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Equipment Discussions >> Refractors

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Niklo
professor emeritus


Reged: 03/29/13

Loc: Bavaria
Re: Viewing sessions with my Istar127mm achro . new [Re: beanerds]
      #6074314 - 09/11/13 02:02 AM

Hi Brian,
so the CA is better controlled than in the old C102HD? Do you own one of the new very cheap Synta 4" f/10? They should have a better controll of the CA, too but probably they are still not reaching your 127 f/8? That would be an interesting test to compare them. With normal glass sorts it should be the other way round a 4" f/10 should have much less CA than a 5" f/8.
Istar seems to use special glass that has very little CA (it would be interesting to let you refractor be tested but that's probably too much work). So just be happy to have an extraordinary good achromat and enjoy it
Cheers,
Roland


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: Viewing sessions with my Istar127mm achro . new [Re: Niklo]
      #6074421 - 09/11/13 05:41 AM

Thanks Roland , I had my C102 back in the late 90's on an EQ3 mount , it was good but I think the coating technology of today is much better and not to mention ( as I said ) the final figuring of my Istar 127mm f8 does make a difference .

On the testing , hell yes ! I am in Australia so I will let mine and everyone's eyes and brain that looks thru it be the testers ,,,
No negative comments yet , even a TelVue 127 owner was impressed , He asked if my Istar was a triplet , high praise indeed .
I wont be selling mine any time soon , I built it .

Brian.

Edited by beanerds (09/11/13 05:48 AM)


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RGM
scholastic sledgehammer
*****

Reged: 09/15/03

Loc: Burks Falls, Ontario, Canada
Re: Viewing sessions with my Istar127mm achro . new [Re: beanerds]
      #6074534 - 09/11/13 08:03 AM

Brian, nice photo of Venus. I am also happy with the colour control of my Istar scope. I have a Fringe Killer and Lumicon minus violet filter on my filter wheel, but hardly use them. I just do not notice much, if any, improvement. Small amounts of CA are there in out of focus tests, but once the object is focused, CA is very minor on brighter objects.

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Niklo
professor emeritus


Reged: 03/29/13

Loc: Bavaria
Re: Viewing sessions with my Istar127mm achro . new [Re: RGM]
      #6074572 - 09/11/13 08:40 AM


Quote:

Brian, nice photo of Venus. I am also happy with the colour control of my Istar scope. I have a Fringe Killer and Lumicon minus violet filter on my filter wheel, but hardly use them. I just do not notice much, if any, improvement. Small amounts of CA are there in out of focus tests, but once the object is focused, CA is very minor on brighter objects.



Hi Bob,
you have a 5" f/12 so the CA is even less than in the 5" f/8. Istar seems to do a very good job.
The Venus picture is very nice. Could one of you Istar refractor owners take a photo of Jupiter? That should probably be a very nice picture with a lot of details.
Clear skies,
Roland


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: Viewing sessions with my Istar127mm achro . new [Re: RGM]
      #6074582 - 09/11/13 08:45 AM Attachment (28 downloads)

Bob I hear you mate , its the new generation of Achromats happening here I think . .
They are very good , Imagine paying $350 for a perfect 127mm objective , in a cell ,,, even 7 years ago ??? .

Here is a way over exposed moon shot , where ? is the CA that some people call the end all and be all in a refractor lense ???, I bet a few will see some on their moniters ?? .

Brian.

Thanks Istar , again .

Edited by beanerds (09/11/13 08:47 AM)


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David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Viewing sessions with my Istar127mm achro . new [Re: beanerds]
      #6074624 - 09/11/13 09:12 AM

Quote:

.

and hey guys , Steve and David , come on Guys , its a 127mm f8 Achromat what do you expect ?? .





The only reason I commented on the purple fringing is because you posted this:

"One more showing the lack of CA in my Istar 127mm f8 Achromat !!!"

I took that to mean that there was no CA. Had you said how little fringing or the tiny amount of fringing or some such thing, I would have agreed and never made a comment. However, I assumed that you meant there was no fringing. In fact, the picture doesn't look bad.

David


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Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Viewing sessions with my Istar127mm achro . new [Re: David Pavlich]
      #6074675 - 09/11/13 09:44 AM

Hi Brian,

I believe this image was taken afocally, and it looks to fairly low power given the whole moon is showing and it's small. Most likely you are seeing the objective is being stopped down by the exit pupil being much larger than the camera lens/diaphragm and so it's effectively making the objective a much longer F-ratio than normal, which of course improves all aberrations.

There has been a very detailed discussion of this lately on the ATM forum. The afocal images are only reliable under certain conditions (very high power to keep the exit pupil of the EP small), and a lot of cases of people posting images this has not been the case.

