At those distances your main problem is lighting the subject.
Chuck Norcutt
On 5/13/2016 6:28 PM, Chris Trask wrote:
With the 7mm extension tube I can focus down to 8mm, which is good enough
for me. The 14mm takes me down to 4mm, similar to the shortest of the Vivitar
extension tubes.
Good. You've got it! I guess we'd better get those +0.5 diopter lenses
while we can. :-)
Chuck Norcutt
On 5/13/2016 4:20 PM, Chris Trask wrote:
Doing the math as an estimate, letting f be an "equivalent registry
distance", I find that the extension tube needed to equate to a +0.5
diopter close-up auxiliary would be 3.154mm thick, which is close to my
earlier thumbnail guesstimate.
f is simply the focal length of the lens. When an object is at infinity
the image is formed at distance = the focal length.
S1 is the object distance from the lens and S2 is the distance to the
image formed by the object. If S1 = infinity then S2 = f. As the
object comes closer the image distance starts increasing until when S1 =
f then S2 will equal infinity.
But all of these distances are relative to the optical center of the
lens. Not easy to determine in a modern lens.
Chris
When the going gets weird, the weird turn pro
- Hunter S. Thompson
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