Jump to content


Photo

First Impressions of the Lunt 152mm f/8 ED-APO

  • Please log in to reply
24 replies to this topic

#1 Charlie Hein

Charlie Hein

    Voyager 1

  • *****
  • Administrators
  • Posts: 12307
  • Joined: 02 Nov 2003
  • Loc: 26.06.08N, +80.23.08W

Posted 06 May 2014 - 03:27 PM

First Impressions of the Lunt 152mm f/8 ED-APO

By William Paolini

#2 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 19865
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 14 May 2014 - 05:59 PM

Bill, nice report.

Now I see why you have an interest in reports for the the >5" unobstructed class of instrument. :lol:

I'm looking forward to reading about your further adventures with the big ED doublet.

- Jim

#3 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 4374
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 19 May 2014 - 07:48 AM

A nice write up, but I am puzzled by this...

"...the Lunt-152 is designated as an “ED-APO” which is the popularly used nomenclature in the marketplace to indicate semi-apochromatic performance."

How did this come about, and why does it imply "semi-apochromat." ED is clearly Extra-low Dispersion, and APO is the grammatically challenged but widely used abbreviation for apochromat. There's nothing here implying "almost an apo" or anything like that.

It seems more like something the marketing folks came up with - it sounds nice and uses two terms that have come to imply "goodness and desirability" in a refractor.

Just puzzled, Alan

#4 GHarris

GHarris

    Vostok 1

  • -----
  • Posts: 138
  • Joined: 06 Jun 2009

Posted 22 May 2014 - 02:24 PM

A nice write up, but I am puzzled by this...

"...the Lunt-152 is designated as an “ED-APO” which is the popularly used nomenclature in the marketplace to indicate semi-apochromatic performance."

How did this come about, and why does it imply "semi-apochromat." ED is clearly Extra-low Dispersion, and APO is the grammatically challenged but widely used abbreviation for apochromat. There's nothing here implying "almost an apo" or anything like that.

It seems more like something the marketing folks came up with - it sounds nice and uses two terms that have come to imply "goodness and desirability" in a refractor.

Just puzzled, Alan


A 6" ED doublet refractor is something that isn't always available new on the market. Meade sold some over a decade ago, and Tak's fluorite FS152 is well known, but for years there hadn't been anything like these available to buy new.

One reason for that, in my opinion, is that they're an inherent marketing headache. Achromats are sold on their affordability. APO triplets are sold on their as-perfect-as-possible images, with cost considerations thrown right out the window. How do you market something that sits in between them? You almost have to criticise one or both of the more well-known alternatives to make a space for the newcomer. Given the squeeze it's no wonder that a few wooly terms come into play.

For visual-only observers I think these scopes make a lot of sense, if a 6" refractor is what you want. The cost of the higher-end triplets is just a bit too far over the "appallingly expensive" mark for some of us. Or if you want to spend the amount a triplet would come to, there's an opportunity cost involved in spending it all on the OTA. E.g. Have you tried binoviewing yet? The price difference between the ED152 and a 6" APO triplet may comfortably pay for some of the best binoviewer kits you can obtain, and that combo might do more for your subjective enjoyment of the view than a more-perfect level of colour correction on a triplet with a single eyepiece. Other examples can be imagined of course.

There's a debatable, highly subjective argument for/against *any* 6" refractor if you are a visual-only observer who just wants the best view for a certain budget and portability/size class, but the ED152 is a welcome niche in the market for those of us who do want a refractor of this size without giving up too much in either the wallet or image quality (from CA).

Anyhow I'm just glad Markus Ludes did bring these scopes to the market, however they get labelled. Mine (which is labelled as the APM ED152-1200K) has worked really well in the outreach role I bought it for and I have high hopes for its continued use in that role.

I'm glad someone like Bill has had a chance to review this scope - it was sorely in need of a competent observer to give it a try and then sing its praises!

#5 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 4374
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 22 May 2014 - 03:25 PM

I am certainly glad to see such a scope on the market, but I am puzzled by the claim that "ED-APO" is used to indicate "semi-apochromatic" performance.

Clear skies, Alan

#6 BillP

BillP

    Voyager 1

  • *****
  • Posts: 11397
  • Joined: 26 Nov 2006
  • Loc: Vienna, VA

Posted 22 May 2014 - 09:15 PM

I am certainly glad to see such a scope on the market, but I am puzzled by the claim that "ED-APO" is used to indicate "semi-apochromatic" performance.

