Photographic Lenses FAQ
This FAQ contains a list of Frequently Asked Questions about lenses. It is intended for photographers. It defines terms, gives a large number of formulas, discusses depth of field issues, vignetting, diffraction, lens aberrations, and the Modulation Transfer Function.
This FAQ about Photographic Lenses was compiled and written by David Jacobson with numerous contributions by others.
This is the Lens FAQ. It is a technical document describing a lot of optics related information of use to photographers. It does not answer questions about particular commerical lenses. You won't find out whether Canon or Nikon is better. But you will find all sorts of formulas and technical information.
01. What is the meaning of the symbols in the rest of this FAQ?- photo lenses FAQ: 01. What is the meaning of the symbols in the rest of this FAQ?
- 02. What is the meaning of focal length? In other words, what about a 50mm lens is 50mm?
- photo lenses FAQ: 02. What is the meaning of focal length? In other words, what about a 50mm lens is 50mm?
- 03. What is meant by f-stop?
- photo lenses FAQ: 03. What is meant by f-stop?
- 04. What is the basic formula for the conditions under which an image is in focus?
- photo lenses FAQ: 04. What is the basic formula for the conditions under which an image is in focus?
- 05. What is the formula for magnification?
- photo lenses FAQ: 05. What is the formula for magnification?
- 06. For a given lens and format what is angle of coverage?
- photo lenses FAQ: 06. For a given lens and format what is angle of coverage?
- 07. How do I correct for bellows factor?
- photo lenses FAQ: 07. How do I correct for bellows factor?
- 08. What is meant by circle of confusion?
- photo lenses FAQ: 08. What is meant by circle of confusion?
- 09. What is hyperfocal distance?
- photo lenses FAQ: 09. What is hyperfocal distance?
- 10. What are the closest and farthest points that will be inacceptably sharp focus?
- photo lenses FAQ: 10. What are the closest and farthest points that will be inacceptably sharp focus?
- 11. What is depth of field?
- photo lenses FAQ: 11. What is depth of field?
- 12. What is Depth of Field Preview?
- photo lenses FAQ: 12. What is Depth of Field Preview?
- 13. Where should I focus my lens so I will get everything from some close point to infinity in focus?
- photo lenses FAQ: 13. Where should I focus my lens so I will get everything from some close point to infinity in focus?
- 14. Are there some simpler approximate formulas for depth of field?
- photo lenses FAQ: 14. Are there some simpler approximate formulas for depth of field?
- 15. I have heard that one should use a long lens to get a shallow depth of field and a short lens to get a large depth of field. Is this true?
- photo lenses FAQ: 15. I have heard that one should use a long lens to get a shallow depth of field and a short lens to get a large depth of field. Is this true?
- 16. If I focus on some point, and then recompose with that point not in the center, will the focus be off?
- photo lenses FAQ: 16. If I focus on some point, and then recompose with that point not in the center, will the focus be off?
- 17. If I get glasses (or bifocals) will my focusing be off?
- photo lenses FAQ: 17. If I get glasses (or bifocals) will my focusing be off?
- 18. What are vignetting and light falloff?
- photo lenses FAQ: 18. What are vignetting and light falloff?
- 19. How can I tell if a lens has vignetting, or if a filter is causing vignetting?
- photo lenses FAQ: 19. How can I tell if a lens has vignetting, or if a filter is causing vignetting?
- 20. For panoramic pictures, where is the best place to pivot the camera?
- photo lenses FAQ: 20. For panoramic pictures, where is the best place to pivot the camera?
- 21. What is diffraction?
- photo lenses FAQ: 21. What is diffraction?
- 22. What is the diffraction limit of a lens.
- photo lenses FAQ: 22. What is the diffraction limit of a lens.
- 23. What are aberrations?
- photo lenses FAQ: 23. What are aberrations?
- 24. Can I eliminate these aberrations by stopping down the lens?
- photo lenses FAQ: 24. Can I eliminate these aberrations by stopping down the lens?
- 25. Why do objects look distorted when photographed with a wide angle lens?
- photo lenses FAQ: 25. Why do objects look distorted when photographed with a wide angle lens?
- 26. How does focal length affect perspective?
- photo lenses FAQ: 26. How does focal length affect perspective?
- 27. What is "MTF".
- photo lenses FAQ: 27. What is
- 28. What is SQF?
- photo lenses FAQ: 28. What is SQF?
- 29. What are "elements" and "groups", and are more better?
- photo lenses FAQ: 29. What are
- 30. What is "low dispersion glass".
- photo lenses FAQ: 30. What is
- 31. What do APO and Apochromatic mean?
- photo lenses FAQ: 31. What do APO and Apochromatic mean?
- 32. What is an "aspheric element"?
- photo lenses FAQ: 32. What is an
- 33. What is a teleconverter?
- photo lenses FAQ: 33. What is a teleconverter?
- 34. How does a teleconverter affect exposure, focusing, depth of field and image quality?
- photo lenses FAQ: 34. How does a teleconverter affect exposure, focusing, depth of field and image quality?
- 35. What is the difference between using a teleconverter at the time the picture is exposed vs. enlarging more in the printing process?
- photo lenses FAQ: 35. What is the difference between using a teleconverter at the time the picture is exposed vs. enlarging more in the printing process?
- 36. How can I take "close up" pictures.
- photo lenses FAQ: 36. How can I take
- 37. What is the optimum aperture for a pinhole camera?
- photo lenses FAQ: 37. What is the optimum aperture for a pinhole camera?
- 38. How can I use my photographic light meter or camera to measureillumination?
- photo lenses FAQ: 38. How can I use my photographic light meter or camera to measureillumination?
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