Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Refractors

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | (show all)
De Lorme
professor emeritus
*****

Reged: 12/30/08

Re: CA Reduction filters new [Re: A. Viegas]
      #6161437 - 10/27/13 08:33 PM

Dave, Did the Moon remain a light yellow with the 82A combined with the Longpass? I thought there would be a shift to the blue. Also did you place the 82A in front or behind the Longpass and would doing either make a differance?
Thanks for the follow up review. De Lorme


Post Extras: Print Post   Remind Me!   Notify Moderator  
russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: De Lorme]
      #6161572 - 10/27/13 10:03 PM

Quote:

Dave, Did the Moon remain a light yellow with the 82A combined with the Longpass? I thought there would be a shift to the blue. Also did you place the 82A in front or behind the Longpass and would doing either make a differance?
Thanks for the follow up review. De Lorme




The 82A didn't make any confirmable difference in color. The Moon still looked the same yellow when the 82A was used with the 495 longpass. What the 82A did do was make certain lunar features really stand out in combination with the longpass. The two filters make a great pair in combination for lunar observations.

Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: Eddgie]
      #6161646 - 10/27/13 11:01 PM

Quote:

Well then, I suppose that there must be some value, but I have owned the Vixen 140 and used different filters and never felt like it really made the telescope perform better than some smaller APOs, and for me, the difference was not much different than using simple color filters, which often enhance some details at the expense of others.




What filters did you use to try reducing CA? Your review of the Vixen 140NA was in 2004. I've studied this intensively since buying the Vixen 140 several years ago. I was very satisfied with the Baader Fringe Killer but after reading some comments about #8 light yellow and the Baader 495 Longpass I decided to do a comparison. As I'm reporting the 495 Longpass makes a significant difference in image sharpness and the CA is completely removed. The lumicon minus violet filter is probably useless for a large achro because it doesn't cut significantly between 420 and 475nm.

Quote:

You put on this or that filter and this or that detail improves, but this or that other detail would be harder to see.




For what type of observing? I've yet to find anything that did not reveal more detail with the Baader 495 Longpass than without - simply because it is possible to get much sharper focus with the CA removed.

Quote:

My advice though would continue to be to always prefer a smaller APO over a larger achromat of any kind.




When did you change you mind on this? I won't quote from the article directly, but in your 2005 review of the Meade 152mm ED you said that a 102mm APO didn't wow you at all, that you sold your 102mm APO for a 102mm Vixen achro because it was almost as good for a lot less cost. You went on to say that you sold your 4" achro for a Vixen 140NA because the 4" achro just didn't cut it.

Look, people evolve and change their mind about things, but I think your arguments are based upon different experiences. You've not provided any specifics to lead me to believe that you've intensively compared views with and without any of the specific filters I'm using to note if they improve the performance of the achromat.

Quote:

There is to much energy loss in an achromat and no filter made can refocus that energy.




Nobody has said that the filter does refocus the light. I think most people understand that filters of all types remove stuff - be it light of certain colors, or dust particles, or coffee grinds.

Quote:

My goal is to get people to avoid thinking that they can approach APO levels of performance simply by buying an achromat and sticking a filter on it




What aspect of APO performance? My Vixen 140NA is every bit as sharp as my Vixen 80mm f/7.5 fpl-53 ED doublet when I put that 495 longpass filter on it - and it provides a lot more light than the 80mm ED.

Quote:

and when excellent ED and APOs simply offer much better performance even in less aperture my advice is to go smaller and APO than larger and filter.




How much smaller do you think an APO can be and still outperform an achro filtered with a filter that completely removes the CA? The Baader 495 longpass transmits over 90% of the light from 510 nm and longer and actually transmits 95+% of the light from 530nm on. Even if the filtered Vixen 140NA was losing 20% of the light compared with an unfiltered APO (and it is certainly less than that) it would still be performing at the level of a 125mm APO in terms of total light - although the distribution across wavelengths will be different.

