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Ts 152mm f5.9 widefield extravaganza

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#51 jag767

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Posted 30 April 2020 - 10:05 AM

Jag, I'm really glad you're enjoying your scope. They are a lot of fun for me.

For grins, try making a 4" (ore even a 4.5") aperture mask out of cardboard or other stiff paper, and look at the moon again. You may be surprised.

Jeff


I intend to try a few things. I'm curious to compare with my f11ed on moon and planets for kicks. Achro or not, there was a ton of detail in the eyepiece.
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#52 SeattleScott

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Posted 30 April 2020 - 10:24 AM

Jag, I'm really glad you're enjoying your scope. They are a lot of fun for me.

For grins, try making a 4" (ore even a 4.5") aperture mask out of cardboard or other stiff paper, and look at the moon again. You may be surprised.

Jeff

I made a 4” mask for my 6” F8. It helps considerably on planets.

Scott

#53 SeattleScott

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Posted 30 April 2020 - 10:35 AM

I'd recommend either the Baader Fringe Killer or (if you can find one) the discontinued William Optics VR-1. The latter is the best MV filter I've ever used. Has the same color balance as the FK, but more aggressive violet reduction.

Doubtful we'd ever see one, but I wonder what happens if you use lanthanum glass in one of the elements? Seems to work fine for ED doublets; not sure it'd make a palpable difference in a fast achro.

Either way, a 6" frac is a lot of fun. Especially under dark skies when keeping the power low.

Clear Skies,
Phil

Istar was the most recent one to make Lanthanum doublets. But they were not much less than the budget 6” Apos today. Being able to buy a 4” ED for $600 or a 6” for $2,250 pretty much kills the idea of something in between an achro and an ED.

Think of it this way. My 6” F8 standard plain Jane achro is good up to 150x on DSO. Which is about all I ever use for DSO . Maybe M13 is better at 200x. But without stepping up above say 10” aperture you probably aren’t going to use more than 150x on DSO often. And more than 10” aperture tends to put you in a different class portability wise than the 6” achro. Personally I use my 6” on a Sphinx Mount. So my 6” achro works great for DSO but not well for planetary. Just using Lanthanum to eliminate 30% of CA isn’t going to make it a good planetary scope. It would still be a DSO scope, just a more expensive one. So the Lanthanum achros never really took off, although I was tempted by the Istar Aries to get a faster 6” achro with color correction maybe closer to my 6” F8. But again it was $1,700 or whatever. Just no market for that now.

Scott

#54 SeattleScott

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Posted 30 April 2020 - 10:39 AM

It's such a big scope it makes your kitchen appliances look tiny smile.gif

All kidding aside I think that would be a good option for me in the winter when there's snow on the ground and I can't use my 8" dob. I wonder how the unobstructed aperture would compare to an XT8. Could be a nice option for deep sky.

I compared my 6” F8 achro to my Vixen 8” F4 newt. I found image brightness roughly similar. The achro gave more pleasing views of open clusters. Just tighter stars.

The 8” F6 Dob has a bit smaller CO so the stars might look a bit tighter. But I bet the 6” achro still wins on open clusters. Dob wins in portability.

Scott
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#55 jag767

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Posted 30 April 2020 - 11:27 AM

Im not sure if I want to use it stepped down, I will likely mess with filters first. I could be (and probably am) wrong, but my thought process is even filtered, you should end up with better resolution than a 4". Either way, I'm going to try and see! 😅
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#56 Jeff B

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Posted 30 April 2020 - 11:34 AM

I intend to try a few things. I'm curious to compare with my f11ed on moon and planets for kicks. Achro or not, there was a ton of detail in the eyepiece.

For me, that's part of the fun with the equipment side of this hobby.  It lends itself to easy experimentation and comparisons.  The only concern with using stops is that, with my experience testing dozens of lenses in DPAC, many, if not the majority, have subtle, circular zones right smack in the middle.  However, this is were they do, by far, the least damage to the wave front, but at reduced aperture, they will cover a larger portion of that aperture than they did before.  But, it's soooo easy to try an aperture stop and check things out.   

