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TAL 150PM - not enough in-focus!

Crunchard

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Crunchard

Crunchard

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Went to attach my DSLR to my TAL last night.

Initially couldn't see a bean (or a star) but then realised the TAL has a screw off lense holder, so you can attach the t-ring directly to the focuser, so off that came.

Problem was that my t-ring did not tighten up all the way, got nearly halfway and then stopped - so there was still 2-3mm worth of thread showing.

With the focuser all the way in the camera was still out of focus, only slightly bit enough to make M13 very blurry :(

So on to my pleas for help...

  • Does anyone know if there is a specific t-ring to use?
  • Is it a case of dumping the rock-solid-wouldn't-melt-if-you-threw-it-into-the-sun TAL rack'n'pinion?

Or have I missed something completely?

Yours scratching his head .... oh and visually it is fine, even with my eye mashed up against my TV 8mm ;)

Cheers

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AndyH

AndyH

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Hi.

Is your 150P one of the older ones with the 1.25" focuser? I think the 2M possibly had a similar or same type?

I've got some pics on here ........ http://www.flickr.co...86911@N08/sets/ ......... I put the pics on as a visual aid with a discussion with JasonP and his older 2M, which has a very different mechanism with a 32mm I/D eyepiece holder.

When the eyepiece adapter(47mm long) is unscrewed from the focuser, the thread revealed is the Russian camera thread, M42x1. If I remember correctly the size for the T-thread is M42x0.75 . This might explain why your ring doesn't thread on all the way?

Have you checked the springs on your mirror cell? Mine were nearly mashed flat and close to being useless. I put some new springs on, last week, which helped. They were longer than I wanted, therefore pushing the mirror 'up' somewhat. This sounds like this would be a bonus for you and your camera focus probs?

Andy.

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Crunchard

Crunchard

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Cheers guys - I think the primary mirror is the thing I will check ... either that or get something else to tick the astrophoto box.

The TAL is about 10 years old, so not too old in TAL terms.

Will keep you updated :)

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Crunchard

Crunchard

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I tried to take a couple of pics this morning ...

Compression spring (is it sprung? :))

post-13336-0-35982500-1350376399_thumb.j

And the bottom of the cradle:

post-13336-0-86884500-1350376451_thumb.j

There is about 2-3mm of visible thread between the middle thumb screw, the rest is non-threaded.

Cheers, Jeff

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AndyH

AndyH

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Mmmm. How very strange.

Looks like it's already had an attempt at a mirror push up, unless that's how the 150P's come like. I'd defo give nicnac a pm and ask him what his rear cell looks like.

On my 2M, which has an identical cell, the original spring, sits on the back of the mirror cell(at the bottom on your pic). There's no bottom washer, only the top one.

Here's what mine looks like............

:icon_scratch:

Andy

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Crunchard

Crunchard

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And there was me thinking you were being clever :)

I only took the one pic, so will check again tonight - might be one spring that is like that!

Oh, and like your thumb screws - that must make collimation a lot easier!

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AndyH

AndyH

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Oh, and like your thumb screws - that must make collimation a lot easier!

They do, but, being F8, you need arms like Michael Phelps to twiddle em whilst keeping an eye at the eyepiece. Normal humans have no chance.

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Crunchard

Crunchard

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Ok, have taken the rear cell off and had a good look around. All the collimation screws are setup as per the picture, they have a double washer system, with a ridge to stop the washer going to the floor. Clearly bigger washes or springs would negate that but I'm not sure if the fitting at the bottom would take it.

What I have done is set the mirror up as far up as I can - fingers crossed those 2mm help with the focus on the DSLR.

It really isn't far off as this pic of M'something or other (can't remember now) shows.

post-13336-0-19641100-1350739241_thumb.j

Cheers, Jeff

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nicnac

nicnac

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Yeah, that pic was taken with the drawtube fully in. The TAL comes into focus zone when the drawtube is about two thirds the way racked out, the isnt any shadow cast onto the primary when viewing.

great bit of kit

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