Decision made - down birds's path for planetary

[davidpretorius]

Well, I have gone to the Aluminium fabricators and got a rough price on a tube. $300 ish. The addons ie ideas that dave wants, but may not work:


detachable into 4 sections for transport
detachable peltier cooling system
large alt bearing for dob driver or mel bartels or servo cat etc
variable mirror cell to take 10" to 14" mirrorsI am dropping off my scope less mirror next tueday for them to look at to see if there are any other ideas they may have. Whats the bet when the great seeing will be next week?

Anyway, I have until next year Jupiter opposition to get this right!

[Robert_T]

Good one DP - should be able to come up with something pretty special and still have plenty of change left over from what a C14 would cost you. For me convenience is still everything. I need something I can easily pull out and setup and stow away quickly otherwise I know I wont use it. Guess I'm stuck with SCTs;)

cheers,

[davidpretorius]

thanks rob, great image in AS&T by the way!!

At the end of the day, a SCT and Titan will be at my house some time down the track, but for the next 5 years, this is the most cost effective way for me.

[ving]

your a braver man that me dave :P
look forward to seeing the results...

[Miaplacidus]

(Brave is not the word, Ving.)

David, David, snap out of it man! I've seen your images. What on earth are you aiming for? An extra hundredth arcsecond of resolution? Detail on Pluto? Come on, leave something for NASA and ESA, will you?

Well, good luck,

Brian.

[Lester]

Good on ya Dave,

But the bar is getting so high, man there will be some Good shots next Jupiter opposition.

[davidpretorius]

:d

[davidpretorius]

that is :D

[matt]

Hey Brian

Surely you can see poor DP has "The Fever"?:lol:

[stringscope]

Fantastic DP:thumbsup: . Can't wait to see the results.

Of course you are going to those lengths, why not consider an integrated equatorial platform as well:D .

Cheers,

[davidpretorius]

nope eq stuff is for girls!,

being mainly interested in planetary, i reckon the ease of plonking the scope on the ground and then start tracking is the way to go. no polar alignment for me :D

[asimov]

You wouldn't know how to use an EQ thats why!:screwy:

dobs suck:D

[davidpretorius]

:d

[davidpretorius]

damn forum, won't let me do a cheezy grin by itself so here it is :D

by the way my master, grass hopper here, bird suggests i get at least a 16" diameter tube, what size does my master suggest???

[asimov]

For what size mirror grass-hopper??

[davidpretorius]

well 10 to start with, but 14 eventually.

also Bird has just informed this newbie ATM grasshopper that a 10" f5 and a 14" f5 will not have the same focal length....so...... i will have to have two spider/focusser positions....would that be right?

I would like to be able to get GSO mirrors which i assume are f5.

This is going to be the contraptions of all contraptions

[h0ughy]

mmmm Dave, what can I say but good luck and best wishes. Icecream in Hell Eh!

[Miaplacidus]

Naw, Davo, just make the 14" F3.57!

[davidpretorius]

hey brian,

a little maths help please, how do i convert f 14" @ f3.57 to a mm focal length.

How would this steep light cone be on planetary? Is this the right lingo?

[Miaplacidus]

You serious?:)

10 x 5 = 14 x 3.57 = 50 inches = 50 x 25.4 mm = 1270 mm

Or thereabouts...

Coma galore, though

[davidpretorius]

this is where i am getting confused.

How do i know that my f5 10" scope has a 1250mm focal length and therefore what would a f5 14" scope have as a focal length?

I assume the focal length will determine the placement of the secondary and and placement of the hole for the focusser.

Basics I know, but I can't quite get my head around it

[Lester]

1250mm

[Lester]

Dave a 14" f5=1750mm fl

To overcome having to shift the focuser, have extra room behind the primary, so that when you put in the longer fl 14" it is further down the tube.

[davidpretorius]

I think i see what you are saying, keep the focal length the same, just change the ratio for a larger mirror

[davidpretorius]

how did you work that out lester, you smart fellow?

[davidpretorius]

arrrgh, i see, 14" x 25.4 x 5 = 1778 mm....


i see the light!

[davidpretorius]

10" x 25.4 x 5 = 1270mmm hey this easy!!

now if i move the mirror 500mm, the balance will be up the poot for the dob base.


can't atm be easy????

[Starkler]

Focal length = f-ratio x aperture

[davidpretorius]

thanks geoff

[asimov]

If you had a girly EQ you could just slide the tube up the cradle a bit to balance.....lawn-hopper..

[Starkler]

So many things to consider when designing a newt.
THe gurus will say your ota should allow at least 1.5" clearance all around the mirror.
Having a fatter ota will mean needing a bigger secondary to catch all of the light cone and bring the focal plane to a point outside the ota.

Everything is a comprimise.

I would be very wary of a 4 piece tube with regard to mechanical rigidity considering that high quality planetary imaging is demanding on collimation.

[asimov]

:thumbsup:

[iceman]

Wow, a 16" diameter tube.. that's not going to collapse any smaller than your current tube!

[asimov]

Anything on paper yet Dave re the 4 piece design?

[davidpretorius]

not yet, the current scope goes to fabricators on tuesday. I am thinking of two or 3 piece like birds vertically, but then each section can broken down into 1/2 circles.