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02-05-2015, 07:34 PM   #1
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Cropping to 400mm from 300mm

Am I correct that one would crop by 25% to go from a 300mm to a 400mm image.

I was going to get a 1.4x, but have read many times it is better to just crop.

In the below image I took 25% (of the pixels) off the width and 25% (of the pixels) off the height of the image. (oops, I think I actually cropped to 79% on the height). But that's the idea, right?

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Last edited by Michael Piziak; 02-05-2015 at 07:47 PM.
02-05-2015, 07:45 PM   #2
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Looks great.
02-05-2015, 08:08 PM   #3
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Certainly a moderate crop is more convenient than a TC, and in some ways better--but at significant levels of cropping as compared to a TC (e.g., a 2x TC versus equivalent cropping of 1/2 height and 1/2 width) the TC will provide higher resolution--assuming the lens is excellent, a good quality TC is used, and not (significantly) limited by sensor or film resolution.
02-05-2015, 08:32 PM   #4
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I feel a bit of cropping is almost always essential in fast moving action shots as this. With or without a TC you do not always have time to get a perfect framing of the action. It has often moved on by the time you get zoom worked out. For this one I would be tempted to leave more of the wake on the left in frame and trim off a bit more from the right and top. I would not worry too much about percentages. The final composition counts for far more than pixel count.

02-06-2015, 06:08 AM   #5
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QuoteOriginally posted by Michael Piziak Quote
Am I correct that one would crop by 25% to go from a 300mm to a 400mm image.

I was going to get a 1.4x, but have read many times it is better to just crop.

In the below image I took 25% (of the pixels) off the width and 25% (of the pixels) off the height of the image. (oops, I think I actually cropped to 79% on the height). But that's the idea, right?
That's the right idea. In Photoshop what I do is turn on the ruler guides in pixels, look at the image size, take 25% off height and width (multiply by 0.75). Select the crop tool and enter the new values in pixels into the crop tool. Then starting from the upper left corner drag the crop selection until the width or height lines up with the new size. Since you entered both values the crop tool will keep the proper aspect ratio. Move the crop selection to where you want it and commit the crop. Check the image size to see if it is correct.

There are no doubt other ways to do this, some probably simpler or more elegant but it works for me.
02-06-2015, 08:33 AM   #6
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Your shot looks good. As long as it's sharp and clean, cropping works fine. The longer the lens, the more difficulty you will have with motion blur, especially a sports shot with a moving target. I shoot a lot of flat track and ice motorcycle races and I have much better results cropping my shots. The racers love them and they don't give a hoot about file size. I don't worry about whether 25% or 50% exactly equals a particular focal length, I just crop to get the composition the way I want it. I fully realize that some consider this a mortal sin. I just do what works. I have long glass and I use every mm of it at times, especially for birds and wildlife but for sports shots, I generally shorten up a bit and crop.
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