A little calculation using f/calc: 1 - Full frame 5" subject equals to a rough 1:5 ratio. 2 - Using your 50mm lens you'll get 1:5 at 30 cm., i.e. you need an extension tube. 3 - At f/1.4 and 30 cm. (1 ft) your 50mm will yiekd less than 3mm depth of field (with a .033 COC).
Hope this helps, Flavio - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .