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ISTAR 8" F8.8 With Chromacorr II

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#1 James Ling

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Posted 15 June 2013 - 05:30 AM

Hi ALL....

As I have acquired the ISTAR 8" F8.8 for more than 2.5 years, only this year I made the decision to enhance its performance by getting the Chromacorr II...

As I do not want to purchase just the Chromacorr II, and then spend time to make the spacers and getting it properly aligned, I go directly to Valery, and he configured the Chromacorr II for my ISTAR 8" F8.8, so that it is just plug and use straight away....

The Chromacorr II is shipped two weeks ago, and arrived last week, but I only went to my local post office to collect it, since I am working oversea, and back during the weekend....

REgards

James Ling

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#2 James Ling

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Posted 15 June 2013 - 05:37 AM

Last weekend supposed to do the chromacorr II field test at my friend's roof top observatory, whereby my ISTAR has been left at his place since the last shootout....

But my friend only discover that his motorized canopy is stuck, and damaged , during the very last minute, we have no choice but to get it repaired , and do the Chromacorr II field test in another week...

REgards

James Ling

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#3 James Ling

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Posted 15 June 2013 - 05:44 AM

Although the replacement part for the motorized canopy has not being replaced , but the contractor already did a temporary fix..., as such tonight we are going ahead with the Chromacorr II field test, even though we are now hit with heavy haze, from Indonesian fire.....

I hope this field test will be a positive one, transforming the ISTAR 8" F8.8 from classic achro to ED APO (visual)....
after tonight 1st field test at my friend's roof top observatory...

Our prime target will be the 7 days old moon and Saturn....

Will update all of you, after I am back from the field test tonight....

REgards

James Ling

#4 Gord

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Posted 15 June 2013 - 08:31 AM

Congratulations James!

I think you are going to be _very_ impressed! :jump:

I had mine out last night and the views are very apochromatic. It will allow you to unleash all the potential of your lens!

Look forward to hearing your report!

Clear skies,

#5 Jeff B

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Posted 15 June 2013 - 09:54 AM

Me too Gord. Last night here in SW Ohio was one of those rare special nights with stable air and a dry clear atmosphere. The Moon and Saturn were spectacular then later came M13 (wow).

I used the following with my 11" F12 D&G achromat, Intes Deluxe diagonal and Denk IIs (most eyepieces were pairs of my good old Celestron Silver Top Plossls):

7" aperture stop, 4" spacer infront of the diagonal, Chromacor I U-1. Complete APO performance, even at the 300X max. Even the lateral color was reasonnably well controlled at low-ish powers (110-150X). I soon progressed to the 8.5" stop as the lens and atmosphere calmed.

8.5" aperture stop, 4" spacer, Chromacor I U-1. This is a definate sweet spot for this lens and typical seeing around here. Complete APO performance similar to using the 7" stop but the resolving power of the larger aperture was immediately obvious. The transitions from lunar crater ridges to the shadows over the floors was striking. The crater floors were jet black at any magnification up to my max of 300X. There was that distinct, sharply etched rubble effect that good optices immediately display, as a friend of mine said, "Like somebody took a handfull of sharp pebbles and threw them out onto the surface around the craters." Saturn was amazing with the planets ball looking like a hard boiled egg yolk. Many, many white streaks were visible (as well as moons), Cassinni's completely obvious all the way around, Enke's and Crepe visible with care. So I put in the 9.5" stop.

9.5" aperture stop, 2" spacer and Chromacor I N. Similar to the 8.5" stop with the extra inch aperture noticable but a little purple starts to be seen on lunar crater walls. No purple on Saturn, which is yellowish anyway. Quickly moved to the full 11" aperture.

Full 11" aperture with no spacer and Chromacor I O-1. WOW take everything I said about the 8.5" stop and add 40% better resolution and almost 2X brightness. The planet looked 3D and the rings were taking on that subtle, rough phonograph record look. Satrun looked commpletely etched and "fake", "that can't possibley be real!" Boy it was though. The increased resolution at full aperture was well worth the penalty of slightly more secondary spectrum. I did not look at the Moon this way as it was now low in the sky, but I rarely use full aperture on the Moon anyway so I turned the big guy loose on M13 (WOW), Izar & the double double(both beautiful but I typically use the 7" & 8.5" stops for doubles)and Vega (FANTASTICALLY, intensly, bright blue embedded in a beautiful, subtle, dim purple).

Conventional wisdom would say that the Chromacor O-1 would not be suitable for this lens at full aperture and lead to decided over correction. However, that's not the case as this combination is killer. I suspect this works as the lens at full aperture is mildly undercorrected and perhaps the O-1 is not really an O-1 (some, like my U-1, were missed marked). But for what ever the reasons, the combination WORKS and works WELL, giving color performance almost identical to a 4" F12 achromat using the AP Max Bright diagonal and a 4" F15 using the Intes diagonal (The Intes diagonal is excellent but does have a very subtle, but noticable yellow tint to it, like a very weak minus violet filter which works most effectively with the D&G using the 9.5" aperture stop and full aperture.). Yeah there was a bit of purple on Vega but the contrast between it and the intense pure blue of the star was strikingly beautiful.

So James, not to steal your thread but what did you come up with? One of my ATM projects is an 8" F9 achromat and I just happen to have a Chromacor II N. :grin:

Jeff

#6 James Ling

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Posted 15 June 2013 - 11:23 AM

Hi Gord and Jef....

Thanks for the sharing on your experience on using the chromacorr....

Hi ALL...

As I just returned back form my friend's place , after 2 short hours of testing...the chromacorr II with my ISTAR....

Although tonight the weather is very hazy, but yet I can see something different between using the chromacorr II ....

1. The 7 days old moon is still bright enough, to see the improvement on the CA level....

2. Without using the chromacorr II , we can see the thin stripe of greenish-yellow CA, on the curve edges of the 7 days old moon...
With the chromacorr II, the the thin stripe of greenish-yellow CA, is still there, although it seems to be lesser...

3. Without using the chromacorr II , we can see the the purple CA, on the curve edges of the 7 days old moon..., which is many times thicker then the green colour...
With the chromacorr II, the purple CA is completely gone....

I took both photos with my camera phone, but the result did not show exactly what is seen..., between actual visual, and downloaded onto computer...
(Photo shown is with chromacorr II)

REgards

James Ling

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#7 James Ling

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Posted 15 June 2013 - 11:43 AM

Hi ALL...

I did point the ISTAR to Saturn, but due to the hazy sky condition, I could only able to use my 9mm Nalger to power up Saturn till 200X...

I tried to use my 4.8mm Nalger , but the image breakdown...

At 200X, both the views from with and without the chromacorr II could not show the big difference, as the ISTAR itself already a killer at moderate power....

In fact tonight there are 5 moons spotted, with four very bright one , like a trapezium on top of Saturn, and one very faint one, very close and below Saturn...

Is the view from the chromacorr II seems easier to pick up the faint one, although I also manage to see it without the chromacorr II...

The ISTAR during my last shootout at my friend's place when the condition is right, you can power it up to above 300X, but surrounding the image is not clean, but tonight I cannot verify how the chromacorr II will show at higher power on the planet saturn...

I will need to do more testing, in order to see the full benefit of the chromacorr II....

Regards

James Ling

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#8 John Huntley

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Posted 15 June 2013 - 12:18 PM

Interesting results James :)

It will be interesting to see if Valery has any comments to make but from my experience of using Chromacor I's and II's with chinese 6" F/8 achromats I think you might be able to get even better colour correction than that.

Even with the CC 1 I was seeing virtually no CA rim around the lunar limb at focus. The CC 2 made the scopes colour free to my eyes except on the brightest of stars and then there was just a very slight splash of purple.

Perhaps some experimentation with the spacing of the Chromacor / diagonal would be worthwhile ?

Baader Fine Tuning Rings are good for this as well as the traditional 2" filter rings.

