Depth of field on FX compared to DX

[the_local_jacko]

I currently have a 24-70mm 2.8G which I used on my DX Nikon D90 and I love the ability to throw the background out of Focus and get a lovely bokeh for portraits. I am looking to buy a FX body and wondered whether I'd still achieve the same bokeh effect from the lens on an FX body?

To summarise my question : If I theoretically shot two images, one on FX and one on DX at f2.8 on the same 70mm lens at the same distance to subject. Would the depth of field alter between the two images? Or would the DOF be the same except the FX shot would have more of the out of focus background in the frame?

 

[donut]

a larger format ( sensor ) gives less dof

 

[the_local_jacko]

a larger format ( sensor ) gives less dof

So theoretically the background would be even more out of focus in the scenario above?

 

[wyx087]

the DOF be the same except the FX shot would have more of the out of focus background in the frame?

This one.

But then, if you get the same framing, the DoF will be thinner because you are closer to the subject.

 

[specialman]

DoF remains the same.

What you see is just different depending in the sensor.

 

[donut]

yes , but im not sure if the out of focus bit gets to a certain level of out of focus and then levels out , but i would think for a side by side comparison the larger sensor would be more out of focus

 

[Steve Smith]

For the same field of view, you will get less depth of field.

So if you are used to using an 18mm lens on DX and change to a 28mm lens on FX, at similar aperture settings, you will see less depth of field.


Steve.

 

[the_local_jacko]

Thanks. This kind of backs up my understanding.

I currently only have the 24-70 which will work with FF. I will eventually buy something in the 105 range which would allow me to match the framing which I currently have on DX at 70mm and have even shallower DOF. In the meantime however I wanted to understand exactly what effect shooting at 70mm would have on DOF if I switched to FX.

 

[wyx087]

crop is exactly that, crop of full frame. you get wider/taller field of view and larger view finder.

in actual photography terms, going FX means better control on depth of field, and lenses feels to become wider.

 

[HoppyUK]

For the same field of view, you will get less depth of field.

So if you are used to using an 18mm lens on DX and change to a 28mm lens on FX, at similar aperture settings, you will see less depth of field.


Steve.

^^^ This.

The change in DoF is equal to the crop factor, eg 50mm lens at f/4 on DX gives the same framing and DoF as 75mm lens at f/6 on full frame (1.5x crop factor, from same distance).

Check actual figures on this DoF calculator http://www.dofmaster.com/dofjs.html

 

[HoppyUK]

DoF remains the same.

What you see is just different depending in the sensor.

No. The size of the sensor is at the heart of it and drives all other contributing factors.

DoF only exists as a measurable entity when all the contributing factors are specified - format (CoC), focal length, distance, aperture - and the final image is viewed from a standard distance. Change any single element and everything else changes with it.

 

[specialman]

No. The size of the sensor is at the heart of it and drives all other contributing factors.

DoF only exists as a measurable entity when all the contributing factors are specified - format (CoC), focal length, distance, aperture - and the final image is viewed from a standard distance. Change any single element and everything else changes with it.

Brain. Turned. To. Mush.

So DoF always relies on a plane, such as a sensor, to actually exist and in turn, that sensor size determines the DOF?....

You know this circle of confusion? It's not by chance the shape of my face with a confused look on it?...

 

[woof woof]

Brain. Turned. To. Mush.

The sensor size can influence what you do, ie. the focal length you use will/may be influenced by the sensor size as will/may the camera to subject distance you shoot at etc and these things affect the DoF as can other things you do further down the line like the amount of magnification applied when you print/view.

The best way to make sense of all this IMVHO is to do some simple real world comparative tests with cameras with different sized sensors. These days some of us are lucky enough to have FF and APS-C or MFT cameras. FF and MFT make especially good toys to play with as the numbers are easy to deal with, MFT being a x2 crop system. If you have equivalent lenses like 50mm for FF and 25mm for MFT and lenses that'll work on both cameras all the better.

 

[specialman]

To be fair, I should know all this shizzle but technical stuff is something I find hard to retain in my head. Plus, I just plonk lenses on cameras, select f-stops and go with what looks good - its worked for Mr so far

 

[HoppyUK]

Brain. Turned. To. Mush.

