Bokeh on full frame vs crop

Started Jun 26, 2012 | Discussions
TheRattt
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Bokeh on full frame vs crop
Jun 26, 2012

Hi

Simple (and completely bonkers?) question probably!

Say you have for example a 85mm 1.2 Lens, a 1,6x crop body and a 1.0x full frame body.

Say then you shoot a subject at 5m distance with the aperture wide open. Will the crop body then have a narrower depth of field because of the 1,6x crop and therefore create a "creamier bokeh" than shooting with the same lens in the same situation with a full frame?

I fully understand that a crop frame magnifies 1,6x (canon) but I can't quite wrap my head around how this will affect the out of focus areas. One should think that this lens would result in a very blurry and creamy bokeh on a crop camera, like shooting with a full frame and a (85x1,6)=136mm 1.2 lens? But when I look at pictures taken with a lens like this it always seem like the full frame pictures have a nicer bokeh to them.

Please help me understand this 100% Thanks

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Kjeld Olesen
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Re: Bokeh on full frame vs crop
In reply to TheRattt, Jun 26, 2012

A couple of notes ...

If you go into equivalent focal lengths, you must also account for equivalent f-numbers. If the apparent focal length ingreases, then the apparent f-number also increases as the aperture diameter stayed the same - hence, the 85/1.2 does not stay a "f/1.2" lens at an apparent 136 mm focal length - rather it becomes something like an apparent f/2.0 lens in terms of apparent focal length/apperture diameter.

Secondly, in with your two cameras, do you shoot both images at 5 meters, or do you move the cropping camera backwards to keep the same framing of your subject?

Rgds/Kjeld

TheRattt wrote:

Hi

Simple (and completely bonkers?) question probably!

Say you have for example a 85mm 1.2 Lens, a 1,6x crop body and a 1.0x full frame body.

Say then you shoot a subject at 5m distance with the aperture wide open. Will the crop body then have a narrower depth of field because of the 1,6x crop and therefore create a "creamier bokeh" than shooting with the same lens in the same situation with a full frame?

I fully understand that a crop frame magnifies 1,6x (canon) but I can't quite wrap my head around how this will affect the out of focus areas. One should think that this lens would result in a very blurry and creamy bokeh on a crop camera, like shooting with a full frame and a (85x1,6)=136mm 1.2 lens? But when I look at pictures taken with a lens like this it always seem like the full frame pictures have a nicer bokeh to them.

Please help me understand this 100% Thanks

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rsn48
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Simple answer
In reply to Kjeld Olesen, Jun 26, 2012

Nothing is as simple as it seems, but I'll try and keep my answer simple. If you have a subject stand 12 feet away and shoot with the same lens, lets say an 85mm with two different cameras, a crop and full frame, then the full frame with a narrow depth of field will (might) have better bokeh than the crop camera.

Realize the quality of bokeh is both lens dependent, subject dependent, distance dependent, and background distance from subject dependent. So assuming you are shooting with an 85 with great bokeh, lets say the Sigma 85 and the background is a number of feet behind the subject, the full frame camera image should come out a tad better.

But now as the above poster suggested there can be equivalencies, then the formula gets more complicated. We could throw on a 50mm on the crop sensor camera, if Canon and now you have an 80mm lens, yada yada yada....

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Lemming51
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Re: Bokeh on full frame vs crop
In reply to TheRattt, Jun 26, 2012

All things being equal: 85mm f/1.2 at 5m subject distance, both the sensors will record the identical image at the center. Same perspective, same depth of focus. The full frame will record more periphery around that central image. Crop the image from the full frame to match that captured by the 1.6, and enlarge to the same print or viewing size and they will have identical depth of field.

But all things are rarely equal. Typically, to get the same subject framing the two users are going to use the same lens but at different distances (different perspective), or different focal length lenses at the same subject distance.

TheRattt wrote:

Hi
Simple (and completely bonkers?) question probably!

Say you have for example a 85mm 1.2 Lens, a 1,6x crop body and a 1.0x full frame body.

Say then you shoot a subject at 5m distance with the aperture wide open. Will the crop body then have a narrower depth of field because of the 1,6x crop and therefore create a "creamier bokeh" than shooting with the same lens in the same situation with a full frame?

I fully understand that a crop frame magnifies 1,6x (canon) but I can't quite wrap my head around how this will affect the out of focus areas. One should think that this lens would result in a very blurry and creamy bokeh on a crop camera, like shooting with a full frame and a (85x1,6)=136mm 1.2 lens? But when I look at pictures taken with a lens like this it always seem like the full frame pictures have a nicer bokeh to them.

Please help me understand this 100% Thanks

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Lemming51
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Re: Bokeh on full frame vs crop
In reply to Lemming51, Jun 26, 2012

Lemming51 wrote:

All things being equal: 85mm f/1.2 at 5m subject distance, both the sensors will record the identical image at the center. Same perspective, same depth of focus.

P.S. Didn't menthion by name, but both sensors record the same bokeh as well.

The full frame will record more periphery around that central image. Crop the image from the full frame to match that captured by the 1.6, and enlarge to the same print or viewing size and they will have identical depth of field.

But all things are rarely equal. Typically, to get the same subject framing the two users are going to use the same lens but at different distances (different perspective), or different focal length lenses at the same subject distance.

TheRattt wrote:

Hi
Simple (and completely bonkers?) question probably!

Say you have for example a 85mm 1.2 Lens, a 1,6x crop body and a 1.0x full frame body.

Say then you shoot a subject at 5m distance with the aperture wide open. Will the crop body then have a narrower depth of field because of the 1,6x crop and therefore create a "creamier bokeh" than shooting with the same lens in the same situation with a full frame?

I fully understand that a crop frame magnifies 1,6x (canon) but I can't quite wrap my head around how this will affect the out of focus areas. One should think that this lens would result in a very blurry and creamy bokeh on a crop camera, like shooting with a full frame and a (85x1,6)=136mm 1.2 lens? But when I look at pictures taken with a lens like this it always seem like the full frame pictures have a nicer bokeh to them.

Please help me understand this 100% Thanks

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kasinp
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Re: Bokeh on full frame vs crop
In reply to TheRattt, Jun 26, 2012

TheRattt wrote:

Hi

Simple (and completely bonkers?) question probably!

Say you have for example a 85mm 1.2 Lens, a 1,6x crop body and a 1.0x full frame body.

Say then you shoot a subject at 5m distance with the aperture wide open. Will the crop body then have a narrower depth of field because of the 1,6x crop and therefore create a "creamier bokeh" than shooting with the same lens in the same situation with a full frame?

I fully understand that a crop frame magnifies 1,6x (canon) but I can't quite wrap my head around how this will affect the out of focus areas. One should think that this lens would result in a very blurry and creamy bokeh on a crop camera, like shooting with a full frame and a (85x1,6)=136mm 1.2 lens? But when I look at pictures taken with a lens like this it always seem like the full frame pictures have a nicer bokeh to them.

Please help me understand this 100% Thanks

This isn't perfect but it gives a pretty good simulation of what you will see.

It supports your observation that crop bokeh is no match for FF (other things being seemingly equal).

http://kingfisher.in.coocan.jp/boke2/bokekeisan2e.html

PK

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kjbkix
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Re: Bokeh on full frame vs crop
In reply to kasinp, Jun 26, 2012

Thanks a lot for just giving me a ridiculously distracting toy to play with...

This isn't perfect but it gives a pretty good simulation of what you will see.

It supports your observation that crop bokeh is no match for FF (other things being seemingly equal).

http://kingfisher.in.coocan.jp/boke2/bokekeisan2e.html

PK

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TheRattt
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Re: Bokeh on full frame vs crop
In reply to kjbkix, Jun 27, 2012

Thank you for the answers and your patience with my newbieness.

Ok, so for the sake of a 'real world' scenario;

If i have a canon 85mm/1.2L, a 7D body and a 5D body. A tripod at 0 metres, a human subject (looking straight into the camera) at 3 metres and a "bokeh friendly" ....christmas tree at 10 metres.