#9 KerryR

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Posted 15 June 2013 - 03:08 PM

Hey Jeff,

I'm curious about what process you use to determine the length of the spacers, the one(s) between the C-cor and diag, you use with the various aperture stops. Mind discussing? I don't want to hijack the thread, so if another should be started, let me know...

I'm always looking for ways to further understand/optimize my C-cor-N and Synta 6" f8...

#10 Jeff B

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Posted 15 June 2013 - 03:27 PM

Hey Jeff,

I'm curious about what process you use to determine the length of the spacers, the one(s) between the C-cor and diag, you use with the various aperture stops. Mind discussing? I don't want to hijack the thread, so if another should be started, let me know...

I'm always looking for ways to further understand/optimize my C-cor-N and Synta 6" f8...


For basics you need to first determine if your scope is a bit undercorrected (which the majority of the Synta scopes seems to be in my experience) neutral, or overcorrected ( a relatively small number) in green light using a deep green or deep yellow filter(or both)using a star test.

We can then try to get the best performance out of your Chromacor N. Is yours a Chromacor I or II?

Also, I've written extensively about my Chromacors. So has Valery. You can try a search here and dredge up some postings.

Yes a new thread would probably be best.

Jeff

#11 James Ling

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Posted 15 June 2013 - 07:30 PM

Hi ALL...

Thanks for your comments and suggestions...

Below is the photos shot comparison I made showing with and without chromacorr II.....

Regards

James Ling

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#12 timps

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Posted 15 June 2013 - 09:02 PM

Hi ALL...

Thanks for your comments and suggestions...

Below is the photos shot comparison I made showing with and without chromacorr II.....

Regards

James Ling


I prefer the without chromacorr II image.

#13 mikey cee

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Posted 15 June 2013 - 11:54 PM

So the Chromacorr makes the Moon look yellow?? I don't believe I'd care for that. :thinking: Mike

#14 ValeryD

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Posted 16 June 2013 - 02:54 AM

Hi all,

I can't tell exactly what James need to tweak now, coz he didn't test the Chromacor-II under clear sky and with
different eyepieces.

When the object shows a greenish-yellow rim, this normally mean that a large focal length eyepiece was used and that this eyepiece has it's own later color.

So, the proper test should be as follow:

1. When the laser collimator is installed in the focuser's 2" adapter, the laser beam should strike the objective lens exactly in the center. In this case the focuser is well collimated.

2. Chromacor-II should be installed in the 2" adapter in the focuser with no play. Just very little - enough to install the Chromacor. Chinese 2" adapters in standard 6" refractors have too much play.

3. Point the telescope with CC-II in place on a bright white star. Install 10mm or shorter eyepiece and look at the star. No purple halo should be seen around the star when it is in the center of the FOV.

4. Defocus the star somewhat before and after focus. One will see some residual chromatic CA. The residual CA halo before and after focus must be very symmetrical. If one side of the defocused star has more color and the opposed side has less color, this mean that Chromacor's optical axis is not coincide with objective optical axis.
One must slight tilt the Chromacor-diagonal rig along the direction of the color asymmetry.

Once the symmetry of the defocused star (or planet) will be reached, then the Chromacor is properly collimated.
Now all objects being placed near the center of the FOV will be color-free.

The only problem can be the atmospheric dispersion - so, such a test must be done on a star near zenit.

Hope this help.


Valery.

#15 James Ling

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Posted 17 June 2013 - 02:14 AM

Hi Valery...

Thanks for the instruction for the proper test that I need to conduct , and making the adjustment....

I already notice the big shift of view of both the moon and Saturn when I interchange the chromacorr II against my other diagonal...

I will use a laser collimator to ensure is concentric, before doing the chromacorr II retest again, as I can adjust the 5 ISTAR countercell holding screws.....

Unfortunately heavy haze from Indonesia fire just stuck us last weekend, and looks like it will take a few weeks to a month for the blue sky to appear again.....

I hope I can do another test in two weeks time, as my friend is also tied up with his personal commitments in coming few weeks...since this is our school vacation....

One question I wanted to ask, is that the visual view through the chromacorr II seems to be smaller as compared to the view without chromacorr II...

