Prime focus achived. Problem solved.

[Pinwheel]

When I had my 8" f4 newt I could fit my DSLR straight on & shoot. Now, I upsized to a 12" F5 dob and as some of you know I have no Prime focus with this model (BT302-b). So with advise from an IIS member the solution is to either shorten the tube by 50mm or raise the Primary mirror by 50mm. I decided not to cut and came up with a cheap solution to raise the mirror.

I went down to the local Cabinet maker and had him cut me two perfectly round 300mm diameter x 25mm disks of chipboard for $5 each. While he did that I went to the bolt shop & bought 6x 85mm matching thread bolts also $5.00. So I have my $15 Primary adapter. All assembled perfectly, re did the colmination & I tested it all out on a road sign 3 km away. See Pic.

It works, I have Prime focus with the DSLR however NOW I've lost all Eye Piece focus completely! I can't use the reflector for eyeball viewing unless restored to original.

[MrB]

Since you've pushed the focal plane 50mm further out, your focused probably doesn't have enough travel. Try an extension tube between the focuser and the eyepiece.

[Pinwheel]

Thanks Simon I didn't think of that!:thanx:

[MrB]

Sorry, focused should have read focuser, damn autocorrect :lol:

[Pinwheel]

I understood PER FECT LEA..:P

[MattT]

Now you need a 50mm extension tube???? for eyepieces, get a pair of bino's and get viewing two eyed with zero problems with focusing…hopefully :D
My Newt needs a 50mm extension tube for mono and no extension for binoviewing. Just a thought. It is an imaging Newt supposedly.
Matt

[raymo]

Hi Pinwheel, Just hold an EP up to the focuser [not in it] and move back from the focuser until the view comes into focus, which will show you how
long the extension tube needs to be; and add a bit extra because
different EPs require the focuser to be further out than others.
Glad you're getting it sorted.
raymo

[Pinwheel]

Matt T, I had a better idea, I'll try my Passive 3D glasses that came with my new tele! ;)

[Pinwheel]

Raymo, I've worked that part out & guess what, My 2" to 1.25" ep adapter has a filter thread behind it, so I just need a 2" tube with a filter thread and it's all done. Getting closer now! :D

[ZeroID]

I've used a Barlow with the lens removed as a temporary extender. Just unscrews and is about 2" of extra length.

[Pinwheel]

I've ordered a 1.25" extention 2" tube from Bintel for $29.95.

Tube has arrived and problem solved.