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67mm Fl conversion lens for Televue 55mm Plossl

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#1 john hraba

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Posted 09 June 2020 - 02:50 PM

During a phone conversation with Televue yesterday I asked about the soon to be introduced 55mm to 67mm conversion lens for their 55mm Plossl.  I was refered to Al Nagler who shared several pieces of information I had not heard.  Al said that the lenses had just come in and was eager to make sure that I understood that adding the lens to the Plossl would require about 1" more outfocus than the Plossl without the add-on lens, either using the focuser or by adding an extension tube.  I asked if the new lens would improve the off axis performance, specifically the field curvature, of the eyepiece.  Al responded that the performance would improve but that he was unable to quantify by how much.

 

Following the discussion I asked when or if I could order the new lens.  I was told the cost of the lens is $95 plus shipping if ordered from Televue and that I could place an order then.  I bit my lip and ordered one.  I will be glad to share my results with the lens once I have had a chance to try it and compare it to to my Russell 50mm.  Considering the weather here in this part of Alabama at this time of year I am not sure when that might be.


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#2 PEterW

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Posted 09 June 2020 - 03:11 PM

... let’s see who gets the new lens (and clear skies) first. Will be interesting to see what the view looks like with 2.48x speed up!

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#3 Neptune

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Posted 09 June 2020 - 04:20 PM

So this added lens screws into the bottom or up into the existing 55mm Plossl?  It converts the 55mm to a 67mm BUT with a reduced apparent field of view to around 42 degrees?   The field stop is what it is at 46mm  diameter.  right???


Edited by Neptune, 09 June 2020 - 04:29 PM.


#4 Jeff Morgan

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Posted 09 June 2020 - 04:59 PM

That sounds like an automatic purchase to me!

 

Picked up the phone hoping they were working late tonight, but apparently not. I"ll order mine in the morning.



#5 gatorengineer

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Posted 09 June 2020 - 05:52 PM

Looks a little two big for an MN74 10.4 mag and a 16.8mm exit.  Would likely waste a little light.

 

Since this is most likely a reducer flattener it will likely screw into anything 2" wonder how it would do with a Pan grenade?  41 pan... 


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#6 Gavster

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Posted 09 June 2020 - 11:30 PM

Looks a little two big for an MN74 10.4 mag and a 16.8mm exit.  Would likely waste a little light.

 

Since this is most likely a reducer flattener it will likely screw into anything 2" wonder how it would do with a Pan grenade?  41 pan... 

it only works on the 55mm plossl, as confirmed by David Nagler. My understanding is that to install it you need to unscrew the top of the 55mm (the eyeguard bit) and attach the lens there, rather than attaching it to the bottom of the barrel like a reducer.

 

I am intrigued by the indication that the adapter will improve the edge correction. Currently the outer    part of the 50 degree fov of the 55mm plossl is not shown due to the 40 degree fov of the nv monocular cutting it off. So the worst corrected bit of the fov is not shown when using the 55mm plossl. The adapter effectively squeezes this outer part into the nv fov (67mm eyepiece with a 40 degree fov) so showing the worse corrected bit of the tov - the adapter would need to improve the edge correction quite a bit imo to show an overall better corrected fov. Will be very interesting to see the results for $95.


Edited by Gavster, 09 June 2020 - 11:41 PM.


#7 Mike Lockwood

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Posted 10 June 2020 - 10:15 AM

Looks a little two big for an MN74 10.4 mag and a 16.8mm exit.  Would likely waste a little light.

 

Since this is most likely a reducer flattener it will likely screw into anything 2" wonder how it would do with a Pan grenade?  41 pan... 

No light will be wasted, a NV objective can handle a larger exit pupil than that.

 

The TV lens screws into the top of the eyepiece, not the bottom, and is made specifically for the 55mm Plossl.  I hope to have one of them and some decent weather soon to compare.



#8 Dale Eason

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Posted 10 June 2020 - 10:36 AM

I have trouble with my 10 F3  feather touch and SIPs having enough back focus for the TV55 as it is without the new lens.  The feather touch focuser is adjustable but I have it at the in focus needed for one of my eyepieces as well.  I had to add a 3/4 inch spacer around the TV55 to keep it out far enough.



