On Mon, Jan 7, 2013 at 1:22 PM, Boris Liberman <[email protected]> wrote: > On 1/7/2013 9:07 PM, Darren Addy wrote: >> >> Honestly, I think the best option is the Pentax O-GPS1 if you shoot >> Pentax models that are compatible. What can be done with them is >> amazing. Like any photography, wide field is easier to do than >> telephoto (which gets increasingly more difficult with focal length). >> But check out what this guy did with a K-5, an O-GPS1 and a 200mm f2.8 >> lens: http://poirierstephane.free.fr/photos/index.php?/category/132 >> AMAZING. I recently purchased an O-GPS1 to go with my K-5 and intend >> to start with my Super-Multi-Coated Takumar 135mm f2.5 v2 along with >> some more wide field stuff... just as soon as I get the fires in my >> life put out. >> : \ > > > I should support year suggestion, Darren. It simply makes the most sense. > However I wonder if 500mm lens is something that software on the camera and > in the GPS module could work with. Mostly likely they will, but it needs to > be double checked.
It *can* do it, but with distended objects (like nebula, galaxies & clusters) the most important thing is getting photons to the sensor. You can only do that in two ways... faster optics or longer shutter speeds. When you increase the focal length you are decreasing the amount of time that the O-GPS1 can move the sensor to keep up (meaning your maximum shutter speed open time is reduced). In addition to reducing your "shutter speed" you are also losing 3/4 of the light with an f8 mirror lens over using a more common f4 200mm or 300mm. Put another way, you would need to stack 4 exposures taken with the 500mm f8 to equal the photons on the sensor with an f4 lens (8 if comparing to an f2.8 lens). -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