So DoF always relies on a plane, such as a sensor, to actually exist and in turn, that sensor size determines the DOF?....

You know this circle of confusion? It's not by chance the shape of my face with a confused look on it?...

To be fair, I should know all this shizzle but technical stuff is something I find hard to retain in my head. Plus, I just plonk lenses on cameras, select f-stops and go with what looks good - its worked for Mr so far

Not sure you need to know more than that in practise For really critical working, an awareness of (all) the contributing factors is all you need, then look it up on DoFmaster or your mobile phone app, or simply tweak it until it looks right.

The thing about DoF is that it's an optical illusion and the trick only works in any measurable/comparable way when all factors are included (as listed earlier). They all affect one another and it all starts with the sensor* and ends with the rendered image, eg print, and the final viewing distance.

DoF is ALL about magnification, including the lens aperture (it's the physical diameter that matters). With that as a starting point, it's easy to see how anything that affects size (either of capture or viewing) will have an influence. The reason why sensor size is key is because of the way we work - that is with a camera with a fixed size sensor and we adjust focal length etc to suit. If we started with a fixed focal length lens and then varied the size of image capture by cropping it, then the lens would become the central aspect. But we don't

*Actually, the international standard for DoF calcs starts with the basic assumption that if we view a 10in print at a distance equal to the diagonal of around 12in, then any detail smaller than 0.2mm cannot be differentiated by the naked eye. This is then translated into the circle of confusion size, which is the first thing that goes into a DoF calculation.
DoF calc hold good for any size of output, so long as the viewing distance standard is maintained, ie move back to look at a big image. From this it is also evident that if you view an image at 100% on screen from close distance, then all standard DoF calcs go out of the window!

 

[specialman]

Is this a good explanation?

[YOUTUBE]Pdq65lEYFOM[/YOUTUBE]

Seems pretty easy to understand, although I still can't get my head around viewing distance (of a print for example) and how it has an effect on DoF, other than the perceived effect that a 2D rendering of bokeh has when it tricks the eye....

 

[HoppyUK]

Is this a good explanation?

[YOUTUBE]Pdq65lEYFOM[/YOUTUBE]

Seems pretty easy to understand, although I still can't get my head around viewing distance (of a print for example) and how it has an effect on DoF, other than the perceived effect that a 2D rendering of bokeh has when it tricks the eye....

Yes, good explanation of the CoC and cool graphics Note the table at the end that shows the full frame CoC as 0.029mm (usually rounded to 0.03) and the APS-C CoC as 0.019mm. The difference is the crop factor

Viewing distance of a print is critical because of the optical illusion thing. If you view from a closer distance, you can see more detail and things that previously appeared perfectly sharp don't any more. Same as when you look at the camera's LCD where the small image shows almost everything to look sharp, but then zoom in and suddenly it doesn't!

 

[specialman]

I thought the graphics were cool

Viewing distance of a print is critical because of the optical illusion thing. If you view from a closer distance, you can see more detail and things that previously appeared perfectly sharp don't any more. Same as when you look at the camera's LCD where the small image shows almost everything to look sharp, but then zoom in and suddenly it doesn't!

I understand what you're explaining but to me, but the actual 'science' of DoF (i.e. the measurements relating to lens, aperture etc) aren't affected by the final print, only the perception, the 'illusion' of what the viewer sees? Actual DoF cannot be changed after the capture surely? The whole idea that when you inspect a print from varying distances the level of detail changes is also dictated by A) the print quality ( resolution plus paper stock etc), and B) the DoF of our own vision....

I understand viewing distance can have a massive impact over how the viewer can appreciate an image; in a typical magazine for example, the viewer is expected to read 10pt copy and look at an A3 image all in one go... it's never going to work but that's relative to the limitations of our eye, isn't it?

This is starting to push both the functioning of my brain and my vocabulary

Why did I open my big mouth...

