Focal Reducers for ED Refractor

Dear Sirs,


Will this product:


http://www.astronomics.com/main/product.asp/catalog_name/Astronomics/category_name/7U1FFR2KKXEB8L34WN0HW6E3L3/product_id/1360


Correctly work with these products, providing there is approprate(factory recommended) spacing between the Field Flattner Lens and the CCD focal plain? If so, why? If not so, why not?



http://www.astronomics.com/main/product.asp/catalog_name/Astronomics/category_name/9UVB2628RW1E9JE6EKJJ10T407/product_id/AT80EDT

http://www.astronomics.com/main/product.asp/catalog_name/Astronomics/category_name/9UVB2628RW1E9JE6EKJJ10T407/product_id/AT111EDT

I am making a non technical assumption that if the Field Flattener, Focal Reducer is made for a specific focal length, and that it does not matter what scope it goes on as long as the focal lenghts match or are close. Is there a "Rule of Thumb" of how to match FF/FR to a refractor or does the FF/FR design need to match a particular lens design?

Thank you,


A

My best guess is "no" that flattener will not work
well with those scopes. That flattener is designed to
work with the TeleVue NP line of 4-element scopes which
already have a very flat field. The 3-element scopes you
indicate probably have more field curvature.

It is easy to make some generalizations about simple
doublet scopes, where the field curvature is closely
related to the focal length. For those, a flattener
designed for one 600mm focal length doublet will probably
work well on a different 600mm doublet. But 3 and 4
element scopes are much more difficult to generalize.

If you could get the manufacturers to tell you the
field curvature radius of both the scope and flattener,
that would be one way to figure it out.