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152 f/5.9 K9/F4 Doublet

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#1 BillP

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Posted 27 August 2015 - 06:17 PM

Was wondering if anyone has seen this before (TS 152mm f5.9 Großfeld refractor with 3" Crayford)...

https://translate.go...t-text=&act=url

 

Looks interesting, a wide field achromat but not the standard flint-crown doublet so it perhaps has better color correction.  There is even a color crossing graph on the lens -- http://www.teleskop-...-farbfehler.jpg

 

Was wondering what this scope's color would be compared to a conventional flint-crown achormat at an appropriate focal ratio.  Claim here is that this combo will suppress some of the color; the color blur for a conventional achromat of this aperture and focal ratio would be = 11.7 (152 f/8 = 8.6 for comparison). 

 

As the marketing states:  In Japan this refractor is even sold under the name Nerius as Halbapo.  The glasses of the 2-element lens come from Ohara (Japan) - The combination of K9 and F4 enables better color corrector.


Edited by BillP, 27 August 2015 - 06:18 PM.


#2 stevew

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Posted 27 August 2015 - 08:18 PM

Some how I don't think it's any different than the Astro Telescope 152 that Hands on Optics and Canadian Telescopes used to sell.

 

http://www.cloudynig...scopescom-r2612

 

Steve


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#3 KevH

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Posted 27 August 2015 - 09:44 PM

That reviewer stated that there was no false color on the lunar surface.  How is that possible?  False color was readily apparent with my old 4" f11 as well as my old Stellarvue 80ED... both also made by Kunming.  That is a magical 6" f5.9 scope!


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#4 Jan Owen

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Posted 27 August 2015 - 10:16 PM

Some how I don't think it's any different than the Astro Telescope 152 that Hands on Optics and Canadian Telescopes used to sell.
 
http://www.cloudynig...scopescom-r2612
 
Steve


It appears to be the same Kunming United Optics scope that's been branded by a number of different sellers, including Canadian Telescopes, Astro Telescopes, and I think even APM may sell it in Europe with a different brand name (it's on their web page as a 6" f/5.9 Starwave, but you have to do some extra digging to ferret it out - apparently they only sell it in Europe)... There's plenty CA in these scopes, but they also have gotten largely very good reviews overall (even from Ed Ting), so they're clearly doing something right, if you can get by the CA... For DSO work, they should be fine. Just stay away from bright objects!!!

Truth be known, I've been considering buying this same scope from TS myself, since Gary Hand, Canadian Telescopes, and Astro Telescopes no longer sell them, and even APM apparently doesn't want to sell to the US (though I haven't posed the question to them directly), and that eventually led me to TS...

Edited by Jan Owen, 27 August 2015 - 10:33 PM.


#5 nicknacknock

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Posted 28 August 2015 - 12:02 AM

I had this telescope for a few months and Jan's post above covers the history of the telescope.

 

Some comments stemming from personal experience (and from seeing how my observing buddy uses it - he bought it off me):

 

1. I found the weight too much for the aperture (11.3 kilograms with rings and dovetail) and being an Alt/Az guy, I got tired quickly of setting it up, as it takes me the same time to setup my 12" dob (let's ignore cooling here for a minute, although in my usual weather conditions, the dob needs only 15 minutes more to acclimate courtesy of a cooling fan).

 

2. It rides pretty good for visual on a Celestron AVX mount (that's how my buddy uses it), so it doesn't need very heavy or expensive mounts to use. For Alt/Az use you would need a beefy mount for it and definitely a nice strong tripod. The scope has a lot of mass and needs to ride well to perform.

 

3. It gives more or less the same image as a standard 8" dob in terms of light gathering (or so it feels), only sharper. Let's ignore chromatic aberration on really bright stars here.

 

4. Not a good idea to view the moon and planets with it, although a Baader Minus Fringe filter or a yellow #8 filter improves contrast (added bonus makes the moon look like Swiss cheese). It does have better correction than a standard achromat, but this is not a planetary / lunar scope. See point 5 below.

 

5. Shines with deep sky objects if you are happy with the aperture, loves a Telrad and a Nagler 31mm with a passion. This is a wide field instrument which can handle quite a lot of magnification on DSO as well.

 

6. TS ships worldwide and since you are based in the US, you don't pay VAT so reduce the selling price you see by 19%.

 

I miss that scope but I don't miss all the fuss of setting it up. If I go down that road again, I will head in the direction of the new APM 140mm. At f7 and a weight of 6-7 kilos, it should offer much better correction, handle lunar and planetary "sufficiently" well and be more gentle on mounting requirements.

 

Bill, I thought you were planning on going with the 120mm f5 achro (yes, I had one of those as well, the TS is a much better scope). What gives?


