I recently bought a Canon 550D. The problems is when I take a picture through the ViewFinder, the image gets blurry and out of focus. But when I use Live Mode, the image is sharp and in focus. What can be the problem?
There could be a few possible explanations:
- You are not placing the AF point on the exact location you want.
- You are using a fast lens wide open and are moving a lot after focussing.
- You are using AF-C and are focussing and recomposing without using Back Button Focus. Due to this, the image is first brought into focus and when you recompose, it goes out of focus again. In order to be able to focus and recompose, you should use back button focussing even if you use AF-S.
- You are using manual focus through the viewfinder and your diopter is not adjusted properly.
- You are using a very very slow shutter speed which is causing motion blur that you are mistaking for AF failure.
- As @xenoid stated, there could be something wrong with your AF system. Could be:
- A dirty AF sensor
- A damaged AF sensor or
- The sensor needs recalibration.
Phase detection requires a lens that is sufficiently open. IIRC on these models the official specs require f/5.6 but lenses that open at f/6.3 sometimes work.
If you get the focus confirmation beep then your phase detection sensor/circuit is possibly mis-calibrated or failing, and if you don't then the sensor might be dirty (check the bottom of the body under the mirror) or the small auxiliary mirror behind the main mirror might be stuck.
A possibility: you are looking at the 18 megapixel images on a computer screen, whereas the viewfinder image is very small. Typically, mirrorless cameras have only few megapixels on the viewfinder whereas the sensor resolution is measured in tens of megapixels, and nobody complains of low mirrorless camera viewfinder resolution.
Thus, there is an order of magnitude difference between what you see on computer screen and what you see through the viewfinder.
It's perfectly possible the focus is bad, and that you don't see it in the viewfinder due to low magnification, but on a computer screen you can magnify it to pixel level (pixel peeping), and you see the missed focus.
Most likely this is a focus issue you just won't notice on the viewfinder due to low magnification. With superhuman eyesight, you would also see it in the viewfinder.
A possible cause that is missing:
The EOS 550D has a dioptre setting for the viewfinder. This is for people wearing glasses who want to take pictures without glasses. When the camera does autofocus and this setting is changed, the viewfinder will be unsharp, though the picture will be fine.
On my Olympus the dioptre setting wheel is in an awkward place so it gets (un)set every now and than.