Depth of field: Full-frame lens vs. APS-C lens, both on APS-C sensor

[Braineack]

He didn't say he thought inferior products were better. He never said Canon was better.
He wanted to switch to Nikon but stated that the Nikon 70-200 has a focal breathing problem. Whereas the Canon 70-200 lens does not.
He stated that the 70-200 lens he uses too much and felt the focal breathing issue presented a greater issue than gaining the benefits of switching to Nikon.

The Canon 70-200 exhibits the same breathing "issue" and Matt Granger has illustrated Canon is actually the worst between the Nikon, Canon, and Tamron versions as far as focus-breathing is concerned.

I was also hyperbolizing.

 

[theraven871]

Derrel and Wayne are correct and Braineack's math is correct. In an appropriate comparison of like photos smaller sensor cameras produce more DOF.

To make any meaningful comparison in this discussion you must make a comparison of similar photographs. The content and perspective in the two compared photographs must be identical as must also be the photographic conditions -- same exposure, which means same f/stop etc. Therefore both photographs must be taken from the exact same location and the angle of view of the camera/lens systems must be adjusted to produce identical content. Both photographs must be taken using the same photographic conditions, i.e. exposure. All other comparisons are worthless.

Comparing like photographs using different format cameras a photo taken with a smaller format sensor will have more DOF than the same photo taken with a larger format sensor.

..........f^2
H = ----------
..........Nc

The above equation is standard. If you dispute it then you're denying accepted math and are certifiable.

"H" is hyperfocal distance, "f" is focal length, "N" is f/stop and "c" is circle of confusion. It is likewise accepted math that c is determined by the size of the format. If you think sensor size does not effect DOF please show examples of this equation in which changing "c" has no effect on "H."

If you do the math for the above equation so that two different format cameras are taking the exact same photograph you get different values for "H" proving mathematically that you get more DOF from a smaller sensor camera. The math in the illustration below is correct. Hyperfocal distance for the 7D is closer to the camera and that means there's more DOF.

Joe

You just compared two different lenses on two different sensors.
If you compare a 50mm prime on a full frame sensor and a 50mm prime on a cropped sensor, look at the DEPTH OF FIELD.
Even at the same aperture, the depth of field will be smaller on the full frame.
That's all I'm trying to say.
I'm not talking about full frame vs APSC lenses. I'm talking about the same lens on different sensors.

 

[theraven871]

He didn't say he thought inferior products were better. He never said Canon was better.
He wanted to switch to Nikon but stated that the Nikon 70-200 has a focal breathing problem. Whereas the Canon 70-200 lens does not.
He stated that the 70-200 lens he uses too much and felt the focal breathing issue presented a greater issue than gaining the benefits of switching to Nikon.

The Canon 70-200 exhibits the same breathing "issue" and Matt Granger has illustrated Canon is actually the worst between the Nikon, Canon, and Tamron versions as far as focus-breathing is concerned.

I was also hyperbolizing.

I'm glad you pointed this out. I looked and found Matt's video where he demonstrated this.
I'm looking to switch to Nikon and this helps my confidence.

 

[Ysarex]

Derrel and Wayne are correct and Braineack's math is correct. In an appropriate comparison of like photos smaller sensor cameras produce more DOF.

To make any meaningful comparison in this discussion you must make a comparison of similar photographs. The content and perspective in the two compared photographs must be identical as must also be the photographic conditions -- same exposure, which means same f/stop etc. Therefore both photographs must be taken from the exact same location and the angle of view of the camera/lens systems must be adjusted to produce identical content. Both photographs must be taken using the same photographic conditions, i.e. exposure. All other comparisons are worthless.

Comparing like photographs using different format cameras a photo taken with a smaller format sensor will have more DOF than the same photo taken with a larger format sensor.

..........f^2
H = ----------
..........Nc

The above equation is standard. If you dispute it then you're denying accepted math and are certifiable.

"H" is hyperfocal distance, "f" is focal length, "N" is f/stop and "c" is circle of confusion. It is likewise accepted math that c is determined by the size of the format. If you think sensor size does not effect DOF please show examples of this equation in which changing "c" has no effect on "H."

If you do the math for the above equation so that two different format cameras are taking the exact same photograph you get different values for "H" proving mathematically that you get more DOF from a smaller sensor camera. The math in the illustration below is correct. Hyperfocal distance for the 7D is closer to the camera and that means there's more DOF.

Joe

You just compared to different lenses on two different sensors.
If you compare a 50mm prime on a full frame sensor and a 50mm prime on a cropped sensor, look at the DEPTH OF FIELD.
Even at the same aperture, the depth of field will be smaller on the full frame.

I compared the same photograph taken with two different cameras (sensor sizes). A comparison that would be interesting and meaningful to a photographer.

You can't take the same photograph with a 50mm lens on a FF camera and also a cropped sensor camera. So if you compare an apple with an orange and proclaim that they're different what was the point of your comparison? My niece would say, "duuuuhhhhhh."

Joe

 

[theraven871]

Derrel and Wayne are correct and Braineack's math is correct. In an appropriate comparison of like photos smaller sensor cameras produce more DOF.

To make any meaningful comparison in this discussion you must make a comparison of similar photographs. The content and perspective in the two compared photographs must be identical as must also be the photographic conditions -- same exposure, which means same f/stop etc. Therefore both photographs must be taken from the exact same location and the angle of view of the camera/lens systems must be adjusted to produce identical content. Both photographs must be taken using the same photographic conditions, i.e. exposure. All other comparisons are worthless.

Comparing like photographs using different format cameras a photo taken with a smaller format sensor will have more DOF than the same photo taken with a larger format sensor.

..........f^2
H = ----------
..........Nc

The above equation is standard. If you dispute it then you're denying accepted math and are certifiable.

"H" is hyperfocal distance, "f" is focal length, "N" is f/stop and "c" is circle of confusion. It is likewise accepted math that c is determined by the size of the format. If you think sensor size does not effect DOF please show examples of this equation in which changing "c" has no effect on "H."

If you do the math for the above equation so that two different format cameras are taking the exact same photograph you get different values for "H" proving mathematically that you get more DOF from a smaller sensor camera. The math in the illustration below is correct. Hyperfocal distance for the 7D is closer to the camera and that means there's more DOF.

Joe

You just compared to different lenses on two different sensors.
If you compare a 50mm prime on a full frame sensor and a 50mm prime on a cropped sensor, look at the DEPTH OF FIELD.
Even at the same aperture, the depth of field will be smaller on the full frame.

I compared the same photograph taken with two different cameras. A comparison that would be interesting and meaningful to a photographer.

You can't take the same photograph with a 50mm lens on a FF camera and also a cropped sensor camera. So if you compare an apple with an orange and proclaim that they're different what was the point of your comparison? My niece would say, "duuuuhhhhhh."

Joe

My line of thinking is that you can get a 50mm 1.8 prime for both a full frame or crop sensor.
Took a photo with both @ f1.8 you will notice that the full frame has more bokeh.
Its slight, but its there. Is it worth spending the money for full frame? Possibly, but probably not.
I'm wondering if I'm talking about something entirely different than everyone else.

I'm not saying that the physical aperture of a lens actually changes when you put it on a cropped sensor. That would require us to be in the Twilight Zone.
What I'm saying is that an identical lens will take different pictures when mounted on a full frame vs cropped sensor.
The majority of my point is that to find out what the EQUIVALENT lens would be on a full frame, you would need to multiply BOTH the focal length and the aperture by the crop factor.
Everyone seems to understand that a 50mm lens on a crop sensor will have the equivalent focal length of 75mm (if its a 1.5x crop)
My entire point was that if you shot that 50mm lens @ f1.8 on a crop sensor, the equivalent performance would be that of f2.8 . NOT f1.8.
Thus, a 50mm 1.8 lens on a cropped sensor has very near performance to a 75mm f2.8. Its still a 50mm 1.8, but it functions differently when on a crop sensor.
A lens on a crop sensor at f1.8 is different from a lens on a full frame sensor at f1.8.

What is upsetting to me is that we use the same terms for both formats. A 50mm f1.8 on a cropped sensor is a very different experience than a 50mm f1.8 on a full frame.
For marketing purposes, it would be more accurate to instead name a APSC 50mm 1.8 a 75mm f2.8 instead. Because that's the performance you're going to get out of it.
Yes, technically speaking the lens physically hasn't changed. It just will perform differently. That's all that matters to me.
My point is that people want to convince consumers that a 17-50 f2.8 lens (on a crop sensor) will perform the same as a 24-70 f2.8 (on a full fram). That's just not true.
Yes, the focal range will be near the same but the depth of field on the cropped lens will not be the same at f2.8 as it is on the full frame.
The depth of field on the cropped sensor lens @ f2.8 will be very close to the full frame lens @ f4.

My point is that while I admit that f2.8 on a crop sensor is still a fast aperture, sometimes you want that extra bokeh. I buy f2.8 lenses to shoot at f2.8. If I'm shooting at f2.8 I want the bokeh that f2.8 delivers. Not f4.

 

[Braineack]

Yes, the focal range will be near the same but the depth of field on the cropped lens will not be the same at f2.8 as it is on the full frame.

The depth of field on the cropped sensor lens @ f2.8 will be very close to the full frame lens @ f4.

My point is that while I admit that f2.8 on a crop sensor is still a fast aperture, sometimes you want that extra bokeh. I buy f2.8 lenses to shoot at f2.8. If I'm shooting at f2.8 I want the bokeh that f2.8 delivers. Not f4.

This was a better way to put it.

You should use the caveat "in regards to DOF" especially when speaking about aperture, which controls the exposure as well. You didn't before and I think that's where everything fell apart.

 

[CameraClicker]

I compared the same photograph taken with two different cameras (sensor sizes). A comparison that would be interesting and meaningful to a photographer.

You can't take the same photograph with a 50mm lens on a FF camera and also a cropped sensor camera. So if you compare an apple with an orange and proclaim that they're different what was the point of your comparison? My niece would say, "duuuuhhhhhh."

Joe

It's only a comparison that would be interesting to some photographers. Have you noticed we are all talking about different parts of the same thing. Frequently we make brief statements that are true in certain circumstances, but don't really illuminate sufficiently to permit the information to be used/understood in other situations.

Bokeh comes mostly from focal length, aperture, and distance to subject/distance to background. If a smaller/larger sensor allows you to move with respect to your subject/background, that movement will be what affects the bokeh. Put a 50 mm f/1.8 lens on a crop body, or on a full frame body, and you will be able to go and shoot with the same ISO, same shutter speed, and same aperture, and you will get an image with the same exposure, but different framing. If you want more bokeh, get a full frame body because for any given focal length, you can stand closer and still fit your subject in. Get a medium format camera because the much larger sensor will let you stand even closer! Standing closer is the part that will deliver more bokeh. Same lens, same distance to subject, same aperture, same DOF, different framing if you have different sensor sizes.

 

[CameraClicker]

My point is that while I admit that f2.8 on a crop sensor is still a fast aperture, sometimes you want that extra bokeh. I buy f2.8 lenses to shoot at f2.8. If I'm shooting at f2.8 I want the bokeh that f2.8 delivers. Not f4.

See, this is the thing. Mostly I don't care about bokeh. I want f/2.8, or even f/1.4 to be able to deliver extra shutter speed when it is dark. And, usually the prime lens I am using on a crop body is the same lens I use on a full frame body. So an 85 mm f/1.4 lens serves equally well on both bodies since I'm not framing someone's portrait, and frequently I'm not going to move, or can't move, anyway. But I can often crop further with either sensor.

 

[astroNikon]

Isn't bokeh also related to the number and shape of aperture blades in the lens.
Thus another reason to use the same lens at the same aperture setting in multiple comparisons.
Since Bokeh is the out of focus points of light and not just OOF background ??

 

[theraven871]

My point is that while I admit that f2.8 on a crop sensor is still a fast aperture, sometimes you want that extra bokeh. I buy f2.8 lenses to shoot at f2.8. If I'm shooting at f2.8 I want the bokeh that f2.8 delivers. Not f4.

See, this is the thing. Mostly I don't care about bokeh. I want f/2.8, or even f/1.4 to be able to deliver extra shutter speed when it is dark. And, usually the prime lens I am using on a crop body is the same lens I use on a full frame body. So an 85 mm f/1.4 lens serves equally well on both bodies since I'm not framing someone's portrait, and frequently I'm not going to move, or can't move, anyway. But I can often crop further with either sensor.

I completely understand what you're saying.
Sometimes you really need fast apertures, especially if you're doing any night photography. I don't know of any exposure difference that would apply when using a crop vs full frame lens.
However, sometimes you want a fast aperture for the stylized bokeh effect to help make portraits pop. But bokeh is an effect only.
If you don't care about bokeh, then my point was lost on you.

 

[theraven871]

Isn't bokeh also related to the number and shape of aperture blades in the lens.
Thus another reason to use the same lens at the same aperture setting in multiple comparisons.
Since Bokeh is the out of focus points of light and not just OOF background ??

I believe that the number of aperture blades as well as the shape (some are more rounded) can affect the shape and "quality" of the bokeh.
But it shouldn't affect the amount.

