burkphoto Loc: High Point, NC

1:1 in macro context is magnification... completely different from 1:1 being a square aspect ratio... Both are valid in photography. 1:1 in a darkroom is one part of solution A plus one part of solution B... "to make one quart of developer (etc.)."

cactuspic Loc: Dallas, TX

The minute he used auto focus, he is no longer shooting at exactly 1:1, unless he coincidentally was at the exact distance to shoot 1:1, as burkephoto said. If you have a tripod that takes an Arca Swiss plate, the easiest, cheap way to get to 1:1 is to use an Arca type plate on either the tripod ring if your lens has on, or on the camera body perpendicular to the camera back. Then set your lens to 1:1 and slide the camera into final position using live view to determine when focus is achieved. For the most part, true 1:1 focusing is not a requisite of anything unless you are using it to scale the subject. Many tripod macro shots taken at "1:1" are not precisely 1:1 but they are close due to manual final focus. When shooting insects without a tripod, true 1:1 is achieved by setting the magnification first , then focusing by leaning in.

jackm1943 Loc: Omaha, Nebraska

That's exactly what I ran into in my earlier posts. But by moving back a mm or two, it worked fine for focus bracketing.

therwol Loc: USA

I would agree, but in my case when I was photographing 35mm negatives and slides, I wanted the images to fill the camera's sensor entirely, and since they were the same size as the sensor, 1:1 was necessary.

wmurnahan Loc: Bloomington IN

If so that would be a sq.

burkphoto Loc: High Point, NC

Precise 1:1 is UNdesirable if you are using Negative Lab Pro in Lightroom Classic. You need a little area around the frame to do an eye dropper white balance on the film base.

If you are not using NLP, check this out: https://www.negativelabpro.com

therwol Loc: USA

Understood. I was not using that program at the time I took the photos. I was using the Color Perfect Photoshop plugin for negatives which requires that everything outside of the picture be cropped out or it influences the color balance.

User ID

Try reading the openning post. Look for the phrase "set the lens to 1:1". Its well hidden in plain sight.