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150mm F5 achro + a new Chromacor. First test.

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#1 ValeryD

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Posted 29 March 2010 - 03:38 AM

Yesterday evening I tested a new, special version of a Chromacor-I with a very good (no SA) 150mm F/5(!) Sky Watcher achromat.
Due to such fast F/ratio a standard Chromacor-I will work poorly, introducing much of spherical aberration and it's color correction power will be less noticeable.
A new version of a Chromacor-I has been designed specially
for such a ultrafast achromats.
The new version has shortened back focal length and therefore it does not work with 2' diagonal. It works in combination Chr + 2' visual back + 1.25' star diagonal.

My primary goals were:

1. Is such a Chromacor can be precisely collimated in such an ultra-fast achromat.
2. How good is a resulting color correction.
3. What is the difference in performance between unaided achromat and with special Chromacor installed.


1. After installing a Chromacor, it took only 10 minutes to collimate it precisely. No coma, no asymmetrical color fringes were finally seen. Image of a star at 188x magnification was round and absolutely symmetrical.
But firstly I removed a slop in a focuser (adjusting two 1.5mm allen screws). Following more precise adjusting of the same screws allow me to collimate a focusing tube. After a collimation procedure a focusing tube became fully concentric with telescope optical axis.
After these first collimating steps I installed a Chromacor and pointed it on distant (1 mile away) bright mercury street light. It's image was symmetrical.
Then I pointed a telescope at Procion. Star was round and fully symmetrical at 188x (Aries SPL 4mm eyepiece).
Collimation was spot in and now I can test a telescope.
Conclution: despite of ultra-fast F/5 focal ratio, a new Chromacor can be easily precisely collimated.


2. First targets were Procion and Sirius.
Sirius was already very low above south-west horizon and showed much of atmospheric dispersion. However, in focus, no violet fringes around it were seen. The star has it's natural slightly bluish color. But I knew, that some residual violet should be seen (according my computer simulations). Atmosphere this evening was not ideal in transparency and Sirius was very low above horizon. So, violet can be attenuated by atmospheric dust and humidical particles.
I pointed my telescope on Procion. Atmospheric dispersion was much less disturbing, atmospheric extinction was much less than with Sirius. Procion is a 0m magnitude white star — bright and hot enough to have strong violet emission in it's spectra. However I wasn't able to see any violet fringe around this star. The only colors I saw were atmospheric dispersion. Then I have recollected, that my eyes can have different color perception. I looked at Procion by my left eye and have seen a very weak very deep violet fringe around it. But it was almost illusive.
The last hard test for color correction was a distant bright mercury street light. In focus it shows no false colors, no at all.
Conclution: color correction in such a combo (150mm F/5 achro + new Chromacor-I) is very very good and fully corresponds to computer simulations. completely APO-like performance.
Very much like in my 125mm F/8 ED doublet BORG.


3.The difference in performance between un-aided 150mm F/5 achromat and the same achromat aided with new version of a Chromacor-I (F version, «F» states for Fast) is really dramatic. Much more dramatic, than in the case of 150mm F/8 achromat + standard Chromacor-I. While in un-aided telescope Sirius, Procion and a bright mercury lantern literally bathed in a dark blue and purple fringes, in a telescope with the Chromacor F they were in their natural colors, pure and clear.
Mars showed no albedo features in un-aided telescope. More so, I wasn't able to focus it
precisely - in each moment I wasn't sure I found best focus. With Chromacor F installed
Mars was free of false colors fringes, has it's pure natural colors and was crisp. Some albedo
features were seen. Seeing was not good enough for detailed observing, but the difference was absolutely dramatic. With Chromacor F installed this scope has full planetary capability.

Valery Deryuzhin.

#2 Cotts

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Posted 29 March 2010 - 06:59 AM

Well done Valeri. Why don't you manufacture a 6-inch f/5 refractor with a built-in, pre-aligned Chromacorr? (User alignable as well) Such a scope would be very popular, I suspect. Then you could produce an 8-inch f/5 or f/6 which would be even more popular.
Dave

#3 JacobD

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Posted 29 March 2010 - 07:10 AM

But how many 150mm F5 achros from Synta are spherical aberration free??

I think that Valery has rare one!

How many you need to buy for choose that one?

#4 astroneil

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Posted 29 March 2010 - 07:23 AM

Same thought occurred to me.

#5 AlienRatDog

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Posted 29 March 2010 - 08:12 AM

So we cannot use 2" eyepieces with it? Also us the Chromacor in general going to come back?

#6 Cyclop_si

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Posted 29 March 2010 - 08:13 AM

is positioning/mounting of the new Chromacor as critical as is with old version?

#7 ValeryD

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Posted 29 March 2010 - 08:31 AM

But how many 150mm F5 achros from Synta are spherical aberration free??

I think that Valery has rare one!

How many you need to buy for choose that one?


You will not believe me, but I just gave a call to a local dealer and ask him. He told me, that he has only one single such telescope at his stock. He checked it and it was null spherically! A lottery Jack pot hit, I do understand, but it happens!


