3 replies to this topic

[ols]

So, I happen to have a single 2.5x Powermate (this is 1 1/4” diameter) and I wondered what overall magnification would be if I added it between my telescope and binoviewer. Here is what i came up with, measuring drift timing across the eyepiece image of a tower on a mountain a few miles away (sidereal tracking on using my Rainbow mount.)

 

The set-up is a Tak100DZ with Maxbright binoviewers and Baader T2 diagonal. I attached the Powermate directly to the binoviewer T2 coupling nut using with the Powermate T-ring adapter. If I added a GPC, it was screwed into the diagonal on the binoviewer side. Between the diagonal and the Powermate, I used a Baader 1 1/4” cliklock with an extra 15mm spacer below it so that the long barrel of the powermate would not bottom out in the diagonal. Extra spacers needed to reach focus with the Powermate were placed between the scope and the the diagonal (i forgot to take a picture but hopefully this explains what went where.) Anyway, comparisons are to a baseline set-up with no Powermate and no GPC. Same eyepieces used throughout.

 

(Please note I am rounding magnifications to the closest .05 as “close enough” given my assumption for some measurement error)

 

Powermate 2.5x and no GPC:  Magnification 2.35x

Powermate 2.5x and 1.25GPC: Magnification 2.6x

Powermate 2.5x and 1.7GPC: Magnification 2.85x

 

FWIW, here are magnification comparisons with no Powermate and the GPC screwed into a 1 1/4” nosepiece which was then screwed into the binoviewer T2 coupling nut

No Powermate and 1.25 GPC: Magnification 1.2X

No Powermate and 1.7 GPC: Magnification 1.45X

No Powermate and 2.6 GPC: Magnification 2.7X

 

 

Overall, I guess I was surprised that there was not more of a magnification “multiplier effect” from having the Powermate in-line together after the GPC. Maybe the magnifications are added together instead of multiplied? 
 

I definitely could not explain how magnification lenses work exactly, but I do wonder if i did something wrong? Or perhaps there is a more correct order for where to place both a Powermate and a GPC if you are going to try to use them together?  For now my take away is that adding a Powermate doesnt add another significantly different magnification option compared to just using the 2.6GPC by itself for maximum magnification. Unless I did it wrong, lol. 
 

thanks for any thoughts!

Edited by ols, 03 February 2025 - 02:11 PM.

[balcon3]

So, I happen to have a single 2.5x Powermate (this is 1 1/4” diameter) and I wondered what overall magnification would be if I added it between my telescope and binoviewer. Here is what i came up with, measuring drift timing across the eyepiece image of a tower on a mountain a few miles away (sidereal tracking on using my Rainbow mount.)

 

The set-up is a Tak100DZ with Maxbright binoviewers and Baader T2 diagonal. I attached the Powermate directly to the binoviewer T2 coupling nut using with the Powermate T-ring adapter. If I added a GPC, it was screwed into the diagonal on the binoviewer side. Between the diagonal and the Powermate, I used a Baader 1 1/4” cliklock with an extra 15mm spacer below it so that the long barrel of the powermate would not bottom out in the diagonal. Extra spacers needed to reach focus with the Powermate were placed between the scope and the the diagonal (i forgot to take a picture but hopefully this explains what went where.) Anyway, comparisons are to a baseline set-up with no Powermate and no GPC. Same eyepieces used throughout.

 

(Please note I am rounding magnifications to the closest .05 as “close enough” given my assumption for some measurement error)

 

Powermate 2.5x and no GPC:  Magnification 2.35x

Powermate 2.5x and 1.25GPC: Magnification 2.6x

Powermate 2.5x and 1.7GPC: Magnification 2.85x

 

FWIW, here are magnification comparisons with no Powermate and the GPC screwed into a 1 1/4” nosepiece which was then screwed into the binoviewer T2 coupling nut

No Powermate and 1.25 GPC: Magnification 1.2X

No Powermate and 1.7 GPC: Magnification 1.45X

No Powermate and 2.6 GPC: Magnification 2.7X

 

 

Overall, I guess I was surprised that there was not more of a magnification “multiplier effect” from having the Powermate in-line together after the GPC. Maybe the magnifications are added together instead of multiplied? 
 

