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

Semi-Apo/Fringe Killer Needed?

  • Please log in to reply
29 replies to this topic

#1 cmac7203

cmac7203

    Vostok 1

  • *****
  • topic starter
  • Posts: 127
  • Joined: 14 Feb 2016
  • Loc: Minnesota

Posted 19 March 2018 - 04:46 PM

Howdy Forum Posse,

 

I've read quite a lot from you all over the past couple days on this subject, but obliquely as people have debated the merits of either scope. During those posts the topic of CA comes and goes but not necessarily the use of these filters or even a minus violet specifically.

 

I am very close to pulling the trigger on either a StellarVue 102-Access or a Astro-Tech AT102ED tonight or tomorrow. I am 90% visual with occasional snaps via my Hyperion lenses.

 

So, here's the question: Do you think a CA-reducing filter (e.g., Baader Semi-Apo or Fringe Killer) is necessary...or even helpful...for these scopes? Seems like with f/7 I am going to avoid a lot of it.

 

Thoughts?



#2 Joe1950

Joe1950

    Cosmos

  • *****
  • Posts: 7881
  • Joined: 22 Aug 2015
  • Loc: South New Jersey

Posted 19 March 2018 - 04:53 PM

I have a Celestron C80ED. It is a two element objective, f 7.5, one element using FPL-53 glass. I see no chromatic aberration at all in focused images or in out of focus star images.

 

If any is there, I don't see it at all.

 

So I would not add a filter to the scope you are getting.

 

Good luck and enjoy!


  • terraclarke and cmac7203 like this

#3 Auburn80

Auburn80

    Viking 1

  • *****
  • Posts: 514
  • Joined: 01 Apr 2013

Posted 19 March 2018 - 05:07 PM

I have the 102 Access and see no need what-so-ever for a filter. I can't speak to the AT102ED but even if it does have a touch of color on brighter stars; any filter will probably do more damage to the total brightness of the image than the clarity lost to CA.

 

My $.02 and Good Luck!


  • terraclarke, jeremiah2229, Joe1950 and 1 other like this

#4 AxelB

AxelB

    Viking 1

  • -----
  • Posts: 863
  • Joined: 22 Mar 2015

Posted 19 March 2018 - 05:11 PM

Try the scope first. Chances are you won’t need a filter.

CA reducing filters are useful with achromatic refractors. The best "filter" is an apo refractor, be it a triplet or even just a good ED doublet.

On achros, filters allows us to trade light for lower AC (better sharpness) by cutting out certain wavelengths.

Edited by AxelB, 19 March 2018 - 05:11 PM.

  • Joe1950 and cmac7203 like this

#5 dusty99

dusty99

    Vostok 1

  • *****
  • Posts: 176
  • Joined: 13 Jun 2009

Posted 19 March 2018 - 05:11 PM

 

 

So, here's the question: Do you think a CA-reducing filter (e.g., Baader Semi-Apo or Fringe Killer) is necessary...or even helpful...for these scopes?

 

 No


Edited by dusty99, 19 March 2018 - 05:53 PM.

  • Crow Haven, Joe1950 and cmac7203 like this

#6 junomike

junomike

    Hubble

  • *****
  • Moderators
  • Posts: 15161
  • Joined: 07 Sep 2009
  • Loc: Ontario

Posted 19 March 2018 - 05:12 PM

Although I probably wouldn't be happy with the CA correction of the Astro-Tech I doubt I'd use a Filter as the "yellow" tint imparted is more distracting (at least for this OTA).

Out of the two however, I'd prefer the Stellarvue as It's an FPL-53 Doublet and should have excellent color correction


Edited by junomike, 19 March 2018 - 07:27 PM.

  • Crow Haven, Auburn80, Joe1950 and 1 other like this

#7 Crow Haven

Crow Haven

    Fly Me to the Moon

  • *****
  • Posts: 6077
  • Joined: 09 Jan 2009
  • Loc: S.Oregon Coast USA

Posted 19 March 2018 - 05:17 PM

Try it and see.  I don't feel a need for filters with my 102 ED.


