Thanks for comments.
Brent,
First of all: price
Others difference:
Texts from Explore Scientific about it:
Quote:
A Focal Extender does exactly what the name implies; it extends the effective focal length of the lens that it is used in conjunction with, thus producing higher magnifications for imaging and visual applications.
Focal extenders are similar to a Barlow or tele-negative lens, but there is one important difference between the two ... ...When you use a standard Barlow or tele-negative lens to increase the magnification of your optical system, your results will be dependent on where you place the Barlow in the optical chain.
Explore Scientific Focal Extender, even if the distance is changed, the magnification remains the same... ...You can place your Focal Extender anywhere along the optical chain between an eyepiece or a camera, and if you are supposed to get 2x magnification, you will get 2x magnification.
|
You loose the possibility of increase "magnification" with extension tube. Undoubtly a Televue Powermate is a better option.
The different internal optic makes focus more easy with Focal Extender. There aren't change in "magnification" factor if you add any accessory or by its position inside the focuser.
I need test more it. I want know if I can get more resolution with extension tube.
It is very important remember that
with direct focus over sensor of camera, the optic system (telescope, camera, barlow or Focal Extender) doesn't magnify.
It projects the image over a flat surface: the sensor.
You got appearance of magnification because of resolution. More pixels, more resolution. Less area of image projected over sensor, more resolution: you can see two craters or only one crater with the same pixels amount of sensor. Therefore. you will see the only one crater with appearance as it was magnified. But
there isn't magnification.
