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Homebrew crosshair

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#1 zolytech

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Posted 14 August 2019 - 02:07 PM

Greetings to all,

 

Does anyone have hands-on experience how to make crosshair, and where to position it in an eyepiece and finder?

   - I want to experiment and custom make one or two mainly for different size of eyepieces, would come very handy on starparties and outreaches.

Thanks in advance,

Z



#2 S.Boerner

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Posted 14 August 2019 - 02:23 PM

I've super glued two pieces of fine wire across the field stop of a few old eyepieces.  It seems to work ok and sharp with the rest of the field, but it is really hard to get the the two pieces of wire perpendicular to each other.

 

Start with eyepieces that have an accessible field stop.


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#3 photoracer18

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Posted 14 August 2019 - 02:53 PM

Yeah you have to position it at the focal plane. Some eyepieces designs have it in the middle of the lens and some are below the bottom of the lenses.

Most factory ones tend to be Plossls these days but in the past they were generally simple eyepieces like MA or even Ramsden, Huygens, etc. Some also come with a focusing collar on top. Just remember that you won't be able to see the crosshairs against a black sky very well without illumination. Not something you can do well with wire crosshairs. I remember doing long exposure slow film in the 60's guiding by eye with a hi-power guidescope and without illuminated crosshairs it was not easy. Lucky we don't have to do that anymore. Most old school finder scopes used wire crosshairs at the eyepiece field stop and they don't stay straight forever. I have several I need to fix for restorations.


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#4 ngc6352

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Posted 14 August 2019 - 06:00 PM

I did it with a cheap Celestron Kellner with 2.5 lb monofilament as an alignment eyepiece.  Works OK, but

the monofilament is HUGE in the FOV.  I wanted a 25mm alignment EP for my SCT/GOTO GEM.  Did it several years

ago; still have it; still works.  Glued to the field stop.



#5 clearwaterdave

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Posted 14 August 2019 - 06:55 PM

I used my beard hair and super glue.,it worked fine.,but was fat.,lol.,I did it to a Meade 26mm plossl and a 23mm Vite 62*.,cheers.,



#6 luxo II

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Posted 15 August 2019 - 01:40 AM

You could use spider silk.

Find an old table fork and remove the inner tines leaving the outer two only

Find a fresh web (early morning is best) and collect the silk by winding it around the tines of the fork.

With care you can stretch the silk across the retaining ring and it will stick.

Should last for months, and easily replaced.

#7 Jon Isaacs

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Posted 15 August 2019 - 02:04 AM

I have done cross hairs to two eyepieces. One was a StellarVue finder eyepiece with damaged crosshairs, the other was a 24mm TeleVue Wide field.

 

When I asked Don Pensack about how to do it, his recommendation was to use heavier than normal wire, that way the cross hairs would be visible even against a dark sky.  Those fine wires are fragile and difficult to see.

 

My method was pretty simple.  I got some 0.004" diameter hard brass wire from my friend at a machine shop, it's EDM wire.  Hard brass stays straight. 

 

I removed the barrel from the eyepiece, both had the field stop in the barrel.  Care is needed because some eyepieces use the barrel to secure the elements in the eyepiece.  Panoptics are like that, the 24mm Wide FIeld is like that.  Keep that body pointed up so the elements cannot slip out. 

 

I measured the diameter of the barrel where the field stop was mounted using calipers.  Then I cut the cross hairs to length using nail clippers.  I made them slightly smaller than the bore near the field stop.

 

The rest was eyeballing it. I used tweezers to pickup the cross hairs and placed the cross hair on the field stop.  I jockeyed the position using a tooth pick until I was comfortable with the position. Then I put a drop of super glue on the end of the wire.  I used a tooth pick for that too.  I then placed the second cross hair on the field stop, moved it around until it looked good to my eye and added two more drops of super glue to hold it.

 

I reassembled the eyepieces.  It has been working for me, I really like the way it turned out.  The wires are easy to see under dark skies.  They might be a little big but that made them easier to work with.. 

 

Jon


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#8 SteveInNZ

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Posted 15 August 2019 - 03:46 PM

Now you're taking me back to the good old days. :)

 

As others have said, pick an eyepiece with a field stop that you can get to easily. The best material I found was to get a piece of clear plastic (I used the sprue from plastic models), heat a section until it melts and then stretch the two ends apart. You'll get a very thin thread that is robust enough to work with. You put four drops of glue on the field stop and lay the thread down on to it. You need a glue that's not plastic solvent based. I don't like super-glue as it out-gasses and leaves a white residue on everything.

The clear thread works well with a reasonably bright star as it gives you a small cross of light, so it doesn't need illumination in a lot of cases.

 

Steve.



#9 howardcano

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Posted 15 August 2019 - 04:15 PM

I used dark brown Lhasa Apso hair.  It's quite thin.  At the time, it was also very easily available... on clothes, rugs, pillows, etc.


Edited by howardcano, 15 August 2019 - 04:18 PM.

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#10 wrnchhead

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Posted 15 August 2019 - 04:33 PM

I have done this also using EZ Line, which is for rigging model ships. I don't know if it's worth $10 if you're only going to do one crosshair, but the elastic property makes it a cinch to get straight lines, and a pretty huge margin of tension that works. 

