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DPChallenge Forums >> Photography Discussion >> Camera setting help needed
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09/28/2017 05:31:12 PM · #1
A friend in another group wrote this:
For some reason I cannot wrap my head around this one. I teach a photography class for jr high/high school kids. One student sent me her pictures for the aperture lesson, and using aperture priority mode she took pictures of the same subject by only changing the aperture. (the lesson was teaching how aperture changes DOF) The ISO stayed the same, and the shutter speed changed accordingly. The depth of field did NOT change at all, and the images got brighter as she closed the aperture down. She is using a Nikon DSLR. What am I not seeing that would cause this? My brain must still be foggy from Summer break.....

After someone commiserated but could offer no help, she added, "Thanks, Amanda. It seems backwards to me, also. She sent the files and I looked at the settings and they are what she said they were. So, in other words, f/22 is super over exposed, and f/5 is dark. Shutter speeds appear to be normal for the settings she used.
She used a basketball to focus on, and is about 6 feet away from it, and the ball is maybe 6-10 feet away from her background. Lens length is about 50mm on all of them.
She did the assignment twice on two different days, and this happened both times. It's very possible she is doing something wrong, but I can't figure out what.

Can anyone here shed any light on this?

09/28/2017 05:43:17 PM · #2
Not sure about the exposure issues at this point -- posting a couple of examples might help, but I wonder if the DOF isn't changing because of the set-up, framing, etc. If you can't post images maybe you can post the EXIF ...

I think a better demonstration for DOF would be to line up an object with some kind of regular indicators running away from the camera (e.g. a string of Xmas lights, picket fence) to introduce more than two sample points.
09/28/2017 07:08:13 PM · #3
I think the exposure issue combined with the DoF clue makes this clear... the aperture wasn't actually opening and closing. The camera *thought* the aperture was changing, so it dutifully metered, calculated exposure, and used the shutter speed that would be expected. DoF didn't change because the aperture was stuck. And exposure was dark at f/5 and bright at f/22 because the aperture was stuck somewhere between. I'm guessing it is stuck at f/8.
09/28/2017 07:37:03 PM · #4
Isn't logic great? :-)

ETA: Presumably it's stuck at the aperture for which she got the most nearly correct exposure.

Message edited by author 2017-09-28 19:42:55.
09/28/2017 07:52:23 PM · #5
Auto exposure for what the camera is metering? Center, outside, all?

09/28/2017 10:26:23 PM · #6
try setting camera to manual and work from there.
09/29/2017 01:55:21 PM · #7
Thanks, All. I've forwarded your comments and suggestions to my friend. Happy to entertain any further thoughts you might have.
10/04/2017 11:15:09 AM · #8
I also recommend reading the relonch camera review on fixthephoto.com
I was really impressed with this type of camera, it seems they will perfectly suit many newcomers. What do you think about this?
10/04/2017 11:29:50 AM · #9
I am just a hack, so all I can offer is what I've run into.

DOF to me seems as much about how to compose the shot as it is about optics.

Yeah, there are certain rules that don't change, but if you have the background distance moreso, then it's easier to notice differences in DOF.

Having something right in front of you with objects ten feet away makes it easy to blur (f/2.8), or accentuate(f/22), the background with aperture. If you stand ten feet from an object, with something two feet in back of it, you'll never be able to tell the difference from the rendered images with different aperture settings. I have never relied solely on aperture to get that sweet background blur. You have to have help from the subject material.

It's funny, 'cause my entry in Shallow DOF was wholly contingent on placement of subject/background. 5.6 isn't that super wide of an aperture, yet the DOF makes it look like it.

10/04/2017 02:23:34 PM · #10
I agree it is all perspective. Distance from objects play a larger roll over optics. It's hard to get a sense of DOF with no actual depth. Now with that said you can go right the opposite with having very little distance and a great DOF with a lower aperture. I would suggest take the hardware out of the equation. Let the student try it from a camera that is know to work properly. This will close you in on the issue.
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