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Can I create a lens that will function as a magnifying glass or spyglass with Minor Illusion by using the illusion as a focus to warp or bend light as a lens might?

Alternatively, can Prestidigitation create a spyglass or magnifying glass?

You create a nonmagical trinket or an illusory image that can fit in your hand and that lasts until the end of your next turn.

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Permanently replacing these valuable objects is beyond the capabilities of these spells.

Minor illusion says:

If you create an image of an object--such as a chair, muddy footprints, or a small chest--it must be no larger than a 5-foot cube. The image can't create sound, light, smell, or any other sensory effect.

I'd rule that magnification is an "other sensory effect", so this doesn't work. See this great answer for further details. Further, minor illusion stipulates:

Physical interaction with the image reveals it to be an illusion, because things can pass through it.

It seems to me that because it is an illusion and things pass through it unimpeded, light would pass through the glass unmodified, so it would not function to magnify what you are looking at - magnification requires the light to interact with the medium it passes through, which is not how minor illusion works.

Prestidigitation says:

You create a nonmagical trinket or an illusory image that can fit in your hand and that lasts until the end of your next turn.

A spyglass is not a trinket. It's worth 1000gp. Examples of trinkets can be found on this table in the basic rules. None of these come even close to the value of a spyglass (their values aren't even listed - they aren't worth much at all).

This ruling is further supported by the Sage Advice Compendium when it says:

What kinds of things count as “nonmagical trinkets” for prestidigitation? Prestidigitation can create a little bauble, the nature of which is up to the spellcaster and the DM. See the Trinkets table in the Player’s Handbook for examples.

That's the closest thing to a RAW answer we have here, and I think it's pretty clear, especially with the explanation from Sage Advice. Further, there's a pretty clear (to me at least) sense in which these spells are not meant to create things of significant value, and magnifying glass and a spyglass are valued at 100 gp and 1000 gp, respectively. Why does this value matter? A cantrip than can be cast at will with no cost serves as a functional permanent replacement for these items if they are allowed to create them.

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    \$\begingroup\$ I didn't feel the value of the item mattered since the items disapeared quite quickly and were mainly for roll playing. \$\endgroup\$ Commented Jul 25, 2020 at 23:03
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    \$\begingroup\$ The issue is that an at will cantrip that can produce these item is a functional permanent replacement for having them. I’ll make that clearer in the answer. \$\endgroup\$ Commented Jul 25, 2020 at 23:04
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    \$\begingroup\$ Good answer upvoted for the detail in response to what a "trinket" means. However, magnification should not fail because it is a "sensory effect" - how does one sense magnification? Rather, it should fail because "Physical interaction with the image reveals it to be an illusion, because things can pass through it." That is, the real light would pass through the illusory lens unmodified rather than being bent (magnified). This reasoning is used in several of the answers given to the question you link as a "great answer". \$\endgroup\$
    – Kirt
    Commented Jul 26, 2020 at 8:20
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    \$\begingroup\$ To be clear, one senses magnification with the eyes. \$\endgroup\$ Commented Jul 26, 2020 at 8:23
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    \$\begingroup\$ @Kirt Thanks, I finally got around to adding in your suggested improvements nearly two years later. \$\endgroup\$ Commented Feb 11, 2022 at 13:02
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Yes. Both of these items are listed on lists of Trinkets, with drawbacks attached.

One of the Gothic Trinkets listed in Curse of Strahd is the following:

A spyglass that always shows the world suffering a terrible storm

Thus, using Prestidigitation to create a spyglass should be possible, but it'll always show the view of an area being battered by a terrible storm, regardless of the actual weather.

Similarly, Mordencainen's Tome of Foes lists the following as an Elven Trinket:

A crystal lens made of ivory and gold that causes anything observed through it to appear to be surrounded by motes of multicolored light

Thus, it should be possible to use Prestidigitation to create a magnifying glass, as long as it causes all objects or creatures observed by it to be surrounded with motes of multicoloured light.

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  • \$\begingroup\$ Neither of those trinkets specify magnification \$\endgroup\$
    – Caleth
    Commented Jun 12 at 11:17
  • \$\begingroup\$ @Caleth The words "spyglass" and "lens" imply magnification. That is their nature. \$\endgroup\$
    – Kirt
    Commented Jun 12 at 13:45
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    \$\begingroup\$ @Kirt lenses in sunglasses don't magnify, they change colour / brightness. "A spyglass that always shows the world suffering a terrible storm" changes what you see, but doesn't necessarily magnify it \$\endgroup\$
    – Caleth
    Commented Jun 12 at 13:50
  • \$\begingroup\$ @Caleth The definition of lens includes sunglass lenses not because they magnify, true, but because they protect the eyes. Which of these does the Elven Trinket do? What definition of lens does it meet? A trinket that showed the world suffering a terrible storm but did not magnify it would not be a spyglass - it would be "a tube of metal and glass that shows the world suffering a terrible storm." \$\endgroup\$
    – Kirt
    Commented Jun 12 at 14:11
  • \$\begingroup\$ @Kirt A listing in a particular dictionary isn't necessarily exhaustive. In any case, a crystal will protect the eye to some extent. "a tube of metal and glass" is a spyglass. If it doesn't do anything, it's a pretty useless spyglass, but the mentioned one does do something. \$\endgroup\$
    – Caleth
    Commented Jun 12 at 14:19
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For Minor Illusion? Yes.

You create a sound or an image of an object

Is a magnifying glass an object? Yes it is.

Creating an image of something must include refraction or else any transparent object you created - such as a glass cup - would be invisible. A glass cup is only visible from how it refracts light, it is visible in water but if a glass cup is submerged in a fluid that has the same refractive index as glass it becomes invisible.

The image of an object includes refraction.

Magnification is just a specific type of refraction.

The key limitation is:

The image can't create sound, light, smell, or any other sensory effect.

This does not say "no light can come from the image" only that it cannot create the light.

Refracting light is not creating light. If you're in a dark room and uncover a lens that refracts light to a point, that does not create light.

Just to pre-empt this, just because you could create a magnifying lens or even a series of magnifying lenses, that wouldn't allow you to reliably create a functional telescope or microscope. You'd have to know what sort of lens of what refraction and what distance. Your DM may require a relevant tools or skill proficiency to even attempt this or at the very least that you have seen a telescope before.

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