Alley in Pisa, Italy

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I have recently bought Macro lens(Tamron 90mm) and been experimenting with it, My camera is Canon EOS 1000D and it has only 2.5" LCD screen.

Immediately after taking the picture, How can one check whether interested area is in sharp focus (especially if you have shallow DOF and photographing bugs eyes, petal edges , pollen etc.?

I have seen people zooming in and check for sharpness, How much zoom-in can approximately tell that particular area is in focus? If we zoom in 100% naturally everything is going to look almost pixellated?

Objective of question is, What usually photographers do to quickly check whether image has come up sharp or not?

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A similar question: photo.stackexchange.com/questions/13204/… –  Imre Jul 6 '11 at 13:32
1  
I'd suggest that it's not the size of the screen that's the issue but the low resolution. I moved from a 1000D to a 550D last year, the screen size (2.5" vs 3") is a minor increase but there's a huge increase in resolution (230,000 pixels vs 1,040,000) –  ChrisFletcher Jul 6 '11 at 14:14

2 Answers 2

up vote 4 down vote accepted

The LCD is great to check for sharpness on-the-field but you need to know your camera's 100% magnification ratio.

When you zoom-in into the LCD view, most cameras display a magnification ratio as X times from the fit-to-fill size of the LCD. So initially, it is one and when you get to say 4X, the image is magnified 4 times in both directions. As you keep increasing magnification, you will reach a point that depends on the sensor AND LCD resolution where the pixels are one-to-one. This ratio is usually between 8X and 11X on a modern DSLR.

If you go beyond that, which you can in models of the last few years (I cannot imagine why someone thought this was a good idea), cameras will interpolate pixels and start blurring the image which works against checking sharpness.

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This sounds right. I'm making an hypothesis around your answer and say that, assuming that your sensor and your screen both have the same aspect ratio and that the camera uses the full screen for image (not for picture info), the zoom factor at which you're seeing the picture 1:1 would be (sensor pixel count)/(screen pixel count). I Think this can also be calculated using only short side pixel dimensions or long side pixel dimensions. Let me get hands on my camera to test... :) (I'm also assuming the camera uses full resolution for display an not some low-res preview) –  Jahaziel Jul 6 '11 at 15:33
    
@JZL - Yes, modulo aspect ratio differences, that is generally correct. Cameras use the full-resolution for the post-shot review once you start zooming in. The same thing is NOT true of the Live-Preview which often uses pixel-binned output to read the sensor at 30+ FPS, so the Focus-Check magnification is usually more coarse than zooming in after the shot. –  Itai Jul 6 '11 at 15:49

I think zooming about 50-80% tells if an image is sharp or not, and I don't think there are any better solution to check in the field. It's true that in the LCD screen pics always look beautiful and you've got big surprise when you transfer them to a mac/pc with a large screen:).

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I have stopped using LCD for checking sharpness - it fooled me so many times. I always take multiple exposures of the same scene (or try to at least) like 3-6. –  Rafal Ziolkowski Jul 6 '11 at 9:43
    
@Rafal yes correct, but most of the times you can't take multiple shots, unfortunately –  Kreker Jul 6 '11 at 13:50

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