help working out plz

[astrokat]

ive a 6"sct ive just got a 6.3 focal reducer what will this make my scope now? what would it be close to in size eg 5" or 4" scope

thanks toby

[Beyond_Vision]

The focal reducer will reduce the focal length by a factor of 0.63. It lowers the F number of the scope which will increase the field of view of the scope. This will allow you to capture a brighter image over a given exposure time than without the focal reducer.

Regards

Kevin

[John]

It's still a 6" scope - but a faster one !.

[russ]

ive a 6"sct ive just got a 6.3 focal reducer what will this make my scope now? what would it be close to in size eg 5" or 4" scope

thanks toby

You maybe getting confused with 'stopping down' where the aperture (6") is reduced to something smaller, like 5" or 4".

Your 6.3 reducer will change the focal length from 1500mm to 945mm. Which means you can then devide your eyepieces into the new focal length to workout their new magnifications and then their new true field of view.

Russ

[astrokat]

ahhh right so it does not reduce the focal lenth loads im just tring to work out in layman what sort of objects i will be able to frame i thought it reduceds it so it would be the equivalant of say a smaller scope if you understand what i mean

thanks toby

[russ]

Yes, you'll be able to frame a lot more. Be the same as having a 6" f6.3 instead of a 6" f10. Bigger FOV for imaging and visual.

[astrokat]

right ok just looked it up a 4" has a focal of 1000 just gives me a idea when u see some on elses image saying eg imaged with 4" i got a idea what im looking at im very new to all this lol

thanks toby

[haitch]

right ok just looked it up a 4" has a focal of 1000 just gives me a idea when u see some on elses image saying eg imaged with 4" i got a idea what im looking at im very new to all this lol

thanks toby

The effect of a foal reducer is to make it as if it was shorter not narrower. Probably be easier to visualise if it wasn't a folded scope (just pretend for the following).

The focal length is down to the curve of the mirror or lens(es) in most scopes rather than diameter although SCTs are normally 10:1 ratio of focal length to diamater (f10)

as they are easy to make that way. My dob if f4.5 without reducing the focal length and some long refractors can be f15 or more.

An F10 has a focal length 10x longer than it's diameter, you aren't changing the width but changing the angle of the cone of light being focussed as if the focal length were only 6.3x it's diameter. If you were stopping down the diameter you would increase the F ratio because the length would be a higher multiple of the smaller diameter.

Hope I'm making sense - should be in bed as flued up but gas leak up the road and pneumatic drills make sleep difficult even at 1.30am! :mad::mad: