Jump to content


Photo

Visual color correction np101 vs TEC 140?

  • Please log in to reply
63 replies to this topic

#51 Kent10

Kent10

    Apollo

  • *****
  • Posts: 1267
  • Joined: 08 May 2012

Posted 05 August 2014 - 08:09 PM

Pezdragon, have you made a decision yet regarding your NP101.  Do you think you would keep it for the wider views it produces over the Tec.  I have a Tec 180 and I am considering getting a 4 inch for wider views.  But I may take my binoculars out for a while as Bill suggests to have some fun and see how I like those wide views.  I always have to worry about astigmatism though with the larger exit pupil.

 

Thanks.



#52 Pezdragon

Pezdragon

    Explorer 1

  • *****
  • Posts: 60
  • Joined: 10 Jun 2013
  • Loc: Bay Area, Ca.

Posted 06 August 2014 - 01:02 AM

No, not yet. I would miss the relative ease of the NP-101 on the DM 4 as opposed the TEC on the EM200. One is a 2 tripper and the other a 6 tripper to set up. But I have to say, the wide flat field of the 101 is it's only optical saving grace once I got to compare the two.The TEC's color correction is to my eyes as good as the 101's and in planetary performance the TEC takes it to church.

  Seeing as I would lose about half it's value if I sold it I have to wonder if it's worth it as I would probably never get to replace it, but the suggestion of replacing it with some excellent binoc's intrigues me....thinking Zeiss here....

 Anyway...it's a bit low priority here as I need to find quickly a new home for myself.....rough roads lately...

pez



#53 gnowellsct

gnowellsct

    Fly Me to the Moon

  • *****
  • Posts: 6839
  • Joined: 24 Jun 2009

Posted 06 August 2014 - 11:50 PM

 

 

There was a thread recently about the TEC140 and its colour correction.


I think this is the thread:

Purple haze around Sirius with a TEC? (140)

For what it's worth, I see no purple haze in my NP-101 on any target.

Jon

 


I have a NP127 and I see a purple haze on planets and bright stars. And the color in intra/extra is obvious.

Can't compare both telescopes, but I would bet for a similar color correction.

 

 

 

Danged if I know the why and wherefores of color correction, but since this topic comes up about six times a year, I have read that optimizing for photographic color correction may entail some sacrifice in *visual* color correction.   As a *visual* instrument, I consider the color correction in the NP101 to be a tad inferior to the color correction on my Vixen ED102SS F/6.5.

 

That was surprising to me once upon a time, but these days I am hesitant to draw any conclusions.  First off the f/6.5 is an easier FL to work with, and second off, the NP101 is considered a great scope for astrophotography, but the Vixen ED102SS (out of production for a decade in any case), is ok-to-good but not great, from results I have seen of other astrophotographers.

 

Greg N



#54 gnowellsct

gnowellsct

    Fly Me to the Moon

  • *****
  • Posts: 6839
  • Joined: 24 Jun 2009

Posted 07 August 2014 - 12:02 AM

I am quite skeptical of claims of "false color" in TEC or recent-vintage AP refractors, just as I am of recent claims of false color in the Tele Vue "NP" refractors, which, by all the accounts I have heard over the years, were designed, and widely acknowledged, to be virtually 100% color-free. I have looked through TEC and AP scopes on numerous occasions, and I was always struck by the perfection of the views -- and I have good vision. Maybe it's the folks who see false color who have vision problems, or maybe they are seeing false color caused by eyepieces or atmospheric refraction or their own eyeglasses. Who knows???

If you want to see what a TEC 140 can do photographically, hang out on the Yahoo TEC Group and see the images as they are posted. The high quality of the images is astonishing.

 

Well don't be too harsh.  Color correction IS an obsession, and I must say on this score I was delighted with my FS128 which I sold to a friend, and also delighted with my GT130, my new arrival.  

 

There are, I think, two major sources of continually infused confusion in these debates, which can come from well meaning people who haven't quite been initiated into all the details.

