Description
Opticron 40862 HDFT Zoom Eyepiece for HR, ES, GS, IS, MM2 and MM3 Telescopes
Terrestrial telescopes are most commonly used for high magnification viewing over long distances in daylight. Image quality at different magnifications will depend on the optical system, the quality of glass used and the coatings applied to the surfaces of each lens. There are however a few general rules that can be applied in determining the right specification for your needs. Firstly, the relationship between magnification, objective lens dia. and the size of the eye pupil, and secondly the quality of the optics inside the scope.
In normal daylight, when the pupil is dilated to between 2 and 3mm, a 66 mm telescope will deliver optimum performance, (the balance between magnification and image brightness) between 22x and 35x magnification i.e. when the exit pupil diameter equals that of the iris. In low light when the pupil becomes larger, dilating to between 5 and 7mm depending on age, optimum performance can only be obtained by using a lower magnification eyepiece or using a larger objective lens telescope such as an 80mm or 100mm. The higher the magnification, the greater the image and colour distortion. These effects can be dramatically reduced by using ED or Fluorite combination objective lenses that minimise chromatic aberration, but are expensive. At magnifications of 30x or lower, the benefits of these objective lenses are hardly noticeable when compared to conventional glass objectives.
The best way to assess the actual brightness of any telescope and eyepiece combination when choosing for daytime terrestrial use, (assuming equal optical systems) is to calculate the exit pupil diameter in the same way as with a binocular and making a trade-off between image brightness and magnification desired. For general daytime terrestrial observations good compromise magnifications are between 20x and 30x for a 60mm, 25 to 35x for a 66mm and 25 to 40x for an 80mm.
- Eye relief (mm): 22~17
- Eye relief (inch): 0.9~0.7
- Waterproof: No
- Length (mm): 76
- Width (mm): 50
- Depth (mm): 50
- Dimensions LxWxD (mm): 76x50x50
- Weight (g): 206
