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Ts 152mm f5.9 widefield extravaganza

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#151 jag767

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Posted 25 May 2020 - 06:56 AM

1. If the cluster looked dimmer then by definition it didn’t look as good. Larger color-free aperture equals more light.
2. Whether you see CA or not is irrelevant. It is in the design of the optic. You can’t see CA when used at low powers but that doesn’t mean it goes away, it just means that at low powers the aberration is too small to see. Of course, at low powers fine details are also too small to see. CA is always there. A better-figured lens will not change the amount of CA present, only a design change can do that.
3. The differences will manifest themselves when compared side-by-side and at higher powers.

Which point above are you disagreeing with?
Which point above is opinion and not fact?
Where did I say I “prefer” anything?
Where did I say these 6” refractors were inferior in "all" areas?

If you read my earlier post you would know I also own a fast achromat and love it for what it does.

No telescope is perfect. If you think these are then you are mistaken.

And BTW, you don’t have a clue about me so stop posting derogatory personal comments.

Bob


You clearly find it inferior, owning it or not. And you are 100% posting your opinion as fact. Thats not derogatory, that's how you are representing yourself.

You have your own thoughts, and again that's cool, but mine directly contradict yours. Also fine. To me, a view through a refractor is superior to a reflector. It's just what I like. Nothing you say will ever change that, regardless how irritated and defensive you get lol.
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#152 bobhen

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Posted 25 May 2020 - 08:09 AM

You clearly find it inferior, owning it or not. And you are 100% posting your opinion as fact. Thats not derogatory, that's how you are representing yourself.

You have your own thoughts, and again that's cool, but mine directly contradict yours. Also fine. To me, a view through a refractor is superior to a reflector. It's just what I like. Nothing you say will ever change that, regardless how irritated and defensive you get lol.

I just said I love my fast refractor. And now you put words in my mount by saying I find the view inferior. 

 

You keep making inferences without answering my questions.

 

Will you please point out where I posted opinion and not a fact? You can’t just say things without backing them up. Well, you can but then they don’t hold water.

 

I don’t find the view in fast achromats inferior in ALL cases or I would not have one would I. In CERTAIN cases on CERTAIN objects it is absolutely and unquestionably inferior. If a fast achromt were the best at everything, there would be no need for other designs that do things better. If you can’t understand that, you are mistaken.

 

When a fast achromat is used “OUTSIDE of its specialty niche”, you still might like the inferior view it presents – and that’s okay.  But that does not change the “fact” (not opinion) that it is still an inferior view when “compared to other designs” that are “not hampered” with the fast achromats aberrations.

 

I only get irritated when people attack me personally; otherwise I’m a kitten.

 

Bob


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#153 jag767

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Posted 25 May 2020 - 08:24 AM

Dude go have your coffee, relax. Its an online forum, nothing we say amounts to a hill of beans. I'm not responding with a cogent rebuttal because whats the point? To continue the discourse? You're ready to blow a gasket already, I'm not going to add to it. Let's just leave it at I like my 6" fast achromat for more uses than you do. Cool?

#154 russell23

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Posted 25 May 2020 - 08:40 AM

Thanks, Bob, but a 6" apo would be a bit rich for my blood (or bank account). Maybe the 8" SCT would be the better choice. I love globulars, but really I like to look at everything. As you say, the 6" achro would be good on nebulae, and, of course, wide-field views. I think the ideal set-up for me would be a dual mount, like the Losmandy Alt/Az, with a longer focus scope for higher magnification views on one side and this 6" achromat on the other. 

There is another option worth considering.   The 6" achromat with the Baader 495 Longpass filter:

 

https://agenaastro.c...-2-2458311.html

 

When I had a Vixen 140NA this filter made a tremendous difference for the scope.  In particular, with star images. It eliminated purple fringing completely without dimming the image to any extent that I could be sure.  The reason, if you look at the transmission curve, is that most of the light it removes is not focused in the image anyway.  

 

At any rate, without the filter I found star images were soft at 100x and greater.  With the filter the stars became pinpoint sharp. In particular stars in globular star clusters, tight open clusters, and double stars that were blurred out of visibility due to CA would pop nicely with the filter.  I was able to use the Vixen 140 at much higher magnifications with the filter than without.

 

When I had that scope the 495LP filter spent 100% of the time on the star diagonal.  It cleaned up the sky background as well so I found it was possible to tease more fine detail out of certain nebula with the filter than without.  The filter does remove the Light pollution bands at 405 and 436nm so that probably is another factor that helps with the sky contrast - though I think mostly that was just removal of the blurred light.

