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Using Televue eyepieces in Denkmeier II binoviewer

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#1 OivindM

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Posted 09 September 2023 - 01:49 AM

I wanted to get higher magnification than my Denkmeier 21mm eyepieces provides with the Denkmeier II binoviewer on my 80mm refractor, so I purchased a pair of Televue Delite 11 mm eyepieces. I was very surprised to see that the barrel diameter of the Televues are slightly narrower than the Denkmeiers, so the Televues actually do not fit snugly into the binoviewer, and thus gives two images that does not merge. Obviously this is a setup that I cannot use (I tried to tape the notches on the Televues, but this does not help, it is the main part of the barrel that are too narrow for the binoviewer).

 

Have anyone used eyepieces other than Denkmeiers in a Denkmeier II bionviewer? Do the Denkmeier eyepieces have wider barrels than all other eyepiece brands?

 

All help would be greatly appreciated.

 

Øivind



#2 ngc7319_20

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Posted 09 September 2023 - 02:14 AM

I use TeleVue in my Denk II all the time.  They are OK.  If the Denk compression eyepiece holders are trying to grip in the undercut area, you can lift up the eyepiece a few mm, so it grips outside the undercut.  Sometimes I put rubber O-rings on the barrels to raise up the eyepieces a little bit.

 

Do you have a caliper, micrometer, etc., to accurately measure the eyepiece barrels?  It would be interesting to know what numbers you get.



#3 OivindM

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Posted 09 September 2023 - 02:40 AM

I have tried to lift the Televues up a bit, but the holders will not tighten enough to grip the barrels, the barrel diameter is simply to narrow (the undercut is not he problem). Which type of Televues are you using? Unfortunately, I do not have any device to measure the diameters of the barrels.



#4 donniesoprano

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Posted 09 September 2023 - 06:10 AM

Typically shorter focal length eyepieces are harder to merge due to tolerances like this.  I think many people have issues as they approach 10mm.  I think you’d be better off using a barlow in front of the BV with the 21mm eyepieces to achieve the magnification you seek.

 

The binoviewer eyepiece holders are not 100% precision instruments and can have some play just like focuser holders…and as you’ve found there’s tolerances +/- in the eyepiece barrel as well.

 

ds


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#5 OivindM

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Posted 09 September 2023 - 10:34 AM

I did consider using a barlow or powermate in front of the binoviewer, but I m not sure if this would work (or give higher magnification than I already have) since I am using the OCS and power switch already (the OCS and the power switch combined gives me a maximum of about 3 times the magnification of my 21mm eyepieces alone).



#6 donniesoprano

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Posted 09 September 2023 - 01:33 PM

If you use a Powermate or other telecentric barlow, the magnification will be the advertised amount, or close enough to not matter too much, generally (except certain models, the TV 5x comes to kind).  Non telecentric barlows will have an increased magnification factor and may create unusable situations with binoviewers.  There’s a page on Televue’s site that discusses telecentric barlows and magnification.  There are several threads here discussing telecentrics with binoviewers.

 

I use a 1.6x ocs on my bino with 32mm plossls to reach focus on my refractors.  I use the SVbony 2x telecentric in addition to that setup and the 32mm eyepieces have almost the same scale and fov as the 17mm plossls I have….essentially 2x.

 

Perhaps look for some longer focal length eyepieces that will take the 3x more comfortably…and avoid the barlow/powermate route, since you have a powerswitch…

 

ds


Edited by donniesoprano, 09 September 2023 - 01:35 PM.


#7 ngc7319_20

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Posted 09 September 2023 - 02:41 PM

...Which type of Televues are you using? 

I use many types of TeleVue eyepieces in Denk II...  Plossl, Nagler Types "1", 2, 5, 6, Panoptics, Delos.   None had the problem you describe.  But I have not tried Delite.

 

Can you put tape on the entire Delite 1.25" barrel?  Or just a narrow piece along the entire length on one side -- like a "stripe" down the 1.25" barrel.  Does that help?  

