I have an image taken with an 800mm lens, 24M pixel sensor.
I'd like to crop the image as if it were taken with a 1.4 extender (1.6 crop factor, i.e. 1120mm eq.). 24M pixels sensor.
I want to compare the cropped image to a photo using a real extender, to compare quality.
Is there any easy way to do thet with any of the photos hope tools? Ideally I'd also to have a crop area that can be moved around to frame the image to select the area to be cropped.
p.s. i don't think the adobe website, and forums in particular, are easy to navigate, so don't spend a lot of time searching that forum list. do your best and we'll move the post (like this one has already been moved) if it helps you get responses.
Put the camera on a tripod. Take one shot with the 800 and the one with the extender. set guidelines on the 800 image to where the image frame is on the extender image or you can combine the extender image, set the blend mode to difference, and scale it to match the 800 image. Then you have the crop area of the 800 and canvlow it up to compare with the extender image.
It's generally best to keep the pixel structure intact. Upsampling can only degrade quality, never improve it. It's last resort.
However, there is a dark horse consideration here: the quality of the lens. Most lenses are sharp in the center - but markedly softer, and with more optical flaws, toward the corners. Primes in the standard to short telephoto range (50 - 150 mm) can usually be expected to be truly corner-to-corner sharp.
Cropping gets rid of those bad corners, and so you could say that improves the overall quality. Even, perhaps, with slight upsampling and subsequent re-sharpening.
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