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There is a really detailed discussion on achieving microscope-magnification using a small focal length lens in reversed configuration.

How to make a microscope with a DSLR camera?

I wish to know which of the following might help in increasing the magnification:

  1. Using a second wide angle lens in reversed lens, in series
  2. Using a narrow angle lens in regular orientation, between the camera and reversed lens
  3. Using an extension tube between the reversed ring and camera.

Which of the above will work, or is there a better way to improve the magnification?

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auto bellows

You may use extensión rings or auto bellows to obtain greater magnífication, with normal or reversed lens.

  • So what happens if the length of bellows or extension tubes needed to get the magnification I desire for a specific lens exceeds the distance required from the image plane to the subject for that magnification? – Michael C Jun 14 '18 at 23:35
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Given the right conditions, all three methods listed in the question can be useful to increase magnification.

Which is best will depend upon the specifics of the lens(es) involved, the desired magnification, and how that affects the working distance of the entire combination.

If it’s not too much to ask, can you please mention in short what will the effect of the listed 3 methods on desired magnification and working distance.

That's entirely dependent upon the specifics of the lenses involved. Adding a 25mm extension tube to a 24mm lens has a very significantly different impact than adding a 25mm extension tube to a 300mm lens. The physical length of each piece will also limit what can be accomplished in terms of greatest magnification before the front of the lens is further from the film/sensor plane than the subject distance required to get the desired magnification. There are a multitude of variables that must be considered including focal length, physical dimensions, the optical design/formula for each piece involved, etc.

For a more specific answer you need to ask a more specific question.

  • If it’s not too much to ask, can you please mention in short what will the effect of the listed 3 methods on desired magnification and working distance. – karthikeyan Jun 16 '18 at 1:56
  • @karthikeyan That's entirely dependent upon the specifics of the lenses involved. Adding a 25mm extension tube to a 24mm lens has an entirely different impact than adding a 25mm extension tube to a 300mm lens. For a more specific answer you need to ask a more specific question. – Michael C Jun 16 '18 at 4:05
  • Since the magnification achievable is inversely related to the focal length, I am using the smallest focal length at my disposal. So if 25 mm extension tube is added to a 18mm lens(Nikon 18-55), and 50mm tube is added to the same, will the magnification keep increasing? Will there be any aberrations that I have to worry about if I keep on increasing my tube length? – karthikeyan Jun 17 '18 at 6:03
  • You can only increase your length until the front of the lens passes the place where you need the subject to be, relative to the camera's sensor/film plane, for the specific magnification provided by that amount of extension. With macro work, magnification is ultimately a function of the ratio of the distance between the optical center of the lens to the sensor and the distance from the subject to the sensor. – Michael C Jun 17 '18 at 12:31
  • "Will there be any aberrations that I have to worry about if I keep on increasing my tube length?" It will depend on what aberrations are demonstrated by the lens(es) involved. Any uncorrected aberrations in the lens(es) will be magnified with an increase in the magnification ratio. – Michael C Jun 17 '18 at 12:34

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