 

As many have said, and it's been my experience too, the moon is a solar system object special case where even "lowly" achromats can excel, providing very sharp views despite the "CA", as it has such a very large range of contrasts associated with its surface due to the abrupt shifts from the brightness of the sunlit surface and the abrupt blackness of the shadows.   I think you may have already witnessed a bit of that.  Saturn will also reveal itself rather well too.  I find that planet's rather yellowish, boiled egg yolk, appearance lends itself to the yellowish tint that an achromat displays at high power.  Jupiter is the toughest target for me with an achromat as it displays very subtle color contrasts over its surface.  However, I bet you will be surprised despite that when Jove rolls around.  Mars can also fair well as I'm convinced the design of these particular vintage achromats bring the red focus closer to the green/yellow, letting blue bloom a bit.  It will serve Mars better than you might expect as well.  

 

So, IMO, you have a bit more than a one trick pony (great low power, coma free views).  Rather it can do other tricks quite well but with certain limitations and a bit of training and experimentation by the rider. 

 

Jeff


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#57 j.gardavsky

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Posted 30 April 2020 - 12:30 PM

Im not sure if I want to use it stepped down, I will likely mess with filters first. I could be (and probably am) wrong, but my thought process is even filtered, you should end up with better resolution than a 4". Either way, I'm going to try and see!

- Stepping the aperture down to about 2/3 will reduce the spherical aberration, and eventually show the diffraction ring around the Airy disc. It can be also helpful on the close doubles.

 

- Filters help. Through the blue passband filter 470nm, the GRS and details in the bands become better visible.

Using a red filter, and even the green filters on Mars is a widespread practice.

 

Best,

JG



#58 jag767

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Posted 30 April 2020 - 01:17 PM

- Stepping the aperture down to about 2/3 will reduce the spherical aberration, and eventually show the diffraction ring around the Airy disc. It can be also helpful on the close doubles.

- Filters help. Through the blue passband filter 470nm, the GRS and details in the bands become better visible.
Using a red filter, and even the green filters on Mars is a widespread practice.

Best,
JG


Well, I have a lot to mess with. In regards the spherical error, I have to say, the view is surprising flat!

#59 SeattleScott

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Posted 30 April 2020 - 03:16 PM

Im not sure if I want to use it stepped down, I will likely mess with filters first. I could be (and probably am) wrong, but my thought process is even filtered, you should end up with better resolution than a 4". Either way, I'm going to try and see! 😅

I tried a Baader filter but prefer the cardboard aperture mask. YMMV. A lot has to do with your tolerance for color balance. Maybe 6” with filter is technically better resolution, but the aperture mask is more aesthetically pleasing since everything isn’t mustard.

Scott

Edited by SeattleScott, 30 April 2020 - 03:29 PM.

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#60 SeattleScott

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Posted 30 April 2020 - 03:25 PM

For me, that's part of the fun with the equipment side of this hobby. It lends itself to easy experimentation and comparisons. The only concern with using stops is that, with my experience testing dozens of lenses in DPAC, many, if not the majority, have subtle, circular zones right smack in the middle. However, this is were they do, by far, the least damage to the wave front, but at reduced aperture, they will cover a larger portion of that aperture than they did before. But, it's soooo easy to try an aperture stop and check things out.

As many have said, and it's been my experience too, the moon is a solar system object special case where even "lowly" achromats can excel, providing very sharp views despite the "CA", as it has such a very large range of contrasts associated with its surface due to the abrupt shifts from the brightness of the sunlit surface and the abrupt blackness of the shadows. I think you may have already witnessed a bit of that. Saturn will also reveal itself rather well too. I find that planet's rather yellowish, boiled egg yolk, appearance lends itself to the yellowish tint that an achromat displays at high power. Jupiter is the toughest target for me with an achromat as it displays very subtle color contrasts over its surface. However, I bet you will be surprised despite that when Jove rolls around. Mars can also fair well as I'm convinced the design of these particular vintage achromats bring the red focus closer to the green/yellow, letting blue bloom a bit. It will serve Mars better than you might expect as well.

So, IMO, you have a bit more than a one trick pony (great low power, coma free views). Rather it can do other tricks quite well but with certain limitations and a bit of training and experimentation by the rider.

Jeff

My 6” F8 achro can certainly deliver pleasing views of the Moon and planets. Certainly worth looking at those gems. However, even with a Baader filter, an 8” Dob kind of took my achro out behind the woodshed on Jupiter and the moon. It wasn’t necessarily a huge difference, but an obvious one. It would be interesting to have a rematch with my aperture mask, but I bet the Dob would still win. Bottom line, these big achros are not planetary scopes, but planets are still well worth the look.

Scott
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#61 j.gardavsky

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Posted 30 April 2020 - 03:45 PM

My 6” F8 achro can certainly deliver pleasing views of the Moon and planets. Certainly worth looking at those gems. However, even with a Baader filter, an 8” Dob kind of took my achro out behind the woodshed on Jupiter and the moon. It wasn’t necessarily a huge difference, but an obvious one. It would be interesting to have a rematch with my aperture mask, but I bet the Dob would still win. Bottom line, these big achros are not planetary scopes, but planets are still well worth the look.

Scott

On the Moon,

I mount the Baader Solar Continuum (540nm) narrow (10nm) passband filter, and take the Pentax SMC XO 2.5 eyepiece. And the views through my 6" F/5 are breathtaking, missing just more aperture for more resolution.

 

JG



#62 SeattleScott

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Posted 30 April 2020 - 04:04 PM

Well that’s something I wouldn’t have thought of. Basically a white light solar filter to eliminate CA? Maybe I should try my full aperture white light filter as a first test?

Scott

#63 jag767

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Posted 30 April 2020 - 04:14 PM

On the Moon,
I mount the Baader Solar Continuum (540nm) narrow (10nm) passband filter, and take the Pentax SMC XO 2.5 eyepiece. And the views through my 6" F/5 are breathtaking, missing just more aperture for more resolution.

JG


This is interesting. How would this compare to a 4" apo?
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#64 SeattleScott

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Posted 30 April 2020 - 04:21 PM

By only taking a narrow passband in the center of the visual range, it would seem this approach would effectively eliminate CA much how narrowband filters eliminate CA on nebulae. It would make the view much dimmer obviously, and might affect the color balance. But it should essentially give CA free views. The catch is the target needs to be very bright, like the Moon. It is an interesting idea for sure.

Scott

#65 kmparsons

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Posted 30 April 2020 - 04:25 PM

Wow! This scope definitely goes on my wish list. I would love to mount it on something like the Losmandy AZ8 alongside a longer-focus scope for higher magnifications. If you could get the whole set up out under truly dark skies you would be in stargazer heaven. 


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#66 SeattleScott

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Posted 30 April 2020 - 04:31 PM

It’s a rarity because you get the build quality of an Apo with a more affordable achro. It has long been on my wish list but I cheaped out and got a Meade 6” F8 instead. My son’s favorite color is red, and he loves the couple red eyepieces he has. I might just have to get the red Altair version of this scope for HIM someday,...I’m sure HE would love it...and my wife wouldn’t be on me about buying more telescopes for ME...
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#67 jag767

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Posted 30 April 2020 - 04:46 PM

It’s a rarity because you get the build quality of an Apo with a more affordable achro. It has long been on my wish list but I cheaped out and got a Meade 6” F8 instead. My son’s favorite color is red, and he loves the couple red eyepieces he has. I might just have to get the red Altair version of this scope for HIM someday,...I’m sure HE would love it...and my wife wouldn’t be on me about buying more telescopes for ME...


Thats part of what I like about it. I dont mind a little economy (fixed dewshield, non rotating focuser) as long as the focuser is good and the objective does its job, but this is every bit as decked out as their 152ed doublet, just the different lens. Very eager for the next clear night!

#68 j.gardavsky

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Posted 01 May 2020 - 04:11 AM

This is interesting. How would this compare to a 4" apo?

The refractors achieve the best Strehl in the typical range of the wavelengths 540nm - 560nm.

On my budget 6" F/5 comet hunter achro, even with the Solar Continuum filter (540nm) there is still some spherical aberration, and this should be less on your slower 6" F/5.9, which is also expected to have a finer manufactured and assembled optics. Spherical aberration and spherochromatism decrease with the decreasing speed of the doublets.

 

I would say,

that with the Solar Continuum filter, you would not see any significant performance drop on your 6" F/5.9 achro, against lets say the Vixen ED 114/600 SS (F/5.3), when comparing the achromatic and the ED doublets with the speeds between F/5 and F/5.9

 

So far I have seen the reports on the 6" F/5.9 written by experienced observers, they have rated your 6" F/5.9 designed by Kasai as a really very good achromat.

 

Looking forward to your reports,

JG


Edited by j.gardavsky, 01 May 2020 - 08:27 AM.

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#69 Phillip Creed

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Posted 01 May 2020 - 09:30 AM

One possibility to do a "layered" CA reduction plan--use both an aperture stop and a minus-violet filter.  When your f-ratio matches your aperture in inches, there's only so much an MV filter can do by itself.

A 4" aperture stop takes the scope from a 6" f/5.9 to a 4" f/8.8.  Even without filters, a 4" f/9 is a large improvement in color error vs. a 6" f/5.9, though you would lose resolution.  And a 4" f/9 would certainly be easier on the MV filter vs. full aperture.  My experience with MV filters is that they are good for roughly mimicking an achro that is 1.5X - 2.0X longer in terms of color error.  So a 6" f/6 might behave like a 6" f/10 achro (still plenty of CA, but definitely better), while a 4" f/9 would be more like a 4" f/15 achromat.

And having looked through an Edmund Scientific 4" f/15 achro, I can say as long as they're figured well, they're formidable planetary scopes.

Clear Skies,

Phil


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#70 Jon_Doh

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Posted 01 May 2020 - 01:34 PM

Turn it to the moon and up the magnification.  I think you'll be very pleasantly surprised.


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#71 jag767

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Posted 01 May 2020 - 06:38 PM

Yeah...sometimes more aperture just gives more. Really hard to argue otherwise after looking through it.

#72 daquad

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Posted 01 May 2020 - 07:10 PM

I have the Altair Starwave red version.  I use it at powers that yield wide fields for deep sky (3 degrees, 28X, to ~ 0.8 degrees, 102X).  The moon looks sharp in spite of the purple shadows.  I can go to 50X/inch for double stars. 

 

Have not tried it on the planets yet, except Venus which displays a beautiful purple aura surrounding the crescent.  Maybe in terms of CA it is as good as a 6" f/8, but I wouldn't know because I have never looked through the latter.  

 

I have verified that it is operating at full aperture.  

 

Dom Q.


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#73 jag767

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Posted 01 May 2020 - 07:49 PM

Yeah I saw that myself on the moon, thats why all of a sudden I'm mildly curious about lunar Nd planetary work with it. I also verified the aperture.
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#74 SeattleScott

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Posted 01 May 2020 - 07:54 PM

The filter isn’t a neutral density filter. It is a solar filter. The end result is greatly dimming the image but they do it in completely different ways. A neutral density filter dims across the entire spectrum so you would still have CA, it would just be dimmer. The solar filter dims by only allowing a narrow wavelength, eliminating CA.
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#75 Jeff B

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Posted 01 May 2020 - 09:00 PM

So Jag, we had some nice clear and calm time here in SW Ohio this evening.  Hopefully it's coming your way. waytogo.gif

 

Jeff

 

BTW, as others have hinted at, I personally love the deep, intense purple glow of Vega in a big achromat.  




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