 

[HoppyUK]

I thought the graphics were cool



I understand what you're explaining but to me, but the actual 'science' of DoF (i.e. the measurements relating to lens, aperture etc) aren't affected by the final print, only the perception, the 'illusion' of what the viewer sees? Actual DoF cannot be changed after the capture surely? The whole idea that when you inspect a print from varying distances the level of detail changes is also dictated by A) the print quality ( resolution plus paper stock etc), and B) the DoF of our own vision....

I understand viewing distance can have a massive impact over how the viewer can appreciate an image; in a typical magazine for example, the viewer is expected to read 10pt copy and look at an A3 image all in one go... it's never going to work but that's relative to the limitations of our eye, isn't it?

This is starting to push both the functioning of my brain and my vocabulary

Why did I open my big mouth...

Erm, no. DoF does not exist as a meaningful concept until the final image is output - either on screen or in print or whatever - and is viewed under set conditions of size and distance. You can measure it at the moment of capture, which is what the CoC defines, but it doesn't mean anything significant until the final viewing because print size and viewing distance makes just as much difference as sensor size and focal length, ie everything can change dramatically. DoF calculators simply assume this as a given, as is the average human eye acuity.

You either have to agree and accept this (recommended!) or go your own way and draw up your own method of assessment, but the same parameters apply. The thing is, it's an accepted standard so however you go about it, it's a sound basis that everyone understands.

FWIW, I think the accepted measures for DoF (ie CoC) are a bit loose and behind the times. We tend to make bigger images these days, and look at them more closely. In which case, apply a smaller CoC and draw up a your own scale, or do as I do and when for example the calculation says f/5.6 for a group shot, I use f/8 when it's important to get everyone sharp from front to back.

 

[specialman]

HoppyUK - not arguing, my little brain just struggles with the thought that even though we accept that we can use an accurate, scientific calculator to work out DoF (i.e. the area that'll be sharp using the kit we shoot with) this is not the actual line in the sand... realistically, when people talk about getting depth of field by choosing a particular f-stop (as most people do) they're only doing half a job because they're output is as critical as the settings they used to capture in the first place.

I do what you do - I generally overestimate at times but moreso because I'm not actually taking exact measurements of distances, just estimations - although I never use a DoF calculator because A) I'm too lazy, B) I often don't have time, and C) it takes away some of the fun of making those choices in the first place

Certainly enlightening, if only to realise that the physics of optics are far more complex than often made out, but it does kind of sanitise things somewhat IMO.

I think we're the only ones left in the room and we'll be expected to turn the lights out soon

 

[HoppyUK]

HoppyUK - not arguing, my little brain just struggles with the thought that even though we accept that we can use an accurate, scientific calculator to work out DoF (i.e. the area that'll be sharp using the kit we shoot with) this is not the actual line in the sand... realistically, when people talk about getting depth of field by choosing a particular f-stop (as most people do) they're only doing half a job because they're output is as critical as the settings they used to capture in the first place.

I do what you do - I generally overestimate at times but moreso because I'm not actually taking exact measurements of distances, just estimations - although I never use a DoF calculator because A) I'm too lazy, B) I often don't have time, and C) it takes away some of the fun of making those choices in the first place

Certainly enlightening, if only to realise that the physics of optics are far more complex than often made out, but it does kind of sanitise things somewhat IMO.

I think we're the only ones left in the room and we'll be expected to turn the lights out soon

No, you can't argue with the facts, that's the physics of it, though it's true a lot of folks don't fully appreciate the significance of the print size and viewing distance part of it is, and how fundamental that is to the whole process. But I'm sure you do this kind of thing instinctively, and will take a lot more care over an editorial shot that's maybe going to be used across a double-page spread to open a nice big feature article, than you will over a basic product shot that's never going to be bigger than 1/8th page

And while DoF calcs can appear to be extremely accurate, like 4.63ft to 9.84ft or something, that's just how the maths works and it's nothing like that in practise. Call that 5-10ft or 1.5-3m is plenty good enough, give or take a bit.

I rarely use a DoF calculator, though I have got a few key numbers printed on a small table and stuck inside the lens cap, in case of brain fade. You just get to know what's going to be there or thereabouts, then if needs be I'll check it visually by zooming in on the LCD, and maybe tweak the aperture or shift the focus point a bit if it's critical or marginal. DoF is part of the mix and often a balancing act, with diffraction sometimes being a consideration, or soft edge sharpness with some lenses maybe, and exposure considerations of course.

 

[specialman]

.... But I'm sure you do this kind of thing instinctively, and will take a lot more care over an editorial shot that's maybe going to be used across a double-page spread to open a nice big feature article, than you will over a basic product shot that's never going to be bigger than 1/8th page ...

Have you been spying on me? Caught red-handed

 

[SimonH]

I don't see it mentioned already, but anyone wanting to test out the relationship of sensor size versus depth of field should remind themselves/explore the Brenizer method.

If you don't know it, it's a way of reducing the apparent DoF by image-stitching multiple images to create a faux large sensor effect.

Good explanation and demonstration here: http://blog.buiphotos.com/2009/07/the-brenizer-method-explained-with-directions/

 

[woof woof]

I thought the graphics were cool

...DoF cannot be changed after the capture surely? The whole idea that when you inspect a print from varying distances the level of detail changes is also dictated by A) the print quality ( resolution plus paper stock etc), and B) the DoF of our own vision....

I understand viewing distance can have a massive impact over how the viewer can appreciate an image; in a typical magazine for example, the viewer is expected to read 10pt copy and look at an A3 image all in one go... it's never going to work but that's relative to the limitations of our eye, isn't it?

I know exactly where you're coming from

My view is that when you choose the camera settings and shooting position and then press the button the image is captured... DoF and all... and by "captured... DoF and all" I mean that how the image will look when printed at A5 and viewed from 18inches away or A3 and viewed from 2m away is decided when you set the camera up and take the shot.

Viewed like that you can't change the DoF after the image is captured. All you can do is display and view the image in different ways that either hide or make more obvious the inherent characteristics that were decided when you took the shot.

For example if I take a shot with thin DoF and print it out postage stamp sized no one will know that the DoF is very thin unless they examine it under a magnifying glass.

This shot looks like front to back DoF but in reality the point of focus is close to the camera and it only looks like front to back DoF because everything is small in the image. Print the image larger and the thin DoF will be immediately apparent.

Other images like this next one are more obviously shallow DoF and the only way you'd be able to hide it would be to print it so small it'd be next to meaningless as an image.

In this last image there's front to back DoF under normal print and viewing and to make it appear less than front to back DoF you'd really have to print it quite large. So large in fact that IMVHO if you intended to print it that large you wouldn't have taken the shot with that gear and at those settings.

I disagree with how some people view this issue and the importance they give to DoF tables and especially the CoC. To me DoF tables are just a guide (anyone can make up their own) and the CoC is virtually an irrelevance (to me) as the manufacturers have made cameras and lenses that largely take care of the issue, ie. FF CoC=0.03, MFT CoC=0.015, see a pattern here? MFT is a x2 crop format and needs to be magnified more than a FF shot to get the same sized final image.... however... even though it's a x2 crop it's easily possible to get perfectly good A3 images and the pixels are smaller and the lenses are sharper than FF pixels and lenses and even if they're not (I often use legacy lenses) it's still possible for the image to be magnified a little more and give a good enough final image at output sizes good enough for many people.

The only time I've ever had to think about CoC in over 40 years of taking pictures wasn't with a camera in my hand at all but when producing images for a stage play, people at the back needed to see a certain level of detail and they couldn't change their viewing distance. In circumstances like that your CoC may be... what? It depends upon the distance to the back of the stalls, 2 inches? three? In photography it's (the CoC) honestly never ever mattered to me. You have to know the basics and you have to keep in mind what output size you want and how you're going to view the images but as long as you choose kit that'll meet your needs you can then pretty much put the CoC on the back burner IMVHO.

What matters more to me than worrying about the science of CoC is aperture, focal length and camera to subject distance as I know that the gear I have (FF and MFT) is perfectly capable of producing an A3 image which is the largest I've ever made and that that image will be good enough to be viewed normally and indeed good enough to be examined quite closely by most people

 

[HoppyUK]

<snip>

I disagree with how some people view this issue and the importance they give to DoF tables and especially the CoC....

