I've looked through old posts here and a few other sources but still have a few questions, specifically about the relationship between the objective and tube lens and how changing focal lengths and apertures of the tube lens will impact the image produced by the combined lenses.
For the sake of examples I am considering a Mitutoyo M Plan Apo 10x paired with a Canon R5 and EF 200mm f/2.8L ii prime lens as the tube lens. At this time a DIY tube lens using raynox or others is a tad intimidating so I'd prefer to use more out-of-the-box solutions if possible, plus I already have the EF 200mm lens.
My understanding from reading some helpful posts here is that the magnification is proportional to the tube lenses focal length relative to the objective's. For instance, using a 300mm lens for the tube lens instead of 200mm as designated for the M Plan Apo 10x should result in a magnification of 15x (1.5x greater than the listed magnification on the objective).
- Is that correct?
- If so, what are the drawbacks of altering the tube lens focal length to change magnification instead of using a separate objective?
- Essentially, can I safely change the tube lens focal length to save money on buying multiple objectives?
- Is that correct?
- If so, how does the image circle size change as the tube lens focal length is increased or decreased? Could I just change the tube lens focal length to get better sensor coverage, or to cover a medium format sensor?
- What impact does changing the aperture of the tube lens have on the final image?
- Does stopping down the aperture improve image quality or does that increase diffraction?
- Is there a formula or calculator available that will give the effective F-stop aperture of the combined lenses?
Apologies for the many questions, and a big thank you in advance for any insight shared!