----- Original Message -----
Sent: Sunday, February 15, 2004 5:34 AM
Subject: [M]: RE: Thread Data


> Roger:
>
> Great info. You thread data is worth saving. One question though. What
> is the thread size for the screws used to mount things on the top of the
> scope? I have a dovetail plate that I want to mount piggyback on my 8"
> LX200GPS, but it came without the screws to attach it to the scope. If
you
> or anyone else knows the screw size, please pass it along and I'll go to
> the hardware store to buy what I need.
>
> Thaks,
>
> Bill
There are two threads used. The smaller ones (where the finder fits), are
8-32 UNC, and the larger ones (where things like Losmandy rails fit), are
10-32 UNC (I think I have this right, saying it 'off my head' - no comments
please... :-).
Worth saying, that I'd get stainless bolts if possible. Aviation companies
have these, and they prevent any nasty corrosion problems.

Best Wishes

> -----Original Message-----
> Sent: Saturday, February 14, 2004 4:23 PM
> Subject: [M]: Thread Data
>
> Attached is the text of my 'thread list', slightly modified. One new piece
> of data added. One new 'caveat', and one typo corrected.
>
> -------------------------------
>
> This is a list, of some threads used in telescopes and accessories. Some
> are
> 'from specifications', while others have been taken from measurements.
> There
> are also some notes about 'oddities', with some parts, and in a few cases
> other data covering such things as the design 'focal plane' distance.
>
> Meade:
> Rear Port on 10" and larger models (excluding the C16)
> 3.25" * 16TPI
> 2" SCT 2" * 24TPI
> ETX Rear Port 1.375" * 24TPI
> This is to me, an 'oddity', since in general Meade threads are imperial,
> but
> the external measurement, seems to be fractionally 'oversize', and the
> thread is really closer to 35mm OD.
>
> Celestron:
> Rear port on C11 C14 etc. 3.3 * 16TPI
> Many of the scopes outside diameters, measure slightly 'small', at about
> 3.29", but cutting to 3.3 for the outside of the thread teeth, gives a
good
> fit, with reasonable clearance.
> The rear cell on the smaller scopes, and on the rear of the adapter
> attached
> to the larger scopes, is the 2" SCT thread above.
> On the 1.25" 'visual back', the external thread, is:
> 1.38" * 24TPI
> This is very close to the thread on the ETX, but is very slightly larger.
> The relationship of these two threads, is definately an 'oddity'. In most
> cases, accesories for each, will fit the other, provided they are slightly
> 'oversized' on the Meade fitting...
>
> General:
> M42/Pentax. 42mm * 1mm
> This is the thread on the older StarLight camera noses, and on quite a few
> odd accessories.
> The focal plane, is meant to be at 45.46mm from the camera face (45.5mm to
> the _rear_ of the film on a normal camera 'body').
> T42 42mm * 0.75mm
> This is the thread on the extension tubes supplied by Meade/Celestron, for
> their focal reducers, on the rear of some OAG's, and on a lot of camera
> attachments. The newer Starlight SVX-H9 family have this thread.
> This is the thread normally called simply the 'T' thread. Beware though,
> that a lot of accessories that refer to a 'T' coupling, may use the
> alternative 'T bayonet', so make sure you are dealing with 'T-threaded'
> accessories when buying parts...
>
>
> CS 1" * 32TPI
> This is the thread found on some WebCams, and on the Starlight guide
camera
> for the SVX. The focal plane, is meant to be at 12.5mm from the face.
> C 1" * 32TPI
> Identical to the 'CS', but with the focal plane at 0.69" from the nose
> (17.526mm).
> The commonest 'webcam' lens thread, is 12mm*0.5
>
> Filters:
> 1.25" eyepieces. These take filters measuring
> 28.4 * 0.6mm
> This is another 'oddity'. Technically, there is a standard for camera
> filters, which are 99%, in 1mm (or occasionally in 0.5mm) steps, with
> pitches of 0.6mm, 0.75mm, and 1mm, according to size. The version used on
> telescopes, is (I believe), an imperial 'conversion', which has been
> modified to bring it 'in line' with the filter standard. I suspect the
> 'orginal', was:
> 1.125" * 42TPI.
> There are a couple of old 'Leica' filters, which show this same 'between
> the
> steps' sizing.
> Occasionally, some old filters turn up, which are very 'tight' in the
> modern
> threads (the imperial measurement, is 0.007" larger).
> 2" eyepieces. 48mm * 0.6mm
> Again there is an 'oddity' here. Generally, on threads, the 'bore' is cut
> to
> the specified size, and the thread to fit inside is made a few thousands
of
> an inch 'small', to give a comfortable fit. Some Meade 48mm filters, seem
> to
> be made with this thread slightly 'oversized', making them unconfortably
> tight (to the point where in some cases they won't fit...), in some other
> makes of eyepiece. Beware....
>
> Others:
> Takahashi, use an assortment of 'unusual' threads. So their eyepiece
> extension tubes, use 43mm * 0.75mm. The 'Rear
>
> Port' , on their scopes, is normally 72mm * 1mm.
> Borg use a similar (even larger!), assortment of threads, offering
adapters
> to many other makes, as well as their own variants. Fortunately, they
> publish a good list of the threads available, at:
> http://www.sciencecenter.net/hutech/techdocs.htm
> The 'component catalogue', gives the thread sizes for each end of the
> adapters in their range of products, including, the thread sizes used to
> fit
> many other makes of scope (Takahashi, Televue, Vixen etc,). This is
> therefore a 'gold mine' for anybody wanting to make adapters. :-)
>
> 'Base' threads.
> Camera tripod 1/4 * 20TPI. This is the thread in the side of an SBIG
> camera, and
>
> also in the base of ETX scopes.
> 5/16 * 18TPI. This is the thread in the top of most
>
> Meade/Celestron tripods.
> 3/8 * 16TPI. This is the thread into the base of several scope
>
> (the LX200, and the Celestron C11 for instance).
> 1/2 * 13TPI. This is the _centre bolt_, on the LX200 models.
> Generally, all the imperial bolts are 'UNC' tooth form (60 degree). The
> metric threads are also this shape.
>
> Best Wishes
>
> --
> --------------------------------------------------------------------
> |A beard! A beard! cried Fly Nicholas. 'By God, that's a good one!'|
> | (Chaucer) |
>
>
>
>
>
>
>
>

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