<snip>

When you look at any image under any circumstances and say " this is sharp, but that is not" you are making a judgement on the acceptable size of the circle of confusion.

That is how sharpness is measured, that's why it's important - fundamental in fact.

 

[specialman]

.....Viewed like that you can't change the DoF after the image is captured. All you can do is display and view the image in different ways that either hide or make more obvious the inherent characteristics that were decided when you took the shot......

I suppose that was what I was initially trying to say.

As mentioned before, for many people (me included) 'depth-of-field', as a measure of what is in focus and what is isn't, is determined in front of the lens by the choice of f-stop and focal length when the shutter is pressed....

I was talking to someone today about what HoppyUK was explaining in relation to DoF and the CoC, a guy who's like a sponge when it comes to photography because he's just starting out. He got it straight away although he admitted it's pretty heavy stuff. But he did say that it (the 'illusion') seemed almost like an add-on to initially taking the photograph. The image has been captured, that can't be changed. But of course, as you display the image you have to change your viewing distance depending on the size of the print and that in turn dictates how closely you can assess the detail.... when we talk about this part are we taking into consideration any factors such as print res and how the paper takes the ink to show detail?

I really shouldn't be perpetuating my apparent stupidity but i suppose it's better than another 'what DSLR' thread

 

[HoppyUK]

I suppose that was what I was initially trying to say.

As mentioned before, for many people (me included) 'depth-of-field', as a measure of what is in focus and what is isn't, is determined in front of the lens by the choice of f-stop and focal length when the shutter is pressed....

I was talking to someone today about what HoppyUK was explaining in relation to DoF and the CoC, a guy who's like a sponge when it comes to photography because he's just starting out. He got it straight away although he admitted it's pretty heavy stuff. But he did say that it (the 'illusion') seemed almost like an add-on to initially taking the photograph. The image has been captured, that can't be changed. But of course, as you display the image you have to change your viewing distance depending on the size of the print and that in turn dictates how closely you can assess the detail.... when we talk about this part are we taking into consideration any factors such as print res and how the paper takes the ink to show detail?

I really shouldn't be perpetuating my apparent stupidity but i suppose it's better than another 'what DSLR' thread

No, DoF calcs assume perfection in all other areas. If you want the Full Monty on sharpness, then you have to measure MTFs for lens, sensor/film, and paper/monitor and they all cascade one on top of the other, losing some sharpness at each stage Only your eyes and acuity of vision have a set standard for DoF (eyes have an MTF rating too!) as stated earlier, though that obviously varies a bit from person to person.

This is not often a problem, but can be. Some lenses will run out of sharpness around the edges before they reach the DoF requirement, or if you try to look very closely at a small colour print some very fine detail will get lost in the blur of the emulsion, same as looking very closely at the camera's LCD without enlarging it will just show a load of dots.

There's theory and there's practise. Theory is good so you know what the parameters are and how best to manage them, but practise is what matters

 

[woof woof]

When you look at any image under any circumstances and say " this is sharp, but that is not" you are making a judgement on the acceptable size of the circle of confusion.

That is how sharpness is measured, that's why it's important - fundamental in fact.

But as I said and IMVHO talk of CoC is largely irrelevant to most people. It's simply not something that many will ever have to worry about in their photographic lives, and yet it takes up so much forum space and causes so may heated discussions.

Another point I've made before but is worth saying again. DoF tables are not the word or the Lord carved in stone. They're constructed based on a set of (reasonable, but still) assumptions relating to specific image sizes and viewing distances, assumptions which may or may not be agreed with by the person taking and producing the image and if that's the case there's nothing to stop anyone deciding to construct their own DoF tables based upon their own requirements and their own CoC. This is something that people sometimes do in effect, they look at tables and decide to use the next value.

What matters to me in relation to DoF is format size, aperture, focal length and camera to subject distance and yes CoC is a basis of that but as the kit has been designed and made and is capable of producing the result I want at an image size I'm happy with it can fade to the back of the queue whilst aperture, focal length and camera to subject distance have a much more obvious effect.

