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I'm new to photography and I can't get a nice DOF. I read up on all the technicalities that involve DOF and I still can't get it right.

For example, if you take a picture very close to an object, zoomed out, and then move further back and zoom in would the pictures show the same DOF given the aperture was adjusted?

With my kit lens (EF-S 18-55mm 1:3.5-5.6 IS) I can't change the aperture below f/5.6 when zoomed in (or f/3.5 when zoomed out) so I cannot create a nice DOF. Also, my kit lens has its sweet spot around f/7.1 and since I want my pictures to be sharp I want to shoot with that aperture.

So my basic questions are:

Do I need a new lens with a maximum wider aperture to achieve the outcome I want?

Does focal length really influence DOF? If so, why can't I change DOF by getting closer to the object? Am I doing something wrong?

I'm interested in street (especailly at night)/landscape and animal photography and my body is a Canon E550D RebelT2i (crop factor 1.6).

Thank you in advance!

marked as duplicate by mattdm, Philip Kendall, scottbb, Michael C lens Dec 16 '16 at 2:27

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For example, if you take a picture very close to an object, zoomed out, and then move further back and zoom in would the pictures show the same DOF given the aperture was adjusted?

DOF will almost certainly not be the same. You're right to point out that your lens (1:3.5-5.6) will automatically adjust its aperture as you zoom. If you make no other compensation, this will adjust your exposure, so to keep consistent exposure you should also adjust shutter speed or ISO to offset the aperture change invoked by zooming - but that's a side point.

The depth of field is proportional to the distance from the subject. So if you had a lens that had a fixed maximum aperture throughout its zoom range, then under your scenario (stand near, take a shot, step back some way, zoom in, take shot with same framing) - the depth of field will be different. To give you an example with some dummy numbers to give you a sense of what's going on - if you shoot a face from 1 metre at f/2.8, you might have a depth of field that's in focus approximately 1cm from front to back. Now walk back 10 metres, zoom in and take another shot at f/2.8 and your depth of field might now be 5cm or something like that. In the first shot, only the eyes are in focus. In the second shot, so is the nose and so are the ears.

So in your case where the aperture is adjusting, you can almost certainly guarantee the depth of field will not be the same simply because for your second shot the aperture will almost certainly be the same at 10m and 20m but different at 1m. So from 1 to 10m you might fluke it and get the same DOF, but from 10m to 20m you cannot.

so I cannot create a nice DOF

You need to tell us what you consider "nice". Shallow? Or deep?

my kit lens has its sweet spot around f/7.1 and since I want my pictures to be sharp I want to shoot with that aperture

Ok - that's a great starting point. If we know we want that fixed, then we also know from earlier in my answer we can still adjust depth of field by moving toward the subject, or away from it. If you fix your aperture then walk towards and away, find the closest and furthest distances from your subject that make great compositions for you - then inspect the images closely on a PC screen to see the difference in depth of field.

Do I need a new lens with a maximum wider aperture to achieve the outcome I want?

It depends on the outcome you want. A wider aperture will allow shallower depth of focus. A second benefit to wider aperture - even if you stop it down to f/7.1 (although a different lens will have a different sweet spot) is that your auto focus system uses all available light with the aperture wide open. This means in low light your AF will perform better on a lens supporting wider aperture - even if at time of exposure you program it to stop down to a small aperture.

Does focal length really influence DOF? If so, why can't I change DOF by getting closer to the object? Am I doing something wrong?

It's not focal length, per se, but it is distance to subject. The depth of field can in fact be calculated based on your distance from subject - there are websites where you can key in various values and measures to do this, but I don't have a link to hand. Moving closer - while retaining the same aperture - will make your DOF shallower. Perhaps your camera's adjustment of aperture due to zoom is offsetting this. You can test this by taking 2 shots from different distances without adjusting focal length (ie. without using zoom) between shots.

I'm interested in street (especailly at night)/landscape and animal photography

Very cool :) But even knowing your preferred subject matter doesn't tell me what kind of shot you'd like to take :) Hope the above gets you on your way though!

  • @yourcantryreachingme I want to create a nice shallow DOF but keep most of the background in the frame. For example, if you compare these pictures: link the photographer wants to demonstrate how you can affect the DOF. I can easily achieve, though in worse quality due to the lens, the left picture but I cannot get it to look like the right one. If I try to I will most certainly always end up with a less blurry background. – Chris Dec 16 '16 at 4:35
  • Today I tried to play around with DOF. I zoomed out and went closer to the object to see if the background blur changes and apart from the background blur not changing (I adjusted the aperture this time) I can't get as close to the object as when backing up and zooming in. My lens won't focus, even manually, if I get too close, so I have to back up and zoom in a little. I want to be more in control of that so I'm not sure if I should try a different lens. – Chris Dec 16 '16 at 4:48
  • Another question: Will my DOF become shallower/narrower or deeper if I zoom out to 18mm and go closer to the subject? I just tried to take a portrait of my wife and I can't get the background to blur. It's only slightly blurred! The lights in the background aren't circular at all. I saw another post where someone tried to illustrate the bokeh effect with a kit lens compared to a prime 1.8 lens and the author had a nice bokeh effect with the kit lens! What am I doing wrong? If I move away from the subject and zoom in I can't get everything in the frame as I did when zoomed out :( – Chris Dec 16 '16 at 5:54
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Do I need a new lens with a maximum wider aperture to achieve the outcome I want?

Maybe. I'm not sure what you're trying to achieve -- lots of depth of field, meaning objects at a variety of distances from the camera are all in focus or nearly so, or narrow depth of field, where your subject is in focus and the background is an unrecognizable blur, or something in between.

Depth of field is determined by aperture, but also by the camera-to-subject:camera-to-background distance ratio. If you want lots of background blur, move your subject away from the background and close to the camera. Having a lens with a large aperture (like f/1.4 or f/2) gives you more flexibility, but if you can place the subject and the camera relative to the background, you can still take nice shots with a slower lens. In fact, learning to do that with a slower lens will help you make better use of a faster lens when you eventually get one.

  • I think I need more practice but I can't get the pictures to look insanely crisp. I think it's the lens because even at my lenses sweet spot I won't get as crisp of a picture I could get with a prime lens. What do you think? I have the option to rent some lenses. Maybe I should do it and try some out to see where my boundaries as a beginner are to fully unfold the possibilities of a better lens. Do you have any recommendations for lenses? – Chris Dec 16 '16 at 4:53

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