Why recommend a superzoom for deep dof?

Started May 16, 2012 | Discussions
Joyless
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Why recommend a superzoom for deep dof?
May 16, 2012

In the following post:
http://forums.dpreview.com/forums/read.asp?forum=1032&message=41517480

bobn2 recommends using a superzoom instead of a dslr for "decent" dof, whatever that might be.

The thread reached the 150 post limit before I could ask there, so I try here instead.

Can anyone elaborate on this? Why would a superzoom be better? I've seen the argument made before, but never a reason, so I wonder.

My sarcasm detector isn't all that great so have I perhaps misunderstood this?

Jo

Draek
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Re: Why recommend a superzoom for deep dof?
In reply to Joyless, May 16, 2012

To put it simply: a smaller sensor gives you more DOF for a given field of view and aperture, and while it's true you can stop down the aperture further to match the DOF of the smaller camera then raise the ISO to compensate, if you know you'll be doing so most of the time you're better off going with the kit that's lighter and cheaper.
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citizenlouie
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Re: Why recommend a superzoom for deep dof?
In reply to Joyless, May 16, 2012

Joyless wrote:

In the following post:
http://forums.dpreview.com/forums/read.asp?forum=1032&message=41517480

bobn2 recommends using a superzoom instead of a dslr for "decent" dof, whatever that might be.

The thread reached the 150 post limit before I could ask there, so I try here instead.

Can anyone elaborate on this? Why would a superzoom be better? I've seen the argument made before, but never a reason, so I wonder.

My sarcasm detector isn't all that great so have I perhaps misunderstood this?

Jo

I think it's a sarcasm. But if you want to know the basis of that argument here it is:

Every time you double the focal length, you half the DoF. For example, 100mm @ f/2 has the DoF half of that of 50mm @ f/2, or if you put the other way around, 100mm @ f/2.8 has the same DoF of 50mm @ f/2.

That's why he suggested a superzoom, because a super zoom usually have something like 400mm or 500mm on the telephoto end, which gives a very shallow DoF, even with aperture like f/5.6 or f/6.3.

However, the problem of that is, 1) superzoom has very small sensors, you get more noisy photos, 2) not everything can be shot with 400mm or 500mm telephoto, because it'll just cover a very small portion of the scene you want, or you'd have to stand obscenely far away to shoot that scene.

Hope that helps.

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Ed Rizk
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Re: Why recommend a superzoom for deep dof?
In reply to Joyless, May 16, 2012

Simple. Smaller sensors, like smaller apertures, create deeper depth of field. The physics of it is explained all over the internet, but the common analogy is to squinting your eyes.
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GaryH1125
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Re: Why recommend a superzoom for deep dof?
In reply to citizenlouie, May 16, 2012

citizenlouie wrote:

Joyless wrote:

In the following post:
http://forums.dpreview.com/forums/read.asp?forum=1032&message=41517480

bobn2 recommends using a superzoom instead of a dslr for "decent" dof, whatever that might be.

The thread reached the 150 post limit before I could ask there, so I try here instead.

Can anyone elaborate on this? Why would a superzoom be better? I've seen the argument made before, but never a reason, so I wonder.

My sarcasm detector isn't all that great so have I perhaps misunderstood this?

Jo

I think it's a sarcasm. But if you want to know the basis of that argument here it is:

Every time you double the focal length, you half the DoF. For example, 100mm @ f/2 has the DoF half of that of 50mm @ f/2, or if you put the other way around, 100mm @ f/2.8 has the same DoF of 50mm @ f/2.

That's why he suggested a superzoom, because a super zoom usually have something like 400mm or 500mm on the telephoto end, which gives a very shallow DoF, even with aperture like f/5.6 or f/6.3.

However, the problem of that is, 1) superzoom has very small sensors, you get more noisy photos, 2) not everything can be shot with 400mm or 500mm telephoto, because it'll just cover a very small portion of the scene you want, or you'd have to stand obscenely far away to shoot that scene.

Hope that helps.

