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Thread: Finding it hard to focus

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    Finding it hard to focus

    Help! I have been having this issue with getting the focus spot on and wondering is anyone has had the same problems.

    It mainly happens in low light/indoors and preparing a portrait shot. With the light (or lack of) the screen is useless as it is pretty much black, especially if using a high f stop. And the AF doesn't know what to do for the same reason. So its manual focus by looking through the view finder. This is where i fail, i can't seem to get it right on consistently which is worrying me. Sometimes they even look ok on the screen, until I get them home on the pc and see that I missed it.

    Am I missing something or are there any tricks to use, or do I need to get my eyes checked?
    Cheers, Keith
    Sony A300, Tamron 70-200 2.8, Kenko 2x Teleconverter, Tamron 17-50 2.8, Sony 50 1.4, Strobes - Sony F42AM x 2, radio triggers, plus some studio gear.

    www.keithsmithphotography.com.au | flickr

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    Sir Rattus79 - The Proclaimant
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    It comes from the low light and a lack of contrast for the af system to "see". The simple fix? A flashlight. shine and focus.
    Greg Bartle,
    I have a Pentax and I'm not afraid to use it.
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    Amor fati! ving's Avatar
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    nikon has an af assist light which can help in total darkness... i dont know about sony...

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    Go the Rabbitohs mudman's Avatar
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    if you can adjust the screen brightness it may help.
    have a look in your custom settings options.
    cc and enjoy

    Photography is painting with light

    K7, Pentax 18-250mm zoom, Pentax 100mm macro, Sigma 50-500mm
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    Thanks for those idea, will definately give them a go, worth a shot

    It has a pre-flash (x2) when it has trouble with the AF in darkness, but I find that annoying for every shot.

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    Yep, if you can, use a torch to focus and then you'll be fine. AF can hunt around for ages trying to find something to focus on, and generally it will go to whatever bit of light you have.

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    a torch will do it...but of course you can just flick your lens to manual and do it the old fashioned way

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    A royal pain in the bum! arthurking83's Avatar
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    first of all which lens?
    Second of all, live view in darkness is all but useless, even if you increase screen brightness. All you will see is more noise!

    Auto focusing on a lower end consumer camera will always be a teetering affair. Teetering on the brink of non operability!! .. Sorry to say this, but the AF module will almost certainly be lacking in ability in low light... compared to a higher end camera body that is.

    lastly!.. (and this worries me a little) you said "...especially if using a high f stop...".
    I'm not 100% sure on how Sony's(Minolta's) work, but I'm sure they use the modern and accepted method of wide open aperture until it's required to do it's work.
    That is, the aperture on all modern cameras/lenses is held in the wide open position, until it's required to be stopped down to the value selected by the operator.

    So if you mount the 50mm/1.4, and you select f/8, the lens will always be held open to the f/1.4 value, until you do one of two things. The reason it stays held in the wide open position is to aid in focusing and viewing through the viewfinder. The aperture will only stop down to the f/8 value(in this example) when you make the exposure OR press the DOF preview button, if you have one on the camera.
    i'm pretty sure that using liveview(the rear screen) will also maintain the aperture wide open too.

    So when you say 'especially if using high f stops' the aperture value selected will make no difference to how well/easy/if!! the AF will work in low light. But the lens chosen will!
    If you use your 50/1.4, and you have trouble auto focusing in low light, then it may be time to update to a more capable camera body(with known better AF ability).

    50/1.4 is about as good as it gets in terms of focusing ability in low light. If there is trouble with AF in low light with that lens, then the blame can only be focused(pun intended) on the camera's ability.

    The other points made re using external lighting such as flashes torches etc.. are good ones. But you haven't mentioned what part of a scene in particular you're having trouble focusing on. Note that Auto Focus has a better chance of achieving it's intended function if you have a scene with a lot of contrast for it to focus on!
    eg. focus on a jumper is easier for the camera if the jumper is a series of black and white vertical lines(sorry couldn't resist a Collingwood plug there! ).. anyhow, it;s easier than if the jumper was a solid black colour.. or grey or even white! a solid colour has no contrast for the af module to detect.. especially in low light. In very bright light it may detect the contrast in the weave pattern, but in low light it'll look like a white wall. no contrast.. no AF!

    Also!, try to focus on someone's eye, in low light, from a distance away can also confuse the af system. Better cameras will be less easily confused, but from a full body shot distance using a 50mm lens(say 3meters away) the eye may be too small for the focus area to clearly make a distinction. In low light, this is made worse.

    manually focusing without a proper manual focusing screen, on a modern camera is close to impossible. I recently got myself a better focusing screen for my camera as it allows more accurate focusing. the problem with manually focusing a DSLR is that through the viewfinder you see an image as you would at f/5.6(and the DOF that comes with it), but you probably set the lens to f/2.8 or wider. The difference in where you think the plane of focus is, compared to where it actually is, is called pot luck. There is no way you will know where it is, as the DOF you see(through the vf) is a lot deeper than the reality.
    if you set the lens to f/5.6, then what you see, is what you get. Your ability and precision in achieving focus then determines whether you do so or not for that image.
    The wider you set the aperture, the less accurately you see the DOF(and hence the point of focus).
    Changing to a more accurate focusing screen is then fraught with a darker viewfinder image!.. so there is no free lunch here.

    tips? I have none. you can focus bracket, which is what i used to do with my manual lenses before I changed my focusing screen. Now I have to get the shot in one as I changed the vf screen, and I need to get my mioney's worth(and the practise, to make perfect ).. but up until I made that change, and using my fastest manual lens.. I used to take a burst of 3 shots. I used to get an image as close to focused as I thought was right, learned to either move myself(sway) back and forth and shoot three shots. I found through trial and error that I used to focus behind where I though was right(through the viewfinder image), so used to sway backwards to compensate. Funnily enough it generally worked.. but no guarantee! all of this is hit and miss.

    if you want guarantees, get a better body! A850 or A900 from what I understand of Sony bodies are as good as it gets!

    alternatively and far more cheaply, you could get a more precise vf focusing screen. they can be good, are always better with faster type lenses.. such as f/2.8 or faster. But work badly with slower kit type lenses.. the screen gets very dark, and in low light.. almost impossibly so!(to the point where you may not see a thing through the vf!)

    I personally like the idea of having a high powered led torch handy.. but shining a torch in peoples faces is so uncool.. i only use mine for my landscape type images.
    Nikon D800E, D300, D70s
    {Nikon} -> 50/1.2 : 500/8(CPU'd) : 105/2.8VR Micro : 180/2.8ais : 105mm f/1.8ais : 24mm/2ais
    {Sigma}; ->10-20/4-5.6 : 50/1.4 : 12-24/4.5-5.6II : 150-600mm|S
    {Tamron}; -> 17-50/2.8 : 28-75/2.8 : 70-200/2.8 : 300/2.8 SP MF : 24-70/2.8VC


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    I have this trouble with the H2 as well. I have found the torch the most help, get it to focus then turn it on to manual focus, take the shot, switch it back to auto. Bit of a fiddle but the important thing is that it works and is a quick fix.
    Odille

    “Can't keep my eyes from the circling sky”

    My Blog | Canon 1DsMkII | 60D | Tokina 20-35mm f/2.8 AF AT-X PRO | EF50mm f/1.8| Sigma 150-500mm F5-6.3 APO DG OS HSM | Fujifilm X-T1 & X-M1 | Fujinon XC 16-50mm F3.5-5.6 OIS | Fujinon XC 50-230mm F3.5-5.6 OIS | Fujinon XF 18-55mm F2.8-4R LM OIS | tripods, flashes, filters etc ||

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    Thank you arthurking for taking the time to write so much about this for me.


    Quote Originally Posted by arthurking83 View Post
    first of all which lens?
    Second of all, live view in darkness is all but useless, even if you increase screen brightness. All you will see is more noise!
    All lenses really. And yes I agree, live view is totally useless in the dark.

    lastly!.. (and this worries me a little) you said "...especially if using a high f stop...".
    I'm not 100% sure on how Sony's(Minolta's) work, but I'm sure they use the modern and accepted method of wide open aperture until it's required to do it's work.
    That is, the aperture on all modern cameras/lenses is held in the wide open position, until it's required to be stopped down to the value selected by the operator.
    I was just referring to the live view again here as the screen just gets too dark even in semi-darkness.

