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What inch scope is my scope?


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I keep seeing reference to the inces of a scope, such as 8" etc. I would like to know what inch my scope is - How do I work it out?

I have a Skywatcher Evostar 120ED - I have looked on retailers sites and googled the scope, but can not see reference to the inch of the scope.

Dumb question I know - Sorry! :(

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Skywatcher Evostar 120ED DS-Pro Outfit - 120mm (4.75) f7.5 Apochromatic Optical Assembly.

120mm diameter objective, 120mm = 4.75 inches.

900mm focal length.

The sizes quoted, inches or mm refer to the diameter of the objective lens or mirror.

For whatever reason mirrors are often refered to in inches and lens in mm.:(:icon_scratch::)

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Hi,

120mm is a good size refractor. I've heard the SW 120ED is a great scope. There will always be some nebula or galaxy that is too faint for your scope, whether it be 5", 10" or 20". Enjoy it as there are plenty of things to see with it.

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Blimey - Is that all? I've just read that to see the Christmas tree nebula, you'd be needing a 10" scope - Is that more for observing or imaging as well?

Thanks for all your answers folks - Brilliant :(

Observing - the light for observing is dependant on the size of aperture and the quality of the optics.

The light for imaging is dependant on the focal ratio of your scope (the faster the better) and the sensitivity of your camera. Image size is dependant on the focal length of your scope and the pixel size of the camera.

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Don't be downhearted about scope size in inches even with an 8" there's stuff you can't see. Given the vagaries of the uk weather and the fact that the astro 'must sees' are seasonal there will be more than enough to see with your scope to keep you going a long time.

I also have a 4" scope refractor and it's actually my scope of choice to use.

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Hi Swag72,

Don`t be discouraged by what you think you can`t see with your scope! Stephen James O`Meara viewed all 400 Herschel objects with his 4-inch refractor (albeit, under pristine Hawaiin skies), and in his comparitive tests he believes he has proven that a 4-inch refractor can perform as well as an 8"-10" reflector under very dark skies.

I realize that you're probably not observing under such terrific skies as O`Meara, but I think he makes a valid point.

I think people tend to underestimate the quality of the sky`s transparency and seeing conditions in determining whether this or that object might be visible in their scopes. My philosophy is to try anyway--and often. Last summer I checked for Stephan`s Quintet at the beginning of every observing session and one night I was able to clearly see two small galaxies; but when I checked again 2 hours later, they weren`t visible at all.

Edited by tuc
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Look like Mr O'Meara and I would agree :( every time I suggest my Tal 100 can give my 8" a drubbing I get shot down :)

The best view I have had of Andromeda was with the 4" admittedly under a dark sky but it was the best defined view I have had of it.

Edited by Astro_Baby
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No. Filters don`t work on diffuse galaxies. Dark skies are best for hunting down fainter galxies. I don`t know what the quality of your skies are in Spain, but it must be good as I`ve heard that the rain stays mainly in the plain. (sorry)

Edited by tuc
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