Your explanantion on DOF is great but you forgot something about superzooms. The 500mm focal length is the 35MM equivilent. The actual focal length would be around 90mm. The superzoom is going to give you a much deeper DOF for the same field of view of a FF camera becuase you will be using a much smaller focal length. In other words the superzoom will give you the same DOF at 500mm that the FF DSLR would give you at 90mm.

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citizenlouie
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Re: Why recommend a superzoom for deep dof?
In reply to GaryH1125, May 16, 2012

GaryH1125 wrote:

Your explanantion on DOF is great but you forgot something about superzooms. The 500mm focal length is the 35MM equivilent. The actual focal length would be around 90mm. The superzoom is going to give you a much deeper DOF for the same field of view of a FF camera becuase you will be using a much smaller focal length. In other words the superzoom will give you the same DOF at 500mm that the FF DSLR would give you at 90mm.

Yes. Depends on the sensor size of course.

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Joyless
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Re: Why recommend a superzoom for deep dof?
In reply to Draek, May 16, 2012

Draek wrote:

To put it simply: a smaller sensor gives you more DOF for a given field of view and aperture, and while it's true you can stop down the aperture further to match the DOF of the smaller camera then raise the ISO to compensate, if you know you'll be doing so most of the time you're better off going with the kit that's lighter and cheaper.
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Let's see if I've got this, f/8 on one system could give the same DOF as f/16 on another system, given that the f/8 system has a smaller sensor than the f/16 system. (By how much?) But f/8 lets in more light than f/16, so the f/16 system will have to do something to compensate (i. e, slow down shutter if motion blur isn't a factor.) But isn't it also true that a larger sensor collects more light than a smaller sensor? I did at least think that was one of the advantages of the full frame sensors compared to the smaller sensors of a crop camera or a compact.
Or am I confusing things here?

Jo

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dsjtecserv
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Re: Why recommend a superzoom for deep dof?
In reply to Ed Rizk, May 16, 2012

Ed Rizk wrote:

Simple. Smaller sensors, like smaller apertures, create deeper depth of field. The physics of it is explained all over the internet, but the common analogy is to squinting your eyes.
--

Smaller sensors only create more depth of field if a lens of a shorter focal length is used. Since it is necessary, with a smaller sensor camera, to use a shorter focal length to create the same field of view for the same shooting position, it is common to associate smaller sensors with greater depth of field. But this is not inherent in the sensor size; if the same focal length is used, the image on the smaller sensor itself is exactly the same as it would be on the larger sensor (but cropped). But because the image on a smaller sensor must be enlarged more to create a print or screen image of a given size, this actually results in slightly less depth of field with the smaller sensor (if the focal length is held constant).

In practice, smaller sensors are used with sorter focal lengths to make the same picture, and the effect of the focal length is much greater than that of the enlargement, with the net result that depth of field is greater.

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dsjtecserv
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Re: Why recommend a superzoom for deep dof?
In reply to citizenlouie, May 16, 2012

citizenlouie wrote:

GaryH1125 wrote:

Your explanantion on DOF is great but you forgot something about superzooms. The 500mm focal length is the 35MM equivilent. The actual focal length would be around 90mm. The superzoom is going to give you a much deeper DOF for the same field of view of a FF camera becuase you will be using a much smaller focal length. In other words the superzoom will give you the same DOF at 500mm that the FF DSLR would give you at 90mm.

Yes. Depends on the sensor size of course.

Not really. The greater depth of field is due to the effect of the shorter focal length, not the sensor size. The image from a smaller sensor, since it must be enlarged more to make a print of a given size, actually would result in slightly less depth of field (everything else, including focal length, being held constant).