Clear skies,


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Niklo
professor emeritus


Reged: 03/29/13

Loc: Bavaria
Re: Viewing sessions with my Istar127mm achro . new [Re: David Pavlich]
      #6075491 - 09/11/13 04:32 PM

Quote:

Quote:

.

and hey guys , Steve and David , come on Guys , its a 127mm f8 Achromat what do you expect ?? .





The only reason I commented on the purple fringing is because you posted this:

"One more showing the lack of CA in my Istar 127mm f8 Achromat !!!"

I took that to mean that there was no CA. Had you said how little fringing or the tiny amount of fringing or some such thing, I would have agreed and never made a comment. However, I assumed that you meant there was no fringing. In fact, the picture doesn't look bad.

David



Hi,
the lack of something does not mean that it is completely missing, does it?
In fact it seems that this 5" f/8 shows very little CA for a 5" f/8 achromat refractors (at least at the photos).
I'm really impressed about that little color fringes seen on the photos. Well done with a good 5" f/8 achromat
If I had a wish free I would ask for a Jupiter photo with this achromat.
Cheers,
Roland

Edited by Niklo (09/11/13 04:35 PM)


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David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Viewing sessions with my Istar127mm achro . new [Re: Gord]
      #6075817 - 09/11/13 08:39 PM

Quote:

Hi Brian,

I believe this image was taken afocally, and it looks to fairly low power given the whole moon is showing and it's small. Most likely you are seeing the objective is being stopped down by the exit pupil being much larger than the camera lens/diaphragm and so it's effectively making the objective a much longer F-ratio than normal, which of course improves all aberrations.

There has been a very detailed discussion of this lately on the ATM forum. The afocal images are only reliable under certain conditions (very high power to keep the exit pupil of the EP small), and a lot of cases of people posting images this has not been the case.

Clear skies,




Interesting observation, Gord. That leads me to ask if the image of Venus is prime focus or afocal?

David


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tubehead999
scholastic sledgehammer
*****

Reged: 11/25/08

Loc: Kennesaw, GA
Re: Viewing sessions with my Istar127mm achro . new [Re: beanerds]
      #6076054 - 09/11/13 11:04 PM

Yeah, there is a little obvious CA, at least on my monitor, but , what is important , is if it makes you happy?

Hey, it is an achro,...achromats aren't magical......it is all about the physics...

My story;
I had an ISTAR 100/1200 one time, it was "alright".
Little over 1/4 wave, I paid 300 for the objective in cell with shipping.
I sold it for 200 shipped, what I figured it was actually worth.
I bought off the web site , which had an objective with a test report of 1/6th or close as an advertisement of the quality of the objective I was to receive.
Yes, I was disappointed that what I received was not what was advertised.
Was the objective I bought a "good" objective? Yes, I believe so.
Was it a "killer ' objective? No
Can one see the difference between a measured wavefront of 1/4 and 1/6th at the eyepiece? Yes.
Was I about to send it back and complain because I didn't get what I expected to receive?

No, because I don't have the time to play those kind of games. My curiosity has been satisfied.

I sold it with full disclosure of the interferometry report. I am sure the new owner is enjoying the glass and he got a "deal".

Another observer and I actually did a compare between the ISTAR 100/1200, the Carton 100/1300 and a Jaegers 103/1575. All in home-brew OTAs. Simple compare..Saturn. The Jaegars won.

Draw your own conclusions.


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stevew
Now I've done it


Reged: 03/03/06

Loc: British Columbia Canada
Re: Viewing sessions with my Istar127mm achro . new [Re: beanerds]
      #6076120 - 09/11/13 11:49 PM

Quote:


Steve and David , come on Guys , its a 127mm f8 Achromat what do you expect ?? .
This shot equates to about 90x thru the eyepiece .


Brian.



Bri, the image of Venus, and the Moon look great for color correction! Very impressive for an Achromat.
Congratulations on a fine refractor.
I hope you get many years of enjoyment out of it.

Steve


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: Viewing sessions with my Istar127mm achro . new [Re: David Pavlich]
      #6076245 - 09/12/13 01:25 AM

Sony A200 DSLR straight in the focuser at the native 1000mm fl of the telescope , sized for CN's ( from 1.07mb to 128kb ) , zoomed in and cropped by windows media centre , that's it .
Brian.
Quote:

Quote:

Hi Brian,

I believe this image was taken afocally, and it looks to fairly low power given the whole moon is showing and it's small. Most likely you are seeing the objective is being stopped down by the exit pupil being much larger than the camera lens/diaphragm and so it's effectively making the objective a much longer F-ratio than normal, which of course improves all aberrations.

There has been a very detailed discussion of this lately on the ATM forum. The afocal images are only reliable under certain conditions (very high power to keep the exit pupil of the EP small), and a lot of cases of people posting images this has not been the case.

Clear skies,




Interesting observation, Gord. That leads me to ask if the image of Venus is prime focus or afocal?

David




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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: Viewing sessions with my Istar127mm achro . new [Re: stevew]
      #6076249 - 09/12/13 01:30 AM

Thanks Steve , I like the way my Istar performs , well above the $360 I payed for it , I cant be happier with it .
Brian.
Quote:

Quote:


Steve and David , come on Guys , its a 127mm f8 Achromat what do you expect ?? .
This shot equates to about 90x thru the eyepiece .


Brian.



Bri, the image of Venus, and the Moon look great for color correction! Very impressive for an Achromat.
Congratulations on a fine refractor.
I hope you get many years of enjoyment out of it.

Steve




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Niklo
professor emeritus


Reged: 03/29/13

Loc: Bavaria
Re: Viewing sessions with my Istar127mm achro . new [Re: tubehead999]
      #6076377 - 09/12/13 05:54 AM

Quote:

Yeah, there is a little obvious CA, at least on my monitor, but , what is important , is if it makes you happy?

Hey, it is an achro,...achromats aren't magical......it is all about the physics...

My story;
I had an ISTAR 100/1200 one time, it was "alright".
Little over 1/4 wave, I paid 300 for the objective in cell with shipping.
I sold it for 200 shipped, what I figured it was actually worth.
I bought off the web site , which had an objective with a test report of 1/6th or close as an advertisement of the quality of the objective I was to receive.
Yes, I was disappointed that what I received was not what was advertised.
Was the objective I bought a "good" objective? Yes, I believe so.
Was it a "killer ' objective? No
Can one see the difference between a measured wavefront of 1/4 and 1/6th at the eyepiece? Yes.
Was I about to send it back and complain because I didn't get what I expected to receive?

No, because I don't have the time to play those kind of games. My curiosity has been satisfied.

I sold it with full disclosure of the interferometry report. I am sure the new owner is enjoying the glass and he got a "deal".

Another observer and I actually did a compare between the ISTAR 100/1200, the Carton 100/1300 and a Jaegers 103/1575. All in home-brew OTAs. Simple compare..Saturn. The Jaegars won.

Draw your own conclusions.



Thank you for your report. It's a pity that the objective wasn't 1/6 wavelength. You probably had bad luck
How was the CA comparing the Istar 100/1200 with the Carton 100/1300?
Saturn isn't a perfect object for comparing the CA but better than no comparison
Clear skies,
Roland


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Viewing sessions with my Istar127mm achro . new [Re: stevew]
      #6076393 - 09/12/13 06:26 AM

Quote:

Brian, Good shot of Venus, hard to believe its only an achromat.
Does Venus show about the same color correction visually?

Steve




When I view Venus in a reflector (or color free refractor) against a dark sky, I normally see the blue and red-orange edges that are the result of the atmospheric refraction. I would expect to see that in this image as well but I am not seeing it.

Jon Isaacs

Edited by Jon Isaacs (09/12/13 06:27 AM)


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star dropModerator
contra contrail
*****

Reged: 02/02/08

Loc: Snow Plop, WNY
Re: Viewing sessions with my Istar127mm achro . new [Re: Jon Isaacs]
      #6076881 - 09/12/13 12:17 PM

When I zoomed in on the Venus image it looks like the bottom of the purple fringe has a very slight reddish tint.

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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Viewing sessions with my Istar127mm achro . new [Re: star drop]
      #6077549 - 09/12/13 06:11 PM

Quote:

When I zoomed in on the Venus image it looks like the bottom of the purple fringe has a very slight reddish tint.




When I zoomed in, I saw the purple fringe, didn't see any red, it might be there. What makes Venus extra challenging for an achromat is that there is blue-violet, orange-red thing going on underneath the existing chromatic aberration. So if you filter the purple, you filter the atmospheric refraction too.

Jon


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: Viewing sessions with my Istar127mm achro . new [Re: Jon Isaacs]
      #6077690 - 09/12/13 08:42 PM

Thanks for your observations and comments guys I do appreaciate them , yes it has a tiny amount of CA and venus was getting fairly low down in the mirk ( 40*) but as many people and I said its very , very good for a 127mm f8 achromat .
I will try for a Jupiter shot over the weekend and post one or two up for your appraisal .

Thanks ,
Brian.


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: Viewing sessions with my Istar127mm achro . new [Re: beanerds]
      #6081567 - 09/15/13 06:05 AM Attachment (11 downloads)

Could not get Jupiter this weekend , morning clouds ,both mornings but I will try again in the morning (Monday) .
Here is the 'Acid" test I use on any telescope again in-case anyone has forgotten , full sun on a white roof .
Brian.


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