#9 Mike Lockwood

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Posted 10 June 2020 - 11:00 AM

That's normal, Dale.  I have the same spacer.

 

A simple barrel extender may be the solution if more out-focus travel is needed.  Seems like Al might have had one of those on the 55mm when we used the prototype lens at WSP......



#10 Jeff Morgan

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Posted 10 June 2020 - 12:16 PM

All confirmed - just ordered mine. This is so new Al was not even sure what the price was (he had to check) and the documentation is not yet complete.

 

Expected to ship next week.

 

Edit - Al did mention "better correction" but did not get into details. FOV is reduced to 40 degrees matching that of the device. It seems reduction is the primary selling point.


Edited by Jeff Morgan, 10 June 2020 - 12:18 PM.

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#11 john hraba

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Posted 10 June 2020 - 02:11 PM

For anyone interested in seeing Al Nagler demo the installation of the new lens on a Televue 55mm Plossl at the 2020 Winter Star Party you can view the video at:

https://astronomytec.../tag/al-nagler/


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#12 Jeff Morgan

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Posted 12 June 2020 - 02:58 PM

Got my shipping notice from Tele Vue today, three day Priority Mail.

 

Given our typical June weather, excellent chance to test it out this dark moon window.


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#13 Gavster

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Posted 15 June 2020 - 04:42 AM

Mine has just arrived today in the post in the UK, pretty impressive given it was only sent on Friday!

It’s very easy to install as per these photos, hopefully I’ll get a chance to test it out later today. Looking forward to getting my refractors working at sub f2 and my c11 at about f2.5.

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Edited by Gavster, 15 June 2020 - 04:44 AM.

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#14 Neptune

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Posted 15 June 2020 - 06:53 AM

For my situation, being strictly visual with a C-11, I just don't see how this offers any real benefit.   67mm with 40 deg.  vs.   55mm and 50 deg.



#15 chemisted

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Posted 15 June 2020 - 07:17 AM

For my situation, being strictly visual with a C-11, I just don't see how this offers any real benefit.   67mm with 40 deg.  vs.   55mm and 50 deg.

This is designed to be used with an image intensifier that can utilize a larger exit pupil than the human eye.  If you do not have one of these devices than you are probably right in your assessment.  See post #11 above for a video of Al Nagler explaining this.


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#16 Neptune

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Posted 15 June 2020 - 08:43 AM

This is designed to be used with an image intensifier that can utilize a larger exit pupil than the human eye.  If you do not have one of these devices than you are probably right in your assessment.  See post #11 above for a video of Al Nagler explaining this.

Thanks for clarifying.


Edited by Neptune, 15 June 2020 - 08:43 AM.


#17 ManuelJ

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Posted 15 June 2020 - 08:52 AM

Any europe dealer?


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#18 PEterW

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Posted 15 June 2020 - 11:43 AM

But direct at the moment, there are a few EU suppliers who might do a they refine their NV offerings.
Peter

#19 Jeff Morgan

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Posted 15 June 2020 - 04:15 PM

For my situation, being strictly visual with a C-11, I just don't see how this offers any real benefit.   67mm with 40 deg.  vs.   55mm and 50 deg.

 

The 40 degree AFOV of the NV eyepiece is the limiting factor in all cases. Going afocal with a Plossl (or an Ethos!) doesn't change that.



#20 Gavster

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Posted 15 June 2020 - 06:25 PM

I’ve just managed to have a first go.

Wow! I’m impressed. I used my f5.3 Tak fsq85 under London sqm18 skies.

Not only is the effective speed increased to a very fast f2 giving brighter views than the f2.5 using the 55mm plossl the edge correction was much better.

Here’s a phone image of the North America nebulae, first with the 67mm adapted plossl, then with the 55mm plossl on its own. The difference on the edge stars is obvious. I think I’ve just found the perfect afocal eyepiece for me! The 67mm adapted plossl even plays well with my 0.75x gso rc reducer giving a super fast effective speed of f1.5 ish with a large fov of around 7 degrees. This combo is shown in the third image below.