Of course, the shape and quality is a very subjective argument.

 

[Ysarex]

Derrel and Wayne are correct and Braineack's math is correct. In an appropriate comparison of like photos smaller sensor cameras produce more DOF.

To make any meaningful comparison in this discussion you must make a comparison of similar photographs. The content and perspective in the two compared photographs must be identical as must also be the photographic conditions -- same exposure, which means same f/stop etc. Therefore both photographs must be taken from the exact same location and the angle of view of the camera/lens systems must be adjusted to produce identical content. Both photographs must be taken using the same photographic conditions, i.e. exposure. All other comparisons are worthless.

Comparing like photographs using different format cameras a photo taken with a smaller format sensor will have more DOF than the same photo taken with a larger format sensor.

..........f^2
H = ----------
..........Nc

The above equation is standard. If you dispute it then you're denying accepted math and are certifiable.

"H" is hyperfocal distance, "f" is focal length, "N" is f/stop and "c" is circle of confusion. It is likewise accepted math that c is determined by the size of the format. If you think sensor size does not effect DOF please show examples of this equation in which changing "c" has no effect on "H."

If you do the math for the above equation so that two different format cameras are taking the exact same photograph you get different values for "H" proving mathematically that you get more DOF from a smaller sensor camera. The math in the illustration below is correct. Hyperfocal distance for the 7D is closer to the camera and that means there's more DOF.

Joe

You just compared to different lenses on two different sensors.
If you compare a 50mm prime on a full frame sensor and a 50mm prime on a cropped sensor, look at the DEPTH OF FIELD.
Even at the same aperture, the depth of field will be smaller on the full frame.

I compared the same photograph taken with two different cameras. A comparison that would be interesting and meaningful to a photographer.

You can't take the same photograph with a 50mm lens on a FF camera and also a cropped sensor camera. So if you compare an apple with an orange and proclaim that they're different what was the point of your comparison? My niece would say, "duuuuhhhhhh."

Joe

My line of thinking is that you can get a 50mm 1.8 prime for both a full frame or crop sensor.
Took a photo with both @ f1.8 you will notice that the full frame has more bokeh.
Its slight, but its there. Is it worth spending the money for full frame? Possibly, but probably not.
I'm wondering if I'm talking about something entirely different than everyone else.

I'm not saying that the physical aperture of a lens actually changes when you put it on a cropped sensor. That would require us to be in the Twilight Zone.
What I'm saying is that an identical lens will take different pictures when mounted on a full frame vs cropped sensor.
The majority of my point is that to find out what the EQUIVALENT lens would be on a full frame, you would need to multiply BOTH the focal length and the aperture by the crop factor.
Everyone seems to understand that a 50mm lens on a crop sensor will have the equivalent focal length of 75mm (if its a 1.5x crop)
My entire point was that if you shot that 50mm lens @ f1.8 on a crop sensor, the equivalent performance would be that of f2.8 . NOT f1.8.
Thus, a 50mm 1.8 lens on a cropped sensor has very near performance to a 75mm f2.8. Its still a 50mm 1.8, but it functions differently when on a crop sensor.
A lens on a crop sensor at f1.8 is different from a lens on a full frame sensor at f1.8.

What is upsetting to me is that we use the same terms for both formats. A 50mm f1.8 on a cropped sensor is a very different experience than a 50mm f1.8 on a full frame.
For marketing purposes, it would be more accurate to instead name a APSC 50mm 1.8 a 75mm f2.8 instead. Because that's the performance you're going to get out of it.
Yes, technically speaking the lens physically hasn't changed. It just will perform differently. That's all that matters to me.
My point is that people want to convince consumers that a 17-50 f2.8 lens (on a crop sensor) will perform the same as a 24-70 f2.8 (on a full fram). That's just not true.
Yes, the focal range will be near the same but the depth of field on the cropped lens will not be the same at f2.8 as it is on the full frame.
The depth of field on the cropped sensor lens @ f2.8 will be very close to the full frame lens @ f4.

My point is that while I admit that f2.8 on a crop sensor is still a fast aperture, sometimes you want that extra bokeh. I buy f2.8 lenses to shoot at f2.8. If I'm shooting at f2.8 I want the bokeh that f2.8 delivers. Not f4.