 

Sometimes if there are merge problems, it can help to rotate the eyepieces in the holders.  Rotate one eyepiece until the images come closest to merging.  Then try rotating the other eyepiece.



#8 OivindM

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Posted 14 September 2023 - 10:19 AM

I use many types of TeleVue eyepieces in Denk II...  Plossl, Nagler Types "1", 2, 5, 6, Panoptics, Delos.   None had the problem you describe.  But I have not tried Delite.

 

Can you put tape on the entire Delite 1.25" barrel?  Or just a narrow piece along the entire length on one side -- like a "stripe" down the 1.25" barrel.  Does that help?  

 

Sometimes if there are merge problems, it can help to rotate the eyepieces in the holders.  Rotate one eyepiece until the images come closest to merging.  Then try rotating the other eyepiece.

I tried both suggestions, but none of them fixed the problem. A narrow piece of tape prevents the eyepiece from going into the holder, so the eyepiece is too narrow by a very small margin. Thanks anyway!



#9 ngc7319_20

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Posted 16 September 2023 - 01:43 PM

I had a look at my Denk II.  There is a simple mod you can do which doubles the tightening range.  It you unthread the black eyepiece locking ring, below that is a black "C" shaped collet which tightens around the eyepiece barrel.  One side of the collet ring is strongly beveled, and normally that side goes down into the binoviewer.  The other side of the collet ring is at nearly right angles.  If you remove the collet ring, flip it over, and put it back in -- it will go much tighter.  Maybe see if that fixes your issue with the Delites being loose.


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#10 OivindM

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Posted 18 September 2023 - 11:20 AM

I had a look at my Denk II.  There is a simple mod you can do which doubles the tightening range.  It you unthread the black eyepiece locking ring, below that is a black "C" shaped collet which tightens around the eyepiece barrel.  One side of the collet ring is strongly beveled, and normally that side goes down into the binoviewer.  The other side of the collet ring is at nearly right angles.  If you remove the collet ring, flip it over, and put it back in -- it will go much tighter.  Maybe see if that fixes your issue with the Delites being loose.

Thanks. I have already tried this and it does not help. Unfortunately.



#11 Deep13

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Posted 04 October 2023 - 10:55 AM

Wow. I use TV Ploessls in my Denk 2s. I've never had that problem. Of course, the Ploessls are an old design (mine do have undercuts) and, being labeled Japanese, are made in a different factory than Delites.



#12 noisejammer

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Posted 12 October 2023 - 11:24 AM

I had the same problem with my Denk II binoviewers and Televue eyepieces.

 

I eventually resorted to the Baader Clicklock system (which works well.) Initially, I thought about modifying my Denks (I discussed it with Denis) but got lazy and bought a set of Baader MkV's instead.


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#13 cahanc

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Posted 15 October 2023 - 06:49 PM

I had the same problem with my Denk II binoviewers and Televue eyepieces.

 

I eventually resorted to the Baader Clicklock system (which works well.) Initially, I thought about modifying my Denks (I discussed it with Denis) but got lazy and bought a set of Baader MkV's instead.

How do you like the MarkV's?  Any issues?



#14 noisejammer

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Posted 16 October 2023 - 09:01 AM

How do you like the MarkV's?  Any issues?

 

TL;DR - In short, I should have gone this route first.

 

The Mk V is first class optically, optically short, very high contrast. I can use any eyepieces, irrespective of whether they have undercuts or not.

 

At low power, you can ignore the GPC and choose either the Zeiss spec prism or the BBHS mirror. This offers the widest true field possible in a 1.25" binoviewer. I use a 35mm Masuyama pair and achieve a bit more than 1.5° true field at 31x with my TOA150. My APM 115/805 offers 2.2° true field at 23x with some vignetting.

 

Above ~50x, I use a GPC and above 100x I use a Tak 1.6x extender or A-P Barcon. Both work fine at up to 300x (230x) which is where I am exit pupil limited.

 

Unless your available back focus is critical, I suggest the T2 BBHS diagonal as a first choice rather than the Zeiss spec prism. The Zeiss spec prism does however offer slightly better contrast.
 


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