Jump to content


Photo

Televue 7.4 Plossl VS Edmund RKE 8mm

  • Please log in to reply
9 replies to this topic

#1 Charlie Hein

Charlie Hein

    Voyager 1

  • *****
  • Administrators
  • Posts: 12326
  • Joined: 02 Nov 2003
  • Loc: 26.06.08N, +80.23.08W

Posted 22 June 2013 - 06:21 AM

Televue 7.4 Plossl VS Edmund RKE 8mm

By Larry Beach

#2 Rachal

Rachal

    Vostok 1

  • *****
  • Posts: 135
  • Joined: 07 Apr 2009
  • Loc: Alexandria LA

Posted 22 June 2013 - 09:40 AM

Interesting article, Larry. Thanks. :)

#3 H-D Moose

H-D Moose

    Lift Off

  • *****
  • Posts: 18
  • Joined: 17 Jan 2010
  • Loc: Southeast Virginia

Posted 22 June 2013 - 05:48 PM

There are those people who do love the RKE eyepieces but opinions vary whether the 'new' Edmund Optics RKEs are comparable to the 'old' Edmund Scientific versions. I don't have any of the Edmund Optics branded ones so I can't offer my own opinion.

Thank you for taking the time to do the comparison and showing that the price tag doesn't necessarily equate to image brightness & performance. When it comes to planetary viewing, RKEs with their three glass surfaces do yield very nice views.

I would like to make note of two things:

(1) The $59 price you quoted jumped to $85 about 2-2.5 years ago for a new Edmund Optics RKE:

http://www.edmundopt...e-precision-...

(2) RKE actually stands for Rank Kaspereit Erfle as was discovered once the original copyright papers were posted online by a fellow CN'er.

Cheers,

Troy

#4 H-D Moose

H-D Moose

    Lift Off

  • *****
  • Posts: 18
  • Joined: 17 Jan 2010
  • Loc: Southeast Virginia

Posted 22 June 2013 - 05:51 PM

Duh ... I meant 'Trademark'. RKE trademark!

#5 Bill Steen

Bill Steen

    Vostok 1

  • -----
  • Posts: 179
  • Joined: 15 Dec 2012
  • Loc: Broken Arrow, Oklahoma

Posted 22 June 2013 - 08:05 PM

Excellent article! Just curious, what was the telescope used?

Thanks,

Bill Steen

#6 H-D Moose

H-D Moose

    Lift Off

  • *****
  • Posts: 18
  • Joined: 17 Jan 2010
  • Loc: Southeast Virginia

Posted 22 June 2013 - 11:05 PM

4th Paragraph:

The telescope I was using was my Celestar 8 Deluxe, built in Approx the year 1998 ...

#7 David Knisely

David Knisely

    Hubble

  • *****
  • Posts: 15630
  • Joined: 19 Apr 2004
  • Loc: southeastern Nebraska

Posted 22 June 2013 - 11:48 PM

4th Paragraph:

The telescope I was using was my Celestar 8 Deluxe, built in Approx the year 1998 ...


Almost any halfway decent eyepiece (which the RKE is) will perform pretty well at the f/10 of an SCT (especially when you are apparently ignoring the star images in the outer parts of the field). It is the performance of an eyepiece off-axis (and at shorter f/ratios) that is the real telling point as to the quality and effectiveness of a particular design. That off-axis performance should *never* be ignored in any reasonable comparative review. In a really good eyepiece, the outer field performance should be at least somewhat comparable to the on-axis performance. Try doing this comparison at f/ratios below f/7 (and look at the *entire* field of view), and the problems with a 3-element eyepiece will begin to really show themselves. There, the Tele Vue may regain the edge, especially, although even a top of the line Plossl will have some outer field problems at f/5 and below. Clear skies to you.

#8 WRAK

WRAK

    Apollo

  • -----
  • Posts: 1171
  • Joined: 18 Feb 2012
  • Loc: Vienna, Austria, Europe

Posted 24 June 2013 - 03:13 PM

"I briefly looked at Izar (Epsilon Bootes) and saw a nice clean separation of it's Golden Primary and Saphire Blue secondary at 2.8" apart, It has always been my favorite double. I did not use my 127mm Mak because the secondary Star lies in the defraction ring."

With an 127mm Mak assuming CO 0.2 the first diffraction ring has a distance of ~1.5" to the center of the primary and certainly not 2.8".
Wilfried

#9 orion61

orion61

    Aurora

  • *****
  • Posts: 4750
  • Joined: 20 Oct 2007
  • Loc: Birthplace James T Kirk

Posted 24 June 2013 - 09:45 PM

There are those people who do love the RKE eyepieces but opinions vary whether the 'new' Edmund Optics RKEs are comparable to the 'old' Edmund Scientific versions. I don't have any of the Edmund Optics branded ones so I can't offer my own opinion.

Thank you for taking the time to do the comparison and showing that the price tag doesn't necessarily equate to image brightness & performance. When it comes to planetary viewing, RKEs with their three glass surfaces do yield very nice views.

I would like to make note of two things:

(1) The $59 price you quoted jumped to $85 about 2-2.5 years ago for a new Edmund Optics RKE:

http://www.edmundopt...e-precision-...

(2) RKE actually stands for Rank Kaspereit Erfle as was discovered once the original copyright papers were posted online by a fellow CN'er.

Cheers,

Troy

Thanks for that correction, The main thing I wanted to express wasn't any kind of negative about the Televue,
I love their products.
To answer a question the main difference I have seen was in the field stop, They were not as refined and I saw a few nicks and bumped. I had anewer one with an Astroscan.
I had nearly forgotten about it thanks for jogging my memory!
The optical quality did not jump out as being inferior.
Other comments made from other members that favored the Televue may mean there could have been some quality differences in both.
Another couple comments were the price jump. It seems I saw the approx $60.00 from the Edmund web site the last time I looked, I have my set so I am guilty of not visiting that often.
Also reguarding the Izar issue with it getting in the way of my defraction ring, It wasn't the best of viewing and I believe it is separating now and not getting closer. I do remember an issue I took a mental note of. 1/2 arc second isn't a lot of distance.... but within the ability of a "good C8"
I know there are better lenses out there, I was just a bit pleased and surprised they were as close as they were.
I wouldn't mind doing this with a number of these lenses newer and older.
One thing for darn sure neither are going out of my collection soon.
Thank you all for the comments and taking the time reading
the piece. have a great Summer!
Orion

#10 Darren Drake

Darren Drake

    Mercury-Atlas

  • *****
  • Posts: 2807
  • Joined: 09 Oct 2002
  • Loc: Chicagoland

Posted 28 June 2013 - 12:46 PM

"Another stunner was the fact I could see 5 of Saturn Moons! I could see the dimmest with direct vision Enceladus shining dimly at -7.04 This normally would not be an issue but I was viewing from my light polluted back yard. Titan was glowing Orangish at -4.94 from the cold Methane in its Atmosphere."

Not sure where these magnitudes came from. They are nowhere near correct...






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics