Blurr Background

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Originally Posted by William W

No. It wouldn't. (well it would have an effect and that would be to make the DoF MORE, not less.)WW

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I am not going to spend time checking out the facts of the situation but I suspect at 720, and even at the smaller aperture, the focal length is longer than what you were using ... so swings and roundabouts .. it would even out :) Prove me wrong if you like :)
[ I listed the focal lengths in another message here ]

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Originally Posted by jcuknz

Your photo does make me want to question WW's divergent opinion on my earlier comment but perhaps we are talking of different things ...

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Maybe.

I have been commenting mainly on DoF and making that DoF the smallest practicable and in that discussion the OP MUST choose a short FL so that the lens can achieve the LARGEST maximum aperture.

Given that if the FRAMING of the SUBJECT remains the same the DoF will remain the same, then increasing the FL will only mean that there will be a DECREASE in the largest aperture available, thus an INCREASE in the DoF.


However - in post #6 I mention that choosing a LONGER Focal Length will affect the quality of the background blur (i.e. the Bokeh) - you might be discussing this.


WW

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Originally Posted by jcuknz

I am not going to spend time checking out the facts of the situation but I suspect at 720, and even at the smaller aperture, the focal length is longer than what you were using ... so swings and roundabouts .. it would even out :) Prove me wrong if you like :)[ I listed the focal lengths in another message here ]

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JC - regarding the DoF there is no "evening out".

If the FRAMING is kept constant and the APERTURE is stopped down, no matter what the Focal Length the DoF will be the same for all practical purposes for most imaging - that's the whole point . . .

There is no need to prove you wrong - it is what it is: and this axiom is well published and is also implicit in the Formulae for DoF.

WW

I cannot fault your argument becuase I have made it numerous times but I suspect there is a difference due to the different gear being used and the degree of magnification, the often ignored factor in DoF and that was what I was refering to with evening out ... just a suspicion without either gear types to gain sufficient data for entering into DoF calculator.

I think the 'same framing' rule may only apply with one type of camera rather than across types ... hence my suspicions.

Another idea to add to the discussion does digital zoom improve or maintain DoF at the end of the optical zoom while achieving a tighter framing. I am thinking that digital zoom, often a big NO-NO in the past, is less so as cameras have more pixels. It does depend on what the photo is going to be used for.

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Originally Posted by jcuknz

I cannot fault your argument becuase I have made it numerous times . . .I think the 'same framing' rule may only apply with one type of camera rather than across types ... hence my suspicions

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Yes, the axiom that keeps DoF the same applies provide the Camera Format (Sensor size / Negative Size) remains the same: if that is what you mean by "one type of camera"

I mentioned that in post #6, here:

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Provided the FRAMING is kept constant for all practical purposes, for most photography, the DoF will remain the same for any given aperture and camera format (this is the Axiom of DoF).

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But the OP is not changing camera formats: the OP is using one camera, so there is no need for suspicion in this case.

WW

LOL The OP may not be changing cameras but I was conparing photos that you took I asssume with a DSLR and those the OP may take with his bridge camera .... so my suspicions remain although I have yet to get around to doing anything to check them out.

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Originally Posted by jcuknz

I think the 'same framing' rule may only apply with one type of camera rather than across types ...

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Same framing rule does cross types which is where the equivalence makes sense. A 35mm f/1.8 lens on APSc being comparable to 50mm f/2.8 lens on full frame, in terms of field of view and depth of field.

Conversely, the FoV and DoF from 35mm f/2 lens on FF camera can be achieved with 24mm f/1.4 on APSc.

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Originally Posted by jcuknz

LOL The OP may not be changing cameras but I was conparing photos that you took I asssume with a DSLR and those the OP may take with his bridge camera .... so my suspicions remain although I have yet to get around to doing anything to check them out.

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To provide useful pictorial examples to the OP of what can be done, and how it can done, with a 'bridge camera' almost exactly the same as what the OP has . . .

the sample photos were made with a Canon Powershot S5 IS, which has a maximum available aperture of F/3.5.

The OP is using a Canon Powershot SX500IS, which has a maximum aperture of F/3.4.

These two cameras are in the same class, though having a very minor sensor size difference: the S5IS is a 1/2.5” sensor and the SX500IS has a 1/2.3” sensor – hardly any difference.

