120mm macro minimum focus distance

<p>Can anyone with a 120 ApoMakro for the C645 please tell me the distance (either from lens front or film plane, but please specify) to minimum focus so that I can look for a tripod which will allow me to focus from above to the ground at 1:1. Haven't got the lens with me at present so can't do it myself. Thank you.</p>

<p>My Pentax 645 120mm Macro is also 1:1, and the min focus is 1.3 feet from the film plane. This ends up being only a few inches from the front element at 1:1. A tabletop tripod might work in a pinch.</p>

<p>The exact distance between lens or film plane and subject depends on how this lens works exactly.<br>

It is an FLE lens, thus it changes focal length a bit when focussing. It probably uses internal focussing too, in which case it drastically changes focal length when focussing.<br>

So knowing its nominal focal length at infinity, and the fact that it reaches up to 1:1, doesn't give enough information about the distances involved.<br>

Comparing it to another lens, of different design, will very likely also not provide the answer.</p>

<p>Assuming, however, that the lens using unit focussing, and ignoring the change to the focal length the floating elements will produce, the distances could be calculated using the numbers in <a href="http://www.zeiss.com/C12567A8003B8B6F/EmbedTitelIntern/Apo-Makro-Planar4_120mm_e/$File/Apo-Makro-Planar4_120mm_e.pdf">Zeiss' data sheet</a></p>

<p>At 1:1 the distance from subject to film plane will be 4*focallength, so 480mm assuming the focal length doesn't change significantly to achieve the 1:1 focus.</p>

<p>...Wayne</p>

 

<p>Plus the distance between the principal planes.<br>

Can be calculated using the numbers on the data sheet. Also assuming that these do not change (much) when the lens is not set to infinity.</p>

<p>Thanks kindly for your answers...I was in fact hoping someone could just open their lens to min focus distance plane and then measure to the lens front with a tape, that would be close enough to let me find a support...my work is not so exacting.</p>

<p>I think you should buy your tripod carefully. Not based on the minimum distance for a 120mm lens -- though that is a good reference point.<br>

Doing macro work -- with some heavy camera mounted -- and tripod legs spead wide out implies a sturdy tripod.</p>

<p>Agreed... my prospective list contains nothing under 5gk (head and legs together)</p>

<p>try kg</p>