Planetary Newtonian anyone

[Rusted]

I have a 10" f/8 by a premium US maker but struggled to make a stiff enough lightweight tube.
A bare tube weighs well over 20lbs without the optics. I am far too old to be lifting such a tube manually.
Mounting it equatorially is a nightmare. Reaching the eyepiece worse still.
A Dobsonian could be a solution but would deny one the ability to produce high-res, lunar or planetary images.
I plan to hang mine on a cross-axis, English mounting when I finish my new 4.3m dome.
My 7" f/12 and 6" f/10 refractors will balance it instead of using counterweights.

Historically, most optics were much longer than today. The market was very different in the past.
Those who lived in flats would not be likely to own any telescope. So there was no need to carry them about.
The demand for easy portability and imaging had largely driven the amateur market for years.
It has forced the acceptance of the SCT and much shorter focus instruments.
Suppliers of optics are rarely asked for a long focus these days.
There is a massive [sic] shortage of affordable mountings with the capacity to properly support these, long instruments.
Moment = M[mass] x L [length] from the fulcrum. [Or mount axes.] Most telescopes are equally heavy at each end.
Meaning that the Moment of the mirror and cell are effectively doubled by the secondary mirror, spider, focuser and eyepiece or camera.

As Peter has intimated, the shallow curve of a long focus optic is not remotely easy to produce.
A smooth optical surface, with a perfect, yet shallow parabola is the work of the master optician.
Most amateur, glass pushers will overshoot into a hyperbola and end up with a rough, zoned surface. 

It is reported that a long focus Newtonian of about 12-15", in a thermally neutral OTA, will outperform any other telescope on planetary detail.
This assumes perfect seeing and included larger aperture APOs, Newts, SCTs and refractors.
Only on the rarest of occasions will the larger optics have cooled to provide their theoretical performance.

[neil phillips]

3 hours ago, Stu said:

This was my longest scope; OO 300mm f6 which was a bit of a beast. For context, the scope beside it is an 8” f20 Mak (OMC200). It wasn’t very stable on the AYODigi II, much better on a dob mount. Anything longer much be completely insane!

Very nice. Stu. I miss big optics.12" For what i am doing does sometimes have a advantage. 

[neil phillips]

2 hours ago, Rusted said:

I have a 10" f/8 by a premium US maker but struggled to make a stiff enough lightweight tube.
A bare tube weighs well over 20lbs without the optics. I am far too old to be lifting such a tube manually.
Mounting it equatorially is a nightmare. Reaching the eyepiece worse still.
A Dobsonian could be a solution but would deny one the ability to produce high-res, lunar or planetary images.
I plan to hang mine on a cross-axis, English mounting when I finish my new 4.3m dome.
My 7" f/12 and 6" f/10 refractors will balance it instead of using counterweights.

Historically, most optics were much longer than today. The market was very different in the past.
Those who lived in flats would not be likely to own any telescope. So there was no need to carry them about.
The demand for easy portability and imaging had largely driven the amateur market for years.
It has forced the acceptance of the SCT and much shorter focus instruments.
Suppliers of optics are rarely asked for a long focus these days.
There is a massive [sic] shortage of affordable mountings with the capacity to properly support these, long instruments.
Moment = M[mass] x L [length] from the fulcrum. [Or mount axes.] Most telescopes are equally heavy at each end.
Meaning that the Moment of the mirror and cell are effectively doubled by the secondary mirror, spider, focuser and eyepiece or camera.

As Peter has intimated, the shallow curve of a long focus optic is not remotely easy to produce.
A smooth optical surface, with a perfect, yet shallow parabola is the work of the master optician.
Most amateur, glass pushers will overshoot into a hyperbola and end up with a rough, zoned surface. 

It is reported that a long focus Newtonian of about 12-15", in a thermally neutral OTA, will outperform any other telescope on planetary detail.
This assumes perfect seeing and included larger aperture APOs, Newts, SCTs and refractors.
Only on the rarest of occasions will the larger optics have cooled to provide their theoretical performance.

These kind of instruments need a permanent housing. Always loved Newtonians They can produce the sharpest images. And large Newtonians Great resolution. Love that 10" F8. 

