Beginner Depth of Field and Focal Length

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Mark65

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Mark
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Hi All,
So I thought I was understanding depth of field.... no, I did not realise it changed with focal length doh!, is it just me being old and a bit slower :rolleyes:.
I am grasping the combination of speed, aperture and iso and how they affect each other, should I stay with the 24-70 on my Z6 and keep it at 50mm focal length or swap it out for a 50mm f1.8, Im going to mainly take images of the grand kids, family and dog or should I just persevere, I think the zoom is just a tad confusing but then I dont think the Z6 I bought was meant as a beginner camera, I may just get the 50mm f1.8 and put the zoom away, not sure at the moment.
I found an app called DOF simulator on android which is very helpful as it shows how each setting affects the image.

play.google.com

DOF simulator – Apps on Google Play

Photo depth of field calculator with visual background blur and bokeh simulation
play.google.com play.google.com

It does show you that photography is not a doddle really as most think it is.

Thanks
Mark
 
Mark65 said:
Im going to mainly take images of the grand kids, family and dog or should I just persevere, I think the zoom is just a tad confusing
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I know this is heretical for a photography forum but I mostly think about DOF in terms of getting as much of the subject as I want in focus rather than getting that hackneyed shallow DOF look.

IMO for general photographs of everyday life it's more important to avoid unwanted blur caused by camera shake or subject movement than to obsess over depth of field. Get the main subject sharp and the rest can look after itself. I think this is especially important when starting out having seen lots of inexperienced photographers produce blurry shots that would otherwise have been really good.

Keep you shutter speed up and concentrate on capturing the moment and getting used to your camera and lens. When you are confident in what you're doing then you can start to get more creative with apertures and shutter speeds.

Please bear in mind that I'm not yer average camera nerd. ;)
 
I would stay with the 24-70, as it's also important to learn how different focal lengths affect the image.
One of the key things to learn is to see what is wanted, and what is unwanted, in a scene, and understand how choice of focal length and camera position can be used to exclude things you don't want, and change the relative size of objects.
 
I’d say persevere.
But I’d also say that it is a doddle.

When you decided you wanted to be a photographer, it wasn’t so that you could navel gaze about the relationship between FL and DoF. Surely it was to capture memories or make pictures.

So now you know that if you use a WA lens and focus in the middle distance at a reasonable Aperture then you have a massive DoF, but if you use the same Aperture at 400mm and 30ft away the DoF will be shallow.

You don’t need to know how many mm or m DoF you have, you just need to acknowledge the principle. Likewise; understanding the relationship between ISO, SS and Aperture.

Bank that knowledge, set auto iso, Aperture priority (2.8 for 1 grandkid 5.6 group, f8 if they’re moving around) choose your focus point, let the camera focus on them and get on with making pictures. That is a doddle :)
 
Phil V said:
...set auto iso, Aperture priority (2.8 for 1 grandkid 5.6 group, f8 if they’re moving around) choose your focus point, let the camera focus on them and get on with making pictures. That is a doddle :)
Click to expand...
The rider to that is in aperture priority with auto ISO some cameras will still select too slow a shutter speed to freeze action. I'm speaking from experience here.
 
I like shallow DOF mainly because it puts emphasis on the subject as opposed to the wheelie bin "or whatever" in the back or foreground.
 
It is a real pain with 85mm +
I often find that less is in focus than i would like

you can get an app on your phone to know exact DOF but you need to know the distance roughly
 
Keep the 24-70mm lens, get the 50mm too, if & when.

Forget the DoF Simulator, just play, take shots with different f/. numbers, different focal lengths, object & background distances. Have fun.
 
soupdragon said:
I like shallow DOF mainly because it puts emphasis on the subject as opposed to the wheelie bin "or whatever" in the back or foreground.
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Too many people use shallow DOF as a crutch because they don't pay attention to the whole frame. Often a slight repositioning of the camera in relation to the subject can remove background clutter. But that's too advanced for a beginner, as is using shallow DOF. The crucial starting point is to enjoy taking photos that capture moments that matter to you, later your can look for 'mistakes' and work out how to avoid them in future.

