sterling_bjorndahl

<p>As Allan Jamieson said, there is also a 100mm f/4 macro. It is considered to be better quality than the 135/4. It is rarer and more expensive. It came with a matched "Life-Size Converter" to achieve 1:1 (screws onto the front of the lens, like a close-up filter but better quality). Some units sold on the used market are missing the converter.<br> A great source of lens information for the P67 family is at http : // antiquecameras . net / pentax6x7lenses.html<br> Sterling</p>

<p>While I agree with most of Patrick's post, there is one statement I disagree with: "Facts are that the exposure to ultra high frequency radio emission from cell phones is far more problematic...."</p> <p>Citation needed. That's not ionizing radiation. Back when ionizing radiation was discovered it didn't take long to learn that it had a profound effect on tissue. Some bad judgement calls were made on how to use that effect, but everyone quickly agreed that there was an effect. That's not the case with non-ionizing radiation from cell phones, where there may be a small number of studies indicating a small effect - but given how many years of exposure humans have accumulated so far with no alarming spikes in age-adjusted effects across the population, and the lack of solid theoretical grounds for indicating that there should be some effect (going back over 100 years), I am convinced that we have a solid understanding of radio waves at those frequencies, and that you are far, far more in danger of harm if you go out in the sunlight without adequate protection against UV radiation. The sun is going to kill you from radiation long, long before your cell phone will.</p> <p>More on topic, though is Rodeo Joe's concerns about gamma emitters. There is some gamma radiation to be sure, but the primary decay mechanism in the Thorium chain is alpha and beta particles, not high energy photons. The detailed study in NUREG-1717 out of the U.S., table 3.1.7 shows that in the Thorium decay chain, gamma radiation exposure is 5 to 7 orders of magnitude less than the total radiation (assuming exposure in air). The gamma radiation is 1/100,000th to one ten millionth of the total radiation for each product in the thorium decay chain.</p> <p>According to Wikipedia, in the U.S. the estimated average background radiation is 3.1 millisievert per year, depending on where you live. According to NUREG-1717 the additional exposure for an average photographer would be 0.007 millisievert per year (60 hours of use per year). For a "serious" photographer (180 hours of use per year) the additional exposure would be 0.02 millisievert per year. That's their definition, not mine; if you want the details, google NUREG-1717 or go to http ://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1717/nureg-1717.pdf. A single air flight between New York City and Los Angeles is an additional 0.04 millisievert, or twice what a "serious" photographer would get from the lens in a whole year. Tobacco users inhale alpha emitting particles; smoking a pack of cigarettes a day for a year increases your radiation exposure by a whopping 0.36 millisieverts, or about 10% more than background radiation alone.</p> <p>People who are more concerned about radiation from the lens than they are about a single trans-continental air flight should attempt to understand the math better.</p> <p>This assumes the lens remains intact. If it gets ground down or polished and particles get into the air and from there into one's lungs, that would probably be very bad for the lungs.</p>

<p>There are some threads over at Pentax Forum that might help:<br> http://www.pentaxforums.com/forums/48-pentax-medium-format/180301-6x7-lightmeter-not-working.html<br> http://www.pentaxforums.com/forums/48-pentax-medium-format/292835-pentax-6x7-meters-needle.html<br> Good luck!<br> Sterling</p>

<p>I use a macro lens on my DSLR for "scanning" my 6x7 slides. I haven't tried printing larger than 16"x20" with that, but it had no problem with that size. If you want higher resolution you can get very close and shoot 1/4 of the slide at a time, combining the 4 shots using panorama stitching software.</p>