Why a Poor Depth of Field?

[Michele0513]

Hello, and thanks in advance to any who answer

I have the Canon Rebel T3i 1100D with the 18-55mm kit lens, and for some reason am getting a really shallow depth of field in all my pictures. I have taken close to 1000 shots in every mode from ADEP to full auto in more "test" situations than would be practical to list, but the photos are still bad.
Here's one I shot this morning, and yes I know that it's not a great picture in terms of composition and all. I just wanted to show a quick example of the D.O.F. issue.




* The pup's head is approximately 3" wide, the ear-to-ear distance maybe 6".
* Distance to subject was around 2.5' (maybe a little more)
* Taken in Aperature Priority mode with a setting of 1/16
* Focal Length 37mm
According to the Depth of Field calculator I use, I should have been able to get 6.2" of focused depth at only 2 foot away (it showed a near/far measurement of 1'9.3"/2'3.5"), so it would be a little deeper for the extra inches away the pup was at. But as you see, barely the 3" head width is in focus, and that's spotty.

A screen shot of Canon's DPP software screen shows the active focal points in red, and most (though not all) of what's within those points is pretty much in focus, but *where* is the 6"+ depth of field?

 

[Guidenet]

Michele0513 wrote:

The ear farthest away from the camera gets blurry pretty fast, as does the tip closest. Considering my focal points and the DOF I was supposedly able to get at that f-stop and subject distance, it didn't make sense to me. I've posted another photo further down the thread that illustrates the same situation with completely different settings and shooting scenario.No matter what, I'm getting a maximum of about 3" DOF at best.

I guess my big question in all of this is... is it the settings I'm using, are these normal results for DSLR cameras (my only experience before this was in the 80s with a Sekor Mamiya) or is there something wrong with the camera? I need to know so I can return it under warranty if so.

Just for the heck of it, adjust the aperture and stare down and make sure the aperture changes a little with each full stop. If you have one, try another lens.

 

[AnthonyL]

Michele0513 wrote:

Hello, and thanks in advance to any who answer

Firstly well done for giving all the information and an example which is often missing.

I have the Canon Rebel T3i 1100D with the 18-55mm kit lens, and for some reason am getting a really shallow depth of field in all my pictures. I have taken close to 1000 shots in every mode from ADEP to full auto in more "test" situations than would be practical to list, but the photos are still bad.
Here's one I shot this morning, and yes I know that it's not a great picture in terms of composition and all. I just wanted to show a quick example of the D.O.F. issue.



* The pup's head is approximately 3" wide, the ear-to-ear distance maybe 6".
* Distance to subject was around 2.5' (maybe a little more)
* Taken in Aperature Priority mode with a setting of 1/16
* Focal Length 37mm
According to the Depth of Field calculator I use, I should have been able to get 6.2" of focused depth at only 2 foot away (it showed a near/far measurement of 1'9.3"/2'3.5"), so it would be a little deeper for the extra inches away the pup was at. But as you see, barely the 3" head width is in focus, and that's spotty.
A screen shot of Canon's DPP software screen shows the active focal points in red, and most (though not all) of what's within those points is pretty much in focus, but *where* is the 6"+ depth of field?

All active points is generally not considered the best. Most Canon shooters would select centre focus only and make sure that focus was on the (nearest) eye. All points can tend to focus on the nearest point it hits. It can't focus on all 3 points.

Canon DPP will only shows the points that were active. If you move the camera after you have locked focus (half-pressed) the focus points will simply show over the new position even if you are not focused on that, ie if you prepared for this photo then moved the camera over the hose pipes it would look as if the focus points was over the hose pipes.

Can you confirm that you have the 18-55 IS and not just the 18-55, ie you have an Image Stabilisation switch?

I wonder if the ears were moving a bit. 1/50th is a bit slow for live objects. Also f1/16 can start to introduce softness due to diffraction though that doesn't appear to be your issue on my less than optimum screen.

