DoF

Dom7

Dom7

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Dominic
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Hey everyone!

I have recently taken delivery of a Sony A65 and have only really just started playing around with it. I have currently only got the 18-55 kit lens.

I am trying to get started with some basic shots, to try to achieve a shallow DoF. I know that I need to set my aperture as low as possible (I think?). What else should I be looking to do? Local/Zone/Spot focussing? As my current shots are coming out OK, but not as contrasting as I want, I really want to take some images with the background really cut out.

My initial thought it that I would need better lenses, like a 50mm 1.7 or something along those lines as my kit lens is 18-55 3.5...

Any help is much appreciated. :)
 
The factors affecting dof are aperture, focal length and distance to subject. In terms of shallow dof effect you should also try to maximise the distance between your subject and any background.

So, before shelling out on any kit, try using your kit lens at 55mm. Open the aperture right up, get close to your subject and get your subject away from anything behind it.

If you still want a shallower dof then you either want a lens with a wider aperture or possibly a telephoto.
 
To get really shallow you do really need the 50 1.7 you suggest. While the 55 at 5.6 should give you the best you can get with your lens it is never going to get you what a 1.7 will.
 
Having my kit lens at 55mm will surely only give me an aperture of 5.6 though right? I was of the understanding that I should have my lens at 18mm and at 3.5f to get a better DoF? I think I understand how I can make this work though, it was always a plan to get a 50mm asap and then a zoom lens :)
 
Dominic, this is taken from Digital Photo magazine on 'How To Blur Backgrounds With A Wide Aperture'.

Start by switching your camera to aperture priority (A or AV), then zoom your lens to around 55mm. Dial the aperture down to its lowest f/number - on a kit lens this is usually f/5.6 at 55mm.

This will open up the lens to the widest it can go and give really blurred background. Finally, set your ISO to the lowest it can go (either 100 or 200).

The guy took a portrait shot of a girl in a poppy field and the poppies were really blurred.

Hope this helps.
 
Dom7 said:
Having my kit lens at 55mm will surely only give me an aperture of 5.6 though right? I was of the understanding that I should have my lens at 18mm and at 3.5f to get a better DoF? I think I understand how I can make this work though, it was always a plan to get a 50mm asap and then a zoom lens :)
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Have a look at this DoF calculator and input some figures, following the advice above http://www.dofmaster.com/dofjs.html You also have to input the camera, as the sensor size changes things (you get less DoF with larger sensors).

The other thing that gives the impression of shallower DoF is longer focal length. While the DoF doesn't actually change (if the size of the main subject stays the same in the frame) the field of view narrows, cutting out a lot more background and making it look less cluttered. This gives the impression of less DoF.

If it's portraits, a cheap short cut to the kind of images you're probably after is a 50mm f/1.8 lens.
 
Dom7 said:
Having my kit lens at 55mm will surely only give me an aperture of 5.6 though right? I was of the understanding that I should have my lens at 18mm and at 3.5f to get a better DoF? I think I understand how I can make this work though, it was always a plan to get a 50mm asap and then a zoom lens :)
Click to expand...

Focal length makes a difference to DoF so while you would assume that 3.5 is always better than 5.6 it is not the case. You will discover this when you get a zoom lens as at 250 and 5.6 DoF is low even when the subject is a good distance away.
A lot of people have a 50 1.n as they are usually good value due to popularity/amount made and you may find, like me, that it is the only lens you end up using.
 
or maybe even buy a 35mm f1.8 or 50mm f1.4 for some tasty, lack of dof

Les :thumbs:

I have the 35mm f1.8 and its a cracking lens, even wide open at f1.8 and I too shoot with a Sony a65
 
OP.

To get the shallowest DoF you'll probably need to use the longest zoom end of your lens at the widest aperture and the shortest possible camera to subject distance. It'll probably also help, as stated above, to try and get your subject forward of the background.
 
ernesto said:
Focal length makes a difference to DoF so while you would assume that 3.5 is always better than 5.6 it is not the case. You will discover this when you get a zoom lens as at 250 and 5.6 DoF is low even when the subject is a good distance away.
A lot of people have a 50 1.n as they are usually good value due to popularity/amount made and you may find, like me, that it is the only lens you end up using.
Click to expand...

No, technically is does not - see post #6.

You get a stronger impression of greater stand-out of the subject from the background with longer focal length, but it's a field of view effect, not a DoF effect.
 
Many suggestions here and I appreciate that. Im ideally looking to add a 50mm, 35mm and a zoom lens to the collection. Still considering a 35-105mm Minolta also.
 
HoppyUK said:
No, technically is does not - see post #6.

You get a stronger impression of greater stand-out of the subject from the background with longer focal length, but it's a field of view effect, not a DoF effect.
Click to expand...

Yes, technically it doesn't but just trying to state that 18 3.5 will not be better than 55 5.6 just because 3.5 is lower when using in likely situations.
 
Hmmm. People do over complicate the DoF thing and make what should be a simple explanation ever more complex.

The best thing to do is to take a few shots at different zoom lengths, apertures and camera to subject distances and then view them on the computer. Ten minutes testing and viewing the results will almost certanly be worth more than 10 hours reading explanations and DoF tables on the net.
 
Agree, but Dominic will only find out that a 50 1.7 would give him more of what he wanted (and as he already had a 50 1.7 in mind he already knows that :) )
 
Thanks everyone, it clears things up slightly. Had a few practice shots last night trying to achieve this and can see the images improving already so thank you.

Yes ernesto, the 50mm prime was always at the top of my list! :)
 
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