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dsjtecserv
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Re: Why recommend a superzoom for deep dof?
In reply to Joyless, May 16, 2012

Joyless wrote:

Draek wrote:

To put it simply: a smaller sensor gives you more DOF for a given field of view and aperture, and while it's true you can stop down the aperture further to match the DOF of the smaller camera then raise the ISO to compensate, if you know you'll be doing so most of the time you're better off going with the kit that's lighter and cheaper.
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Let's see if I've got this, f/8 on one system could give the same DOF as f/16 on another system, given that the f/8 system has a smaller sensor than the f/16 system. (By how much?) But f/8 lets in more light than f/16, so the f/16 system will have to do something to compensate (i. e, slow down shutter if motion blur isn't a factor.) But isn't it also true that a larger sensor collects more light than a smaller sensor? I did at least think that was one of the advantages of the full frame sensors compared to the smaller sensors of a crop camera or a compact.
Or am I confusing things here?

Note that Draek said "for a given field of view and aperture". In order for a smaller sensor camera to produce the same field of view as a larger one, it will need to use a shorter focal length. The greater depth of field is provided by the shorter focal length, not by the size of the sensor.

Draek was also pointing out the you could achieve the same deeper depth of field with the larger sensor camera and its longer focal length, but you would need to stop down to a smaller aperture, and increase ISO to compensate for the loss of shutter speed.

I'd recommend not complicating this by getting into the amount of light collected by the larger sensor area, since that doesn't have anything to do with your question about depth of field.

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Draek
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Re: Why recommend a superzoom for deep dof?
In reply to Joyless, May 16, 2012

They can capture more light, but they might not necessarily do so; the theory is that, for the same framing and shutter speed, a given sensor at f/8 will capture roughly the same amount of light as one 2x as large at f/16, thus having roughly the same amount of noise and roughly equal DOF. Roughly, because to determine it properly you'd have to deal with an equation involving F-stops and T-stops of each lens, real ISO settings, quantum efficiency of each sensor, noise floor, circle of confusion, enlargement size, and probably a few other variables I'm forgetting right now.

Of course, it's all purely academic and for 99.99% of situations the rule of thumb "DOF increases as sensor size decreases" works quite well.
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GaryH1125
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Re: Why recommend a superzoom for deep dof?
In reply to Joyless, May 16, 2012

Joyless wrote:

Draek wrote:

To put it simply: a smaller sensor gives you more DOF for a given field of view and aperture, and while it's true you can stop down the aperture further to match the DOF of the smaller camera then raise the ISO to compensate, if you know you'll be doing so most of the time you're better off going with the kit that's lighter and cheaper.
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Let's see if I've got this, f/8 on one system could give the same DOF as f/16 on another system, given that the f/8 system has a smaller sensor than the f/16 system. (By how much?) But f/8 lets in more light than f/16, so the f/16 system will have to do something to compensate (i. e, slow down shutter if motion blur isn't a factor.) But isn't it also true that a larger sensor collects more light than a smaller sensor? I did at least think that was one of the advantages of the full frame sensors compared to the smaller sensors of a crop camera or a compact.
Or am I confusing things here?

Jo

There are three factors that effect DOF; Actual Focal Length, F-stop, and distance to subject. Strictly speaking none of these have anything to do with sensor size. A small sensor camera will give you the exact same DOF as a FF camera when the three factors are the same. Where you run into issues is that focal length on P&S cameras is usually given in 35MM equivilent and not actual focal length. The reason for doing this is people are more interested in the field of view a lens will give as opposed to the depth of field.

Lets just say that you have a large sensor camera that requires a lens with a with a focal length of 100mm to frame your subject. Because of the smaller sensor your P&S might require a focal length of 25mm to get that same shot. If you double your DOF field every time you half your focal length the small sensor camera will have four times the DOF as the FF camera because you have halved the focal length and then halved it again.

Small sensor cameras will give you larger DOF because you are using shorter focal lengths than you do on larger sized sensors to get the same field of view. Shorter focal lengths mean larger DOF field regardless of the sensor size.

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Joyless
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Re: Why recommend a superzoom for deep dof?
In reply to dsjtecserv, May 16, 2012

dsjtecserv wrote:

Note that Draek said "for a given field of view and aperture". In order for a smaller sensor camera to produce the same field of view as a larger one, it will need to use a shorter focal length. The greater depth of field is provided by the shorter focal length, not by the size of the sensor.