But this means to get an APO that actually significantly outperforms a filtered Vixen 140NA you need an APO with a minimum aperture of 140mm and that is where they start to get really expensive.


Quote:

But if it improves the performance in any way, then I guess I can't argue the point that it is not worth doing be it expensive bandpass filters, or simple color filters.

I'll keep out of the way of your work to promote these kinds of filters. If there are enough people saying that there is a meaningful improvement, then clearly I am wrong on the topic and I won't distract people from that message any longer..




You're welcome to make your case. That is what this forum is for. Your point of view on the quality of view you can get from a filtered achromat is just very different than my experience with the filters I've been reporting on.

Quote:

But I would still suggest that anyone reading this contemplating a big achromat study the topic of encircled energy very closely and consider buying a smaller APO or ED instead.




Assuming a Baader 495 longpass that transmits over 90% from 510nm and longer, 80% at 490 nm and zero % of light below 475nm such that there is no CA evident and no loss of sharpness and contrast from CA, what aperture APO do you think would be appropriate to replace a 5.5-6" achro and not provide noticeably less light than the filtered achro. I suggested at a minimum the filtered 140 is providing as much light as a 125mm APO and probably it is closer to a 132mm APO for total light - again without the same wavelength distribution because the 400-470nm wavelengths are completely blocked.

Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
De Lorme
professor emeritus
*****

Reged: 12/30/08

Re: CA Reduction filters new [Re: russell23]
      #6161676 - 10/28/13 12:04 AM

Thanks Dave I'm going to order one. Again thanks for doing
these comparisons. The Longpass really makes a differance.
I cannot wait to try the 82A. De Lorme


Post Extras: Print Post   Remind Me!   Notify Moderator  
eklf
Pooh-Bah
*****

Reged: 05/12/07

Loc: Carrboro, NC
Re: CA Reduction filters new [Re: russell23]
      #6161934 - 10/28/13 07:06 AM

Thanks Dave for taking the time to conduct and document the performances of these filters. Your objecive descriptions and clear demarcation of subjective perceptions were very helpful, and overall very informative. I have 127 F6.5 so I am naturally interested in the filter performances. I recently acquired #8, #11,and #12 filters, but havae not had the time to comapare them yet. On a single night's brief comaprison I felt the #11 to offer better performace on the moon compared to #8 (but somewhat dimmer), and siighty better than #12 (but with a somewhat greenish tinge that I found more pleasing than the yellow of #12). If you get a chance pop in a #11 for a different feel.

Thanks again for a well documented and informative sereis fo posts.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: CA Reduction filters new [Re: eklf]
      #6162121 - 10/28/13 09:44 AM

It seems to be that there is a difference between the theoretical science, ie, physics of light scattering/focusing and what the human eye actually sees. And there is a difference in achros, not just from brand to brand, but from telescope to telescope within a brand. I've looked through achros that were so bad no filter was going to make any difference. And I've looked through some that the view was so good you didn't need any filter. That one produced a view that was sharp, contrasty, bright with no discernible CA except on the very brightest stars. Then applying a Fringe Filter stacked with a Deep Sky Filter not only removed the CA, but improved the contrast while rendering a neutral (true) color with no noticeable light loss.

One six inch achro shows significant CA on the moon with a purple field washed across the moon's surface while the other achro of the same aperture and f ratio did not. I didn't have an APO next to the second achro to compare the view, but I did have a larger aperture SCT set up nearby and what this achro produced was every bit as good as the view the SCT showed.

Bottom line, in this dumb football player's humble opinion, based on what he's seen through the eyepiece of a few achro refractors and not understanding physics and math at all when it comes to light I certainly can understand why there are folks in each camp. If you've looked through a bad achro you'll be in Edggie's camp and be convinced no filter is going to do any good. I've seen those and I agree they can't be helped that much. But when you have looked through the eyepiece of a well corrected achro you'll understand their value and why somebody would want to own a big six inch achro.


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: CA Reduction filters new [Re: Jon_Doh]
      #6162160 - 10/28/13 10:08 AM

...Or an 8" ...

8"DG vs. 12"Portaball


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: CA Reduction filters new [Re: t.r.]
      #6162394 - 10/28/13 12:13 PM

Quote:

...Or an 8" ...

8"DG vs. 12"Portaball





That thing looks like a missile


Post Extras: Print Post   Remind Me!   Notify Moderator  
russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: De Lorme]
      #6163305 - 10/28/13 08:40 PM

Quote:

Thanks Dave I'm going to order one. Again thanks for doing
these comparisons. The Longpass really makes a differance.
I cannot wait to try the 82A. De Lorme




Thanks for the positive feedback! I was really surprised by the longpass because I have been very satisfied with the Fringe Killer. For me the longpass has replaced the FK as my filter of choice.

Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: eklf]
      #6163313 - 10/28/13 08:45 PM

Quote:

Thanks Dave for taking the time to conduct and document the performances of these filters. Your objecive descriptions and clear demarcation of subjective perceptions were very helpful, and overall very informative. I have 127 F6.5 so I am naturally interested in the filter performances. I recently acquired #8, #11,and #12 filters, but havae not had the time to comapare them yet. On a single night's brief comaprison I felt the #11 to offer better performace on the moon compared to #8 (but somewhat dimmer), and siighty better than #12 (but with a somewhat greenish tinge that I found more pleasing than the yellow of #12). If you get a chance pop in a #11 for a different feel.

Thanks again for a well documented and informative sereis fo posts.




Thank you!

Interesting! I just looked at the transmission curve data for the #11. It has an overall transmission of 40% but let's in a little more light at blue wavelengths. The #8 has 83% transmission overall. Have you had a chance to compare the CA reducing effects of the #11 compared with the other two?

Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: Jon_Doh]
      #6163339 - 10/28/13 08:58 PM

Quote:

It seems to be that there is a difference between the theoretical science, ie, physics of light scattering/focusing and what the human eye actually sees. And there is a difference in achros, not just from brand to brand, but from telescope to telescope within a brand. I've looked through achros that were so bad no filter was going to make any difference. And I've looked through some that the view was so good you didn't need any filter. That one produced a view that was sharp, contrasty, bright with no discernible CA except on the very brightest stars. Then applying a Fringe Filter stacked with a Deep Sky Filter not only removed the CA, but improved the contrast while rendering a neutral (true) color with no noticeable light loss.

One six inch achro shows significant CA on the moon with a purple field washed across the moon's surface while the other achro of the same aperture and f ratio did not. I didn't have an APO next to the second achro to compare the view, but I did have a larger aperture SCT set up nearby and what this achro produced was every bit as good as the view the SCT showed.

Bottom line, in this dumb football player's humble opinion, based on what he's seen through the eyepiece of a few achro refractors and not understanding physics and math at all when it comes to light I certainly can understand why there are folks in each camp. If you've looked through a bad achro you'll be in Edggie's camp and be convinced no filter is going to do any good. I've seen those and I agree they can't be helped that much. But when you have looked through the eyepiece of a well corrected achro you'll understand their value and why somebody would want to own a big six inch achro.




Good points! What you are saying reminds me of the recent thread here about respacing the lenses of an achromat to reduce CA. Perhaps with poorly set achromat lenses filters won't lead to much improvement.

With my scope the filters make a huge difference.

Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
SimonL
member


Reged: 09/17/07

Re: CA Reduction filters new [Re: russell23]
      #6168422 - 10/31/13 12:44 PM

Do you people use the 1.25" size or 2" version of the longpass filter?

Post Extras: Print Post   Remind Me!   Notify Moderator  
De Lorme
professor emeritus
*****

Reged: 12/30/08

Re: CA Reduction filters new [Re: SimonL]
      #6168552 - 10/31/13 01:43 PM

SimonL I use the 1.25 Longpass because it's cheaper.
De Lorme


Post Extras: Print Post   Remind Me!   Notify Moderator  
saemark30
Pooh-Bah


Reged: 02/21/12

Re: CA Reduction filters new [Re: De Lorme]
      #6168709 - 10/31/13 03:19 PM

I guess the OIII filters are the best CA reduction filters around.
Which ones are best? I have seen Lumicon lamination problems with their filters.


Post Extras: Print Post   Remind Me!   Notify Moderator  
coopman
Post Laureate
*****

Reged: 04/23/06

Loc: South Louisiana
Re: CA Reduction filters new [Re: saemark30]
      #6169068 - 10/31/13 06:48 PM

An OIII filter is good for CA reduction? Really?

Post Extras: Print Post   Remind Me!   Notify Moderator  
MrJones
Pooh-Bah
****

Reged: 09/15/10

Loc: Indiana
Re: CA Reduction filters new [Re: coopman]
      #6170105 - 11/01/13 12:03 PM

I wound up using a Wratten #12 with my AR5 after trying many filters. I only used it on the moon and planets. I was a little surprised to find that I thought the Wratten #12 was better than the #8 at everything other than a more yellow tint - and in particular it got rid of the last little bit of observable violet blue CA for me with this scope. After a little research I found some transmission spectra that support this. Note that from these you can see that the Wratten #12 has a sharper cutoff and higher overall transmission. Something to think about!

Wratten #8

Wratten #12


Post Extras: Print Post   Remind Me!   Notify Moderator  
azure1961p
Postmaster
*****

Reged: 01/17/09

Loc: USA
Re: CA Reduction filters new [Re: MrJones]
      #6172673 - 11/02/13 09:56 PM

Trouble with an OIII is its color shift isn't exactly mild and some folks would find it detrimental. Its lousy on Jupiter for example.

Pete


Post Extras: Print Post   Remind Me!   Notify Moderator  
russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: azure1961p]
      #6173465 - 11/03/13 10:43 AM

Quote:

Trouble with an OIII is its color shift isn't exactly mild and some folks would find it detrimental. Its lousy on Jupiter for example.

Pete




Not to mention an OIII filter transmits very little visible light. Look at the transmission curve for the Baader OIII on the Agena website. It has a 10 nm transmission width at 500nm wavelength. It is not intended as a CA reduction filter.

Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
russell23
Post Laureate
*****

Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: MrJones]
      #6173474 - 11/03/13 10:49 AM

Quote:

I wound up using a Wratten #12 with my AR5 after trying many filters. I only used it on the moon and planets. I was a little surprised to find that I thought the Wratten #12 was better than the #8 at everything other than a more yellow tint - and in particular it got rid of the last little bit of observable violet blue CA for me with this scope. After a little research I found some transmission spectra that support this. Note that from these you can see that the Wratten #12 has a sharper cutoff and higher overall transmission. Something to think about!

Wratten #8

Wratten #12




Interesting. These transmission curves differ from the document compiled for Eastman Kodak for all Wratten Filters. That document gives an overall transmission of 83% for the #8 and 73% for the #12. That is consistent with my experience with the Lumicon #'s 8 and 12. I took more photos the other day and the #12 eliminated CA like the 495 Longpass but unlike the longpass was darker than the #8.

I wonder how much variation there is.

Dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
coopman
Post Laureate
*****

Reged: 04/23/06

Loc: South Louisiana
Re: CA Reduction filters new [Re: russell23]
      #6173588 - 11/03/13 11:42 AM

I used my Baader longpass filter in the AR152 last night for the first time and was very happy with the improvement that I noticed. Stars were tighter pinpoints and Vega was a bright yellow star with no bluish halo. It did not seem like I was using an achromat any more. The various colors of other stars were still apparent, i.e., the longpass filter did not change all of the stars to yellow ones. This filter may have found a permanent place in my diagonal.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | (show all)


Extra information
16 registered and 26 anonymous users are browsing this forum.

Moderator:  FirstSight, panhard, star drop, dr.who 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 7556

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics