Proposal for a lens Test

jared_kipe

macrumors 68030
Original poster
Dec 8, 2003
2,967
1
Seattle
So common wisdom says that under similar perspectives, a cropped DSLR has less background blur/more DOF than a non cropped DLSR. With the argument that you have to be farther away from the subject.

I've been thinking about this for a while and have come to the conclusion (in my mind at least) that the only things that should matter for DOF and bokeh will be the distance to the subject, and the angle of view. My prediction is that something like a 50mm on a cropped DSLR (~80mm) with an identical framing of an 85mm lens on a non cropped DSLR will yield similar bokeh and DOF. (at the same f stops)

I do not have the means for this test. So I'm asking for some help. Can someone with access to a 20D and a 5D, and 50mm f1.4 and 85mm f1.8 please set up a scene where you can monitor the bokeh behind an object to focus on. Its a pretty simple test, and if I had the means I would perform it.

Thank you.
 

snap58

macrumors 6502
Jan 29, 2006
310
0
somewhere in kansas
jared_kipe said:
So common wisdom says that under similar perspectives, a cropped DSLR has less background blur/more DOF than a non cropped DLSR. With the argument that you have to be farther away from the subject.

I've been thinking about this for a while and have come to the conclusion (in my mind at least) that the only things that should matter for DOF and bokeh will be the distance to the subject, and the angle of view. My prediction is that something like a 50mm on a cropped DSLR (~80mm) with an identical framing of an 85mm lens on a non cropped DSLR will yield similar bokeh and DOF. (at the same f stops)

I do not have the means for this test. So I'm asking for some help. Can someone with access to a 20D and a 5D, and 50mm f1.4 and 85mm f1.8 please set up a scene where you can monitor the bokeh behind an object to focus on. Its a pretty simple test, and if I had the means I would perform it.

Thank you.
This is with a 85 mm on a 20D at F2 and a 135 mm on a 5D at F2. The FOV should be very close for both, looks like the blur is much better on the 5D.
 

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ChrisA

macrumors G4
Jan 5, 2006
11,610
408
Redondo Beach, California
This issue is much older than digital

jared_kipe said:
So common wisdom says that under similar perspectives, a cropped DSLR has less background blur/more DOF than a non cropped DLSR. With the argument that you have to be farther away from the subject.

I've been thinking about this for a while and have come to the conclusion (in my mind at least) that the only things that should matter for DOF and bokeh will be the distance to the subject, and the angle of view. My prediction is that something like a 50mm on a cropped DSLR (~80mm) with an identical framing of an 85mm lens on a non cropped DSLR will yield similar bokeh and DOF. (at the same f stops)

I do not have the means for this test. So I'm asking for some help. Can someone with access to a 20D and a 5D, and 50mm f1.4 and 85mm f1.8 please set up a scene where you can monitor the bokeh behind an object to focus on. Its a pretty simple test, and if I had the means I would perform it.

Thank you.
People have have LOTS of experiance with this going back 100+ years. Long before there were digital cameras there was film and film comes in different sizes. At the small end we have 35mm which is 36x24mm and then medium formats ranging from 60x45mm to 90x60mm and then view camera in 4x5, 5x7 and 8x10 inch sizes.

The difference between DSLR frame and a full 35mm frame is subtle compared the range of sizes avalable with film.

With film we can choose the format based on the "look" we are after. But now that we are digital we select a format (sensor size) based on our budget. For years photographers used Medium format because to result looked different.

The "look" has some to do with depth of field but more I think with camera to subject distance. It is this distance that controls perspective (the size ratio of forground to background objects) Using a short lens and getting close makes forgound objects look bigger while backing up and using a telephoto lens "flattens" the image. with the larger formats we tend to use relativly wider lenses.

All that said. It is absolutly true that the larger formats have much reduced depth of field. Just try shooting products on a table top with medium format and will get to know f-stops between 16 to 32 well where as with a DSLR you can be at f/5.6 and using much less light. With an even larger format like 4x5 you will need to use tilts and swings to keep the subject in focus as there will never be enough DOF

Bottom line. this is by no means a new subject. It's as old as photography

If you read any of the video forums people there talk about how to capture the "film look" using video. Movie film is the same or our 35mm film but it moves vertically through the camera so the move frames are 24mm wide. high-end "pro-summer" video camera have CCD sensors that are between 8mm and 6mm So the "look of film" has a lot to do with DOF and perspective and is even more pronouced than what we see between film and digital SLRs. But they also have the issue of frame rates, dynamic range and color
 

snap58

macrumors 6502
Jan 29, 2006
310
0
somewhere in kansas
ChrisA said:
Bottom line. this is by no means a new subject. It's as old as photography


All true, but keep in mind that there are (amazingly) a lot of people on this forum that have not ever used film, let a lone medium or large format cameras. For them, this may be a new subject.

There are some real benefits to the FF sensor for some types of photography where shallow DOF and nicely blurred background is desired.