    So if you mount the 50mm/1.4, and you select f/8, the lens will always be held open to the f/1.4 value, until you do one of two things. The reason it stays held in the wide open position is to aid in focusing and viewing through the viewfinder. The aperture will only stop down to the f/8 value(in this example) when you make the exposure OR press the DOF preview button, if you have one on the camera.
    i'm pretty sure that using liveview(the rear screen) will also maintain the aperture wide open too.
    The view finder yes (it doesn't change), but the live view screen unfortunately not, the live view changes with any adjustment of f-stop, shutter speed, iso, etc.

    So when you say 'especially if using high f stops' the aperture value selected will make no difference to how well/easy/if!! the AF will work in low light. But the lens chosen will!
    If you use your 50/1.4, and you have trouble auto focusing in low light, then it may be time to update to a more capable camera body(with known better AF ability).

    50/1.4 is about as good as it gets in terms of focusing ability in low light. If there is trouble with AF in low light with that lens, then the blame can only be focused(pun intended) on the camera's ability.
    I will try it a 1.4 and see how the auto focus goes with it Usually I have not bothered with AF too much and gone straight to manual. I should experiement a bit with it more by the looks of it.

    The other points made re using external lighting such as flashes torches etc.. are good ones. But you haven't mentioned what part of a scene in particular you're having trouble focusing on.
    the face and eyes are usually the place i want to focus on

    Note that Auto Focus has a better chance of achieving it's intended function if you have a scene with a lot of contrast for it to focus on!
    eg. focus on a jumper is easier for the camera if the jumper is a series of black and white vertical lines(sorry couldn't resist a Collingwood plug there! ).. anyhow, it;s easier than if the jumper was a solid black colour.. or grey or even white! a solid colour has no contrast for the af module to detect.. especially in low light. In very bright light it may detect the contrast in the weave pattern, but in low light it'll look like a white wall. no contrast.. no AF!
    I could get them to paint Collingwood stripes on their faces But I may not be too popular then lol.

    Also!, try to focus on someone's eye, in low light, from a distance away can also confuse the af system. Better cameras will be less easily confused, but from a full body shot distance using a 50mm lens(say 3meters away) the eye may be too small for the focus area to clearly make a distinction. In low light, this is made worse.
    yes this is about the situation

    manually focusing without a proper manual focusing screen, on a modern camera is close to impossible. I recently got myself a better focusing screen for my camera as it allows more accurate focusing. the problem with manually focusing a DSLR is that through the viewfinder you see an image as you would at f/5.6(and the DOF that comes with it), but you probably set the lens to f/2.8 or wider. The difference in where you think the plane of focus is, compared to where it actually is, is called pot luck. There is no way you will know where it is, as the DOF you see(through the vf) is a lot deeper than the reality.
    if you set the lens to f/5.6, then what you see, is what you get. Your ability and precision in achieving focus then determines whether you do so or not for that image.
    The wider you set the aperture, the less accurately you see the DOF(and hence the point of focus).
    Changing to a more accurate focusing screen is then fraught with a darker viewfinder image!.. so there is no free lunch here.

    tips? I have none. you can focus bracket, which is what i used to do with my manual lenses before I changed my focusing screen. Now I have to get the shot in one as I changed the vf screen, and I need to get my mioney's worth(and the practise, to make perfect ).. but up until I made that change, and using my fastest manual lens.. I used to take a burst of 3 shots. I used to get an image as close to focused as I thought was right, learned to either move myself(sway) back and forth and shoot three shots. I found through trial and error that I used to focus behind where I though was right(through the viewfinder image), so used to sway backwards to compensate. Funnily enough it generally worked.. but no guarantee! all of this is hit and miss.
    bracketing is a great idea, and bursts also would better the odds of a good shot.

    if you want guarantees, get a better body! A850 or A900 from what I understand of Sony bodies are as good as it gets!
    yes saving up for one of these now

    alternatively and far more cheaply, you could get a more precise vf focusing screen. they can be good, are always better with faster type lenses.. such as f/2.8 or faster. But work badly with slower kit type lenses.. the screen gets very dark, and in low light.. almost impossibly so!(to the point where you may not see a thing through the vf!)
    will check these out, they sound like a great tool. espcially now I have my collection of faster lenses building up.

    I personally like the idea of having a high powered led torch handy.. but shining a torch in peoples faces is so uncool.. i only use mine for my landscape type images.
    Yes anything TOO high powered could knock someone off their chair lol

    Thanks for all the tips, much appreciated!!!!

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