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In case a human eye has "good enough" focused objects in 1.5 meters and when getting closer, the quality of image loses, how to calculate the amount of diopters to get focused picture (let's say, in the same way, on the verge of getting worse, but still good enough) on the distance about 0.5 meters?

I see that I have two "focal points" here - on the object and one the retina. If the distance to the object changes, what formula could be used to adjust the lens so that the image is still in focus on retina?

Could I calculate this like 2.5 diopters for 0.4 meters minus 0.67 diopters gives about 1.83 diopters or this is not so easy and additive approach could work here, so I have to use another formula with the proportions and 19 diopters for human eye as a basis?

This is an extension of my previous question How to calculate the amount of diopters needed to get focused point closer to an eye? since I realized that it was not quite correct. I need to move a specific "focal point" from 1.5 meter to 0.4 meters still having focused on retina.

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  • $\begingroup$ If you just want to quick extend or modify a question, you can always edit the old one instead of creating a new one $\endgroup$
    – controlgroup
    Commented Jul 19 at 0:08
  • $\begingroup$ @controlgroup, but this would invalidate the comments and accepted answers. Is this a good idea to accept the answer (which is correct for the initial question) and then change the question in a way that makes the answer incorrect? $\endgroup$
    – Damir Tenishev
    Commented Jul 19 at 11:02
  • $\begingroup$ Generally no, that's not a good idea, but it's also hard to get answers on a question that seems like a duplicate. $\endgroup$
    – controlgroup
    Commented Jul 19 at 16:22
  • $\begingroup$ Well, I put some effort to make it more precise How to calculate power of glasses for reading knowing comfortable distance to see? and as the result I get it closed. I have no idea how to make this question well worded. Could you please help me here? $\endgroup$
    – Damir Tenishev
    Commented Jul 19 at 18:22
  • $\begingroup$ I think it just seems like in your previous question you're asking for the community to check your work that you've already done rather than ask a question about the underlying physics concept. We usually like the latter type of question; if you were to ask the question in the title in the body of your post (how do you calculate lens power given reading distance?), it would probably be answered, but the body of the post makes it seem like you're just trying to get the community to double-check your work for you. $\endgroup$
    – controlgroup
    Commented Jul 19 at 18:25

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