Small focusing problem with my Bintel...

Lomu · #1 08-01-2014, 07:41 PM

Howdy all,

apologies for the tone of my first post- but I have a (hopefully) small issue with a scope that I've bought for my kids.
It's a Bintel 8" Dob- awesome piece of gear, except I've not been able to see anything through it. It's all assembled, but the focus mechanism does nothing. The knobs spin, but the eyepiece mechanism doesn't move.
I've done a quick search, and apparently the trick is to play with the two thumbscrews underneath- one's a locking screw, and the other is a tension screw.
I've tried this, but to no avail. Surely I can't be the only one that's experienced this issue?
All help appreciated,
Darren

barx1963 (Malcolm) · #2 08-01-2014, 08:08 PM

Hey Darren. Well done on buying an awesome scope for the kids.
Yes the knobs are the trick. One will lock the focuser in position when it is tightened, the other will release the focuser so it drops down when it is loosened, but tightening it will allow the focuser to move. Unfortunately i cannot remember which is which (sorry).
The second knob needs to be adjusted so the movement is just right for you. Keep trying, if it is still giving you trouble I would ring Bintel, from experience they are always happy to help with things like this!

Cheers

Malcolm

noeyedeer (Matt) · #3 09-01-2014, 05:04 AM

hi Darren, the screw closest to the scope will prevent the focuser from moving using the knobs, and the second one will prevent the focuser from sliding in and out. I've been caught out a few times. best bet is to have he one furthest away from the scope secure, so the tube doesn't slide without having to turn the knobs.
the one closest to the scope can be not so tight as to allow the knobs to move the focusing tube.

so the one closest to the scope is the locking screw, and the other one is the tensioner. honestly ivdont know what the deal is with those, but I usually have it set like how I've described. .. tensioner tight (tight enough that my heaviest eyepiece doesn't make the tube slide when the scope at low altitude), and locking loose.(loose enough so the knobs move the focuser in and out)

nice stuff indeed for the kids!

matt

ps .. my version of the knobs is the actual focuser things, not the screws.

word of warning .. never over tighten anything either with the thumbscrews. enough pressure to prevent it from sliding at its minimum tightness with the weight involved is ample. you still want a smooth slide when adjusting focus, not a gluggy movement. like Malcolm mentioned play around and you will work it out what best suits you.

The_bluester (Paul) · #4 09-01-2014, 09:27 AM

Not having seen the Bintel branded dob up close to confirm makes this a little bit of a guess, they ahve a craford style yes?

Typically on the focussers, the screw that is directly in between the focus knobs (Inline with the shaft) is the tension screw and it needs to be set just tight enough that the knobs will move the focusser against gravity with whatever the heaviest eyepiece or other peice of kit you will use installed in the holder. The locking screw is just that and you would generally keep it just tight enough to keep the focusser from moving in use (Bumping the EP with your eye for instance) Looser than that and you might spend the night chasing the focus around, tighter and it is unnessesarily so and might put marks on the focusser tube and make it's action less smooth. Genrally I would loosen it slightly to set focus and then firm it up again, if the focus was inclined to move otherwise.

louie_the_fly (Stew) · #5 09-01-2014, 11:07 AM

Gidday Darren. I had this happen to me on New Years Eve. Got the scope out for people to have a look-see and my crayford focuser wouldn't adjust. Grrr. Got it sorted though. It was the lock screws underneath. As someone else said, make sure they're not over tight. I leave the 'lock' slightly loose and the tension screw (the one in line with the focuser shaft) just nipped up firm but not tight.

You might want to consider stripping it down and giving it a once over. I did it as soon as I bought mine and it made a huge difference to the feel. I have a file that shows how. (I originally downloaded it from the web, so I won't take credit for it). PM me if you want a copy as it's too big to upload.

Stew.

astro_nutt · #6 10-01-2014, 01:39 AM

A dab of Goss Dry Lube on all the screw threads will make life easier too!

Lomu · #7 10-01-2014, 06:58 AM

Quick update:

Many thanks to all the contributors. I've managed to get the focuser behaving again.
It's an odd sort of arrangement. The screw closest to the tube doesn't appear to do anything at all (though I'm sure it does) so it's just left loose. The one closer to the eyepiece...I just gradually adjust it until it 'grabs', test the focuser, adjust, etc. Took all of two minutes.
Spent the afternoon peering at the moon. The detail is quite extraordinary- in fact we found with the 9mm eyepiece that the image is 'too large' so we had to use the 15mm instead.
Now, to build that observatory...