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Old Jan 31, 2006, 5:10 PM   #11
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Example 3. (please read my last post just above these example shots first).

A typical indoor portrait shot of my fiance's father (I held the camera very steady - I have a good hand) and he didn't move. The same results happen using tripod. (I've also done that). I focussed at his nose, but all of his face, including the tip of his nose is quite out of focus.

A friend of mine has a Nikon D50 and I can get it to focus at f1.8 with his camera and fast lens!! With my lenses I need to get to aboutf6.3 or more usually f8for any portrait like this to be "decently sharp" indoors and of course using such a slow setting means you have HUGE exposure times and it's not practical (not enoughbackground blur either)! But outdoors such a shot will work fine at

Canon Digital Rebel XT / 350D with 50mm f1.8 lens at f1.8, ISO 400 and 1/40sec exposure time.


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Old Jan 31, 2006, 5:19 PM   #12
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Example 4. (please read my last post just above these example shots first).

Close up of an instruction booklet. I focussed on the "S" in "USB", but I would say the AF seemed to chose the centre offocus (central point of DOF?)to bethe"S" of "Quick Startguide"...

Canon Digital Rebel XT / 350D with 50mm f1.8 lens at f1.8, ISO 800 and 1/400sec exposure time.

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Old Jan 31, 2006, 5:37 PM   #13
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and finally.... example 5 - taken outdoors in brighter light ( a good one!!) please read my last post just above these example shots first.

This is a photo I made of a twig, but STILL at aperature f1.8 Apart from some bad chromatic aberrations because of the high contrast and the wide open lens, I think this is a "shot that worked" because the area I focussed on (the central cluster of buds) is clearly IN focus!!! Why can't it do this indoors?

Canon Digital Rebel XT / 350D with 50mm f1.8 lens at f1.8, ISO 100 and 1/4000sec exposure time.


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Old Jan 31, 2006, 10:43 PM   #14
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pj1974 wrote:
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I know according to its specifications that the Canon 350D / Rebel XT's auto focusis supposed to operate from EV +0.5to 18 (at ISO 100). I looked up on the net what +0.5represents e.g. EV +1 (one) ="distant view of lighted skyline"and EV +5 (five) is "Night home interiors, average light. School or church auditoriums.
That's the metering range of most camera - did they really specs the AF range in the manual???

What AF mode is the camera set on? Single-shot AF or AI/Servo AF for example?

What I've found is the single-shot mode AF is actually focus priority - i.e. the camera won't release the shutter unless the focus is confirmed.
Whereas in AI/Servo the camera's AF is actually in shutter release priority instead - i.e. the camera will fire even if the focus is not yet achieved... in dimly lt area the AF algorithm may take a little bit longer to perform, but if you force the shutter it will release anyway. and subsequent shots will hopefully track the subject if you hold the shutter release down in action shots for example


I'm just guessing here, but my camera is not behaving like yours (I actually turn my flash AF illuminator off in the CF function since this is kind of 'tacky' to scan your subjects) and it's focusing correctly in the dark :sad:

With a 65W incandescent bulb, 50mm f/1.4 @ 45 degree:
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Old Feb 1, 2006, 4:02 AM   #15
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NHL, Yes, they DO give the autofocus metering in the manual... and the effective METERING range is different, at 1 - 19 EV.

Yes sorry I didn't mention before, all these were made with the Single Shot AF mode.

When you say: "I actually turn my flash AF illuminator off in the CF function since this is kind of 'tacky' to scan your subjects" do you refer to the AF illuminator of your Speedlite or the built in flash!??

As I see you can get focus with your 50mm f1.4 which I can't get with my 50mm f1.8. Maybe time for a new "low light" lens......

Thanks for your help! Anyone else got advice or had a similar problem?

Cheers,

Paul
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Old Feb 1, 2006, 5:55 AM   #16
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It seems likely that your camera needs calibration.

The only other thing to check is this; the actual AF area may be mis-aligned with the etched squares.

It's also probably a bit bigger than the square suggests - this may be relevant, depending on the degree you have cropped your examples, but it seems unlikely in this case.

Try some tests to see whether this seems to be the problem.

For example let's assume that the AF area is below the etched square. If you turn the camera into portrait mode with the button on the bottom then it should be focussing to the left, and if you turn the camera then through 180 degrees it should be focussing to the right.

You could also turn the camera upside-down and see whether it looks like it's back-focussing.

If the focus problem changes with the camera orientation then I would guess it's an alignment issue. If the camera consistently front focusses regardless of orientation it's likely a FF issue.

