16 replies to this topic

[donald41]

I've been reading about the 6" f/8 reflector, and everyone seems to really like them. what is it about this scope that is so likeable? over other reflectors. i had one a long, long time ago and can vaguely remember liking the views through it but not sure why. is it the f/8 that's the thing. thanks, don   

[emflocater]

6" f/8 reflector is nice because its still fairly portable. Its aperture and focal length allows great views of many DSO's while offering great views of all the planets and their Moons. Our Moon looks incredible through the eyepiece as well.The f/8 is also forgiving when it comes to collimation if not perfect compared to f/6 and shorter focal lengths.

 

A nice all around jack of all trades master of none type telescope! I have had mine now for over 50 years and I enjoy the visual views every time I peer through the eyepiece, especially the double cluster in Perseus.

 

Cheers

Don

[tcifani]

I'm very happy with my 6" F/8, although I'll admit that if it somehow magically transformed into an 18" Obsession UC I wouldn't complain. 

[Garyth64]

When I first made my 6" f/10 in 1966, it was in a sonotube, and had a pipe fitting mount.  It was a grab and go for me.  I could easily carry it out of the mud room and outside.  I still have the scope and use it today, but it is now in an aluminum tube and a bit heavier.  As said before, it has a lot of plus's going for it.

Edited by Garyth64, 18 September 2023 - 09:23 PM.

[CHASLX200]

I've been reading about the 6" f/8 reflector, and everyone seems to really like them. what is it about this scope that is so likeable? over other reflectors. i had one a long, long time ago and can vaguely remember liking the views through it but not sure why. is it the f/8 that's the thing. thanks, don   

No real coma to bother you. Not as hard to collimate and can be as good as a 6" ED if the optics are great.

[alnitak22]

I've been reading about the 6" f/8 reflector, and everyone seems to really like them. what is it about this scope that is so likeable? over other reflectors. i had one a long, long time ago and can vaguely remember liking the views through it but not sure why. is it the f/8 that's the thing. thanks, don   

I think it’s the combination of size, performance, and price. My 6”f/8 cost about 300 bucks when I got it 27 years ago. Yet in THREE separate side by sides against my friend’s 4” Tak apo on the moon and planets, the reflector edged out the setup costing over 10 times as much when the mount was figured in. So there’s that. Collimation is as easy as tying your shoes on this scope (i check collimation every few months, and it rarely needs more than a tweak), and it weighs just a little over 30 lbs and has a nicely constructed carry handle. I can easily carry it around in one hand and even up and down stairs. And I’m hardly a he-man. It’s also very easy on eyepieces with the f/8 light cone. My 6” f/12 Mak will beat the Newt but only up over 250x and only on the moon and planets. The Newt shows the DSOs I can see in my sky a little better. Years ago folks like Dickson called the 6” f/8 reflector the best bang for the buck in astronomy. I think that is still the case.

Edited by alnitak22, 18 September 2023 - 07:17 PM.

[ShaulaB]

This is an excellent scope for a beginner. It can magnify the Moon and planets without resorting to tiny focal length, eyelash-brushing short eye relief eyepieces. As has been said, collimation is a breeze. There are a lot of 6 inch f5 scopes being sold today, and they are not as versatile as an f8.

 

Any vehicle can drive a 6 inch f8 Dob to darker skies, although a larger vehicle might be necessary to haul a pier-mounted GEM for it. Remember those old Edmund's scopes? All 110 Messier objects are viewable in a 6 inch f8. Re-aluminizing the mirrors costs much less due to the smaller size.

[Big_Eight]

I have a 6 inch f5 tabletop and when I'm out at a dark site it's really great for DSO's.

I like it because it is shorter than an f8 and collimation is still easy. I have a small stand built for it to set it on.

Planets and stars from my backyard are stellar! Nothing wrong with a 6 inch.

My in-laws saw Saturn for the first time through it and it was fun watching their reactions!

Edited by Big_Eight, 18 September 2023 - 07:25 PM.

[mayhem13]

I've been reading about the 6" f/8 reflector, and everyone seems to really like them. what is it about this scope that is so likeable? over other reflectors. i had one a long, long time ago and can vaguely remember liking the views through it but not sure why. is it the f/8 that's the thing. thanks, don   

Yes Don, it’s the slower focal ratio that is so loved by many users. The slower speed means less light scatter within the tube and improved contrast. The longer focal length allows for deeper sky observations of smaller targets. It is also easier to achieve near perfect Collimation allowing the user to squeeze the last bit of optical quality from the mirrors. They’re not too big or heavy, nor expensive nor difficult to master…..what’s not to like?…..

