The TeleVue 12mm Nagler Type 4 combines a popular focal length with an ultra wide 82 degree field comfortable longer eye relief.
Stock Status: in stock
Eyepiece Focal Length :
Aparent Field :
Eye Releif :
Weight (ounces) :
Barrel Diameter (inches) :
1.25 and 2 inches
Enter your telescope's specifications:
Focal Length (mm)
Exit pupil represents the diameter of the column of light exiting the eyepiece.
Magnification is simply the ratio of telescope aperture to exit pupil. Fox example, using a telescope with
100mm aperture and an exit pupil of 2mm yields a magnification of 50X.
There are both upper and lower limits to the useful range of exit pupils.
The typical human eye pupil dilates to a maximum of 7mm when fully dark adapted.
This figure decreases with age. Using an exit pupil that is larger than this upper limit simply
spills the light onto an area of the eye not capable of receiving data. At the opposite end of the range,
a smaller exit pupil means less area on the eye is collecting data. Images brightness decreases with decreasing
exit pupil. Deep space objects grow dimmer rapidly as the exit pupil falls below 1 mm. The planets also
start to become noticeably dimmer when the exit pupil falls much below 0.5 mm.
Our eyepiece calculator provides warnings and error messages based upon the value of the exit pupil.
These are intended to be guidelines as opposed to hard rules. There is no harm in violating these guidelines,
but your enjoyment of the telescope may be diminished if you do.
The TeleVue 12mm Nagler Type 4 combines a popular focal length with more comfortable longer eye relief. It features both a 1.25-inch and 2-inch barrel, meaning that it can be placed in either size of focuser or star diagonal. The inner 1.25-inch barrel is threaded for 1.25-inch filters. This eyepiece also features an adjustable eye cup so that it may be used with or without eyeglasses.