DIY Crosshairs

[Stub Mandrel]

I wanted a dirt-cheap crosshair eyepiece for a finder scope.

I bought a dirt cheap opticstar 25mm plossl, on the basis it won't matter if I wreck it and it's only for a finder so great quality not needed. Luckily the field stop is made as a plastic ring with a sharp edge. I took two strands of very fine wire from a very thin multistrand cable. I flattened the wire by rolling it between two flat surfaces after cutting to length. I used a cocktail stick to apply polystyrene cement to the stop ring and fine tweezers to place the wires and nudge into position.

 

[Hallingskies]

That's clever.  How did you keep the wires so straight and tensioned?

[Stub Mandrel]

53 minutes ago, Hallingskies said:

How did you keep the wires so straight and tensioned?

Rolling between two hard surfaces make them very straight. They are short and light enough not to need tensioning.

[Peter Drew]

I always used human hair, well my hair anyway.    ?

[Stub Mandrel]

8 hours ago, Peter Drew said:

I always used human hair, well my hair anyway.    ?

I did consider it, but I don't think I have the skill.

[Astrobits]

I've always used silk strands, direct from the cocoon if possible. Thinner than human, or other, hair and wire.

The trick in keeping flexible thin strands straight is to have the strands longer than the frame requires and stretch them over a large aperture in some stiff card holding in place with adhesive tape. At this point you can adjust the strands to be at 90 deg to each other easily. This is then placed over your frame, carefully centered, and blobs of glue applied at the touching points. When dry use a craft knife to cut the strands where required.

Nigel

[Peter Drew]

1 hour ago, Stub Mandrel said:

I did consider it, but I don't think I have the skill.

I understand. It takes a lot of experience to pluck the right one.    ?

[Peter Drew]

8 minutes ago, Astrobits said:

I've always used silk strands, direct from the cocoon if possible. Thinner than human, or other, hair and wire.

The trick in keeping flexible thin strands straight is to have the strands longer than the frame requires and stretch them over a large aperture in some stiff card holding in place with adhesive tape. At this point you can adjust the strands to be at 90 deg to each other easily. This is then placed over your frame, carefully centered, and blobs of glue applied at the touching points. When dry use a craft knife to cut the strands where required.

Nigel

Yes, this is the procedure I used to fix the hairs. I found the thicker hairs to be more easily seen against the sky background.

[Stub Mandrel]

14 minutes ago, Peter Drew said:

Yes, this is the procedure I used to fix the hairs. I found the thicker hairs to be more easily seen against the sky background.

I imagine silk needs to be illuminated?

[Stub Mandrel]

25 minutes ago, Astrobits said:

I've always used silk strands, direct from the cocoon if possible. Thinner than human, or other, hair and wire.

The trick in keeping flexible thin strands straight is to have the strands longer than the frame requires and stretch them over a large aperture in some stiff card holding in place with adhesive tape. At this point you can adjust the strands to be at 90 deg to each other easily. This is then placed over your frame, carefully centered, and blobs of glue applied at the touching points. When dry use a craft knife to cut the strands where required.

Nigel

For the EP I used, the field stop is about 20mm down a tube. To put tesnsion on I would have to drill holes. I'm now tempted to get another cheap EP, turn up a little LED torch and make an illuminated one. My daughter has fine fair hair in suitable lengths. Sadly mine has been much to short since 1987...

[Gina]

I replaced a broken cross-hairs with my own hair a while back.  Very fiddly job.

[Astrobits]

Traditionally, cross-hairs were made of spider silk, particularly from Orb-Web spiders. Having walked into Orb-Web spiderwebs I can attest as to how remarkably strong their silk is.

I have tried fine wire but even the finest I could lay my hands on was, to my mind, too thick as the target could get lost behind them. The solution to that was to defocus the finderscope so the stars were discs which could easily be centered on the cross-hairs. Unfortunately that rather limited the faintness of stars that could be used.  However, having done your first one it will be easier to remove it and do another one if you want to try a different 'hair'.

What got me more frustrated was the three screw adjustment system used on many finderscopes. This led me to designing and making my own finderscope mounting that has push and lock in horizontal and vertical planes separately.

Nigel

 

[Merlin66]

I recent got a mate here in Oz to add crosswires to a 28mm eyepiece....

He uses a fine fibre optic thread - works very, very well.

 

[Chriske]

In the (very) old days observatories kept spiders exclusively to harvest their silk to be used as crosshairs. A long time ago there was article about it in a astronomical magazine.
I'll look it up...

Baby's hair is very thin so for that purpose I 'harvested' hair of my son when he was (very)little...

[Chriske]

This is not the one I was referring to but it'll do(I think..)

http://www.amerisurv.com/PDF/TheAmericanSurveyor_BediniAlongCameASpiderPart2_May2005.pdf

[Chriske]

https://owlcation.com/stem/The-patriotic-black-widow-spiders-of-World-War-II