Shooting with either camera (wide open with focus on subjects eyes) would result in the pretty much the same quality of out-of-focusness on the xmas tree (and the area in focus on the subject will be the same - lets say the eyes and ears are both sharp)? The only difference being the 7D would result in a image that was just like you had cropped an image from the 5D i photoshop (apart from the change in mpix)? Would I be right in making this statement?

What Kjeld Olsen said about equivalent focus lengths and accounting for equivalent f-stops threw me off a bit, because now I am thinking f1.2 -> f2 - well then you would need better light to capture the image with the 7D than the 5D (?!). And surely 1.2 would result in a blurrier out-of-focus than f2 if distances are constant as described above (?) Did you mean that for this to apply I would have to move the background, subject and tripod 1,6x further apart with a full frame/136mmf2 to get the same image as a 7D 85mm/1.2 at 3 metres?

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TheRattt
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Re: Bokeh on full frame vs crop
In reply to TheRattt, Jun 27, 2012

Thank you for the link to the tool btw. According to this tool my above statements might be right!

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Eric Sorensen
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Here's where the full frame will look better...
In reply to TheRattt, Jun 27, 2012

TheRattt wrote:

Thank you for the answers and your patience with my newbieness.

Ok, so for the sake of a 'real world' scenario;

If i have a canon 85mm/1.2L, a 7D body and a 5D body. A tripod at 0 metres, a human subject (looking straight into the camera) at 3 metres and a "bokeh friendly" ....christmas tree at 10 metres.

Shooting with either camera (wide open with focus on subjects eyes) would result in the pretty much the same quality of out-of-focusness on the xmas tree (and the area in focus on the subject will be the same - lets say the eyes and ears are both sharp)? The only difference being the 7D would result in a image that was just like you had cropped an image from the 5D i photoshop (apart from the change in mpix)? Would I be right in making this statement?

In your above example - that is all true. But if you don't crop the 5D image (why waste all those pixels?) and just step forward to get the same framing as the 7D, you are at a closer focus distance, which GREATLY decreases the DOF and, with the Canonball F1.2, your bokeh will be very pronounced and creamy indeed.

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Keith Z Leonard
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Re: Here's where the full frame will look better...
In reply to Eric Sorensen, Jun 27, 2012

True, you will also get less stuff in focus, so it's a matter of what the photograph requires. If you frame the image the same with the 2 cameras then you will be closer to the subject with the 5d than with the 7d, which changes your DOF calculation, the bokeh though (as I understand it) is a function of the lens.

Bokeh is about the quality of out of focus areas rather than the amount of blur. A 50 f1.8 on a 35mm format camera at f2 doesn't have better bokeh than the 50 f1.2 L or Sigma 50 f1.4 @ f2 on an aps-c sensor. The blur will be greater with the 35mm camera, but the quality of the blur will be better with the better lens (rounded aperture blades, etc...)

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TheRattt
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Re: Here's where the full frame will look better...
In reply to Keith Z Leonard, Jun 27, 2012

Thanks guys. This all makes sense now. I get how the more flexible framing distance of the 5D allows a narrower DOF and creamier bokeh.

What confused me in the first place was this idea that a 85mm lens became a 136mm lens when put on a crop camera (which is often how it is simplified when you read about these things) which in turn I assumed would affect the DOF.

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Keith Z Leonard
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Re: Here's where the full frame will look better...
In reply to TheRattt, Jun 27, 2012

I feel compelled to point out that it isn't really framing "flexibility", it's just different framing. I suppose you can look at it as flexibility if you consider that you can stop down the 5d to get what you want in focus but you cannot open up the 7d more than the lens allows. Both cameras have infinite framing flexibility...You can always back up!

A head shot taken with aps-c at anything other than face forward will take f4-f8 to get both eyes in sharp focus, for 35mm that would be f5.6-f11, both do the job well, but if you want to intentionally have the subject face you and have the hair OOF or the mouth OOF, etc, that's easier to do with a 35mm camera.

This issue is brought up a lot, I don't know how much though it really matters in practice. There are times that it matters, but it's somewhat specialized. The 35mm sensors right now have other advantages that are probably more of an impact, like reduced noise and lower pixel density which gives you sharper apparent images at 100%, which is a big deal to some people. All of the advantages/disadvantages in both directions largely depend upon how/what you shoot.

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