Personally if someone asks me about DoF, actually that's something that's never happened, what has happened is someone asking how I get the subject sharp and the background all burred... I never start with the CoC. I talk about aperture, camera to subject distance and focal length. If someone asked me how to produce something for a play I don't think I'd mention it then either I think I'd just say "Remember that it has to be seen from the back of the theatre."

 

[woof woof]

But he did say that it (the 'illusion') seemed almost like an add-on to initially taking the photograph. The image has been captured, that can't be changed.

IMVHO the time to think about this is before you take the picture.

If you want some detail in the image to be seen from the back of a theatre or maybe even from several hundred yards away then you're going to have to use kit and settings that can capture and then produce the level of detail you want at the size you want so that it can be viewed from that distance.

If you're producing an image something between a passport photo and A3 in size to be viewed what we'd think of as normally I think you've got an easier task, one that can be accomplished with anything from a large chip compact to a FF DSLR with aperture, focal length and camera to subject distance at the front of your mind and with your mind untroubled by thought of the CoC

 

[specialman]

IMVHO the time to think about this is before you take the picture.

If you want some detail in the image to be seen from the back of a theatre or maybe even from several hundred yards away then you're going to have to use kit and settings that can capture and then produce the level of detail you want at the size you want so that it can be viewed from that distance.

If you're producing an image something between a passport photo and A3 in size to be viewed what we'd think of as normally I think you've got an easier task, one that can be accomplished with anything from a large chip compact to a FF DSLR with aperture, focal length and camera to subject distance at the front of your mind and with your mind untroubled by thought of the CoC

There is definitely more emphasis put on captured detail these days, especially as megapixel counts go up. Whether people (both photographers and viewers) actually know how much detail they should be contained in an image to maximise its effect is a different matter. I suppose most people follow the 'more megapixels, more detail' mantra because it seems logical that more equals better. You'll get people who want to stand with their noses up against a A0 print to look at the detail within the image but you'll also get the people who'll do nothing but look at the image as a whole from many metres away and view that way. How someone appreciates any art is very personal. I for one have never had that as my overriding thought when capturing an image, although it is a consideration to some extent. If I thought it totally redundant, I'd be using a low megapixel body, but that's not the case.

Going back to what was said earlier in the thread about the illusion of DoF being dictated by the final output size (and viewing distance), to include this in the picture taking process is, IMO, overcomplicating the picture-taking process somewhat. I wonder how many people actually take this into consideration and whether by not doing so, they're work is any less effective? I certainly don't feel my work suffers as a result of not doing is all the time. Although I can appreciate that for those who do take this route, it adds another dimension to their picture-taking... I suppose it's similar to people who play guitar to play whatever they feel, and those who do the same but follow scales and theory.

In terms of output size, there are few times when it has total influence over my 'work' work (which is the majority of my photography)....when I'm asked to produce an image to fit a specific shape is the most common - at work that is either an image to go over a DPS (A3) or to be used on a cover when the other consideration is where you're going to put headlines, straps, mastheads and covermounts. These are obviously important images within any magazine and clarity (e.g. explanation) and ease of use for the designer are key to making it work. This is creativity with boundaries...

The other is when taking shots for sequences (rig tying etc). These generally go one column width and then the height is dictated by orientation and number of sequence shots. I generally shoot so the image can be left as horizontal or cropped to square because it's safer. The main consideration in this is to give good subject seperation and clarity, which I suppose is akin to what HoppyUK was saying earlier about DoF and output size. But the other fact in this is that readers are expected to follow this as a step-by-step instruction so clarity is expected. This is not artistic intent - I choose an f-stop that gives me sharpness on the subject and not much else - but there is also a lot of thinking going towards colour palette to make it work. This is not artistic work that is aimed to thrill or excite, it's merely instruction and illustration. Maybe this thinking about close-ups is one and the same as what was being discussed earlier regarding illusion?

 

[Steve Smith]

Going back to what was said earlier in the thread about the illusion of DoF being dictated by the final output size (and viewing distance), to include this in the picture taking process is, IMO, overcomplicating the picture-taking process somewhat.

Whislt the size does have a bearing, if you take a photograph of a flower with only the petals in sharp focus and the foreground and background very out of focus, that is what it will look like regardless of print size.


Steve.