This is rare case, of course. But not much more rare case, than with usual telescope 150mm F/8.
We can easily go with a common before practice - to estimate
a SA in a scope and then to order a Chromacor F with about the same SA negative to measured value. I see no real problem here.

#8 ValeryD

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Posted 29 March 2010 - 08:36 AM

So we cannot use 2" eyepieces with it? Also is the Chromacor in general going to come back?


Yes, at moment it seems, that 2" can't be used. But I have an idea how to bypass the given obstacle.

At this moment I can't tell you exactly if a Chromacor is going to come back. No definitive plans at this moment.

#9 ValeryD

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Posted 29 March 2010 - 08:43 AM

is positioning/mounting of the new Chromacor as critical as is with old version?


Yes. But if one do understand what to do, then it is not more difficult than collimation of a secodary mirror in reflectors. Even easier.
In the case of Chromacor return, it will have fully user adjustable diagonal and they all will be factory pre-adjusted and sealed.

The main factors which will define Chromacor's return is
glass availability and enough demand.

#10 ValeryD

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Posted 29 March 2010 - 08:45 AM

is positioning/mounting of the new Chromacor as critical as is with old version?


Yes. But if one do understand what to do, then it is not more difficult than collimation of a secodary mirror in reflectors. Even easier. We will create a fully illustrative page in the Internet and everyone will easily understand what and how to do.
In the case of Chromacor return, it will have fully user adjustable diagonal and they all will be factory pre-adjusted and sealed.

The main factors which will define Chromacor's return is
glass availability and enough demand.

#11 JacobD

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Posted 29 March 2010 - 09:06 AM

Valery,
what about other short refractors, I think about 150mm f5,9 and 150mm f6,5 ??
Is your new chromacor suitable for them??

#12 Jeff B

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Posted 29 March 2010 - 09:46 AM

And the lateral color?

#13 ValeryD

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Posted 29 March 2010 - 12:50 PM

Valery,
what about other short refractors, I think about 150mm f5,9 and 150mm f6,5 ??
Is your new chromacor suitable for them??


Yes, it does. With a bit longer back focal length. Color correction will be even better then.


And the lateral color?


It is small and in visual observing not disturbing at all.
I have placed bright star at the edge of the FOV in 4mm and saw no lateral color.

#14 Edwin Quiroga

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Posted 29 March 2010 - 06:08 PM

Valery, That Chrocamacor is available at the States right now?

#15 AlienRatDog

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Posted 29 March 2010 - 07:02 PM

WE want chromacors!!!

#16 watcher

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Posted 30 March 2010 - 01:10 AM

But how many 150mm F5 achros from Synta are spherical aberration free??

I think that Valery has rare one!

How many you need to buy for choose that one?


Pretty much all of them should be null for SA, or very close to it. They are aspherical lenses. All of the Omni refractors are.

Joe

#17 ValeryD

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Posted 30 March 2010 - 04:06 AM

Valery, That Chrocamacor is available at the States right now?


Only standard versions of a Chromacor-I and II and only second-hand on the AstroMart selling.

#18 AntarcticDave

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Posted 30 March 2010 - 11:12 AM

Valery, great news. I hope the new units can go into production.

#19 skyjim

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Posted 30 March 2010 - 12:35 PM

Dont hold your breath Abe!

#20 Sol Robbins

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Posted 30 March 2010 - 05:51 PM

Valery,

That's good news. I still use my 6" f/8 with Chromacor II the most. After about 10 years it never fails me.

#21 Jim Curry

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Posted 01 April 2010 - 06:59 AM

"The main factors which will define Chromacor's return is
glass availability and enough demand. "

Well with Istar coming out with their version of a CA ameliorator you'd better get shopping for glass... ;)

Jim

#22 ValeryD

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Posted 01 April 2010 - 11:10 AM


Well with Istar coming out with their version of a CA ameliorator you'd better get shopping for glass... ;)

Jim


When, if ever, you will see a REALLY WORKING sample of a color corrector and it will be not a Chromacor and will cost lower, then I will hear your advice.

#23 robboski2004

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Posted 03 April 2010 - 03:26 PM


the main factors which will define Chromacor's return is
glass availability and enough demand. [/quote]

Valery,

please supply a complete list of glass types and i will start looking ! :bigshock:

regards
Ian.

#24 Mark Harry

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Posted 20 April 2010 - 06:42 AM

Count me in. I want one. I have looked hard for good refractor glass, and have FK5 and KzFS4 for an achromat of 5" F/13. Can I shorten up the scope if I design for your Chromacor?
Mark

#25 ValeryD

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Posted 23 April 2010 - 02:58 PM

Count me in. I want one. I have looked hard for good refractor glass, and have FK5 and KzFS4 for an achromat of 5" F/13. Can I shorten up the scope if I design for your Chromacor?
Mark


Mark,

Will you make the objective yourself?
The KzFSN4 glass is quite unstable chemically. It must be
coated in a few hours after the lens is finished and both surfaces are refreshed during 5min polishing.


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