Ah, of course. Thank you. I think I should have known that, or been able to figure it out for myself, but I think I over-complicate matters.

Draek was also pointing out the you could achieve the same deeper depth of field with the larger sensor camera and its longer focal length, but you would need to stop down to a smaller aperture, and increase ISO to compensate for the loss of shutter speed.

I guess this only matters for handheld shots, and/or moving subjects? The post I referenced mention nature/landscape shots and I immediately thought of stationary subjects involving a tripod, where shutter speed might not matter that much? I guess that was a bit narrow minded of me.

I'd recommend not complicating this by getting into the amount of light collected by the larger sensor area, since that doesn't have anything to do with your question about depth of field.

You're absolutely right. These forums are at times very confusing, with terms I don't yet understand being thrown around, but I've started trying to piece it all together. It was the "raise ISO to compensate" that made me bring up light collection, as that's one of those things I'd read that bigger sensors are better at, but never mind that bit.

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Joyless
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Re: Why recommend a superzoom for deep dof?
In reply to Draek, May 16, 2012

Draek wrote:

They can capture more light, but they might not necessarily do so; the theory is that, for the same framing and shutter speed, a given sensor at f/8 will capture roughly the same amount of light as one 2x as large at f/16, thus having roughly the same amount of noise and roughly equal DOF. Roughly, because to determine it properly you'd have to deal with an equation involving F-stops and T-stops of each lens, real ISO settings, quantum efficiency of each sensor, noise floor, circle of confusion, enlargement size, and probably a few other variables I'm forgetting right now.

Right. That last part was quite a bit over my head, but thanks for taking the time to answer. Just out of curiosity though, how rough is roughly? Because I've noticed I can set the shutter to 15 seconds for instance, but I can't set it to 7,5 seconds, the closest is 8 seconds, which I guess is roughly half. Meaning, this isn't about absolute precision, but roughly the same is good enough.

Of course, it's all purely academic and for 99.99% of situations the rule of thumb "DOF increases as sensor size decreases" works quite well.

Indeed, I'm just one of those who like to understand the how and why of things, meaning I'm in way over my head most of the time.

Jo

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tko
tko
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not true
In reply to citizenlouie, May 16, 2012

1) DOF has nothing to do with FL if the subject framing is the same.

2.) If you use a longer FL at the same distance from subject the subject appear closer, with less DOF. That's because of the larger magnification. Twice the magnification gives 1/4th the DOF. So, standing in the same position, zoom in twice as much, 1/4th the DOF.

Every time you double the focal length, you half the DoF. For example, 100mm @ f/2 has the DoF half of that of 50mm @ f/2, or if you put the other way around, 100mm @ f/2.8 has the same DoF of 50mm @ f/2.

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Joyless
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Re: Why recommend a superzoom for deep dof?
In reply to GaryH1125, May 16, 2012

GaryH1125 wrote:

There are three factors that effect DOF; Actual Focal Length, F-stop, and distance to subject. Strictly speaking none of these have anything to do with sensor size. A small sensor camera will give you the exact same DOF as a FF camera when the three factors are the same. Where you run into issues is that focal length on P&S cameras is usually given in 35MM equivilent and not actual focal length. The reason for doing this is people are more interested in the field of view a lens will give as opposed to the depth of field.

Yeah, I understand, thank you. And no, listing depth of field instead of field of view for a lens wouldn't make much sense.

Jo

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Great Bustard
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Answer:
In reply to Joyless, May 16, 2012

Joyless wrote:

In the following post:
http://forums.dpreview.com/forums/read.asp?forum=1032&message=41517480

bobn2 recommends using a superzoom instead of a dslr for "decent" dof, whatever that might be.

The thread reached the 150 post limit before I could ask there, so I try here instead.

Can anyone elaborate on this? Why would a superzoom be better? I've seen the argument made before, but never a reason, so I wonder.

My sarcasm detector isn't all that great so have I perhaps misunderstood this?

