DOF questions and other help.. :)

Jthmeffy

I am extremely new to the photography world - Just got my first camera ever (40D).

I really have no idea what I am doing (slowly learning and all), but have restricted myself to mostly using manual settings for my shots. I think I have an understanding of shutter speed, I kinda get aperture, and I kinda get color temp (basically to make your whites white, correct?).. but I dont really get metering.. help?

Also, I am confused on Depth of Field.. For this pic, I used my 40D, the packaged 28-135mm lense, and my flash. 1/100th shutter, f/3.5, ISO 400, and my lense was at 28mm. I thought the background would be a little more out of focus.. were all of the background objects too close? Or could someone just help me out with shutter speed, aperture, metering, color temp... etc.. LOL, the manual doesnt help much at all beyond telling me how to set the values - As you can see, I just dont know much at all.

gregneil

Your depth of field is dependent on lens length, aperture, and the distance to your subject. I don't think I could explain it well from a technical standpoint, although I know others here can. Here's a couple links that might help:

Bob Atkins
Wikipedia

In your shot, the background isn't very blurry because you're using a pretty wide angle, and you're a decent distance from the subject. You should play around with the depth of field calculator on Bob Atkin's website (or this one) to get a feel for how DOF is affected by different criteria.

Generally, a wider lens won't give you that "blurred" background look, even with a wide-open aperture, unless you're super super close to the subject. It's much easier to create that look when you're "zoomed in".

Anyway, I hope that's helpful. Keep playing around and it'll start to make sense...

Nikolai

It's your WA (wide angle) that is the culprit.
According to DOFmaster online DOF calculator, you got the following values:

Assuming Subject distance 10 ft
DOF Near limit 7.93 ft
DOF Far limit 13.5 ft
DOF Total 5.6 ft
In front of subject 2.07 ft (37%)
Behind subject 3.53 ft (63%)

As you can see, not paper-thin DOF...
Step back and increase the focal length...

Also, make sure that camera doesn't switch to something else automatically when the flash is popped/activated. Mine likes f/4.0 at 1/60s ..

HTH

pathfinder

You must be shooting your 40D in Program Mode when using flash then, Nikolai. Try using flash with your camera in Manual Mode and see if you don't like that better. You won't have to put up with 1/60th of a second!

Usually you expect a shallow DOF at a wide aperture like f3.5, but wide angle lenses create the illusion of lots of depth of field, unless you shoot from VERY close to your subject. APS sensor cameras have more DOF than a full frame 35mm camera also.

Jthmeffy

I am using a normal angle zoom lense, but I was up close to the bike and did not zoom at all

pathfinder

You said you were shooting at 28mm. Those of us who shoot full frame think of 28mm as wide. On a 40D with its 1.6 mag factor, 28 x 1.6 = 44.8 which is close to 50 mm, so I guess it is a ~ "normal" lens.

The background isn't really tack sharp either, but just very cluttered.

Jthmeffy

pathfinder wrote:

You said you were shooting at 28mm. Those of us who shoot full frame think of 28mm as wide. On a 40D with its 1.6 mag factor, 28 x 1.6 = 44.8 which is close to 50 mm, so I guess it is a ~ "normal" lens.

The background isn't really tack sharp either, but just very cluttered.

mag factor? *cries* ignorance not bliss in this case

Jthmeffy

Ok, I just took some pictures of a battery.. All were at 135mm and ISO 400.

1/250s and f/30



1/250s and f/5.6



1/30s and f/5.6



I think I am starting to get the idea..

pathfinder

Whether a lens is a telephoto or a wide angle, is NOT intrinsically a function of its focal length, but of the size of the desired image circle at the film plane. A lens for an 8 x 10 inch view camera may be a wide angle, but the same focal length lens on on point an shoot ( with a tiny sensor ) may be a strong telephoto.

The 1.6 mag factor is a way to estimate the angle of view of a typical lens for a full frame 35mm camera on a crop sensored body like a 40D or a D70.

A 80 mm lens on a full frame "35mm film" camera is the equivalent of a 50mm lens on an APS crop sensored body like a 40D. (50mm = 80mm/ 1.6) .

Eg; a 50mm lens on a crop body looks the same through the viewfinder as an 80mm lens would on a full frame body. 50mm x 1.6 = 80 mm

Crop sensor bodies need smaller image circles than full fame, which are smaller than a 5x 7 in or 8 x 10 in view cameras. The lens on a camera system must create a 'real' image in the image plane large enough to cover the full area of the emulsion or sensor. Obviously, a point and shoot with a sensor 8 x 11 millimeters has a much smaller image circle required, than an 11 x 14 inch view camera.


When discussing DOF, the two major things that affect it are distance to the subject and aperture. People always say that wide angle lenses have more DOF than telephotos, but the real truth is that actual focal length has a very minimal effect of DOF if the subjects size at the image plane is held constant.