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REFERENCE: Post #4:

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Here are some examples using a PowerShot S5 IS which has a Maximum Available Aperture of F/3.5:

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WW

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Originally Posted by RobertsMx

Same framing rule does cross types which is where the equivalence makes sense.

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I concur.
I purposely chose not to mention "Equivalence".

WW

I had thought that the difference in magnfication between APS-C and 1/2.3 sensors would have a greater effect on DoF than the CiC calculator tells me it has and would compensate for the smaller aperture being used at 720 ... but it doesn't.

BUT WAIT ! I go to another DoF calculator [ dofmaster ] and enter the same data and it tells me the opposite ... instead of 200% larger it is 50% smaller .....:)

So depending on which calculator you use I am correct and incorrect in my original statement.

But JC . . . no looking up any DoF calculator or comparing APS-C cameras - will change the fact of how the OP can get shallowest DoF for any given framing . . .

and that is for the OP to ONLY use F/3.4. on his camera.

WW

I am not familiar with the SX500, but f/3.4 is likely limited to wide angle FL and gradually goes down to f/5.8 at max FL (129mm) which may actually provide a reasonably shallow DoF.

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Originally Posted by RobertsMx

I am not familiar with the SX500, but f/3.4 is likely limited to wide angle FL and gradually goes down to f/5.8 at max FL (129mm) which may actually provide a reasonably shallow DoF.

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Depends what you term "reasonable".

For the FRAMING of Tight Head Shot (such as the first sample image I posted), when using a camera with 1/2.3" or a 1/2.5" sensor - the DIFFERENCE in the DoF F/3.4 and F/5.8 is around about double.

In measurement terms:
- at F/3.4 the DoF is about 25 cm or about 10 inches
- at F/5.8 the DoF is about 45 cm or about 18 inches


As you can see by the samples that I posted, and the EXIF I provided a similar PowerShot Camera's lens will hold the Maximum Aperture to at least a Focal Length of 72mm (EXIF reads the 135 format 'equivalent' Focal Length).

We can expect a similar performance from the OP's camera.

Having the Maximum Aperture available to "Equivalent" FL =72mm, allows for quite a reasonable range of Perspectives, at various shooting distances. . . not limited to only the wide angle.

However doubling the DoF probably has a more (deleterious) effect in most shooting situations, if the object of the exercise is to get the shallowest DoF.

Especially consider as soon as the FRAMING becomes even a little bit WIDER, for example like a Bust Shot - (e.g. the Man and the Little Boy) - the DIFFERENCE between the DoF at F/3.4 and at F/5.8 will be MUCH greater.

WW

Bill, yes, moving closer will have an effect on DoF. But so does changing FL even with a smaller aperture. Moving closer may not always be an option either, also considering similar framing. Here are three images I took with two different lenses at different aperture settings on APSc camera, while making an attempt to keep the subject framed identically. Actual focal length and aperture is followed by approximate FF equivalent FL and aperture in parenthesis for each:
Image #1: Sony NEX-3, 35mm, f/2 (50mm, f/3)
http://i678.photobucket.com/albums/v...psd441eafd.jpg
Image #2: Sony NEX-3, 70mm, f/4 (105mm, f/6)
http://backup.cambridgeincolour.com/...ps22992c5c.jpg
Image #3: Sony NEX-3, 70mm, f/2.8 (105mm, f/4)
http://i678.photobucket.com/albums/v...ps5241f8f0.jpg

#1 and #2 are fairly close, and #3 has a shallower DoF. An estimated effect can also be figured using the actual focal length and actual f-stop. For example, 35mm and f/2 indicate at 17.5mm iris (f/2 = 17.5). Likewise, 70mm, f/4 is also 17.5mm. And 70mm, f/2.8 us 25mm. Larger iris indicates shallower DoF. Conversely, had I used my 200mm lens at f/8 (again, an iris size of 25mm), I would expect similar DoF as #3 assuming I kept the framing the same.

Manu,
Of course changing the FL affects the DoF. That was previously mentioned by me.
Also it is possible to get a “reasonable” DoF with a longer Focal Length and using a smaller aperture.
We have already established we agree on these points.

Of course moving closer to get the framing required and to use the largest aperture might not be possible.