There was a persistent error in this thread that sensor size is not a factor in determining DOF. My post here was to correct that error. What you're talking about is related but you're still sounding a bit confused with the whole equivalence concept. For example one of my favorite lenses that I used to take portraits was a 150mm f/2.8. I shot that lens on a 6x7 camera -- a 60mm x 70mm negative not a puny little 36mm x 24mm negative. I could say that I bought that f/2.8 lens to shoot at f/2.8 not the equivalent f/5.6 it would be on a FF camera. If I'm shooting at f/2.8 I want the bokeh that f/2.8 delivers -- not f/5.6.

Joe

 

[CameraClicker]

Isn't bokeh also related to the number and shape of aperture blades in the lens.
Thus another reason to use the same lens at the same aperture setting in multiple comparisons.
Since Bokeh is the out of focus points of light and not just OOF background ??

I suspect most people who want bokeh shoot wide open, so the blades are out of the way. Bokeh is actually the quality of the out of focus parts, which is slightly different than DOF.

Joe still hasn't convinced me that sensor size is a factor. The way he adjusts for sensor size is the factor.

 

[theraven871]

Derrel and Wayne are correct and Braineack's math is correct. In an appropriate comparison of like photos smaller sensor cameras produce more DOF.

To make any meaningful comparison in this discussion you must make a comparison of similar photographs. The content and perspective in the two compared photographs must be identical as must also be the photographic conditions -- same exposure, which means same f/stop etc. Therefore both photographs must be taken from the exact same location and the angle of view of the camera/lens systems must be adjusted to produce identical content. Both photographs must be taken using the same photographic conditions, i.e. exposure. All other comparisons are worthless.

Comparing like photographs using different format cameras a photo taken with a smaller format sensor will have more DOF than the same photo taken with a larger format sensor.

..........f^2
H = ----------
..........Nc

The above equation is standard. If you dispute it then you're denying accepted math and are certifiable.

"H" is hyperfocal distance, "f" is focal length, "N" is f/stop and "c" is circle of confusion. It is likewise accepted math that c is determined by the size of the format. If you think sensor size does not effect DOF please show examples of this equation in which changing "c" has no effect on "H."

If you do the math for the above equation so that two different format cameras are taking the exact same photograph you get different values for "H" proving mathematically that you get more DOF from a smaller sensor camera. The math in the illustration below is correct. Hyperfocal distance for the 7D is closer to the camera and that means there's more DOF.

Joe

You just compared to different lenses on two different sensors.
If you compare a 50mm prime on a full frame sensor and a 50mm prime on a cropped sensor, look at the DEPTH OF FIELD.
Even at the same aperture, the depth of field will be smaller on the full frame.

I compared the same photograph taken with two different cameras. A comparison that would be interesting and meaningful to a photographer.

You can't take the same photograph with a 50mm lens on a FF camera and also a cropped sensor camera. So if you compare an apple with an orange and proclaim that they're different what was the point of your comparison? My niece would say, "duuuuhhhhhh."

Joe

My line of thinking is that you can get a 50mm 1.8 prime for both a full frame or crop sensor.
Took a photo with both @ f1.8 you will notice that the full frame has more bokeh.
Its slight, but its there. Is it worth spending the money for full frame? Possibly, but probably not.
I'm wondering if I'm talking about something entirely different than everyone else.

I'm not saying that the physical aperture of a lens actually changes when you put it on a cropped sensor. That would require us to be in the Twilight Zone.
What I'm saying is that an identical lens will take different pictures when mounted on a full frame vs cropped sensor.
The majority of my point is that to find out what the EQUIVALENT lens would be on a full frame, you would need to multiply BOTH the focal length and the aperture by the crop factor.
Everyone seems to understand that a 50mm lens on a crop sensor will have the equivalent focal length of 75mm (if its a 1.5x crop)
My entire point was that if you shot that 50mm lens @ f1.8 on a crop sensor, the equivalent performance would be that of f2.8 . NOT f1.8.
Thus, a 50mm 1.8 lens on a cropped sensor has very near performance to a 75mm f2.8. Its still a 50mm 1.8, but it functions differently when on a crop sensor.
A lens on a crop sensor at f1.8 is different from a lens on a full frame sensor at f1.8.

