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New Chromacor - RayCorr

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#26 Psion

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Posted 21 July 2018 - 01:25 PM

Maybe the new chromacorr raycorr improved that?
Clear sky,
Roland


We will see Roland. We have to try design very good corrector.

#27 Jeff B

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Posted 21 July 2018 - 03:13 PM

Another issue I've run across with my Chromacors concerns using a bino-viewer in the system.  

 

Most viewers have an optical path length of 4.5 to 5.0" or so.  If you want the achromat to be bino-friendly (no barlow type of device used) , this length needs to be taken into consideration because it adds distance between the nose of the Chromacor and the focal plane.  To compensate for this, you have to ditch the  2" diagonal (which typically have optical path lengths of 4.5 to 5 inches) and look straight through with the viewer (literally a pain in the neck) or go with a slower objective, which, in this case, F12 is the fastest with a standard 2" diagonal.   Basically, I have found that for every F stop over 8, I need to add an inch of distance between the Chromacor and the focal plane over that of the standard design distance (about 161 mm from the Chromacor's back shoulder at the end of the threads).  For example, a 6" F10 would require about two extra inches of spacing.  This is why bino-viewer use, the slowest scope I use the viewer with is F12.   Now if I go with a 2" diagonal with a shorter than average optical path length (like the Baader BBHS with quick change adapter), I can use the viewer and Chromacor in a faster system, closer to F10. 

 

But it's not that easy.  As I place a given chromacor further up in the optical path for slower optical systems,  it can add too much correction, making the system over-corrected in yellow/green.  Fortunately, the Chromacors came in different "flavors" for various degrees of SA correction of the objective lens so I can choose one which displays under-correction (a Chromacor U1 for example) for my slower achromats.  One advantage of using the Chromacors with slower systems is that as the objective gets slower than F8, the tolerances for good performance (spacing, and collimation) become wider.

 

Now say you will be using a barlow type of corrector with your viewer.  Well you have to see where focus is relative to cyclops viewing and space the Chromacor accordingly.  Oh, and don't forget about variations in where various eyepieces put their field stops.  Eyecrazy.gif  

 

So, such correctors really do need to be matched to the objective lens and system to work at their best and that's why there can really be no such thing as a "universal" corrector.

 

But when you do find the right combination, they can be very, very effective, giving APO performance in the middle of the FOV.  Most recently, I've matched up my Chromacor II, N, with an achromat stopped down to 8.25" aperture at F13 using my Denk II bino-viewers that truly does give APO performance over about the middle 4 to 5  arc minutes of the real FOV with excellent SA correction.

 

Jeff



#28 Riccardo_italy

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Posted 22 July 2018 - 02:22 AM

Just my two cents. A ray-corr makes sense if you are able to produce an "ED like" 7"-8" telescope as fast as possible at a good price point.
Ideally if you are able to produce an 8" f6 scope at a good price point and lightweight enough to be visually used on an eq6, it may sells. Of course, if the ray-corr is removable and usable in other scope, that's a good bonus.

#29 garret

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Posted 22 July 2018 - 03:20 AM

 

which 6" ED costs 1670 Euros? In Germany I haven't seen one

Including MwSt/ tax Euro 1999.= : https://www.teleskop...-Refraktor.html

 

But TS has a big problem with this telescope: https://www.cloudyni...150-on-the-way/

 

This telescope is just too cheap for a expensive Chromacor, a simple 'minus violet' or Contrast Booster filter is the way to go.


Edited by garret, 22 July 2018 - 08:30 AM.


#30 Astrojensen

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Posted 22 July 2018 - 03:43 AM

This telescope is just to cheap for a expensive Chromacor, a simple 'minus violet' or Contrast Booster filter is the way to go.

From what we hear so far, it doesn't need one. At all. 

 

 

Clear skies!

Thomas, Denmark


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#31 Astrojensen

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Posted 22 July 2018 - 04:00 AM

If I was asked about five years ago, I would have said that there was definitely a market for a chromatic corrector system, even if the price was upwards of $1500, but today, with the introduction of the APM 152 ED and the Sky-Watcher 150 ED, I just don't see it as possible any more. At least not as a common product. It simply doesn't make economic sense any longer for the vast majority of amateur astronomers, when you can get a 6" f/8 ED semi-apochromat for ~$2000 - $3000. 

