The battery test with 40D, and a Live View question

After reading much-ado about front- and back-focusing lately, I decided to give the old battery test a go on my new 40D w/ 28-135mm kit lens. Seemed like a good lunchtime project. Here are the results of the center battery (from left to right: auto-focus with IS on, live view manual focus with IS on, auto-focus with IS off, live view manual focus with IS off):

F5.6, 1/3s, ISO 100



None of the pics showed the front or rear battery in focus, so I cropped the center battery only to compare live view w/ auto-focus side-by-side. All images are JPEG's straight from the camera with default settings, then cropped and scaled 50% using Gimp.

I probably should repeat the test with a smaller aperture, though in reading about these tests I haven't seen anyone mention 1) what aperture to use, or 2) how far the camera should be from the closest battery (mine was 2').

Basically it looks to me like the auto-focus did a good job. My question is: why do the Live View shots look ever-so-slightly brighter in both shots? Might be a newbie question, but I'm askin' it anyway.

some light might have gotten in via the rear view finder? Try to always have it covered if you're using live view (or for other reasons don't have your eye on it)

ISRocks said:

some light might have gotten in via the rear view finder? Try to
always have it covered if you're using live view (or for other
reasons don't have your eye on it)

Click to expand...

Ah, that was probably it. Like I said, I'm a newbie (and that includes using viewfinders). Thanks!

Interesting test. What zoom/focal length were you using? I'm also wondering what f stop is appropriate and at what distance should the lens be.

Bret L. said:

Interesting test. What zoom/focal length were you using? I'm also
wondering what f stop is appropriate and at what distance should the
lens be.

Click to expand...

Well, the test certainly wasn't my idea (unless you're referring to non-IS versus IS). I'm not sure who came up with the "battery test", but I've seen it discussed on these forums since the first day I came here.

I really don't know if there's a right or wrong, better or worse fstop to use. I think what we're trying to test is the proclivity (or lack thereof) of the camera/lens to focus a little in front of the object, or a little behind it. I believe the furthest and nearest batteries are just there for our visual reference -- not to "fool" the AF into choosing the wrong one or anything like that. I certainly could be wrong though.

At any rate, I was just a little shy of 135mm since the focus distance was around 2'. I think I'll repeat the test with the lens wide open, stopped down halfway, then all the way.

ISRocks said:

some light might have gotten in via the rear view finder? Try to
always have it covered if you're using live view (or for other
reasons don't have your eye on it)

Click to expand...

--When using live view the mirror is up & light wont get thru the viewfinder, so has no affect.
Brian Schneider

Brian D. Schneider said:

--When using live view the mirror is up & light wont get thru the
viewfinder, so has no affect.

Click to expand...

You're right of course. I missed the part of his comment about live view. When I took the test shots with AF (not using live view), the camera was on the floor and on a 2 second timer. There was nothing in front of the viewfinder eyepiece to block out ambient light, which probably explains why those pictures were a bit darker than the Live View shots.

Brian D. Schneider said:

--When using live view the mirror is up & light wont get thru the
viewfinder, so has no affect.

Click to expand...

in the contrary,

I think the light leaking from the viewfinder happens when the picture is being taken, it means that's when the shutter is released and the mirror is up.

Liveview or not liveview, the leaking is not before and not after, but exactly at the same time when the shutter is released (and at that time the mirror is up).

Before or after the shutter release the leaking light never gets recorded.

right?

You might also want to try the test at the wide end of the zoom.

This test only bears relevance when shooting at maximum (wide open) aperture, it's point is about accurate plane of sharp focus using AF.

e.g.

f2.8 lens at a relatively close focusing distance @f2.8 focused on the centre battery (where centre is 6" away, front is 4" away and rear is 8" away for example) should result in the centre battery being in sharp focus and not the others, a wider aperture wil simply increase the plane of apparent sharp focus thereby negating the point of the experiment, different focal lengths on azoom is valid as some lenses have differing af accuacy at different lengths.

IS is only relevant hand held at low-ish shutter speeds, if the camera is tripod mounted for example IS can worsen the situation
--
http://www.the-photograph.co.uk

m1ks said:

IS is only relevant hand held at low-ish shutter speeds, if the
camera is tripod mounted for example IS can worsen the situation

Click to expand...

Yes, that's precisely why I was interested in doing this test with the camera sitting still (on the ground -- kind of like a tripod -- not in my hand). The IS didn't appear to affect the results at all. But that could also be due to the fact that I was using the 2 second timer. Maybe the IS shuts off in the time it takes between releasing the shutter button, and when the shutter is released 2 seconds later.

Bret L. said:

You might also want to try the test at the wide end of the zoom.

Click to expand...

Yeah, I'll try that. The reason I went with the tele end of the zoom is because at the wide end the batteries appear pretty small in the frame (even with the camera at the minimum focusing distance). Much easier to judge focusing when the batteries are huge.

Josh_Henly said:

My question is: why do the Live View shots look ever-so-slightly
brighter in both shots? Might be a newbie question, but I'm askin'
it anyway.

Click to expand...

If you are using silent shooting in Live View, then the first curtain is not a mechanical one but electronic. There is probably a small differences in the start times of the electronic and mechanical shutters, a perfect synchronization being probably hard to achieve. Some people had problems with the 40D at higher shutters speeds, the Live View shots being overexposed. The newer 450D has only the silent type (but it's not really so silent) of Live View shooting and some people report a slight underexposure compared to the pictures taken using the OVF. We are talking about manual mode exposures here so the metering has no impact.

Cameras of all other makers have to flip the mirror down and up between the LV and the beginning of the actual image acquisition, sounding like two pictures are being taken and making more vibrations. The electronic first curtain shutter in LV is used only by Canon and it offers a kind of mirror lock up. If the exposure difference bothers you, having a 40D, you can disable silent shooting in LV.

See these threads:
http://forums.dpreview.com/forums/readflat.asp?forum=1019&thread=27896433&page=1
http://forums.dpreview.com/forums/read.asp?forum=1019&message=28513750
and thw's post from here:
http://forums.dpreview.com/forums/readflat.asp?forum=1031&thread=28556417

wildlife1212 said:

Brian D. Schneider said:

--When using live view the mirror is up & light wont get thru the
viewfinder, so has no affect.

Click to expand...

in the contrary,
I think the light leaking from the viewfinder happens when the
picture is being taken, it means that's when the shutter is released
and the mirror is up.

Liveview or not liveview, the leaking is not before and not after,
but exactly at the same time when the shutter is released (and at
that time the mirror is up).

Before or after the shutter release the leaking light never gets
recorded.

right?

Click to expand...

--Impossible. The light leak through the view finder affects the meter just BEFORE the mirror goes up. If light was leaking DURING the exposure it would simply cause flair of fogging not underexposure.
Brian Schneider

I'm glad that you're getting sharp photos. I am not!

I'm doing the same test you are, but at all most full zoom on my Sigma 17-70mm, the live view/manual focus produces much better focused pictures. Why? At 17mm, the differences are discernable.

Any ideas? It's hard to believe that this focus problem has been here all this time without me knowing it. Then again, I havent really dont any tests as such.

-V
--
My sample photos, feel free to browse
http://www.flickr.com/Andy63_5