Compression is Real

Started 7 months ago | Discussions thread
Bill Ferris
Bill Ferris Veteran Member • Posts: 3,121
Re: Photos Demonstrating Distance to Subject/Background Determines "Compression"

I set up a simple test in my rec room to demonstrate the principles presented and discussed in more detail in the F-stoppers video: link to video

The following three images were made with my Nikon D610 and a Tamron 70-200mm f/2.8 Di VC USD zoom lens. The camera and lens were mounted on a tripod and in the same position for all exposures.

The first two photos are single exposures made at two different focal lengths. Both were made from the exact same distance and perspective on the scene. The last image is a panoramic composite made from 25 exposures. The settings for the exposures used to make the composite were exactly the same as the single exposure made at 200mm. The panorama was made in Lightroom. Notice the upper left corner where the stitch was left blank.

Image #1

Nikon D610 w/ Tamron 70-200mm f/2.8 Di VC USD at 70mm, f/2.8, 1/200, ISO 800

Image #2

Nikon D610 w/ Tamron 70-200mm f/2.8 Di VC USD at 200mm, f/8, 1/25, ISO 800

At 70mm, f/2.8, the lens would have had an aperture of about 25mm. At 200mm, f/8, the lens should have had about the same 25mm aperture. (The Tamron is well-known for having a bit of focus breathing when focused up close.) Slowing the shutter speed from 1/200 to 1/25 compensated for the change in f-stop and allowed for images of equivalent brightness to be captured.

These first two images demonstrate the different manner in which 70mm and 200mm focal lengths will present the same scene, from the same distance and perspective. Here, is the panoramic stitch.

Image #3

Panoramic stitch made in Lightroom from 25 exposures at 200mm, f/8, 1/25, ISO 800. I've cropped the stitch to roughly match the composition of the first image.

If you compare the first image with the panorama, they match in composition and perspective. The photo made at 70mm, f/2.8 has a slightly shallower depth of field. This is a product of the Tamron's focus breathing. The focal length was probably closer to 175mm, which would have made the lens aperture (f/8) about 22mm. The smaller aperture used to photograph the scene from the same distance accounts for the slight difference in depth of field.

Otherwise the single photo made at 70mm and the panoramic stitch of exposures made at 200mm are a good match. This demonstrates the fact that two lenses of different focal length used with the same camera from the same location to photograph the same scene will capture identical perspectives. Their renderings of the scene will be different: the shorter focal length will capture a wider angle of view, and subjects visible in both photos will appear smaller in the image made at the shorter focal length. However, both the position and size of the subject relative to the background will be identical in both photos.

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Bill Ferris Photography
Flagstaff, AZ

 Bill Ferris's gear list:Bill Ferris's gear list
Nikon D610 Fujifilm X-T20 Nikon AF-S Nikkor 16-35mm F4G ED VR Nikon AF-S Nikkor 70-300mm f/4.5-5.6G VR Tamron SP 24-70mm F2.8 Di VC USD +3 more
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