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Archive 2015 · focus question

  
 
beanpkk
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p.1 #1 · p.1 #1 · focus question


This image resulted from a focus stack of half a dozen or more images. The idea was to get all branches in focus throughout the depth of the tree. And to some extent it worked.

But it didn't work as well as it might. You may have to look closely to see, but the problem is that as the lens focuses it changes magnification slightly. Not being an optics wizard, or a lens wizard, does Canon make a lens that does not change magnification as it focuses?
Is that an impossible thing, optically?

Thanks for any insight,

icy buds and branches by beanp, on Flickr

keith



Jan 30, 2015 at 06:23 PM
Ian.Dobinson
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p.1 #2 · p.1 #2 · focus question


as you focus at different distances your magnification has to change . Magnification is a result of Focal Length and Focus distance . so if you change 1 of those parameters then your mag will change .


Probably your best choice to do what you want is to leave the lens at a fixed focus distance and move the rig from your near to far focus points . best way to do that would be a FOCUS RAIL



Jan 30, 2015 at 06:41 PM
beanpkk
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p.1 #3 · p.1 #3 · focus question


Thanks, Ian. A focus rail in this instance wouldn't work -- it would have to be 3 feet long. And as I move the camera, of course the image size changes, just as it does when I focus. In my ignorance I would think the effect would be about the same.

There may just be no technical way to get this shot. I suppose I could try using a zoom lens and attempt to compensate for the mag changing with focus by zooming. Or I could try shooting from farther away which would perhaps decrease the amount the mag changes.

Thank you for the response.

keith



Jan 30, 2015 at 07:39 PM





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