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Finderscope cross hair

Phaser6

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AndyH

AndyH

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Tis a Tal reticle, that they often supply with their scopes.

Intended to screw into the 25mm plossl and to be used to line up the finder. But in reality it's got a lot more uses.

Haven't seen anywhere sell these new, which is a shame. Sometimes they come up second hand. Probably best to stick a wanted add on UKAB&S or similar.

Andy.

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Qualia

Qualia

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Tis a Tal reticle, that they often supply with their scopes. Intended to screw into the 25mm plossl and to be used to line up the finder. But in reality it's got a lot more uses.

Although I don't use mine that much, it certainly is a useful recticle to have and it's a nice touch that Tal incude it in the general set up kit. I have a little problem with mine, or so I think, for it doesn't screw all the way into the 25mm Tal Plossl and I don't wish to force-screw the little gem. I usually leave it about half way up the threading - if that makes sense.

Anyway, I'm intrigued, Andy, what other uses do you put yours to?

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acey

acey

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The general principle is that the cross-hairs need to be at the focal plane of the eyepiece, so that they will be in focus when you look through.

For a plossl this means putting the hairs across the field stop (a blackened ring at the bottom, inside the silver barrel, which you can see when you turn the lens upside down). A screw-in attachment can do the same job. For a more complex eyepiece (e.g. wide-angle) or finder it means taking the thing apart to access the focal plane, then inserting hairs at the appropriate place. A screw-in attachment won't work in those cases.

But if your finderscope is one that accepts changeable eyepieces, and you're using plossl eyepieces, then a screw-in reticle will work. Alternatively just glue fishing line onto the field stop of a plossl (remove the ring before doing any gluing!). I did this to make a reticle eyepiece.

One problem to look out for: if you normally wear glasses (like me) then the cross hairs will come to focus at some point other than the focal plane. I'm short-sighted and found that I needed to saw off the end of the field-stop ring in order to get hairs in focus. If I were using a screw in reticle then I presumably would have found myself unable to bring them to focus, unless I modified the eyepiece. Or else I'd need to keep my glasses on when using the reticle eyepiece.

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AndyH

AndyH

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Although I don't use mine that much, it certainly is a useful recticle to have and it's a nice touch that Tal incude it in the general set up kit. I have a little problem with mine, or so I think, for it doesn't screw all the way into the 25mm Tal Plossl and I don't wish to force-screw the little gem. I usually leave it about half way up the threading - if that makes sense.

Anyway, I'm intrigued, Andy, what other uses do you put yours to?

I've got a few and I find they have a pretty tight tolerance and possibly vary to a tiny degree which might make some tighter than others. I find a clean out of the eyepiece thread and if necessary a light rub with fine grade sandpaper on the reticle thread, can help.

As for uses.

I use them on some of my finders with the 25mm plossls.

To line up my mount when I'm doing a star timing for another eyepiece. ie: to make sure the star is crossing bang on through the middle of the view.

They could possibly be used for guiding in some dark arts practice?

Andy.

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Phaser6

Phaser6

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What I am after is the little reticle with the cross hairs that is inside a 9x50 finderscope, it screws out. I have one that has been damaged so I wanted to replace it rather than fit a new finder.

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JamesF

JamesF

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I did that photo in a hurry. I realise now it's not particularly clear unless you've taken one apart yourself. The crosshairs are just visible at the top of the eyepiece assembly. It looks like the assembly is the same in each case, but the 9x50 just has the additional flange to screw into the back of the finder.

James

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AndyH

AndyH

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So the reticle screws out with the aid of the two slots? Or does the threaded(?) slotted piece hold the glass in place?

No matter, looks like problem (possibly) solved?

Nice investigation work James.

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Qualia

Qualia

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Thank you for the information, acey and Andy. I will have a look at my crosshair and see if I can get it adjusted to the Plossl. I'll also have a look at the field stop, I never new about that, so all this information is wonderful. Thank you!

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AndyH

AndyH

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Qualia - When you have the screw in reticule bang on focus, it REALLY shows up the most minute of particles on it's surface. Drove me bonkers trying to get it spotless :)

Andy.

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Qualia

Qualia

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I'm going to get it out in a bit and have a look, Andy. Nay, I'm going to go up stairs (I live in a flat but the block's community have 'lent' me the roof top) right now and give it a whirl. Hopefully I'll be finished before these awful Spring storms start and if it needs cleaning, I think it'll be quite a pleasurable and relaxing job whilst the showers fall. Thanks again, Andy for your most kindly attention. You're a star and I really appreciate your time I have taken up. If you're ever in Spain, drop me a line and I'll fix you up a delicious mojito and paella.

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JamesF

JamesF

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It looks like the reticle unscrews, or has a retaining ring that unscrews. I'm not about to take ones I use apart to find out how they fit together, but as I actually want a reticle for other purposes I ordered a couple of finders from astroboot to dismember. I gambled on 8x20s though as I thought it would be a bit unkind to offer someone a solution and then buy it before they did...

James

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