Clear skies, Alan


That is an echo of Markus Ludes from the forum spaces. They were evidently deliberating on what to call it. In the past, if you recall, scopes that did not meet what was felt to be a full apo (whatever that is since the definition slides), were simply called ED and nothing else. Then there was a time not long ago where some were saying semi-APO to say the same thing. When Tom Back brought out the 80mm Planet Hunter he had the same issue on what to call it. He it was more than an achromat and less than an apo. He pondered semi-apo, but then felt that was overly optimistic and called it an Enhanced Achromat.

Truth is that there is no strict standard for the term APO in the consumer space. Popularly it should be colorless in focus and it is probably called an APO in todays market. Achromats have their standard. Everything in between is name as you go :lol: My own recollections as a consumer are that APO means no color and the older ED meant little under certain circumstances. Given how this scope performs, IMO the space between the old ED only designation and the full APO is about where it is...so ED-APO makes sense to me and follows my interpretation of the market for the past 10-15 years. :shrug: At any rate...what I put in the write up is how Markus characterized it in my readings. I tend to agree.

#7 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 4374
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 23 May 2014 - 10:48 AM

Since the majority of apochromats contain an ED element, it makes little sense to me.

It would be easy enough to simply specify the chromatic focal shift over a specific range of wavelengths, realizing, of course, that this is only part of the story. Although it is the part many folks focus on.

Clear skies, Alan

#8 davidpitre

davidpitre

    Soyuz

  • *****
  • Posts: 3554
  • Joined: 10 May 2005
  • Loc: Central Texas

Posted 23 May 2014 - 08:09 PM

Since the majority of apochromats contain an ED element, it makes little sense to me.

Regardless, the term ED has been an industry standard term for quite some time for semi apos. I think anyone who does even a cursory information search recognizes the current accepted meaning of "ED refractor". It is perhaps not the best term that could be used, but I think the current meaning is clear.

#9 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 4374
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 23 May 2014 - 09:18 PM

David,

The world of achromats and apochromats is already confusing enough without embracing rather meaningless marketing terms. As I said, far better to talk about chromatic focal shift.

A search of ED and APO [sic] turned up references that simply said they were apochromats, so I would say the meaning is far from clear. Examples here and here.

Clear skies, Alan

#10 russell23

russell23

    Skylab

  • *****
  • Posts: 4284
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 24 May 2014 - 07:47 PM

Does it matter? Any ED scope has very little CA visually. Anybody that reads will be able to figure out what they are getting.

But if we want a standard what is wrong with "ED doublet" and "ED triplet"?

Dave

#11 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 4374
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 25 May 2014 - 08:48 AM

Does it matter? Any ED scope has very little CA visually. Anybody that reads will be able to figure out what they are getting.

But if we want a standard what is wrong with "ED doublet" and "ED triplet"?

Dave


Dave,

I think it matters. It's nice to have some factual information about purchases, something beyond the marketing hype. This allows for a much better, informed decision.

Unfortunately consumers are largely courted with buzzwords and jargon, rarely with factual information. It's a shame we don't demand better.

It can be done, as can be seen here.

Clear skies, Alan

#12 jrcrilly

jrcrilly

    Refractor wienie no more

  • *****
  • Administrators
  • Posts: 33736
  • Joined: 30 Apr 2003
  • Loc: NE Ohio

Posted 25 May 2014 - 10:58 AM

Does it matter? Any ED scope has very little CA visually.


That's not true. Some ED doublets are too fast and/or use just-barely-ED glass and thus don't really control CA all that well. Some have been barely distinguishable from conventional flint-crown achromats. Anyone remember the TV Pronto?

You need to know the aperture, the F ratio, and the Abbe index of the ED glass to be able to predict the color control that could, in a well-designed ED doublet, be achieved. Even if those numbers are good, that still doesn't mean that a given design works well. It just means that a good design with those parameters and a well matched flint element could.

#13 russell23

russell23

    Skylab

  • *****
  • Posts: 4284
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 25 May 2014 - 12:55 PM

Does it matter? Any ED scope has very little CA visually.


That's not true. Some ED doublets are too fast and/or use just-barely-ED glass and thus don't really control CA all that well. Some have been barely distinguishable from conventional flint-crown achromats. Anyone remember the TV Pronto?

