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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 22 Jun 2007 (Friday) 02:42
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How do you focus one object, and leave everything else blurry?

 
CanonAmerican
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Jun 22, 2007 02:42 |  #1

http://www.usa.canon.c​om …/PS_G7/sample_i​mage_2.JPG (external link)

I mean, does it have to do with aperture? Because even if I use aperture(and open the lens) using low aperture, I still get everything in a very high resolution. It's not like I photograph something and everthing else is blurry.
How did they manage to marvelously capture that purple flower, and at the same time leave its background blurry?




  
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Box ­ Brownie
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Jun 22, 2007 02:58 |  #2

Hi

Yes, it is effectively the choice of aperture that will dictate the DoF (depth of field).

But you do not say what camera you are using, so the aperture to get such an effect will need to be wide open i.e. f2.8 not f16(or wider end if for example when using a tele zoom and being fairly close to the subject ~ the choice of lens and subject distance have a bearing that I am finding hard to describe). Now what I am describing is the typical scenario when using a dSLR but if you are using a P&S you have the other 'issue' with DoF, that is the relationship of the sensor size. With a P&S the sensor size is tiny comapred to a dSLR and because of the limitations (I think you need to look up 'circles of confusion' for scientific argument about this one) even with a wide open aperture you get little DoF effect that you are trying to achieve. However, if it has a Macro setting and you can get in really close tothe subject then you see an improved effect but do not expect the P&S to give the sort of result you see from a dSLR

HTH :)


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PaulDB
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Jun 22, 2007 02:59 |  #3

It is indeed to do with the aperture. The lower the F stop number the shallower the depth of field and the more blurry the background gets.

Try setting your camera to AV mode then set the F stop as low as it will go. Set the camera to center focus point and run some test shots. Also note, the further the item in focus is away from the background the better 'blur' you will get.

EDIT - Damn you beat me to it!


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CanonAmerican
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Jun 22, 2007 03:16 as a reply to  @ PaulDB's post |  #4

I'm using A540 PS.
Thank you so much for your tips, I'm going to try it and upload the results.
How does the camera know which is the object that I want to photograph, and which exactly is the background? I did notice that I have a green square when I use aperture, but how do I change its location?
Moreover, why does the F increase itself everytime I zoom in? If I want to take a 2.5F + Macro picture? I just can't ! Everytime I zoom in the F increases itself, and when I zoom out it decreases to a low number. How will I be able to take pictures like the one they took in the aformentioned 1st post if I can't use macro and zoom in without the F going up everytime I do it.




  
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Box ­ Brownie
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Jun 22, 2007 03:40 |  #5

CanonAmerican wrote in post #3419632 (external link)
I'm using A540 PS.
Thank you so much for your tips, I'm going to try it and upload the results.
How does the camera know which is the object that I want to photograph, and which exactly is the background? I did notice that I have a green square when I use aperture, but how do I change its location?
Moreover, why does the F increase itself everytime I zoom in? If I want to take a 2.5F + Macro picture? I just can't ! Everytime I zoom in the F increases itself, and when I zoom out it decreases to a low number. How will I be able to take pictures like the one they took in the aformentioned 1st post if I can't use macro and zoom in without the F going up everytime I do it.

I have looked at the spec for the A540 I hope the following gives you some more help.

1) The Max aperture is f2.6 at the wide end of the zoom and f5.5 at the tele end hence the changes you are reporting.

2) It has a multi point AF and a 'fixed' centre/single point - I presume this is selectable in the settings.

3) Minimum focusing distance is 5cm (2 inches) but it does not say it has a specific Macro mode.

I suggest you set it for the single centre AF point, use AV mode and choose the maximum aperture BUT try both wide angle and tele and get really close to the main subject and fill the frame with that main subject and if the other surrounding background 'subjects' are far enough away you should get a nice result.

I hope that makes sense and have fun trying the various settings etc. Oh and do post some images soon for any added feedback you wish to ask about.

:)

PS I hope you have the manual because when starting out it is your friend because "we" cannot know about the setup of a camera unless "we" have it, so only you can check and change the settings according to the manual.


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CanonAmerican
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Jun 22, 2007 04:22 as a reply to  @ Box Brownie's post |  #6

What's a wide angel and tele ?How do I choose it?




  
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Box ­ Brownie
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Jun 22, 2007 05:13 |  #7

CanonAmerican wrote in post #3419742 (external link)
What's a wide angel and tele ?How do I choose it?

You have already used the zoom and that is what I am refering to. When you use the zoom you will see that at one 'end' the view has more in it so to speak - this is wide angle, at the other end of the zoom where you have isolated a specific part of the scene by zooming in - that is the tele end of the zoom.

HTH :)

PS Have you got the manual for the camera?


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Vitruvius
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Jun 22, 2007 08:32 |  #8

very often you zoom buttons will be labeled W and T which is what they refer to.

Some thing you can also do to isolate the flower and blur the background is when you compose your shot. The further away the background is from your subject the better that background blur will be.

The way the camera "knows" what you subject is and what your background is, is by distance focusing, thats why you usually have that green box in the center or several points around the screen, it will use those to find the range and auto focus on them.




  
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CanonAmerican
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Jun 22, 2007 13:04 as a reply to  @ Vitruvius's post |  #9

I don't understand a few things, it seems like you guys are contradicting yourself.
1) 'Use maximum aperture' - if I boost my aperture to maximum value, wouldn't it give me the contradicted result I want? I thought that the lower the aperture is, the blurrier the background will get.
2) 'Zoom in and isolate the center(the object you want to take): If I indeed zoom in, wouldn't it be hard for me to get any background at all? Wouldn't the object fill the lens, hence I won't have a chance to even capture any blurry background?


I'm sorry for my questions, but you guys are professionals, and I look up to you, but it's all so new to me. BTW - I do have the manual :)




  
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In2Photos
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Jun 22, 2007 13:17 |  #10

CanonAmerican wrote in post #3421747 (external link)
I don't understand a few things, it seems like you guys are contradicting yourself.
1) 'Use maximum aperture' - if I boost my aperture to maximum value, wouldn't it give me the contradicted result I want? I thought that the lower the aperture is, the blurrier the background will get.
2) 'Zoom in and isolate the center(the object you want to take): If I indeed zoom in, wouldn't it be hard for me to get any background at all? Wouldn't the object fill the lens, hence I won't have a chance to even capture any blurry background?

I'm sorry for my questions, but you guys are professionals, and I look up to you, but it's all so new to me. BTW - I do have the manual :)

1. Aperture is a ratio. So when it was mentioned earlier that your max aperture was f2.6 it should have been written f/2.6. So a smaller f number is actually larger (f/2.6 is larger than f/5.5).

2. DOF is more than just aperture. Focal length, distance to subject and distance from subject to background also affect DOF.

One thing not mentioned here is that P&S cameras use a small sensor and a smaller lens. The result is smaller lens opening which will also yield a greater DOF. IT may be very difficult to blur the background wiht your camera.


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miralee
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Jun 22, 2007 13:27 |  #11

No expert for sure, but it's my understanding that maximum aperture = smaller f#. The smaller the f# is, the more "open" the lens is.

Even if you zoom in, you should still have some background left - just zoom in enough to where the object is nicely framed. I think this is where it's more effective if there is some distance between the object you're trying to focus on and the background, too.

If you play around with it you'll get some shots to show you how it works. I got these just playing with my camera, not knowing what was doing - both are zoomed quite a bit. (the xt, no the p&s, I haven't tried it with my p&s - I should sometime)
http://www.flickr.com/​photos/9209004@N04/591​279719/ (external link)
http://www.flickr.com …591279365/in/ph​otostream/ (external link)

ln2Photos beat me to it, and knows more than I do anyway :)


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CanonAmerican
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Jun 22, 2007 13:42 as a reply to  @ miralee's post |  #12

Awesome explanation dude, and thanks for your images SoCal, they look great.
I'll upload the images tomorrow, I already have a vision...




  
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Box ­ Brownie
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Jun 22, 2007 13:50 |  #13

Just for the record the image you linked to in your OP was taken with the G7 at f4.0

Now when you look at the image it seems to have been framed such that the camera was quite close to the main flower ~ possibly no more than a couple of feet away but the flowers furher back were likely anoth couple of feet at leats and the building 100's of yards away. IMO we have all covered the various aspects to be aware of and as Mike says and I mentioned a P&S because of its small sensor size will challenge you to get just the look you trying to acheive but as shown in the link you found it is possible wit careful choice of subject matter.

Best of luck and I look forward to seeing the results of your vision :)


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klynam
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Jun 22, 2007 14:15 as a reply to  @ Box Brownie's post |  #14

This doesn't exactly answer the question...but I've always referred to this as "selective focus" and I believe the term generally used to describe the aesthitic quality of the end result as "bokeh". (Can someone back me up or set me straight on this ???)


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Jun 22, 2007 14:17 |  #15

klynam wrote in post #3422074 (external link)
This doesn't exactly answer the question...but I've always referred to this as "selective focus" and I believe the term generally used to describe the aesthitic quality of the end result as "bokeh". (Can someone back me up or set me straight on this ???)

Selective focus is correct. And Bokeh refers to the quality of the Out-of-Focus highlights in the image.


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How do you focus one object, and leave everything else blurry?
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