Nikon D40 Apeture woes

[Amphoteric]

Hello everyone,

It seems I am posting alot of topics here recently. Anyway, I am trying to do various things with Depth of Field. I use a Nikon D40 camera and am shooting in Apeture mode. I have shot things from a close distance with both f3.8 (largest setting) and f28 (smallest), yet the items in the background are in focus on both pictures. It would seem that no matter what my apeture size, I cannot get my depth of field to change. Does my shutter speed affect this? Any help would be appreciated.

Thanks

 

[andrew07]

there are 3 things that affect DOF

aperture
focal length
and distance from the subject



have you checked your focal length?

 

[Sw1tchFX]

beat me to it.

 

[Big Mike]

Aperture, focal length and distance to subject will all play a factor.

Try setting up something (or someone) and getting close to it. For example, a can of Coke on a table. If you shoot it from two feet away and use an aperture of F3.8...the wall on the other side of the room, should be fairly out of focus. If you stop down to F22, both the can and wall should be in focus...or at least the wall should be much more in focus.

If you back up from the can...the effect of using a shallow DOF will be lessened because the difference between the camera and the subject will be closer to the distance from the subject to the background.

You can try the same experiment outside with a distant background. Take a photo of someone with a wide aperture and background quite far away. The background should be out of focus. If you move closer to the background and or use a smaller aperture, the background will become clearer.

As for focal length, the longer the lens, the more shallow the DOF...so when you want to blur out the background, use a longer focal length.

 

[Helen B]

Could you post examples, with the EXIF data intact. I suggest f/3.8, f/8 and f/28, to show the difference between f/8 and f/28 caused by diffraction, just as a side issue.

Thanks,
Helen

 

[Mike_E]

Just an exorcise to give you a feel for it- go to a train track -a straight section- and snap off all of the different combinations of aperture and focal length that you have (the closer to the track/ground you are the easier it will bee to see). Take notes so that you will know which shot is what. Don't use anything but Manual and be sure to still pay attention to the meter and adjust with shutter speed.

You should then be well on your way to getting it straight. (especially if you remember to measure how far the cross ties are apart.)

 

[Amphoteric]

Alright, so you are saying that the closer I am to the object (and thus the background) the shorter my focal distance and thus the more clear the background will be?

me-------------->can---------------->background = fuzzy
...........me------>can---------------->background = clearer

Is that right?

PS: Mike E. Dont know where any train tracks are near me.

 

[Big Mike]

me-------------->can---------------->background = fuzzy
...........me------>can---------------->background = clearer

No, you've got that backwards. The closer you are to your subject, the fuzzier the background will be.

 

[Mike_E]

You don't have to have train tracks, a straight road with a gravel shoulder would do- as long as you have the camera close to the ground so that the distance from the lens to the ground doesn't become an issue. What you are looking for is something that is fairly straight so that you can tell where good focus starts and stops. Marking off the distance in these will help to learn what you will have as far as DoF on other shots.

 

[Amphoteric]

No, you've got that backwards. The closer you are to your subject, the fuzzier the background will be.

Alright, here is an example (I dont know how to get the exif data). I took this photo with my camera practically touching the railing. I took one at f3.8 and one at f28. In both the backgrounds are about as sharp as in this image.

http://img523.imageshack.us/my.php?image=angledstepsyc1.jpg

And just so I got this straight:

f3.8 = fuzzy background
f28 = clearer background

 

[Big Mike]

Alright, here is an example (I dont know how to get the exif data). I took this photo with my camera practically touching the railing. I took one at f3.8 and one at f28. In both the backgrounds are about as sharp as in this image.

I think I see your problem...it looks like you may be focusing on the background....so no matter what aperture you use...it will be in focus. However, the railing that is close to the camera should be more out of focus with a large aperture and it should be more in focus with a smaller aperture.

And just so I got this straight:

f3.8 = fuzzy background
f28 = clearer background

That's correct...provided that you are focused on something that is well in front of the background.

 

[Amphoteric]

I think I see your problem...it looks like you may be focusing on the background....so no matter what aperture you use...it will be in focus. However, the railing that is close to the camera should be more out of focus with a large aperture and it should be more in focus with a smaller aperture.

Hmmmm, I did focus on the railing, not the background. However, it would seem riddiculous to argue that I didnt do something wrong since the laws of physics didn't just up and decide to mess with me. I guess I will just chalk it up to a "my bad" and try it again on something a little further away.

 

[Big Mike]

I wasn't quite sure what you had focused on...it didn't help that the whole shot seemed to be a bit blurry. This experiment will work much better if you use a tripod, or something to support the camera...also, don't touch it when you fire it (use the self timer)....especially when shooting at F22. Otherwise, the long shutter speed required will cause the whole photo to be blurry from camera shake.

 

[93rdcurrent]

Another thing to try is the dial on the right of your eyepiece. Don't know the name of it but it moves both up and down and has ridges on it. If you get the shot in focus and the picture is out of focus that may be part of the cause. Play with it both up and see if that helps.

Next question... are you using manual or auto focus? Definitely try this shot as manual if you didn't.