Jump to content


Photo

CA Reduction filters

  • Please log in to reply
210 replies to this topic

#126 russell23

russell23

    Skylab

  • *****
  • Posts: 4380
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 03 November 2013 - 06:25 PM

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

#127 gdd

gdd

    Apollo

  • -----
  • Posts: 1456
  • Joined: 23 Nov 2005
  • Loc: Lynnwood, WA (N/O Seattle)

Posted 03 November 2013 - 07:06 PM

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

#128 azure1961p

azure1961p

    Voyager 1

  • *****
  • Posts: 10352
  • Joined: 17 Jan 2009
  • Loc: USA

Posted 04 November 2013 - 02:01 AM

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

Pete

#129 Jon_Doh

Jon_Doh

    Viking 1

  • -----
  • Posts: 999
  • Joined: 16 Sep 2011
  • Loc: On a receiver's back

Posted 04 November 2013 - 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.

#130 russell23

russell23

    Skylab

  • *****
  • Posts: 4380
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 04 November 2013 - 09:42 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.


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

#131 saemark30

saemark30

    Apollo

  • -----
  • Posts: 1141
  • Joined: 21 Feb 2012

Posted 04 November 2013 - 02:23 PM

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

#132 saemark30

saemark30

    Apollo

  • -----
  • Posts: 1141
  • Joined: 21 Feb 2012

Posted 04 November 2013 - 02:32 PM

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

#133 russell23

russell23

    Skylab

  • *****
  • Posts: 4380
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 04 November 2013 - 05:00 PM

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

#134 russell23

russell23

    Skylab

  • *****
  • Posts: 4380
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 04 November 2013 - 05:01 PM

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.

#135 *skyguy*

*skyguy*

    Surveyor 1

  • *****
  • Posts: 1986
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 07 November 2013 - 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 ...

#136 Jon_Doh

Jon_Doh

    Viking 1

  • -----
  • Posts: 999
  • Joined: 16 Sep 2011
  • Loc: On a receiver's back

Posted 08 November 2013 - 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.

#137 *skyguy*

*skyguy*

    Surveyor 1

  • *****
  • Posts: 1986
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 08 November 2013 - 10:11 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.


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

#138 *skyguy*

*skyguy*

    Surveyor 1

  • *****
  • Posts: 1986
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 08 November 2013 - 02:23 PM

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!

Attached Files



#139 Jon_Doh

Jon_Doh

    Viking 1

  • -----
  • Posts: 999
  • Joined: 16 Sep 2011
  • Loc: On a receiver's back

Posted 08 November 2013 - 02:44 PM

Excellent!

#140 t.r.

t.r.

    Skylab

  • *****
  • Posts: 4443
  • Joined: 14 Feb 2008
  • Loc: 1123,6536,5321

Posted 08 November 2013 - 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?!?! :mrevil:

#141 De Lorme

De Lorme

    Viking 1

  • *****
  • Posts: 843
  • Joined: 30 Dec 2008

Posted 11 November 2013 - 09:19 PM

I had about an hour the other night to look at the moon before the clouds rolled in and was comparing the Longpass,
80A and the Moon and Sky Glow. The LongPass was again the real winner. The Moon and Sky Glow wasn't as much a help
as previous reported and the 80A made the Moon dimer.
Because on the web it said if you have 5" or bigger than go
with 80A not the 82A. In trying the M&SG coupled to the Longpass I thought it was worse. I was disappointed because
it's not what I saw the first time I used them together.
I'm going to try the 82A and see what happens. I'm really
glad I bought the Longpass. De Lorme

#142 Dakota1

Dakota1

    Viking 1

  • *****
  • Posts: 614
  • Joined: 18 Oct 2010
  • Loc: West of the Mississippi

Posted 11 November 2013 - 09:28 PM

I had a heck of a time finding the Baader 495 longpass filters. I finally found the 2 in and 1 1/4 sizes at Adorama. They are now out of the 1 1/4 but they said they still have the 2 in as of today. Thanks

Bill

#143 russell23

russell23

    Skylab

  • *****
  • Posts: 4380
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 12 November 2013 - 05:28 PM

I had about an hour the other night to look at the moon before the clouds rolled in and was comparing the Longpass,
80A and the Moon and Sky Glow. The LongPass was again the real winner. The Moon and Sky Glow wasn't as much a help
as previous reported and the 80A made the Moon dimer.
Because on the web it said if you have 5" or bigger than go
with 80A not the 82A. In trying the M&SG coupled to the Longpass I thought it was worse. I was disappointed because
it's not what I saw the first time I used them together.
I'm going to try the 82A and see what happens. I'm really
glad I bought the Longpass. De Lorme


I think you will like the 82a with the Longpass. I thought it made features really pop.

Dave

#144 De Lorme

De Lorme

    Viking 1

  • *****
  • Posts: 843
  • Joined: 30 Dec 2008

Posted 12 November 2013 - 06:38 PM

I just ordered the Lumicon. This is such great fun. The weather is going to be clear tonight so I'll be out looking at the moon. De Lorme

#145 spongebob@55

spongebob@55

    Viking 1

  • *****
  • Posts: 880
  • Joined: 26 Dec 2011
  • Loc: Bergen Co. New Jersey

Posted 17 November 2013 - 12:38 PM

I tried the longpass on the moon about a week ago. I wasn't impressed by the results. First, let me say that I was out previously and had tried it on bright stars and was very impressed. It did seem to make the CA almost disappear (using my 102mm f9.8 achromat.) But on the moon, it made hardly any difference on the edge CA and made the moon too yellow for my liking. Now there's hardly any CA with my scope anyway! So I just observed w/o the long pass filter. Next up will be Jupiter, but since I just got a new hip Monday, it might be some time before that happens. Darn it!
Sbob

#146 De Lorme

De Lorme

    Viking 1

  • *****
  • Posts: 843
  • Joined: 30 Dec 2008

Posted 17 November 2013 - 12:43 PM

Hang in there Sbob it will get better. De Lorme

#147 *skyguy*

*skyguy*

    Surveyor 1

  • *****
  • Posts: 1986
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 17 November 2013 - 01:24 PM

Two nights ago, I imaged the moon with and without mt 495 Longpass filter using a $40 dollar 70mm f/5.71 (400mm) achromatic refractor. The moon was still low in the sky .... however, I was interested in just testing the filter, not getting a pretty picture. What I did notice immediately when looking at the moon through the viewfinder with the 495 filter ... the moon was sharper and it was easier to find the perfect focus!

The unfiltered moon image is unprocessed. The only Photoshop processing done on 495 filtered image was AutoColor, AutoTone and a reduction in saturation in the yellow channel to remove some residual yellow color.

Overall, the filter does seem to produce an image with greater contrast and it did a good job of removing chromatic aberrations and restoring lost detail along the edge of the moon. Of course, there is always the possibility that some or all of the increased detail could be the result of better seeing and/or better focus between the two images. However, the 5X blowup of Mare Humboltianum (top and slightly to the right of the posted images) does show the removal of the CA allowing the detail of the mountains along the lunar rim to be revealed. At least that's my take on what is happening. :thinking:

Attached Files



#148 *skyguy*

*skyguy*

    Surveyor 1

  • *****
  • Posts: 1986
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 17 November 2013 - 01:25 PM

Unfiltered moon image:

Attached Files



#149 *skyguy*

*skyguy*

    Surveyor 1

  • *****
  • Posts: 1986
  • Joined: 31 Dec 2008
  • Loc: Western New York

Posted 17 November 2013 - 01:26 PM

495 Longpass filtered moon image:

Attached Files



#150 Rutilus

Rutilus

    Surveyor 1

  • -----
  • Posts: 1873
  • Joined: 17 Dec 2010

Posted 17 November 2013 - 01:41 PM

Out of interest, at what point would we say(i.e. f/10, f/12, f/15 etc.) that the benefit of these filters becomes reduced.
Here are 4 images taken with my 6" f/15. For two of them, I used Baader filters, natural un-filtered and a #12 Yellow filter.

Attached Files








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics