Exposure Issues 20D - Auto OK - P Mode not

gpgold

All of the setting help in response to my last post was very useful. So I'm coming back to the well. I started doing test shots as I am reading my manual and the exposure was great in full auto, but blown out in P mode. I'm wondering why that would be.

Regards,

Gary

DoctorIt

cuz P mode is for punks.

But seriously, P mode freaks me out and I have yet to figure out what good its for and what makes it different from full out green "Auto" mode. I think it uses black magic to figure out exposure, so I'm not surprised you're getting inconsistent results.

gpgold

DoctorIt wrote:

cuz P mode is for punks.

But seriously, P mode freaks me out and I have yet to figure out what good its for and what makes it different from full out green "Auto" mode. I think it uses black magic to figure out exposure, so I'm not surprised you're getting inconsistent results.

I thought it just allows you to change shutter and aperture - as well as AE Mode.

Gary

DoctorIt

gpgold wrote:

I thought it just allows you to change shutter and aperture - as well as AE Mode.

It is an AE mode, so that part of your reply is confusing. But yes, of course, it only differs from Full Auto in the respect that you can shift it (Ap or Sh), but only after you compose the shot, and meter - which means you have to hold the shutter down halfway while adjusting either aperture or shutter. Which brings me back yet again to: why on earth would you use P mode?

Sorry as this has turned into a hijack about P mode... Based on the camera's operation, if you do not do any shifting, the exposure should be identical in either Full Auto or P mode. Unless... this is where I don't know the 20d enough.... the only way it could be different is if the metering mode is different. P mode is still considered a "creative" mode by Canon, which means that you should be able to set the metering mode yourself. Full Auto is just that, full auto, and I'm pretty sure that uses matrix metering. Again, I'm just drawing from memory of my 300D here, so you'll have to check your own manual. Or you could just try changing the metering mode while in P. If it lets you change it (it won't while the dial is on Full Auto), then you can deduce you were metering differently than Full Auto does.

Wow, can't believe I turned that hijack into a reasonable answer!

gpgold

DoctorIt wrote:

It is an AE mode, so that part of your reply is confusing. But yes, of course, it only differs from Full Auto in the respect that you can shift it (Ap or Sh), but only after you compose the shot, and meter - which means you have to hold the shutter down halfway while adjusting either aperture or shutter. Which brings me back yet again to: why on earth would you use P mode?

Sorry as this has turned into a hijack about P mode... Based on the camera's operation, if you do not do any shifting, the exposure should be identical in either Full Auto or P mode. Unless... this is where I don't know the 20d enough.... the only way it could be different is if the metering mode is different. P mode is still considered a "creative" mode by Canon, which means that you should be able to set the metering mode yourself. Full Auto is just that, full auto, and I'm pretty sure that uses matrix metering. Again, I'm just drawing from memory of my 300D here, so you'll have to check your own manual. Or you could just try changing the metering mode while in P. If it lets you change it (it won't while the dial is on Full Auto), then you can deduce you were metering differently than Full Auto does.

Wow, can't believe I turned that hijack into a reasonable answer!

Not bad really! Yes you can change metering mode between three varients when in P. I tried this AM. I didn't get yesterdays overexposure, but the lighting was very different (overcast today).

Gary

Richard

Rtfm
So, I cheated a bit and looked at the manual. Look at the table on page 148 and you will see that many options are not available to you in Auto mode.

As to why you are getting blown out shots in P mode but not Auto it may be that the camera is doing a better job at selecting the ISO in Auto than you are in P (you must set it manually). Auto mode always uses evaluative metering, AI focus and automatic AF point selection, while P does whatever you tell it to do. Perhaps if you examine each setting when you shift into P mode you will discover why you are not getting the results you expect.

Hope this helps.

gpgold

rsinmadrid wrote:

So, I cheated a bit and looked at the manual. Look at the table on page 148 and you will see that many options are not available to you in Auto mode.

As to why you are getting blown out shots in P mode but not Auto it may be that the camera is doing a better job at selecting the ISO in Auto than you are in P (you must set it manually). Auto mode always uses evaluative metering, AI focus and automatic AF point selection, while P does whatever you tell it to do. Perhaps if you examine each setting when you shift into P mode you will discover why you are not getting the results you expect.

Hope this helps.

You are right. I will track all settings and do a comparative tomorrow.

Thanks!

Gary

DoctorIt

rsinmadrid wrote:

So, I cheated a bit and looked at the manual. Look at the table on page 148 and you will see that many options are not available to you in Auto mode.

As to why you are getting blown out shots in P mode but not Auto it may be that the camera is doing a better job at selecting the ISO in Auto than you are in P (you must set it manually). Auto mode always uses evaluative metering, AI focus and automatic AF point selection, while P does whatever you tell it to do. Perhaps if you examine each setting when you shift into P mode you will discover why you are not getting the results you expect.

Hope this helps.

But how can you? Per my recollection, there's no way of knowing what focal point (for example) Full Auto is using. ISO sure, that's in the exif, but AF point is not.

And ISO wouldn't necessarily affect exposure, you would see a difference in the photo, but shouldn't see drastic overexposure in the P case - only if it was spot or center metering a dark spot in an otherwise bright image.

Richard

DoctorIt wrote:

And ISO wouldn't necessarily affect exposure, you would see a difference in the photo, but shouldn't see drastic overexposure in the P case - only if it was spot or center metering a dark spot in an otherwise bright image.

You are right, of course, that the camera should be able to get a proper exposure regardless of the ISO. I have never used Auto mode on the 20D so I don't really know when or why it changes the ISO. I do know that on my Canon P & S it never changes the ISO in Auto mode, you need to switch to P and set it manually to get anything over 100. Still, something seems to be giving Gary trouble and I'm just trying to think of what might be changing.

erich6

Gary,

I'm thinking the metering mode may be the most likely culprit. Also, where you using a tripod? Sometimes a slight variation in camera position will cause the camera to meter differently, particularly in tricky lighting conditions.

Erich

DoctorIt

erich6 wrote:

Also, where you using a tripod? Sometimes a slight variation in camera position will cause the camera to meter differently, particularly in tricky lighting conditions.

Very good question - I went ahead and assuming the test was tripod mounted.

erich6

DoctorIt wrote:

Which brings me back yet again to: why on earth would you use P mode?

I don't use P mode anymore but when I started learning SLR photography I used it quite a bit. The benefit of P mode is that you can shift the exposure. Your point is very valid: hey, if I know I want to shift, why not do it in Av or Tv mode when I can set it even before I compose the shot and press the shutter halfway? Well, the benefit of P mode is that it provides a "poor-man's" exposure safety control. In entry-level cameras (like the 300D) you didn't have a custom function that would let you "save the shot" if you set an shutter speed and the aperture cannot be set to give proper exposure. In P-mode, the camera won't let you set a condition that doesn't result in proper exposure (assuming you don't change the EV settings incorrectly).

gpgold

erich6 wrote:

Gary,

I'm thinking the metering mode may be the most likely culprit. Also, where you using a tripod? Sometimes a slight variation in camera position will cause the camera to meter differently, particularly in tricky lighting conditions.

Erich

I wasn't using a tripod - I'll try that tomorrow.

Regards,

Gary