 

http://www.hobbyworl...roller=category



#11 Jon Isaacs

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Posted 15 August 2019 - 08:02 PM

Some thoughts and considerations for finder reticule eyepieces:

 

- The virtue of the hard brass wire is that it does not require tensioning to be straight. This means it relatively easy to do eyepieces with recessed field stops.

 

- Most reticule eyepieces are simple designs and poorly corrected in a faster scope. Since finders are typically around F/4, this means a messy view.  A year or two back, i purchased the standard 20 mm 70 degree illuminated reticule eyepiece for use in my finders, primarily an SV-50.

 

I was badly disappointed.  The rericule was overly bright and bled into the field. The eyepiece was a mess off-axis. I considered it unusable and gave it away. I decided I could do better.

 

- I had an old TeleVue 24 mm Wide Field. I was my first really decent eyepiece but it had some damage from a previous owner and had seen a lot of use. It's not a 16 mm Type 5 Nagler but it's sharper by far than a normal finder eyepiece and it has the virtues that the field stop is accessible and the ring is wide enough to glue to.

 

- Works very well, it's reasonably sharp across the field and offers a 6.8 degree TFoV at 8.3x. 

 

Cross hairs are an important part of my star hopping technique. I align the cross hairs with the vertical and horizontal axes of the scope. Since the finder focuser is at an angle, these axes are not intuitive. The aligned cross hairs allow me to match the horizontal and vertical star fields in Sky Safari. I need only one star in each axis for precise pointing..

 

- If I were doing it from scratch:  a well corrected eyepiece that's affordable that's has a large field stop but it needs to be 25 mm or less so there's something to glue to. 

 

20 mm Explore Scientific 68 degree..

 

- 0.004" hard brass. Thin is not good, it's not visible under dark skies.

 

Jon


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#12 Sarkikos

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Posted 16 August 2019 - 06:41 AM

The brightness of illuminated reticle eyepieces is easily corrected.  Brush over the light in the illuminator with dark red or brown paint.  I use car touch-up paint.  If it's still too bright, apply another coat of paint.  Repeat until the illumination is at the level of brightness you desire.  I like illuminated reticle eyepieces at dark sites.  

 

Mike



#13 Jon Isaacs

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Posted 16 August 2019 - 08:10 AM

The brightness of illuminated reticle eyepieces is easily corrected.  Brush over the light in the illuminator with dark red or brown paint.  I use car touch-up paint.  If it's still too bright, apply another coat of paint.  Repeat until the illumination is at the level of brightness you desire.  I like illuminated reticle eyepieces at dark sites.  

 

Mike

 

I see no need for an illuminated reticule.  It's just one more thing to get in the way, to fail. The 0.004" cross hairs are easily seen even under the darkest skies. Why use light when dark works just fine?

 

However, I think the biggest disadvantage to illuminated reticules for finder eyepieces is that the eyepiece has to be designed for it, that severely limits ones choices and as far as I can see, eliminates the possibly of using a good quality, well corrected wide field eyepiece as a finder eyepiece.

 

With a decent wide field eyepiece, the finder can double as a mini-richest field scope and provide some stunning views of it's own.  

 

Jon



#14 andycknight

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Posted 16 August 2019 - 09:43 AM

Hi,

 

Many years ago I made a crosshair eyepiece out of an old broken "cheap and nasty" pair of binocular eyepieces.

 

The eyepieces themselves were nothing special (~45 degree Kellners), but to my surprise the doublet element was a fully corrected plano-convex achromatic doublet. (i.e. in a good Kellner, it's normally overcorrected to compensate for the singlet's false colour)

 

I therefore threw the singlet lenses and made a symmetrical Plossl out of the 2 doublets. (with curved surfaces facing one another, positioned so they nearly touch with a spacer made out of a few wraps of black card) It was a major improvement over the original Kellner design and performs very well indeed. The focal length is about 18mm.

 

The crosshairs were made with some very thin enamelled copper wire from a toy motor. This was blackened with a permanent marker, since otherwise it gave weird reflections I did not like. The wire was stretched slightly (between 2 pairs of pliers) to make it straight and then carefully positioned and superglued across the field stop.

 

Since the 2 achromats normally make a slightly different focal length, it will be necessary to make another spacer (or file down the retaining ring slightly) to get the field stop back into sharp focus.

 

gallery_135796_6581_84961.jpg

 

I simply used sellotape lol.gif to make the 1.25" push fit barrel the correct size.

 

gallery_135796_6581_66998.jpg

 

I do have an illuminated crosshair eyepiece - but the image is not as sharp and the illuminated reticule is a magnet for 'in-focus' dust. Also the contrast is poor due to the uncoated reticule and 'shiny black surfaces' inside. The good thing about real crosshairs is that they cause no image degradation and also allow you hide annoyingly bright stars anywhere in the field of view.

 

PS :- Jon is spot on regarding the use of slightly thicker cross hairs. They can be seen much easier against the sky background. Also if you are guiding the trick is to carefully de-focus until the star is very slightly larger than the crosshair, it is then very easy to spot if the star is even a fraction off dead centre.

 

Regards

 

Andy.


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#15 Tom K

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Posted 16 August 2019 - 09:46 PM

About 30 years ago I made one out of a three year old's hair coated with glow in the dark paint that I used to manually guide a 2120 LX5 with a film camera piggybacked on top. It would last about 30 minutes!


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