  • Joe1950 and cmac7203 like this

#8 T1R2

T1R2

    Mercury-Atlas

  • -----
  • Posts: 2839
  • Joined: 11 Jun 2013
  • Loc: NeverWhere, 35*N

Posted 19 March 2018 - 05:19 PM

Howdy Forum Posse,

 

I've read quite a lot from you all over the past couple days on this subject, but obliquely as people have debated the merits of either scope. During those posts the topic of CA comes and goes but not necessarily the use of these filters or even a minus violet specifically.

 

I am very close to pulling the trigger on either a StellarVue 102-Access or a Astro-Tech AT102ED tonight or tomorrow. I am 90% visual with occasional snaps via my Hyperion lenses.

 

So, here's the question: Do you think a CA-reducing filter (e.g., Baader Semi-Apo or Fringe Killer) is necessary...or even helpful...for these scopes? Seems like with f/7 I am going to avoid a lot of it.

 

Thoughts?

no, you wont need a filter for the SV102 Access, these are some of the best Apo doublet's on the market.


  • cmac7203 likes this

#9 sg6

sg6

    Soyuz

  • *****
  • Posts: 3971
  • Joined: 14 Feb 2010
  • Loc: Norfolk, UK.

Posted 19 March 2018 - 05:37 PM

For visual with either scopes you mention you will likely not need a filter. If the presence of CA is likely to bother you, and that in turn means that first it has to be present, then get a triplet. My reason for this is simply that if a "fringe killer" worked then why do we by a $1000 apo triplet scope when a $600 ED doublet and a filter would supposidely do the same?

 

The other aspect to remember is that an ED doublet is ultimately an achro with a fancy glass element. Both have a flint element and a crown element. The performance is decided by which flint and crown elements.


  • Gabby76 and cmac7203 like this

#10 ssmith

ssmith

    Messenger

  • *****
  • Posts: 497
  • Joined: 28 Jun 2012
  • Loc: Colorado

Posted 19 March 2018 - 05:41 PM

For visual use there is usually no need for a filter.  ED doublets are usually very well corrected visual use.  For photographic use you will definitely pick-up fringing in your images if you don’t use a filter.   Some of that can be corrected or muted during processing - depends on the subject matter.


Edited by ssmith, 19 March 2018 - 05:42 PM.

  • Joe1950 and cmac7203 like this

#11 daquad

daquad

    Apollo

  • *****
  • Posts: 1072
  • Joined: 14 May 2008

Posted 19 March 2018 - 06:37 PM

No way.  Why add a CA reduction filter when you already have the CA very well suppressed?  The filter is another optical surface that can only reduce light throughput and possibly introduce other aberrations without doing anything for CA reduction.  Use a CA reduction filter for fast (low focal ratio) achromats that are used at high powers such as a 6" f/6  or f/8 achromat, for example.  


Edited by daquad, 19 March 2018 - 06:37 PM.

  • cmac7203 likes this

#12 howardcano

howardcano

    Ranger 4

  • *****
  • Posts: 319
  • Joined: 06 Aug 2017
  • Loc: Olathe, KS

Posted 19 March 2018 - 06:39 PM

I'm pretty satisfied with my Astro-Tech AT102ED without the filter.  The Baader 495 does remove a little purple from Sirius, but for most other targets there's no need for it.


  • cmac7203 likes this

#13 Astro-Master

Astro-Master

    Vostok 1

  • ****-
  • Posts: 174
  • Joined: 09 May 2016

Posted 19 March 2018 - 07:30 PM

I would go with the StellarVue 102.  My friend has one, and I see no CA through his scope.  StellarVue has

better quality control, and is a hand made scope.  Forget the fringe filters.


  • cmac7203 likes this

#14 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 73125
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 19 March 2018 - 11:47 PM

For visual with either scopes you mention you will likely not need a filter. If the presence of CA is likely to bother you, and that in turn means that first it has to be present, then get a triplet. My reason for this is simply that if a "fringe killer" worked then why do we by a $1000 apo triplet scope when a $600 ED doublet and a filter would supposidely do the same?

 

The other aspect to remember is that an ED doublet is ultimately an achro with a fancy glass element. Both have a flint element and a crown element. The performance is decided by which flint and crown elements.

 

Not this again.  The same exact thing can be said about a triplet.  There are achromatic triplets out there, ones that have no better color correction than the standard 1 part in 2000 longitudinal focus variation. They're rare because it doesn't make economic sense.  The color correction of a triplet also depends on the glasses chosen. 