 

[HoppyUK]

The thing about output size and viewing distance, is quite a lot of the time you can forget about it because viewers tend to unconsciously and automatically compensate for it.

The DoF standard may be derived from that 10in wide print viewed from 12in (the diagonal length) but this holds good for any size of image providing the viewing distance equal to the diagonal is maintained. This is exactly what happens in reality, when if you hand someone a small 6x4in print, they will tend to bring it closer to their eye. Give a set of prints to your gran and she'll reach for her reading glasses.

With something A4 magazine size, about 14-15in is a comfortable distance, and with an A3 double-page spread, I tend to hold that at full arms length, or if it's an exhibition print on the wall, step back a bit. Taken to extremes, a huge street poster looks fine from across the road, because the relationship between image size and viewing distance is maintained.

That's why the DoF theory works for most purposes and has endured as a robust standard. It only fails when we look at big images very closely, like 100% viewing on screen. Landscapes is another example where I would take more care, as I like to stand back and take in the whole scene, then move closer to see a bit more detail.

Comparing the DoF standard to pixels is quite sobering, if taken literally - it equates to just 1.1mp That's roughly the resolution of a decent monitor. There's a bit more to it than that though, where those cascading MTFs come into the whole business, the point there being that perceived sharpness has more to do with image contrast than it has with pure resolution.

 

[KIPAX]

if i take a picture of something 20 yards away... will the dof differ between a ff and a 1.3 crop

if i take a picture from varying distance but equally half fill the frame...will the dof differ between a ff and a 1.3 crop

anyone got a simple answer please?

 

[HoppyUK]

if i take a picture of something 20 yards away... will the dof differ between a ff and a 1.3 crop

Yes. And the subject will be framed differently too.

if i take a picture from varying distance but equally half fill the frame...will the dof differ between a ff and a 1.3 crop

anyone got a simple answer please?

Yes.

 

[KIPAX]

Yes. And the subject will be framed differently too.
.

hence why the second question

THANKS for the simple answer.. I ahve been using FF for a while but only recently on my 400mm at f2.8 .. just last few weeks.. It just seems very thin..

 

[HoppyUK]

hence why the second question

THANKS for the simple answer.. I ahve been using FF for a while but only recently on my 400mm at f2.8 .. just last few weeks.. It just seems very thin..

The difference isn't much Tony - between 1.3x crop and FF it's f/2.8 vs f/3.6, ie 0.7 stops (same DoF, for subject framed the same). Conversion is f/number x crop factor, so 1.4x crop factor would be exactly one stop difference.

 

[KIPAX]

Its noticable for me.. and I did feel more comfortable at f3.5... but I was thinking maybe calibration out.. but then convinced myself not.. its just slightly too thin....makes abig difference.. players head slightly forward and its OOF But shooting a static person its loverly.. just too thin for action I find.. Just needed to confirm what i was feeling was wrong..

was going to ask the question but this thread came up as a suggestion when i was writing the subject.... neat thing that

 

[HoppyUK]

Yes, I can see that you'd notice that. When DoF is shallow like at 2.8, the transition from sharp to unsharp covers such a small distance that a stop or so is often more noticeable than say between f/8 and f/11.

 

[sk66]

OK, maybe I'm off on this one.
My understanding is DOF *on the sensor* is strictly a matter of FL, Subject Distance, and Aperture. (I.e. what's sharp and what's not at a pixel level.) With FL and distance each having twice as much effect on DOF than aperture does.

Then we add in COC for prints which is fairly "standard" (larger prints get viewed from further), and this is where the difference comes in between DX/FX. But, here's the problem I see. If you crop the image, or if you do fancy resampling, or selective sharpening/blurring prior to printing then you've "changed" the COC. The other problem I see is that editing/evaluating is done on a computer and not at final print/viewing size.

It seems to me that we should just concern ourselves with sharpness at the pixel level. We all know that if you look at a "soft" image at 50% (from the same distance, i.e while editing), or if you view it from twice as far then it appears sharper; that's all COC really is.

 

[sk66]

Or is there a way to edit/evaluate images based upon final print/viewing size? Without printing that is...and if it's not for print, then how could you ever account for display resolutions?