Originally posted by cleaverx So any loss with crop factor could be gained with ability of the larger sensor in K-1 if shooting with full frame lenses. Crop image (36 divided by 1.5 ) on 36 MP by 1.5x and you get 24 MP. Same as K-3. Dynamic range, low light, high ISO are better in K-1.
All you need to know about this is that the Pentax K-1 crop is the same as 15 MP on a K-3, so you actually gain the difference between a mx. of about 2000 lw/ph on cropped K-1 to get the 27 lw/ph on a K-3. So if you crop to APS_c size you get about 30% more resolution using a K-3. A K-3 is about 2700 lw/ph.
To be equal to a K-3 you need about a .75 crop on the K-3 image 3600x .75=2700, so if you crop the K-1 image 25%, you'll have virtually the same image as a K-3. Anything more than a 25% crop and k-3 would have given you a better image, both in terms of reach, and straight up in resolution. So in K-3 vs K-1 terms, 400 k-3 = 500mm K-1 taking into account the difference in resolution and the crop factor. Because of the difference in pixel densities it's not a straight 1.5, the K-3 also has 1.5 more pixels in the area of the K-3 crop. The actually K-1 advantage is about 1.25.
IN any case, if you're used to your lens on a 24 MP APS-c sensor looking though the K-1 viewfinder is going to be a disappointment. But if you have the long glass and are willing to carry it the K-1 will get you better images.
If you crop more than this the K-3 will give you a better image. This is a 24 MP image.
A similar image uncropped.
You get a lot more, but I'm throwing out the K-1 advantage because it's not needed for how I want to crop.
Here's the same type of image taken with a K-3 although I expect it's actually taken a little closer.
if I took the same image with the K-1 there would be a smaller bird (less centre resolution) and more of the scenery around it.
It comes down to, what do you want? Bird or surrounding scenery.
In some cases you want more of the surrounding scenery.
In some cases you can get close enough to the bird the K-1 is the better image but in this case that wasn't the case. Even though the birds was so close I hade a 36MP file uncropped, the DoF at minimum focusing distance was so narrow, the shot isn't as good as it could have been.
And in shots like this where my final file was 11.5 MP taken with the K-3, the K-1 image would have cropped down to about 7 MP, with a significant loss of resolution.
That would cost me 37% of my resolution.
So that's what it comes down to real world in many situations. The difference between 11.5 MP file and a 7 MP file or a similar breakdown, because you didn't take your K-3
Every now and then you do get an image with the K-1 that is better than anything you might get with a K-3, superior DR, higher ISO range, more resolution, higher shutter speeds possible.
But most of the time I'm shotting with the K-3, faster burst, deeper buffer, quicker buffer refresh rate. When I really want to be sure, I bring both, I shoot with the K-3 when the subject is at a distance in good light, and the K-1 when the subject is close or the light is poor. But long story short, in I'd say 75% or your birding shots, using the K-1 is going to cost you. Either in IQ of the final crop, or the weight of the lenses you are carrying. Much of my shooting these days is done at 500mm ƒ4.5. You get a lot more reach with a K-3. But like everything else, you can gain a lot more by having your K-1 with you for the times you can use it. In fact it is very hard for me to find a K-1 birding image that isn't cropped below the level where the math says I should have used a K-3. I did find a couple though. As is becoming my usual answer, if you want to cover every eventuality, you need both, but for birding, the K-3 should come first. Unless you value the 25% of the images taken where the K-1 is better at 36 MP than the K-3 is at 24 MP. And 25% is probably on the high side. The low estimate would be 90% K-3, 10% K-1.
K-3 420mm Goldfinch says happy shooting.