Canon 50D. A strange problem.

Silver pixels

Silver pixels

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John
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My son, who's reasonably new to photography, uses a 50D with the 100/400 lens. One of the same combinations that i use.
He's long complained of not getting sharp images and assumed "user error". We were out together over weekend and , having set mine up, i asked to look at his.

I was amazed to see that, even though it was beeping "focus confirmation", it didn't look in focus through the viewfinder. The shots however, while not "biting" sharp,(RAW) weren't too bad. I took his kit home and set it up on a tripod, using a box with very small writing on as a subject, i adjusted the "diopter" and added some sharpening "in camera". Sure enough, i get "focus confirmation" beep but it looks anything but sharp through the viewfinder. i then engaged "live view" and magnified by 5 and the image was sharp, as it was when uploaded to my PC.
Has anyone else had similar experiences or has anyone any suggestions to offer as to what could be the cause of this please?

Thanks to all in anticipation. No doubt, there'll be many idea's and i look forward to your input.

Cheers

John
 
I've just had potentially the same issue with my Canon 5D2, I found that my images were not as sharp as expected when using a fairly old and humble 28-105mm lens. I checked this lens and subsequently all my other EF fit lenses and carried out an AF micro adjustment procedure to correct back and forward focusing, which varied from lens to lens. The Canon 50D also has this capability and it's found in the custom menu.

There is more than one way to check if the lens/camera combination is functioning correctly. Focus charts can be found via Google which are then photographed at an angle with the camera on a tripod and aimed at a centre line. The end result will be an image which will illustrate where the actual point of focus is. Plenty of videos on YouTube illustrate this but my long steel rule and upright target were not as easy to use as I hoped.

Another method is to use live view. In Live View, the screen is showing exactly the sensor can see. Again, with the camera on the tripod, view a target parallel to the sensor, I used a card with fine print and manually focus the lens in live view for the sharpest possible image. Turn off live view, carefully turn on Auto focusing without moving the camera and half press the shutter to engage AF, whilst observing the focus scale on the lens if present. If the lens does not move, the AF is correct. If it moves one way or the other, the lens/camera combination is back or forward focusing and needs adjusting. This is the method I used and it allowed very accurate adjustment.

The Micro Adjustment is in the Custom Menus. It allows adjustment in the range of plus or minus 20 units. Again, plenty of videos show this on YouTube. The camera recognises which lens is attached to it and will use any amended adjustment figure from that point on. I soon learned which way was required for adjustments and prime lenses are easy to do. Zooms are potentially more difficult, it could be accurate at one end of the travel but not the other, it might be necessary to decide where accuracy is most required, say 400mm rather than 100mm. The aim of the adjustment is to attempt to acheive no movement in focus when going from Live View MF to normal AF.

I found my Tamron 90mm and 70-300mm VC lenses were spot on, no adjustment. Both Canon lenses, 50mm and 28-105, needed -5 and +14respectively. A Sigma 12-24 need -4. An elderly Cosina 19-35mm was almost off the scale at -20. After this procedure, the camera really does focus properly, but I was surprised by the scale of the variances. If a lens still needs adjustment after reaching the end of the adjustment scale, it would need to go back to the manufacturer.

I know that I'm completely lacking in the L Glass Department, but this exercise has highlighted to me the importance of owning DSLRs which have this adjustment capability. No entry level Canons or Nikons have it, it seems only to be present in the higher end cameras. I note that the Canon 60D does not have this facility although the 50D does. I intend to carry out the same exercise on my back up Nikon D7000, a camera that has a bit of a reputation for Mal-adjusted AF.
 
Perhaps the pentaprism is out of alignment with the af sensors?
 
If the images are in focus (and they are in live view but not the viewfinder) it must be a diopter / VF issue?

Do either of you use glasses or contact lenses? If so, it's important to use them when you set the diopter!
 
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Silver pixels said:
My son ... has long complained of not getting sharp images
...
I get "focus confirmation" beep but it looks anything but sharp through the viewfinder. i then engaged "live view" and magnified by 5 and the image was sharp, as it was when uploaded to my PC.
Click to expand...
OK, are your son's images actually sharp when looked at on the PC? If not, that's user error. You've proved that the equipment can take sharp images.

Next, your images recorded by the sensor are actually sharp, so there's nothing wrong with the lens or with the camera's autofocus mechanism. If the images aren't sharp in the viewfinder, then logically there is a fault somewhere in the optical path from mirror to focusing screen to pentaprism to viewfinder. There's not much that can go wrong with a viewfinder (assuming you have set the dioptre adjustment correctly), and it's hard to see what could possibly happen to the pentaprism. So my money is on either the mirror or the focusing screen being slightly out of alignment.
 
Many thanks for your responses, some of them in great depth and all are very much appreciated. Especially the bright and bushy tailed at 5.46 and 6.58 am LOL. My own conclusions were that, the image to the sensor being sharp, it has to be a mirror or focussing screen issue, the latter being the prime suspect. I may try removing and replacing it to see what, if any difference, that makes.

Once again, many thanks.

John
 
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