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musherrob

reducing focal length ! with what ?

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Hi All...Have borrowed(he a,int getting it back!!) my sons Canon eos 300......So here goes !! I have a Tal 2 f/8 I can,t appear to reach the point where the focus is at the camera view finder(no lens attached).The focussing tube is at it lowest extent but still unable to focus.I know that i will need the t-ring adaptor and eyepiece extension.So what piece of eqiupment do i need or dispense with to obtain focus..Ta ;) .Rob

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You will need a 1.25" to T thread adaptor and an EOS T ring for the camera body, BUT.....

From what you are saying the focus is to close to the tube to allow the camera body to focus...Hmm - well you can either try to find a low profile (shorter) focuser and hope that works - or- move the main mirror up the tube to position the focus further out from the tube.

That's about the limit of the easy options.....

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There are only three options on the Tal-2 to achieve focus. 1.) Move the primary mirror up the tube. 2.) Replace the focuser for a low profile version or 3.) Use an M42 to Canon EF adaptor on the focuser tube.

The thread on the focuser tube of the Tal-2 is an M42x1, it does come with an M42x1 to M42x0.75 (T-thread) adaptor but this does not allow the camera to reach focus.

I got a low profile Canon EF to M42 adaptor from eBay, screw it on directly as in the attached pictures and you should be able to achieve focus (just with a millimeter or two to spare). You cannot use a normal T Adaptor as it is far too thick.

Get one with an AF confirm chip on it as shown, these really help to find correct focus, just place the centre AF spot on the brightest star you can find and slowly rack in and out of focus, when focus is achieved the camera will Beep as normal - works every time.

I also modded my adaptor to fit a light pollution filter into the imaging train, this is possible because of the smaller mirror on an APS-C camera such as the 400D (and I guess the 300 is similar). If contemplating something similar you MUST ensure the distance of the protrusion inside the camera body is no more than the standard EFS lens, I checked the depth against my EFS 18-55 lens and the protrusion inside the camera is 0.5mm less than the lens. If you are in any doubt do not attempt this mod, if the mirror hits the filter it will shatter.

Brendan

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Thanks Brendant..Is the glass i see on the adaptor an IR/UV Filter if so what spec/size thread is it ?:icon_salut:Thanks

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Brendant..What sought of price are we looking at for one of these adaptors ?If not a rude question..Ta Rob

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Are the focusers on the Tal 2M different from other Tals ?

The end of that focuser looks different from my Tal's, they

don't have a thread on them but you get a seperate adaptor

with the M45 thread on it.

You still have a problem though using it to attach to a canon

T-ring.

Kathleen

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Rob, the adaptor costs between £20-30 from memory with an AF confirm chip, a plain ring without can be got for around £10. The glass you see is a 1.25" Baader Light Pollution filter, the black ring is a custom adaptor I made to attach it to the M42 adaptor ring.

Kathleen, you may well be right as there was a discussion on here some time ago that some of the Tal-2's have different focusers, mine does hava a separate adaptor for using eyepieces which screws off to leave the bit you can see in the first image.

As I tried to explain in the first post the thread that is left is an M42 x 1mm Pitch, this is not a T thread, a T thread is M42 x 0.75mm pitch so a Canon T-Ring is useless as you say, it is the wrong thread and far too thick. You must use a thin adaptor as in image 2 to have any chance in achieving focus - an M42 x 1 (standard lens fit for older cameras with screw fit lenses) did work on my Tal-2M focuser tube but if yours does not match the picture then it will probably not work.

Brendan

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Hmmmmn thats interesting Bredant, my adaptor is like this :

and comes in two pieces, the back of the main adaptor is M42 as you

say and the little screw on adaptor converts the thread to fit the canon T-ring.

Bit of a bummer really if you don't have a camera using that thread but I've asked Milamber to make me an adaptor which should hopefully allow me to attach a camera.....I hope ;)

Sorry to have side tracted your thread Rob.

Kathleen

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How does one properly move the primary mirror? Is there a guide on how to do this somewhere, I've been searching without any luck. Is it difficult to maintain proper alignment of the mirror when you move it? (Explorer 130P)

I can *just* about focus with a 25mm EP, but prime focus isn't possible, even with the T-ring screwed directly onto the focuser.

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