# Microtops sunphotometer sun target optics

For atmospheric radiation observations, a portable piece of equipment such as the Microtops sunphotometer (pictured below) is useful.

Image source: Solar Light

However, while I can borrow this equipment, its price is way out of my league.

The 'Sun Target' optics intrigues me, it is designed to indicate when the optics in the instrument are pointing directly at the sun (a white dot appears in the center of the sun target when this is achieved), however, I can not figure out how these optics work.

What optical principles allow the Microtops sun target to work?

• As a side note: The right way to find out how a product works is by buying one and by taking it apart. Everybody in the industry does that. If you want to build a competing design you first study the industry leaders' technology. The upfront cost for that is small compared to the burn that results from reinventing the wheel. In many cases the first glimpse at a product already tells you that the competition is actually smart and that the price is justified. Once you know that, any further singing in the bathtub is usually discouraged by a smart product manager. Dec 29 '14 at 23:30
• Side note continued: In those rare cases where the only competing product in the market is poorly designed (also something that you can only learn by taking it apart) there is an attack vector, but those are rather rare events... there are plenty of smart people out there! Dec 29 '14 at 23:30
• As mentioned its price is way out of my league, can only borrow one, much less pull one apart.
– user60063
Dec 29 '14 at 23:32
• Just to clarify, as the question states, I am only asking about the optics principles for that particular component.
– user60063
Dec 30 '14 at 5:27