You need to know the aperture, the F ratio, and the Abbe index of the ED glass to be able to predict the color control that could, in a well-designed ED doublet, be achieved. Even if those numbers are good, that still doesn't mean that a given design works well. It just means that a good design with those parameters and a well matched flint element could.


But those numbers are provided for most of the scopes. They say FPL-53 or FPL-51 or FK-61 in the description. Why does the name matter in this case? It is very subjective as to what is an APO and what is not. Is any scope with ED glass and any visible CA a semi-APO? At what magnification should the standard be at which that is assessed? How much CA before it can no longer be called an APO? I've read people describing traces CA even with some ED triplets.

It just seems the simplest thing is to call a scope an ED doublet APO or an ED triplet APO if it uses ED glass. Then leave the particulars of glass types for the description. People can figure out the rest. Longer f/ratio at a given aperture and glass type means less CA. Larger aperture at a given f/ratio means more CA. Better glass types means less CA. Better figure means better performance. I don't see there being any agreement coming over when the term APO should vs should not be used with these ED doublets.

I'm not trying to be difficult. I just think the emphasis should be on the parameters being provided in the literature for the scope rather than worrying about splitting hairs on what is vs what is not an APO when these modern ED doublets have very little visual CA.

Dave

#14 Scott in NC

Scott in NC

    80mm Refractor Fanatic

  • *****
  • Administrators
  • Posts: 15104
  • Joined: 05 Mar 2005
  • Loc: NC

Posted 25 May 2014 - 07:26 PM

Very nice, well-written and informative report, Bill! Thanks so much for sharing that.

#15 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 19865
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 26 May 2014 - 12:03 PM

Besides, such scopes follow a long tradition of slowish ED doublets branded as "APOs"; Meade's made-in-USA, f/9 ED doublet line being the grand daddy of such instruments.

I think the market has had plenty of time to adjust to the optimistic use of the term "APO" on refractors.

- Jim

#16 dvb

dvb

    different Syndrome.

  • *****
  • Posts: 6170
  • Joined: 18 Jun 2005
  • Loc: Vancouver, Canada

Posted 26 May 2014 - 03:37 PM

Any predictions how it will perform as an imaging scope?

#17 Scott Beith

Scott Beith

    SRF

  • *****
  • Administrators
  • Posts: 44472
  • Joined: 26 Nov 2003
  • Loc: Frederick, MD

Posted 26 May 2014 - 07:36 PM

Does it matter? Any ED scope has very little CA visually.


That's not true. Some ED doublets are too fast and/or use just-barely-ED glass and thus don't really control CA all that well. Some have been barely distinguishable from conventional flint-crown achromats. Anyone remember the TV Pronto?

You need to know the aperture, the F ratio, and the Abbe index of the ED glass to be able to predict the color control that could, in a well-designed ED doublet, be achieved. Even if those numbers are good, that still doesn't mean that a given design works well. It just means that a good design with those parameters and a well matched flint element could.


But those numbers are provided for most of the scopes. They say FPL-53 or FPL-51 or FK-61 in the description. Why does the name matter in this case? It is very subjective as to what is an APO and what is not. Is any scope with ED glass and any visible CA a semi-APO? At what magnification should the standard be at which that is assessed? How much CA before it can no longer be called an APO? I've read people describing traces CA even with some ED triplets.

It just seems the simplest thing is to call a scope an ED doublet APO or an ED triplet APO if it uses ED glass. Then leave the particulars of glass types for the description. People can figure out the rest. Longer f/ratio at a given aperture and glass type means less CA. Larger aperture at a given f/ratio means more CA. Better glass types means less CA. Better figure means better performance. I don't see there being any agreement coming over when the term APO should vs should not be used with these ED doublets.

I'm not trying to be difficult. I just think the emphasis should be on the parameters being provided in the literature for the scope rather than worrying about splitting hairs on what is vs what is not an APO when these modern ED doublets have very little visual CA.

Dave


A good thread from the past: link

#18 russell23

russell23

    Skylab

  • *****
  • Posts: 4284
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 27 May 2014 - 11:13 AM

Does it matter? Any ED scope has very little CA visually.


That's not true. Some ED doublets are too fast and/or use just-barely-ED glass and thus don't really control CA all that well. Some have been barely distinguishable from conventional flint-crown achromats. Anyone remember the TV Pronto?

You need to know the aperture, the F ratio, and the Abbe index of the ED glass to be able to predict the color control that could, in a well-designed ED doublet, be achieved. Even if those numbers are good, that still doesn't mean that a given design works well. It just means that a good design with those parameters and a well matched flint element could.


