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Equipment Discussions >> Eyepieces

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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
TeleVue Paracorr Type 2 vs. Type 1
      #4028695 - 09/05/10 09:43 PM

Last night I compared my newly arrived TeleVue Paracorr Type 2 with my older TV Paracorr Type 1 on my 24" Starmaster FX f/3.7 Lockwood tracking dob. My scope was carefully collimated, as usual, and I spent 4+ hours observing deep sky objects from open clusters, planets, planetary and bright nebulae, and globular clusters. The seeing was ~1 arc-sec, RH < 50%, temp remaining at 70 deg. F. all night, and the transparency was superb. The eyepieces used were: 21, 13, 8, 6mm Ethos and a Nagler 3.5mm. The elevation of the observing site is 2,700 ft. on Fremont Peak in California, about one hour's drive from where I live in Monterey by the Pacific Ocean.

By dark, I started my observing comparison between the two Paracorr's by using my older Paracorr Type 1 first as my basis. I inserted a 13mm Ethos eyepiece into the Paracorr providing 200X and a 30' fov and pointed the scope to the globular cluster M15 in Pegasus. M15 was slowly slewed all around the fov in the 13mm eyepiece to see the effect on its many fine stars. The view showed what I was used to: coma-free stars only 3/4 out from the fov center. At the fov edge, a small amount of coma still remained. This performance has always been similar for my other Ethos eyepieces. In contrast, the TV Paracorr Type 2 performed much better with regards to reducing coma. In fact, it eliminated it! With all the Ethos eyepieces and 3.5mm Nagler, there was no coma seen at all. Sharp stars right to the edge of the fov in all eyepieces. I am very happy about this. With regards to object detail performance at the eyepiece fov center, I didn't see any difference between the two Paracorr's. Nor did I see any overall fov contrast differences.

There is one issue I did see: my new Paracorr Type 2 shows extraneous light entering into the view if there is any light still remaining outside in the way of twilight or someone's flashlight (white or red). In the Type 2's design, the longer barrel pushed the field lens (the outer lens) down all the way to the end of the focuser barrel exposing the unbaffled lens to incident light and to any extraneous light outside of the Dob. This shows up while looking in the eyepiece as a full diameter (one side to the other) crescent shaped light reflection hugging the edge of the fov opposite from where the light is entering at the Paracorr's field lens. The Type 2's longer barrel now positions the field lens all the way down to the end of the focuser tube in my Starlight focuser. The field lens is now exposed to light coming in at an angle at the Dob's upper assembly. I switched both Paracorr's back and forth to see this effect and see where the field lens was positioned while standing in front of my Dob's upper assembly and secondary mirror. My older Type 1's barrel and field lens is positioned and hidden (still baffled) farther up inside the focuser barrel. It's baffled against extraneous light. I could easily see the Type 2's field lens having no baffle protection from the focuser tube in its operating position. The extraneous light seen in my eyepiece's fov (in the shape of a 3-day old crescent Moon hugging one side) was only apparent if there was still enough light remaining outside: like someone's flashlight at a distance pointing at my scope or the evening twilight 1-2 hours after sunset. At the time, we were observing Venus one hour after sunset and I was seeing the crescent shaped reflection covering 30% of the view in my Ethos 13mm. I switched back to my Paracorr Type 1 and this reflection wasn't seen. This front-end Paracorr light leak is a big difference between the two Paracorr's. I would appreciate hearing from anyone else who observes this issue with their new Type 2 Paracorr's. Thanks.


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gb_astro
sage


Reged: 01/01/08

Loc: Sydney, Australia
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4028730 - 09/05/10 10:08 PM

And possibly dew formation?

gb.


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a__l
professor emeritus


Reged: 11/24/07

Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: gb_astro]
      #4028925 - 09/06/10 12:40 AM

To cut pipes truss. If not suffices length to replace focuser with long travel.
Variant to add light baffle. But I would prefer the first variant, including because of dew.


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Cyclop_si
professor emeritus
*****

Reged: 03/13/08

Loc: Slovenia
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: a__l]
      #4028997 - 09/06/10 02:21 AM

As alternetive to longer focuser drawfube, Paracorr 2 can be probably extended with filter threaded tube extenders (like TeleVue 2" skirt or Badder Hyperion 14 mm or 28 mm extenders).

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thrawn
scholastic sledgehammer


Reged: 03/14/10

Loc: Los Angeles, CA
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Cyclop_si]
      #4029019 - 09/06/10 03:08 AM

Hey that's an intersting report about the new model Paracorr.

Are you thinking about adding baffling somewhere to help that issue?

And a n00b question here: when you say the seeing was 1", does that mean that you could not have black space split a 0.8" double, say? That's pretty poor seeing I guess.


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JimMo
I'd Rather Do It Myself


Reged: 01/08/07

Loc: Under the SE Michigan lightdom...
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4029228 - 09/06/10 09:30 AM Attachment (112 downloads)

Interesting, I hadn't noticed that. I just put the PC2 in the focuser to check and mine IS baffled a little by the 2" draw tube. Even so, I could see it dewing up, especially here in Michigan. A small 12v. blow dryer might have to become part of my kit.

