Photography Tips – Focal Length Changes 3 Things – Focal Length Explained 2

Photography Tips – Focal Length Changes 3 Things – Focal Length Explained 2

January 13, 2020 97 By Peter Engel


When you change the focal length of your lens either by zooming in and out or perhaps by putting on a short wide angled lens not only are you changing the magnification that’s what makes far off things come closer you’re changing three other things as well. You’re gonna have an impact on perspective, depth of field and field of view, field of view is like how much you can get into the picture. To explain this Jane and i have spared no expense in building our specially painted field of view demonstrating engine. All of this is the made using the finest
quality garden shed materials, let me just put these lenses down here, so i can say what i mean. Now you imagine this silver painted drain rods beautiful that they are are the barrel of the lens, this is kind of what you’re gonna see through your lens, and this bit here, the bicycle wheel is the glass at the end. If i have a wide-angle lens a short focal length that’s this distance here is short. I’ve got a very wide field of view, as i look along these rods what i can see pans out all the way across over there, to the side all the way out to the hills over there, it’s a very wide field of view. If i’d zoomed the lens by increasing this bit, the focal length, what happens is it draws in the field of view, you see how these rods are getting closer and narrower, because of this i think we should call long lenses ‘narra lenses’ but we don’t unfortunately, we’re stuck with what we’ve got. How does it impact real life? let’s go and have a look at this through a camera. Beginning with a wide-angle lens and a wide field of view we’re gonna use this rock here, this stone is the anchor point for this little film. Now as you can see except roughly on the left hand side third filling the frame, over this side of the picture you’ve got those bushes along the side of the road there, over here on the other side you can’t you see there’s a little
standing stone over there and then the brown field beyond going all the way to the horizon. If you wanted to get the same shot of this stone but without all that going on either side you’d need to narrow the field of view and you’d do that by using a longer lens. With a long lens the first thing you’d probably notice is there seems to be more stones in this shot, that’s a perspective thing we’re gonna
talk about that in a minute just ignore it. Think about the field of view, this business remember the bushes over on that side of the road they’ve all gone now haven’t they and the edge of the picture on this side are the bushes way on the top of the hill there. Similarly on the other side of the stone the brownfield where the frame did end that’s now disappeared hasn’t it, we’ve excluded that and it’s edging on the greenfield down the other side of the stone here. Yeah our friend the stone is the same size in this shot as it was in the wide angle shot, it’s occupying the same space in the frame. Now because of the magnification aspect Jayne’s had to move back with the camera in order for it to fit but it’s in the same place and we’ve excluded stuff down either side. The other characteristic of the wide lens is perspective, it stretches things out, it moves them further apart so something that’s close to the lens will seem quite large and will pull towards it, stuff that’s further away will seem tiny. See these rocks up behind here, they look really tiny and like they’re a huge distance away, they’re not let’s pace it out, look, one, two, three, four, five, six, seven eight, nine, ten, eleven, twelve, thirteen, fourteen fifteen, sixteen, seventeen, eighteen, nineteen, twenty twenty-one places that’s all it is from
where you are to this rock here. but it looks really really tiny like it’s off into the distance, that’s because the short lens that expands perspective. let’s take a quick look at it with a longer lens, it’s the same shot, keeping this stone the same size in the picture. Now we mention there seem to be a lot more stones in the shot, there are no more stones in this shot to a moment ago, what has happened is the magnification
part has compressed perspective, long lenses flattened things together they draw stuff that’s a long way away and they bring it forward and they kind of stack them, bom ,bom, bom, bom, bom like that, one behind the other and that’s what’s going on at the moment. The rock behind this one, the stone behind this one is till only twenty one paces away from where i am, it hasn’t changed at all despite the fact it looks considerably closer, that’s about perspective stacking that’s
how you get those shots of mountain ranges going off into the distance and
coming together and we’ve done it with a bunch of standing stones. Short lenses, that’s wide lenses with all the wide field of view they also have a massive depth of field, depth of field is how deep the focus of your shot is, how much you’ve got sharp from in front of the camera to off into the distance. Now just now when i walked back over there to where that cow is now playing around with our rock i was sharp all the way wasn’t i? from here back to there and as i come towards you now i’m still sharp up to about here that means the death of focus with a short wide lens stretches from what three, four feet in front of the camera in this case Janes video all the way to the horizon, that is an immense amount of depth of field. The final part of this puzzle is the long lens and depth of focus, now depth of focus, depth of field it’s the same thing now as i’m walking towards you i’m slowly shifting myself out of focus. The camera is focused on the stone i was standing next to, and as i’m coming forward i’m getting myself more and more soft in your view finder. In a moment to when i got about five or
six feet in front of the camera i’ll be very soft indeed i reckon i look positively drunk by now. Now then if Jayne just re-focuses the camera on me so that i come sharp there we go that’s better isn’t it. I’m nice and sharp, but look any stones that are behind me look, they’ve gone completely soft. If i move towards the camera if you remember with a short lens, i could come all the way up to three feet and and i was still nice and sharp, look if i start walking towards you now i reckon i’m out of focus here. This is an inherent thing with a long
lens it has a shallow depth of field very shallow depth of field if i was to walk back up this way the same sort of thing would happen as i’m going backwards i’m getting softer in the shot as well just like when i went forward. It’s more pronounced when i come close to
the camera so if you start doing close-up work with
the long lens and it’s a great tool for close up work you’ve got to be very very careful with your focusing because your depth of field is very very shallow with a long lens.