Wide Aperture - Need a little help with focus

cleanpig · Jan 21, 2013

Hello!

I've recently bought a nikon 50mm 1.8 prime lens for my Nikon D3200 and I'm very satisfied with it. However I have a slight problem with it which I can't correct no matter what I tried.
I'm still inexperienced with this lens so I don't quite understand a lot of things yet. (I had 18-105 zoom lens before)

I tried to shoot a figure, first from 1 meter via a tripod with ISO 100/400 and F2.0 <-> F4.0 (with matching shutter speed to get correct exposure). I took a few photos and I realized the following:

The lens blurs the FOREGROUND too!! The knife in the pictures is blurred even though I wanted it to be also in focus! I've attached a few test pictures and you can see that around F2.0 <-> F4.0 the knife the figure is holding is totally out of focus!!
I knew of this effect, but what surprised me is that it wouldn't disappear even after:

-increasing aperture (the knife was clear after F11)
-moving away/moving closer
-Changing focus priorities(I even done manual focus)
-Changing area tracking (from single points, to 3D, then Auto, then Dynamic)
-Changing lights

I've tried everything I could, but I couldn't make the knife clear in wider apertures, where the background is nicely blurred! I tried shooting my girlfriend after this with the same "concept". Her hand was held out, the other one was behind her and the same thing occurred I shot from around 1,5 meter and her hand was blurred, her body was in perfect focus and the other hand, which was behind her, was a little blurred.

So what can I do to make the WHOLE figure in focus and the background blurred? I should have separated the background even further? Or did I messed up some of the settings? Can you guys help me a little to understand this? This is very important for me, because I want to learn model/cosplay photography and I have to learn how to make the whole model in proper focus.

The pictures has not been edited in any way, its pure RAW converted into JPG (so I can upload them). If you need further information please ask and I'll submit them.

Thank you very much for all the help and answers!!
-cleanpig

weepete · Jan 21, 2013

Have a look at a depth of field calculator, that'll give you an idea of where you need to position things too keep them in focus

cleanpig · Jan 21, 2013

I've checked a DOF calculator on the net. I've made the following settings:

Type: Nikon D3000 (no 3200, so I choose this)
Focal length: 50mm (is this should be 50mm? Since I got a DX camera. It should be 75mm instead?)
F-stop: F/2.0
Distance: 200 cm

So based on this the answer is:

Depth of field
Near limit	193.9 cm
Far limit	206.4 cm
Total	12.5 cm

So this means the picture will be in focus in 12,5 cm?? Oo I don't quite understand this. So if my model helds out her arms the F-stop should be around 8-11 to get proper focus?
How can I make the background all nice and "blurred"? (More separation I think..)

This is a lot harder than I thought...

Anyways, thanks for the answer! I'll keep on learning this...

weepete · Jan 21, 2013

Hmm,

Here's what I got for a D3200 at f2.0

Subject*distance* 1*m
*
Depth*of*field*
Near*limit* 0.99*m
Far*limit* 1.02*m
Total* 0.03*m
*
In*front*of*subject* 0.01*m (49%)
Behind*subject* 0.02*m (51%)
*
Hyperfocal*distance* 62.6*m
Circle*of*confusion* 0.02 mmt

Or in short at f2.0 your dof is very thin at 30mm when you are 1m away from your subject. Anything 20mm behind your focal point will be in focus and 10mm in front, which is why the knife is blurred.

What size is your model? (From knife tip to her head)

weepete · Jan 21, 2013

At f11:

Subject*distance* 1*m
*
Depth*of*field*
Near*limit* 0.92*m
Far*limit* 1.09*m
Total* 0.17*m

In*front*of*subject* 0.08*m (46%)
Behind*subject* 0.09*m (54%)
*
Hyperfocal*distance* 11.1*m
Circle*of*confusion* 0.02 mm

This will give you a dof of 170mm, with anything 80mm in front and 90mm behind your focal point in focus. If you want more blur in the background place the subject further away from it. Any dof calculator where you input your camera make should take the crop factor into accoount so just use your actual focal distance on the lens

SCraig · Jan 21, 2013

Depth of Field is just that, a DEPTH. It has a near limit and a far limit, where the near limit is the point where things come into acceptable focus and the far limit the point where things go back out of focus. That depth will vary based on aperture, distance to subject, focal length, and sensor size.

cleanpig · Jan 21, 2013

The figure is roughly 23 cm in height! Thanks for all the help guys! I'll download a DOF calculator to my phone or print it and start to memorize the numbers. :3

SCraig · Jan 21, 2013

cleanpig said:
The figure is roughly 23 cm in height! Thanks for all the help guys! I'll download a DOF calculator to my phone or print it and start to memorize the numbers. :3

Height doesn't have anything to do with it unless it's laying down flat, it's the horizontal distance between the camera and subject. Take a shot of a yardstick or ruler and it will become perfectly clear. Raise the back end so you can see it clearly and aim right in the middle.

Memorizing DOF numbers won't help either since it changes. Aperture, distance to subject, focal length, and sensor size combined determine the DOF for each shot, and it will always be different. What you have to do is start to learn how it works and how to use it or deal with it.

cleanpig · Jan 21, 2013

So I just have to "get used to it" via practicing. Hm, okay, I shall work on it... Thanks for all the help guys! :3

SCraig · Jan 21, 2013

cleanpig said:
So I just have to "get used to it" via practicing. Hm, okay, I shall work on it... Thanks for all the help guys! :3

Same thing all the rest of us have had to do

Once you've dealt with it a while it's not hard to make a knowledgeable guess as to how much aperture you need. Plus, with a digital camera you have the advantage of being able to look at the LCD on the back and see if what is important is in focus.

cgipson1 · Jan 21, 2013

use this Online Depth of Field Calculator

cleanpig · Jan 21, 2013

Yes, that's what I found too.

Thanks anyways. ^^

cgipson1 · Jan 21, 2013

Keep in mind that DOF has sharp focus both before and after your actual focus point (usually 50%/50%.. but depending on other factors, it can even be like 30%/70%). So if you focus on the face of your figurine... than you are wasting the DOF that is behind that point. If you focus on the knife, you are wasting the DOF before that point. If you focus between the knife and the face (with adequate DOF calculated), then you can use a larger aperture (smaller DOF) because you are using all of the DOF, not just part of it.

Make sense?

cleanpig · Jan 21, 2013

Focus on the face? Hm... I knew of the manual settings in the LCD when I press the arrow is to move that little box where I want. That is what you are talking about?

cgipson1 · Jan 21, 2013

cleanpig said:
Focus on the face? Hm... I knew of the manual settings in the LCD when I press the arrow is to move that little box where I want. That is what you are talking about?

What were you focusing on? I would use manual focus... and put the focus where I wanted it visually! Forget Autofocus.. and the little moving box... if you want precision focusing for something like this, do it manually! That is why we use manual focus in Macro Photography.. it is much more precise.