Should I Dremmel 3cm off my Altair f/4 carbon fibre tube???

[Chris]

I would cut the tube. A 4inch grinder and a 1mm cut off disk is all it takes apart from a mask. Easy as. Just go slow as to not heat up the resin too much. I did a lot of carbon cutting making this

That is a spectular scope you've made there! I hope your new mirror set arrives on time but even with the GSO f/4 set the results are great!

Cuttings CF is not for me but I have nearly finished my 6" f/5 mini Dob which is made from a 10p off cut of furniture pine

[Chris]

Chris, have you thought about adapting this focuser onto the scope. Maybe it will work.

http://www.teleskop-express.de/shop/product_info.php/info/p6122_Skywatcher-2--Linear-Power-Newtonian-focuser---short-design---1-10-transmission.html

Hi, I've been looking at focusers on the TS site funnily enough What do think about this one?

http://www.teleskop-express.de/shop/product_info.php/info/p974_TS-2--Low-Profile-Rack-And-Pinion-Newtonian-Focuser---holds-accessory-up-to-8kg.html

Its one of the lowest profile ones I can find, you could hang a horse off it, and the price looks fairly good. I'm selling my Atik titan, filter wheel and filters so I might be able to wangle a focuser in with my kit reduction if needs be I'm also considering the Baader Steel track low profile.

http://www.365astronomy.com/2-nt-steeltrack-crayford-focuser-for-newtonian-telescopes-bf-30mm-p-693.html?zenid=4c4e93af052be6821b4719f2718e15f6

I have no idea if you need an extra base plate for them so I will dig around if it comes to this.

Chris

[Chris]

Sorry Mods can't edit my post, i forgot to mention these one as well:

http://www.telescopehouse.com/acatalog/Revelation-Superfocus-2-inch-Newtonian-Rack-n-Pinion-Focuser.html

Al.

Now that looks like a great buy, I'll definately keep it in mind, thanks

[Chris]

Agree with jake, old 150 skywatchers all had this problem. Many people did mods to place the corrector on the inside of the focuser tube. Do some searches on this forum on mods to 150. If I find the thread I will post.

Thanks. I used to have an old blue tube 200p with this issue and it was especially annoying because it would come so close to focusing before running out of travel. I take it placing the CC inside the focuser does something more than just remove the physical length it adds to the imaging train, if so then this could be an option and obviously it would be an excellent thing for CCD imagers to do

Chris

[Chris]

Btw you got a deal picking it up at that price

You're right, I have to say even though this is a problem that should never happen on one of these f/4's, I can't hold too much of a grudge having only payed 360 pounds for it. The quality of it is well above the last f/4 I tried and its collimation is silky smooth and it seems to stay put! Using it for some visual with my 13mm Nagler and seeing it just mounted there in my obsy I must say I'm slightly taken with it despite not yet being able to use it for its intended purpose

Chris

[Chris]

Hi, Chris,

just caught up with the thread again.

Congratulations on the twins!! I hope all goes well.

It would be a good idea, as mentioned, to try and find out exactly how far short of prime focus the system is. If you are really close, then expending the bolts sounds like a good plan. If it comes down to cutting the tube, then seeking expert advice would be my first move. We have a small carbon fibre firm locally, maybe there is one near you? 

Anyway, good luck with the twins.

Gordon.

Thanks Gordon, bless you

I think its a little way off coming to focus (see pic), but I've decided that I'm not touching the tube, I will get round it probably with a combination of a low profile focuser and longer bolts and springs.

The pic shows how close to focus I came

[laser_jock99]

I wonder if you could take the tube to your local engineering workshop and drop it in their horizontal metal saw machine.

Any good workshop will have a machine like this

http://www.machinetools.net.tw/m_pic/DF9B3F65-F124-479B-9F67-DE94DBEA58D2/1257387913087939400.jpg

You'll get a nice straight cut in about 2 minutes!

[Macavity]

I suppose this is why Telescope Service now sell custom Fast Newts. 

http://www.teleskop-express.de/shop/product_info.php/info/p5033_TS-8--F4-UNC-Newtonian-Telescope---optimized-focus-position---Carbon-tube.html

Hard to accommodate all circumstances. One size does not fit all etc.

Contemplating moving the mirror slightly up the tube myself - To get a

bit more in-focus to use with a focal reducer. I only need a few mm?

(The irony is that a weak Barlow would easily produce extra out-focus)

The only caveat - These systems seem (surprisingly?) close tolerance.

It would seem they even design the things. lol. Something to play with:

http://stellafane.org/tm/newt-web/newt-web.html (For FUN & education mostly?)

[Skyline]

Both focusers look good, telescope house sells the same focuser from the TS site cheaper. It should fit that 8" tube no problem. If you did need to shimmy it, you could just use some of that black hard foam material which you find on mouse mats or some of those round rubber tap washers underneath each screw.

Al

[Chris]

Both focusers look good, telescope house sells the same focuser from the TS site cheaper. It should fit that 8" tube no problem. If you did need to shimmy it, you could just use some of that black hard foam material which you find on mouse mats or some of those round rubber tap washers underneath each screw.

Al

Great Idea about the mouse mat, thanks