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David

focal reducer

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David

Hi everyone. Please bear with me as I am a newbie to astrophotography. I cuurently own a Skywatcher Startravel  ST120 ( focal length 600, f5) and an 8" Meade LXD55 SCT (focal length 2000, f10). I have been looking at purchasing a focal reducer for the SCT (Meade f/6.3) to help with my images however I am correct in thinking that my ST120 with a 2x barlow would give me similar results or am I over simplifying things. Thanks

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Graham

Not quiet sure what you are asking David.

The F/R would bring the Meade up to the speed of the ST 120.

A Barlow on the ST would slow it down to the speed of the Meade but with far reduced light gathering capabilities. 

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David

OK Thanks Graham, I didn't take into consideration the exposure factor of connecting a barlow to the ST 120. Now that you have mentioned the light gathering effect it clicked in my simple brain. I was only looking at it from a point of view of the focal length. Thanks again.

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Sunny Phil

The focal ratio determines the brightness of the image but a larger aperture at the same focal ration gives better resolution.

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philjay

Its all down to reducing the focal length, the fr you mention will take it down to f6.3 yes, which is slower than a startravel. You can get faster focal reducers for sct,s but what you gain in speed you lose in flat field. These fast focal reducers are ok (ish) for small chip ccd cameras but poor for larger chip cameras.

Trying to get fast, wider field images with an f10 sct isnt easy, Celestron and their Fastar compatible sct,s are the best way of doing this.

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