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Stray light

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#1 Nerd1

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Posted 08 February 2024 - 12:32 AM

Does anyone else get stray light when using your binoviewers? I get light bouncing around in my optical path. If so how do you fix it? What should I check. I am using a pair of Denkmeier 2s with power switch. It happens with all three sets of eyepieces that I use.



#2 Eddgie

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Posted 08 February 2024 - 09:13 AM

Does anyone else get stray light when using your binoviewers? I get light bouncing around in my optical path. If so how do you fix it? What should I check. I am using a pair of Denkmeier 2s with power switch. It happens with all three sets of eyepieces that I use.

What kind of telescope? If you are getting internal reflections, a likely culprit is that the binoviewer is not in axial alignment to the telescope optical axis. If the focuser is tilted, the the light rays will not enter perfectly parallel to the optical axis of the binoviewer. 

 

If it is a dob, remove the eyepieces, and with the binoviewer in the focuser, and the focuser fully racked out, see fi the secondary is centered in view. If not, but the scope is in collimation without the binoviewer, then the focuser may need to be collimated. Sadly, not all Dob focusers can be collimated so that becomes a more difficult situation because you may have to resort to shimming the focuser (and this assumes that the secondary mirror is properly centered in the optical tube).  You can also try collimating with the binoviewer in the focuser. 

 

If it is a refractor, I would suspect the same thing but here, you would need to use a laser in the binoviewer to make sure that the spot hits the exact center of the lens. 

 

I have dealt with off axis glare twice, and both times it was an alignment issue. If the BV is not pretty closely aliened and centered on the optical axis, then the light entering the prisms at an angle can cause problems.

 

Don't know if this is your problem, but this is where I recommend you start. 


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#3 Nerd1

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Posted 08 February 2024 - 01:03 PM

What kind of telescope? If you are getting internal reflections, a likely culprit is that the binoviewer is not in axial alignment to the telescope optical axis. If the focuser is tilted, the the light rays will not enter perfectly parallel to the optical axis of the binoviewer.

If it is a dob, remove the eyepieces, and with the binoviewer in the focuser, and the focuser fully racked out, see fi the secondary is centered in view. If not, but the scope is in collimation without the binoviewer, then the focuser may need to be collimated. Sadly, not all Dob focusers can be collimated so that becomes a more difficult situation because you may have to resort to shimming the focuser (and this assumes that the secondary mirror is properly centered in the optical tube). You can also try collimating with the binoviewer in the focuser.

If it is a refractor, I would suspect the same thing but here, you would need to use a laser in the binoviewer to make sure that the spot hits the exact center of the lens.

I have dealt with off axis glare twice, and both times it was an alignment issue. If the BV is not pretty closely aliened and centered on the optical axis, then the light entering the prisms at an angle can cause problems.

Don't know if this is your problem, but this is where I recommend you start.

Thanks Eddie, I think you hit the nail on the head. My Refractor focuser has some sag in it when the Binoviewers are in the diagonal. Because when I use a single eye piece piece my target is not in the same place. Looks like I need to tune it for the he weight of the Binoviewers. The scope is TS Optics Photo Line 125mm SD Doublet.

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#4 betacygni

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Posted 08 February 2024 - 01:12 PM

If this only happens near bright stars or objects just outside the field of view this is quite normal, internal reflections within the binoviewer. Some are better or worse in this regard.

Edited by betacygni, 08 February 2024 - 01:12 PM.


#5 Nerd1

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Posted 08 February 2024 - 01:46 PM

If this only happens near bright stars or objects just outside the field of view this is quite normal, internal reflections within the binoviewer. Some are better or worse in this regard.

It happens on the moon and Jupiter specifically.

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#6 betacygni

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Posted 08 February 2024 - 01:49 PM

It happens on the moon and Jupiter specifically.

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That sounds normal to me then, assuming they are just outside the field of view. All my binoviewers do that to some degree on anything bright.

#7 Nerd1

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Posted 08 February 2024 - 02:17 PM

That sounds normal to me then, assuming they are just outside the field of view. All my binoviewers do that to some degree on anything bright.

Good to know, I think my focuser on my Refractor still needs a little tweaking. Thanks.

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#8 Eddgie

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Posted 08 February 2024 - 04:15 PM

If this only happens near bright stars or objects just outside the field of view this is quite normal, internal reflections within the binoviewer. Some are better or worse in this regard.

 I don't know if it is supposed to be "normal." It has only happened to me twice, and both times it was caused by a tilted focuser, and in both cases, I corrected the problem by collimating the focuser. 


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#9 Nerd1

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Posted 08 February 2024 - 04:19 PM

Thanks for the replies, I think I've solved the problem, my focuser needed some adjustments. But I won't be able to test until the clouds go away. Thanks for the replies, I had the day off so I spent it tuning and cleaning my equipment.

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#10 betacygni

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Posted 08 February 2024 - 07:10 PM

I don't know if it is supposed to be "normal." It has only happened to me twice, and both times it was caused by a tilted focuser, and in both cases, I corrected the problem by collimating the focuser.

Interesting, I’ve owned 5 different models of binoviewers, all to some extent showed some flaring when bright objects are just outside the FOV, in all my scopes. Some are definitely worse than others though, unless we are possibly talking about different things.

#11 Nerd1

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Posted 14 February 2024 - 03:39 AM

I figured out what the problem was. There was a small metal screw for the focuser, with a very shiny end just barely sticking up from behind a baffle in my OTA. Coated it thoroughly with flat black paint,  no more flashing lights in my Binoviewer. 


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#12 oakzaa

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Posted 30 March 2024 - 09:12 PM

That sounds normal to me then, assuming they are just outside the field of view. All my binoviewers do that to some degree on anything bright.

Is it normal if the reflections only happen on the left side of the binoviewers? I only ever see star reflections on the left eyepiece of my binoviewer, have swapped the eyepieces around as well and it only ever appears on the left eyepiece.



#13 betacygni

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Posted 30 March 2024 - 11:32 PM

Is it normal if the reflections only happen on the left side of the binoviewers? I only ever see star reflections on the left eyepiece of my binoviewer, have swapped the eyepieces around as well and it only ever appears on the left eyepiece.

Can’t say I’ve ever noticed exactly if reflections happen on one or both sides, since I’m obviously observing with both eyes open. The light does travel a different path to each eye, so I’d imagine it’s a possibility to only effect one side. I’ll try to pay more attention next time I have my scopes out.
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