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Baader 495 Longpass filter with ST80

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#1 russell23

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Posted 08 August 2014 - 10:53 PM

Jon Isaacs loaned me one of his ST80's a few months ago to test out the effects of the 495 Longpass filter on CA.  With my Vixen 140NA there is considerable CA and the longpass filter eliminates the violet fringing.  Weather has been lousy and tonight was actually the first night with excellent skies for which I could test it out on the Moon. 

 

I used the ST80 with a 2x Barlow and a 5.5mm Meade UWA which gives 145x.  The CA without the filter was not bad, but there was some loss of sharpness and contrast evident without the filter.  The 495 Longpass is just as effective with the ST80 as with the Vixen140.  Purple fringing is eliminated and contrast is improved noticeably.  Lunar features were sharper and cleaner with the filter than without.

 

There was one crater near the terminator which had a smaller crater on the rim.  I did not notice this small crater until I added the Longpass filter.  Then I was able to remove the filter and spot the crater, but it lost some sharpness when the filter was removed.  

 

That said, the ST80 had much less CA than the Vixen 140.  So the relative effects are not as dramatic even though the final result is the same.  I think from this experience that the 495 Longpass is a excellent for a large aperture achromat, but you might get away with just a #8 light yellow with a ST80.

 

A final note - the moon wad quite spectacular using a 32mm Brandon and 2x Barlow (25x) with the ST80.  

 

Dave


Edited by russell23, 08 August 2014 - 10:53 PM.


#2 spongebob@55

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Posted 09 August 2014 - 09:35 AM

I'll be using my 495 with my 102 f./9.8 tonight, so see if there's much difference.  I don't see much CA in that scope, but your post inspires me to test it out, and see if the contrast will be boosted with the almost full moon at our public event tonight.

Thanks

Bob



#3 t.r.

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Posted 10 August 2014 - 06:46 AM

So far, in my limited observations comparing the #8 to the 495LP in my C102GT F/9.8 I prefer the #8 yellow on all objects. It seems to preserve other colors and lets them show through while still tackling the CA, while the 495LP kills CA dead, but color shifts everyhting to a deep yellow tint, with no other colors allowed to show. I haven't tried my C80SS F/5 with the 495LP yet, thats next for the rest of the year, but as you state Dave, I'm probably going to prefer the #8...again.



#4 russell23

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Posted 10 August 2014 - 08:36 AM

Hi Tim,

 

I think there must be a tipping point where the CA becomes severe enough to warrant the 495 LP.  In my experience with the ST80, the CA reduction by the 495 LP is exactly the same as  with the Vixen 140.  However, the CA with the ST80 is not that objectionable to begin with.  So I think if I decided to buy a ST80, I would use the #8 light yellow.  I would expect the same with the 102mm F9.8 achro's.  But when you get to a 127mm f6.5, 150mm f/5.9-8, Vixen 140NA, you are dealing with a scope with such severe CA that the 50% CA removal with the #8 LY still leaves a lot of image degrading CA.  That is when the 495 LP really makes its most beneficial impact.  

 

It it was nice of Jon to loan me his ST80 so that we could get some additional experience on this.  It seems like the for 102mm and smaller achromats the #8 should be sufficient.  For 127mm and larger achromats the 495 LP will be very beneficial.  What would be interesting is to find someone that could compare the #8 and 495 LP on 120mm f/5 and 120mm f/8.3 achromats.  I would bet with the f/5 you would want the 495 LP and with the f/8.3 the #8.

 

Dave

 

So far, in my limited observations comparing the #8 to the 495LP in my C102GT F/9.8 I prefer the #8 yellow on all objects. It seems to preserve other colors and lets them show through while still tackling the CA, while the 495LP kills CA dead, but color shifts everyhting to a deep yellow tint, with no other colors allowed to show. I haven't tried my C80SS F/5 with the 495LP yet, thats next for the rest of the year, but as you state Dave, I'm probably going to prefer the #8...again.



#5 saemark30

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Posted 13 August 2014 - 03:24 PM

I am interested in comparing the #8 to the 495 on a 6" f/8 achromat.

I suspect and hope the #8 will be good enough.



#6 Josef1968

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Posted 15 August 2014 - 06:43 AM

Hello!

 

The 495 ist a big option for b/w imaging on big achromats!

 

http://www.sternwart...0.at/tipps.html



#7 jrbarnett

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Posted 16 August 2014 - 09:39 AM

Dave, this thread and the other active one in this forum, and your filter article over on Astromart, has me thinking again about filtration in my 6" f/5.9 achromat.  I have a Sirius MV-20 "minus violet" filter but have no idea as to its bandpass prescription, or how it differed from the more prominent Sirius MV-1.  I also has, for a brief time, the Orion Minus Violet filter.  I have a full set of 1.25" color filters, too (10 filters in all) including the light yellow.

 

I find the 6" f/5.9 almost unusable for planetary, lunar or even moderately bright double star work with some kind of secondary spectrum suppression.  For example, even Rasalgethi at a feeble magnitude of 2.9 produces plentiful fringing at 80x or more.  The MV-20 cleans it up only partially so that the fringing at around 120x is reduced by an estimated 70%.

 

I'll give the light yellow filter a try on the scope, but in the meantime have a question for you since you've been at this for awhile:  Do you believe that there is *any* secondary spectrum suppressing filter that will render a 6" f/5.9 suitable for planetary work?  By suitable I mean allowing the scope to deliver the entire potential of its aperture, or very nearly so, at target-typical magnifications?

 

Thanks!

