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Equipment Discussions >> Refractors

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mikey cee
Postmaster
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Reged: 01/18/07

Loc: bellevue ne.
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6017365 - 08/10/13 10:49 AM

James it looks to me like either the Chromocorr is dimming the image or the same shutter speed was not used. This can affect the blue intensity. Can it not? Mike

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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: mikey cee]
      #6017576 - 08/10/13 12:58 PM

Hi Mike....

Yes, you are right... it seems that from the photo shot, the one using chromacorr II is dimmer...
But visually , is not easy during the day, to determine a major difference in the brightness.

I checked both photos file on its details, and since I set ISO to auto, the camera itself will select the one that it determines is correct...
The chromacorr II photo ISO is 320, while without chromacorr is 500.
The shuttle speed is 1/100 sec for both photos.

But one thing for sure, I want to emphasize on what I have seen through visually from the 3 scopes which I have, when using the chromacorr II...

1. 152 APM ED APO. without the chromacorr II the view during daytime at the same statue the contrast is very sharp and clear...without CA.
But with the chromacorr II, it become soft and contrast is worst..., and CA is presence (violet), and you can tell the difference very obvious...

2. C6RF8. without the chromacorr II the view during daytime at the same statue the contrast is not sharp and clear...with plenty of CA.
But with the chromacorr II, it become sharper and contrast is improved...,but still cannot match the APM ED APO, and although CA is presence but is reduced drastically (especially the violet), and you can tell the difference very obvious...

3. 8" ISTAR.
The 1st attempt at my friend's roof top observatory with poor and cloudy weather, cannot show any significant difference in term of CA and surface details of the moon...
Today is my 2nd attempt, and although is a daytime comparison, the following are being observed...
without the chromacorr II the view during daytime at the same statue the contrast is very sharp and clear...but with CA and is a bit intrusive. (like the C6R F8)
But with the chromacorr II, the contrast is still sharp and clear..., and CA is presence, but very minimal and not intrusive, and you can tell the difference very obvious...caused the view is more pleasing....
I cannot conclude at this moment , whether the surface details does improved, but for sure the overall visual view is much better , which is mainly due to the drastic reduction of CA...Until this coming weekend when I test it at Saturn, I should be able to tell the difference under a clear sky...

And I now really envy those who has / have received their 8" R30/35 version.... coz I know is definitely much better in terms of performance, especially with a well controlled and reduced CA, over my classic model....

REgards

James Ling


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A. Viegas
Pooh-Bah
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Reged: 03/05/12

Loc: New York City/ CT
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: Gord]
      #6018793 - 08/11/13 11:00 AM

James,

If its possible I would be curious to see the difference in visual performance using a Viloet Fringe killer or a semi APO filter versus the Chromacor. I suppose it's all a matter of preference, but there is obviously a very large financial step from achromatic to true APO and along the way I was wondering how effective some of these filters are versus a more expensive Chromacor. For my 6" R30 I detect very little Violet fringing at low power, on lets say Altair or Vega... But at higher power, like anything over 100x it starts to become much more apparent. At very high power like 250x to 300x or more it's not practical to use as the CA is just too overpowering...

Al


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: A. Viegas]
      #6020300 - 08/12/13 07:53 AM

Hi Al Viegas.

I have a WO minus 1 filter, which I have tried previously onto my Istar, and it doesn't improve at all.....
And I still prefer to use polarized filter to dim down the brightness when i am looking at the moon...
For other objects, I don't use any filter at all.....
Coz i prefer to look at DSO such as star clusters, nebulae,etc....

I know your 6" R30 can perform better than most of the doublets, with the same focal length, except the ED doublets....
And since I am now testing the chromacorr II , in this 8" Istar, I would think is worth the price to pay for.... , But for a 6" R30 doublet, with the chromacorr II added, it is not able to get even near to my APM ED doublet...as i have tested the chromacorr II onto my C6R F8....maybe you should consider it carefully, before getting one to try it out....
Perhaps the Istar Raycorr , may be introduced very soon, and is specially designed for R30 version...., which people like you are and others like Mike, are the one best benefited, and I am definitely going for one as well....

Regards

James Ling


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A. Viegas
Pooh-Bah
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Reged: 03/05/12

Loc: New York City/ CT
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6020307 - 08/12/13 08:02 AM

Thank you James... My conclusion is the same. I will wait on the RayCorr and see how effective it is. Aside from that it's just knowing the Istar is a high quality build achromatic with or without some meaningful amount of CA reduction using the R30/35. I find the visual view in the refractor to be much more pleasing than in my SCT which are exclusively now Mallincams... Hopefully Istar delivers on the RayCorr.