 

Jon Isaacs.  


  • junomike, Far Star, Joe1950 and 2 others like this

#15 alex_d

alex_d

    Messenger

  • *****
  • Posts: 407
  • Joined: 29 Apr 2016
  • Loc: kaysville utah

Posted 20 March 2018 - 03:17 AM

For visual with either scopes you mention you will likely not need a filter. If the presence of CA is likely to bother you, and that in turn means that first it has to be present, then get a triplet. My reason for this is simply that if a "fringe killer" worked then why do we by a $1000 apo triplet scope when a $600 ED doublet and a filter would supposidely do the same?

 

The other aspect to remember is that an ED doublet is ultimately an achro with a fancy glass element. Both have a flint element and a crown element. The performance is decided by which flint and crown elements.

Ive been under the impression that triplets were mainly purchased for imaging and doublets for visual, dont most or all doublets pretty much eliminate it completely for visual? Ive noticed none at all in mine day or night no matter how bright the object. Maybe with some doublets some CA is present? Honestly ive only ever looked through one "mine"


  • cmac7203 likes this

#16 AxelB

AxelB

    Viking 1

  • -----
  • Posts: 863
  • Joined: 22 Mar 2015

Posted 20 March 2018 - 05:39 AM

If it can be detected photographically, it’s because it’s there and it reduces sharpness. The rest of the story is just about what level of image quality you’re looking for.
  • cmac7203 likes this

#17 junomike

junomike

    Hubble

  • *****
  • Moderators
  • Posts: 15161
  • Joined: 07 Sep 2009
  • Loc: Ontario

Posted 20 March 2018 - 06:39 AM

Ive been under the impression that triplets were mainly purchased for imaging and doublets for visual, dont most or all doublets pretty much eliminate it completely for visual? Ive noticed none at all in mine day or night no matter how bright the object. Maybe with some doublets some CA is present? Honestly ive only ever looked through one "mine"

IME this only holds true for those made with FPL-53 using F7 (or greater) F-Ratios.  FPL-51 Triplets, (F7 or less) tend to show some CA but not enough to bother some people and far less than an Achromat.


  • cmac7203 likes this

#18 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 73125
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 20 March 2018 - 05:36 PM

If it can be detected photographically, it’s because it’s there and it reduces sharpness. The rest of the story is just about what level of image quality you’re looking for.

 

The reason color correction is more important photographically is that cameras capture a much broader spectrum than the human eye .  This means that a broader spectrum must be in focus . Poor color correction results in purple halos around stars. 

 

Regarding the AT-102ED and it's color correction: I reviewed the very first AT-102ED in the US and later purchased it.  That was more than 10 years ago.  I had it for two years , used it a great deal,  i never felt the need to use a filter.  On the toughest objects, a tiny amount of CA was visible.  Venus.. 

 

https://www.cloudyni...h-at102ed-r1690

 

Here's a couple of photos i took with the AT-102ED.. 

 

6223239-Osprey 2 Bright CN.jpg
 
The Osprey is a classic image that would show color fringing, a bird against a bright sky .
 
3866937-shrike at Palo Verde.jpg
 
I figure the Shrike was about a half mile away.  Shrikes are about 9 inches in length. 
 
Jon

  • Crow Haven, Far Star, Joe1950 and 1 other like this

#19 Joe1950

Joe1950

    Cosmos

  • *****
  • Posts: 7881
  • Joined: 22 Aug 2015
  • Loc: South New Jersey

Posted 20 March 2018 - 07:21 PM

If I can save a thousand or two, I'll put up with the hint of purple on Venus. Not much else to see on it anyhow!

 

Plus, and not to get the triplet folks angry, I would take a triplet without complaining... they are more sensitive to alignment and collimation, etc., than a doublet. Not the kind of lens you'd want to take apart and clean - from what I hear.*

 

And If you get one of those oil filled triplets you have to change the oil every 3000 observations! shrug.gif

 

 

*Seriously I've never had and likely never will have a triplet so I'm not trashing them as opposed to an ED doublet. I just know that with my C80ED, I don't see any CA, and the out of focus star images are virtually the same color also. So to get an 80mm refractor with no noticeable color for $300 works for me. Especially with a really good DPAC figure, which counts.

[attachment=1024839:DPAC C80.jpg]

I'm all for using what you have and enjoying it, rather than checking and worrying about whose grass is a slightly darker shade of green. Sometimes I think CN stands for Competitive Neurosis rather than Cloudy Nights.


Edited by Joe1950, 20 March 2018 - 07:32 PM.

  • Jon Isaacs and Far Star like this

#20 terraclarke

terraclarke

    Hubble

  • *****
  • Posts: 18114
  • Joined: 29 May 2012
  • Loc: Third from the Sun

Posted 21 March 2018 - 11:35 AM

Definitely no need whatsoever with the SV102-A.


  • Joe1950 likes this

#21 BarrySimon615

BarrySimon615

    Pa Bear

  • *****
  • Posts: 4135
  • Joined: 01 Mar 2004
  • Loc: New Orleans, LA

Posted 21 March 2018 - 12:27 PM

As others have said, an ED/apo doublet or triplet will either not benefit at all from additional filtration help or what little benefit you may have in chromatic aberration correction (perhaps more correctly "suppression")  will be offset by an overall color shift either minimal or pronounced.

 

Where a filter like a Baader Long Pass 495 or the relatively new Baader "semi-apo" filter will help would be with a traditional achromat.  The faster and larger (objective diameter) the achromat is, the more chromatic aberration it will have and the more it can potentially benefit from a filter that suppresses the chromatic aberration.

 

Among my herd of telescopes the ones that would benefit most from filters like the two I mention above would be my Jaegers 6" f/5 achro, my Orion ST120 f/5, my Celestron Vixen SP C102 f/9.8, my Vixen NA 140 f/5.7, and my Antares 127 mm f/9.4.  The Baader 495 really cleans up and sharpens the image, but there is a decided yellow cast to the background.  I just recently purchased the Baader Semi-Apo filter but I have not had the opportunity to try it yet.  I will check it out the next clear opportunity we have. Supposedly it will impart a more neutral background color along with a chromatic aberration fix.

 

The following telescopes do not need any help in correcting chromatic aberration and either of the two filters I have are not needed with them.  I may try them at least once for "grins and giggles" but I do not anticipate any benefit - Tak TOA 130, TMB SS130, AP Star12 ED, AT 111 f/7, AT 102 EDF, ES 80 triplet.

 

Barry Simon


Edited by BarrySimon615, 21 March 2018 - 08:44 PM.


#22 daquad

daquad

    Apollo

  • *****
  • Posts: 1072
  • Joined: 14 May 2008

Posted 21 March 2018 - 06:12 PM

Jaegers 6" f/5 apo? lol.gif 



#23 BarrySimon615

BarrySimon615

    Pa Bear

  • *****
  • Posts: 4135
  • Joined: 01 Mar 2004
  • Loc: New Orleans, LA

Posted 21 March 2018 - 08:44 PM

Jaegers 6" f/5 apo? lol.gif

Oops!  Mistake corrected.

 

Barry Simon


  • Jon Isaacs and Joe1950 like this

#24 Exnihilo

Exnihilo

    Apollo

  • *****
  • Posts: 1286
  • Joined: 02 Aug 2010
  • Loc: Tempe, AZ

Posted 23 March 2018 - 03:55 PM

 

The Osprey is a classic image that would show color fringing, a bird against a bright sky .
 
 
 
I figure the Shrike was about a half mile away.  Shrikes are about 9 inches in length. 
 
Jon

 

Those are nice bird pics!

 

 

I've got two F5 achros; I typically don't use a filter, but maybe I'd go for a semi-apo.


Edited by Exnihilo, 23 March 2018 - 03:57 PM.


#25 Joe1950

Joe1950

    Cosmos

  • *****
  • Posts: 7881
  • Joined: 22 Aug 2015
  • Loc: South New Jersey

Posted 23 March 2018 - 04:31 PM

I've had both the Semi APO and the Contrast Booster. Someone once compared the two and found that the Contrast Booster removes just about all CA in most cases while the Semi APO will remove about 80-85%

 

I would agree with that. But, the semi APO added less color shift, almost none, and the colors with that were very natural. Plus, with some scopes and eyepieces, the contrast boost seemed to have an effect on the image. Not the case with the Semi APO.

 

Read the specs and description on them. They do work and will clean up a good amount of CA, if you don't go crazy with magnification.

 

Just my impression.




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