How do DSLRs focus indoors?


Apr 15, 2009
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#1
Hey Guys,

I own a 450D and recently got myself a walk around 18-135mm EFS lens to play with.

I've been having problems recently with focusing, especially in indoor areas and rooms with half the lights turned on. When I hit the focus button, the camera gets a lock and the red dots on the focusing plate light up.

Thing is when I take the photo and blow it up 100% on the computer, they are very often out of focus.

I don't have this problem much outdoors and I'm beginning to think that DSLRs use several methods when it comes to focusing.

Correct me if I'm wrong, but do DSLRs use infrared light to help focus in darker areas? If so, how do I know if my infrared light is spoilt?

If not, are there other reasons as to why my focusing is off? I had my focusing plate changed about a month ago, I'm not sure what else might be causing this problem. I hate to think it's the 18-135mm lens that's causing the bad focusing since it's new.

Below is an attached image I took, the person in front is suppose to be the main focus but as you can see he's not as sharp as I'd like. Bumping the iso up to 1600 wasn't some thing I like to do, but I thought it might help increase the shutter, the picture is still blur, I seldom get this problem until this month only, after using the camera for over a year.


Andrew
 

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chiangkxv

Senior Member
Jul 5, 2008
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#2
I think the main problem with your blur pictures is due to handshake instead of focusing problem.. At indoor, the is insufficient light, thus camera need a slower shutterspeed to get a proper exposure, whereas at outdoor, light is sufficient, thus camera is able to take a picture with a faster shutterspeed that eliminate handshake problem..

do post one of your problem picture for discussion. :D
 

chiangkxv

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Jul 5, 2008
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#3
Camera needs to detect contrast to focus lock. build in LED/pop up flash are common AF assist that camera body use to detect contrast in low light situations..
 

dleugene

New Member
Apr 9, 2010
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#4
Most of your blurred portion is due to fast moving subject. What focusing point your are using???Manual or automatic?

One thing for sure is that the shutter speed is not enough to stop motion which in turn causing your photo to be not sharp.

Can you provide the EXIF further understand what went wrong.
 

Reportage

Senior Member
Nov 24, 2008
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#5
Spinworx.

take note with the lighting at suntec, very difficult to get a frozen shot even with high iso.

was at an event once when i was starting out...here is the event video.

Exhibition.
[YOUTUBE]9OC_fEI72R8[/YOUTUBE]

Time Attack.
[YOUTUBE]oc78ROvqgjs[/YOUTUBE]

Couldnt freeze a single shot with my skills at that time. unless you have fast glass like 50mm f/1.8 and space to get everything in frame, ask nicely if can use flash.
 

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Diavonex

Senior Member
Sep 23, 2008
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#6
When shooting in low light, there's also a problem with very narrow DOF because your aperture is normally wide open. It can make your pictures look out of focus.
 

daredevil123

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Oct 25, 2005
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lil red dot
#7
TS, your picure is in focus. Just look at the face of your subject. The glasses and everything are all in focus.

The amount of high ISO noise is making things blur and may give you the impression that it OOF. Also, since it is dark, your camera probably slowed down the shutter speed, causing motion blur. This blur also adds to that impression that your picture is OOF.

Looking at your picture, again, it is definitely in focus. Not too bad a pic, I must say. All you need is to run the picture through some external noise reduction software and it will come out nicely.

If you really want to freeze motion and get vivid colors with low noise, you need to get an external flash gun.
 

daredevil123

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Oct 25, 2005
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lil red dot
#8
Spinworx.

take note with the lighting at suntec, very difficult to get a frozen shot even with high iso.

was at an event once when i was starting out...here is the event video.

Exhibition.


Time Attack.



Couldnt freeze a single shot with my skills at that time. unless you have fast glass like 50mm f/1.8 and space to get everything in frame, ask nicely if can use flash.

Dude, I really don't understand what you are doing here. On one hand you are talking about how hard it is to freeze motion in indoor shots in Suntec... And you posted, as examples, VIDEOS??????. I thought when people post some pictures or videos up, it is to support and explain further what they are trying to say. You are really not making any sense dude... :dunno:
 

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ZerocoolAstra

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Mar 13, 2008
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#9
Hi TS... It seems like the person of interest in your photo is very close to your camera?