But those numbers are provided for most of the scopes. They say FPL-53 or FPL-51 or FK-61 in the description. Why does the name matter in this case? It is very subjective as to what is an APO and what is not. Is any scope with ED glass and any visible CA a semi-APO? At what magnification should the standard be at which that is assessed? How much CA before it can no longer be called an APO? I've read people describing traces CA even with some ED triplets.

It just seems the simplest thing is to call a scope an ED doublet APO or an ED triplet APO if it uses ED glass. Then leave the particulars of glass types for the description. People can figure out the rest. Longer f/ratio at a given aperture and glass type means less CA. Larger aperture at a given f/ratio means more CA. Better glass types means less CA. Better figure means better performance. I don't see there being any agreement coming over when the term APO should vs should not be used with these ED doublets.

I'm not trying to be difficult. I just think the emphasis should be on the parameters being provided in the literature for the scope rather than worrying about splitting hairs on what is vs what is not an APO when these modern ED doublets have very little visual CA.

Dave


A good thread from the past: link


That is a good thread! One statement that struck me on the first page was the person that said his ED scope was much closer to an APO he observed with than an achro. I think that goes along with what I was trying to say. If you had a continuum line of amount of CA. The ED doublets on the market today are much closer to the APO end of the line than the achro end of the line. So arguing over whether these scopes should be called "APO" or "semi-APO" just doesn't seem productive.

The discussion in that thread talked about how to quantify it, but manufacturers don't consistently provide that information.

I still don't know what a "semi-APO" would be in practice. Either the CA is easy to detect (achro) or you have to look hard for it if seen at all (APO). It seems to me that manufacturers are not messing around with producing borderline instruments. They either make an achro. Or they use ED glass that pushes the CA into the hard/impossible to see visually category.

Dave

#19 oldtimer

oldtimer

    Apollo

  • *****
  • Posts: 1331
  • Joined: 13 Nov 2008
  • Loc: Lake County Illinois

Posted 29 May 2014 - 02:07 PM

If the amount of CA defines an APO does my 76mm 1200mm fl achro, which shows no color, qualify as an APO?

#20 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 4374
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 29 May 2014 - 10:14 PM

No. Although the modest aperture and long focal length result in little or no visible secondary color, the variation in focus from C to F is still about 1 part in 1800.

Clear skies, Alan

#21 russell23

russell23

    Skylab

  • *****
  • Posts: 4284
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 30 May 2014 - 08:59 AM

If the amount of CA defines an APO does my 76mm 1200mm fl achro, which shows no color, qualify as an APO?


That is a question I have. If the numbers being discussed on this thread are how APO is defined, then Alan is right. It would be possible to come up with a system for classifying the CA effects of refractors. But there are so many variables I doubt it would be easy to get agreement.

Dave

#22 Gert K A

Gert K A

    Mariner 2

  • -----
  • Posts: 291
  • Joined: 16 Jul 2012
  • Loc: Copenhagen, Denmark

Posted 07 June 2014 - 06:06 AM

Thanks for this report, I love it.
That is a very desirable “semi-APO” :grin:

#23 JCAZ

JCAZ

    Messenger

  • -----
  • Posts: 458
  • Joined: 11 Aug 2009

Posted 17 June 2014 - 10:18 AM

Nice review, but is this really necessary?

"Disclaimer - Given difference between equipment, seeing conditions, observer physiology, and observer psychology (i.e., likes, dislikes, and expectations), your outcomes can be different when compared to those in this article. All advice and information in this article is given in good faith as an amateur astronomer and hobbyist and is based on sources believed to be reliable and accurate at the time of release. The author does not accept legal liability or responsibility for the content of the advice or information or any consequences arising from its use, and should not be considered a substitute for professional advice. It is the responsibility of the user to make their own decisions about the relevance, accuracy, currency and reliability of information found in this article. The advice and information in this article does not necessarily reflect the views of the organizations hosting the article."

#24 Deep13

Deep13

    Mercury-Atlas

  • *****
  • Posts: 2734
  • Joined: 25 Jan 2005
  • Loc: NE Ohio

Posted 26 July 2014 - 05:57 PM

what's the retail cost?

#25 coopman

coopman

    Gemini

  • *****
  • Posts: 3450
  • Joined: 23 Apr 2006
  • Loc: South Louisiana

Posted 27 July 2014 - 09:20 AM

$3,990.00






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics