Originally posted by ddhytz I'm all for embedding photos to illustrate a concept pertinent to the topic at hand. This certainly was not one of those moments.
Originally posted by JeffJS Huh??
Parfocal lens - Wikipedia, the free encyclopedia
While the minimum focal distance may change with focal length on different (separate) lenses, explain to us how that changes the definition of Parfocal... That is Not the case with mine. I cannot focus any closer with 35mm than I can with 105mm. Demonstrated in the photo below, there is only one focus distance scale. As the distance scale shows, the closest (non macro) focus, is about 1.5 meters, for both 35 and 105.
Here's a photo of the lens to use as a guide.
Thank you for the link to the Wikipedia entry! I didn't understand parafocal the first two times it was explained in this thread but the third time is always the charm!
All kidding aside, the lens is parafocal (parfocal?) only from the distance of 5 feet to infinity. Since you own this very lens, you must be aware that it has a macro feature that enables you to focus at a distance under 5 feet.
Are we now discounting the macro feature of this lens? Because the macro feature is certainly is NOT parafocal.
Originally posted by monochrome Well, that statement doesn't work. Either it is a true zoom or it isn't, not just some of the time.
According to the manual I referenced earlier, Pentax says the minimum focusing distance for this lens is 5 feet. The same measurement is printed on the Distance Scale right on the lens. There is no statement of at which focal length the minimum focusing distance is achieved. Zoom in to the maximum focal length, focus, zoom out to recompose. Focus is maintained.
At least that's what Pentax says,
But what do they know.
I'm not about to argue with you or the Pentax manual. Based on your past posts, you are certainly more knowledgeable than I am about Pentax cameras and lenses. Therefore, pray tell how you would categorize this lens.
- At a distance of 5 feet to infinity, it will not lose focus between 35mm and 105mm.
- Once you shift the focus ring and focus to a distance of under 5 feet, it will quickly lose focus between 35mm and 105mm.
- The macro section (green line) has no distance scale, simply because the focal distance changes from 35mm to 105mm once it focuses at a distance of under 5 feet.
I agree with you that a parafocal must retain focus along all distances, but this lens does not fall under that stringent criterion, hence why I labeled it as varifocal earlier in the thread.