Agree with the rest that the 'blurness' is probably mainly due to hand-shake rather than poor focus.
Another point which I THINK can help is to stand back a bit, because the further away the subject is, the less obvious any slight movement will be.
If you want more 'spinners' in focus, then it'd be a good idea to stand somewhere where a few of them are about the same distance from your camera, thus they will be on the same focus plane. Otherwise front guy sharp but back guy blur yet not very blur... also not so appealing.
 

ZerocoolAstra

Senior Member
Mar 13, 2008
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#10
Dude, I really don't understand what you are doing here. On one hand you are talking about how hard it is to freeze motion in indoor shots in Suntec... And you posted, as examples, VIDEOS??????. I thought when people post some pictures or videos up, it is to support and explain further what they are trying to say. You are really not making any sense dude... :dunno:
I got no idea what the videos have to do with the issue that TS has brought up.
Might as well put up some comedy videos for our entertainment... :bsmilie:
 

Apr 15, 2009
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#11
Hi Guys,

Thanks for the feedback, I went back and took a look at my settings and noted that I had it at Shutter Priority for this one and had the ISO at 800


By focusing point I'm guessing what you mean is where had my camera found a lock, I had all 9 points turned on and the focus was set to One Shot AF. I was expecting the two players at the back to blur out considering I just wanted the front object to be clear. I understand from daredevil that my picture is sharp by looking at the features of the object's face, but at 1/80 exposure, I was expecting the logo on his shirt to be sharp as well.

One thing to note also was that I noticed when I have my camera at 18mm, a group photo I took had focal blur even after the focusing plate gave me a lock when the red dots flashed. Sorry no photo for this one, I had it deleted before I decided to post here for help. =(

btw what's TS stand for?
 

ZerocoolAstra

Senior Member
Mar 13, 2008
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#12
TS = thread starter.
In this case, it refers to you :)

your focus distance was just over 1m.
With the dude spinning that top, I'm guessing he's moving quite abruptly. I don't think you can 'freeze' his movement at 1/80.
If he was a little further away from you, the severity of his movement would be reduced.

I prefer to select my focus point manually, rather than let the camera decide. Otherwise sometimes it chooses the subject, and sometimes it chooses the background.
 

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Apr 15, 2009
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#13
I prefer to select my focus point manually, rather than let the camera decide. Otherwise sometimes it chooses the subject, and sometimes it chooses the background.
Lol, yep I do select my focus point manually from time to time, but I'm sure for this one, the dots that lit up were second last 2 dots from the right of my 9 point AF, hence the subject was in that portion of the frame. =)
 

daredevil123

Moderator
Staff member
Oct 25, 2005
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lil red dot
#14
Hi Guys,

Thanks for the feedback, I went back and took a look at my settings and noted that I had it at Shutter Priority for this one and had the ISO at 800


By focusing point I'm guessing what you mean is where had my camera found a lock, I had all 9 points turned on and the focus was set to One Shot AF. I was expecting the two players at the back to blur out considering I just wanted the front object to be clear. I understand from daredevil that my picture is sharp by looking at the features of the object's face, but at 1/80 exposure, I was expecting the logo on his shirt to be sharp as well.

One thing to note also was that I noticed when I have my camera at 18mm, a group photo I took had focal blur even after the focusing plate gave me a lock when the red dots flashed. Sorry no photo for this one, I had it deleted before I decided to post here for help. =(

btw what's TS stand for?
If you want more control over DoF (what is sharp and not sharp), I suggest you do not use Shutter priority. Get a external flash, and the flash will freeze motion of your subjects beautifully.

And you are using dynamic area AF, which means you are handing focus control over to the AI of the camera. If you want very precise control on what is clear and what is not, I really suggest you use single focus point. For speed, maybe you should just do a focus lock and recompose. At F5, focus lock and recompose will not cause problems.
 

night86mare

Deregistered
Aug 25, 2006
25,541
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0
www.pbase.com
#15
Hey Guys,

I own a 450D and recently got myself a walk around 18-135mm EFS lens to play with.