At deep DOFs, diffraction softening limits the resolution of the lens. For example, by f/16 on FF (f/10 on 1.6x), there won't be that much difference between a superzoom and a top-notch prime.

So, may as well go with the convenience of a superzoom if your photography is going to be limited to deep DOFs, ideally, on a smaller format.

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citizenlouie
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Re: not true
In reply to tko, May 16, 2012

tko wrote:

2.) If you use a longer FL at the same distance from subject the subject appear closer, with less DOF. That's because of the larger magnification. Twice the magnification gives 1/4th the DOF. So, standing in the same position, zoom in twice as much, 1/4th the DOF.

That I absolutely do not understand. Maybe you can explain to me why 4/3 sensor's DoF is said to be 2 stops more than FF's DoF.

4/3's magnification is twice of that of a FF, so supposedly it would have 1/4 of FF's DoF? I thought 4/3 has more DoF.

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dsjtecserv
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Re: not true
In reply to citizenlouie, May 16, 2012

citizenlouie wrote:

tko wrote:

2.) If you use a longer FL at the same distance from subject the subject appear closer, with less DOF. That's because of the larger magnification. Twice the magnification gives 1/4th the DOF. So, standing in the same position, zoom in twice as much, 1/4th the DOF.

That I absolutely do not understand. Maybe you can explain to me why 4/3 sensor's DoF is said to be 2 stops more than FF's DoF.

4/3's magnification is twice of that of a FF, so supposedly it would have 1/4 of FF's DoF? I thought 4/3 has more DoF.

Cropping isn't magnification. Magnification refers to to the relative size of the actual image projected onto the sensor, compared to the actual size of the object. Depth of field is directly affected by magnification, but not at all by cropping. Greater magnification (either by use of a longer focal length or change in shooting distance) changes the actual image projected on the sensor. Mere capture of a lesser part of the image doesn't change the image itself.

The greater depth of field associated with the smaller sensor of the four-thirds sensor is due to the use of a shorter focal length to achieve the same framing of the subject. In order to achieve the same framing on a smaller senor, the image must be smaller; thus the magnification must be less, which correlates to greater depth of field.

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Barrie Davis
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DoF....greater with short f-length [??]
In reply to Joyless, May 16, 2012

Joyless wrote:

dsjtecserv wrote:

Note that Draek said "for a given field of view and aperture". In order for a smaller sensor camera to produce the same field of view as a larger one, it will need to use a shorter focal length. The greater depth of field is provided by the shorter focal length, not by the size of the sensor.

Ah, of course. Thank you. I think I should have known that, or been able to figure it out for myself, but I think I over-complicate matters.

Trouble is, it isn't really true.... !! And it is more complicated than it might first appear.

  • Short f-length lenses do not really have "more DoF" than long focus lenses.

Short focus lenses get more in the shot, which means for any one size of picture, ALL the detail has to be smaller, just to get it in. Reproducing image detail smaller makes it appear sharper even where it is slightly blurred, with the result that DoF appears greater. It is the smaller image scale that does it... NOT the short f-length.

It can be proven that short and long lenses have the same DoF at the same aperture by normalising the image scale between them.... which is to say, enlarging up the wide angle image so that the actual detail compared is the same size as in the tele shot.

Read more about it here

http://toothwalker.org/optics/dof.html

Scroll down to the pictures of Gromit the Dog in yellow oilskins.... and read it ALL.

There are many more examples of this myth-busting right across the web... A good site to explore in full is Cambridge in Colour... here is the "Understanding Depth of Field" page.

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

Nevertheless, it is true that superzooms do give substantially greater DoF, framing for framing, aperture for aperture....

  • ...and it really IS because the sensor is pretty darn small. It is so small as it is in order to get a lens that has a super zooming range, and with a usable range of apertures to get acceptable light levels passed without being the size of a wastepaper bin !

Indeed, small sensor cameras have a lot going for them. Those with modest range of zoom are pocketable, while those with super range zooms are vastly flexible in capability, and all in one package which isn't huge.
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