 

- The color correction of the new ED's is just as good as that possible with a correcting system or just a hair worse. 

 

- The new f/8 EDs are MUCH more portable than older f/15 scopes and buying a 6" f/8 achromat and equipping it with a $1500 corrector lens to achieve what a $2000 scope does better is just plain stupid. 

 

- The new EDs don't have any issues with lateral color

 

- Nor do they have any issues with alignment of the corrector

 

- The new EDs work perfectly with binoviewers. You don't need to worry about corrector spacing and alignment, etc. 

 

 

Unless you can make a 7" f/8-10 achromat with corrector that has a fully color corrected field without lateral color over at least a 0.5° field (the diameter of the Moon), which works with binoviewers and solar wedges without any problems and costs less than $5000, I suspect the idea of a chromatic corrector is, for all practical purposes, dead for most amateurs. 

 

 

Clear skies!

Thomas, Denmark


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#32 Astrojensen

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Posted 22 July 2018 - 04:09 AM

Far more interesting to a minority of amateur astronomers would be the introduction of 6" EDs with f/ratios longer than 8 and the same glass types as the APM and Sky-Watcher 150mm's. With f/ratios of 10 - 12 (or even 15) they would have much superior color correction, possibly approaching triplet apochromats of half the f/ratio. I am already accustomed to longer achromats, so a 150mm f/12 with nearly perfect color correction for ~$3000 - $3500 (or even just the lens for ~$2500) would be HIGHLY interesting to me. 

 

But you'll need to act VERY quickly, before everyone and their grandmother runs out and buy 6" f/8 APM and Sky-watcher EDs and the market gets saturated and all potential customers for a 6" f/12 ends up with a f/8 instead and don't want to change, because they will then be forced to sell their f/8 EDs at a substantial loss. 

 

In other words, I think it'll remain a dream, too.

 

 

Clear skies!
Thomas, Denmark


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#33 macdonjh

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Posted 22 July 2018 - 06:36 AM

I will keep this short: I own a D&G 6" f/12. I considered a ChromaCorr a few years ago but did not think the extra $1000 at that time to be a good value: I already liked the view through my scope. Therefore I will not consider a $1400 unit now.

#34 macdonjh

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Posted 22 July 2018 - 06:41 AM

I also think long "apos" are a hard sell these days. I have seen a couple of threads gauging interest in 4" f/10 EDs that went nowhere. It seems refractor users want fast scopes for photography or compactness and if they want apo performance they are now willing to pay for EDs or triplets.

#35 Wildetelescope

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Posted 22 July 2018 - 07:41 AM

I have a 8.5" F12.5 achromat at our outreach facility, the CA is not enough to warrant an expensive correction system.
Visitors get so excited at seeing Saturn first time any extra halo colour just adds to the spectacle.


I think that more or less says it all. Saw the comet impacts on Jupiter with a 10 inch refractor in the ninteties. Never even noticed the CA that must have been there.

Jmd

#36 Astrojensen

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Posted 22 July 2018 - 09:06 AM

I also think long "apos" are a hard sell these days. I have seen a couple of threads gauging interest in 4" f/10 EDs that went nowhere. It seems refractor users want fast scopes for photography or compactness and if they want apo performance they are now willing to pay for EDs or triplets.

Well, I'm not so sure about that: https://astro-theke....aktur/produkte/

 

The upcoming 105/1000mm triplet has generated quite a bit of interest in Germany.

 

 

Clear skies!
Thomas, Denmark



#37 Jeff B

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Posted 22 July 2018 - 10:17 AM

I will keep this short: I own a D&G 6" f/12. I considered a ChromaCorr a few years ago but did not think the extra $1000 at that time to be a good value: I already liked the view through my scope. Therefore I will not consider a $1400 unit now.

Actually, with a properly placed U1 chromacor, you might well be shocked at the improvement in the central portion of the FOV.  

 

Yeah, $1000 USD is a bit steep for one, I suspect if you look around long enough, you can find one in the $800-$900 range, and as they are hard to scrounge out, you would have no problem reselling later if you found it not to your liking.   

