In association with the eye piece, it increases the magnification up to 1,5 to 3 times.
A photo we took of Jupiter and Saturn without Barlow lens
And with a Barlow lens
FINDERSCOPE
Can be a small refractor or a simple "star pointer" , fixed in parallel with the tube of the telescope.
It needs to be adjusted before each observation session.To do so, look at a bright sky object with low magnification.
MOTOR
In astrophotography, for exposure times of more then 10 seconds, motorised tracking of an equatorial mount is warranted, to counter the rotation of the earth.
FILTERS
- SUN FILTERS
ALWAYS ON THE APERTURE !!!
Eye piece sun filters (sometimes given with low quality telescopes) are prohibited : they heat up, explode and may cause serious eye injury.
- BLUE, ORANGE, RED, GREEN FILTERS
enhance details on the planets and the moon.
We took this photo of the moon without filter :
We added a green eye piece filter :
- NEBULA FILTERS :
for deep sky observation, such as galaxies and nebulae.
They filter atmospheric light and enhance faint deep sky objects.
They can be used on binoculars and in front of an eye for naked eye observation.
There are 2 types :
- Broad band (LPF = Light Pollution Filter) : they filter a little bit of each light ray from the light spectrum, giving an image of inadequate contrast.
- Narrow band ( O-III , UHC = Ultra High Contrast, Deep sky filter) : very usefull, each is specific for certain types of nebulae or galaxies. But they filter too much light, thus decreasing the brightness of the image. Therefore, they should be used with larger apertures that allow more light in.