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DPChallenge Forums >> Tips, Tricks, and Q&A >> Larger depth of field with Canon Rebel 18-55
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 06/19/2009 11:21:31 PM · #1
I am not a fan of shallow DOF, and love to shoot flowers. I love the new camera, but we're having a bit of a personality conflict. It wants to have such a narrow DOF that the tips of the flower petals are in focus, but the center of the flower is not. I've been using the A-DEP setting, and trying to get the aperture into the higher numbers, but it does not always seem to help. My eyesight is so poor, I'm tired of thinking I've got good, crisp, nicely focused shots only to have a mostly blurry shot when I download them.
Any hints / tips of what makes for a shallow DOF or for a deeper DOF? I know it is a rookie question, but it has been a long time since I shot film, and this camera has a MUCH shallower DOF than my AE-1 ever thought of having.
06/19/2009 11:24:54 PM · #2
Originally posted by dtremain:
I am not a fan of shallow DOF, and love to shoot flowers. I love the new camera, but we're having a bit of a personality conflict. It wants to have such a narrow DOF that the tips of the flower petals are in focus, but the center of the flower is not. I've been using the A-DEP setting, and trying to get the aperture into the higher numbers, but it does not always seem to help. My eyesight is so poor, I'm tired of thinking I've got good, crisp, nicely focused shots only to have a mostly blurry shot when I download them.
Any hints / tips of what makes for a shallow DOF or for a deeper DOF? I know it is a rookie question, but it has been a long time since I shot film, and this camera has a MUCH shallower DOF than my AE-1 ever thought of having.


Perhaps I'm not reading right, or you are confused about shallower and deeper depth of field. But.

To get a shallower depth of field(less in focus) you need to open the lens as far as it will go smallest number it will go to, get as close as it will focus, and still get a reasonable shutter speed using your iso. To get deeper depth of field stop the lens down(bigger number).

Matt
 06/19/2009 11:58:48 PM · #3
I think he does want a deeper DOF. I had the same issue yesterday morning. The DOF was so narrow that a relatively flat flower was not all in focus. Things that contribute to a wide DOF (more in focus)

-Narrow aperture (higher F-stop)
-Short focal length (Less zoom)
-Distance from subject (further away gives wider DOF)

Much of which in counter to taking closeup shots of flowers. The kit lens really isn't the best thing for this. Let me dredge up the one I shot yesterday...
 06/20/2009 12:07:47 AM · #4
Here's the thing of it:

1. DOF is a function of the physical size (diameter) of the aperture, not the f/stop. The smaller the aperture, physically, the greater (deeper) is the DOF. The larger the aperture, physically, the shallower the DOF becomes.

2. The f/stop is a ratio between the diameter of the aperture and the focal length of the lens; a 25mm aperture is f/2 on a 50mm lens, f/4 on a 100mm lens, and f/8 on a 200mm lens; so f/2 on a 50mm lens has the same DOF, when focused at the same distance, as does f/8 on a 200mm lens, more or less. There are other factors, but this is the main one.

3. If you are used to P&S cameras, they have VERY small sensors and, consequently, their lenses are of very short focal length and the physical apertures at a given f/stop are correspondingly small. Net result: surprisingly deep DOF on close-up shots.

4. With your Rebel, on the other hand, the lenses for a given angular coverage, on its much larger sensor, are substantially longer, and thus the DOF at a given f/stop is considerably shallower. It's the price we pay for larger sensors and better detail.

The solution is to use a tripod, shoot in calm conditions, and stop down further, basically. Or make a virtue out of the shallow DOF by placing it exactly where you need it to be. It helps a whole LOT if you carefully align the plane of the sensor with the primary plane of the blossom, as well.

R.
 06/20/2009 12:30:02 AM · #5

This was with my 28-300 zoom.
F 6.3
1/400th second
ISO 400
300mm focal length at about 1 foot from the flower.

I think I did fairly well for a lens that isn't meant for this. I was concentrating on trying to get the veins in focus, but like yourself, the DOF was very shallow. There was also a breeze blowing, so I had to maintain a high shutter speed. You can see the tips of the petals are slightly OOF compared to the rest.

I think if this is the kind of photos you like to do, then perhaps a real macro lens is in your future.
06/20/2009 08:30:46 AM · #6
Bear_Music - that was a great explanation! It definitely fit with my experience, and explains part of my confusion with the Rebel - I was trying different things with the zoom, and that was confusing me on the ap #. Also, you are right on with the prosumer vs. rebel - my Fuji S700 had a fairly deep DOF, and flower shots were a no-brainer with the problem being getting the ground out of the in-focus area.
Yo_Spiff - thanks for the image and comments.
Everyone else - thanks a lot for the feedback. At least I have some idea of what to do to make things better.
06/20/2009 08:36:49 AM · #7
Originally posted by Yo_Spiff:

I think if this is the kind of photos you like to do, then perhaps a real macro lens is in your future.