 

1.  God hates color correction.  That is why Jupiter, Mars, Saturn and the moon will show red/blue fringing due to atmospheric refraction, fringing that will show in a Newt or any other apochromatic instrument, and which even shows to the naked eye (on the moon).  This red-blue fringing is often interpreted as a telescope artifact and in a world of I-heard-that can be the source of persistent misunderstandings.

 

2.  Eyepieces have can have their own chromatism--either lateral color or even small amounts of on axis color which a neurotic apo owner after an hour or two might actually detect.

 

To these two main highways (lateral color being the main item to retain from #2) we can add a third, which often comes up with TEC and Sirius--I remember reading it 8 years ago, might even have been Roland chiding someone who was criticizing TEC for having color on Sirius.  

 

It is basically this: if you want to make an apo to withstand the brutality of a visual observation of Sirius for color correction, you are likely going to have to sacrifice some color correction in the photographic ranges for which these scopes are typically optimized.  Sorry I can't explain the details but it makes sense to me because everything in astronomy  involves tradeoffs, and in fact, everything in engineering design of all types rerpresents tradeoffs between performance, weight, cost, and so on.

 

There is little doubt that TEC 140s are among the finest astronomical refractors in the world and compete in a very elite world with such names as Astro-Physics, Televue, Zeiss, Pentax, and so on.

 

Greg N



#55 ManuelJ

ManuelJ

    Viking 1

  • -----
  • Posts: 777
  • Joined: 19 Dec 2005
  • Loc: Madrid, Spain

Posted 07 August 2014 - 01:53 AM

 

 

 

There was a thread recently about the TEC140 and its colour correction.


I think this is the thread:

Purple haze around Sirius with a TEC? (140)

For what it's worth, I see no purple haze in my NP-101 on any target.

Jon

 


I have a NP127 and I see a purple haze on planets and bright stars. And the color in intra/extra is obvious.

Can't compare both telescopes, but I would bet for a similar color correction.

 

 

 

Danged if I know the why and wherefores of color correction, but since this topic comes up about six times a year, I have read that optimizing for photographic color correction may entail some sacrifice in *visual* color correction.   As a *visual* instrument, I consider the color correction in the NP101 to be a tad inferior to the color correction on my Vixen ED102SS F/6.5.

 

That was surprising to me once upon a time, but these days I am hesitant to draw any conclusions.  First off the f/6.5 is an easier FL to work with, and second off, the NP101 is considered a great scope for astrophotography, but the Vixen ED102SS (out of production for a decade in any case), is ok-to-good but not great, from results I have seen of other astrophotographers.

 

Greg N

 

 

Well, the NP101 was designed from the beginnings of time as a visual instrument, not as an astrograph. The IS model was later added as a patch to make it more viable for photography, with a new focuser and bigger back lens opening for less vignetting. But it's design has not changed and it's still a refractor designed for visual.

 

You cannot expect to have an F/5 Petzval with perfect color correction, 97% of Polystrehl. As with the TEC 140, the numbers and observations are there, you can deny it or learn to live with it. It's not a claim, there are evidences.

 

Just enjoy your scopes :)



#56 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 20486
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 10 August 2014 - 11:27 AM

I am quite skeptical of claims of "false color" in TEC or recent-vintage AP refractors, just as I am of recent claims of false color in the Tele Vue "NP" refractors, which, by all the accounts I have heard over the years, were designed, and widely acknowledged, to be virtually 100% color-free. I have looked through TEC and AP scopes on numerous occasions, and I was always struck by the perfection of the views -- and I have good vision. Maybe it's the folks who see false color who have vision problems, or maybe they are seeing false color caused by eyepieces or atmospheric refraction or their own eyeglasses. Who knows???

If you want to see what a TEC 140 can do photographically, hang out on the Yahoo TEC Group and see the images as they are posted. The high quality of the images is astonishing.

It's like they say, "Ask the man that owns one."  :grin:

 

It's not difficult nor does it require  either excellent or poor vision to elicit a little false color from a TEC 140.  All that is needed is a bright white or blue white target and high magnification.  I've never tried with an NP101, but I suspect I could do it if I tried.  I've seen a greater amount of false color in NP127s though than in TEC 140s.  And before an apologist jumps in with the NP127 reformulation quip, these were both recent 127s.

 

None of this is enough secondary spectrum to right home about.  I'd put the TEC's false color at around 1/250th the amount one sees in a 95mm f/15.7 achromat and 1/7500th the amount you'd see in a 6" f/5.9 achromat.  But it's there under circumstances where its hardest to hide.

 

Still, for less than $6k at 5.5", the TEC remains the greatest do-everything-well bargain in refractors IMO.  It's cheap and lightweight for its class an aperture.  It's well made.  It holds its value well (unlike Televue or Takahashi which tend to depreciate quite a lot for current offerings; you can pick up $11k TOA-150s in the $8k range frequently).  It's readily available used or new (waits are short for a new one as bespoke items go). 

 

- Jim



#57 Markab

Markab

    Mariner 2

  • *****
  • Posts: 251
  • Joined: 15 Dec 2012
  • Loc: Kansas City USA

Posted 10 August 2014 - 12:23 PM

I owned a recent AP130GT and, yes, there was false color. Not objectionable, mind you, but it was there. My current AP Traveler also shows false color, but as earlier said, it is on bright objects at high magnifications. More false color certainly shows up in my Tak fluorite doublets, but even those have better color correction than many Chinese triplet so called "apos".



#58 gnowellsct

gnowellsct

    Fly Me to the Moon

  • *****
  • Posts: 6839
  • Joined: 24 Jun 2009

Posted 10 August 2014 - 10:07 PM

I owned a recent AP130GT and, yes, there was false color. Not objectionable, mind you, but it was there. My current AP Traveler also shows false color, but as earlier said, it is on bright objects at high magnifications. More false color certainly shows up in my Tak fluorite doublets, but even those have better color correction than many Chinese triplet so called "apos".

 

Yeah what's up with that?  (The Chines triplet apos that aren't apo)



#59 Cotts

Cotts

    Just Wondering

  • *****
  • Posts: 4895
  • Joined: 10 Oct 2005
  • Loc: Toronto, Ontario

Posted 10 August 2014 - 11:30 PM

On seeing false colour on Sirius at high power in a TEC or TAK or TV or AP or what-have-you:  Don't look at Sirius!!   The only reason to look at Sirius is to see 'The Pup' and a bit of purple isn't going to hide the Pup compared to the overwhelming scintillation of Sirius itself.  

 

Even worse, don't look at Venus at higher powers, either.  99/100 times you look at Venus after dusk or before dawn she will be less than 30-35 degrees above the horizon and the red-blue of atmospheric dispersion will either hide any actual false colour that may exist or make you think you're seeing false colour, well, falsely.  If you look at Venus in the daytime to gain altitude the bright blue of the sky will mask any purple/violet false colour so you're no further ahead. Venus is the worst possible choice for CA testing for these reasons.

 

Don't look at most other first magnitude stars, for that matter - there's nothing special to see, except for Castor which is a nice double star but, at about 1.3 magnitude, will not show any purple at any power in any  140-155mm TAK/TEC/ZEISS/AP/APM Apochromat.  Same for Antares....  Visually, every star fainter than 1.5 magnitude will be colour-free in these good scopes.

 

The first two places to look for false colour in high-end APO's that actually means something  would be the Moon and Jupiter.  I doubt any of the above APO's show any purple/violet in crater shadows or around Jupiter.  My TEC 140 certainly doesn't...

 

Dave



#60 Pezdragon

Pezdragon

    Explorer 1

  • *****
  • Posts: 60
  • Joined: 10 Jun 2013
  • Loc: Bay Area, Ca.

Posted 11 August 2014 - 02:04 AM

Thank you Mr.Cotterell, I agree completely with that.



#61 Scott99

Scott99

    Mercury-Atlas

  • *****
  • Posts: 2924
  • Joined: 10 May 2007
  • Loc: New England

Posted 11 August 2014 - 12:02 PM

I owned a recent AP130GT and, yes, there was false color. Not objectionable, mind you, but it was there. My current AP Traveler also shows false color, but as earlier said, it is on bright objects at high magnifications. More false color certainly shows up in my Tak fluorite doublets, but even those have better color correction than many Chinese triplet so called "apos".

