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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