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Edited by Gavster, 15 June 2020 - 06:50 PM.

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#21 chemisted

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Posted 15 June 2020 - 06:44 PM

Great job!!!  Having Al Nagler becoming a NV participant has really paid off.


Edited by chemisted, 15 June 2020 - 06:45 PM.

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#22 Jeff Morgan

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Posted 16 June 2020 - 04:27 AM

I'll second what Gavster says. This one is a winner.

 

If you are using a 55 Plossl, you want this. Only real quibble I might have is eye placement. Only noticed it because I had the batwing eyecup off for a few photos and forgot to put it back on. With the batwing in place, no worries. Brighter images and edge of field aberrations significantly reduced.

 

All manner of difficulties tonight: Sheriff visit (friendly, all good), passing high cloud bands, a pack of curious javelina, and shooting the first dozen or so objects with the focusing mask over the objective ... sigh. Elephant Trunk still looked pretty good despite that!

 

Still sorting through the images, but I will share this one: Sagittarius Star Cloud. TMB 130SS f/7 refractor, Mod 3C, iPhone X, ISO 100, 1/3 second, 45 frame average, no filters. SQM 21.4. Perhaps a tiny bit overexposed, but note the edge of field stars.

 

Oh - the Sheriff visit. There is a fire ban (dry season here) and someone reported a violation nearby. They were curious about the equipment, so we showed them a few targets. M13 with the 12.5 mm Docter: "That's nice" (unimpressed and trying to be nice). I popped the NV eyepiece into the focuser and "that's nice" turned into "Wow! Joe, come look at this!' 

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#23 simoneb

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Posted 16 June 2020 - 07:51 AM

Thank you Gavin and Jeff for your pictures! I am waiting for my 67mm lens today, and since we have had great weather in NYC these days I expect to try it out tonight.

The only thing I do not understand is how the increased exit pupil does not "collide" with the 15mm clear aperture of the TNVC/TV adapter. For example with f/5.3 and 0.75x reducer, the exit pupil is 16.85mm, so this should not be able to clear the adapter opening without loss of light. I am planning to use the 67mm lens with my Borg f/3.6, which would yield an exit pupil of 18.6mm, way over the 15mm opening of the adapter. To this purpose I also bought an additional TNVC/TV adapter and I was planning to opening up the aperture (with a mill, others in the forum have done that), but at this point I am starting to questioning if this is really necessary, I mean if Tele Vue is not concerned about this, why should I? I am not an optical engineer, there must be some reasons for which this works anyway, but at the same time I do not understand how it can work. I must be missing something, hopefully someone can clear this up.

Simone 



#24 simoneb

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Posted 16 June 2020 - 08:56 AM

UPDATE to my previous post. I just spoke with David at Tele Vue. First of all I must say that every time I speak with someone at Tele Vue, I am always impressed at how nice they are, it seems like if they are genuinely happy when one calls, very nice people.

As for the TNVC/TV adapter with the 15 mm opening, they are obviously aware about this and David confirmed that the new 67 mm lens product is going to require an updated TNVC/TV adapter having a larger opening (I think I understood up to 22 mm). The new adapter will be available in the next manufacturing run maybe next month. In the meanwhile it is perfectly fine to mill out the existing adapter to open up the aperture, but I will not do that, I will keep my adapters with 15 mm opening for the slower systems having exit pupil smaller than 15 mm (which is the majority of the cases anyway), and I am going to purchase one of the new adapters next month for my fastest setup with the 67mm lens.

Simone     


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#25 Kathi

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Posted 16 June 2020 - 09:01 AM

Thanks for all the informations. Sounds great!

I want to order it too.

 

But I can't phone because I am disabled with my voice and my speaking and so I am limited to written communication.
And my family can't speak English enough to phone in English.
Is it possible to order from TeleVue in written words? If not, it is very unfair for people with disabilities like me!

Kathi


Edited by Kathi, 16 June 2020 - 09:02 AM.



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