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10-12-2016, 02:18 PM - 1 Like   #1
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To crop or not to crop...

There has been some debate whether to crop a relatively large sensor or simply use a small sensor like the Q for any given FL of glass if you need magnification.
When I compared the Q-S1 to a comparable K5 crop I came to the conclusion that the Q-S1 was the better option.

However with a m4/3 sensor I'm not so sure - see pic. I seem to get better crops out of m4/3 sensor than with the APS sensor.
If so I'm wondering if it might be because there is a sweet spot between magnification and sensor resolution and the m4/3 sensor is closer to that sweet spot (more optimal).

Take a look for yourself. Note: this file was not ideal - there was some burning on the head of the bird as well as the ISO being on the high side but it is a realistic result of what I actually get so I used it.


Last edited by wildman; 10-14-2016 at 02:21 AM.
10-12-2016, 03:37 PM   #2
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Normally you can crop down to a 6 megapixel image without losing a lot of noticeable detail. It really depends on the size of the printed image. If you don't plan to enlarge it very much, you can get away with a much lower pixel count. But generally speaking a six megapixel crop is a good reference. There is a host of other factors that can influence your ability to crop/print. One is the distance to the subject versus the focal length of the lens. There is always going to be turbulence, moisture, dirt and dust in the air. All of which can contribute to a lower quality image when using a long lens for long distances. obviously the shorter the distance, the better the focus. when comparing cropped images, you need to control all of the factors that could influence the image. Even the light can affect the ability to crop an image. You should not just rely on random images. You can probably take several shots with the same camera, of different subjects, and some images you would be able to crop more than others without losing noticeable quality. As far as cropping a full-size sensor versus using a crop sensor, a crop sensor is equal to a cropped image from a full-size sensor. Not much if any difference. The only real difference is that you can crop what you want more easily in the computer then you can in the field. So for me I'd rather have a full-size sensor with the equivalent size pixel than a crop sensor. Rather than having just a cropped sensor. Unfortunately at this time I cannot afford a K1. So I use what I have.

Joe.
10-13-2016, 07:21 AM   #3
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I think I need to do some real world practical testing on my own.
So in the next few days I will try some test shots and crops using the Q, m3/4 and K5 sensors and see what happens.
I'll get back to this thread with some examples when I'm done.

Last edited by wildman; 10-14-2016 at 04:54 AM.
10-14-2016, 05:14 AM   #4
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QuoteOriginally posted by promacjoe Quote
generally speaking a six megapixel crop is a good reference.
As a practical test I did just that.
Off of a DNG RAW file from the K5 - 2928x3264px FF (16mp) to 2445x2445px (6mp) crop and a pretty average quality shot just to keep it real.
Being a RAW file I did do a modest bit of sharpening otherwise RAW files are unrealistically dull.
What I'm most struck by is how modest a crop 6mp is off a 16mp sensor.

The following two are more like the real world amount of crop I often deal with. From a K20 jpg.


Last edited by wildman; 10-18-2016 at 12:32 PM.
10-14-2016, 12:31 PM   #5
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As I said, there are a lot of variables that go into this. A 6 megapixel image is just a reference. It does not mean you can't crop any more than that, it just means that in some cases you are gonna start losing picture quality. the closer you are to the subject., the better the focus. The better the focus, The more detail you will preserve when you crop the picture. How much you can crop also is determined by how large you wish to print the picture. you can always crop until you start seeing the individual pixels in the printed image. But at that point your image does not look as good as it could. And depending on how good your focus is, you may not have enough detail to do that much cropping. Don't get too hung up on this. Nothing is set in stone. But It is always a good idea to test your equipment. See what your camera/lens combination will do under certain conditions. Find out what conditions are best for your camera/lens combination. learn from it and use it to your advantage. And as I said, a crop sensor is equal to cropping the image from a full frame sensor. All things being equal there's no real difference. Other than your being able to crop a full frame image, in the computer in several different ways to get the image you want.

Joe.

