How do I work out how much DoF I have?

[wendyg]

Beginners question

I understand the idea of depth of field, and am quite at home with the concept that big apertures (small f number) equals shallow DoF, and small apertures give a large DoF.

Is there a way of working out how big the zone of sharpness is at any given f-number? Does it relate to the focal length of the lens?

I just need a rough guide eg f5.6 = 4mm DoF, f8 = 1m DoF f16 = 100m DoF, f22 = infinity or close as dammit!

Thanks

[flat-planedCrank]

wendyg said:

Beginners question

I understand the idea of depth of field, and am quite at home with the concept that big apertures (small f number) equals shallow DoF, and small apertures give a large DoF.

Is there a way of working out how big the zone of sharpness is at any given f-number? Does it relate to the focal length of the lens?

I just need a rough guide eg f5.6 = 4mm DoF, f8 = 1m DoF f16 = 100m DoF, f22 = infinity or close as dammit!

Thanks

It does depend on the focal length of the lens, but also on the distance the lens is focused to (and of course the aperture).

A decent explanation - http://en.wikipedia.org/wiki/Depth_of_field


Cheers.

[Simpo Two]

wendyg said:

Is there a way of working out how big the zone of sharpness is at any given f-number?

There is, but in the time you can work it out with a slide rule and a tape measure, you can either use DOF preview or take a shot and have a look

[wendyg]

flat-planedCrank said:

wendyg said:

Beginners question

I understand the idea of depth of field, and am quite at home with the concept that big apertures (small f number) equals shallow DoF, and small apertures give a large DoF.

Is there a way of working out how big the zone of sharpness is at any given f-number? Does it relate to the focal length of the lens?

I just need a rough guide eg f5.6 = 4mm DoF, f8 = 1m DoF f16 = 100m DoF, f22 = infinity or close as dammit!

Thanks

It does depend on the focal length of the lens, but also on the distance the lens is focused to (and of course the aperture).

A decent explanation - http://en.wikipedia.org/wiki/Depth_of_field


Cheers.

Just looked at Wiki (your link not working btw) and blimey thats way more complicated than I thought. Is there even a rule of thumb?

[Simpo Two]

wendyg said:

Just looked at Wiki (your link not working btw) and blimey thats way more complicated than I thought. Is there even a rule of thumb?

Yep, you can either use DOF preview or take a shot and have a look After a while you can make a fair guess anyway.

Oh hang on, you're the one that looks for really tecchy not-related-to-real-life answers aren't you? I'll get me coat, you can get some log tables!

[wendyg]

Simpo Two said:

wendyg said:

Is there a way of working out how big the zone of sharpness is at any given f-number?

There is, but in the time you can work it out with a slide rule and a tape measure, you can either use DOF preview or take a shot and have a look

Seriously, the reason the question came up was that I went out with my and my sisters kids to a play park. My eldest nephew is now 8, and was happy to climb and pose. I wanted to capture the movement, so I wanted a fairly quick shutter speed, and the light was a bit dull (cloudy day), so I opened up the aperture. The shots looked OK in the camera, but when I got them on the computer i was dissapointed to find that his knee was in focus but his face wasn't.

[AndWhy]

Any chance it could be movement rather than focus that has frozen the knee but not the head? It might help if you could post the image or, if possible, the EXIF data from the image file.

[flat-planedCrank]

wendyg said:

Just looked at Wiki (your link not working btw)..

Strange works fine for me, perhaps its a different browser thing...


Cheers.

[wendyg]

Simpo Two said:

Oh hang on, you're the one that looks for really tecchy not-related-to-real-life answers aren't you? I'll get me coat, you can get some log tables!

Are you always so nasty, or have you had a bad day?

I am a total beginner here, and I've had hints and tips previously which surprised me with their simplicity, such as the idea of keeping the the shutter speed reciprocal to the focal length to keep things sharp.

What other really stupid questions have I asked, that would merit such a violent and belligerent response?

[rustyspit]

wendyg said:

flat-planedCrank said:

wendyg said:

Beginners question

I understand the idea of depth of field, and am quite at home with the concept that big apertures (small f number) equals shallow DoF, and small apertures give a large DoF.

Is there a way of working out how big the zone of sharpness is at any given f-number? Does it relate to the focal length of the lens?

I just need a rough guide eg f5.6 = 4mm DoF, f8 = 1m DoF f16 = 100m DoF, f22 = infinity or close as dammit!

Thanks

It does depend on the focal length of the lens, but also on the distance the lens is focused to (and of course the aperture).

A decent explanation - http://en.wikipedia.org/wiki/Depth_of_field


Cheers.

Just looked at Wiki (your link not working btw) and blimey thats way more complicated than I thought. Is there even a rule of thumb?

You could try putting a few values into this site to get a feel for your combination of camera/lens:
http://www.dofmaster.com/dofjs.html 

...or you may get lucky and find that your lens already has a depth of field scale printed on it, although unfortunately that seems to be increasingly uncommon.

[Scho]

wendyg said:

I just need a rough guide eg f5.6 = 4mm DoF, f8 = 1m DoF f16 = 100m DoF, f22 = infinity or close as dammit!

Thanks

not so simple.

i have a 50mm lens.

if i focus on my outstretched hand and take a pic at f4 i'l have feck all depth of focus. according to dof master 0.7 ft total ( http://www.dofmaster.com/dofjs.html )

if i focus on the car in the middle distance and take a pic at f4 the whole car will be in focus and more. according to dof master 40 ft total

the CLOSER your focusing point is the LESS depth of focus you get at a given aperture.

this is why you get very thin plane of focus in macro photography.

hope this helps :-)

[Simpo Two]

wendyg said:

Simpo Two said:

Oh hang on, you're the one that looks for really tecchy not-related-to-real-life answers aren't you? I'll get me coat, you can get some log tables!

Are you always so nasty, or have you had a bad day?

I am a total beginner here, and I've had hints and tips previously which surprised me with their simplicity, such as the idea of keeping the the shutter speed reciprocal to the focal length to keep things sharp.

What other really stupid questions have I asked, that would merit such a violent and belligerent response?

Not violent and belligerent at all, merely dispensing advice gained from 25 years with various SLRs, and with a touch of humour (the !) that I'm sorry missed its mark. You seem to want to define everything with an oscillosope and micrometer. Photography isn't like that. Your specific need has in fact made my original answer more valid. You're photographing chidren at play. You don't have time to say 'Hold it right there, I'll just get my notebook and tape measure and see how far your knee is from the sensor plane'. Unless you're in a studio environment, the best way is, and I repeat, use the DOF preview button, or, if you don't have one or it makes the VF too dark to see accurately, take a best guess, look at it and adjust if nedcessary. That's how you build up an instinctive feel for what DOF you will get at various focal lengths and apertures. I'm all in favour of reading manuals but ultimately you have to jump off and start practicing. Learn by doing.

I'm sorry you thought my answer was glib, or not sufficiently scientific to satisfy you, but that really is my best advice. Your question was not stupid, and I didn't say it was. It's a valid question but you don't seem to be able to accept a simple, proven, pragmatic, quick answer.

Edited by Simpo Two on Thursday 1st May 12:01

[Elderly]

wendyg said:

said:

wendyg said:

Is there a way of working out how big the zone of sharpness is at any given f-number?

The shots looked OK in the camera, but when I got them on the computer i was dissapointed to find that his knee was in focus but his face wasn't.

Maybe not DOF at all - maybe you have a front or back focus problem with your camera/lens combination, or you just 'missed' with your focus point as you realesed the shutter? I assuming you are using an autofocus camera.

[VxDuncan]

The depth of field vaires according to the focal length, so the longer the lens the shallower the depth of field for a given apperture, so it's not easy to answer your question without know what lens you have, and if it's a zoom it gets really complicated!

In the good old days when everybody who used an SLR had to set the apperture manually lenses had a scale on them, so that for any focal length and apperture you could line up the two lines on the focus distance scale and see the close and far focus limits. Don't really get those anymore, they were great! (thinks of getting out the tippex on the lens..)

[C&C]

Another option (depending on which camera you have) is that some cameras have an exposure mode which will automatically try to maximise depth of field. For example on a Canon 40D there's a mode called "A-Dep" where it will try to set an appropriate aperture to get the main subjects (highlighted by the focus points in the viewfinder) all in focus.

Don't ask me how it works out what are the main subjects, or how useful it is in reality as it's not a mode I've actually used, but it may be of help in the situation you described.

[wendyg]

Simpo Two said:

wendyg said:

Simpo Two said:

Oh hang on, you're the one that looks for really tecchy not-related-to-real-life answers aren't you? I'll get me coat, you can get some log tables!

Are you always so nasty, or have you had a bad day?

I am a total beginner here, and I've had hints and tips previously which surprised me with their simplicity, such as the idea of keeping the the shutter speed reciprocal to the focal length to keep things sharp.

What other really stupid questions have I asked, that would merit such a violent and belligerent response?

Not violent and belligerent at all, merely dispensing advice gained from 25 years with various SLRs, and with a touch of humour (the !) that I'm sorry missed its mark. You seem to want to define everything with an oscillosope and micrometer. Photography isn't like that. Your specific need has in fact made my original answer more valid. You're photographing chidren at play. You don't have time to say 'Hold it right there, I'll just get my notebook and tape measure and see how far your knee is from the sensor plane'. Unless you're in a studio environment, the best way is, and I repeat, use the DOF preview button, or, if you don't have one or it makes the VF too dark to see accurately, take a best guess, look at it and adjust if nedcessary. That's how you build up an instinctive feel for what DOF you will get at various focal lengths and apertures. I'm all in favour of reading manuals but ultimately you have to jump off and start practicing. Learn by doing.