 

Now you will still see some deep red CA on brighter stars with the filter because it is a longpass. I found that was mainly a deep, deep red that flickered with brighter stars.  However, the Vixen 140 is a petzval achromat with an f/11.4 objective so with a 152mm f/5.9 you are going to see more of the red.  I noticed the same when I had a 120mm f/5 achromat - more red fringing left with the filter than I had seen with the Vixen 140.

 

The other thing about the filter is it is a yellow filter.  So bright stars appear a golden yellow like Capella.  Not everyone that has tried the 495LP likes the color shift.   I always found the color shift inconsequential for deep sky.  The visual improvement was significant enough and Capella has a beautiful color so other bright stars looking like that was not a big deal to me.   The color may not be the most pleasant for the Moon, but there you could switch to a #21 orange filter which really boosts lunar contrast anyway.  For planets, well nobody ever said a fast 6" achromat was an ideal planetary scope.  You could always use an aperture mask in combination with different planetary filters for the planets.



#155 SeattleScott

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Posted 25 May 2020 - 09:45 AM

1. If the cluster looked dimmer then by definition it didn’t look as good. Larger color-free aperture equals more light.

2. Whether you see CA or not is irrelevant. It is in the design of the optic. You can’t see CA when used at low powers but that doesn’t mean it goes away, it just means that at low powers the aberration is too small to see. Of course, at low powers fine details are also too small to see. CA is always there. A better-figured lens will not change the amount of CA present, only a design change can do that.

3. The differences will manifest themselves when compared side-by-side and at higher powers.

The above does not mean that the fast achromat did not produce a pleasing view – they can and do.

Bob

Ok let’s break this down. First he says the dimmer cluster did not look as good. He is specifically referring to someone saying the view of M13 through an achro was just as sharp as an 8” mirrored scope, just a bit dimmer. So I would tend to agree with Bob. All else equal the brighter view is better, for DSO anyway.

CA is always there, whether you see it or not. This is true. Although at low-moderate magnifications where the eye cannot detect it, I feel like that does make the CA irrelevant at least for those targets at those magnifications.

Now yeah at medium-high power it can be an issue. I remember a shootout between my 100ED and AR102 and DSO views were essentially identical until about 100x. Over 100x the achro views were still nice, but side by side you could see some softness in the achro. So I agree with Bob on that, and limit my 6” achro to 150x as a result, even on DSO.

Overall I tend to agree more than disagree, and he certainly doesn’t come across as an achro hater, even saying in many situations they provide a more pleasing view. I think the real point of his post is that there is also a place for a larger mirrored scope. Which I agree with. I have a 6” achro and I have larger mirrored scopes. They all have their place. So Bob isn’t bashing achros from what I see. He is just making the point that they are somewhat niche instruments that are best when complimented by other scopes.

Scott
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#156 kmparsons

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Posted 25 May 2020 - 11:18 AM

Thanks, Voyager I, that is a most helpful suggestion! As Bob suggested earlier, the Orion 120mm f/5 would be a less expensive wide-field scope. I assume that this filter would work just as well with it. The Orion 120mm is one of the scopes most often praised here at CN. Even with tube rings and an improved focuser (which I would want), the price is right. I am hoping to get out to far west Texas this summer--maybe the Guadalupe Mountains, the Davis Mountains, or the Chihuahuan Desert for some truly dark skies. The summer Milky Way and a wide-field scope under pristine skies....Sounds like heaven!



#157 jag767

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Posted 26 May 2020 - 10:52 AM

Here's a reasonable question. To cut out light pollution, I spend a lot of time with an Orion ultrablock filter DSO hunting. With the limited light spectrum I am looking through, would the difference between this and an apo still be evident?

I ask because I did a small experiment. On both a tree limb and neighbors chimney, I brought the magnification to 250x. Unfiltered, well, you can guess. Then I tossed the ultrablock in there. Super sharp, as in sharper than unfiltered through my 4" f11ed.

#158 SeattleScott

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Posted 26 May 2020 - 11:29 AM

The Ultrablock will eliminate CA from the view. It will also effectively eliminate galaxies and globs, and do a number on open clusters.

I had a teacher once who blew a hole through his house with a shotgun to kill a mouse. He got the mouse, but...

Scott
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#159 jag767

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Posted 26 May 2020 - 11:34 AM

The Ultrablock will eliminate CA from the view. It will also effectively eliminate galaxies and globs, and do a number on open clusters.

I had a teacher once who blew a hole through his house with a shotgun to kill a mouse. He got the mouse, but...

Scott


😂. I have a mechanics meme that starts with a wrench and ends with a torch, sadly too profane to post, but I catch your drift.

