A query on focal lengths


ardnirun

New Member
Sep 22, 2008
553
0
0
Serangoon
#1
Hi all,
recently acquired a CZ jena biometar 80mm in pentacon 6 mount...it came with a p6 to m42 adaptor and i top this off with a m42 to k-mount adaptor..

the p6 to m42 adaptor is about 3-4cm "tall" and putting it onto the biometar extends its length..it reminds me of a extender tube now...

since its 80mm....multiplying by 1.5 makes it 120mm after crop...

i was wondering..would this p6 to m42 adaptor actually make my biometar longer in focal length?


i dun have a longer lens or a superzoom to confirm the lens focal length so i was wondering if any of you guys ever used a pentacon 6 mount camera with a p6 to m42 on a APS-C DSLR..
 

giantcanopy

Senior Member
Feb 11, 2007
6,232
2
0
SG
#2
Hi all,
recently acquired a CZ jena biometar 80mm in pentacon 6 mount...it came with a p6 to m42 adaptor and i top this off with a m42 to k-mount adaptor..

the p6 to m42 adaptor is about 3-4cm "tall" and putting it onto the biometar extends its length..it reminds me of a extender tube now...

since its 80mm....multiplying by 1.5 makes it 120mm after crop...

i was wondering..would this p6 to m42 adaptor actually make my biometar longer in focal length?


i dun have a longer lens or a superzoom to confirm the lens focal length so i was wondering if any of you guys ever used a pentacon 6 mount camera with a p6 to m42 on a APS-C DSLR..
no. the 120mm will still remain 120mm. the adapter/s only served to make sure ur lens focuses to infinity on the dslr. If u look at it in another way, the pentacon bodies have longer flange-focal distance to achieve infinity focusing. u will need to "add some thickness" to do the same on ur DSLR ( which has a shorter flange focal distance i assume ) .

( but of course while using on an APS-C , the crop factor applies, the lens focal length does not change )

ryan
 

ardnirun

New Member
Sep 22, 2008
553
0
0
Serangoon
#3
no. the 120mm will still remain 120mm. the adapter/s only served to make sure ur lens focuses to infinity on the dslr. If u look at it in another way, the pentacon bodies have longer flange-focal distance to achieve infinity focusing. u will need to "add some thickness" to do the same on ur DSLR ( which has a shorter flange focal distance i assume ) .

( but of course while using on an APS-C , the crop factor applies, the lens focal length does not change )

ryan
ahh
okok...thanks....
 

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