Right after I took that shot I set it down on the deck (for added stability) and took a shot of the yard with auto focus. DPP shows that the bottom 6 focal points were lit/working, but not one single part of the picture is really in focus, even when it's not blown up.

Try more photos with centre focus only.

So... is it the camera, the lens, or me? I really need to be able to shoot tabletop still lifes with at least a couple of inches depth of field that would stand up under scrutiny being blown up to 100%.

You would never look at prints that closely.

And please don't say "Well buy X mega expensive setup." It took me 4 years to save up enough for this one, so I need to learn to work with what I have. But at this point, I'm not getting good results... even for snapshots I probably wouldn't be able to get a decent photo of 3 grandbabies in a sandbox without blurring all but one of them's noses! What am I doing wrong?

You should be able to quite quite adequate photos with that lens (providing it is IS). The lens is at it sharpest at around f/8 so you might want to try some photos with centre focus, f/8, at a lower ISO and a faster shutter speed, and change your position to get the DOF you want and see what you get.

If you are still struggling you might need to try some focus tests using eg

http://www.dphotojournal.com/download-free-focus-test-chart/

And do the newspaper test (something with good print quality). You need to make sure you are completely square and perfectly still (tripod + remote or timer).

 

[Michele0513]

Thank you, this is all very helpful!


For the focus points, I used multiple because I thought that maybe by having more than one it would help increase the DOF. You know... if it sharpens out a certain distance from one focal point, then maybe having multiples would do an even better job? I didn't know that a single would be better. I've never adjusted the AF tracking, so yes it's probably is locking that too.


I did the paper test you described and it seems like there is no serious problem with the camera (a major relief!) The AF shot was reasonably clear, with each of the "surrounding" shots blurring just slightly more for every half inch away from the original point the camera was moved. Wasn't even all that noticeable for about the first inch. That being said, this lens is definitely a little softer than I would prefer overall. Not exactly blurry, just... soft. Is there anything I can do settings-wise to compensate for that a bit until I can save up for a better one? Along with what you've already mentioned, that is.

 

[Michele0513]

Well shoot, I can't see it changing one bit! Just to make sure I wasn't supposed to hold down any buttons or anything: all I did was put it in Manual and then use the menu to click/scroll across the aperture readings (while staring "down the barrel" of course). Was there anything else I should have done?

If not, then I guess the EXIF data is showing that I'm shooting at different f-stops, but the lens isn't actually doing it. Any fix for that?

 

[Michele0513]

I think Guidenet may have found the problem: it doesn't appear as if the lens is working right.

 

[Michele0513]

Thanks IainD

 

[Michele0513]

Ack! I was so close with that one! LOL

 

[iancrowe]

Nobody else seem to have so I plugged Michele's numbers into DoFMaster and guess what?

Michele you are seeing exactly what you should see assuming the camera focused on the near cheek of your dog (centre auto-focus point as shown in your second image).

At 2.5ft (30inches) with a T3 camera, a focal length of 37mm an an aperture of f/16 this gives a depth of field of 9.92" which is divided 4.16" in front of the focus point and 5.76" behind.

With these figures I would expect to see the back of the rear ear going out of focus.

If you want more depth of field shorten your focal length and get in closer.

If you zoom down to 20mm and close in to 20inches from your subject your depth of field at f/16 goes up to 17.2", 5.4" in front and 11.8" behind. This would work much better for a focus point on the near cheek.

This is the sort of thing which really bites when you consider macro with a 60mm or 100mm and a distance to the object of 8-10" (I'll leave it to the reader to run the numbers and discover what real shallow depth of field is).

Can I suggest you spend some time plugging numbers from previous images into DoFMaster to get some feel as to what is happening.

By the way. The good news is there is nothing wrong with your camera.

Hope this helps

Ian

 

[IainD]

Don't worry, Michael! It will all work. remember to have fun!

I just read a book by a wedding photographer and he says he just sets his aperture on f6.3 and adjusts ISO and shutter time! That makes it easy, I guess but is no good for learning DOF.

Take lots of shots and compare. See what works!

