Re: Minimum focus distance & DOF relative to extension (tubes)?
On 17/07/2011 00:38, Leon Altoff wrote: I need a high resolution ruler. Any decent engineer's 6" rule should have a bunch of 1/64ths on. Some school suppliers sell filmstrips of microscope eyepiece graticules. About 1cm divided into 100. If you are really stuck, I could put one in the post for you. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: Minimum focus distance & DOF relative to extension (tubes)?
Hi Darren, When doing macro I've always found that magnification is more important than minimum focusing distance. I usually set up a combination and photograph a ruler and while I'm at it measure the distance between the front of the lens and the subject just for good measure so I know what I can fit under the setup (usually a tank of sea water). It's annoying when you get down to 1.5mm or so filling the frame - I need a high resolution ruler. For depth of field the same rules apply as always. The problem being that the web site you showed doesn't have enough decimal places to tell you the details. I've found a few calculators that do, but they are few and far between and the usual answer is "not a lot". Leon On 17 July 2011 03:03, Darren Addy wrote: > Two questions: > Forgive my ignorance, but is there a formula or table somewhere > telling me what sort of minimum focus distances can be achieved with > different Takumars with the various Pentax extension tubes, or does > one simply have to experiment? > > Seems like somewhere there should be someone who quantified it, but maybe not. > > DOF can be calculated knowing the focal length, f-stop, subject > distance and film/sensor size > http://www.dofmaster.com/dofjs.html > but is there a similar calculator that takes into account extension amount? > > Darren Addy > Kearney, Nebraska > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. > -- Leon -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: Minimum focus distance & DOF relative to extension (tubes)?
On Sat, Jul 16, 2011 at 12:03:47PM -0500, Darren Addy wrote: > Two questions: > Forgive my ignorance, but is there a formula or table somewhere > telling me what sort of minimum focus distances can be achieved with > different Takumars with the various Pentax extension tubes, or does > one simply have to experiment? > > Seems like somewhere there should be someone who quantified it, but maybe not. > > DOF can be calculated knowing the focal length, f-stop, subject > distance and film/sensor size > http://www.dofmaster.com/dofjs.html > but is there a similar calculator that takes into account extension amount? Not directly, no. If you think about it, there can't be a simple one; different lenses with the same focal length can have different mimimum- focussing distances. It's possible to calculate a pretty good approximation for any given lens, but in practice it's probably easy just to experiment - to get really accurate results you'd need to know how the effective focal length of the lens assembly changes with change in focussing distance, and that depends on the optical formula of the lens. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Re: Minimum focus distance & DOF relative to extension (tubes)?
You know about this site don't you. http://kmp.bdimitrov.de/lenses/primes/normal/index.html It has minimum distances for Pentax k-mount lenses. Regards, Bob S. On Sat, Jul 16, 2011 at 12:03 PM, Darren Addy wrote: > Two questions: > Forgive my ignorance, but is there a formula or table somewhere > telling me what sort of minimum focus distances can be achieved with > different Takumars with the various Pentax extension tubes, or does > one simply have to experiment? > > Seems like somewhere there should be someone who quantified it, but maybe not. > > DOF can be calculated knowing the focal length, f-stop, subject > distance and film/sensor size > http://www.dofmaster.com/dofjs.html > but is there a similar calculator that takes into account extension amount? > > Darren Addy > Kearney, Nebraska > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. > -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
Minimum focus distance & DOF relative to extension (tubes)?
Two questions: Forgive my ignorance, but is there a formula or table somewhere telling me what sort of minimum focus distances can be achieved with different Takumars with the various Pentax extension tubes, or does one simply have to experiment? Seems like somewhere there should be someone who quantified it, but maybe not. DOF can be calculated knowing the focal length, f-stop, subject distance and film/sensor size http://www.dofmaster.com/dofjs.html but is there a similar calculator that takes into account extension amount? Darren Addy Kearney, Nebraska -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
