Some copies of the DA 50-200 are surprisingly sharp for an inexpensive lens. I worked with it a while before the 60-250 was released and found it more than adequate.
Paul via phone On Apr 17, 2015, at 9:20 AM, Eric Weir <[email protected]> wrote: >> On Apr 11, 2015, at 9:59 AM, Stanley Halpin <[email protected]> >> wrote: >> >> You didn’t say what focal length. >> Assuming you were using 200mm at 20’, f/11 the depth of field would be 4”. >> 50mm at 20’, f/11 would be 5’9” >> >> The one app I am using to calculate these numbers doesn’t want to use an >> aperture smaller than f/11. >> The other app says 2’11” for 200mm, f/22 at 20’ but I am not sure I quite >> trust that. >> >> Note that >> 1 - using f/22 you are going to be encountering diffraction softening which >> would certainly affect the small flowers. >> 2 - the 50-200 is not known to be super sharp. And most zoom lenses of that >> variety, even the very best, will be “soft” when used at longer focal >> lengths like 200mm. >> 3 - Shooting from 20’ away, with a 200mm lens you need a rock-solid tripod, >> use mirror-up remote trigger. A reasonably fast shutter speed is also called >> for. If you are shooting at f/22 then you will either need a lot of light or >> a high ISO. >> >> In short, there could well be other factors which affect your image’s >> apparent sharpness other than the issue of proper focus and depth of field. > > Sorry for the late response. But thanks, Stan—and to Jack, Peter, and Mark, > too. > > Update. I learned a lot here. I think I’ll have to keep studying it, though. > Studying and testing it out in practice: (1) I didn’t know that focal length > was a factor in determining DOF, (2) I hadn’t even heard of diffraction > softening, or maybe I did and it just didn’t register with me. (3) I didn’t > realize the DA 50-200 was not especially sharp. (5) It never occurred to me > that haze, dust, and thermal distortion would be a factor when focusing at > longer distances. > > In the case I described, I was not actually focusing at infinity. I don’t > know now why I described it that way. I can say that I was assuming that the > smaller the f/ the greater the depth of field, and that with f/22 the depth > of field was huge. I would estimate that in the cases that concerned me I was > actually focusing at between 20’ and 25’. (I was using a tripod, ISO 100, and > aperture priority, resulting in slow shutter speeds.) A quick scan of the > images in LR shows that I was using the lens at various focal lengths. I’ll > take a closer look at the better and worse images to see if I can see how all > the factors cited interacted to produce the result I got. > > A question: If, as Peter says, diffraction begins to take its toll at f8-f11, > of what use are smaller apertures? > > ------------------------------------------------------------------------------------------ > Eric Weir > Decatur, GA USA > [email protected] > > "What does it mean...that the world is so beautiful?" > > - Mary Oliver > > > > > > > > > > -- > 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. -- 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.
