Jump to content

740427863_Terminatorchallenge.jpg.2f4cb93182b2ce715fac5aa75b0503c8.jpg

Focal reducer?


Astorix
 Share

Recommended Posts

A focal reducer is a positive lens placed between the objective and the prime focus. It reduces the focal length of the objective and reduces the focal ratio. Most reducers, to work properly, usually have a design distance (between the reducer and the focus)

For SCT's the standard reducer is a x0.63 which changes a f10 system to a f6.3, and requires a distance of 110mm. This gives a wider field of view and brighter images; easier for photography.

Ken

Link to comment
Share on other sites

ok without meaning to sound horrible i am still relatively new to this and not really sure what that means.. could you or some one please explain in more simple terms, for etc i do not know what f10 is or what sct? actually is. :p

Link to comment
Share on other sites

SCT = schmidt-cassegrain telescope.

Focal length = how far it is from the first lens or mirror in a telescope to the prime focus point (where you put an eyepiece or camera)

A focal reducer is a lens you put on the eyepiece side of a telescope that effectively makes the image smaller. The same effect could be achieved if you could somehow shorten the focal length, hence "focal reducer". The opposite effect can be achieved with a barlow lens, which is a focal extender: it magnifies the image by effectively increasing the focal length.

People who take astro pics like focal reducers, as Ken says, because they allow you to take shorter exposure images with wider fields of view. Not sure how useful they are for visual work.

Link to comment
Share on other sites

f10 is an example of a focal ratio.

Focal ratio is the focal length of a telescope divided by the size of the primary lens or mirror.

So, for example, I have a refractor with a 900mm focal length and 100mm lens at the front. The focal ratio (f) is therefore:

900mm/100mm = 9.

Again, as Ken says the shorter the focal ratio the brighter the image. The longer the focal ration the greater the contrast.

Because a focal reducer reduces the effective focal length it also reduces the focal ratio.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.