What is upsetting to me is that we use the same terms for both formats. A 50mm f1.8 on a cropped sensor is a very different experience than a 50mm f1.8 on a full frame.
For marketing purposes, it would be more accurate to instead name a APSC 50mm 1.8 a 75mm f2.8 instead. Because that's the performance you're going to get out of it.
Yes, technically speaking the lens physically hasn't changed. It just will perform differently. That's all that matters to me.
My point is that people want to convince consumers that a 17-50 f2.8 lens (on a crop sensor) will perform the same as a 24-70 f2.8 (on a full fram). That's just not true.
Yes, the focal range will be near the same but the depth of field on the cropped lens will not be the same at f2.8 as it is on the full frame.
The depth of field on the cropped sensor lens @ f2.8 will be very close to the full frame lens @ f4.

My point is that while I admit that f2.8 on a crop sensor is still a fast aperture, sometimes you want that extra bokeh. I buy f2.8 lenses to shoot at f2.8. If I'm shooting at f2.8 I want the bokeh that f2.8 delivers. Not f4.

There was a persistent error in this thread that sensor size is not a factor in determining DOF. My post here was to correct that error. What you're talking about is related but you're still sounding a bit confused with the whole equivalence concept. For example one of my favorite lenses that I used to take portraits was a 150mm f/2.8. I shot that lens on a 6x7 camera -- a 60mm x 70mm negative not a puny little 36mm x 24mm negative. I could say that I bought that f/2.8 lens to shoot at f/2.8 not the equivalent f/5.6 it would be on a FF camera. If I'm shooting at f/2.8 I want the bokeh that f/2.8 delivers -- not f/5.6.

Joe

I'm not confused about the equivalence. This is a beginners forum thread.
I want to ensure that anyone that buys a 17-50mm f2.8 lens for a crop sensor doesn't expect the exact same performance as a 24-70mm f2.8 full frame. Too often people are comparing lenses for crop sensor cameras to their full frame counterparts.
I completely understand how medium formats compound what I'm trying to say. (I shot Pentax 645 for years)

The point is that I see so many advertisements for cropped sensor lenses where they state something similar to: "its just like having the 24-70 with f2.8".
Its a lie. Exposure may be similar, but the depth of field at 2.8 is different than at f4.
Most of the people I speak with buy the 2.8 lenses because they want the bokeh effect. That's what I meant when I said "I buy f2.8 to shoot at f2.8".
I don't want someone to get the impression that the depth of field performance at f2.8 is the same on both crop or full frame.
There are differences between crop sensors and full frame. Just the same as there are differences between full frame and medium format.
I'm only attempting to highly what the marketing teams don't state clearly. I'm not attempting to say one format is superior to the other.
They have different performance.

So, coming full circle. You cannot expect a 50mm f1.8 lens to have the same performance if mounted to a crop sensor, full frame or medium format.
Despite what marketing teams what consumers to think, the format size makes a difference.

I don't even know what you're talking about anymore. I really don't.
The title of this thread is DEPTH OF FIELD.
Depth of field changes based on sensor size, focus distance, and aperture.
f2.8 has a very different depth of field on APS-C, 35mm or Medium Format.

 

[Ysarex]

I compared the same photograph taken with two different cameras (sensor sizes). A comparison that would be interesting and meaningful to a photographer.

You can't take the same photograph with a 50mm lens on a FF camera and also a cropped sensor camera. So if you compare an apple with an orange and proclaim that they're different what was the point of your comparison? My niece would say, "duuuuhhhhhh."

Joe

It's only a comparison that would be interesting to some photographers. Have you noticed we are all talking about different parts of the same thing.

There does seem to be a lot of cross talk going on here. My concern is with this error stated in post #13: "I have full frame and APS-C bodies, and prime lenses, so I got out a tripod, a target and a tape measure. Sensor size has no effect on DOF."

I posted a correction in post #43.

Frequently we make brief statements that are true in certain circumstances, but don't really illuminate sufficiently to permit the information to be used/understood in other situations.

Bokeh comes mostly from focal length, aperture, and distance to subject/distance to background. If a smaller/larger sensor allows you to move with respect to your subject/background, that movement will be what affects the bokeh. Put a 50 mm f/1.8 lens on a crop body, or on a full frame body, and you will be able to go and shoot with the same ISO, same shutter speed, and same aperture, and you will get an image with the same exposure, but different framing. If you want more bokeh, get a full frame body because for any given focal length, you can stand closer and still fit your subject in.

Moving the camera alters perspective and produces a different photograph -- not a valid comparison.

Get a medium format camera because the much larger sensor will let you stand even closer! Standing closer is the part that will deliver more bokeh. Same lens, same distance to subject, same aperture, same DOF, different framing if you have different sensor sizes.

Moving the camera alters perspective and produces a different photograph -- not a valid comparison.

Joe