lenses - internal focus or not

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swarbrick
Posts: 3
Joined: 11.02.2009 20:06

lenses - internal focus or not

Unread postby swarbrick » 11.02.2009 21:00

I have just obtained the trailware and am quite excited about the software. My interest is landscape rather than pure macro, for example flowers foreground, mountains behind.
I understand that a normal focusing lens will change the magnification of an object and this has implications for the near end of the spectrum - a few inches from the lens. An internal focusing lens does not change the size of the object (although I do notice that objects come and go at the edge of the picture as you change focus!).
I don`t own an internal focusing wide angle lens. I have a large-format monorail camera, but taking four or more 6 x 12 cm panoramas to get 1 scanned working image doesn`t appeal to my pocket! So 35mm digital it is.
Have people only gotten good results (in the area I mentioned) from internal focusing lenses? Can the software adequately compensate for changes in magnification, of foreground flowers for example? I`m not looking to print large, but only to obtain reasonably sharp and convincing images for digital projection (6 x 2 metre screen, mind you).
Thanks
Ian

swarbrick
Posts: 3
Joined: 11.02.2009 20:06

Unread postby swarbrick » 12.02.2009 13:39

I see no one`s biting, but I found something out in the meantime. "Internal focus" on these modern lenses does not mean that the lens doesn`t change length when focusing, only that the front element doesn`t rotate. So the magnification does change, as the focusing mechanism is still in front.

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Dan Kozub
Posts: 355
Joined: 24.03.2004 18:14

Unread postby Dan Kozub » 13.02.2009 13:16

Please check this post:
http://forum.helicon.com.ua/viewtopic.php?t=1141
I think this is what you mean.

Anyway the program is able to compensate for such magnification so in most cases this should not be a problem.

Charles Krebs
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Joined: 06.04.2005 08:00
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Unread postby Charles Krebs » 28.02.2009 09:56

Ian,

The program handles the "magnification" changes fine. But that's not the big problem. If the lens entrance pupil moves at all when focus is changed while shooting such a stack (near to far landscape, wide angle lens), then objects (especially those very near the lens, and toward the edges of the frame) will shift to different positions relative to objects that are more distant. It's as if they have moved to different locations in each shot. It present the software with an impossible task.

To see what I mean try this....

Hold up a finger a few inches in front of your eye and off to the side. Keeping the finger in the same location, move your head forward and back several inches. In your peripheral vision notice how dramatically the relative position of your finger to some distant object changes as your head is moved.

Charlie

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Unread postby Guest » 18.03.2009 10:33

Thank you, Charles. can I therefore assume that in the case of an "internal focus" lens (where the length is not changed by focusing), the entrance pupil of the lens also does not move? Buying such a lens for my Fuji S2 digital camera would save me a lot on film costs using my monorail camera! With thanks


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