New Refractor

[Visionary]

I recently acquired a new refractor. The only thing I don't like about the scope is the Focuser. I would like to order a new Focuser for the scope. How do I measure the scope for a new Focuser? Do I measure the outside or OTA or is there some other measurement that's required?

[omegacrux]

What's the scope ?
Usually id of the tube
3 screws hold the focuser in the tube easily removed

David

[dannat]

Which scope Is it, does the focusers have screws to remove to measure the flange distance

[Visionary]

Yes, it does have three screws. The scope is a AOE. The label describes the unit as a 102mm but upon removal of the Focuser I found the internal measurement to be 125mm! I am guessing the OTA has been incorrectly labeled and that it is a 6" Achromatic scope! Given the origins would be almost certainly Chinese my gues is that it is a 125mm or 6" scope.
So, I checked x3 times the internal measurement at 125mm. Should I order a 6" or 120mm from Bintel? I would like to place the order tonight's as I have some other parts to order from Bintel.
I took the scope outside today to aline the finder scope. I was VERY surprised I was expecting chromatic aberration, there was some purple fringing but it was acceptable. The fringing was more noticible at near focus (terrestrial) and once cranked out to reasonable distances 1km there was very little fringing.
Cheers

[brian nordstrom]

:D The diameter of the tube really means nothing , you have to carefully measure the lens diameter , remove the dew shield off the front and measure the size of the main ( front ) lens .
Any chance of a photo ? this would help a lot .

Brian.

[Visionary]

Unfortunately the measurements work against me! Though the measurement a the Focuser is 125mm and the bit I have to pay for... The lens is 102mm! I took your suggestion, I attempted to remove the dew shield, it was stuck fast. I managed to confirm the size of the objective by very carefully lowering a 120mm piece if soft plastic into the void of the dew shield, measuring determined that the objective is 104.
The bugger is this, I didn't pay very much for the scope. The Focuser is really nmarginal. The tube size internally is 125mm meaning I need to shell out $250 odd for a new Focuser due to the size of the tube.
Photos should be attached. Many thanks for the heads up. Cheers!

[Visionary]

The scope does look very handsome on its Mizar mount! I believe the OTA is powered coated, the finish is brilliant with the smoothness only powder coating seem too produce. Once I removed what little dust was on the tube is really shone! The other "oddity" is the tight ring that the OTA produces when struck, a very well formed and very solid tube.
I really don't mind shelling out for a new Focuser, the way the mount slews through the sky and the over all feel of the unit it screams quality. Again, thanks heaps!

[ZeroID]

David, it is normal for the OTA to be larger than the objective diameter. It allows components to stay outside the optical path and light baffles, lens cells etc to be mounted. My 102mm Lunt OTA is about 120mm.

[brian nordstrom]

:thumbsup: Very handsome indeed David !! , yes as Brett says the over sized tube is a good thing as it allows larger and more efficient baffles to be fitted. , my iStar 127mm has a tube 140mm in diameter .
Out of curiosity what focused are you thinking of getting? , cheers .

And oh yes I have one of these Mizar mounts , they are very solid and well built.

Brian.

[MattT]

Hi David,
Can you take a photo showing the focuser end clearly?
On my photo there are two scopes with the same 86mm focuser fitting. The smaller scope screws directly to the tube and the bigger one goes into the flange which has an internal 86mm diameter.
Being able to see what you have will help.
Matt

[Visionary]

Gentlemen,
You have again quickened my learning curve! Of course, once you describe it, it is self evident the tube must be larger than the objective! The Focuser I purchased is the larger Bintel Crayford @ $250. I also purchased a Meade 4000 56mm, these two items are the LAST Astro items I am going to be buying for a very, very long time. I have spent quite a bit of money but over all I am pleased with the result.
Matt, the internal measurement is 112mm, cross checked verified etc: you maybe able to see one of the three screws that retain the Focuser, indeed it was just as you described!
Cheers
David

I purchased the Meade Eye piece from B&H Photographics in the States. I purchased it direct freight was about $17 Aust all up about $70 odd Aust. This is half what I would have paid elsewhere! Take a look at the price of scopes! I believe this may create waves within the Aust market place. It is a bit of a worry.