I definitely could not explain how magnification lenses work exactly, but I do wonder if i did something wrong? Or perhaps there is a more correct order for where to place both a Powermate and a GPC if you are going to try to use them together?  For now my take away is that adding a Powermate doesnt add another significantly different magnification option compared to just using the 2.6GPC by itself for maximum magnification. Unless I did it wrong, lol. 
 

thanks for any thoughts!

The 2.5x Powermate is different from the other Televue Barlows. The magnification it gives actually goes down the farther it is from the field stop of the eyepiece. See the following graph:

https://www.televue....?id=53&Tab=_app

I think that is why you are getting less magnification than you expected. In addition, I think it is recommended to place the GPC as close as possible to the Binoviewers in order to get best correction; placing it before the Barlow may affect magnification and it will likely correct the prism aberrations less efficiently.

[EboO]

balcon3 is right, I did the same with a PM2.5 and a MBII and magnification is near to 2.1-2.2 due to lightpath in bino (110mm).
And you must use GP in the nose of the bino to reduce as possible aberrations.

Edited by EboO, 05 February 2025 - 01:28 AM.

[ols]

Thanks.
Here are some follow-up measurements based on your suggestions. The revised numbers I got seem to make more sense to me than my original attempt.

I re-ordered the configuration and it took a few days for the constant low clouds here to clear out and be able to re-do some testing.

 

The new configuration is as follows: GPC (if used) screwed into 1 1/4” nosepiece which is screwed directly into T2 coupling nut on the binoviewer, so the GPC is now as close as possible to the binoviewer. When the 2.5x Powermate is in the set-up, it comes next - the nosepiece on the binoviewer drops into the regular eyepiece holder of the Powermate. The Powermate barrel drops into a 1 1/4” clicklock screwed onto the T2 diagonal. (I also add a 15mm spacer between the clicklock and the diagonal so the Powermate barrel doesnt hit the diagonal stop.) Any extra spacer needed to reach focus (depends on which GPC is used) goes between the diagonal and the telescope.

 

The first thing I decided to do was a sanity check on the magnification of the 2.5x Powermate used the usual way if monoviewing. I put my single Powermate between one of the eyepieces and the binoviewer and compared the drift time with and without the Powermate. I compared for just 2 configurations - first, with no GPC in the nosepiece and then with the 1.25x GPC in the nosepiece. Magnification based on drift time calculated to be 2.45x and 2.50x respectively when the Powermate was added below the eyepiece (no doubt imperfect measuring on my part, but seemed to confirm my measurement technique is in the ballpark overall. phew.)

 

I then repeated the measurements from my first attempt (plus added a couple using the 2.6x GPC as well) and got the following calculated magnifications, compared to a baseline drift time measured with no GPC and no Powermate:

 

No PM, 1.25x GPC: magnification  1.2x

No PM, 1.7x GPC: magnification  1.4x

No PM, 2.6x GPC: magnification  2.7x

 

2.5x PM. No GPC: magnification  2.3x

2.5x PM, 1.25x GPC: magnification  2.65x

2.5x PM, 1.7x GPC: magnification  3.2x

2.5x PM. 2.6x GPC: magnification  6.3x

 

For what its worth, I had originally expected the combined magnification of stacking Powermate and GPC would be equal to multiplying the two individual stand alone magnifications together. The numbers i measured this time seem consistently closer to this than my first attempt (not exact, but hopefully within rounding/measurement error.)

 

My overall takeaway though is still that I dont really see a useful extra magnification option from adding a single Powermate compared to just using a GPC of your choice. It was still kind of fun to do the experiment though.

Edited by ols, 05 February 2025 - 10:16 PM.