How fast is realistic?

[MattJenko]

Hi All,

This is a generic type question with a specific example. I use a dedicated flattener/reducer on my ED80 and it works great, but I was wondering what determines the optimal reduction of an F-ratio for any given scope? Is there a scientific approach one can take, or is it more to do with just getting a correct correction (for want of a better phrase) and the reduction of the F-ratio simply stems from the field correction that was required for that particular scope?

I ask as I have recently acquired a lovely little AA Lightwave 60mm triplet. It has a native F7 and from the AltairAstro site I can see that there is not a dedicated flattener per se, just a 0.8 and 0.6 flattener/reducer for this range with a description saying it is suitable for F ratios above 6. Is one intrinsically 'better' and why?

Thanks as always,

Matt

[xtreemchaos]

matt you have been thinking the same as me,i will be watching your post with interest,thanks for posting.all the best.charl.

[MattJenko]

charl - might have to repost this in the science forums to see if anyone there knows

[xtreemchaos]

great mate i watch out there, ive tryed my ed80 with a cheap 50% reducer and field was so wide you could almost see behind you,i havent got the stock reducer/flaterner yet ive got to save my pennys.all the best.charl.

[ollypenrice]

Fast is expensive and if there are any free lunches out there I have yet to hear of them...

Olly

[Earl]

as Olly says Fast is not cheap.

You can get Fast and have to tinker lots to get it to perform, think of a SW Quattro, (They do deliver in the right hands though)

Tak do a F2.8 newt which again has its focuser issues some will say but the resuls off one work well are amazing.

[MattJenko]

I understand the expense of good and fast from my hanging around the forum and on vendor sites, just wondered how much you can push existing higher F-ratio systems with reducers and if there is any science to the optimal reduction. I know it will depend on the quality of the reducer etc, just wondering which reducer to get for my new little addition to my frac family. Cheers again.

[Earl]

I understand the expense of good and fast from my hanging around the forum and on vendor sites, just wondered how much you can push existing higher F-ratio systems with reducers and if there is any science to the optimal reduction. I know it will depend on the quality of the reducer etc, just wondering which reducer to get for my new little addition to my frac family. Cheers again.

it depends on whar reducer is made most between .7-.8 overall best results go with the matched reducer, you can push it further but normally at the expence of image circle.

[ollypenrice]

Trying reducer X with refractor Y can be expensive because there are lots that don't work! Sometimes guests send me images using combinations which have all sorts of nasty issues even with high end kit. I would only use a combination known to work.

Olly

[FraserClarke]

The cameras on professional telescopes are effectively very fancy focal reducers (combined with filter wheels, gratings, focusing mechanisms, etc), and they tend to work around F/2. Going faster is possible (I've seen designs for F/0.9 cameras), but is expensive, complex, and usually only works in very specialized cases.

A hyperstar is probably the closest you'll get in the amateur world I guess...