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Equipment Discussions >> Refractors

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russell23
Post Laureate
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Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: coopman]
      #6173645 - 11/03/13 12:17 PM

Quote:

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.




Great! It makes a big difference for sharpness and contrast. To this point in my continuing tests of the #8 light yellow, #12 yellow, Baader Fringe Killer, and Baader 495 Longpass, I find the 495 Longpass to be the best. The #8 and FK improve the contrast and sharpness, but the 495 Longpass eliminates the CA with no significant dimming of the object. The #12 eliminates the CA but causes some definite dimming.

Dave


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Jon_Doh
professor emeritus


Reged: 09/16/11

Loc: On a receiver's back
Re: CA Reduction filters new [Re: russell23]
      #6173904 - 11/03/13 02:59 PM

I wonder if there is another filter you could combine with the Longpass to restore/correct the color?

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SimonL
member


Reged: 09/17/07

Re: CA Reduction filters new [Re: Jon_Doh]
      #6174189 - 11/03/13 06:04 PM

A 2" size filter can be placed ahead of a 2" diagonal and used from imaging without vignetting.

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SimonL
member


Reged: 09/17/07

Re: CA Reduction filters new [Re: SimonL]
      #6174203 - 11/03/13 06:10 PM

Would you use the Longpass 495 doing imaging?

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russell23
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Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: Jon_Doh]
      #6174223 - 11/03/13 06:23 PM

Quote:

I wonder if there is another filter you could combine with the Longpass to restore/correct the color?




Not without severely reducing brightness. I used a 82A with the Baader 495 Longpass and there was a barely detectable color shift blueward, but still yellow. For lunar views it did create additional pop for features.

Dave


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russell23
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Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: SimonL]
      #6174232 - 11/03/13 06:25 PM

Quote:

Would you use the Longpass 495 doing imaging?




I'm visual only, but with the color shift involved with the Longpass I guess that would depend upon what you are looking for when imaging. Really I would think for imaging a smaller APO would be the better choice.

Dave


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gdd
scholastic sledgehammer


Reged: 11/23/05

Loc: N Seattle suburb, WA
Re: CA Reduction filters new [Re: Jon_Doh]
      #6174298 - 11/03/13 07:06 PM

Quote:

I wonder if there is another filter you could combine with the Longpass to restore/correct the color?





The 495 longpass is a yellow filter that works by blocking out the blue end of the spectrum past 495nm. To restore/correct the color you would need to add the blue back in. Filters cannot add color that is not there, and even if it could the added blue would be out of focus and recreate the blue haloes you are trying to remove. The only way to partially correct the color is to replace the 495 longpass with a lighter yellow filter, maybe a Number 8 which passes a bit more of the blue end.

If you were imaging you could use 495 longpass to create the red and green channels of an color image using a DSLR or OSC camera, then use a blue filter by itself to replace the blue channel.

Gale

Edited by gdd (11/03/13 07:13 PM)


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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: CA Reduction filters new [Re: coopman]
      #6174786 - 11/04/13 02:01 AM

Well - Vega is not a yellow star by any stretch. Perhaps an effect crested by the filter?

Pete


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Jon_Doh
professor emeritus


Reged: 09/16/11

Loc: On a receiver's back
Re: CA Reduction filters new [Re: gdd]
      #6175057 - 11/04/13 09:25 AM

The reason I asked is because when you combine a Moon and Skyglow filter with the Fringe Filter it restores color very close to natural. Some CA will still be present on bright objects like Vega, but the result is not as strong as the semi apo, which uses the same concept, but with more filtering and thus greater light loss.

Regardless of the slight color shift I do like how well the Longpass filter works for astrophotography. I haven't seen any CA in photos taken with this filter and the shift in color can easily be corrected in Photoshop. If nothing else, this filter makes astrophotography a reality with an achro.


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russell23
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Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: Jon_Doh]
      #6175085 - 11/04/13 09:42 AM

Quote:

The reason I asked is because when you combine a Moon and Skyglow filter with the Fringe Filter it restores color very close to natural. Some CA will still be present on bright objects like Vega, but the result is not as strong as the semi apo, which uses the same concept, but with more filtering and thus greater light loss.

Regardless of the slight color shift I do like how well the Longpass filter works for astrophotography. I haven't seen any CA in photos taken with this filter and the shift in color can easily be corrected in Photoshop. If nothing else, this filter makes astrophotography a reality with an achro.




That is true, you can photoshop the colors to restore neutrality and the filter eliminates the CA so you don't have to mess with that. You are right in that sense that the 495 Longpass makes the achro suitable for AP. I guess the one thing that Ed points out that is relevant here is that because the defocused light is not restored any details that the blue wavelengths carry more strongly than other wavelengths would be lost.

From my point of view visually, that lost information is not as critical as the fact that I can see more details with the filter than I can without the filter simply because the image is sharpened up.

Dave


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saemark30
Pooh-Bah


Reged: 02/21/12

Re: CA Reduction filters new [Re: azure1961p]
      #6175587 - 11/04/13 02:23 PM

What do you think about a K2 yellow filter?
Is it as good as a #8, stronger or weaker?


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saemark30
Pooh-Bah


Reged: 02/21/12

Re: CA Reduction filters new [Re: saemark30]
      #6175612 - 11/04/13 02:32 PM

And a #12 filter looks to behave like the Longpass 495 filter.

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russell23
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Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: saemark30]
      #6175894 - 11/04/13 05:00 PM

Quote:

And a #12 filter looks to behave like the Longpass 495 filter.




Yes, but the #12 has a visually detectable dimming effect as compared with the 495 Longpass. I've seen this both in daytime pictures and nighttime comparisons of the Moon, Jupiter, and nebulous deep sky objects such as emission nebula and partially resolved star clusters. All of these appear brighter with the 495 Longpass than with the #12.

Dave


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russell23
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Reged: 05/31/09

Loc: Upstate NY
Re: CA Reduction filters new [Re: saemark30]
      #6175895 - 11/04/13 05:01 PM

Quote:

What do you think about a K2 yellow filter?
Is it as good as a #8, stronger or weaker?




I've never tried the K2 so I can't say.


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*skyguy*
Carpal Tunnel
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Reged: 12/31/08

Loc: Western New York
Re: CA Reduction filters new [Re: russell23]
      #6181108 - 11/07/13 01:48 PM

I just got my Baader 495 Longpass filter in the mail, today! I can't wait to try it out on several achromatic refractors I own.

However, all the talk about about its suitability for use in astrophotography has me confused ... especially the posts on how the color shift can be easily corrected in Photoshop. Since most of blue end of the spectrum has actually been blocked/removed ...I really don't see how the blue can be restored.

I tried Photoshoping one of posted 495 filtered images and while I could get a reasonably color balanced image, a large part of blue fringing was also restored and now very visible in the image!

If someone would post the work flow in Photoshop detailing the steps to color balance a 495 filtered image ... that would be really great!

Thanks ...


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Jon_Doh
professor emeritus


Reged: 09/16/11

Loc: On a receiver's back
Re: CA Reduction filters new [Re: *skyguy*]
      #6182374 - 11/08/13 07:33 AM

Go to filter menu, select Lens Correction and check Chromatic Aberration box. This will automatically remove most if not all of the CA. Additional adjustments can be made with the sliders. In Lightroom go to Lens Correction in the Develop Module and check the CA box.

Frankly, with this filter I haven't seen the purple halos you typically see in photos taken with achros. The only adjustment that seems is necessary is removing the yellow cast this filter introduces on bright stars. That's easy to fix in Photoshop or Lightroom too.


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*skyguy*
Carpal Tunnel
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Reged: 12/31/08

Loc: Western New York
Re: CA Reduction filters new [Re: Jon_Doh]
      #6182621 - 11/08/13 10:11 AM

Quote:

Go to filter menu, select Lens Correction and check Chromatic Aberration box. This will automatically remove most if not all of the CA. Additional adjustments can be made with the sliders. In Lightroom go to Lens Correction in the Develop Module and check the CA box.




Thanks ... sounds good ... I'll give it a try!


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*skyguy*
Carpal Tunnel
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Reged: 12/31/08

Loc: Western New York
Re: CA Reduction filters new [Re: *skyguy*]
      #6183072 - 11/08/13 02:23 PM Attachment (25 downloads)

I haven't had the chance to test my 495 Longpass filter on the night-sky ... clouds, clouds and in the near future more clouds!

However, I couldn't resist testing it out in the daytime ... between the rain and snow showers! I used my very inexpensive 70mm f/5.7 (400mm) achromatic refractor and an unmodified Canon DSLR. The test object was an old barn located about 600 feet from the camera. The posted test image shows a 3X enlargement of the corner of the barn's roof with several foreground power lines. Color correction was done in Photoshop (no other processing was done) using only the "Auto Color" and "Auto Tone" buttons ... which elicited from me the very much coveted "Oh, WOW!" exclamation when the processed image was displayed! When compared to the original unfiltered image ... the corrected, filtered image looked like a blue fog had been lifted right off it! This image showed a significant increase in sharpness and contrast over the unfiltered image along with an almost total reduction of chromatic aberration. However, the exposure time of the filtered image did need to be increased from 1/500th of a second to 1/350th of a second to equalize the total exposure between both images. I've become a convert!

I'm looking forward to the opportunity to try this filter out under the stars ... if it ever clears up ... maybe early March!


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Jon_Doh
professor emeritus


Reged: 09/16/11

Loc: On a receiver's back
Re: CA Reduction filters new [Re: *skyguy*]
      #6183105 - 11/08/13 02:44 PM

Excellent!

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t.r.
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Reged: 02/14/08

Loc: Upstate NY
Re: CA Reduction filters new [Re: *skyguy*]
      #6183112 - 11/08/13 02:47 PM

Can't wait to see if a few pics can be passed off as ED doublets or even an apo..who's gonna give it a try?!?!

Edited by t.r. (11/08/13 02:47 PM)


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