I'm not sure if you're implying that a "real" macro lens will help with the DOF situation, but just to clarify things, it won't. There are many advantages to these lenses, but added DOF isn't one of them :-)

R/
 06/20/2009 10:28:43 AM · #8
Purely rumor and conjecture on my part since I don't know anything, but...I heard that using a longer lens and extending it all the way from further back gives a larger field of focus. But like I said I could be wrong (and probably are). I'm still learning all this stuff myself.
 06/20/2009 10:35:42 AM · #9
Originally posted by NathanW:
Purely rumor and conjecture on my part since I don't know anything, but...I heard that using a longer lens and extending it all the way from further back gives a larger field of focus. But like I said I could be wrong (and probably are). I'm still learning all this stuff myself.


This was shot with a 28-135 at 130mm.
 06/20/2009 11:36:35 AM · #10
Originally posted by NathanW:
Purely rumor and conjecture on my part since I don't know anything, but...I heard that using a longer lens and extending it all the way from further back gives a larger field of focus. But like I said I could be wrong (and probably are). I'm still learning all this stuff myself.


Actually, no. At very close focus (macro) distances, all that really matters is the magnification. If I have, say, 1:4 magnification (image on sensor is 1/4 the size of the real object) then my DoF will be the same regardless of the focal length used (assuming aperture setting is the same).

Keep in mind that many commonly published formulas for DoF are not intended for macro distances. They are simplified equations that ignore things that matter only at very close focus.
 06/20/2009 11:42:41 AM · #11
Originally posted by NathanW:
Purely rumor and conjecture on my part since I don't know anything, but...I heard that using a longer lens and extending it all the way from further back gives a larger field of focus. But like I said I could be wrong (and probably are). I'm still learning all this stuff myself.


For a given reproduction ratio (1:1, 2:1, whatever) at a given aperture (physical aperture, not f/stop) DOF is the same regardless of the focal length of the lens. In other words, a 50mm macro lens, focused at 1:1, at f/4 will have the same DOF as a 100mm macro lens, focused at 1:1, at f/8... What this means, effectively, is that to get the same DOF from the longer macro lens you need to stop down 2 stops, which means you are working with a slower shutter speed.

R.

I see Kirbic and I crossed on this one...

Message edited by author 2009-06-20 11:43:28.
 06/20/2009 01:56:10 PM · #12
Originally posted by Bear_Music:
I'm not sure if you're implying that a "real" macro lens will help with the DOF situation, but just to clarify things, it won't. There are many advantages to these lenses, but added DOF isn't one of them :-)

No, I didn't mean to imply it would help wit the DOF issue, but it will help him get closer. The 18-55 kit lens, as well as my 28-300, have a minimum focus distance of about 12". Since my Tammy goes to 300mm I can get closer with it, but for tiny items, it's still not always enough.
 06/20/2009 05:39:36 PM · #13
Originally posted by Yo_Spiff:
Originally posted by Bear_Music:
I'm not sure if you're implying that a "real" macro lens will help with the DOF situation, but just to clarify things, it won't. There are many advantages to these lenses, but added DOF isn't one of them :-)

No, I didn't mean to imply it would help wit the DOF issue, but it will help him get closer. The 18-55 kit lens, as well as my 28-300, have a minimum focus distance of about 12". Since my Tammy goes to 300mm I can get closer with it, but for tiny items, it's still not always enough.


Gotcha.

R.
 06/20/2009 09:40:16 PM · #14
Just a couple of comments--

The minumum focus distance is measured from the plane of the sensor, not the end of the lens. You may see a circle with a line through it on your camera body. This is the plane of the lens. So a 12 inch minimum focal distance may be only six or eight inches from the end of your lens.

You can stop down to get a wider DOF, but at some point diffraction effects will cause your images to get blurry again. The rule of thumb is that f/13 is about the narrowest aperture you should use on a 1.6 crop camera.

Message edited by author 2009-06-20 21:40:28.
 06/20/2009 10:13:57 PM · #15
Originally posted by hankk:
The rule of thumb is that f/13 is about the narrowest aperture you should use on a 1.6 crop camera.

Probably a good rule of thumb. For normal shooting, I try to keep it around F7.1 when conditions allow. Higher or lower as needed.
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