Either way, it probably needs to go to Canon for a service.
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Old Feb 1, 2006, 7:27 AM   #17
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pj1974 wrote:
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When you say: "I actually turn my flash AF illuminator off in the CF function since this is kind of 'tacky' to scan your subjects" do you refer to the AF illuminator of your Speedlite or the built in flash!??
The actual red IR beam patterns from an external mounted flash - I rarely use this (most effective on a featureless blank wall for example)

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Old Feb 1, 2006, 7:37 AM   #18
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NHL, aha.... I understand what you mean! If you are "scan" your subjects with the near IR beam from a mounted external flash.. I could understand it's a bit "tacky" as you wrote before.
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Old Feb 1, 2006, 7:41 AM   #19
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Thanks Peripatetic for your kind and helpful advice (as usual!)

Actually I did check for the possibility of the AF area itself being misaligned (not in the marked squares) (I read about this possibility elsewhere also). But actually this is not the case as when e.g. a focus line on a test paper is NOT in the square it won't focus. But when the line IS in the square, it focusses immediatley. And I have tried other areas of the screen and focus areas, so I'm quite sure the AF points are not misaligned.

However.... I have a confession to make.... (gulp!) I just discovered thatactually my indoor shots with the other lenses I have (kit lens 18-55mm and 28-135mm) are quite good. Some of the early indoor shots I made with my DSLR suffered from lack of experience, but when I checked closer I realise maybe I was still getting used to my DSLR (I have only had my Canon XT / 350D for 2 months now and the first week or two I used all lenses indoors- but since then have used my 50mm f1.8 lens indoor (because of it's better low light aperture) but was always disappointed....

And so now I did some more testing (e.g. using all 3 lenses) and I can conclude it seems my slower lenses DO focus all right indoors, actually I was surprised when I looked at them, they are quite accurate and good with or without flash. Just obviously because they don't have a very wide open maximum aperture I need a tripod or to hold it v steady or lean on a wall or something because otherwise they might be blurred due to me not holding it steady enough. I do use IS which is handy too.

So silly me (hangs head in shame....:sad: ) I guess I got so annoyed at my indoor shots using the F1.8 and went silly testing that, so I didn't really test accurately my other 2 lenses indoor anymore.

But it's still weird that I can seem to get good in focus photos using my F1.8 (even at that aperture of 1.8) outdoors!!! (even fairly close subjects). Maybe that lens has a particularly problem with low light focus... as it's an older lens design maybe that's possible?

I DO notice that when it focuses indoors it has that sort of "2nd short focus correction" movement and that varies / is inconsistent (I look carefully at the focus ring moving when it's mounted on a tripod and focussing on a stationary / high contrast subject), but 95% of the time it seems to "front focus".

So I guess I will need to stop using the 50mm f1.8 lens and take it back to Canon for a replacement / alignment.

Anybody got ideas how to do that from Romania (to UK?) where I bought the lens (and camera) in UK. Romania's camera service is something I probably wouldn't want to use (no offence meant, but customer service and quality of things like that here aren't taken very seriously!)

Thanks again for all your help. I think you all (including NHL, John and also Jim "ala Moderator") have helped me very much in analysing the problem and coming to a conclusion. So the 28-135mm will not just remain on my camera 95% of the time for outdoor shots, but also now indoor... I just use the kit lens when I need a wide angle shot (but most of my photography seems to use the 28-135mm's reach)

As per usual, thanks folks on Steve's digicams for being a helpful team!

Best wishes and thanks again NHL, peripatetic, Jim and John!!

Paul
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Old Feb 3, 2006, 5:13 PM   #20
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PJ

I originally had the front focus complaint with my 350D with my Sigma 28mm 1.8 lens. Portraits were not especially sharp and conducting a few tests as seen here I discovered that it would front focus consistently. The focus object would seem quite "soft" whilst things slightly closer would be perfectly sharp. For example, if I focussed on the ears (or something behind the plane of their face) of my subject then their face and eyes would be spot on - otherwise it would look soft.

Contacting Canon revealled a substantial delay in returning the camera from repairs and depending if the camera was within tolerances, they might not adjust the alignment anyway. I ended up finding out how to adjust the 350D myself and now it's perfect. I may get an occasional out of focus shot "wide open" but it's under extremely close distaces with avery small DOF.

My other lenses (Tamron 24-135mm, 18-55mm kit) seem to be OK although the larger DOF might be masking any minor discrepancies but the 28mm is perfect compared to the original alignment.

How did you get one with your problem?

Cheers Paul
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