 

Just a thought.

 

Jeff



#38 Jeff B

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Posted 22 July 2018 - 10:26 AM

"PETER DREW, on 20 Jul 2018 - 1:33 PM, said:

 

I have a 8.5" F12.5 achromat at our outreach facility, the CA is not enough to warrant an expensive correction system.
Visitors get so excited at seeing Saturn first time any extra halo colour just adds to the spectacle."

 

"I think that more or less says it all. Saw the comet impacts on Jupiter with a 10 inch refractor in the ninteties. Never even noticed the CA that must have been there.

Jmd"

 

Actually, I've found a lot of truth to this too.  The "lay person" at outreach is completely thrilled and just does not comment on the CA at all.  Shoot, when Vega is overhead, I regularly do comparisons with/without the Chromacor in tow using the 11" D&G achromat.  To a person, and there have been dozens, they all like the view of Vega without the Chromacor.  "It's so much prettier".  And, if the truth be known, so do I.

 

Jeff


Edited by Jeff B, 22 July 2018 - 10:27 AM.

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#39 Psion

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Posted 22 July 2018 - 12:02 PM

 

Unless you can make a 7" f/8-10 achromat with corrector that has a fully color corrected field without lateral color over at least a 0.5° field (the diameter of the Moon), which works with binoviewers and solar wedges without any problems and costs less than $5000, I suspect the idea of a chromatic corrector is, for all practical purposes, dead for most amateurs. 

 

What about this - buy Bresser achromat 150/1200 (600 EUR), extend tube for 250mm and install new lens 180mm F8 (1500 EUR) + RayCorr (1200 EUR) and together you have APO 7" for 3400 EUR.  Is it a bad idea?

 

Buy achromat 200mm F8" (4400 USD) + RayCorr (1500 USD) and you have APO 8" for 5900 USD.


Edited by Psion, 22 July 2018 - 12:06 PM.

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#40 Astrojensen

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Posted 22 July 2018 - 01:08 PM

What about this - buy Bresser achromat 150/1200 (600 EUR), extend tube for 250mm and install new lens 180mm F8 (1500 EUR) + RayCorr (1200 EUR) and together you have APO 7" for 3400 EUR.  Is it a bad idea?

 

Buy achromat 200mm F8" (4400 USD) + RayCorr (1500 USD) and you have APO 8" for 5900 USD.

Now we're talking, but how large a corrected field would the RayCorr have? And would it work with a binoviewer? I use binoviewers for lunar/planetary, so this is quite important to me, and, I suspect, to a lot of others. 

 

Even so, I am not in a financial position to buy it now, I need to save up for quite some time. 

 

 

Clear skies!

Thomas, Denmark



#41 Max Lattanzi

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Posted 22 July 2018 - 01:41 PM

Thomas,

 

Obviously I cannot speak for the RayCorr, but be assured that the Chromacor does correct the field of a Mark-V for planetary/lunar work.

 

-- Max


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#42 Starhawk

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Posted 22 July 2018 - 02:24 PM

I think there was just a block of time where people born at a certain time had viewed one of those scopes as a dream scope.  That has faded out- and now there are plenty of them.

 

And has been pointed out, the cost of decent sized achromat + a complex corrector isn't all that different from a decent sized ED scope, or even some triplets. Personally, the slow speed of the big Achros also means going for small field, which is something the EDs move away from as well.

 

-Rich

 

 

With the advent of "inexpensive" 6" ED doublets, such a device is just not going to make it for that aperture and under.  The total cost of the system would be just too much at that aperture.  Sure, in that aperture, it can give you superior correction (CA and SA) over a portion of the FOV centered on axis but it will display lateral color beyond that field.  And that's just fine for the planets, double stars, globs and the moon (if you're using mono-centric eyepieces) but it is a limitation which the the ED doublet does not have to anywhere near that degree.

 

So , IMO and IME, these devices really start to become useful, and cost effective (a sufficiently small percentage of the system cost), with large, slow apertures 7" and above.  Indeed, to me, they make a whole lot of sense at apertures 8" and above and no faster than F9.  And that's exactly how I use my Chromacors.  But even then you start bumping up against other designs like the Zerochromat, so again the bigger the aperture, the more sense they make to me.

