Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

APM 2" 1.5x barlow - any experiences?

  • Please log in to reply
10 replies to this topic

#1 RJF-Astro

RJF-Astro

    Messenger

  • -----
  • topic starter
  • Posts: 467
  • Joined: 13 Aug 2018
  • Loc: Zeist, Netherlands

Posted 27 May 2020 - 02:22 PM

Hi all, I am looking at the APM 2" coma-correcting telecentric 1.5x barlow as a way to increase the focal length of my new TS-Optics 6" f/4 UNC newton. Are there any experiences with this barlow? Especially for imaging? 

 

If it works like it should, it can effectively replace my 6" ritchey-chretien with 0.67x reducer. Both configurations will give me around 900mm f/6. The big advantage of using one scope is that I can use the benefits of my newton. It has an upgraded focusser and carbon fibre tube, compared to the RC. And I can keep my motorfocus attached, where I have to swap it now when I want to use another scope.



#2 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 46,210
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 28 May 2020 - 04:29 PM

First, If it does correct coma, then eyepiece position relative to the lens would be critical and the Barlow would not work with anything other than newtonians.

That's possible, but I only see a 2.7x one still available.

 

I might suggest you'd be better served with a legitimate coma corrector, like the GSO, as you might get better coma correction.

https://www.astrofotoblog.eu/?p=856

https://www.cloudyni...tor-compariosn/

https://www.asztrofo...don-1-resz.html

https://www.flickr.c...02/14033952529/



#3 RJF-Astro

RJF-Astro

    Messenger

  • -----
  • topic starter
  • Posts: 467
  • Joined: 13 Aug 2018
  • Loc: Zeist, Netherlands

Posted 29 May 2020 - 02:34 AM

Hi Don, thanks for your reply. It's this one, announced in november last year. I am specifically looking at 1.5x barlow because of the extra resolution while still maintaining f/6. I do have a coma corrector which does not change the focal length. I will use it for imaging only, and according to APMs website it should be suited for that, including the use of an off-axis guider and filter wheel.



#4 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 46,210
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 29 May 2020 - 09:26 AM

Interesting.  When I search APM's site for APM products, it is nowhere to be found.

Yet you pulled up the page.

Search must return different results for different search engines.

It looks interesting.



#5 25585

25585

    Cosmos

  • *****
  • Posts: 8,959
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 29 May 2020 - 01:10 PM

https://www.apm-tele...ric-1.5x-barlow

 

I wonder how it compares to an Astrophysics BARADV. https://www.astro-physics.com/baradv

 

To the OP, there is an Antares 2" 1.6x ordinary Barlow, which is a good performer, and a lot less expensive https://agenaastro.c...s-2ubstl.html  


Edited by 25585, 29 May 2020 - 01:13 PM.

  • stevew and vdog like this

#6 Starman1

Starman1

    Vendor (EyepiecesEtc.com)

  • *****
  • Vendors
  • Posts: 46,210
  • Joined: 23 Jun 2003
  • Loc: Los Angeles

Posted 29 May 2020 - 01:12 PM

https://www.apm-tele...ric-1.5x-barlow

 

I wonder how it compares to an Astrophysics BARADV.

 

To the OP, there is an Antares 2" 1.6x ordinary Barlow, which is a good performer, and a lot less expensive https://agenaastro.c...s-2ubstl.html  

The difference is that regular barlows do not correct coma as they magnify.

The APM he is talking about does.



#7 25585

25585

    Cosmos

  • *****
  • Posts: 8,959
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 29 May 2020 - 01:18 PM

It would be cool if Tele Vue developed a supplementary lens system for their Paracorr 2, so increasing its magnification to 1.5x or more but not compromising its coma correction in any way.



#8 BillP

BillP

    ISS

  • *****
  • Posts: 20,002
  • Joined: 26 Nov 2006
  • Loc: Spotsylvania, VA

Posted 29 May 2020 - 01:24 PM

The coma correcting characteristic of the 2.7x was indeed there when I compared it to other Barlows of the same magnification, but that it was slight.  Ornamentally nice that the coma on stars in the far off-axis was slightly less, but not of much practical use.  If one is after coma correction of their main objective, then best to get one that has sufficient strength to actually correct it all instead of making the coma just slightly less strong coma.  So a dedicated coma corrector is the only way to go.  In all other respects the APM 2.7x was quite a good Barlow and better IMO than much of the field of current Barlows in or near 2.7x (2.5x to 3x).


Edited by BillP, 29 May 2020 - 01:27 PM.

  • RJF-Astro likes this

#9 RJF-Astro

RJF-Astro

    Messenger

  • -----
  • topic starter
  • Posts: 467
  • Joined: 13 Aug 2018
  • Loc: Zeist, Netherlands

Posted 30 May 2020 - 02:44 AM

Thanks Bill! That is the kind of information I am looking for. Coma correction is important to me, although I will be using it mostly during galaxy season so edge performance is less important.  I will wait for now, and see if any reviews pop up on the 1.5x.



#10 sixela

sixela

    Hubble

  • *****
  • Posts: 15,383
  • Joined: 23 Dec 2004
  • Loc: Boechout, Belgium

Posted 05 June 2020 - 08:07 AM

It's not a one group barlow but a telecentric two -group barlow precisely to avoid it. Which also means that there's no cheating to make it a barlow with another factor. And the coma correction is indeed only optimal with the focal plane of the eyepiece or the sensor a whopping 95mm from the end of the M54 thread.
 

First, If it does correct coma, then eyepiece position relative to the lens would be critical 


Edited by sixela, 05 June 2020 - 08:11 AM.


#11 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 85,034
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 05 June 2020 - 08:34 AM

It's not a one group barlow but a telecentric two -group barlow precisely to avoid it. Which also means that there's no cheating to make it a barlow with another factor. And the coma correction is indeed only optimal with the focal plane of the eyepiece or the sensor a whopping 95mm from the end of the M54 thread.
 

 

So how does it perform in a coma free scope since coma correctors add coma of the opposite sign to correct the coma?

 

Jon




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics