The difference between a F3.3 and F6.3

[garethmob]

Hello guys

just wondering really, what the difference between the two reducers are above.    i know an SCT ISNT the greatest at widefield, but for widefield the 3.3 looks better (with FLOs fantastic view finder thingy)   but how does it work? does it reduce the F by 3.3 / 6.6 (which in my head should be telling me that 6.3 would be better) or does it reduce it to 3.3/6.3.

if any one can help

also,  is the meade better than the celestron or are they much of a muchness?

many thanks

Gareth

[rowan46]

It reduces to 3.3 its only suitable for planetary  imagng with small sensors however, something like a webcam. By all accounts its not very good if you want to use a focal reducer in an sct stick to the 6.3 its apparently much better. I haven't tried both reducers only the celestron but from what I have read  both are much of a muchness

[garethmob]

all i plan on using it for really rowan is currently visual,   im not really into webcam imaging, i prefer my widefield normal with my astrotrac (which sort of defeats the point of an SCT i know) but still   

is the reducer similar then to how the faststar system works in the celestron,  reducing it from F10?  to F1?

[John]

My understanding is that the F/3.3 reducer is purely designed for imaging. The F/6.3 can be used for visual or imaging. I used to use on with a C5 and then a C8 and thought it worked quite well although only with 1.25" eyepieces.

[rowan46]

all i plan on using it for really rowan is currently visual,   im not really into webcam imaging, i prefer my widefield normal with my astrotrac (which sort of defeats the point of an SCT i know) but still   

is the reducer similar then to how the faststar system works in the celestron,  reducing it from F10?  to F1?

No the fastar works by taking a mirror  out of the equation. In an sct the light is bounced off the the primary onto the secondary and the then back out to the hole in the bottom of the primary.  The fastar takes out the secondary leaving it as a place to put your imaging gear thus shortening the light path, reducing focal length and consequently lowering the f ratio.  the celestron and meade reducers work in the same way as focal reducers on refractors. they shorten the light cone at the back of the scope i think

[John]

As I understand it the primary mirror of an SCT is very fast and spherical rather than parabolic. I think the 8" F/10 SCT's have a primary with a focal ratio of F/2. It's the secondary that amplifies and corrects this into an F/10 system.

[Dave In Vermont]

For a hand's-on look at these involving a video-cam, and in general, this is a very good document:

http://www.mallincam.net/uploads/2/6/9/1/26913006/focal_reduction_for_dummies.pdf

Note - it is in Pdf. format. Though written around the MallinCam video-cams, the principles remain perfectly valid.

Enjoy!

Dave

[alan potts]

I used to use my 12 inch with an F6.3 reducer and you can use it with 2 inch eyepieces and diagonal. However you can only go to 27 or 28mm with a 68 degree FOV, after this you get a vignette around the sides of the FOV. I did a fair amount of work on this and did an extensive review which is posted somewhaere back in the eyepiece section I believe. I always thought that the cream would be the 26mm Nagler giving the maximum possible but I was wrong, it had blackened edeges, however the 24mm Meade UWA did work which shows how close to the wind you sail with this. Now though I tend to only use the scope un-reduced with a 41mm Panoptic giving much the same view but with less glass in the light path.

The F3.3 reducer is rubbish for visual forget it, it is fair good though with a video camera I am lead to believe.

[Merlin66]

The x0.33 was designed for webcam sized chips...

IMHO not suitable for visual (or much else!)

[Don Pensack]

Hello guys

just wondering really, what the difference between the two reducers are above.    i know an SCT ISNT the greatest at widefield, but for widefield the 3.3 looks better (with FLOs fantastic view finder thingy)   but how does it work? does it reduce the F by 3.3 / 6.6 (which in my head should be telling me that 6.3 would be better) or does it reduce it to 3.3/6.3.

if any one can help

also,  is the meade better than the celestron or are they much of a muchness?

many thanks

Gareth

The f/3.3 reducer was designed for small chip cameras.  It pinches a 38mm wide field down to 12.5mm on the 8" SCT, for instance.  It really doesn't work well for visual use because the illuminated field is so narrow.

The f/6.3 reducer, on the other hand, allows you to reach the maximum visual field of an 8" SCT with normal 1.25" eyepieces, like a 32mm Plossl.

What a reducer does NOT do is illuminate a larger field than the instrument is capable of.

Make sure, if you use the f/6.3 reducer visually that you keep your eyepiece field stop diameters to 30mm or less or you may notice fairly severe vignetting in the outer field.

If you can find the earlier Celestron, made in Japan, get that.  Otherwise, the Meade and Celestron are fairly equivalent.

Make sure you get the reducer for the SCT and not the reducer for the new Edge HD or ACF--they have different correction.