Regards

James Ling

#16 BluewaterObserva

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Posted 17 June 2013 - 02:28 PM

I used my Chromacor I N with my home made 8" F/9 for nearly a decade. It is a difference that has to be experienced to be fully appreciated indeed. The 8" F/9 lives as a dedicated Solar telescope now so I just listed my Chromacor N in the classifieds.

#17 ValeryD

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Posted 17 June 2013 - 04:14 PM

I used my Chromacor I N with my home made 8" F/9 for nearly a decade. It is a difference that has to be experienced to be fully appreciated indeed. The 8" F/9 lives as a dedicated Solar telescope now so I just listed my Chromacor N in the classifieds.


Can you start the thread about your 8" F/9 telescope's second life? I now too in the solar astronomy with my SW150/750 deeps sky telescope transformed in to a dedicated Solarscope with H-a 0.7A filter and second 0.7A filter as a double stack.

#18 BluewaterObserva

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Posted 17 June 2013 - 04:21 PM

Not real sure it would be worthwhile for most....

I use a really old 1000 Oaks .8A filter. The proms are nice and bright though. I would like to try something double stacked on it at some point though.

#19 Jeff B

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Posted 03 July 2013 - 07:33 AM

James, have you had a chance to continue your use of the Chromacor II with the 8"?

Jeff

#20 James Ling

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Posted 03 July 2013 - 09:53 PM

Hi Jef....

The timing on receiving this chromacorr II is really not a good time, whereby the Indonesian fires , is causing the whole region, to be blanketed by a thick haze...

The fires already burnt for more than one month, and now maybe 75% are pulled down , and the weather is improving, with blue sky coming back....But this is followed by daily heavy downpour....
But this is not over yet, as it depends on the wind direction...

This weekend, I may arrange to have a short session at my friend's place again to test the chromacorr II.....when I returned back from oversea work assignment....
Just hope the planned session is not affected by the rain or haze....

REgards

James Ling

#21 James Ling

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Posted 07 July 2013 - 10:09 AM

Hi All...

This weekend , although I have no chance to try out the chromacorr II with my 8" ISTAR, but I managed to test out with my C6R F8, during the day time,as the sun is still shining through the cloudy sky....

I have used a statue at around 500M away, and using a 9mm nagler to view at the object...

Without the chromacorr II, as the light from the Sun hit the statue, the edges of the whole statue shows the greenish yellow tint, which is indicated in the photo attachment...

When the chromacorr II is plugged directly into the focuser of the C6R F8, the differnce is very obvious....
Only a smaller greenish yellow tint is visible, and is only at the head of the statue...

And the surface detail of the statue which have many porous marking are easily visible, which without the chromacorr II, is very faint....

And is very obvious, the chromacorr II is working fine with my C6R F8....And I may bring this combination for my coming side walk, which is also the 1st qtr moon.

The testing on my ISTAR is re-scheduled to next weekend, which again is subjected to the weather.

Regards

James Ling

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#22 Jeff B

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Posted 07 July 2013 - 10:38 AM

The thing really does work! I almost hate to suggest this but a comparison between the CR6 w/Chromacor II and the APM 152 F8 would be most interesting.

BTW, I should have an 8" F8.8 achromat ATM project completed within the next couple of months and I've N, O1 and U-1 in Chromacor I's and a Chromacor II N. It should be fun to compare notes.

Jeff

#23 James Ling

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Posted 08 July 2013 - 03:46 AM

The thing really does work! I almost hate to suggest this but a comparison between the CR6 w/Chromacor II and the APM 152 F8 would be most interesting.

BTW, I should have an 8" F8.8 achromat ATM project completed within the next couple of months and I've N, O1 and U-1 in Chromacor I's and a Chromacor II N. It should be fun to compare notes.

Jeff


Hi Jeff....

Great to hear that your 8" F8.8 achromat ATM project completed within the next couple of months..
And definitely you are going to have good comparison on the result on using the different types of chromacorr that you have possessed..

