6"f8 or 8"f6 reflector for planetary?

[PurpleFringe]

Hi everyone,

At least two manufacturers I know of produce 6 and 8 inch reflectors with 1200mm focal length making comparisons quite meaningful.

Obviously the 8" ought to be better for DSO's, but I'm very interested to hear from anyone who has real experience comparing these two on lunar / planetary targets, especially with cheaper eyepieces. Any specific information about details that might / might not be visible in one or the other especially appreciated.

Andrew

[NGC 1502]

I've owned in the past 8" F6 and 6" F6, so not quite the same as your enquiry.

If it were me, I'd go for the 8", even for planetary use. It's true that the 6" F8 will be a bit less fussy with collimation and eyepieces.

But as you are aware, a 8" F6 and 6" f8 are both 1200 mm FL, so the tubes are the same length, just the 8" a bit fatter.

The 8" F6 is a nice portable scope, with no real vices that can come from faster focal ratios. Collimation is not as super critical as at F4 or F5, and the secondary size is not extreme.

The greater light grasp is welcome too, larger aperture means greater resolution on planets.

The downsides are greater cost, a bit heavier, and better eyepieces would be a good idea if you are prepared to pay more.

But neither scope is a mistake, see what others say, not just me.

All the best with your choice, Ed.

[PurpleFringe]

Thanks Ed,

I'm thinking the 8" sounds the best option, I think 'greater resolution' out of your list of differences is the one that has the strongest influence on me and would bring me the most pleasure, but it's hard to quantify and get a feeling for the difference. Am also interested in DSOs, so better light grasp appeals too.

Hope I get some other opinions too, come on SGL! Has anyone seen a difference?

[Peter Drew]

8" F6 every time, assuming equal optical quality.

[John]

As above. F/6 is not too hard on eyepieces really. It's worth learning a bit about collimation though as a well collimated scope will show better contrast and resolution which is important in planetary viewing.

[dweller25]

A 6" F/8 newt will show a lot of planetary detail but an 8" F/6 will show more - I know that because some time ago I compared the two side by side on Jupiter. See my drawings in the sketching section, many have been done with an 8" F/6. The 8" is exactly the same length as the 6" and only slightly heavier so it's a;most as easy to store and carry and as mentioned earlier it has better resolution over the 6" - important when Mars comes around.

HTH

[PurpleFringe]

Thanks everyone. Concensus on 8" seems strong and it's helpful to know that F6 is not too much of a problem for cheaper eyepieces.

[rwilkey]

Hi Andrew, I agree with the comments above, an 8" will show more contrast and is the start point for meaningful grasp of light for DSO's, which you say you are also interested in.

[Moonshane]

aperture every time. ostensibly there's no difference in the view between a 6" f6 and a 6" f8 at the same magnification so an 8" f6 will provide more detail/resolution on planets/moon plus better visuals on DSOs.

that said, there is the world of difference between the views through my 6" f11 newt and many 6" f5 newts I have tried, on planets and doubles anyway. for general viewing aperture does rule for visual.