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#6 Vondragonnoggin

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Posted 28 August 2015 - 09:03 AM

I have the Astro-Telescopes version, but these stayed off grid for a little while and it is entirely possible Kunming United went ahead and changed glass types on the one linked by Bill. I never saw them previously touting glass types or extra correction for color. It is a popular scope as an achromat. It seems to me it would be an even more popular scope with color correction over standard achromat but nowhere near apo still and at a reasonable price for a large fast refractor with good 3" focuser.



#7 Toddeo

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Posted 28 August 2015 - 09:37 AM

Here is a size comparison of the CT152 with a 3" focuser - next to a Orion ST80.

Attached Thumbnails

  • CT152-1.jpg
  • CT152-2.jpg
  • CT152-3.jpg
  • CT152-4.jpg
  • CT152-5.jpg
  • CT152-6.jpg


#8 raal

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Posted 28 August 2015 - 10:24 AM

That reviewer stated that there was no false color on the lunar surface.  How is that possible?  False color was readily apparent with my old 4" f11 as well as my old Stellarvue 80ED... both also made by Kunming.  That is a magical 6" f5.9 scope!

This is what he said:

"The c.a. manifests itself as a very thin blue line on the limb of the Moon. It's only moderately bright and no more than a mild distraction. There was no sign of any c.a. on the Moon's surface features. I was a little worried crater rims might show some c.a., but they didn't..."

 

I also don't see much of C.A. at crater limbs and terminator in my Barride Optics 6" f/5 and most probably, that 6" f/5.9 is much better corrected.

Anyhow, the limb is another story, but the surface is OK. I have greater problems with lateral color of my simple eyepieces than from the C.A. of the objective lens.



#9 Sasa

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Posted 28 August 2015 - 10:26 AM

TS Individual 150/900 is great scope. My colleague from work has one. We spent some evenings observing together and few more friends. Unlike SkyWatcher 120/600 which seemed to me soft on globulard already at 70x, this one was still very good even at 176x. For DSO it is definitely great performer as it gives still 3deg FOV plus very reasonable performance at 170x. Even non-astronomera were able to glimps Leo I dwarf galaxy. I can imagine myself bring happy with such scope for couple of yeats.

Edited by Sasa, 28 August 2015 - 10:27 AM.


#10 KevH

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Posted 28 August 2015 - 10:42 AM


That reviewer stated that there was no false color on the lunar surface. How is that possible? False color was readily apparent with my old 4" f11 as well as my old Stellarvue 80ED... both also made by Kunming. That is a magical 6" f5.9 scope!

This is what he said:
"The c.a. manifests itself as a very thin blue line on the limb of the Moon. It's only moderately bright and no more than a mild distraction. There was no sign of any c.a. on the Moon's surface features. I was a little worried crater rims might show some c.a., but they didn't..."

I also don't see much of C.A. at crater limbs and terminator in my Barride Optics 6" f/5 and most probably, that 6" f/5.9 is much better corrected.
Anyhow, the limb is another story, but the surface is OK. I have greater problems with lateral color of my simple eyepieces than from the C.A. of the objective lens.

I know what he said. My question was clearly in regards to seeing none on the surface. Who studies the lunar limb anyway? I must be very sensitive to false color since I could easily see color on the surface of the terminator with scopes from the same manufacturer that have far better color correction.

It's just hard to believe is all. Makes me want to try one.

#11 raal

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Posted 28 August 2015 - 11:14 AM

Sure, it could be the sensitivity difference. It could even be the precision of the lens, but most probably is what we concentrate on looking for.

 

For me, the larger the crater at terminator, the greater the false color. Tiny craters on surface are good, riles, too. I use 3x Barlow on 16mm EP for 140x mag.

My simple EPs love Barlowing, they want me to find the right angle of view and correct centering of my pupil and then it's OK.

What I concentrate on for now, are small craters not too close to terminator. While 2.6 mile craters are obviously craters even in not so good seeing (shadow in the bowl), in moderately good seeing I see 1.9mile craters as craters.

While I'm observing small craters, I don't think of color any more, I'm just chasing the black shadow on the side of a white spot...It's a high contrast object and when seeing permits, it's there, so I'm not loosing it because of false color.



#12 Vondragonnoggin

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Posted 28 August 2015 - 11:39 AM

I use mine stricly for DSO's. Bright objects I stay away from. If th emoon was something I wanted to look at, I wouldn't be leary of looking at it with my Baader Semi-Apo filter in. I have little sensitivity to CA though and planetary/lunar viewing does not interest me much and when it does interest me, I use my MCT. 