[MattT]

112mm does make sense. You would have bought this GSO Crayford,

http://agenaastro.com/gso-crayford-focuser-refractor-telescope-dual-speed-112mm.html

A fine focuser. I use GSO focusers on all my scopes, 3 crayfords and one linear bearing with rigel systems electric stepper motor. Correctly adjusted they are perfect as far as I'm concerned.

Please post a pic when you get it installed.

Matt

[Visionary]

Matt,
That's a super hot price! The Aust price is $250 we are trading below parity with the greenback, but still that's a brilliant price. I purchased a Meade 4000 2" 56mm lens from B&H Photographics (USA) just last week including the difference in the dollar and freight I purchased it @ HALF the Aust price!
I am visually impaired, large lens make it possible to slew around the sky much more quickly than I can with "normal lens".
I took some hots with the refractor this week. I don't have tracking on the scope. Though the scope presents a fabulous image, the image via the camera is jumpy and lacking in definition as a consequence of the Focuser being below par. Though I am spending $250 it's an important purchase as it will deliver a vastly improved scope.
Once the Focuser is installed I will post before and afters with the new Focuser. In addition I will post before and afters of Astro pics. Please remember the mount does not track. I hope to be upgrading the mount with a Japanese tracking system in the very near future.
David

[Visionary]

I had the good folks at Bintel give the refractor the once over and these are their conclusions. The scope is "better" than what I thought, build and optics. It is also larger than what I thought. Bintel's largest focuser at 125mm is way too small. The question as to how to replace the focuser remains open.

[MattT]

David,
Sounds like an odd size tube??? 125mm internal is that correct? Possibly having a flange made by a machinist to match the internal size of your tube and a flange of 96mm for the focuser might be one way to go about it. I did my own flanges for my scope with a drill press and hours of grinding and filing by hand…no lathes here!
Gotta be someone in Sydney that could do it for you….Might be one reason why the scope was a bargain.
Brian…what do you think?

Edit: Just re read your earlier posts where is the 112mm measurement from? I'm a bit confused...

[John0z]

David,

Instead of just throwing money at it, might I suggest that the photos you are taking - might not be due to the focuser as such, but might be due to not being focused properly? That looks like a fairly standard rack and pinion focuser which basically is a hollow tube that moves in an out. One possibility if you still want a focuser is to measure the focuser tube - you might be more likely to get another focuser to screw into that, then use the original focuser for coarse focusing, especially since there is a lock screw - then use the new focuser for fine focusing. I see that there is a helical focuser on sale in the classified - something like that could do the trick. Since you are in Sydney, I might even be able to make an adapter for you - I made one to fit a different helical focuser previously for another IIS'er.

[brian nordstrom]

:D I can see where the confusion is coming from , this scope's focuser fits on the out side of the tube , not inside like most refractors do , the tube will be 112mm od ? and the focuser body would be the confusing 125/127mm diameter .

All you need is an adaptor machined up from alluminum as Matt says that is the GSO focusers 96mm id. and an od of the 112mm? that is the id. of the tube , get the machinist to drill 3x M4 threads at 120 degree centres around the circumference of the 112 diameter section to attach to the tube with a small step down about 10mm long at the outer end about 103mm od diameter and 96mm id with 3x 5mm holes ( again at 120 degree centres ) to attach the focuser to , both will fit straight up to the 120 degree spaceings as its standard ) .

Here is a photo of one I machined up to fit a GSO 84mm od. focuser onto my old ED80 , these have 100mm od tube , fairly simple to any machinist to do and it should not be to expensive $100 max .

Hope this helps .

Brian.

[ZeroID]

Famous last words those are ...... ;)