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Equipment Discussions >> Refractors

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russell23
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Re: CA Reduction filters new [Re: russell23]
      #6153363 - 10/23/13 10:28 AM Attachment (55 downloads)

Baader 495 Longpass:

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Jon_Doh
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Reged: 09/16/11

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Re: CA Reduction filters new [Re: russell23]
      #6153640 - 10/23/13 12:53 PM

The Longpass does much better on a dark sky. Photos taken don't show any CA or color cast that I can tell.

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t.r.
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Re: CA Reduction filters new [Re: Jon_Doh]
      #6153657 - 10/23/13 01:05 PM

The last set of pics remind me of something...imaging is WAY LESS forgiving of CA than the eye alone, so to help put things in a visual only perspective, the first set of pics at 40x illustrates the CA I see visually at about the 150 to 200x range in my C102GT at f/10 with the #8 yellow filter. The second set of pics is really bad...way more than one would see with a filter IMHO. Maybe Dave can expand on what he sees visually with the same scope the pics are taken with...its gotta be less visually!

Edited by t.r. (10/23/13 02:21 PM)


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russell23
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Re: CA Reduction filters new [Re: t.r.]
      #6153851 - 10/23/13 02:46 PM

Quote:

The last set of pics remind me of something...imaging is WAY LESS forgiving of CA than the eye alone, so to help put things in a visual only perspective, the first set of pics at 40x illustrates the CA I see visually at about the 150 to 200x range in my C102GT at f/10 with the #8 yellow filter. The second set of pics is really bad...way more than one would see with a filter IMHO. Maybe Dave can expand on what he sees visually with the same scope the pics are taken with...its gotta be less visually!




The last set of pictures illustrates the relative performance of the scope and filters. The #8 and FK have virtually identical CA reduction performance and the violet fringe is completely removed with the longpass filter but with the noticeable color shift. I think the levels of CA in the photos are similar to what is seen on the brightest stars. The FK removes ~50-60% of the purple fringe on Vega whereas the longpass eliminates the purple fringe on Vega.

Dave


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russell23
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Re: CA Reduction filters new [Re: Jon_Doh]
      #6153857 - 10/23/13 02:48 PM

Quote:

The Longpass does much better on a dark sky. Photos taken don't show any CA or color cast that I can tell.




You are right. For deep sky you won't notice the color shift, but will notice the APO-like pinpoint precision of the stars and the much improved contrast.

Dave


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t.r.
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Re: CA Reduction filters new [Re: russell23]
      #6153869 - 10/23/13 02:55 PM

Is the longpass basically a #12 Wratten? If not, how does it differ?

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russell23
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Re: CA Reduction filters new [Re: t.r.]
      #6153914 - 10/23/13 03:18 PM

Quote:

Is the longpass basically a #12 Wratten? If not, how does it differ?




That's next on my list. I'm ordering a #12 wratten. But the odd thing about it is the published transmission curve of the longpass is that it seems to match the #8 published curves pretty closely, but it doesn't perform at all like the #8. If the published data is to be trusted it looks like this:

#8

400-460-0%
470-5.5%
480-19%
490-41%
500-63.5%
510-78%
520-700-84-92%

#12

400-490-0%
500-1.5%
510-17.3%
520-55%
530-78%
540-700-86-91%

495 longpass

400-470-0%
475-5%
490-80%
500-85%
510-90%
520-700-95%

Dave


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t.r.
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Re: CA Reduction filters new [Re: russell23]
      #6153920 - 10/23/13 03:21 PM

Wow! Thanks for that. The longpass transmits alot more light over a larger range than I thought. Wow!
So the #8 really is the "poor man's" fringe killer...Kudos to D & G for telling me this years ago.


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russell23
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Re: CA Reduction filters new [Re: t.r.]
      #6154042 - 10/23/13 04:29 PM

Quote:

Wow! Thanks for that. The longpass transmits alot more light over a larger range than I thought. Wow!
So the #8 really is the "poor man's" fringe killer...Kudos to D & G for telling me this years ago.




Absolutely correct. I see no discernable difference between the FK and #8 in terms of CA reduction and color shift and contrast/sharpness improvement. I was unprepared for how outstanding the 495 longpass would be on CA elimination.