IainD

 

[Michele0513]

I'm so glad I posted to this forum. I think I've learned as much here in just a few hours as I have in 2 months of trial and error!


I use manual focusing for true still shots (which this was not) but the focal points threw me off with this one and some others for sure. I never even thought of how they "fixed" once the button was pressed... very good to know!


Yes, it's definitely the 18-55 IS and not just the 18-55, and I only turn it off when I'm working with a tripod. For this shot the IS was on, and you're probably right about her ears moving. It's rare for her to sit still long enough to get the photo at all (LOL).


Center focus. Will do


I did do the newspaper test as suggested earlier and the results were ok. The kit lens isn't the sharpest in the world, but enough so that I can live with it, and the AF shot and the few surrounding it in the test were the clearest, so no big problem with the camera. However, somebody else had me look down the lens and see if the aperture thingy (sorry, I don't know the techie term) was moving when I changed settings, and I didn't notice any movement. I'm just waiting to see if I should have been holding down any buttons or anything when I did that test. If not, then it appears that my lens is stuck on f/whatever it is

 

[AnthonyL]

iancrowe wrote:

Can I suggest you spend some time plugging numbers from previous images into DoFMaster to get some feel as to what is happening.

The OP had already run (correctly) the numbers, see the first post.

 

[DJF77]

The blur you encounterd is almost certainly motion blur from having a shutter speed that is to low. If you want to use F16 in anything other than bright sunlight then you'll certainly need to be bumping up the iso to maintain an adequate shutter speed.

As for depth of field, you could put your camera on a tripid, focus on an object a few feet in front of you and take numerous shots at incremental stops (f4, f5.6, f8 etc upto max aperture) this atleast will give you an idea of the depth of field of a given aperture at that focas point. If you keep your iso set at base aperture while doing this you'll also notice the shutter speed declining in incremental stops - you would have to perform this in Aperture priority mode (Av)

 

[happysnapper64]

Michele0513 wrote:

I'm so glad I posted to this forum. I think I've learned as much here in just a few hours as I have in 2 months of trial and error!

I use manual focusing for true still shots (which this was not) but the focal points threw me off with this one and some others for sure. I never even thought of how they "fixed" once the button was pressed... very good to know!

Yes, it's definitely the 18-55 IS and not just the 18-55, and I only turn it off when I'm working with a tripod. For this shot the IS was on, and you're probably right about her ears moving. It's rare for her to sit still long enough to get the photo at all (LOL).

Center focus. Will do

I did do the newspaper test as suggested earlier and the results were ok. The kit lens isn't the sharpest in the world, but enough so that I can live with it, and the AF shot and the few surrounding it in the test were the clearest, so no big problem with the camera. However, somebody else had me look down the lens and see if the aperture thingy (sorry, I don't know the techie term) was moving when I changed settings, and I didn't notice any movement. I'm just waiting to see if I should have been holding down any buttons or anything when I did that test. If not, then it appears that my lens is stuck on f/whatever it is

Hi Michele, Apparently the aperture of the lens stays at its max till you press the shutter button. So if the lens has a max [widest] aperture of, say, f/5.6, & you set it to,say, f/16, the aperture will only change to f/16 after you have pressed the shutter button, so looking down the lens while you change the aperture, you will not see any movement. I hope this is correct, as I was unaware of this till I read on a thread here a few weeks ago. :-D [smilley only applies if I am correct!!]

 

[Alleg1]

Michele0513 wrote:

Thank you, this is all very helpful!

For the focus points, I used multiple because I thought that maybe by having more than one it would help increase the DOF. You know... if it sharpens out a certain distance from one focal point, then maybe having multiples would do an even better job? I didn't know that a single would be better. I've never adjusted the AF tracking, so yes it's probably is locking that too.

I did the paper test you described and it seems like there is no serious problem with the camera (a major relief!) The AF shot was reasonably clear, with each of the "surrounding" shots blurring just slightly more for every half inch away from the original point the camera was moved. Wasn't even all that noticeable for about the first inch. That being said, this lens is definitely a little softer than I would prefer overall. Not exactly blurry, just... soft. Is there anything I can do settings-wise to compensate for that a bit until I can save up for a better one? Along with what you've already mentioned, that is.