I've been having problems recently with focusing, especially in indoor areas and rooms with half the lights turned on. When I hit the focus button, the camera gets a lock and the red dots on the focusing plate light up.

Thing is when I take the photo and blow it up 100% on the computer, they are very often out of focus.

I don't have this problem much outdoors and I'm beginning to think that DSLRs use several methods when it comes to focusing.

Correct me if I'm wrong, but do DSLRs use infrared light to help focus in darker areas? If so, how do I know if my infrared light is spoilt?

If not, are there other reasons as to why my focusing is off? I had my focusing plate changed about a month ago, I'm not sure what else might be causing this problem. I hate to think it's the 18-135mm lens that's causing the bad focusing since it's new.

Andrew
TS, your picure is in focus. Just look at the face of your subject. The glasses and everything are all in focus.

The amount of high ISO noise is making things blur and may give you the impression that it OOF. Also, since it is dark, your camera probably slowed down the shutter speed, causing motion blur. This blur also adds to that impression that your picture is OOF.

Looking at your picture, again, it is definitely in focus. Not too bad a pic, I must say. All you need is to run the picture through some external noise reduction software and it will come out nicely.

If you really want to freeze motion and get vivid colors with low noise, you need to get an external flash gun.

just to add on, after seeing the EXIF, photo taken at 18mm.

could be corner sharpness issues.

focus assist lamp - don't think 450d has it. that is the IR light thing.
 

Reportage

Senior Member
Nov 24, 2008
5,785
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#16
Dude, I really don't understand what you are doing here. On one hand you are talking about how hard it is to freeze motion in indoor shots in Suntec... And you posted, as examples, VIDEOS??????. I thought when people post some pictures or videos up, it is to support and explain further what they are trying to say. You are really not making any sense dude... :dunno:
shows how hard it is to freeze a yoyo player when they are serious and the lighting is just about same so i know how it feels being in TS shoes before.

I dont see anyone else here showing pics of being able to freeze a yoyo demo? anyone? Easy to talk if never try before.

TS, if you are trying to capture the person...i dont see a problem but if you are trying to freeze a yoyo demo in play, even flash at 1/250 may not be fast enough.

If its possible, ask the demo person to show a slow move for photo taking. With flash, hopefully should be enough.

As above have post, choose the focus point manually is more effective...a lot of users use centre focus point most of the time.

as for blurring the background, you are using F/5 and some more you are quite close to the subject. Can clearly see that there is some blurring of the background just that the aperture is not large enough to blur the background more pronounced as opposed to using F/2.8 or F/1.4 or even faster lens. You can search for it under Throwing background out of focus or even bokeh. There is some theory and some practical but should give you some understanding. You will come across word like depth of field, shallow focus, circle of confusion, bla bla bla but with stubborn persistence..you will get the idea. I did.
 

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daredevil123

Moderator
Staff member
Oct 25, 2005
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lil red dot
#17
shows how hard it is to freeze a yoyo player when they are serious and the lighting is just about same so i know how it feels being in TS shoes before.

I dont see anyone else here showing pics of being able to freeze a yoyo demo?

TS, if you are trying to capture the person...i dont see a problem but if you are trying to freeze a yoyo demo in play, even flash at 1/250 may not be fast enough.

If its possible, ask the demo person to show a slow move for photo taking. With flash, hopefully should be enough.
Flash is very fast, at around 1/10000s. The flash is the thing that freezes the motion, not the shutter speed. You need to get your facts straight, or at least understand the concepts before saying anything.

And I really don't see how a VIDEO of a yo-yo demonstration can show "how hard it is to freeze a yoyo player when they are serious". :dunno::dunno::think:
 

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cks2k2

New Member
Feb 12, 2009
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#18
For 450D, focus assist only works with pop-up flash up.
If you look at the top right side of the 450D's front near the grip, the focus assist light is the round thing that emits an orange beam.
 

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