 

Well….6” of aperture isn’t much these days, and when compared to say an entry level 10” f5 Dobsonian the difference in light gathering potential is immense. Of course the 10” Dob requires more experience from initial setup and Collimation to proper use by pairing with eyepieces and practiced observing. Things that appear as fuzzy blobs in the 6” take on definition and detail with 10” of aperture…this is often called ‘aperture fever’ and it’s incurable once infected.

 

I would assert that the 6” f8 reflector is a perfect example of a casual observing instrument…..it’s not heavy or bulky, easy to set up which won’t preclude you from doing so when the itch to observe the night sky happens. Throw it in the back seat….head out to some dark skies and tear down and home by bedtime. End users of these scopes these days are primarily those who cherish that kind of observing freedom or those that no longer have the time or physical ability to handle larger systems. I’d strongly recommend you temper your decisions based primarily on this as the scope that ultimately produces the best views is the one that actually gets used.

 

But all scopes are just hammers…..the magic and precision is in the choice of excellent eye pieces and practiced observing skills where that light is optimally reconstituted into the images you see. Invest wisely here and you guarantee excellent results.

[Illinois]

My first serious telescope is 6 inch F8 and I see many Messier and NGC objects in 6 inch.  You can see all Messier Objects in 6 inch in dark sky.  Planetary is okay for me and I can see Mars’ polar cap at least 200 power when Mars is close to Earth. 

[CrazyPanda]

I've been reading about the 6" f/8 reflector, and everyone seems to really like them. what is it about this scope that is so likeable? over other reflectors. i had one a long, long time ago and can vaguely remember liking the views through it but not sure why. is it the f/8 that's the thing. thanks, don   

IMO a 6" F/8 dob is the perfect beginner scope:

 

1. 6" of aperture is a good taste of what aperture can do for you under good conditions

2. The F/8 focal ratio has numerous advantages for a beginner:

• There is virtually zero coma in the field.
• Inexpensive eyepieces perform nicely at F/8, saving you a lot of money when picking out a nice spread of focal lengths to start.
• Collimation error tolerance is very good. Collimating is the hardest thing for a beginner to do, and an F/8 reflector can almost be eyeball collimated. Minor residual errors won't substantially degrade the view.
• Errors in the optical figure of the mirror are less problematic, so even if it's not a perfect sphere, it can still perform reasonably well.

3. The mount is stable, simple, easy, and intuitive to use. Much better than a table-top form factor which often gets placed on whatever rickety surface the user has available, thus exacerbating vibrations and view wobbles. And MUCH better than crummy undersized EQ mount.

 

The one downside to the scope is the longer focal length results in a narrower view of the sky, which can make it harder to locate objects. However, most 6" F/8 dobs these days seem to support 2" eyepieces. While the secondary mirrors won't fully illuminate 2" eyepieces, having a 2" wide angle can help show a wider swath of the sky, thereby compensating for the longer focal length when it comes to finding targets.

[Sebastian_Sajaroff]

6" F/8 is easy to carry (4'4" x 7"), not so heavy and yet is able to deliver interesting views.

It's not strict on collimation like an F/5 or F/4 would be, and is very tolerant with cheap eyepieces.

[walt r]

Errors in the optical figure of the mirror are less problematic, so even if it's not a perfect sphere, it can still perform reasonably well.

 

Yes, f/8 is nearly a Sphere and easy to obtain a good parabolic figure (a good figure becomes much harder as the f/ decreases).

This means the chance of getting a 'good' mirror has increased.

[gene 4181]

    Cools very quickly , good for those nights when its a spur of the moment  observing session .   All those old UO orthos and konigs work so well in it. 

[emflocater]

    Cools very quickly , good for those nights when its a spur of the moment  observing session .   All those old UO orthos and konigs work so well in it. 

University Optics Kellners work superb with 6" f/8 reflectors as well!

 

Cheers

Don

[alnitak22]

    Cools very quickly , good for those nights when its a spur of the moment  observing session .   All those old UO orthos and konigs work so well in it. 

Good points. I had my 6” f/8 reflector for several years before I got my TV85. For the Newt, I had a mix of UO orthos, TV Plossls and Celestron Ultimas and loved them all. Still do. However when I got the TV85 I tried some Naglers, Pans, Radians and Pentax XLs, and the Newt of course loved those too. The view of the Double Cluster in the Newt and the 24 Pan in  my sky is spectacular. For high power with the Newt, my 5 and 6 UO orthos give stunning images and I’m not bothered by the short eye relief. However, my 5 and 6 Radians give just as good if not better an image and for longer sessions, the more comfortable eye relief does make a difference.

[CrazyPanda]

Yes, f/8 is nearly a Sphere and easy to obtain a good parabolic figure (a good figure becomes much harder as the f/ decreases).

This means the chance of getting a 'good' mirror has increased.

Just saw the error in my quote - I meant to say "Even if it's not a perfect parabola", not "sphere":