PS, the images that you posted look extremely good. Although I do see a little bit of loss of image quality in the largest crop. You are obviously getting a very good focus with that lens. but if you are at 200 feet away, With a lens that will give you the equivalent size image, You would probably see a big difference in image quality.

Last edited by promacjoe; 10-14-2016 at 12:39 PM.
10-15-2016, 03:33 AM   #6
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QuoteOriginally posted by promacjoe Quote
the images that you posted look extremely good. Although I do see a little bit of loss of image quality in the largest crop. You are obviously getting a very good focus with that lens. but if you are at 200 feet away, With a lens that will give you the equivalent size image, You would probably see a big difference in image quality.
I usually shot very small birds. Their comfort zone starts at about 35 feet or so and that is the optimal distance I try to shot at.
I use a 560mm APO fluorite triplet scope. It easily out resolves any sensor I may have. So far as distance is concerned I can start seeing air turbulence starting at about 60 feet with this glass. So far as focus is concerned I cut my teeth in photography back in the day on the ground glass of a Rollieflex so manual visual focus has become second nature to me.

Here's a 1mp crop off the K20 sensor just to push things a bit. Now I'm at, or beyond, the limits of the sensor ...
... so I'll try a 1mp crop off K5 sensor just for comparison's sake. Note I did clean up some junk around the neck on this one.

The first one is a female Oriole the second is a Male Cape May Warbler in full spring breeding plumage.

Last edited by wildman; 10-18-2016 at 12:33 PM.
10-16-2016, 03:59 PM   #7
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QuoteOriginally posted by promacjoe Quote
....You are obviously getting a very good focus with that lens. but if you are at 200 feet away, With a lens that will give you the equivalent size image, You would probably see a big difference in image quality.
Did you leave a word out of the last sentence? I don't quite understand your last sentence. Are you saying that he would get even better IQ if he had a longer lens so he didn't need to do any cropping at all?
10-16-2016, 06:05 PM   #8
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"You are obviously getting a very good focus with that lens. but if you are at 200 feet away, With a lens that will give you the equivalent size image, You would probably see a big difference in image quality."

QuoteOriginally posted by reh321 Quote
Did you leave a word out of the last sentence? I don't quite understand your last sentence. Are you saying that he would get even better IQ if he had a longer lens so he didn't need to do any cropping at all?
I agree it is somewhat ambiguous:

"a lens that will give you the equivalent size image" = same apparent magnification?
"You would probably see a big difference in image quality" = up or down?

It is clear he would rather crop a big sensor in PP than a small sensor with big glass out in the field.
But I will let him speak for himself.

A couple of crops off the m4/3 sensor at about a distance of 40 feet.
2 and 0.8 mp.


Last edited by wildman; 10-18-2016 at 12:33 PM.
10-17-2016, 09:48 AM   #9
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The amount of crop you can get from a particular image is solely dependent on how good the focus is on that image and how much you intend to enlarge the image in the final picture. For instance if the final picture is going to be used as an icon on your computer, you can crop to 128 x 128 or further, And still get a good image for what you are doing. The further away the subject is, The more air you are going through. Air contains dust, moisture and thermal distortion. Even air itself can cause distortions in your image regardless of the other factors. This is why the best telescopes are mounted on the highest mountains and even in space. Also the subject itself can affect the focus of the picture. A slight movement can blur the picture. The point I was trying to make, Is that there is no magic point that you can crop to and still get a good picture. You can crop until you start seeing the individual pixels. Or you can crop until you see a slight blur to the picture, relative to the size you want to print it at. And what you see on the monitor is not always what you get. There are smoothing algorithms in the printer that will affect your picture. you need to test your camera lens combination. You need to find out what conditions give you the best results. And avoid the conditions that are not favorable to a good picture. That does not mean you should not take an opportunity that arises. Get the picture that you can get, evaluated and learn from it. So what if you cannot crop it to get the picture you want. At least you have the picture. And that is the best way to learn.

Joe.
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