Wayne, this is really not complicated. If you wanted to recreate the shot with a stitched small format image and with the exactly same DOF you would obviously use a 35 mm lens.
DOF is a function of focal length, aperture and distance. It is independent of image size.
Perspective does not depend on focal length.
I'm not sure how I can express it more clearly. I've given you a link to a tutorial that carefully explains it step by step. I'm not sure in what other way to explain it to you.
None of that takes into account the case like this where the aspect ratio difference between the two formats is involved. I am well aware of what that article is saying but I disagree that holds the same when there is also aspect ratio difference like there is between LF,MF and 35mm DSLR.
wayne seltzer wrote:
None of that takes into account the case like this where the aspect ratio difference between the two formats is involved. I am well aware of what that article is saying but I disagree that holds the same when there is also aspect ratio difference like there is between LF,MF and 35mm DSLR.
The only thing the aspect ratio difference does is crop the image differently. All of the object relationships within the frame remain the exact same irrespective of format or lenses used if the camera position does not change.
As an example, shoot (from the same position) a shot with a 24mm lens on FF35, a 50mm lens on 6x6 MF film and a 90mm lens on 4x5. The 24mm lens using FF 35 will provide the widest angle shot (widest aov). Crop that 35mm wide angle image to exactly match what you get with the MF and 4x5 aspect ratios respectively and everything in the frame will be exactly the same... same size and the relationships between all the objects in the frame will be the exact same. This is an example of how perspective does not change regardless of lens, format or aspect ratio and is a fundamental principle of photography.
As Tariq says, the aspect ratio is just like the focal length in that it simply crops away what isn't inside the frame.
Imagine making a 3:2 square with your two hands and looking at a scene. Now slide your hand slightly up until the frame is 4:3 aspect ratio instead. You will see slightly more in the square, but the scene looks otherwise the same. That is what aspect ratio is. Focal length is moving your hands closer and further from your eye.
The relationships between the items in the scene cannot be change. The mountains and the trees will always have exactly the same relationship if you stand in the same spot.
But you won't have equivalent resolution.
Say a mfdb sensor is like two 35mm sensors,one on top of each other in the vertical direction and pixel pitch are the same.Then each of the two 35mm sensors would have to capture half of the vertical distance of the scene to get equal resolution.
You need for the smaller sensor system to match the pixel pitch in the vertical direction with a Tele lens and then stitch to get the same scene size.
Tariq Gibran wrote:
The only thing the aspect ratio difference does is crop the image differently. All of the object relationships within the frame remain the exact same irrespective of format or lenses used if the camera position does not change.
As an example, shoot (from the same position) a shot with a 24mm lens on FF35, a 50mm lens on 6x6 MF film and a 90mm lens on 4x5. The 24mm lens using FF 35 will provide the widest angle shot (widest aov). Crop that 35mm wide angle image to exactly match what you get with the MF and 4x5 aspect ratios respectively and everything in the frame will be exactly the same... same size and the relationships between all the objects in the frame will be the exact same. This is an example of how perspective does not change regardless of lens, format or aspect ratio and is a fundamental principle of photography. ...Show more →
Yes, you can do that but you are losing resolution doing that. You are basically squeezing the same amount of scene vertically that you captured with the mfdb into a sensor with half the vertical height.I agree that you end up with the same size ratios of foreground and background objects and same aov but at the cost of resolution.
Does that make sense?
Well, yes, that has always been the main point of using a larger format. A 6x7 frame is much larger than a 35mm frame so you have better resolution - at least when we're talking film.
As for digital, it gets more complicated. A P21+ digital back (44.2 x 33.1mm) has a resolution of 18 megapixel while a Sony Alpha 900 (24x36 mm) has a resolution of 24.6 megapixel. So in that case the smaller format will provide a higher resolution image.
There are however modern digital medium format backs that have a resolution over 80 megapixels. That again is dwarfed by the resolution you can get by stitching.
Resolution does depend on size, but the real limiting factor is the pixel density of the sensors available at a given time, combined with the resolution of the optics available. An example of extremely close resolving capability between to widely different sensor sizes, is the Nikon 12 MP 36x24 mm sensors (D3s) and the 10 MP 8x6 mm sensor in the Olympus XZ-1. The Test scene at DPreview shows virtually identical resolution between those two (RAW). That gives an indication that it is possible to make future 35 mm systems with the resolving capability of today's large formats.
wayne seltzer wrote:
Yes, you can do that but you are losing resolution doing that. You are basically squeezing the same amount of scene vertically that you captured with the mfdb into a sensor with half the vertical height.I agree that you end up with the same size ratios of foreground and background objects and same aov but at the cost of resolution.
Does that make sense?
This discussion, the one that you agreed upon with Spyro's observation, was never about resolution or enlargement capability to begin with. Spyro said as much at the start. That aspect is obvious and I would think a no brainer. It is often (though not always) the reason for choosing a larger format or more MP to begin with. At this point, it seems like you are taking the discussion in circles and it really can't go anywhere else.
