Telescopes

I have this cheap telescope that I want to manipulate to increase it's field of view/decrease magnification for an electronic eyepiece. Is there something I can do with the primary mirror? Do companies make the reverse of barlow lenses?

There are "focal reducers" that shorten the focal length of refractors. This is the opposite of the Barlow lens.
You can buy them, but they are specifically designed for particular scopes, and are expensive, probably more than what your scope costs. They come in 0.33, 0.50, and 0.63 power.
Making your own is possible. If you get two long focus objective lenses (a pair of front lenses from 7×35 binoculars) held close together, curved side almost touching curved side, that would be a good one.
You cannot use this on a mirror Telescope like a Newtonian because there is not enough space between the small diagonal mirror and focusing eyepiece to put one.
There is nothing you can do with the primary mirror to change the way it focuses light.

Are there any drawbacks to the variable magnification telescope eyepiece?

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