Dave


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russell23
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Re: CA Reduction filters new [Re: russell23]
      #6156504 - 10/24/13 10:34 PM

I finally got around to ordering the #12 and 82a filters. I will see how the 82a impacts the color shift of the 495 Longpass and compare the CA reduction of the #12 with the longpass. I suspect that unlike the longpass the #12 will cause noticeable dimming.

Dave

BTW, I ordered the filters from Agena and had a shipping notice and tracking number 11 minutes later...wow!


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russell23
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Re: CA Reduction filters new [Re: russell23]
      #6160294 - 10/27/13 08:02 AM

The #12 and 82A filters arrived from Agena yesterday. There were nice clear skies this morning so I took out the scope to compare the #8 and #12 Lumicon filters against the Baader Fringe Killer and 495 Longpass with my Vixen 140 refractor.

First I took a quick look at the Orion Nebula with the 495 Longpass filter and the #12 Lumicon. With the #12 I did notice that the bright stars around the nebula and the stars of the trapezium had a golden yellow color. I noticed this with stars fainter than what I have noticed before with the 495 longpass. So I went back to the longpass and I was able to notice a golden yellow in some of the same stars, but it was not quite as obvious. This seems to fit with the transmission curves.

Next I went to the moon at 96x with my 20mm ES68 and 2" 2.4x Dakin barlow before the star diagonal. For this part I put the filters onto the 2" to 1.25" adapter as I swapped through them.

I went with full aperture instead of using the 107mm aperture mask I made last year.

1. No Filter: Obvious purple fringe and purple wash across the face of the Moon. The surface of the Moon had lavender tint to it and larger craters were fringed with purple glow as well. Nothing about the view could be called crisp.

2. #8 Lumicon Light yellow: The purple fringe was reduced in brightness and extent to only 30-40% of the original amount. Some of the highlands craters still showed some hints of purple fringing but it was now possible to get a nice sharp focus of lunar features. The surface of the Moon now looked to my eyes to be a natural white color as the purple tint was gone.

3. Baader Fringe Killer: Just about identical in performance to the #8 Lumicon. Possibly the Baader has a little better CA removal but I cannot be certain about that. Nice sharp features and same natural white view of the Moon as the #8.

4. Baader 495 Longpass: Purple fringing is completely removed. At first look the Moon appears very yellow. However, as the eyes adjust that backs off perhaps ~50% from the initial impression of the color and the Moon then appears to be a very nice golden yellow - which is how bright stars appear with this filter. Lunar features are definitely sharper than with the #8 and FK. Very crisp lunar craters and fine details across the surface seem to jump out more readily than with the #8/FK.

5. #12 Lumicon yellow: The view with this filter is essentially identical to the 495 long pass. Purple fringing is completely removed. The initial yellow impression with the filter does back off after the eyes adjust - although I think the 495 Longpass backs off a little more - and I also felt with Jupiter and brighter stars that they appeared more yellow with the #12 than the 495 Longpass.

So in summary: The #8 wratten and Baader Fringe Killer are essentially identical in performance reducing CA about 60% visually in my estimation with minimal color shift. In fact, it is possible with these filters that because the Moon showed a purple color with no filter that the net effect of these filters is to bring the color back close to neutral as compared with the unfiltered view. My eyes did not see the color of the Moon as yellow with these filters.

The Baader 495 Longpass and #12 wratten completely remove the purple fringing - its gone with these filters. The views with these two filters are virtually identical. They signifcantly sharpen star images and lunar features. I was able to spot a pinpoint sharp star near the Moon that I did not see in the unfiltered view and didn't notice with the #8/FK. The 495 Longpass and the #12 did cause a yellow color shift that is very obvious on the Moon and bright stars. This color shift seemed stronger with the #12 than the 495 Longpass when looking at brighter stars and Jupiter. On the Moon the difference in color shift was less obvious but still detectable after eyes adjusted.

My personal preference among the 4 filters is the Baader 495 Longpass. I really like the complete CA removal that this filter provides. It sharpens star images for deep sky without any obvious dimming of the view. In fact my deep sky experience on other nights has been that the filter makes it even easier to pick out faint stars in clusters than when using the Fringe Killer. So if it is removing some visible light that is normally focused, then it is a small amount of that light and well compensated for by the increased sharpness that comes with the elimination of all purple CA. I will do a more detailed deep sky comparision between the 495 LP and the #12 on the next clear night - possibly that will be tonight.

