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Merging issues at high power

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#1 Mike Selz

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Posted 28 July 2021 - 09:16 AM

I have a LUNT/APM 45 degree ED 100mm series bino I got a few months ago and absolutely adore them, they merge easily in my ES 82 degree 14mm , 9mm 68 degree svbony, and 24mm ES 68’s.

BUT…I wanted to test its power out and have a pair or Orion STRATUS 3.5mm (158 power).

suprisingly, in my south Florida summer humid skies both EPs show super clear images but I can’t seem to totally Merge both EPs, which is frustrating because I’m sure the view would be amazing . Why is it harder to merge at high power? I have that metal collimation tool that came with the binos just haven’t used it as yet. Hmmm, any ideas?



#2 drt3d

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Posted 28 July 2021 - 09:26 AM

It is harder to merge at high powers because even the smallest misalignment is greatly magnified.

 

I would first try to swap right and left eyepieces, if you have not done that already. For the same pair of eyepieces, I noticed that a specific setup R and L works better than the other way around. If this works for you, mark the eyepieces so you can always use it the same way (a good idea for any pair of eyepieces). Not sure why swapping sides would make a difference in theory, but it does in practice.

 

Have you tightened the eyepieces or are you put them in the tubes loose? If you have tightened them, try loosening them. Try playing with them, moving them around to see if merging improves. Don't be afraid to play with them. I doubt that the merging is related to the collimation of the binoculars. It is more related to the eyepieces and how they fit in place.

 

George


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#3 astrokeith

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Posted 28 July 2021 - 09:49 AM

158 power is very (extremely) high for collimation in binoculars! Often a manufacturer will give a maximum power, typically x100 for that class.

 

You would need to collimate - easy enough once you've done it! Just protect the objective lenses well when you use the tool.



#4 TOMDEY

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Posted 28 July 2021 - 11:11 AM

This topic comes up on about one-month centers. The object-space angular co-pointing error is magnified at the eye end by that factor. Bill Cook points out that 2 arc-min as seen at the eyepieces is a good conservative goal. At 158x that is 0.76 arc-sec equivalent object-space collimation integrity... which is really too much to ask without active alignment provision. The lateral R/L differential equivalent at the 3.5mm eyepiece focal plane is a miniscule 2.0 microns (0.00008 inch) which is also asking too much (of both the bino and the eyepiece pairs).

 

So, the only realistic solution is active control of the merging vector. One Binoviewer provides that field alignment provision --- the Denk Binotron. One Binoscope provides that on-the-fly co-alignment provision --- the JMI Reverse Binocular. Without that luxury, the only remining approach is to screw around and hope for the best.   Tom

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#5 CMacD

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Posted 28 July 2021 - 02:23 PM

I have the APM 100 45 and have similar issues with the Delos 4.5. I tend to keep one eyepiece loose and push it gently around until the images can be merged. I hesitate to attempt to collimate the scope myself and lose the dry gas in the instrument. Any other suggestions would be welcome.


Edited by CMacD, 28 July 2021 - 02:43 PM.


#6 oldmanrick

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Posted 28 July 2021 - 06:19 PM

I almost always have these issues at higher magnifications with both of my BTs.  My Lunt 100 45 degree ED is especially sensitive to eyepieces with the "safety cuts" in the outside of the tubes.  The collets of the focusers do not play well with these.  Some brands of eyepieces are better than others.  The ES 82 degree 4.7 and 6.7 pairs that I have seem to be the worst.  Others such as the Docter 12.5 and Pentax XL14 pairs are O.K.  I also have trouble with the Televue Delight 7 pair.  The best are the Baader Morpheus pairs, which don't have the cuts, although I do sometimes have to fiddle around with the 4.5 and 6.5 pairs to get them aligned.

 

I've found that loosening one side up enough to turn it in the focuser will usually get the alignment better, but sometimes I have to try turning both sides, and also make several small turns to find the best combo.  Sometimes I can't get the alignment very good with any amount of fiddling.  Fortunately my eyes and brain will merge the images when quite misaligned, but it tends to give me a headache, and when I put another eyepiece pair in the instrument, it takes a bit tor me to get re-adjusted to them.

 

I also have the adjustment tool that the OP mentioned, and have used it to gain some improvement in overall alignment of the Lunt 100.  For me, it was not easy, and I could never get it perfect.  I would not recommend trying it until you have established a consistent misalignment after fiddling with your eyepiece mounting, and a consistent direction of the misalignment.  My objectives were actually "cross-eyed" originally, and still are, but just not so bad following adjustment.

 

As Tom said above, these eyepieces and the mounts and collets are not exactly precision devices so about all that can be hoped for is to get close enough that a bit of "fiddling" will get you acceptably merged images.

 

Best of luck!

 

Rick


Edited by oldmanrick, 28 July 2021 - 06:21 PM.

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#7 Rich V.

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Posted 28 July 2021 - 07:22 PM

 

I also have the adjustment tool that the OP mentioned, and have used it to gain some improvement in overall alignment of the Lunt 100.  For me, it was not easy, and I could never get it perfect.  I would not recommend trying it until you have established a consistent misalignment after fiddling with your eyepiece mounting, and a consistent direction of the misalignment.  My objectives were actually "cross-eyed" originally, and still are, but just not so bad following adjustment.

 

As Tom said above, these eyepieces and the mounts and collets are not exactly precision devices so about all that can be hoped for is to get close enough that a bit of "fiddling" will get you acceptably merged images.

 

 

I think this is an important point that can't be overstated; don't mess with the eccentric objective cells until you're sure that the problem isn't in the eyepieces or the interface of eyepiece barrel and focuser.  Some eyepieces are not perfectly axially aligned; rotate them and switch them L/R first.  You don't want to make the mistake of ruining the bino's true collimation over a bad eyepiece.  You have to see the same alignment problem with multiple eyepiece pairs before you know if it's really in the binos or not.

 

Rich


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