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turtle86
Pooh-Bah Everywhere Else
*****

Reged: 10/09/06

Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: JimMo]
      #4029398 - 09/06/10 11:10 AM

I've always used a 2" Kendrick dew heater strap on my Paracorr, but that was to keep 2" eyepieces warm without having to mess with the strap each time I changed eyepieces. Sounds like the strap will now also help keep dew off my new Type 2 Paracorr.

The threaded barrel extender and blow dryer ideas sound like good ones for those who don't use a Kendrick-type system.


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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: gb_astro]
      #4029401 - 09/06/10 11:12 AM

The RH was below 50%. Our scopes, vehicles, and all optics were bone dry.

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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: thrawn]
      #4029417 - 09/06/10 11:22 AM

I used 1 arc-sec seeing as a general description of magnitude 6 star sizes at 300X early in the evening while comparing the two Paracorrs. I didn't pay any attention to double stars. My 24" mirror was not fully equilibrated yet. The time was one hour after sunset (7:30pm) until 10pm. I'm not sure I want to add anything to the focuser or Paracorr front end since this might protrude into the primary mirror's light path. This stray light issue was only seen before total darkness after twilight. During normal observing at our site (Bortle 4 darkness scale), I couldn't see it the reflection anymore.

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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: JimMo]
      #4029429 - 09/06/10 11:27 AM

Yes, but as your photo shows, you can see how exposed the field lens of the Type 2 is to the front end of your scope. It is plainly visible from your angle of view and extraneous light will hit this field lens traveling up through the Paracorr barrel and seen in the eyepiece. I believe that's what happened to me.

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turtle86
Pooh-Bah Everywhere Else
*****

Reged: 10/09/06

Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4029466 - 09/06/10 11:48 AM

I'm thinking that a barrel extender might address both the extraneous light issue you raise as well as the potential dew issue raised by another poster in this thread.

Not sure if a barrel extender would work for me as I have an Astrocrumb filter slide...


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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4029500 - 09/06/10 12:03 PM

Attached are three photos I took of my Paracorr in the focuser of my 24" Starmaster f/3.7. Focuser is in approximate focus position. The Type 2 has a larger diameter field lens than the Type 1. Its in-focus position and its larger field lens position almost at the end of the focuser allows it to grab more extraneous light than in the Type 1 model. The Starlight focuser's built-in tube baffling is of no use in this arrangement. I might need to resort to my past scope assemble baffle to protect the Type 2's lens exposure.

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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4029510 - 09/06/10 12:07 PM Attachment (241 downloads)

Here are the photos.

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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4029515 - 09/06/10 12:08 PM Attachment (215 downloads)

Photo 2

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Peter Natscher
professor emeritus


Reged: 03/28/06

Loc: Central Coast California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4029522 - 09/06/10 12:09 PM Attachment (178 downloads)

Photo 3

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4030752 - 09/06/10 11:44 PM

Easy to fix the direct light problem in the new Paracorr:
Install a light shield opposite the focuser extending upward from the UTA.
Indeed, on your scope the secondary is so close to the top of the scope a complete light shield (that goes all the way around) would be beneficial for dew protection AND light shielding.
Here is a link to a picture of what I mean:
http://kenmartin.net/astro/xx12%20light%20shield%201.jpg
It definitely helps contrast.
It can be simple to install and remove.


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a__l
professor emeritus


Reged: 11/24/07

Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Peter Natscher]
      #4030788 - 09/07/10 12:13 AM

Very interesting Feather Touch focuser with integrated Paracorr type 2 as standard. Variant to increase the height of a flat base? What offers the manufacturer? Wait a serial dobson with this option ....

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Shneor
scholastic sledgehammer
*****

Reged: 03/01/05

Loc: Northern California
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: a__l]
      #4034731 - 09/08/10 07:31 PM

Hi Pete,
I, too, think a barrel extender is the best solution, especially in the event people inadvertently point lights at your scope. I may have a similar problem with the 9mm ES100° I recently purchased, which has the field lens and field stop butting right up against the filter threads. I did not have a problem with this on first light, Saturday night, but there was only one other observer and Shot Rock was quite dark.
Clears,
Shneor


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Shneor]
      #4035371 - 09/09/10 01:10 AM

A barrel extender would protrude into the light path, causing diffraction.
A simple light shield does the job without causing any extra diffraction and also serving the additional benefit of reduced dewing issues.


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sixela
Postmaster
*****

Reged: 12/23/04

Loc: Boechout, Belgium
Re: TeleVue Paracorr Type 2 vs. Type 1 new [Re: Starman1]
      #4035484 - 09/09/10 02:42 AM

Quote:

A barrel extender would protrude into the light path, causing diffraction.
A simple light shield does the job without causing any extra diffraction and also serving the additional benefit of reduced dewing issues.




The problem is that the dimensions of the light shield you need depend on the baffling (i.e. how exposed the lenses are). In theory, put a lens fully exposed at the end of a barrel and the light shield needed to ensure only object light reaches the lens is of infinite size.

So a barrel extender (and moving the focal plane so that the barrel extender does not intrude) may be a sensible part of a total baffling solution (usually also including a light shield or a well sized UTA, which is also a baffle). It all depends on what illumination you want at the edge of the field and how large a central obstruction you will accept...

Of course, you actually have bafling *behind* the lens to ensure that whatever shouldn't form the image gets caught *in* the Paracorr. There is such baffling and flocking, actually, and it's fairly effective at eliminating anything caused by grazing light reaching the lenses (which then means you can get away with a smaller light shield).


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