n1as wrote in post #15600045
Thanks all for your input. It will take me a bit to wade through this. The discussion seems to have shifted a bit from my original Q but I'm OK with that as I'm pretty sure my original question has been answered 80 times over in 80 different ways (Yes, I'm tossing some prop's to Canon_Lover for his 80 coment
I have been around long enough to know which topics go in circles page after page.
Your answer was done early, but then you get people arguing semantics, and then there is no hope for you to sift through who is right or wrong even if they are trying to argue the same thing at each other.
Since I am bored with cabin fever myself, I will be generous and give you the final and correct answer to this topic. I suggest you might want to just save yourself a headache and go with what I have posted here.
PART ONE: What defines DOF
DOF is defined by focal length (100mm for example) + Subject Distance + Aperture
The wider the aperture (f2 is wide, f22 is narrow), closer the subject, and longer the focal length, THE thinner DOF and more background blur. Go to the opposite of any of those factors and you increase the DOF to be less thin and less background blur.
PART TWO: What defines crop factor
Crop sensors are nothing different than taking a full frame image into Photoshop and using the crop tool to take out all you want from the edges. There is ZERO difference in optical parameters when doing this. A Nikon D800 has around a 15MP crop sensor's worth of megapixels crammed into the center, and it can shoot in crop mode, or be cropped for the same image in Photoshop. No difference, at all.
PART THREE: What defines FOV
FOV is defined by focal length, where a 10mm lens is wider than a 200mm lens. Taking an image into Photoshop and cropping it will reduce the FOV or Field of View, or otherwise known as Angle of View. A crop sensor is no different than reducing FOV by the same amount in Photoshop. You can easily crop a 10mm image to the FOV of a 200mm image, but you might be looking at some blurry pixels.
PART FOUR: Framing and FOV
If you have a full frame sensor and take a picture of a person's head and fill the entire frame with their head, you must get say 10 feet away with a certain lens, right? If you crop it in Photoshop to the FOV of a crop sensor, then there are going to be missing parts of the person's head, right? YES!
If you have a crop sensor, you must BACK up to not cut off the person's ears on the outside of the frame, when taking that same photo, with the same lens, at 10 feet. Right? YES! You must go to, let's say, 16 feet to get their head back in.
PART FIVE: How it all relates!
Now go back to PART ONE. What did we learn there? Increasing your distance to the subject makes the DOF larger and less background blur when you are using the same focal length and aperture, right? YES! In order to not cut off ears and chins and foreheads, you must back up, OR use a shorter focal length (which we learned in PART THREE makes a wider FOV) to get their full head back into the shot. Backing up to increase subject distance AND/OR using a wider focal length increases DOF and reduces background blur, as we learned in PART ONE, right? YES!
So in the end, the only difference from Full frame and Crop, is that for crop, you must either back up or use a shorter focal length lens to get a person's head to fill the shot without cutting off ears. Both of which make the DOF larger AND reduces background blur.
There is really nothing more to it than that.
You can test ALL of this yourself with any camera, crop or full frame, by just using Photoshop to mimic a smaller sensor than the one you are using.