 

check your eyepieces, they are producing the false color, there isn't any with the AP scopes you mention.  You can obtain the color correction curves from AP if you're curious.   All widefield ep's produce color error, especially at shorter f-ratios like f/5 or f/6.

 

I think the last AP refractors to have any false color at all in the visual range were the EDT's in the mid 90's, and it was miniscule.  As I recall these triplets used FPL-51 or 52 for the ED element.  Once they upgraded to FPL-53 triplets that was it for false color.  actually the EDT's may have been color free as well, the f/8-f/9 focal ratio took care of it.



#62 Markab

Markab

    Mariner 2

  • *****
  • Posts: 251
  • Joined: 15 Dec 2012
  • Loc: Kansas City USA

Posted 11 August 2014 - 09:24 PM

 

I owned a recent AP130GT and, yes, there was false color. Not objectionable, mind you, but it was there. My current AP Traveler also shows false color, but as earlier said, it is on bright objects at high magnifications. More false color certainly shows up in my Tak fluorite doublets, but even those have better color correction than many Chinese triplet so called "apos".

 

check your eyepieces, they are producing the false color, there isn't any with the AP scopes you mention.  You can obtain the color correction curves from AP if you're curious.   All widefield ep's produce color error, especially at shorter f-ratios like f/5 or f/6.

 

I think the last AP refractors to have any false color at all in the visual range were the EDT's in the mid 90's, and it was miniscule.  As I recall these triplets used FPL-51 or 52 for the ED element.  Once they upgraded to FPL-53 triplets that was it for false color.  actually the EDT's may have been color free as well, the f/8-f/9 focal ratio took care of it.

 

I use the Tak LE eyepieces, which are some of the best eyepieces available for color correction, unlike many of the wide field eyepieces available. They have definitely served me well over the last decade or so that I've been using them.  FWIW, they do not show any color in reflectors or my SCT.



#63 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 44338
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 11 August 2014 - 09:43 PM

 

I am quite skeptical of claims of "false color" in TEC or recent-vintage AP refractors, just as I am of recent claims of false color in the Tele Vue "NP" refractors, which, by all the accounts I have heard over the years, were designed, and widely acknowledged, to be virtually 100% color-free. I have looked through TEC and AP scopes on numerous occasions, and I was always struck by the perfection of the views -- and I have good vision. Maybe it's the folks who see false color who have vision problems, or maybe they are seeing false color caused by eyepieces or atmospheric refraction or their own eyeglasses. Who knows???

If you want to see what a TEC 140 can do photographically, hang out on the Yahoo TEC Group and see the images as they are posted. The high quality of the images is astonishing.


I have no intention to convince anyone, if there are people that think that a F/5 petztal, or a F/7 triplet has the same correction that a F/12 fluorite triplet, I'm fine if they are happy believing that :) .

You have to know what to look and where, in normal conditions you will not be paying attention to that. Enjoy your instruments while you can in the meantime.

 

 

The color correction depends not only the focal ratio but also on the aperture.. 

 

 

I can't think of a good reason to keep the NP-101 honestly, unless you have a thing for 4-5 degree ultra low power FOVs.


As good as a 18x wide field view like that might be using a 31T5 in a NP101, for those low powers and wide fields I find an excellent quality pair of binoculars a much more engaging experience.

 

 

I have never looked through a pair of binoculars that offered the overall quality of view of the NP-101 with the 31mm Nagler.  Binoculars have too many compromises..    I am wondering how much eyepiece time you have with the NP-101 out under dark skies???  It's not the scope for everyone but it is an awesome scope to compliment large aperture scopes out where the skies are dark and clear.. 

 

Jon



#64 Scott99

Scott99

    Mercury-Atlas

  • *****
  • Posts: 2924
  • Joined: 10 May 2007
  • Loc: New England

Posted 12 August 2014 - 12:24 PM

fyi here are the published specs for color correction on some of these scopes:

 

TEC140:

less than .02% from 436nm to 1000nm

 

AP Traveler:

Less than 0.01% focus variation from 405nm to 706nm (r to h wavelengths)

 

AP130 GT:

Less than + - 0.006% focus variation from 706nm to 430nm (r to g wavelengths)








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics