Concave magnifier lens Two questions in one Consider a support made from a wide (1m), short (30cm) (approximate sizes just for reference), rigid, empty, open ended cylinder.  Cover the ends with a perfectly flexible transparent sheet. Suck the air out of the contraption. It should look somewhat like a concave lens. The sketch below provides a section view of the "lens".  
Question:  
1 - Would this "lens" concentrate light ?  


*

*I am assuming it would act like a lens because of the difference in density between the inside medium and the outside medium. I am suspecting it would concentrate light because the medium inside is less dense than the outside so it should have the opposite effect of a solid glass concave lens.


2 - What shape will the membranes take under pressure? Will it take the shape that's necessary for a lens?

Temporary Edit to address the "off topic" issue: 
I did a search in physics SE for "What shape" and found lots of questions asking what shape would x material take under x circumstances. Why is mine different? Just because this physics concept would be used in some engineering project later on?
 A: According to this reference https://byjus.com/physics/the-lens-makers-formula/
the lens maker's formula for a lens made of one substance immersed in a different medium is:

In most cases, the surrounding medium is air, and $n_2$ is quite close to $1$ 
 ($1.00029$ for dry air at standard temperature and pressure) $n_1$ is of the order of $1.4$ for many lens materials 
In this case, $n_2$ is still very close to $1$, while $n_1$ is even closer to $1$ approaching exactly $1$ as the pressure inside your air lens reaches zero.
This appears to be a tiny difference,  However, it is enough to change the value of the refractive index ratio from greater than $1$ to less than $1$.  Thus subtracting $1$ from the ratio produces a negative result rather than a positive result for the first factor, and changes a diverging lens to a verrrry slightly converging lens.
A: Your system acts rather like two planar sheets and less like a lens. The fundamental physics of the lens is given by Snell's law, $n_1 \sin(\alpha_1) = n_2 \sin(\alpha_2)$. By using thin plastic sheets you mainly get a shift in the position, but only a tiny change in the direction. Instead of vacuum you should fill it with some oil. 
Sidemark: Your lens is concave. Therefore it would not focus, but defocus an incoming plane wave.
