Orion 8" Reflector Scopes

[JohnnyD333]

Hello SGL,

I was browsing through Orion today and came across two 8" reflector scopes. I currently have a 6" Celestron and will upgrade sometime later in the year. Living in the US, I usually purchase Orion or Celestron. I found these two scopes, the first being an 8" Astrograph

Orion Telescopes: Orion 8" f/4.0 Newtonian Astrograph Reflector Telescope

Looks awesome except that its focal length is only 50mm bigger than my 6"? I don't understand why this is. Looking further I found a cheaper Orion 8" that is a full 250mm bigger than my 6".

Orion Telescopes: Orion 203mm f/4.9 Reflector Tube with Crayford-Style Focuser

Just curious as to why this is. I really like the Astrograph, but I do not know if 50mm is worth another $500. Thanks again SGL.

[John]

I'm guessing that your 6" (150mm) has a focal ratio of F/5 which would give it a focal length of 150mm x 5 = 750mm. The Astrograph 8" (200mm) is an F/4 so 200mm x 4 = 800mm - as you say a small increase in focal length because the Astrograph, although larger in aperture, has a faster focal ratio.

The Astrograph is specificed as it is for imaging - for visual observing I would go for the 203mm F/4.9 or better still a 250mm F/4.7 - you really need more than just a 50mm increase to get a significant increase in performance in my opinion.

[JohnnyD333]

Thanks John, The Astrograph is awesome, its faster and has a cooling fan, but if I am going to upgrade I get aperture fever and 50mm just doesnt justify $500 for me. Also, using a CG5 mount I cant really go beyond 8", I dont care that Celestron sells a 10" on a CG5 that thing looks unstable.

[John]

I agree on the Celestron 10" - it's too much for the CG5.

[gustavo_sanchez]

The Orion 8" F/4 is about $450 right now, and even if it's just 50mm more focal length than your 6", it's faster and will capture more light in less time than your 6". Also, the 8" F/4 has an upgraded focuser which the 8" F/5 does not have. So basically there is a place for it, but if you already have a 6" F/5... you should not buy it. Buy something that complements your scope, such as a long focal length scope (SCT or MCT). The C6 is very nice, portable, and has 1500mm of focal length.

[callisto]

Go for a nice 10" Dob

[JohnnyD333]

Im thinking about an SCT.... the C6 does look nice. Dobs are awesome but Im looking for another imaging scope. Thanks for the recommendations:)