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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?

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    \$\begingroup\$ manual focus or autofocus through viewfinder? \$\endgroup\$
    – Steven Kersting
    Commented Apr 21, 2022 at 18:55
  • \$\begingroup\$ Please give more info. What kind of out-of-focus, is the entire image blurry? What is the shutter speed? Is it Motion blur, or out-of-focus? How are your auto focus points arranged? \$\endgroup\$
    – ErinH
    Commented Apr 21, 2022 at 21:58
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    \$\begingroup\$ Can you please attach examples of images taken with both methods? \$\endgroup\$
    – Alastair
    Commented Apr 26, 2022 at 10:59
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    \$\begingroup\$ First we should determine if it is simply out of focus or is it a different problem. Thru the viewfinder try taking a picture a few meters away at f22 and f3.5. This will tell us if it is out of focus at a wide aperture. Because it will look sharper at f22. You can do this using Av mode. \$\endgroup\$
    – Mark Robin
    Commented Apr 26, 2022 at 23:01

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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.
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  • \$\begingroup\$ You can't make a blurred image sharp by changing the diopters (except if you have replaced the focusing screen with a clear one but than I would not expect hat question). In a DSLR the image is projected on the focussing screen (ground glass normally) and you're looking at this projected image in the viewfinder. \$\endgroup\$
    – kruemi
    Commented May 6, 2022 at 10:19
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In the 550D (and most old DSLRs) live view and viewfinder modes use a different focus technique, phase detection for viewfinder, and contrast detection for live view.

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.

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  • \$\begingroup\$ Out of curiosity (not really related to the question): You say "most old DSLRs" use different focus techniques. Does this mean newer DSLRs work differently in this regard and use the same technique in both cases? \$\endgroup\$
    – luator
    Commented Apr 27, 2022 at 10:28
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    \$\begingroup\$ My EOS 70D (not so recent, but more recent than your 550D) has a "Dual pixel" sensor that lets it also use phase detection in LiveView (but using special photosites from the image sensor, so not the same sensor as used for viewfidner shooting). \$\endgroup\$
    – xenoid
    Commented Apr 27, 2022 at 11:58
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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.

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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.

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    \$\begingroup\$ This would probably explain it if it was the exact other way (image sharp, viewfinder blurry). I don't believe this could explain a sharp viewfinder and blurry image. \$\endgroup\$
    – juhist
    Commented May 3, 2022 at 16:26
  • \$\begingroup\$ And since trough the viewfinder you're looking at an image projected on ground glass you can't make a blurry prjection sharp again... \$\endgroup\$
    – kruemi
    Commented May 6, 2022 at 10:13
  • \$\begingroup\$ @juhist indeed I made it slightly unclear by presenting the other way around. But the idea remains the same. Looking through the viewfinder with a correction of -2 makes the viewfinder unsharp if focused correctly on the sensor and the other way around: if focused correctly in the viewfinder will make it unsharp on the sensor. \$\endgroup\$
    – Menno Hölscher
    Commented May 6, 2022 at 11:13
  • \$\begingroup\$ @kruemi: Care to elaborate on that? Your comment seems beside the point to me. \$\endgroup\$
    – Menno Hölscher
    Commented May 6, 2022 at 11:15
  • \$\begingroup\$ @MennoHölscher sure... To get an image to judge in the optical viwfinder it has to be a "real" image. And the image plane has to be at precisely the same distance to the lens as the sensor is. So you have a ground glass element on which the image is projected. Trough the viewfinder you're looking at that image on the ground glass. If this image on the ground glass is blurry no correction in the viewfinder will make it sharp again (mathematically impossible). \$\endgroup\$
    – kruemi
    Commented May 6, 2022 at 11:40

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