What I am saying (and have only been saying is) that if one wants the SHALLOWEST DoF, then (given the same framing) the largest aperture will produce the shallowest DoF irrespective of Focal Length. . . IF one increases the FL and reduces the aperture and keeps the same framing the DoF will INCREASE.

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RE your samples and firstly only comparing images #1 and #3 – and (this is important) IF the framing is INEDITCAL in each – then:

1 The DoF in #1 and #3 will be very close to the same. This is because the difference that 1 stop makes on the DoF using an an APS-C format is not very much, especially when working at close Shooting Distances.

2 But the DoF in Image #3 will be very slightly MORE than that the DoF in Image #1. This is so, because of Mathematics.



Secondly, and now we are discussing the visual reckoning between the two shots:

1 It will be very difficult to see the difference of the DoF between image #1 and image #3, even IF the framing s exactly the same in each of frames #1 and #3 because as mentioned above the difference will be very slight.

2 When we contrast images #1 and #3 we can note a flaw which will skew the visual reckoning: image #3 is taken from a significantly lower camera elevation than Image #1 which renders the tiled pattern differently in each image.


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Also (just an aside) there appears to be something strange when comparing images #2 and #3: IF these two shots were IDENTICAL except for the APERTURE, why is there such a significant difference in the width of the OoF white section: that surely cannot be explained simply by one stop of aperture change.

WW

Bill, these were approximately set up shots (handheld), which also involved changing shooting distance by moving farther with 70mm lens to keep the framing as close to others as possible.

We seem to be on similar page, however, my point is also considering focal length to go with the aperture. Larger opening will create shallower effect for the same composition. In case of the camera mentioned in OP, the max focal length is 129mm, and the max aperture at this point is f/5.8. That computes to an opening 22.2mm wide (129mm/5.8). For that to be available at f/3.4, the (actual, not equivalent) focal length would have to be about 75mm.

Here is an example of a very shallow DoF, taken with Sony NEX-3. The lens is at 210mm, f/7.1 and complete with 1.7x teleconversion lens (Sony DH1758), taken at night at a parking lot. In terms of FF equivalence, this is 545mm, f/11, plus additional cropping:
http://backup.cambridgeincolour.com/...0eb8cfac_b.jpg

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Originally Posted by RobertsMx

Bill, these were approximately set up shots (handheld), which also involved changing shooting distance by moving farther with 70mm lens to keep the framing as close to others as possible.

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Yes I understood that they were approximate visual examples.

I also understood that dialogue which accompanied the examples stated that Image #3 had a shallower DoF than Image #1 . . .

And that's specifically why I pointed out that the visual examples were flawed. As Image #3 MUST have a LARGER DoF than Image #1 - IF the framings were identical.

I also understood that these example photographs were made specifically to address the commentary which I had made about how to attain the shallowest DoF and to do that - how the Focal Length was irrelevant.

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Originally Posted by RobertsMx

. . . my point is also considering focal length to go with the aperture. Larger opening will create shallower effect for the same composition. In case of the camera mentioned in OP, the max focal length is 129mm, and the max aperture at this point is f/5.8. That computes to an opening 22.2mm wide (129mm/5.8). For that to be available at f/3.4, the (actual, not equivalent) focal length would have to be about 75mm.

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Yes I understand Aperture.

I understand that you can make "reasonable" shallow DoF using the longer end of the camera's lens - we have agreed on that.

But I cannot see what that has that to do with the conversation about getting the shallowest DoF possible: which appears was the sole intent of the demonstration in post #34.

Yes, again I mention I agree that you can get nice shallow DoF shots using the telephoto end of the camera and a smaller aperture.

And moreover, as an additional comment to that: it will be easier to do this when photographing smaller objects like the shell or the frog as opposed to a Portrait.

Also, I note that, it will be easy to show examples of very shallow DoF using and APS-C Format camera rather than using a 1/2.3inch camera . . .


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However, as previously mentioned, my commentary really only revolves around answering the OP's question in the simplest manner possible - and he asked can he get a blurred background using his Powershot 500x - and the answer is yes he can but it will be in limited circumstances.

And the answer is (using Portraiture as an example), he will achieve the aim of having the SHALLOWEST DoF in the easiest manner if he uses only the Focal Lengths which allow the Maximum Aperture to be used and if he Frames the Shot, very tightly.