#160 russell23

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Posted 26 May 2020 - 11:52 AM

Here's a reasonable question. To cut out light pollution, I spend a lot of time with an Orion ultrablock filter DSO hunting. With the limited light spectrum I am looking through, would the difference between this and an apo still be evident?

I ask because I did a small experiment. On both a tree limb and neighbors chimney, I brought the magnification to 250x. Unfiltered, well, you can guess. Then I tossed the ultrablock in there. Super sharp, as in sharper than unfiltered through my 4" f11ed.

That is essentially what I found when I used the Baader 495 LP filter with the Vixen 140NA.  I always felt that the view could not accurately be called an APO view because you were losing a portion of the spectrum.  However, in terms of how tight the star images were, I found the Baader 495 LP seemed to make the Vixen 140 "apo-like" in that respect - sharpness of stars.



#161 SeattleScott

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Posted 26 May 2020 - 12:03 PM

That is essentially what I found when I used the Baader 495 LP filter with the Vixen 140NA. I always felt that the view could not accurately be called an APO view because you were losing a portion of the spectrum. However, in terms of how tight the star images were, I found the Baader 495 LP seemed to make the Vixen 140 "apo-like" in that respect - sharpness of stars.

Except the Baader 495 has much higher transmission than the Ultrablock.

Scott

#162 russell23

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Posted 26 May 2020 - 12:04 PM

Except the Baader 495 has much higher transmission than the Ultrablock.

Scott

Yes it does.  That is why I like it for a large achromat. 



#163 Jon_Doh

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Posted 26 May 2020 - 12:14 PM

1. If the cluster looked dimmer then by definition it didn’t look as good. Larger color-free aperture equals more light.

 

2. Whether you see CA or not is irrelevant. It is in the design of the optic. You can’t see CA when used at low powers but that doesn’t mean it goes away, it just means that at low powers the aberration is too small to see. Of course, at low powers fine details are also too small to see.  CA is always there. A better-figured lens will not change the amount of CA present, only a design change can do that. 

 

3. The differences will manifest themselves when compared side-by-side and at higher powers.

 

The above does not mean that the fast achromat did not produce a pleasing view – they can and do.

 

Bob

I should been more specific, when I said the cluster was dimmer, it was only a bit dimmer and in no way took awya from its beauty of the ability to resolve its stars.   And the absence of CA did make the view more enjoyable.  I suspect my refractor performed better regarding CA than the OP's was due to the fact it was slower.


Edited by Jon_Doh, 26 May 2020 - 12:35 PM.


#164 jag767

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Posted 26 May 2020 - 12:26 PM

That is essentially what I found when I used the Baader 495 LP filter with the Vixen 140NA. I always felt that the view could not accurately be called an APO view because you were losing a portion of the spectrum. However, in terms of how tight the star images were, I found the Baader 495 LP seemed to make the Vixen 140 "apo-like" in that respect - sharpness of stars.


I'm in such heavy LP (outside Manhattan) that I need something to cut it out regardless of what scope I'm using, but found it interesting nonetheless.

#165 jag767

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Posted 26 May 2020 - 12:27 PM

baader 495 is my next purchase 😁.

#166 russell23

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Posted 26 May 2020 - 12:37 PM

baader 495 is my next purchase .

Baader 495 LP filter is not really a light pollution filter.  It is a yellow filter that works really well for cutting purple fringing in a large achromat.



#167 jag767

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Posted 26 May 2020 - 12:39 PM

Baader 495 LP filter is not really a light pollution filter. It is a yellow filter that works really well for cutting purple fringing in a large achromat.


Yup. Want to try the continuum filter for lunar viewing as well (2nd on the list). Both based on comments here.
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#168 jag767

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Posted 27 May 2020 - 05:16 AM

Well, filter order placed. I also forgot i had an Optolong moon and skyglow filter, so dug that out to try as well.
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#169 j.gardavsky

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Posted 27 May 2020 - 10:29 AM

Well, filter order placed. I also forgot i had an Optolong moon and skyglow filter, so dug that out to try as well.

Extravagant filters to extravagant refractor.

 

Just saying,

JG

 

PS: Just ordered some extravagant Zeiss filters, have already enough those astronomy filters as usual.



#170 jag767

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Posted 27 May 2020 - 11:29 AM

Extravagant filters to extravagant refractor.

Just saying,
JG

PS: Just ordered some extravagant Zeiss filters, have already enough those astronomy filters as usual.


Lol. Just giving it the best shot possible against my 4" at higher mags and bright stuff. At lower power it already puts on a better show!
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#171 SeattleScott

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Posted 27 May 2020 - 12:19 PM

Let us know how it goes. I am really considering the solar continuum for lunar viewing.

Scott


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