lalit Posted February 15, 2006 Share Posted February 15, 2006 Hi<p>Last weekend I tried to take a picture of a slihoutte mountain withtwilight sky. I noticed that, my lens at 70 mm was not able to takepicture.<p>Lens was on AF.<br>Aperture was tried between f4 to f16<br>Shutter speed was changed to even 4 to 8 seconds? <p>What am I doing wrong? The low exposure warning would not go away? <p>Thank you and regards, Link to comment Share on other sites More sharing options...
William Kahn Posted February 15, 2006 Share Posted February 15, 2006 What ISO setting were you using? Given the low light conditions, you should have been using at least ISO 400, maybe even 800. Also, autofocus is always problematic in very low light conditions. That's why manual focus is there as an option :-) Link to comment Share on other sites More sharing options...
snakeroot Posted February 15, 2006 Share Posted February 15, 2006 You might try manual focusing and manual settings on the camera, then you can shoot as many tries as you want. I use a tripod and a remote trigger, and at those slow speeds, engage mirror lockup on that 20D. Link to comment Share on other sites More sharing options...
rdkirk Posted February 15, 2006 Share Posted February 15, 2006 Mountains are at infinity. Link to comment Share on other sites More sharing options...
awindsor Posted February 15, 2006 Share Posted February 15, 2006 Neither ISO, aperture, nor shutter speed directly affect AF (except as they reveal the light condition). The maximum aperture of the lens has a strong effect on AF performace. AF should lock on to a strong contrast such as a silhouette but you need to position the AF point directly over the transition since neither sky nor mountain will carry sufficient contrast to allow for AF. As other have mentioned you should be able to manual focus in such a situation. Actually I find the AF on the 20D to be superb. Using a fast lens it will AF in very little light provided the subject has sufficient contrast. What mode were you using? If you use one of the auto modes it might stop you taking a photo if the shutter speed is too slow (I don't know I don't use them). Link to comment Share on other sites More sharing options...
james_symington1 Posted February 16, 2006 Share Posted February 16, 2006 What Alistair has just said is quite correct - focus on the mountain/sky boundary and make sure the AF point is well placed on that boundary. If necessary as soon as you have focussed switch the AF off making sure not to touch the focus/zoom ring and then you can concentrate on optimising your exposure. Link to comment Share on other sites More sharing options...
lalit Posted February 16, 2006 Author Share Posted February 16, 2006 Yes, Manual focusing is an option, but I will try the AF point at the boundary suggestion, that sounds interesting. Thank you all, regards! Link to comment Share on other sites More sharing options...
byronlawrence Posted February 16, 2006 Share Posted February 16, 2006 in that light you probably don't want to be holding your camera. and if you are tripod mounting the camera (which you probably should be doing if you have that little light). then the mirror lock up should be used and manual focusing. and timing for that matter. there is no reason to us any automatic functions, at that point. and set the f stop to f8-f11 and go ahead and be frivoulous,, use ISO 100. you will get some good long exposures then! but if you want to use the auto focus.. then you are on the right track now. Link to comment Share on other sites More sharing options...
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