Just to confirm the issue of focus points, I would set to the centre point which in some cameras is more sensitive than the others and gives you more control.

Using multiple points can lead to less accuracy for this kind of shot. They tend to select the closest part of the subject. They are more useful for tracking moving objects.

As mentioned previosly the convention is to aim at the eye, but you might try aiming at different parts of the subject to get the best result.

 

[Sante Patate]

Michele0513 wrote:

I did the paper test you described and it seems like there is no serious problem with the camera (a major relief!) The AF shot was reasonably clear, with each of the "surrounding" shots blurring just slightly more for every half inch away from the original point the camera was moved. Wasn't even all that noticeable for about the first inch. That being said, this lens is definitely a little softer than I would prefer overall. Not exactly blurry, just... soft. Is there anything I can do settings-wise to compensate for that a bit until I can save up for a better one?

Are you looking at JPEGs? If so, the camera applies a sharpening algorithm to the image before you see it, and dSLRs allow you to change the amount of sharpening from the default, which is often quite low. So, my first step would be to turn up sharpening - or shoot RAW and sharpen each shot in the computer (I believe Canon gives you a free RAW converter with its cameras, but I don't know what it can do).

 

[Michele0513]

Ooh, yes I am viewing jpegs and I didn't know I could change the amount of sharpening in the camera. I don't think I'm skilled enough to deal with RAW yet, so I'll wade through the manual a bit and see how I can change that setting for now.

Thanks

 

[AnthonyL]

Michele0513 wrote:

Ooh, yes I am viewing jpegs and I didn't know I could change the amount of sharpening in the camera. I don't think I'm skilled enough to deal with RAW yet, so I'll wade through the manual a bit and see how I can change that setting for now.

Sharpness, at least on the 450d/Xsi, is one of the settings within Picture style. You can have several picture styles, and choose the one at the time for the shot you want. The 18-55 does need some sharpening applied. You are already using DPP. It's great for people who aren't skilled enough to get the JPG's right first time At worst you just convert what is already there. Just try a couple. Easy enough to set back, or set for RAW+JPG.

 

[AnthonyL]

Michele0513 wrote:

However, somebody else had me look down the lens and see if the aperture thingy (sorry, I don't know the techie term) was moving when I changed settings, and I didn't notice any movement. I'm just waiting to see if I should have been holding down any buttons or anything when I did that test. If not, then it appears that my lens is stuck on f/whatever it is

On the 450d/Xsi there is a button next to where the lens attaches to the body that gives DOF preview by closing the aperture to that dialled in. The rest of the time the aperture is wide open.

Bed time reading - read your manual from start to finish. There's an awful lot of good stuff and even if you don't know what to do with it now at least you will know it's there for when you do need it.

 

[happysnapper64]

AnthonyL wrote:

Michele0513 wrote:

However, somebody else had me look down the lens and see if the aperture thingy (sorry, I don't know the techie term) was moving when I changed settings, and I didn't notice any movement. I'm just waiting to see if I should have been holding down any buttons or anything when I did that test. If not, then it appears that my lens is stuck on f/whatever it is

On the 450d/Xsi there is a button next to where the lens attaches to the body that gives DOF preview by closing the aperture to that dialled in. The rest of the time the aperture is wide open.

Bed time reading - read your manual from start to finish. There's an awful lot of good stuff and even if you don't know what to do with it now at least you will know it's there for when you do need it.

Anthony, I have been meaning to ask what the DOF button was for, I mean apart from the obvious, I used to press it & didn't notice anything happening. I might have dodgy eyes :-D, but looking through the VF or on the LCD screen, I find it Difficult to notice any change. Maybe now I know what I am looking for, it should help. Thank's

 

[Michele0513]

I have read the manual, both when I got the camera in December and then in spots as needed since then. There is no such preview button on the 1100D unless I've REALLY missed something.