 

- Jim


Edited by jrbarnett, 16 August 2014 - 09:44 AM.


#8 gdd

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Posted 16 August 2014 - 10:16 AM

Has anyone tried the even lighter #12 yellow? I only have the #8 yellow to use with my 102mm f/9.8 refractor, but usually use no filter.

 

Gale



#9 De Lorme

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Posted 16 August 2014 - 01:23 PM

Jim, I was looking at the Moon last night and had forgotten I had taken out the 495 Longpass from the diagonal  where it usually sits.

When I realized this I  put it back on and detail on the Moon was so much better.  For $25{amazon plus points} it's been the best purchase

behind CR6"and eyepieces.  I strongly think you should give it a try.  De Lorme


Edited by De Lorme, 16 August 2014 - 01:24 PM.


#10 jrbarnett

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Posted 16 August 2014 - 04:29 PM

Has anyone tried the even lighter #12 yellow? I only have the #8 yellow to use with my 102mm f/9.8 refractor, but usually use no filter.

 

Gale

#12 Yellow is considerably darker than #8.

 

http://www.optcorp.c...inch-f2-12.html

 

http://www.optcorp.c...-25inch-f8.html

 

Regards,

 

Jim



#11 jrbarnett

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Posted 16 August 2014 - 04:47 PM

Jim, I was looking at the Moon last night and had forgotten I had taken out the 495 Longpass from the diagonal  where it usually sits.

When I realized this I  put it back on and detail on the Moon was so much better.  For $25{amazon plus points} it's been the best purchase

behind CR6"and eyepieces.  I strongly think you should give it a try.  De Lorme

Yeah, I think I'll give it a shot - both a #8 2" and a Longpass 2", for diagonal mounting.

 

Any of the other Baader "color correction" type filters worth trying out?

 

- Jim



#12 Sarkikos

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Posted 17 August 2014 - 11:16 AM

However, the CA with the ST80 is not that objectionable to begin with.  

 

CA with the ST80 not that objectionable? Have you viewed Jupiter through the ST80? I object!

 

:grin:

MIke



#13 gdd

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Posted 17 August 2014 - 02:48 PM

 

Has anyone tried the even lighter #12 yellow? I only have the #8 yellow to use with my 102mm f/9.8 refractor, but usually use no filter.

 

Gale

#12 Yellow is considerably darker than #8.

 

http://www.optcorp.c...inch-f2-12.html

 

http://www.optcorp.c...-25inch-f8.html

 

Regards,

 

Jim

 

Oops! Got that backwards.

 

I did some more looking on filters. The #12 yellow is a 500nm longpass, very similar to the baader 495 longpass. The #8 yellow is a 465nm longpass, not quite as severe. The #3 light yellow is a 440nm longpass if you can find one, Might let enough blue through to make for a more natural color. The baader Fringe Color alos allows 50% of the blue between 450nm and 480nm, so again a more natural color might be possible.

 

Gale



#14 jrbarnett

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Posted 17 August 2014 - 06:00 PM

Gale, that number 3 sounds intriguing.  Hmm...:thinking:

 

- Jim



#15 russell23

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Posted 18 August 2014 - 10:54 AM

Dave, this thread and the other active one in this forum, and your filter article over on Astromart, has me thinking again about filtration in my 6" f/5.9 achromat.  I have a Sirius MV-20 "minus violet" filter but have no idea as to its bandpass prescription, or how it differed from the more prominent Sirius MV-1.  I also has, for a brief time, the Orion Minus Violet filter.  I have a full set of 1.25" color filters, too (10 filters in all) including the light yellow.

 

I find the 6" f/5.9 almost unusable for planetary, lunar or even moderately bright double star work with some kind of secondary spectrum suppression.  For example, even Rasalgethi at a feeble magnitude of 2.9 produces plentiful fringing at 80x or more.  The MV-20 cleans it up only partially so that the fringing at around 120x is reduced by an estimated 70%.

 

I'll give the light yellow filter a try on the scope, but in the meantime have a question for you since you've been at this for awhile:  Do you believe that there is *any* secondary spectrum suppressing filter that will render a 6" f/5.9 suitable for planetary work?  By suitable I mean allowing the scope to deliver the entire potential of its aperture, or very nearly so, at target-typical magnifications?

 

Thanks!

 

- Jim

 

Hi Jim,

 

Your question is a tough one.  I look at this in terms of improvement in sharpness.  The filters remove portions of the spectrum so you are going to lose information carried in the 400-500nm range.  I would say that the 495 Longpass filter comes the closest because it eliminates the violet fringe completely.  The 495 Longpass allows for very sharp images compared to the unfiltered view.  It does leaves is the red CA untouched - which is not that severe with my Vixen 140, but could be more severe in other fast achromats depending upon the lense prescriptions.   I found the Fringe Killer filter and the #8 are not that useful for planetary observations with my Vixen 140NA. 

 

Keep in mind the seeing in my area is not that great for planetary observations.   But I did find on some really excellent nights I could get some pretty sharp views of Jupiter with the Vixen 140 at 200x when I use the 495 Longpass filter - and that was full aperture.  When I was using the Fringe Killer - which works the same as the #8, I would not only have the filter on my star diagonal, but I also would use a 107mm aperture mask.  And even with the aperture mask and that filter I could not push to 200x on Jupiter like I am able to with the 495 Longpass filter. 

 

So that is my best answer to you question.   I really had given up using the Vixen 140 for planetary observations until I discovered the 495 Longpass.   For lunar observations the 495 Longpass is great!   Views are very sharp.

 

Best,

 

Dave




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