kye Posted August 26, 2018 Share Posted August 26, 2018 I've been playing with my Canon 700D, Magic Lantern 3x crop mode, and the 55-250 zoom lens (which is 264-1200mm equivalent in crop mode) and I've noticed a funny thing about it. If my kid is on the far side of the football field and I zoom all the way in to 1200mm and then manually focus (which is horrible at this distance on this lens BTW) then when my kid runs towards me and I naturally zoom out, the lens shifts its focus closer to me, effectively keeping my kid in focus, and actually helping me! I know about parfocal lenses that maintain the same focus distance throughout the zoom range, but do lens manufacturers deliberately design lenses so that zooming out helps you to maintain focus like this? Or is it just a random happy coincidence it zooms closer and not further away? Considering that the difference between focusing on players on the other side of the football field and focusing on the cars and houses on the other side of the field is a smaller tweak of the focus ring than there is free play in the focus ring, it's pretty difficult to adjust focus, and combined with the Canon screen and lack of good focus assists (that are fast and clear enough to keep up with sports) it would be nearly impossible to film at larger apertures without this lens behaviour! Link to comment Share on other sites More sharing options...
webrunner5 Posted August 26, 2018 Share Posted August 26, 2018 It has to be a Mistake Canon made on that lens LoL. Otherwise Canon would have patented it! I Never heard of a lens do that. Probably some gears are stripped in the lens! Link to comment Share on other sites More sharing options...
mercer Posted August 26, 2018 Share Posted August 26, 2018 I know that was a trick we used to do with camcorders, zoom in really tight on your subject, get focus and then zoom out and your subject is still in focus. Link to comment Share on other sites More sharing options...
froess Posted August 27, 2018 Share Posted August 27, 2018 3 hours ago, mercer said: I know that was a trick we used to do with camcorders, zoom in really tight on your subject, get focus and then zoom out and your subject is still in focus. that's because it's a parfocal lens. with old cameras, you didn't have punch in focus. you zoomed with your lens, focus and the frame the shot. mercer 1 Link to comment Share on other sites More sharing options...
mercer Posted August 27, 2018 Share Posted August 27, 2018 6 minutes ago, froess said: that's because it's a parfocal lens. with old cameras, you didn't have punch in focus. you zoomed with your lens, focus and the frame the shot. Yup, it’s pretty crazy that a $200 camcorder 15 years ago had a parfocal lens. Link to comment Share on other sites More sharing options...
webrunner5 Posted August 27, 2018 Share Posted August 27, 2018 That is why I Always, and still do love B4 lenses. It is like magic compared to a normal lens. If I buy a PK4 a B4 lens will be one of the first lenses I buy for it. Link to comment Share on other sites More sharing options...
kye Posted August 27, 2018 Author Share Posted August 27, 2018 Yeah, @mercer that's parfocal, which is extremely useful. The XC10 tries to be parfocal by compensating electronically for the lens as you zoom, it's pretty good but only if you zoom slowly. Link to comment Share on other sites More sharing options...
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