 

Technically, the best performance is gotten when the thing is matched to, or part of, a complete system design and the slower the system, the more effective the device can be on and off axis.    

 

So it's a niche market that I see divided into two basic segments, those with existing big, slow achromats and those seeking a new big, slow achromat (though with the system properly integrated into the design, I'm not sure it should still be called an achromat).   System performance is a compromise with the former (unless customized for the lens) and optimized with the later.....but still a divided market and small sized divisions at that.

 

But I'd still like to see a Raycor series and would be curious as to just how much it would cost to have a one-off unit custom made for an 11" F12 achromat.  Even at $3K-$5K USD, it would get my attention. 

 

Jeff


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#43 Riccardo_italy

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Posted 22 July 2018 - 04:33 PM

And has been pointed out, the cost of decent sized achromat + a complex corrector isn't all that different from a decent sized ED scope, or even some triplets.

True up to 6". No longer true for larger diameters.

 

Major challenge for larger diameter is the lenght of the tube: 1000mm is ideal, 1200mm is acceptable and 1500 is the absolute limit for many many people.

 

If someone is able to come up with a 180/1200 achromat + corrector, lightweight enough for visual use on an EQ6 and around 3000€, it will sell. I'm very convinced about that. But the producer has to prove the color correction (maybe it should declare the polystrehl, provides spot diagrams and MTF and a sample for testing).


Edited by Riccardo_italy, 22 July 2018 - 04:35 PM.

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#44 Jeff B

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Posted 23 July 2018 - 11:08 AM

Ok, a little trick and hidden secret I've learned using these things.  

 

Their off-axis lateral color can be used as an Atmospheric Dispersion Compensator, ADC.  This helps with stuff low in the sky like the planets this year.  I simply move the image around the center of the FOV a bit to get rid of the AD.    Works well and for the long focal ratio achromats, I can actually get a little sharper image than directly on-axis.  

 

And ok, I'm a shameless show off. 

 

Jeff

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#45 macdonjh

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Posted 23 July 2018 - 03:08 PM

Astrojensen, the last time I saw any activity on the 4" f/10 there was curiosity but no takers. Of course, I stopped following, so I could be out of date.

Jeff B, my comments were about a personal value judgement. I do not doubt that a ChromaCorr or RayCorr would improve the performance of my D&G. However, I like the images it provides so well now I am not willing to spend $800 or more to make them better. Besides, if I find out you are right, then I have to get a second job...
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#46 Peter Besenbruch

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Posted 23 July 2018 - 03:24 PM

And ok, I'm a shameless show off.

You sure are. ;) That's quite a collection. Interesting point about using the Chromacor as a dispersion corrector.



#47 Astrojensen

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Posted 24 July 2018 - 03:15 AM

You sure are. wink.gif That's quite a collection. Interesting point about using the Chromacor as a dispersion corrector.

You can do that with any eyepiece. 

 

 

Clear skies!
Thomas, Denmark



#48 meade4ever

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Posted 24 July 2018 - 05:43 AM

What about this - buy Bresser achromat 150/1200 (600 EUR), extend tube for 250mm and install new lens 180mm F8 (1500 EUR) + RayCorr (1200 EUR) and together you have APO 7" for 3400 EUR.  Is it a bad idea?

 

Buy achromat 200mm F8" (4400 USD) + RayCorr (1500 USD) and you have APO 8" for 5900 USD.

or buy a 10" zerochromat for 10000 USD :

https://www.cloudyni...actor-for-sale/

 

or a 8" for 8000 USD :

http://zerochromat.net/8



#49 Psion

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Posted 24 July 2018 - 06:44 AM

Yes, I have 8" Zerochromat and I am very satisfied with it. Zerochromat has an advantage - optic design is usable also (at the same time) as ADC for planetary astronomy.


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#50 Jeff B

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Posted 24 July 2018 - 10:44 AM

You can do that with any eyepiece. 

 

 

Clear skies!
Thomas, Denmark

It's easier with the chromacor actually, as you don't have to get too far off-axis.


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