Newtonian Scopes ?

[Parsec]

Just a quick question for anyone with a Newtonian telescope.
Generally, when you observe planets such as Jupiter or Saturn do
you see any cloud bands or any amount of detail ?
Or is this something more in the area for astrophotography.
If I were to pick a apatura, lets look at anything fro 8" - 12".

[rayajko]

Even a small 4 or 6 inch reflector will show cloud belt detail on Jupiter and Saturn with the right atmospheric conditions. An 8-12 inch will show even more intricate detail. An f8 to f-10 refractor would be ideal for planetary studies or a long focus newtonian at f-6 to f-10 would also be good.

Bob

[Parsec]

Ok, that is what I thought.

The reason I asked I was looking through a newtonian 10". I found generally the view was very good. M13 was excellent.

However, Jupiter and Saturn were a wee bit less than I expected. They were more of bright disks with not much cloud definition.

The telescope was a f4.5. I was thinking that had it been a 10" at f8 - 10 the planet defination may have been a bit better because of the longer focal length.

[rayajko]

I have owned several long focus telescopes, from 4" f-15 refractors to a 6" f-12 reflector. They always showed better planetary detail than any short focus scope did.

[Tuguldur]

Hay Ron,

we haven't meet for ages ...

about the planetary viewing, your 10" should work very well. the main problem is that the collimation of you newtonian! And f/4.5 is enough for jupiter but you'll need more on saturn and venus.

Did you ever tried some barlows?

clear skies,
Tuugii

[Parsec]

Hey Tuggii,

Jeez, You had me worried, I thought you got lost in the desert.

The collimation of the 10 inch is done with a laser, so I usually have it in the ballpark.

Yes, I have a couple of barlow's one is a 2X the other is a 5X.

This may sound crazy but I would like to build a 10 or maximum 12 inch Newtonian at f9 or f10. I would not be portable and I could not drive it but it would make a good planetary instrument.

A SC in this apatura would cost $5,000 +, and a lot more if coated.

I built an 8 inch years ago and it turned out pretty good. Even with a 10 or 12 inch at a long focal length does not require a lot of glass removal on the mirror.

Rayajko has a nice one there. The 6" f-12 refractor would be nice. I was looking at one of these a while back. I think it was a Skywatcher on a EQ 6 mount.

I would like to post more but I have to sign off. It is getting dark here and the sky is clear for the first night in a week. I want to get out and find the asteroid Vesta. ( should be just above Jupiter)

Tuggii, it's good to talk to you again.

[Tuguldur]

Ron,

its nice to see you again! yeah, I was kind of lost in the "mind desert"

Do you know your barlow's elements? is it achromatic or maybe apo? apochromatic barlows may suit well with your f/4 and make the focal ratio higher. Probably you've tried them, and how was the results?

Your idea of building a scope is great! I'll help you with everything I can! and about the f ratio, the f/10 sound nice, since its higher than f/8 it will work very good for planets!

However, I hope you've calculated the 12" x f/10 = 2.5m long telescope! ooops...

What are your plans? truss scope?

BTW, good luck on your Vesta observations!

clear skies,
Tuugii

[Parsec]

Hi Tuggii,

I know what you exactly what you mean. I get in the mine dessert at times myself.

If I decide to build a long focal Newtonian I think I have to narrowed down to a couple of possibilities.

A 10 inch F10, or a 12 inch F8.
They would be rather long, but not enough to cause major problems. If it preformed well
?the pain would be wort the pleasure?.

Doing the math I was surprised the amount of glass to be removed from the mirror was less than I expected. Using the Sagitta formula:
S = 2F - sqrt((2F)^20 - (D/2)^2)
The Sagitta of a 10" mirror at F10 = 0.0625 = 1/16 inch = 1.5875mm
The Sagitta of a 12" mirror at F8 = 0.09375 = 3/32 inch = 2.3813mm

Focal length of 10" scope at F10 = 100 inches = 2,540.00mm
Focal length of 12" scope at F8 = 96 inches = 2,438.40mm

The 12 inch at F10 looks good but 120 inch length is getting rather long and cumbersome to deal with.

I am not sure how to deal with the diagonal mirror. But I think if I look at the focal length as a cone. Then determine at what point to change the direction 90 to the eyepiece. Then at that point just calculate the segment of the cone.

The ?rough? grinding of either mirror would not require a lot of labor time. The other thing is the final figuring and polishing should not pose a great problem.
When I calculate the arch of the circle, it appears long focal length mirrors are almost spherical than paraboloid.
I am beginning to think if one was careful and accurate, one could produce a very good mirror at a long focal length.

I have a chemical formula for depositing a silver coating to a material (namely glass).
The only problem is the glass is required to be cleaned with H2SO4 . However, there are other methods just as good. But if absolutely require then I will use the sulphuric acid.

I also have an old vacuum pump and would be willing to try depositing a thin layer of aluminum.

Yes, truss looks good, it at least would make it a bit portable. I could also use a two section tube with a sleeve between the sections

I almost have myself convinced to attempt one of these.


Yes, got Vesta the other night as well as some dimmer Messier objects.

Vesta is just below and to right of M104.

[Philip30]

i have no newtonian scope..
can you give any picture about that or any information..
THANKS and have a NICE DAY..

[laila55]

Hi guys,
I am new here and find Newtonian scope very interseting,
Hope I can laern more about it here, and have a good time discussions here,
Godspeed!

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