame, about 45mm from the back of the lens mount. Reverse the lens, and light bouncing off a subject that's ~45mm from the lens back is gathered and projected onto the frame.

How this affects the minimum focus distance (MFD) varies among lenses. Reverse a 20mm lens, and your MFD stretches from 20mm to 45mm. Reverse a 100mm lens, and the MFD shrinks from 100mm to 45mm. It doesn't matter whether the reversed lens is stacked onto a primary, or sitting at the end of huge extension -- your MFD is either the lens' focal length (straight) or its register (reversed).

And now we return to working GOATSE upon a lens. Stretch away...

08-25-2010, 11:04 AM   #24
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It's possible to do in theory, but you can't do it with an existing camera (you'd have to move the sensor). The Nikon E2 and whatever else was in that series does it. (Tiny sensor, same field of view as a 35mm camera.) It's bad for image quality, and it's bad for light transmission. You might say it's just bad.

No one has (afaik) done it since it became possible to manufacture semi-large (APS-C) sensors at semi-affordable prices.
08-25-2010, 08:10 PM   #25
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Let me qualify everything below by first saying I am not an optical designer, nor am I an engineer. I'm a Home Designer, though, I have taken structural engineering courses as part of my degree, I do not have a background in the type of engineering that would be required to properly solve this problem. That being said, if what I have concluded below is completely off base, please disregard.

I did a little research into Lens design, being the type of person I am - a problem solver - I don't like unanswered questions. I won't go into detail because I haven't done the math and have no desire to pull out my old Calculus books, but it is in theory possible to manufacture a crop correcting lens that could go between the camera body and the main camera lens. It would be prohibitively complicated, both in construction and use. Being that different focal length lenses have different output image characteristics, i.e. the angle of the light exiting the back of the lens, and that some lenses actually have moving rear element assemblies, the crop correcting lens would have to have focusing capabilities. So in order to use it affectively one would have to dial in the focus of the crop corrector for each lens used on the camera. Compounding the problem would be the use of zoom lenses in which every time the focal length is changed, the crop corrector would probably have to be re-focused. This would not apply to all lenses, but would probably hold true for most. Furthermore, the complicated optics required to make such a contraption work would probably introduce unwanted optical artifacts that would negate any benefits of its use in the first place. So basically, as our esteemed administrator said at the beginning of this thread, "you'd have to have some really complex optics which are likely not feasible, and would probably screw up the image quality more than they are worth".

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