As you noticed from your other images, larger apertures, smaller f numbers , have shallowerer DOF. Getting closer to the subject minimizes DOF also. This becomes very apparent when learning to shoot macro. All of a sudden, your DOF is measured in fractions of milllimeters.

Slinky0390

Jthmeffy wrote:

mag factor? *cries* ignorance not bliss in this case

You're in the same boat as me with your 40D as I am with my 30D. They aren't full frame cameras (full frame = 35mm). the 40D has a crop, or mag, or magnification factor of 1.6. Basically if you use a 50mm lens on your 40D you need to multiply 50 by 1.6 and thats the focal length you are really seeing when you take a picture. So on your camera, a 50mm lens would take pictures at 80mm.

Jthmeffy

ah.. that makes sense.. thanks

Are there any online sources that would be helpful to me with my adventure into this new hobby? I am more than a bit out of my element, but I do feel that I am learning a lot and getting better.. I just want to get down all of the features and settings my camera can use and be able to utilize them all before I start to really work on my shooting techniques and theories (rule of thirds, etc).. if that makes ANY sense

Also, I plan on purchasing this book in the next couple of days.. does anyone know anything about this author? Would this be a good buy?

Jthmeffy

Slinky0390 wrote:

You're in the same boat as me with your 40D as I am with my 30D. They aren't full frame cameras (full frame = 35mm). the 40D has a crop, or mag, or magnification factor of 1.6. Basically if you use a 50mm lens on your 40D you need to multiply 50 by 1.6 and thats the focal length you are really seeing when you take a picture. So on your camera, a 50mm lens would take pictures at 80mm.

ah.. i think I actually get the wide angle comment now - so wide angle lenses have a a short focal length to give you a wider view of the area?

Slinky0390

Jthmeffy wrote:

ah.. i think I actually get the wide angle comment now - so wide angle lenses have a a short focal length to give you a wider view of the area?

Mhmm. The shorter the focal length, the wider the plane of view. As for books, I highly recommend The Digital Photography Book Vol. 1 and after you read that The Digital Photography Book Vol. 2. He does a great job of explaining how to get certain shots in plain english, no overly technical terms that you could learn after you get the concepts down pat. I was able to learn a lot more about my camera and what effect certain settings have on the photos.

Jthmeffy

Slinky0390 wrote:

Mhmm. The shorter the focal length, the wider the plane of view. As for books, I highly recommend The Digital Photography Book Vol. 1 and after you read that The Digital Photography Book Vol. 2. He does a great job of explaining how to get certain shots in plain english, no overly technical terms that you could learn after you get the concepts down pat. I was able to learn a lot more about my camera and what effect certain settings have on the photos.

those books look great , I'll add the first one to my list to order this week at least, maybe the second if I can talk the wife into it

Thanks!

NateWagner

I have thought that the DOF change dependant on the camera being cropped or not. I mean, it being at 28mm will have the same DOF if it is on a APS camera or a FF. In which case the 28 still is rather wide even though he's seeing it at nearly 50mm.

Jthmeffy

how's this for some DOF?



good bokeh?

Van Isle

Jthmeffy wrote:

Are there any online sources that would be helpful to me with my adventure into this new hobby?

advanced searching in dgrin.com, google, and I've really found wikipedia great as a start to answers to technical questions, and a portal for more info.

That, and shooting under control conditions, like your battery shots! Great stuff! Keep reading and searching!

VI

Jthmeffy

Van Isle wrote:

advanced searching in dgrin.com, google, and I've really found wikipedia great as a start to answers to technical questions, and a portal for more info.

That, and shooting under control conditions, like your battery shots! Great stuff! Keep reading and searching!

VI

thanks

I definitely will. I just ordered a few books from amazon to help me out a bit

NateWagner

Jthmeffy wrote:

good bokeh?

Well, it definitely does show DOF, the rest of the photo is OOF, however, I'm not sure I would call that good bokeh.

The way I understand it, bokeh is not merely the OOF region, it is the smoothness and teh pleasing to the eye quality of the OOF region. IMHO the background is too blown out to really show good bokeh. Also, and this is more on photo composition it seems that the DOF is too shallow as only a little part of the screw is showing.

I do want to say however, that you do seem to be grasping how DOF works well.

Nate

Jthmeffy

NateWagner wrote:

Well, it definitely does show DOF, the rest of the photo is OOF, however, I'm not sure I would call that good bokeh.

The way I understand it, bokeh is not merely the OOF region, it is the smoothness and teh pleasing to the eye quality of the OOF region. IMHO the background is too blown out to really show good bokeh. Also, and this is more on photo composition it seems that the DOF is too shallow as only a little part of the screw is showing.