Hi Jeff and ALL....

As for the visual view on C6R F8 with chromacorr 2 against the 152 APM ED APO,
Yes, I did a comparison last weekend, and I just want to say the APM ED APO is really performing as per my expectation...as it even didn't show a tiny bit of greenish yellow when viewed through the same statue object with the same 9mm nalger...
The statue's surface through the APM ED APO is able to show much higher clarity of the porous marking as compared to the C6R F8 with chromacorr 2....

The following are the details of what I have seen from both the C6R F8 with chromacorr 2 and the APM ED APO..( refer to photo attachment)

1. C6R F8 with chromacorr 2 only the top of the statue's head shows a small amount of greenish yellow tint...

2. APM ED APO shows not a single trace of CA...on the statue....

3. The C6R F8, with chromacorr 2, when moving the visual view of the statue towards the edge of the eye piece, the greenish yellow tint disappear......and when it at the edge, a small amount of purple violet appears...
For the APM ED APO, there is no appearance of the greenish yellow tint, when moving in the same direction, but a smaller amount of purple violet appears when the statue's head is near the edge.

4. The C6R F8, with chromacorr 2, when moving in the opposite direction, towards the other edge, the greenish yellow tint, still remains, but just at the statue's head....
For the APM ED APO, a very very smaller amount greenish yellow tint appears when the statue's head is near the other edge....

I am not sure whether my C6R F8 lens cell is centered , as I do not have the laser collimator with me now....
Otherwise I may be able to further improve the C6R F8 with chromacorr 2 to match or get close to its contrast detail........

REgards

James Ling

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#24 Jeff B

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Posted 08 July 2013 - 09:32 AM

James, the major limitation for the Chromacor is off-axis lateral color where the red, blue, and green colors start to separate out from each other laterally,just like in a prism. This starts to occur a few arc minutes off axis. For me, this is easily seen on the Moon, for example, starting about half of the way out in the field of view of your typical Plossl eyepiece. I personally don't find it objectionable because I'm always focused (HAH!, just had to say that) on the color free image in the center. Also, a little trick is that for objects lower in the sky, the chomacor's lateral color can actually reduce atmospheric dispersion effects.

So this also shows the attraction of double ED scopes for me in that even though the ED scopes may not be as well corrected directly on-axis as a really good achromat with a well chosen Chromacor, the ED scope, however, has much better correction over a much larger field of view. I too much prefer my good old 4" F9 ED scope over a similar F10 achromat with a Chromacor for daytime use. Saturn, however, is a different story, though, I have to admit that the Chromacor II cost me as much as the two scope combined...ouch.

Jeff

#25 Gord

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Posted 08 July 2013 - 09:36 PM

Hi James,

Glad to see you are finding something to do with your scopes if you can't look at the sky! I may have to try that myself... perhaps try looking at that thing outside that looks like a tornado!

Anyway, I was just going to make the same comment that Jeff did. You will only see the benefit from the Chromacor at/near the center of the field. Works great on planets and doubles and specific features on the moon that you want to look right at.

I myself don't like the look of things as they get farther off axis so wouldn't leave the Chromacor in for example during DSO observing (other than maybe a small globular). This is where the true ED/apo's shine, having things look great everywhere.

The big advantage of course comes in when you start going up in size. At 4-5", there is not really much place for chromatic correction so much since real ED/apo's are so affordable. But the price of them goes up quickly beyond that and the Chromacor comes into it's own!

What is your setup of the Chromacor on the C6R BTW? Are you using any spacers? Jeff would be a good one to comment on this since he has a 6" F8 and a C-II N (Jeff?).

My experience with two different Chromacor's now is that the color correction improvement is really only part of the story (and this echo's comments that Jeff has made before). When I had the incorrectly matched Chromacor O1 in my 6" F10, I saw a dramatic improvement in color correction, but upon closer study, not so much improvement in actual fine details. When I switched to the better matched one (Chromacor-II U1), the difference was _huge_ on all fronts! Basically no color, but more importantly was the detail change (again, in the center area).

Clear skies!






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