How to get maximum depth of field for a given framing

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Originally Posted by joan

You mean the highest possible crop factor ? A crop factor greater than 1 results on a reduction of the field of view of the camera equivalent to what would happen if there was an increase of the focal length of the lenses, but we have seen that this does not significantly affect the DOF (at constant framing and f) ....

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I wish the term "crop factor" had never been coined.

If we instead look at any size of sensor or film, just as the size it is, it is a bit easier to understand how it relates to depth of field. The simplest way to look at it would be if you think of yourself as also being smaller or larger than average, so that the world around you is either a lilliputworld or a giant world. For a small person with a small camera, everything is far away, and far away means the DOF is large. For a giant person with a giant camera, everything is close, so DOF is shallow as anything is taken very close-up.

And then we should not look at focal length in the same way if we make a comparison. Maybe the simplest case is comparing a full frame camera with a µ4/3 camera. The full frame camera uses a 50 mm lens and the µ4/3 camera uses a 25 mm lens. They take the same subject from the same distance, and the 50 mm lens at f/2 has an entrance pupil of 25 mm while the 25 mm lens of the µ4/3 camera has an entrance pupil of 12.5 mm at the same f-stop. The image they take has the same angle of view, but seen from the position of the subject, the spatial angle to the µ4/3 lens is smaller, which implies larger depth of field. So the camera with the smaller sensor at f/2 with this normal lens has the same DOF as the larger one at f/4.

Hi Joan,

Quote:

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Originally Posted by joan

You mean the highest possible crop factor ? A crop factor greater than 1 results on a reduction of the field of view of the camera equivalent to what would happen if there was an increase of the focal length of the lenses, but we have seen that this does not significantly affect the DOF (at constant framing and f) ....

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Acknowledging also Urban's reply, which I think agrees with mine :)

The easy way to think of this is that crop factor not only applies to focal length (for equivalent field of view), it also applies to aperture (for equivalent Depth of Field).

Thus a typical P&S or bridge camera, with a crop factor of 5.5, at an aperture of f/2 has approx. the same DoF as a FF camera at f/11. At f/8, it will equate to f/45-ish. Since a DSLR lens may only stop down to f/16 or f/22, that's a significant gain of DoF and justifies Bill's advice.

For this reason, I use my bridge or P&S cameras for medium close up work.
However, they don't do true macro, so to achieve that (1:1) would entail significantly cropping their images, which would probably highlight other lens and sensor issues.
At this point, the sensible option is break out the DSLR and Macro lens and shoot a heap of images focussed at different distances and focus stack them to achievethe required DoF.

Welcome to the CiC forums from ...

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Originally Posted by joan

You mean the highest possible crop factor?

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You might wish to term it that way and speak of ‘crop factor’ – and that is fine. I am NOT criticising your words.

But understand that the term 'crop factor' is a recently introduced phrase into the photographic jargon and does NOT have any technical nor traditional meaning.

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There are MANY different camera formats (Film and Sensor Sizes) – and always there have been.

‘Crop Factor’ is just a trendy term which has been developed to describe DIGITAL cameras with a SMALLER SENSOR SIZE than 36mm x 24mm.

36mm x 24mm is just ONE camera/film Format – it is known correctly as ‘Standard 135 Format’ and is part of the Group known as: ‘Miniature Format’.

There is also ‘Medium Format’ and that group includes, but is not limited to: 6cm x 4.5cm; 6cm x 6cm; 6cm x 7cm and 6cm x 9cm.

Also there is ‘Large Format’, which includes, but is not limited to: 5” x 7” and 8” x 10”.

There is also ‘Sub Miniature Format’ and that group includes, but is not limited to: APS-C; and various Point and Shoot Cameras

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However, getting back to your question -

I mean exactly the words I wrote:

'If you wish to attain a Maximum DoF for any given FRAMING of any particular Subject, then you should use the SMALLEST Format Camera which is available.'

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Allow me to explain it in another way; in a practical example.

If we frame up EXACTLY the SAME shot in Portrait Orientation of an Half Portrait Shot of a Subject:

We use an EOS 5D and use F/2.8 - we will have a DoF of approximately 4 inches

We use a 60D and use F/2.8 – we will have a DoF of about 11 inches

We use a Canon Powershot SX40HS and use F/2.8 – we will have a DoF of about 36 inches

We use a 5” x 4” camera and use F/2.8 – we will have a DoF of close to only, 1 inch.


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Quote:

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Originally Posted by joan

A crop factor greater than 1 results on a reduction of the field of view of the camera equivalent to what would happen if there was an increase of the focal length of the lenses, but we have seen that this does not significantly affect the DOF (at constant framing and f) ....

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You are confusing three issues.

A ‘crop factor’ is like taking a ‘crop’ out of the centre of the picture. Sure it is ‘like’ using a lens of a different focal length on another camera – but it is NOT the SAME as using a different Focal Length Lens on another camera and then framing the shot the same.

The Field of View of the LENS - the IMAGE CIRCLE the LENS throws - remains the same for that lens IRRESPECTIVE of to what camera the lens is attached.



Also, for the purposes of answering your question – please again note the initial post I made correcting what are exactly the FOUR (not three) aspects of Depth of Field, especially the underlined:

More correctly Depth of Field depends on:
Focal length of the Lens used
Aperture of the Lens used
Subject Distance (Distance to the Plane of Sharp Focus)
Camera / Film Format used



So taking this last factor of DoF into consideration - what I am saying is, simply - if you want the MAXIMUM DoF for any particular Framing of any particular Subject - for example the Half Portrait of the person in the example I gave - then you should use a camera with SMALLEST FORMAT.

This is why it is so difficult to get Shallow DoF with P&S cameras.

And it is also why many Wedding and Portrait Photographers will exclusively choose 135 format (aka "full frame") digital cameras to leverage the very shallow Depth of Field which is NOT possible to get with APS-C format digital cameras.

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If you wish to research these facts further then the technical term is “Concept of Equivalence in Photography” –

And you should then research the "Factors of Equivalence for DoF between different Camera Formats".

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The mathematical predicate for these facts is based in understanding two factors:

• the Circle of Confusion, which changes for each camera format;
• the Resolving Power of the average human eye

These two factors are the first principles upon which the concept of the Depth of Field was derived.


WW

Aside - rant - whinge -

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Originally Posted by inkanyezi

i wish the term "crop factor" had never been coined.

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+1

It makes more confusion, than the incorrect usage of the word "Perspective"

And whilst we are at it, let's put a ban the term "Full Frame Camera" . . . what's my Linhof . . . 'a multi-frame camera' . . . but how much more 'multiframe' than my 645's?

The end of rant.

WW

Thanks to all for your answers. I am afraid that I must go though the different posts and gather more details on many issues that have been mentioned and that I did not know. In other words, there are plenty of things that I must learn. I have found also many tutorials in the site that look very interesting and well explained. Fortunately, we are on Xmas holidays and I'm going to have the time.

Once again, thanks. This is a great site.

Hola,

Here's how I did it for watch photography . . .

http://forum.tz-uk.com/showthread.ph...Depth-of-Field

I too hate the term "crop factor" - a classic in-crowd jargon serving no particular purpose other to keep those pesky outsiders where they "belong".