Apertia · Library
What assumptions belong in a manual lens-kit comparison?
Compare a 50 mm and an 85 mm lens at 3 m with saved Apertia kits: 2087.4 mm versus 1197.5 mm of scene width and 580.1 mm versus 191.7 mm of depth at f/2.8.
What a kit stores
In Apertia a kit is a camera body and a lens: you give it a name such as A7 IV + 85 mm, choose the sensor preset and enter the focal length. The app remembers the last aperture and focus distance used with each kit, and kits stay on the iPhone without an account. The free version keeps one kit; Pro allows unlimited kits and the A/B compare view, where one setting can be pinned as B next to the current one.
Because a kit only holds a sensor preset, a focal length and the last setting, a comparison between kits is only as fair as the conditions you hold fixed. The same focus distance, the same framing and the same near-to-far target are three different questions.
Set up a fair two-lens record
- Create one kit per lens on the same sensor preset, using the real focal lengths.
- Write down which condition stays fixed: camera position, subject framing or detail range.
- Enter the same aperture and focus distance in both kits for a same-position comparison.
- Pin the first result as B and switch kits to see both side by side.
- Note the near limit, far limit and total for each, with the circle of confusion used.
Worked example: same position, two lenses
From one camera position 3000 mm from the subject, a 50 mm lens on full frame covers about 2087.4 × 1391.6 mm of a flat subject, while 85 mm covers 1197.5 × 798.3 mm. At f/2.8 the 50 mm depth of field runs from 2738.222 to 3318.283 mm (580.061 mm); the 85 mm runs from 2907.307 to 3098.994 mm (191.687 mm). The 85 mm result is shallower partly because it shows a smaller part of the scene, so the record must say that framing was not held constant.
- 50 mm · f/2.8 · 3000 mm
- 580.061 mm total
- 85 mm · f/2.8 · 3000 mm
- 191.687 mm total
- Scene width 50 mm / 85 mm
- 2087.4 / 1197.5 mm
Common mistakes
- Ranking lenses by depth of field without stating that the subject size in the frame changed.
- Saving a phone kit and expecting an adjustable aperture; the iPhone preset fixes it at f/1.78.
- Naming a kit after a camera body while choosing a sensor preset that does not match its recording mode.
Scope of a kit comparison
Kits compare planning inputs, not verified lens specifications. Supported apertures, minimum focus distance, distortion and autofocus behaviour come from the manufacturer. Nikon's focal-length guide and the DOFMaster equations listed below explain the two calculations used here.