My 10" f6.3 Hits the sweet spot. Very canny design from OOUK. Short enough focal length to be able to be semi portable. Long enough to start to behave a little more like a planetary Newtonian. Yes times have changed. There are of course solutions to these large long instruments. Namely SCTs  Maks and now recently commercially available Classical Cassegrains But i still think for the enthusiast these long focus scopes. Do hold a interest

[John]

30 minutes ago, neil phillips said:

These kind of instruments need a permanent housing. Always loved Newtonians They can produce the sharpest images. And large Newtonians Great resolution. Love that 10" F8. 

My 10" f6.3 Hits the sweet spot. Very canny design from OOUK. Short enough focal length to be able to be semi portable. Long enough to start to behave a little more like a planetary Newtonian. Yes times have changed. There are of course solutions to these large long instruments. Namely SCTs  Maks and now recently commercially available Classical Cassegrains But i still think for the enthusiast these long focus scopes. Do hold a interest

It's sold now but this long 8 inch newtonian caught my eye recently. Local to me as well:

https://www.astrobuysell.com/uk/propview.php?view=180708

[Rusted]

That is/was a lot of telescope for not much money. 

[Peter Drew]

Looking forward to trying this Rob Miller special.  10.25" F7.something Newtonian with small secondary mounted on an optical window, no secondary spider.    🙂 

[Captain Scarlet]

5 hours ago, Stu said:

This was my longest scope; OO 300mm f6 which was a bit of a beast. For context, the scope beside it is an 8” f20 Mak (OMC200). It wasn’t very stable on the AYODigi II, much better on a dob mount. Anything longer much be completely insane! ...

Haha that is more ridiculous than my SW 300p plus Skymax180 on an az-eq6! Was it a usable set-up?

M

[Stu]

2 hours ago, John said:

It's sold now but this long 8 inch newtonian caught my eye recently. Local to me as well:

https://www.astrobuysell.com/uk/propview.php?view=180708

Yes, that looked nice. Similar to mine but it has the curved vane spider which I always fancied fitting. Wonder how much difference it makes?

[Stu]

1 hour ago, Captain Magenta said:

Haha that is more ridiculous than my SW 300p plus Skymax180 on an az-eq6! Was it a usable set-up?

M

Not really! Two main issues. Firstly the eyepiece height was pretty crazy at the zenith, I felt silly on a short step ladder so the neighbours could see me over the fence! Second the tube had quite a lot of flex in it so it vibrated a bit much. It was much better when supported both sides on a dob mount. The Ayo actually handled the weight quite well though, provided it had enough counterweight on it.

Even crazier was the fact that I bought it from a chap in Scotland who packed it up and shipped it down to me! We must have been mad! It did end up with a bent secondary spider but that was sorted out fairly easily.

[Stu]

1 hour ago, Peter Drew said:

Looking forward to trying this Rob Miller special.  10.25" F7.something Newtonian with small secondary mounted on an optical window, no secondary spider.    🙂 

That’s a serious looking mount Peter!

[neil phillips]

2 hours ago, John said:

It's sold now but this long 8 inch newtonian caught my eye recently. Local to me as well:

https://www.astrobuysell.com/uk/propview.php?view=180708

Yes i saw that too. Very nice planetary scope. Someone out there is in for a treat when jupiter and Mars are riding high in the summer 

[neil phillips]

2 hours ago, Peter Drew said:

Looking forward to trying this Rob Miller special.  10.25" F7.something Newtonian with small secondary mounted on an optical window, no secondary spider.    🙂 

That looks awsome Peter 

[Peter Drew]

26 minutes ago, Stu said:

That’s a serious looking mount Peter!

It certainly is, the RA shaft is 4" stainless steel!  I have mounted it on wheels as it's not a grab & go.     🙂

[Rusted]

10 hours ago, Peter Drew said:

It certainly is, the RA shaft is 4" stainless steel!  I have mounted it on wheels as it's not a grab & go.     🙂

Grab and Heave?

[Stu]

10 hours ago, Peter Drew said:

It certainly is, the RA shaft is 4" stainless steel!  I have mounted it on wheels as it's not a grab & go.     🙂

That looks like a wheely good idea Peter 👍