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Illuminated eyepiece quality

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13 replies to this topic

#1 aalmanni

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Posted 03 December 2020 - 05:46 AM

Hi,

I am looking to add an illuminated eyepiece to help me align the mount.
The question is does the quality really matter? Or any generic one would suffice?
The second question is the cross hair one or the astrometric one?
Thanks

#2 luxo II

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Posted 03 December 2020 - 06:14 AM

To align the mount all you need is a cross hair one. Mine isn’t even illuminated - a bright star defocussed is fine.
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#3 Sarkikos

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Posted 03 December 2020 - 06:57 AM

At dark sites I appreciate the illuminated crosshairs.  If you're star hopping to faint or obscure objects which can't be seen in the finder, a defocused star won't cut it.  You need to see the background stars to position the location of the object behind the crosshairs.

 

I've owned several illuminated eyepieces, and none have been top optical performers.  The usual aberration is some astigmatism toward edge of field.  But as long as they get the job done, they're OK. 

 

My favorite is the Orion 20mm 70 degree illuminated eyepiece.  No, not perfect.  If anyone has found a better one, please let me know.

 

Mike


Edited by Sarkikos, 03 December 2020 - 07:02 AM.


#4 Jon Isaacs

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Posted 03 December 2020 - 10:20 AM

To align the mount all you need is a cross hair one. Mine isn’t even illuminated - a bright star defocussed is fine.

:waytogo:

 

For aligning a GOTO or PUSHTO mount, the stars are bright and defocusing the alignment star to nearly the full field provides an accurate guide. You can use any eyepiece, this is a trick from the days when astrophotographers guided manually.

 

For star hopping with a finder scope, I prefer non illuminated cross hairs.  The cross hairs in most eyepieces are too narrow to be seen under dark skies so I make my own from 0.004" hard brass.  No issues with illuminators that are too bright (all of them) and I can use better corrected eyepieces. Currently I'm using a 24 mm TV Wide field. It's not not the sharpest but it's much sharper than the 20 mm 70 degree Orion...

 

Jon



#5 Sarkikos

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Posted 03 December 2020 - 12:53 PM

If the illuminated eyepiece is too bright, you can always daub over the light with dark red or brown paint or fingernail polish.  Or you can turn it off.  I like having the option.

 

Mike


Edited by Sarkikos, 03 December 2020 - 12:53 PM.


#6 aalmanni

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Posted 03 December 2020 - 01:12 PM

To align the mount all you need is a cross hair one. Mine isn’t even illuminated - a bright star defocussed is fine.

So defocusing the star would allow approximate centering in the eyepiece? in this case I should use the highest power eyepiece, in my case, I have the 10mm plossl

 

Thanks

 

Abdul



#7 aalmanni

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Posted 03 December 2020 - 01:15 PM

At dark sites I appreciate the illuminated crosshairs.  If you're star hopping to faint or obscure objects which can't be seen in the finder, a defocused star won't cut it.  You need to see the background stars to position the location of the object behind the crosshairs.

 

I've owned several illuminated eyepieces, and none have been top optical performers.  The usual aberration is some astigmatism toward edge of field.  But as long as they get the job done, they're OK. 

 

My favorite is the Orion 20mm 70 degree illuminated eyepiece.  No, not perfect.  If anyone has found a better one, please let me know.

 

Mike

Ok, so the eyepiece doesn't have to be high magnification? the 20mm will give 50x compared to the 10mm and 100x

 

Thanks

 

Abdul



#8 Sarkikos

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Posted 03 December 2020 - 01:25 PM

I use the Orion 20mm in a 70mm f/3.9 finder.  (The clear aperture is actually 65mm, so it's really an f/4.3, but that's another matter.)  The focal length is 279mm, yielding 14x magnification with the Orion 20mm.

 

Mike


Edited by Sarkikos, 03 December 2020 - 01:26 PM.


#9 Tamiji Homma

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Posted 03 December 2020 - 02:10 PM

I have a few cross hair eyepieces.  Unless you need super precise star alignment, I don't think you need high quality ones.

 

Here is a few photos:

 

large.jpg

 

From left to right, you see in eyepiece:

 

large.jpg

 

large.jpg

 

large.jpg

 

Close up on center:

large.jpg

 

original.jpg

 

Tammy


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#10 Sarkikos

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Posted 03 December 2020 - 02:36 PM

I use my 50mm or 70mm finders also as rich field telescopes.  I like to have a wider field of view as a contrast to what I see in the main telescope.

 

Mike



#11 Starman1

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Posted 03 December 2020 - 02:37 PM

So defocusing the star would allow approximate centering in the eyepiece? in this case I should use the highest power eyepiece, in my case, I have the 10mm plossl

 

Thanks

 

Abdul

The bright star backlights the cross hairs, making them appear dark on the white star.  it doesn't matter what focal length eyepiece you use.

Where the crosshairs cross is interpolated from seeing the lines--you adjust the star until the secondary shadow is centered on the crosshairs.

I have not been to a site too dark to allow this to happen, and I've been to some pretty dark sites.

 

Unfortunately, NO illuminated crosshair is dim enough to see a lot of stars in the field.  ALL illuminators need to be dimmer than their minimum settings.

As was mentioned, a drop of dark red fingernail polish on the LED will do it.  But note that the batteries in illuminators are VERY short-lived.

If you accidentally leave it on, they're dead in only a couple hours.


Edited by Starman1, 03 December 2020 - 02:44 PM.


#12 Sarkikos

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Posted 03 December 2020 - 02:46 PM

If you daub the light in the illuminated eyepiece with enough paint so it is no brighter then a moderately bright star, I see no problem with it.  How is this going to affect your dark adaptation any more than a moderately bright star?  There is no such thing as illuminated crosshairs that are too bright if you dim the light enough with a coat of paint.  I like the convenience and ease of centering the object location behind the crosshairs.  

 

Mike


Edited by Sarkikos, 03 December 2020 - 02:47 PM.


#13 Starman1

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Posted 03 December 2020 - 02:59 PM

If you daub the light in the illuminated eyepiece with enough paint so it is no brighter then a moderately bright star, I see no problem with it.  How is this going to affect your dark adaptation any more than a moderately bright star?  There is no such thing as illuminated crosshairs that are too bright if you dim the light enough with a coat of paint.  I like the convenience and ease of centering the object location behind the crosshairs.  

 

Mike

You're right.  But they are all too bright as they come from the box.



#14 Jon Isaacs

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Posted 03 December 2020 - 07:41 PM

You're right.  But they are all too bright as they come from the box.

 

Don:

 

When I needed to replace the cross hairs in an eyepiece, you told me most cross hairs were too fine. It took your advice and have had very good performance under dark skies with 0.004" brass wire.  

 

I've had a few illuminated eyepieces, as you say, too bright out of the box, short battery life and they're fragile. Another issue is they require a lot of inward focus because the illuminator much be at the focal plane which puts the focal plane well behind the barrel-body. And then there's the poor correction when used in a finder.

 

The ideal finder eyepiece would be a 16 mm Type 5 with cross hairs, too rich for my blood but doable.

 

Jon


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