I do want to say however, that you do seem to be grasping how DOF works well.

Nate

I was actually trying just to get a think region of the pipeto be in the DOF.. I was happy with it

WilliamClark77

This is always a fun discussion. It'll take you a bit to figure out exactly how the aperture opening (fstop) affects dof at different focal lengths, but once it "clicks" you'll have no trouble looking at a scene and knowing exactly what you need.

A great exercise you can do is to lay a yard stick or tape measure on a table. Set your cam up to a 30-40 degree angle from it. Try to get as close as you can and zoomed all the way in to maximize the effectiveness of slight changes in apertures. A tripod or books stacked up to sit your 40d on will help a lot. Set your cam to focus on the center dot only. Put it in Av (aperture priority) mode. Take repetitive shots from the same place at the same focal length (zoom) focussed on the same spot. Change nothing but the f number. Start out wide open (lowest f number/widest aperture your lens allows). Take shots from there then f5.6, f7.1, f8, f10, etc. Next, zoom out to a wider zoom, like 50mm, and do the same. Then compare the results on your computer.

If you want to actually see the physical difference in f stops to give you an idea as to why a narrower (higher number) f stop causes a slower shutter, put you cam on manual mode, lens on manual focus, and set the shutter speed to like 2 seconds. The exact speed doesn't matter. Just long enough for you to see the blades close. Look into the front of the lens and snap a pic. You should see the blades close in. Wide open they will barely move. Stop down (change the f stop to a higher number/smaller aperture), look into the lens and snap. For every stop the hole the blades leave expossed gets cuts in half. By f30 the blades leave only a pin hole for light to get through. That explains why smaller apertures need a longer shutter speed to properly expose a scene; unless you use flash, but that's a whole nudder can o' worms.

As far as bokeh is concerned, yes, all lenses create an out of focus area. Some lenses, like long primes, just simply make "better" bokeh by creating an abrubt, yet smoothe, transition from focussed to out of focus. In my experience, and I'm sure others will disagree, is zoom lenses don't have as an abrubt transition into oof as primes; which is good for many scenes, but less desirable when you're trying to enhance a subject in front of a busy background.

Good luck and keep askin away. The best thing you can do to learn is shoot, shoot manual modes, shoot more, and ask questions.

Jthmeffy

WilliamClark77 wrote:

This is always a fun discussion. It'll take you a bit to figure out exactly how the aperture opening (fstop) affects dof at different focal lengths, but once it "clicks" you'll have no trouble looking at a scene and knowing exactly what you need.

A great exercise you can do is to lay a yard stick or tape measure on a table. Set your cam up to a 30-40 degree angle from it. Try to get as close as you can and zoomed all the way in to maximize the effectiveness of slight changes in apertures. A tripod or books stacked up to sit your 40d on will help a lot. Set your cam to focus on the center dot only. Put it in Av (aperture priority) mode. Take repetitive shots from the same place at the same focal length (zoom) focussed on the same spot. Change nothing but the f number. Start out wide open (lowest f number/widest aperture your lens allows). Take shots from there then f5.6, f7.1, f8, f10, etc. Next, zoom out to a wider zoom, like 50mm, and do the same. Then compare the results on your computer.

If you want to actually see the physical difference in f stops to give you an idea as to why a narrower (higher number) f stop causes a slower shutter, put you cam on manual mode, lens on manual focus, and set the shutter speed to like 2 seconds. The exact speed doesn't matter. Just long enough for you to see the blades close. Look into the front of the lens and snap a pic. You should see the blades close in. Wide open they will barely move. Stop down (change the f stop to a higher number/smaller aperture), look into the lens and snap. For every stop the hole the blades leave expossed gets cuts in half. By f30 the blades leave only a pin hole for light to get through. That explains why smaller apertures need a longer shutter speed to properly expose a scene; unless you use flash, but that's a whole nudder can o' worms.

As far as bokeh is concerned, yes, all lenses create an out of focus area. Some lenses, like long primes, just simply make "better" bokeh by creating an abrubt, yet smoothe, transition from focussed to out of focus. In my experience, and I'm sure others will disagree, is zoom lenses don't have as an abrubt transition into oof as primes; which is good for many scenes, but less desirable when you're trying to enhance a subject in front of a busy background.

Good luck and keep askin away. The best thing you can do to learn is shoot, shoot manual modes, shoot more, and ask questions.

I have pretty much only been shooting in manual. I am constantly playing with the shutter speed, aperture, ISO, white balance, exposure compensation, etc. Basically, I am trying to get a feel for everything so I know what I need to do in different situations. I need to start messing with picture styles, but I can change everything they set in RAW anyway (right?), so I dont worry about it too much - yet.

dawssvt

There is a lot of good info in this thread. Thanks, guys