Al


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: A. Viegas]
      #6020315 - 08/12/13 08:15 AM

James , just looking at the shots of the statue the CA is a lot better with the Chromocor that's for sure .
It looks about the same reduction I acheaved on my Synta 150mm f8 I have in NZ , that my nephew is using .
It took me a while to tune mine in by cannabalising old 2 inch colour filters without the filter, just the threaded rings to move the Chromocor out away from the diagonal ,trying thinner ones , etc.. some times more sometimes less , but after about 3 months of this , one night it just snapped into place !! , Gotcha .
They work when set up right .
Brian.


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: A. Viegas]
      #6021788 - 08/12/13 10:10 PM

Hi Al Viegas....

yes, I fully agreed with you that the Istar quality, whether is the build or the details seen through the ep are great...

And I am very sure those who have or going to receive the 8" F12 R30, which is now tested and reported by Mike, the CA level should be very much closer or maybe better than my 8" F8.8 with chromacorr II...(just wtg for Mike to take some photos....and put it up in the forum)
My advantage is of course a shorter tube, and my G11 is able to handle my 6Ft long Istar.....

Regards

James ling


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: beanerds]
      #6021804 - 08/12/13 10:16 PM

Hi Brian....

Thanks for the advice....
And that is also why I am making the new attachment or spacer..., which the screw threads allows me to play with the distance of +/-5mm from the pre-determined distance...
The day time visual adjustment for the photo taken, is just a preliminary, as I may need to further adjust the "right" distance , when come to actual night time testing...

This coming weekend, at our star gazing activity, I should be able to further fine-tune the chromacorr II, provided the weather is fine.....(coz is raining the past few days)

Regards

James Ling


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6021897 - 08/12/13 11:16 PM

James , I think from memory the optimal distance from the Chromocorr's front lense to the focal point is 161mm + or - 2mm in a 150mm f8 , so that spacing is critical and depends on the type of 2 inch diagonal you are using .
I used a standard 2 inch GSO mirror diagonal and about 9mm of spacing was required , from memory ,from 4 years ago .
I would not know the optimal distance for your 8 inch , trial and error I am afraid .
Good luck , because when its right on , you will know .
Brian.

Edited by beanerds (08/12/13 11:18 PM)


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Gord
Carpal Tunnel
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Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6022497 - 08/13/13 09:25 AM

Quote:


And I am very sure those who have or going to receive the 8" F12 R30, which is now tested and reported by Mike, the CA level should be very much closer or maybe better than my 8" F8.8 with chromacorr II...(just wtg for Mike to take some photos....and put it up in the forum)
My advantage is of course a shorter tube, and my G11 is able to handle my 6Ft long Istar.....





Hi James,

I wouldn't be so sure about this. Even a 50% improvement in color correction wouldn't match the improvement you are showing in the image above with the Chromacor. There isn't any technical info available yet on this design and there was a post recently here from someone in Czech who seemed familiar with IStar's designer that said the improvement was from the seelinger effect. This would not be an improvement (overall) per se, but rather an optimization at a specific wavelength.

Also an interesting factoid about the Chromacor you might not have known, is that it can correct the spherical aberration at wavelengths other than just green. Normal refractors (even ED's and apo's) are only corrected at green (usually), but with a Chromacor you can have better correction at the other wavelengths too.

But as Brian has mentioned, it will take some playing and once you hit the sweet spot, you will know. Your adjustable spacer sounds like a really good idea! I have other ideas for mine as well, but I really need a lathe.

BTW, how does your objective look in terms of correction in stock form? Over, under, or neutral corrected? Also I wonder what the color balance of yours is as well? Valery has said that the Chromacor is designed best for a traditional C-F balance. In testing I've found mine to have blue closer focus than red, but even in this case the Chromacor improves things greatly. But I wonder if it could be even better if they were balanced. In the same testing, I've found a prism diagonal improved this balance to be neutral again (specifically measured the de-focus) so I would like to see if that improves the Chromacor image as well.

Clear skies,


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: Gord]
      #6024408 - 08/14/13 02:36 AM Attachment (24 downloads)

Hi Gord....

I would not want to say or comment on the result of the chromacorr II at this moment....but we know the CA is well controlled at the central of the view....
And I still can see CA starts appearing, but not that much against without the chromacorr II, when you move the target object away in both directions (greenish-yellow in one direction, and violet in the other direction)

And I am still waiting for the opportunity for the next setup of this ISTAR during the night time, which I hope I can do so on this coming weekend...., and make the adjustment for the trial and error on the spacer distance...

The photo shows a cnetral attachment or spacer I have my machinist machined for me to thread between the diagonal forcuser end, and the chromacorr II end...
The thread that goes into the diagonal end, is able to extend out for at least 10mm....for my trial and error....testing...

REgards

James Ling


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6024412 - 08/14/13 02:41 AM Attachment (29 downloads)

Hi Gord...

And the machined attachment is tested with a laser collimator , after assembled onto my other diagonal and the chromacorr II...
The the assembly is again , mounted onto my Istar forcuser, and the laser beam is projected from the lens front to a wall 3M away, and final adjustment is on the Istar countercell 5 holding screws....

This will ensure my tested object is at the centre of the view....and that is easier for my adjustment on the spacer distance....

Regards

James Ling


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6031666 - 08/17/13 08:04 PM Attachment (48 downloads)

Hi All...

This are two photos I shot from the 8" ISTAR with the chromacorr II, using my canon 550D with 2X barlow...., at the 11 days old moon, during the end of the side walk session at our army club house....

Regards

James Ling


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6031917 - 08/17/13 11:04 PM

Woaw! that's very good James , the chromocor looks to be working very well .
Brian.


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: beanerds]
      #6032445 - 08/18/13 09:04 AM

Hi ALL...

Last night testing done at the 11 days old moon confirmed the following :-

1. Using my TV55mm eye-piece at 33X,there is a thin stripe of greenish yellow CA visible on the edges of the moon.
The amount is very much reduced, more than 50% to 80%,very close to my APM 152 ED APO...

2. When I used my baader zoom eye piece, to power up , and move the edges of the moon closer to the centre of the FOV, the CA completely disappear....IS COLOUR FREE AT CENTRE OF FOV.

3. When I further moved down the edges of the moon away from the centre of the FOV, the slight trace of violet or purple CA appears....

4. When I shoot the moon with my 550D , now the edges are colour free, with the chromacorr II, whereas previously my photo shot, will show the purple or violet at the edges.

Last night beside the moon, having a good visual view, the giant gas planet, is not able to make a good comparison....

It is sighted quite low, less than 30 deg, and with plenty of " atmospheric disturbance ".
I can even power up my Istar to 450X with my 4mm eye-piece..
and still see the view of Saturn and its 2 moons with good contrast, except is not able to show the cassini division very clearly (razor sharp), as well as the cloud bands...

Regards

James Ling


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James Ling
sage
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Reged: 09/18/10

Loc: Singapore
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6042879 - 08/24/13 02:58 AM Attachment (44 downloads)

Hi ALL....

This is a better photo comparison of the moon photos shot through the 8" ISTAR, using the same Canon 550D.
Although they are taken almost 3 years apart by me, but when using the moonlite focuser, the focusing is precise, from the 3" viewer, before the photo shot is taken...

In both occasions, no UV/IR cut or contrast booster are taken...
So the Chromacorr II is able to eliminate the purple or violet CA, when a photo shot is taken.

Regards

James Ling


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Psion
scholastic sledgehammer


Reged: 04/27/05

Loc: Czech Republic, Prague
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6043455 - 08/24/13 11:57 AM

Nice report thanks.

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jrbarnett
Eyepiece Hooligan
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Reged: 02/28/06

Loc: Petaluma, CA
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: James Ling]
      #6044253 - 08/24/13 09:18 PM

The Chromacorr really works!

Brilliant design. Sheer genius on the designer's part.

Very nice images, too, James.

Regards,

Jim


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mitsos68
member


Reged: 06/21/12

Loc: Athens - Greece
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: jrbarnett]
      #6180653 - 11/07/13 09:55 AM Attachment (21 downloads)

Hi,
I am old user of Chr II. I have a 152mm f/8 scope with a fine objective from RR Holland (original strehl 0.95). My focuser catch the diagonal / chromacor complex with a self centering adapter, and the focuser itself is push pull squared adjusted to the OTA. You can magnify the lower part of the scope to sse. Results as perfect you can imagine.
Regards
Dimitris
Athens-Greece


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mitsos68
member


Reged: 06/21/12

Loc: Athens - Greece
Re: ISTAR 8" F8.8 With Chromacorr II new [Re: mitsos68]
      #6180667 - 11/07/13 10:06 AM Attachment (12 downloads)

The focuser complex

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