Photography is best learned one small step at a time.
 
I agree with Phil, be aware of DOF but don't worry about it.
Mark65 said:
Hi All,
So I thought I was understanding depth of field.... no, I did not realise it changed with focal length doh!, is it just me being old and a bit slower :rolleyes:.
Click to expand...
No, it doesn't change with focal length, that's a common misconception.
And nor does it change with the f/number.

It's governed by the effective aperture and distance. The effective (or actual) aperture is the size of the hole through which the light passes, and if, for example, the effective aperture is 10mm then the DOF will be the same with every lens, regardless of the focal length, if it is set to an aperture of 10mm.

Now, the confusion arises because, with (for example) a 100mm lens, a 10mm aperture amounts to f/10
With a 200mm lens, it's f/5 and with a 50mm lens it's f/20. And that's the reason why longer lenses appear to have less depth of field:)
 
What Garry said :)
I don't know what age your Grandkids are but when mine were younger getting a shot with a 50mm f1.8 was easy - if they were posing! so it did not get used much.
At any other time they were moving about so a zoom was essential to keep them in frame. I know that lots of people go on about needing a 50mm or 85mm prime for portraits but you do not need it for general family shots, with my 35mm SLR I preferred a 135mm prime anyway.
 
Garry Edwards said:
Now, the confusion arises because, with (for example) a 100mm lens, a 10mm aperture amounts to f/10
With a 200mm lens, it's f/5 and with a 50mm lens it's f/20. And that's the reason why longer lenses appear to have less depth of field:)
Click to expand...
Shouldn't that be 10mm = f/20 @ 200mm and f/5 @ 50mm?
 
Andrew Benbow said:
Shouldn't that be 10mm = f/20 @ 200mm and f/5 @ 50mm?
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Perhaps I should have explained the formulae.
F= focal length
EF = effective aperture
f/ = lens aperture.

So, divide F by EF and the answer is f/
or
F / EF = f/

F100 / 10 = f/10

It's all a bit theoretical, because the figures only apply at infinity focus. For example, at a 1:1 ratio the lens is physically twice as far from the film/sensor as it is at infinity, so a F50 lens actually becomes F100 - but, theory aside, it's near enough.

I think that one of the challenges that today's photographers face is that we can no longer see the aperture on modern cameras and lenses.
 
Garry Edwards said:
Perhaps I should have explained the formulae.
F= focal length
EF = effective aperture
f/ = lens aperture.

So, divide F by EF and the answer is f/
or
F / EF = f/

F100 / 10 = f/10

It's all a bit theoretical, because the figures only apply at infinity focus. For example, at a 1:1 ratio the lens is physically twice as far from the film/sensor as it is at infinity, so a F50 lens actually becomes F100 - but, theory aside, it's near enough.

I think that one of the challenges that today's photographers face is that we can no longer see the aperture on modern cameras and lenses.
Click to expand...
So with a 10mm diameter ’hole’…
F = 200mm
EF = 10mm
f/ = 200/10 or f/20

F = 50mm
EF = 10mm
f/ = 50/10 or f/5

(which is what Andrew said, rather than the other way around as per the example in your original comment BTW).

So, I agree and understand what you’re getting at, ie the depth of field is nominally determined by the physical size of the aperture and not by the focal length.

From a practical viewpoint; I know that f/8 on say a 24mm wide angle lens, gives more DOF than f/8 does on a 300mm.

I get that it’s due to the difference in the size of the hole rather than the focal length. However, understanding that DOF at the same f-stop differs with focal length, is IMHO a useful thing to remember. That this is due to the different ‘hole’ sizes is useful to know, but I have to say is not my first thought.
 
GeeJay57 said:
(which is what Andrew said, rather than the other way around as per the example in your original comment BTW).
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Yes, I'm old and knackered and make mistakes:)
 
Thanks all, it does sound like more shots = the user experience to get used to it.
I did find the visual representation of the app helpfull.
Mark
 
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