Sure he might get a "reasonable" shallow DoF using the longer end of the lens at the minimum aperture, but for any same sized Subject and the same framing, for normal photography (not close up or macro), using the larger aperture will result in a shallower DoF - and this is very noticeable (much more noticeable) as the camera format gets smaller and/or as the Subject gets bigger.


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Just moving away from examples of very small objects like shells and frogs photographed with APS-C Cameras:

If we took the OP's camera and IF we framed a Person using Focal Length 129mm, (lets say like the framing in my first example) and made a picture at F/5.8 - the DoF would be about 18 inches.

And then we zoomed the camera to a Focal Length where we could use F/3.4 and made exactly the same framing, the second shot will have SUBSTANTIALLY Shallower DoF: the DoF in the second shot will be about 10 inches.

WW

I will briefly re-afirm my position on this subject ... for all the carry-on about OOF backgounds obtained at greaty expense with DSLRs the fact remains it is largely wishful thimking or self delusion, plus a lot of nonsense about good and bad blurr ... and if you are using a bridge camera it is better to polish up on your editing skills.

Working with a 25mm AoV lens for close shots of people is simply ... polite words fail me .... the saving element of this is that working with an 80mm AoV will probably not have much appreciable different DoF than at 25 and the people will not be distorted travesties of the human form. I am trying to word this lightly....

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Originally Posted by William W

Just moving away from examples of very small objects like shells and frogs photographed with APS-C Cameras:

If we took the OP's camera and IF we framed a Person using Focal Length 129mm, (lets say like the framing in my first example) and made a picture at F/5.8 - the DoF would be about 18 inches.

And then we zoomed the camera to a Focal Length where we could use F/3.4 and made exactly the same framing, the second shot will have SUBSTANTIALLY Shallower DoF: the DoF in the second shot will be about 10 inches.
WW

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The argument about size of shell and frog is irrelevant. In the example (shell) illustrating different FL and aperture, the idea was to maintain the size of the shell as recorded at different focal lengths. In the other example (frog), I was simply demonstrating how shallow DoF can be even at f/7.1 when the FL is large (545mm equivalent), that the little frog is barely within it.

As for your example, it is based on the assumption that you have f/3.4 available at telephoto end, and you don't. You have f/5.8 at that focal length. So, if you have calculated 18 inch for Dof at certain distance with f/5.8 and 129mm, try maintaining the same image size at f/3.4 at the max Focal length you can get to with that aperture, and see what DoF you get.

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Originally Posted by RobertsMx

The argument about size of shell and frog is irrelevant. In the example (shell) illustrating different FL and aperture, the idea was to maintain the size of the shell as recorded at different focal lengths. In the other example (frog), I was simply demonstrating how shallow DoF can be even at f/7.1 when the FL is large (545mm equivalent), that the little frog is barely within it.

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A re-read of what was written appears necessary:

There is no ‘argument’ about shells and frogs, merely a statement that we are moving away from those examples to another example using the OP’s camera

However, it was previously pointed out that conclusion from the example using of the three shells is flawed.

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Originally Posted by RobertsMx

As for your example, it is based on the assumption that you have f/3.4 available at telephoto end, and you don't. You have f/5.8 at that focal length.

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No.

That assertion is incorrect. Definitively NOTHING like that was ever written nor even implied.

There is definitely a need for a re-read.

It is quite clear what was written and meant.

Below is the extracted section of what WAS written and attention is drawn the underlined and bolded section for reference:

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If we took the OP's camera and IF we framed a Person using Focal Length 129mm, (lets say like the framing in my first example) and made a picture at F/5.8 - the DoF would be about 18 inches.

And then we zoomed the camera to a Focal Length where we could use F/3.4 and made exactly the same framing, the second shot will have SUBSTANTIALLY Shallower DoF: the DoF in the second shot will be about 10 inches.

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Originally Posted by RobertsMx

So, if you have calculated 18 inch for Dof at certain distance with f/5.8 and 129mm, try maintaining the same image size at f/3.4 at the max Focal length you can get to with that aperture, and see what DoF you get.

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The DoF will be about 10 inches.

That was the point of the example - and the whole point of my original post.

Thanks for asking the question. :)


WW