Eyepiece Reticule

[Mr Spock]

I have a Celestron 9x50 RACI. It's badly let down by the eyepiece which is pants. The FOV doesn't even match an ortho!

So I've tried a few options. First was to move the eyepiece from an old 6x30 finder. That worked, sort of. Because it didn't fit the hole in the Celestron diagonal I glued it on - it came off last night.

I've now fitted a 25mm Celestron Plössl. Nice 50° FOV and very sharp. It gives x7.2 and a 7° field, albeit at a 7mm exit pupil. The diagonal isn't very deep but has three retaining screws, so I'm sure it won't fall out. For now I've glued two bits of wire in to make cross hairs. Despite being very fine wires, they look huge in the eyepiece! 

So I thought about getting a purpose made reticule disc and fitting that to the eyepiece. Has anyone done that? I'm guessing the size I need is 27mm? That seems to be the inside diameter of the eyepiece nosepiece, or as close as I can get with a ruler.

[michael.h.f.wilkinson]

I turned an Antares 25 mm 70 deg EP into an illuminated reticle EP.

I got a reticle from the Surplus Shed, but I am not sure they have a suitable one available.

 

[johninderby]

Look for a TAL screw in reticle. Fits any eyepiece of about 25mm with a standard 1.25” filter thread. Now discontinued but they do show up occasionally. 

Here’s my old and well used one.

 

Edited January 22, 2021 by johninderby

[Dean Hale]

Would this do? https://www.ebay.co.uk/itm/1-25-eyepiece-cross-wire-cross-hair-reticle-attachment/383869031789?hash=item596060956d:g:1NUAAOSwDxdf4Lea

[johninderby]

5 minutes ago, Dean Hale said:

Would this do? https://www.ebay.co.uk/itm/1-25-eyepiece-cross-wire-cross-hair-reticle-attachment/383869031789?hash=item596060956d:g:1NUAAOSwDxdf4Lea

The problem with that one is the crosshair might not focus in an eyepiece. Look at the way the TAL one puts the crosshair high inside the eyepiece barrel. 

Edited January 22, 2021 by johninderby

[Dean Hale]

1 minute ago, johninderby said:

The problem with that one is the crosshair might not focus in an eyepiece. Look at the way the TAL one puts the crosshair high inside the eyepiece barrel. 

I didn't know that. thanks for the tip John.

[John]

I'm just having a look at my Celestron illuminated reticule RACI. I use this with my 12 inch dobsonian. Now I look at it the AFoV of the eyepiece is narrow - about 40 degrees I reckon, comparing it with a plossl.

On mine the eyepiece optics are held in a section that screws up and down in a body which contains the element with the etched cross hairs on and which the illuminator illuminates though a side port. 

Is this like yours Michael ?

[michael.h.f.wilkinson]

In a Plössl eyepiece (and many others) you can attach the reticle to the field stop (as was easy in the Antares Erfle), then it should be in focus

[Mr Spock]

11 minutes ago, John said:

Is this like yours Michael ?

Yes, that's the one. 

 

[Mr Spock]

The 25mm Plössl I have has a field stop inside the nosepiece. That's what I attached the wires to (they are in focus).  I'm wanting a disc to replace the wires - it will fit up against the field stop.

[michael.h.f.wilkinson]

20 minutes ago, Mr Spock said:

The 25mm Plössl I have has a field stop inside the nosepiece. That's what I attached the wires to (they are in focus).  I'm wanting a disc to replace the wires - it will fit up against the field stop.

In the past I have used some hairs from my head (dwindling natural resource in my case too), as these were much thinner than any wires I could find. It wasn't easy to stick them on, however.

[John]

Having fiddled around with mine all afternoon I've decided to live with the 40 degree AfoV. Assuming that the 9x magnification is correct that is a true field of 4.4 degrees which is usable combined with the reticules displayed by my Rigel Quikfinder. 

The problem I found is getting other eyepiece designs field stops anywhere near the focal plane of the finder objective. I can see why the manufacturer needed the odd low profile eyepiece attachment arrangement now. 

 

[Mr Spock]

With the 25mm Plössl it just comes to focus with the objective screwed all the way in, It's tight though. I did consider chopping some of the nosepiece off but can't be sure I'd get it flat.

[Mr Spock]

Just set the scope up and adjusted the finder. I have to say the view through finder with the 25mm Plössl is really crisp and contrasty. Star are pinpoints and the moon looks fabulous.

I might just leave it as is. The cross hairs are big, but, I can centre a star at x257 so I'm quite satisfied with that.