DPChallenge: A Digital Photography Contest You are not logged in. (log in or register
 

DPChallenge Forums >> Tips, Tricks, and Q&A >> Depth of field
Pages:  
Showing posts 1 - 25 of 30, (reverse)
AuthorThread
05/07/2007 01:55:39 PM · #1
I was looking for some help understanding depth of field. I understand that a shallow depth of field will bring a small amount of your photo in focus while a wide depth of field will bring much more in focus. I tried some experimental photos to see if I could see the difference, but I really can't tell. The first one ' . substr('//images.dpchallenge.com/images_portfolio/53509/thumb/508467.jpg', strrpos('//images.dpchallenge.com/images_portfolio/53509/thumb/508467.jpg', '/') + 1) . ' has an aperture of 5.0 while the second one ' . substr('//images.dpchallenge.com/images_portfolio/53509/thumb/508468.jpg', strrpos('//images.dpchallenge.com/images_portfolio/53509/thumb/508468.jpg', '/') + 1) . ' has an aperture of 29.0. Obviously the shutter speed was much faster in the first picture, which freezes the motion of the leaves better at the top of the photo.

These photos were taken with the kit lens for my Canon Rebel XT, so does that have to do with the amount of depth of field you can see? I thought that (apart from the blowing leaves at the top) the photo with the 29.0 aperture would have much more in focus, but that doesn't appear to be the case.

Thank you for any help!
05/07/2007 01:56:48 PM · #2
The DoF will decrease when the focus is nearer to the lens. So the difference is much more obvious on close-ups :)
05/07/2007 02:05:45 PM · #3
Thanks. So why do they say to use a small aperture for landscape photography then? I would assume that the focus would be often much further away in those cases.
05/07/2007 02:08:23 PM · #4
I'm noticing that the images are taken from different heights. If they were taken at the same height as the first (down low) you'd notice that the entire path would be more or less in focus in the shot taken at 29 where you can see the narrow DOF image the path is blurred in the foreground.
05/07/2007 02:08:51 PM · #5
Pay close attention to the ground at the bottom of the photograph- you'll see the difference in the DOF there. In the 5.0 -The ground slowly comes into focus, whereas in the other picture is in focus all the way down.

ew- too slow :)

Message edited by author 2007-05-07 14:09:10.
05/07/2007 02:10:35 PM · #6
Originally posted by tosk:

Thanks. So why do they say to use a small aperture for landscape photography then? I would assume that the focus would be often much further away in those cases.


Maybe what's confusing you is that a wide open lens is a low F-number, and vice-versa. In other words, something like F1.8 would be a wide open lens (large aperture) in a 50mm 1.8. The larger the F-number, the smaller the aperture.

In general, what you want for landscape is sharpness throughout the image, so you want a larger F-number (smaller aperture), and in general you want to focus 1/3 of the way into the image (the field of sharpness is 1/3 in front, 2/3 in back).

I hope this helps.
05/07/2007 02:11:12 PM · #7
Originally posted by Konador:

The DoF will decrease when the focus is nearer to the lens. So the difference is much more obvious on close-ups :)


And in telephoto. DoF (can) become(s) incredibly thin when working with telephoto. The further away you are focusing, the narrower the depth of field.
05/07/2007 02:12:34 PM · #8
Originally posted by tosk:

Thanks. So why do they say to use a small aperture for landscape photography then? I would assume that the focus would be often much further away in those cases.

You're confusing small aperature with small DOF. It's the opposite. Large aperature, more light, less Depth of field. Smaller opening, less light, but larger DOF.

Also note that aperture is writen as a fraction f/5.0 or f/29. 1/5th is larger than 1/29th.

Landscapes are done at smaller aperatures to ensure that everything in the image is in focus.
05/07/2007 02:12:36 PM · #9
It looks like a very nice trail...
05/07/2007 02:14:18 PM · #10
Also, lenses are generally sharper at smaller/midrange apertures (higher f numbers), normally about f/11 I've heard.
05/07/2007 02:15:55 PM · #11
Depth of Field
05/07/2007 02:16:48 PM · #12
I understand some of these comments... I know that 29 is supposed to show you a greater depth of field because it's a small aperture. Why does a telephoto lens make a difference when dealing with depth of field?

