Semi ED / APO

[LDW1]

What is the understanding over here as to the meaning of semi ED / APO that you still see reference to regarding older, used refractors ! I am interested in interpretations as I have one coming this week, circa 2005-2007 !

[John]

I guess that the meaning is that the scope controls CA better than an achromat but not as well as an apochromat ?

I have one - a Tele Vue Ranger. CA is visible around bright targets but somewhat less so than it would be with a conventional achromat of the same specification.

What scope are you expecting this week ?

Some doublets that use an ED or Flourite element show virtually no CA visually at all. Some triplets can show a little more CA than a good ED doublet.

It can be a topic for endless debate in some places !

 

 

 

[LDW1]

6 minutes ago, John said:

I guess that the meaning is that the scope controls CA better than an achromat but not as well as an apochromat ?

I have one - a Tele Vue Ranger. CA is visible around bright targets but somewhat less so than it would be with a conventional achromat of the same specification.

What scope are you expecting this week ?

Some doublets that use an ED or Flourite element show virtually no CA visually at all. Some triplets can show a little more CA than a good ED doublet.

It can be a topic for endless debate in some places !

 

 

 

Its the 127mm Antares that I mentioned this week in another post ! No one on here seems to recognize this Canadian scope !

[John]

I think it is pretty much the same as the Explore Scientific AR127 ?:

https://explorescientificusa.com/products/ar127-air-spaced-doublet-refractor

Telescope Services (TS) in Germany marketed a version of it a while back as well.

The ones that I've seen up for sale in the US (eg: link below) seem to state achromat:

https://astromart.com/classifieds/astromart-classifieds/telescope-refractor/show/antares-127mm-f65-achromat

Perhaps you should expect achromat performance and then, if the CA control is better, that will be a bonus 

At F/6.5 with a 127mm aperture, CA should not be too bothersome even if it is an achromat.

 

 

[LDW1]

1 hour ago, John said:

I think it is pretty much the same as the Explore Scientific AR127 ?:

https://explorescientificusa.com/products/ar127-air-spaced-doublet-refractor

Telescope Services (TS) in Germany marketed a version of it a while back as well.

The ones that I've seen up for sale in the US (eg: link below) seem to state achromat:

https://astromart.com/classifieds/astromart-classifieds/telescope-refractor/show/antares-127mm-f65-achromat

Perhaps you should expect achromat performance and then, if the CA control is better, that will be a bonus 

At F/6.5 with a 127mm aperture, CA should not be too bothersome even if it is an achromat.

 

 

Nothing to do with ES, Antares is a Canadian company ( BC ) who manufacture the tubes etc.here in Canada, select the glass from other sources to higher specs and assemble everything here in Canada ! Testing is extensive, thats well known ! Its doubtful with ES  !

[John]

1 hour ago, LDW1 said:

Nothing to do with ES, Antares is a Canadian company ( BC ) who manufacture the tubes etc.here in Canada, select the glass from other sources to higher specs and assemble everything here in Canada ! Testing is extensive, thats well known ! Its doubtful with ES  !

Well I hope your expectations are met. I have owned quite a few Antares products and they are decent for their cost but not the very best in their niche.  They do usually offer good value though.

As I understand it, the 127mm F/6.5 Antares refractor was made by Jinghua Optical Electronics Co (JOC) who also made Explore Scientific, Telescope Services, Bresser and I believe some Meade products.

 

 

 

 

[LDW1]

3 hours ago, John said:

Well I hope your expectations are met. I have owned quite a few Antares products and they are decent for their cost but not the very best in their niche.  They do usually offer good value though.

As I understand it, the 127mm F/6.5 Antares refractor was made by Jinghua Optical Electronics Co (JOC) who also made Explore Scientific, Telescope Services, Bresser and I believe some Meade products.

 

 

 

 

I have an Antares 102mm, f6.2 refrac. and had an 80mm, f6 as well ! Both put up great views on those great nights but they weren’t professed to be semi anything just excellent quality achros and they were ! This 127mm if you read the old literature from back in 2005-2007, from the Canadian Company that built / put together these scopes they reference semi ed or apo or both for the 2 127mm and 1 154mm models ! As well the chinese company that you reference built scopes for various scope companies is probably correct but my understanding is, like a lot of others do, is that they are built to specs, requirements, wants of the individual scope companies which means the quality / functional ability of each brand of scope could be more or less than another and my understanding of the Antares scopes is that they are closer to the top end of the scale due to stricter controls / requirements of the company ! I have heard / read that a few times through the years from various sources and witnessed it personally with my two vs the half dozen other brands and sizes that I have owned and operated ! So semi or not I am very sure I will get a good scope for what I paid ie approx $300 C !

[John]

Sounds like you already know all about them. Hope you enjoy the scope

[LDW1]

1 hour ago, John said:

Sounds like you already know all about them. Hope you enjoy the scope

I have learned a bit over the years, my only question was where does the word ‘semi’ come in and what does it all mean incl other observers interpretations !  Are you actually getting a little more again for your $ ?

[John]

The scope listed on the Antares website is billed as being an achromatic refractor so it will have a 2 element objective that uses crown and flint glass:

http://www.vectorwarrior.com/antares/1208EQ5.htm

If an ED glass element was used they would certainly say so - ED glass costs a lot more than standard glass and manufacturers and vendors make sure that they emphasise when it is used.

I have heard the term "semi-apo" used over the years that I've been involved in astronomy but I don't think it means much. There was a discussion on the Cloudynights forum last year which might be of interest:

https://www.cloudynights.com/topic/603649-apo-and-semi-apo-difference/

From what I've read, the Antares 127mm F/6.5 achromat seems to be a well thought of scope (though rarely encountered here in the UK) so for your investment ($300 was it ?) you have probably made a sound purchase.

 

 

 

[Stu]

I guess technically any ED doublet is a semi apo, but the decent ones such as the Skywatcher 80/100/120ED are marketed as apos, quite rightly in my opinion, certainly for visual use.

I guess some of the older EDs with less good glass in them would more correctly be termed semi apo, but it is a very grey area with many blurred boundaries. As John said, there are triplets out there which should be apos but show more colour than a good ED or fluorite doublet.

[LDW1]

1 hour ago, John said:

The scope listed on the Antares website is billed as being an achromatic refractor so it will have a 2 element objective that uses crown and flint glass:

http://www.vectorwarrior.com/antares/1208EQ5.htm

If an ED glass element was used they would certainly say so - ED glass costs a lot more than standard glass and manufacturers and vendors make sure that they emphasise when it is used.

I have heard the term "semi-apo" used over the years that I've been involved in astronomy but I don't think it means much. There was a discussion on the Cloudynights forum last year which might be of interest:

https://www.cloudynights.com/topic/603649-apo-and-semi-apo-difference/

From what I've read, the Antares 127mm F/6.5 achromat seems to be a well thought of scope (though rarely encountered here in the UK) so for your investment ($300 was it ?) you have probably made a sound purchase.

 

 

 

Some of the Antares scopes also reference ‘ Vixen Grade ‘ lens, designed to the specs of the older Japanese Vixen scopes so there appears to be something in their wording / meaning ! My understanding and I read it somewhere, but where, was that they were quite selective in obtaining their lens glass and that they were supplied with ED glass which they used in that line that I reference !

Edited July 28, 2019 by LDW1

[John]

20 minutes ago, LDW1 said:

Some of the Antares scopes also reference ‘ Vixen Grade ‘ lens, designed to the specs of the older Japanese Vixen scopes so there appears to be something in their wording / meaning ! My understanding and I read it somewhere, but where, was that they were quite selective in obtaining their lens glass and that they may have been supplied with ED glass at some point !

The "Vixen Spec" Antares refractors were longer focal length achromats, dubbed the "Elite" series.

They were achromats as well. The 105mm had a baffle design issue that resulted in it's objective being stopped to around 95mm effective aperture.

Have you actually got your Antares 127mm F/6.5 now or is it still on it's way to you ?

 

[LDW1]

5 minutes ago, John said:

The "Vixen Spec" Antares refractors were longer focal length achromats, dubbed the "Elite" series.

They were achromats as well. The 105mm had a baffle design issue that resulted in it's objective being stopped to around 95mm effective aperture.

Have you actually got your Antares 127mm F/6.5 now or is it still on it's way to you ?

 

It should be in Mississauga now via Canada Post, 200mi south of me, from Montreal I would hopefully expect to get it tomorrow or Tues. at the latest !

[LDW1]

6 minutes ago, LDW1 said:

It should be in Mississauga now via Canada Post, 200mi south of me, from Montreal I would hopefully expect to get it tomorrow or Tues. at the latest !

Someone mentioned on CN, that Antares scopes weren’t stopped down contrary to some peoples beliefs / statements !

Edited July 29, 2019 by LDW1

[John]

11 minutes ago, LDW1 said:

Someone mentioned on CN, that Antares scopes weren’t stopped down contrary to some peoples beliefs / statements !

I've read a number of reports from different sources that the 105mm F/15 Antares Elite was stopped down to around 95mm but that scope is not the subject of this thread.

I hope you enjoy your Antares 127mm F/6.5 achromat. It should provide a nice balance of unobstructed light grasp and good control of CA for it's focal ratio. For what you have invested, you can't go wrong

[LDW1]

27 minutes ago, John said:

I've read a number of reports from different sources that the 105mm F/15 Antares Elite was stopped down to around 95mm but that scope is not the subject of this thread.

I hope you enjoy your Antares 127mm F/6.5 achromat. It should provide a nice balance of unobstructed light grasp and good control of CA for it's focal ratio. For what you have invested, you can't go wrong

I agree ! Its the first refractor that I have owned with a weight of around 15lb ! It will be interesting to see how my AZ4’s / Twilight I perform ! I know one thing, I will never own another EQ mount, one was enough ! I will figure this out as I go !

[John]

1 minute ago, LDW1 said:

I agree ! Its the first refractor that I have owned with a weight of around 15lb ! It will be interesting to see how my AZ4’s / Twilight I perform ! I know one thing, I will never own another EQ mount, one was enough ! I will figure this out as I go !

I'm an alt-azimuth fan as well. I do have a Vixen GP which is a very good EQ but most of the time it's the AZ4 / Skytee II / Giro Ercole that I go for

Hope you get some clear skies to get the scope under

 

 

[LDW1]

I just got the scope, it was superbly wrapped and is in perfect condition ! I may post a pic when I mount it later today ! Thanx every one for looking / commenting !