Finally, after comparing the filters I went back to the 495 longpass and also put the 1.25" Lumicon #82A filter directly onto the eyepiece. My purpose here was to see if the 82A would shift the color back toward neutral at all. To my eyes the 82A made no difference in color tone of the Moon. However ... I was extremely pleased to find out that the 82A combined with the 495 Longpass gave lunar features a very noticeable extra pop as compared with the 495 alone. I do not believe it was an increase in sharpness because the 495 Longpass provides incredibly sharp views. What the 82A did was make finer Lunar features jump out very clearly - noticeably more so than with just the 495 longpass.

So that is my summary of these filters. Any of these filters provide significant gains on an unfiltered achromat. If you are looking to clean things up to a tolerable level or have a long f/ratio achro then probably the #8 or Fringe Killer will be sufficient. If you are looking for complete CA removal and the sharpest possible views your achro can give - including deep sky - then the 495 Longpass is the best option. The #12 has a little more color shift than the 495 Longpass so that is why I don't rate it equal to the 495 Longpass.

Oh ... I should mention the one drawback to the Baader filters - and this has been a problem with every Baader Filter I have had: 1.25" Semi-apo, 1.25" FK, 2" FK, and now even the 2" 495 Longpass ... the darn threads have a tendency to snag. The last time I put the 495 Longpass on my star diagonal this morning it jammed. From prior experience I know that I will be able to get it off when everything is warmed up, but c'mon Baader - really? Isn't that the oldest part of this equipment? Machining threads? The Lumicon filters are all nice and smooth when they thread. I haven't had a Lumicon filter jam yet.

Dave


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t.r.
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Re: CA Reduction filters new [Re: russell23]
      #6160378 - 10/27/13 09:19 AM

Nice run down on all these...thanks for the work/fun!

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coopman
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Re: CA Reduction filters new [Re: t.r.]
      #6160384 - 10/27/13 09:22 AM

Thanks for all of your efforts on comparing these filters. It was very informative.

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Mike4242
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Reged: 11/02/11

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Re: CA Reduction filters new [Re: coopman]
      #6160418 - 10/27/13 09:50 AM

Thanks for doing that comparison Dave. Very good information there.

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Space Dragon
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Loc: Scotland UK
Re: CA Reduction filters new [Re: Mike4242]
      #6160438 - 10/27/13 10:07 AM

I've also found that Baader threads tend to bind and also on their T2 accessories.
I now try to avoid threading them completely on or giving them a very small amount of fine oil.
I find they can also be fiddly to get the thread on and have to be careful to avoid cross-threading.
Not great in the dark with cold hands.

Edited by Space Dragon (10/27/13 10:08 AM)


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Eddgie
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Re: CA Reduction filters new [Re: russell23]
      #6160474 - 10/27/13 10:28 AM

I have to tell you that after looking at all these pictures, I actually felt that the only "Improvement" was the removal of the fringing, and that the "data" is best presented in the unfiltered views.

I don't seem to see any additional detail with the removal of the fringing.

In fact, in the picture of the trees with leaves taken from a distance, the unfilter view seems to me to present more dynamic range and more detail.

Same with the first branch picture.

The filtered pictures all look very "Flat" by comparisions, as if I am looking though a very lightly frosted glass.

This is why I think of these kinds of filters as being cosmetic.

You remove the fringing, but you don't really put the energy back to where it belongs.

Anyway, that is my own opinion and my own experience. The filters may remove the fringing, but when I tried them, I did not think they really improved my ability to see additional detail.

Anyway, that is what I see when I looked at the pictures. No new detial, and to me, the filtered views all seemed flatter and less contrasty overall than the unfiltere pictures.

First picture of the trees with leaves was the one that I though was the best in terms of the detail I could see in the various colors of the leaves and shading. Band pass picture remnoved the fringing, but left the tree looking kind of flat and dull.

Brances pictures kind of did the same thing to me.

Oh, cosmetically better if the fringe bothers people, but from a raw performace perspective, I don't get it.


Filters cannot refocus energy, They can only take more energy out of the view. The Airy Disk is still reduced by 15% of the energy.


Extended objects still loose their contrast against the background sky.

Filters can't fix these problems.

At lest that is what I see in these pictures.

If people draw their attention away from the fringe and look instead at the details in the picture, I felt like the unfiltered pictures actually seemed to contain the most "Data" and have more range than the filtered views.

Cosmetically, removal of the fringe might be pleasing, but based on these pictures, I can't seem to see that there is any additional detail added.


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russell23
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Re: CA Reduction filters new [Re: Space Dragon]
      #6160837 - 10/27/13 02:16 PM

Quote:

I've also found that Baader threads tend to bind and also on their T2 accessories.
I now try to avoid threading them completely on or giving them a very small amount of fine oil.
I find they can also be fiddly to get the thread on and have to be careful to avoid cross-threading.
Not great in the dark with cold hands.




Ed,

The problem is that the pictures really only are useful for representing the CA removal abilities of the different filters. What you are describing about details you see in these pictures doesn't translate to lunar observations, planetary observations, double star observations, or deep sky observations. I've detailed that in my various posts on this thread and even in what I reported from this morning. I saw far more details on the Lunar surface this morning with the filters than without. The CA blurred away fine details on crater rims and across the lunar surface. Remove the CA and suddenly numerous details are either easier to see or seen that were not seen before.

Same thing when looking at Jupiter. With the Baader Longpass I was able to see sharp views of Jupiter's features at 200x with belt details that are impossible to see without the filter.

I have seen faint companion stars in fields I routinely scan which I had never noticed until I started using the 495 Longpass.

It is impossible to get pinpoint sharp stars above 100x with the Vixen 140 unfiltered. With any of these filters I can easily go to 160x or more and get nice pinpoint sharp stars if the atmosphere allows.

I've noticed more details in partially resolved clusters and even nebula such as M27 with the 495 Longpass.

These are the types of things I am seeing and they are not just cosmetic improvements - they are performance improvements as compared with the unfiltered views. I think it would be worthwhile for you to consider this point: While a filtered 140mm Achromat may not be as good as a TEC 140 APO, a filtered 140mm Achromat IS significantly better than an unfiltered 140mm Achromat. I say this because you keep talking about how the filter can't restore the light not in the airy disk as if that is some argument against the use of a filter with an achromat. It is not. An achromat is what it is and the filters make it better and yes allow the observer to see more details and push the scope to higher magnifications. These filters are not about turning an achromat into an equivalent aperture APO. They are about raising the performance standards of the achro to a higher level.

One thing to keep in mind about the pictures I posted was the day I took those pictures I was dealing with heavy cloudcover and variable amounts of sunlight. That last picture with the Baader Longpass was actually when the sun was getting close to setting and blocked by clouds. Most of the other pictures were taken with brighter sky conditions. If the darn clouds thin out later I will attempt to get some better pictures under more uniform light conditions.

Dave


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t.r.
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Re: CA Reduction filters new [Re: russell23]
      #6160995 - 10/27/13 03:47 PM

Exactly my experiences Dave...perhaps Ed was referring to filter use on SCT's.

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Eddgie
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Re: CA Reduction filters new [Re: russell23]
      #6161145 - 10/27/13 05:35 PM

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.

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

In a smaller APO though, all of the details were visible without any filter (but even here, some simple color filters can enhance the appearance of some features).

But you have convinced me that you see benefit in it, and that is the most important thing. If you are convinced that there is an improvement, then sharing the result with others is of course the right thing to do.

My advice though would continue to be to always prefer a smaller APO over a larger achromat of any kind. There is to much energy loss in an achromat and no filter made can refocus that energy.

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 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.


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..

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.


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A. Viegas
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Re: CA Reduction filters new [Re: Eddgie]
      #6161228 - 10/27/13 06:25 PM

Quote:

My advice though would continue to be to always prefer a smaller APO over a larger achromat of any kind. There is to much energy loss in an achromat and no filter made can refocus that energy.





Really? So you are saying that a 150mm Achromat will produce a less detailed image than an 80mm ED/APO because some of the light is not brought to exact focus? So what is the benefit of larger aperture? Hmmmm... well even the best 80mm APO cannot get you much past 13 magnitude, while 150mm Achromat can easily get to over 14 magnitude. I think you have a better chance of seeing faint DSOs in the larger Achro than the smaller APO and if you want to try and split some tight binaries, certainly the extra aperture helps greatly.

I certainly understand the limitations of the Achro but for those who want to push magnification on the moon or planets the larger aperture trumps the smaller APO, and using filters I suppose can cut down on the annoying fringing. In a perfect world we'd all own AP or Taks...

Al


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