By the way - these are photos of the Ridgeway path which is not far from Oxford, UK. It sure is beautiful this time of year with the carpet of bluebells.
05/07/2007 02:21:18 PM · #13
found a nice explanation after reading this thread

//www.cambridgeincolour.com/tutorials/DOF-calculator.htm
05/07/2007 02:23:02 PM · #14
Originally posted by noisemaker:

Depth of Field

If you have time i recommend reading this, they explain TONS on here..... i love you wikipedia
05/07/2007 02:26:25 PM · #15
Originally posted by Konador:

The DoF will decrease when the focus is nearer to the lens. So the difference is much more obvious on close-ups :)

Konodor is right.

It also is true that the higher the aperture number, the greater the depth of field you will achieve at ANY particular focal distance. That means if you are concerned about greater or shallower DOF, and that is almost always the case for a particulat focal distance, then you need a higher aperature number for greater DOF and a lower number for shallower DOF.

The most disappointing thing about "modern" lenses is that, at least for some of them, they no longer have DOF markings on the lens itself like they did in older lenses that assisted photographers to set aperature correctly. Furthermore, the older cameras had pentaprism focusing that assisted in proper focus which is prerequisite to proper setting aperture for DOF where with "modern" lenses autofocus is assumed to be right, even when it isn't and that has an even more negative impact on our ability to get DOF right.

Until these two features come back, and they will, photographers will continue to have problems both with focusing and with proper DOF in their compositions when using dSLRs.
05/07/2007 02:33:27 PM · #16
Originally posted by stdavidson:

Originally posted by Konador:

The DoF will decrease when the focus is nearer to the lens. So the difference is much more obvious on close-ups :)

Konodor is right.

It also is true that the higher the aperture number, the greater the depth of field you will achieve at ANY particular focal distance. That means if you are concerned about greater or shallower DOF, and that is almost always the case for a particulat focal distance, then you need a higher aperature number for greater DOF and a lower number for shallower DOF.

The most disappointing thing about "modern" lenses is that, at least for some of them, they no longer have DOF markings on the lens itself like they did in older lenses that assisted photographers to set aperature correctly. Furthermore, the older cameras had pentaprism focusing that assisted in proper focus which is prerequisite to proper setting aperture for DOF where with "modern" lenses autofocus is assumed to be right, even when it isn't and that has an even more negative impact on our ability to get DOF right.

Until these two features come back, and they will, photographers will continue to have problems both with focusing and with proper DOF in their compositions when using dSLRs.


If you focus incorrectly then, you can lose DOF by accident? Without this kind of help that you mentioned, is there a way to learn to focus at the right distance?
05/07/2007 02:44:07 PM · #17
Originally posted by tosk:

If you focus incorrectly then, you can lose DOF by accident? Without this kind of help that you mentioned, is there a way to learn to focus at the right distance?


Since the DoF is a range in space, if you focus incorrectly for a given DoF, you will end up with area in front of or behind your subject that wasn't intended to be in focus.
05/07/2007 03:02:53 PM · #18
Originally posted by tosk:

If you focus incorrectly then, you can lose DOF by accident? Without this kind of help that you mentioned, is there a way to learn to focus at the right distance?

Obviously, you intuitively understand the problem.

DOF, at a given focal point, is the distance that things are "in focus" in front or behind that point. That distance increases with higher f/stop numbers regardless of the focal length of your lense. That is what you want to always keep clearly in mind.

The short answer is yes, it will work sometimes if the DOF can be made wide enough by aperture settings to cover both objects after the autofocus decides what should be in focus, but NOT all the time and that is the problem.

Lets say, for example, you want two objects at various distances from you to be in sharp focus. The best way to achieve that is to focus intermediate between the two and allow DOF controlled through aperture settings to control their sharpness. Autofocus lenses probably will not allow you to do that because they always decide what should and should not be sharply focused and that may not be between the two objects of interest that you, the photographer, wants.

But until you have accurate control of focus you will never have accurate control of DOF.

05/07/2007 03:04:50 PM · #19
I've been reading the suggested articles - thanks. I think I'm still not understanding something. This excellent photo ' . substr('//images.dpchallenge.com/images_challenge/315/thumb/153329.jpg', strrpos('//images.dpchallenge.com/images_challenge/315/thumb/153329.jpg', '/') + 1) . ' :) seems sharp both in the foreground and background, even though the aperture is only 8. Obviously this was the correct choice, but why isn't the aperture 22 for a landscape type shot?
05/07/2007 03:14:28 PM · #20
Originally posted by Konador:

Also, lenses are generally sharper at smaller/midrange apertures (higher f numbers), normally about f/11 I've heard.


I think it is about f8-11. Some lenses are ok at f16. From there all lenses start to get soft.
05/07/2007 03:14:35 PM · #21
Originally posted by tosk:

I've been reading the suggested articles - thanks. I think I'm still not understanding something. This excellent photo ' . substr('//images.dpchallenge.com/images_challenge/315/thumb/153329.jpg', strrpos('//images.dpchallenge.com/images_challenge/315/thumb/153329.jpg', '/') + 1) . ' :) seems sharp both in the foreground and background, even though the aperture is only 8. Obviously this was the correct choice, but why isn't the aperture 22 for a landscape type shot?

because it was shot wide angle i assume, f/8 isnt that shallow though, and also the foreground itself isnt that close to the lens so you dont see it much, but sure its all relativly sharp the foreground is sharper than the background a bit
05/07/2007 03:15:53 PM · #22
Originally posted by Nikolai1024:

Originally posted by Konador:

Also, lenses are generally sharper at smaller/midrange apertures (higher f numbers), normally about f/11 I've heard.


I think it is about f8-11. Some lenses are ok at f16. From there all lenses start to get soft.

on most lenses anything over f/11 or f/14 starts to decreasein sharpness, just like ifyou stop up a few from your largest aperture(2.8 or whatever your lens is capable of) will improve in sharpness aswell
05/07/2007 03:20:52 PM · #23
Originally posted by tosk:

I've been reading the suggested articles - thanks. I think I'm still not understanding something. This excellent photo ' . substr('//images.dpchallenge.com/images_challenge/315/thumb/153329.jpg', strrpos('//images.dpchallenge.com/images_challenge/315/thumb/153329.jpg', '/') + 1) . ' :) seems sharp both in the foreground and background, even though the aperture is only 8. Obviously this was the correct choice, but why isn't the aperture 22 for a landscape type shot?

I'm embarrased that you pick one of my own images for your question...

But the short answer is simple; f/8 was the minimum f/stop necessary to have the DOF necessary for the whole scene to be in focus. In reality that was a guess because I used a point and shoot camera capable of manual settings for that picture. I specifically composed the image with foreground objects far enough away that I knew that f/8 would work all the way out to infinity from there. I really could not see that through the lens.

I have a Canon D10 dSLR now with older lenses that have the DOF indicators that I mentioned earlier that I can use to get "proper" DOF based on focus and f/stop.

In the following image the grasses are less than 4 feet from the camera yet the bridge is effectively at infinity from the lense, but BOTH are in focus. I was able to achive that by using the DOF markings of the older lens:
//www.pbase.com/azleader/image/78237044

Note:
Btw, I really don't like that this is my highest rated image and wish I could replace it. Lighting-wise the horizon sucks!

Message edited by author 2007-05-07 15:26:12.
05/07/2007 03:21:31 PM · #24
Well, you had a good idea, to work with practice pictures. Great choice, it´s the best school!

If you want to really view any diference in DoF you will need to respect some rules and concepts:

1) DoF varies across the lenses/camera setup, each one has best and worst apertures to maximum sharpness. This is due difraction. Then to a Rebel XT sensor size the apertule limit is like f16. More than this will not increse shapness as you would expect, rather than, in some cases it can worst the things. Then, due so, you haven´t saw so much diference in sharpness in your pictures.
2) Respect, in test pictures the rule of same view. This improve the comparative features os the test. To do this, put you camera on a place that has no movement (a tripod is recomended), use the self-timer to shoot and only vary one parameter at time. Ex: the aperture.

In "focus" is a part of picture that is fitted in the limits of Near and Far focus points. This region is called DoF. It varies by Focal Length, Subject distance and lens Aperture. To only vary the apperture you need to keep al other variables at same values.

To conclude. If you want to focus to better overall focus (large or depth DoF) you will need to ensure that the focus point is 1/3 way of the longest point you want in focus (DoF accptable area). This can be striving at fist time. Then a studio setup, indoor pictures can improve your feeling and give you more results in the begin.
Remmeber that changing the Focal Length (zoom or lens changes) will modify the Near / Far focus points.
05/07/2007 03:26:25 PM · #25
If all lenses are soft after f11 or f14, why do they offer so many apertures after that point, if no one (who knows what they're doing) would use them?
Pages:  
Current Server Time: 10/21/2019 09:17:48 PM

Please log in or register to post to the forums.


Home - Challenges - Community - League - Photos - Cameras - Lenses - Learn - Prints! - Help - Terms of Use - Privacy - Top ^
DPChallenge, and website content and design, Copyright © 2001-2019 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Proudly hosted by Sargasso Networks. Current Server Time: 10/21/2019 09:17:48 PM EDT.