Aperture impact on light picture

[patav]

Good day, I wanted to take these pictures in order to get some feed back on some of my questions ( I have a Canon 40d with a 50mm 1.8):

1- I would of expected to have picture # 1 looking like picture # 2 in normal mode...why is the camera putting the aperture to 5

2- I would expected to have picture # 1 looking like picture # 2 when having big aperture due to the fact that depth of field would be close.

Let me know what you think...and how I should interpret this. Any links would be appreciated. regards


Picture 1:Mode: Normal ; Speed: 1/320 ; f5 ; FL: 50 mm ; ISO: 500 ; Exposure: Normal

Picture 2:Mode: Manual ; Speed: 1/400; f1.8 ; FL: 50 mm ; ISO: 500 ; Exposure: Normal

 

[Alpha]

They're different because f1.8 is more than a full stop faster than f5, whereas 1/400 is not more than a full stop faster than 1/320. In fact, it's less than half a stop faster. Therefore, it's no wonder more light was let in and #2 came out brighter. That's very screwy.

 

[patav]

I agree but why would the "auto" mode set the f stop to 5.

regards

 

[Helen B]

Number 1 was shot in program mode, ie autoexposure. The lights are affecting the exposure - the metering system tries to set an exposure that would suit a middle grey scene. Number 2 was taken in full manual mode, with just over two stops more exposure (as Max says, -2/3 stop because of the shutter speed difference, +3 stops because of the aperture difference)*.

Number 2 has less depth of field than number 1, because of the wider aperture.

*You can also calculate this using the TV and AV data in the EXIF.
For Number 1 TV + AV = 8.38 + 4.63 = 13.01
For Number 2 TV + AV = 8.63 + 1.63 = 10.26
Difference = 2.75 stops (there are mismatches between the exact TV, AV, shutter speed and aperture numbers, probably because of rounding)

Best,
Helen

 

[patav]

Thank you very much for all your help.