Cropping and image quality

Hey Gang;

Hopefully this is the correct place for this question.

I have been trying to shoot some birds (egrets, osprey, hawks) and generally have to crop the heck out of the picture to get the subject to be any sort of decent size. Unfortunately this yields low quality images

Is there a rule-of-thumb for how much you can crop before the image looks like poo? I am assuming you can get away with more if you are shooting lower ISO.

For example on my 40D, image size 3888x2592, what would yield a decent 1024*768?

I know the solution to the problem is longer glass, but that is expensive and the CFO is not to happy at the moment.

Thanks in advance!

Image quality

Image quality can vary depending on many factors... The amount of cropping, while important, is just one of these factors.

Some other factors that impact the image quality are the quality of the lens itself and the general sharpness of the image (focus and steady hold).

That said, it is difficult to get decent bird pictures (wild birds that is) especially birds-in-flight, if you don't have the proper equipment.

I have a bird feeder right outside the door of my bedroom. Small wild birds congregate arount the feeder and I can shoot from inside my bedroom and get good images with a shorter lens than would be possible without the bait (the feeder) and the shooting blind (my bedroom).

You might be able to replicate these conditions. Using some sort of bait and some way to hide from the birds.

jdando wrote in post #5430983
Is there a rule-of-thumb for how much you can crop before the image looks like poo? I am assuming you can get away with more if you are shooting lower ISO.

For example on my 40D, image size 3888x2592, what would yield a decent 1024*768?

It makes a big difference if you are talking about photos to be viewed on a monitor or paper prints. For monitor viewing, if, after PP, your full sized image looks good at 100% zoom you can crop an area the size of your screen resolution, which if it is 1024x768 is quite a small crop. If your equipment or your shooting and/or PP skills prevent getting a good 100% zoom, then you can't crop out as much, but this is relative so it's impossible to give a simple answer.

If you are talking about prints, then it depends on the size and your subjective judgement of "decent", but I'd say a ppi of about 240 would be adequate for good (maybe not maximal, but good) prints. So for 4x6 you could crop all the way down to 960x1440 while 8x10 or 8x12 would need 1920x2880. If prints with less ppi look acceptable to you - and I've heard people love 180 ppi prints - you can crop even more.

Actually it appears the solution is to get closer to the subjects than to try to crop down to a good image or get longer glass. If I have to crop away more than about 35% of an image is had better be incredible to begin with or otherwise it isn't worth the effort in my case.

But the important things to remember in shooting birds, glass is never long enough nor are you ever to close to a subject.

But with your current glass I would work on getting much closer to your intended subjects. Just like still hunting, finding and using cover and concealment and most importantly being patient and waiting for the subject to come to you instead of chasing it will yeild much better results. And when you do get longer glass the skills in getting close will only payoff even more so.

Get longer glass. 1.4xTC on 70-200mm f2.8 is not that good to begin with.

Cheapest option - Cnaon 400mm f5.6.

BTW - 100% crops from 500mm f4 IS are super sharp. Lot depends on the lens and camera focussing accuracy.

If you shoot a 10 MP shot and crop half of it, you now have a 5 MP image.

To many variables to answer that question.

If you have a large enough monitor, you can set it up to show your images at a specific print size/dpi numbers at a full size print.

Doing the math will tell you how much you can crop an image for a designated print size. But...

The better the image, the more you can safely crop.