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reducer question


a10ken

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Hi folks, I have been looking at getting a focal reducer, but don't understand what the 0.54x / 0.63x /  etc relates to.

my scopes are f6.3 and f14.

how do I calculate using the 0.54x etc and what does the resulting figure relate to??

this is bound to be something simple I just need to get a handle on it.

thanks

ken

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I think they are the factor by which they reduce the focal length, so a 1000mm focal length with 0,54x reducer gives a focal length of 540mm effectively.

It therefore reduces the f number accordingly so f 6.3 becomes 6.3*0.54 = 3.4, so the f number is now f/3.4 - bit faster.

So far the stuff I am supplying looks as if it might be right. May not be the gibberings of an idiot.

The ones with a multiplier are a bit more obvious then the others, I am not sure of the others.

By the way I might be 130% wrong.

I guarantee nothing as being correct or right.

Being honest my approach is simple:
A reducer reduces the focal length so would I have to multiply or divide the focal length by whatever value of the reducer to get something less.

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An f-10 scope employing a .63 reducer effectively becomes f-6.3. The result is to speed the scope up - usually for photography - though the scope's native f-ratio, f-10, remains physically unaltered. Reducers are often combined with flatteners.

It usually helps to understand the opposite which is using a barlow. A 2x barlow effectively doubles the focal length theoretically raising the f-ratio - though it's still physically an f-10 scope.

The barlow magnifies the image you see - whereas the reducer will help get the image onto a camera chip. This is a very simple explanation - so I'm tightening my seat belt and preparing to be blown out of the sky by imagers. lol :)

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An f-10 scope employing a .63 reducer effectively becomes f-6.3. The result is to speed the scope up - usually for photography - though the scope's native f-ratio, f-10, remains physically unaltered. Reducers are often combined with flatteners.

It usually helps to understand the opposite which is using a barlow. A 2x barlow effectively doubles the focal length theoretically raising the f-ratio - though it's still physically an f-10 scope.

The barlow magnifies the image you see - whereas the reducer will help get the image onto a camera chip. This is a very simple explanation - so I'm tightening my seat belt and preparing to be blown out of the sky by imagers. lol :)

Can't consider myself quite an imager yet, but working on it. I'd say a good and concise explanation. Thanks.

One problem I've seen mentioned with reducers is they are a bit specific to the optics of the OTA, there can be problems with internal reflections caused by them. Not as clear a choice as often described. Research carefully.

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Spacing between the camera sensor and reducer can also be an issue.  For example, I believe that Celestron suggest an optimal spacing between the sensor and reducer of around 100mm for their 0.63 reducer (that's from memory -- I may well be wrong on the figure).

James

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Focal reducers do what the others have said they do, which is reduce the focal length by their stated percentage. This speeds up the F ratio accordingly.

However, there's a 'but.' If you image an object which fits on the chip at, say, native F10, there is no point in using a reducer because the reducer will pull in no new light. Only more aperture does that. What the reducer will do is pour the same light from the object onto fewer pixels. But you can do that in software by downsizing your native FL image. No free lunch! (Is there ever, in this game???)

The proper use of a focal reducer is to widen the field of view. That's fine if you want that wider FOV. And if you do want it, there's a bonus in that the global image will get to an acceptable signal to noise ratio faster than it would at native F10. But if you don't want the wider FOV there is no point in using the reducer.

Olly

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