I'm sorry you thought my answer was glib, or not sufficiently scientific to satisfy you, but that really is my best advice. Your question was not stupid, and I didn't say it was. It's a valid question but you don't seem to be able to accept a simple, proven, pragmatic, quick answer.

Edited by Simpo Two on Thursday 1st May 12:01

I am going to continue to take issue with your posts, because you make some unfair accusations to justify the supercilious and spiteful tone of your replies. At what point did I 'seem to want to define everything with an oscillosope and micrometer'

I asked if there was any sort of short-cuts, and the basic reply is that, no, this is one area area which is so complex that there aren't any - an answer that I HAVE accepted, because it is NOT simple, and NOT quick.

I'm starting to wonder, given the vehemence of your posts, seriously, are you confusing me with someone else?

[KarlosFandango]

I think you are taking Simpo a little too literally, he really isn't the monster that he comes across as There is a certain amount of joking and sarcasm but that can be lost over the internet sometimes.

As for depth of field, well, I know what it means but getting it to do what I want is a whole different other matter. If you understand the principal then I guess getting out there and seeing how you can control and inplement it is the best thing to do.

[Simpo Two]

wendyg said:

I'm starting to wonder, given the vehemence of your posts, seriously, are you confusing me with someone else?

Well you seem to be - my testimonials are at: www.blokewithacamera.co.uk/testimonials.htm

I suggest you start thinking a little harder about what you post in public, because I'm getting tired of being insulted. You called me 'violent' and 'beligerent'. I disagreed but rolled over and apologised in the intersts of peace. You came back with 'spiteful' and 'vehement'.

I think you need to practice a litle etiquette, so this forum, which I enjoyed until yesterday, can return to its usual good-humoured state. I did ask you politely by PM to withdraw your defamatory accusations but you chose not to. Now please leave me alone. I'm too old and wise to get drawn into childish 'you said... I said' debates.

Edited by Simpo Two on Friday 2nd May 13:59

[chris.mapey]

Please would Simpo & Wendy choose their weapons from below:



(Sorry)

It appears that all has got a bit out of hand here!

There is always plenty of "lively banter" without recourse to handbags at dawn / mudslinging / name calling (unless you are two well known car 'togs or dare to mention RAW files)...

Depth of Field is a tough one to answer with the info we have here Wendy. (which is what I believe Simpo is alluding to)

There is no one hard and fast rule that can applied to all cameras & lenses with regard to DoF (other than what you already posted about small apertures vs large apertures.)

With regards to using a fast shutter speed to freeze the movement, how fast are the kids going?

If the kids are on a slide, then I'd see it as an ideal opportunity to practice a bit of panning with a slow / medium shutter speed (to blur the background behind the moving subject, rather than "freeze" the image in toto)

What camera are you using, and how's the autofocus set up?

If the camera is choosing the focus point itself then that could explain the focus being sharp on a more prominent knee than a face that could be "hidden" behind a waved arm at the top of a slide perhaps. (I have had this problem too many times, learned the hard way & now I manually choose the focus point of the camera myself)

The key here is to practice with your camera kit - assuming it's digital it doesn't cost anything.

Take the same shot on each exposure in turn (keeping the "film speed" (ISO) the same, so only letting the camera change the shutter speed. You can then compare the shots and get a feel for DoF in each image (assuming you focus on the same point each time) - that's how I got used to my first dSLR & kit lens.

Depending on your camera / lens there may be a DoF scale that relates to apertures around the focus dial - look at the f stop on the lens and the distances next to that to get a "feel" for DoF.

As John (Simpo) has mentioned the use of a DoF preview button (assuming your camera has one) will enable you to see exactly what's in focus in the shot before you take it) could have helped here.

Feel free to ask more q's as needed (or ask Simpo for one of his really useful fact sheets he's compiled about taking great pics - tap into his experience as a pro 'tog - I know I do regularly!)

To sum up, there are three elements to a photo - shutter speed / aperture & (film / digital sensor) sensitivity.

Shutter & aperture you are OK with, it the situation you describe it may be worth tweaking the ISO (film speed) up to 600 / 800 to get the shot you desire, assuming you need a fast shutter speed & a smaller aperture for DoF it's the only variable left to alter

Hope that helps

Chris

[wendyg]

chris.mapey said:

Please would Simpo & Wendy choose their weapons from below:



(Sorry)

OOoow, second row down, second from left, that's lovely!

Seriously though, my upset has been that I think I asked a fairly simple question (and now I know it has a very complex reply) and in my initial question I asked for a rough guide, and in further posts, I asked if there was a 'Rule of thumb' and said that I didn't want highly scientific answers.

Simpo's responses basically accused me of being some sort of mad obsessive, wanting a millimeter perfect answer, which is, as far as I'm concerned, the polar opposite of what I was asking.

I am happy to discuss this in open forum, without insults, but I feel that Simpo's posts were basically unfair, and ultimately very hurtful.