 

Something consistently brought up in achromat discussions is planetary and lunar viewing. I don't understand this argument at all to steer away from fast achromats when there are so many other targets these types of instruments do well with.

 

Even with better color correction, if you know you are sensitive to CA, steer away from these types of scopes if your plan is get a lunar/planetary performer or concentrate on bright objects to tell everyone how the kalaidescope of false color ruined your view.

 

My Astro Telescopes 152 is the my favorite bigger scope and the views of some of the other thousands of objects readily available to me is pretty great.


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#13 Jan Owen

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Posted 28 August 2015 - 01:32 PM

These two reviews cover the scope pretty well.  It could be possible that Kunming United Optics has altered the optical prescription for this objective, but I've heard no indication of this, and I've been following this scope fairly closely for some time now...

 

http://www.scoperevi...com/page1y.html

 

http://www.astromart...?article_id=749

 

http://www.united-op...52mm_F-5.9.html


Edited by Jan Owen, 28 August 2015 - 01:38 PM.

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#14 KevH

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Posted 28 August 2015 - 01:35 PM

I only brought it up since the OP indicated that it was marketed as better than normal color correction and the linked review indicated no observable color on the lunar surface. Had that not been in the review, I wouldn't have responded. It was just a surprising observation. I'm sure it's a fine scope.

#15 jrbarnett

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Posted 20 December 2015 - 12:06 AM

It's odd.

 

Kunming makes the scope.

 

But the version sold by Altair Astro claims Schott glass, but the version by TS claims Ohara glass.

 

Even odder, Ohara makes neither a "K9" or an "F4".  But CDGM makes K9.  And CDGM makes glass used in many other Kunming scopes.  F4 is a Hoya catalog number and a Schott Catalog number (suggesting that TS is mistaken and Altair is being accurate as to glass source).

 

If the scope actually used Ohara glasses the equivalent catalog numbers would be S-BSL7/PBM4.

 

http://universalphot...CDGM_TD-USA.pdf

 

Something fishy here around glass source claims.  :thinking:

 

In any case, this is not a new scope.  It's the same scope that has been sold under many brands for many years.  And the color correction is poor on anything bright at any magnification that is not minimal.  Even the TS color crossing chart shows poor color correction:

 

http://www.teleskop-...-farbfehler.jpg

 

Regards,

 

Jim


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#16 KaStern

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Posted 20 December 2015 - 05:04 PM

Hi KevH,

 

 

I must be very sensitive to false color since I could easily see color on the surface of the terminator with scopes from the same manufacturer that have far better color correction.

 

do not worry, you are allright.

There are some stargazers out there that suffer bad from colour blindness.

 

Cheers, Karsten



#17 Brollen

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Posted 21 December 2015 - 08:38 AM

 

Some how I don't think it's any different than the Astro Telescope 152 that Hands on Optics and Canadian Telescopes used to sell.
 
http://www.cloudynig...scopescom-r2612
 
Steve


It appears to be the same Kunming United Optics scope that's been branded by a number of different sellers, including Canadian Telescopes, Astro Telescopes, and I think even APM may sell it in Europe with a different brand name (it's on their web page as a 6" f/5.9 Starwave, but you have to do some extra digging to ferret it out - apparently they only sell it in Europe)... There's plenty CA in these scopes, but they also have gotten largely very good reviews overall (even from Ed Ting), so they're clearly doing something right, if you can get by the CA... For DSO work, they should be fine. Just stay away from bright objects!!!

Truth be known, I've been considering buying this same scope from TS myself, since Gary Hand, Canadian Telescopes, and Astro Telescopes no longer sell them, and even APM apparently doesn't want to sell to the US (though I haven't posed the question to them directly), and that eventually led me to TS...

 

 

I too have heard the siren's song for this scope and almost pulled the trigger twice, once when HOO/Gary Hand sold them and later I found a used one in Craigslist at a ridiculously low price. The reviews on-whole led to think this might be a very entertaining scope, but in the end the heft, weight & mounting requirements made me back off.

 

Still I wonder ...



#18 Cotts

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Posted 21 December 2015 - 11:36 AM

Hi KevH,

 

 

I must be very sensitive to false color since I could easily see color on the surface of the terminator with scopes from the same manufacturer that have far better color correction.

 

do not worry, you are allright.

There are some stargazers out there that suffer bad from colour blindness.

 

Cheers, Karsten

...or yellowed eye lenses from age and UV exposure...  

 

My own experience from having my lenses replaced due to cataracts ipoints to the above supposition.

 

 After the first (left eye) surgery and before  the second (24 hours) I had one 'new' lens and my 'old' right lens.  The difference in colour rendition between the two was astonishing.  With the new eye whites were really white (for the first time in many, many years), to the point of being bluish-white while the same white object appeared pale yellow/tan with the old eye.  

 

As we all know, a yellow filter is also a minus-violet filter.  If two owners of the same 6" achromat see very different amounts of false colour around bright objects then I would venture to say that the person seeing the most false colour was a) younger, b) had worn UV protection when outdoors for a goodly fraction of his life or c), both.

 

Corollary:  If you have old eyes and you didn't bother with sunglasses etc. for most of your life, go ahead and get the achromat - it may work pretty well for you...

 

Dave


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#19 Mark Harry

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Posted 21 December 2015 - 01:21 PM

 If the 'right' lens shows yellowish color in retinal perception, then blue/violet is not admitted thru the eye's lens. First thing that comes to mind, is cataracts. A clouding, or milky bluish/violet tinge to looking at an eyeball suffering from this. Brilliant observation, Dave.
M.



#20 BillP

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Posted 21 December 2015 - 03:36 PM

Test your color vision -- http://www.xrite.com...-test-challenge


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#21 BillP

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Posted 21 December 2015 - 03:41 PM

In any case, this is not a new scope.  It's the same scope that has been sold under many brands for many years.  And the color correction is poor on anything bright at any magnification that is not minimal.  Even the TS color crossing chart shows poor color correction:

 

http://www.teleskop-...-farbfehler.jpg

 

 

 

But "poor" is relative.  In context though, the question is if this color crossing chart is any better or worse from a standard crown-flint achormat of same aperture and focal ratio?  That is the question I was wondering about.


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#22 KaStern

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Posted 22 December 2015 - 12:11 PM

 

Hi KevH,

 

 

I must be very sensitive to false color since I could easily see color on the surface of the terminator with scopes from the same manufacturer that have far better color correction.

 

do not worry, you are allright.

There are some stargazers out there that suffer bad from colour blindness.

 

Cheers, Karsten

...or yellowed eye lenses from age and UV exposure...  

 

My own experience from having my lenses replaced due to cataracts ipoints to the above supposition.

 

 After the first (left eye) surgery and before  the second (24 hours) I had one 'new' lens and my 'old' right lens.  The difference in colour rendition between the two was astonishing.  With the new eye whites were really white (for the first time in many, many years), to the point of being bluish-white while the same white object appeared pale yellow/tan with the old eye.  

 

As we all know, a yellow filter is also a minus-violet filter.  If two owners of the same 6" achromat see very different amounts of false colour around bright objects then I would venture to say that the person seeing the most false colour was a) younger, b) had worn UV protection when outdoors for a goodly fraction of his life or c), both.

 

Corollary:  If you have old eyes and you didn't bother with sunglasses etc. for most of your life, go ahead and get the achromat - it may work pretty well for you...

 

Dave

 

 

Hello Dave,

 

thank you for very much your report!
I quess the problem you mention may appear more often than colour blindness....

 

Best regards, Karsten

 


Edited by KaStern, 22 December 2015 - 12:34 PM.


#23 KaStern

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Posted 22 December 2015 - 12:32 PM

Hi folks,

 

the longitudinal colour aberration of a traditional flint / crown achromat is 1/2000 or even 1/1800 of the focal length.

For 900mm focal length this translates to 0.45mm or 0.5mm focal difference

between the 546nm green light (e-line) focus and the 486nm blue light (F-line) and 656nm (C-line) red light focus.

 

The chart at TS shows all these three colours and you can see the focal difference between them at the 0.7 zone

(that is where the 656nm and 486nm lines cross, both blue and red have the same focus).

 

As far as I can see the focal difference in that chart is 0.5mm.

 

Cheers, Karsten

 

Edit:
Another point you can derive from the chart is that for 486nm blue light

the focus difference between the edge of the lens and the center of the lens is about 0.8mm.

This is called spherical aberration.

For green light the correction (correction means: correction of the spherical aberration) is far better,

the focus difference between the center and edge of the lens for green light is about 2mm.


Edited by KaStern, 22 December 2015 - 12:53 PM.


#24 Jeff B

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Posted 22 December 2015 - 01:03 PM

Test your color vision -- http://www.xrite.com...-test-challenge

 

Man that test is hard!

 

I scored 15 and in the 60-69 bracket.  The bluer end was where I tended to miss.

 

Jeff


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#25 KaStern

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Posted 22 December 2015 - 01:35 PM

 

Test your color vision -- http://www.xrite.com...-test-challenge

 

Man that test is hard!

 

I scored 15 and in the 60-69 bracket.  The bluer end was where I tended to miss.

 

Jeff

 

 

 

FACT: 1 out of 255 women and 1 out of 12 men have some form of color vision deficiency.

 

Did you know that? :)




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