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C6R lens upgrade

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#1 john@dps

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Posted 17 March 2013 - 11:22 AM

Does anyone know if the Istar 150 R30 lens is a bolt in fit for the C6R tube i have? I cant afford a new scope but the next best thing is to just get a better lens. I think mine is just an average one, and would like to upgrade however I have no desire to make a new telescope and would like to plug and play. Istar gives its specs but i have no specs on the C6R other than 150mm lens, to me that means it should bolt in right? I also have no tools to measure anything like 150mm to 190mm like Istars specs state. My real concern in the fit comes in the fact that the lens is around 900 dollars and if it wont fit my scope I will own a very expensive cup coaster. Thanks

John

#2 Rusted

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Posted 17 March 2013 - 05:25 PM

You ought to ask Istar directly.

The Istar cell would need a matching thread to fit the Celestron tube.
Assuming, of course, that your C6R cell fits on an external thread as does my older CR150.
Does your C6R cell thread on? Or is it bolted?
My CR150 is completely inaccessible for accurate measurement right now. (snow storm)

The Istar illustrations on their website do not show the method of fixing to the telescope tube.
Their website shows 140mm OD tubing. This might fit inside their cells.
Which might be quite a good sliding fit on the Celestron tubing.

It would seem a shame if Istar misses the chance to offer upgrade objectives for the popular Celestron 6" refractors.
It seems such an obvious market for them.
It would probably be very unlikely that their glass precisely fits the Celestron cells.
Which might have been an alternative upgrade route for you.

#3 herrointment

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Posted 17 March 2013 - 06:37 PM

For a couple grand APM is offering a replacement objective made from ED glass. OPT carries it.

#4 john@dps

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Posted 17 March 2013 - 07:07 PM

I've sent an email to Istar and am waiting a reply, though I'm not expecting Istar to be C6R experts. I will check into the apm I didn't know about that one.

#5 dan_h

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Posted 17 March 2013 - 08:56 PM

It would seem a shame if Istar misses the chance to offer upgrade objectives for the popular Celestron 6" refractors.
It seems such an obvious market for them.


The reason the Celestrons 6" f8 is so popular is because they are a pretty decent achromat. Istar would have to offer something significant at a really fair price to convince a lot of Celestron owners that they would get their money's worth in an upgrade. When an upgrade is priced well above the current market value of a scope, it can loose its appeal real fast.

Sure, a $1500 6" ED lens set will sell. A $1000 6" fancy achromat will sit on the shelves.

Just my opinion.

dan

#6 bremms

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Posted 17 March 2013 - 11:38 PM

An R30 would be a little better since it has a less CA, but still like 6" F10.4 tSwapping out a 6" F8 Achromat... no the poly chromatic Strehl is not good at F10.4 or evenF12.

#7 bremms

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Posted 17 March 2013 - 11:43 PM

The Istar lens comes without a tube flange (counter cell) so you could machine one to fit. The Istar R30 lens is VERY heavy. Probably double the weight of the C6r lens.

#8 john@dps

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Posted 18 March 2013 - 11:04 AM

I didnt know that about the weight. Right now im using an etx 90 to counter balance the C6R so I dont have to sit on the ground to view up. Istar just emailed me back and said that they are making adapters as we speak for the C6R to plug and play. They said as soon as they are done with the testing and fitting we will be able to buy them, which from the email sounded like it wont be long since they all ready have prototypes.

John

#9 bremms

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Posted 18 March 2013 - 12:04 PM

The R30 should be an upgrade, but will still have a good bit of color. At 6" I find achromats have noticeable color at F15.
For me, I was used to using longer focus reflectors, so any color is noticeable to me. My 4" F15 Jaegers does have very little, but it can still be seen. My 5" D&G has color too.

#10 john@dps

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Posted 18 March 2013 - 12:30 PM

The color has never bothered me much. I spend most of my time with DSO's and trying and trying to see nebula's from my light poluted back yard in LA. The lens upgrade for me is to get the best view I can get without having an APO. My lens I think is just average because Ive looked through some scopes that had better pin points than mine and most of them werent APO's, they were just good quality scopes and I figure I have a tube why cant I just get a better lens.

Though on a side note I do understand that it is not in the overall best interest of the industry to go around selling just lens, because if one could buy just ed glass for there scope at any give store, why would one buy a new telescope other than apeture or change of style?

John

#11 KerryR

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Posted 18 March 2013 - 08:50 PM

That's kind of exciting news that Istar is going to make plug an play adapters for the C6R.

I have a Chromacor Null that I'd like to pair with a better objective than the stock objective in my C6-R. I looked at Istar a while back, but wasn't confident I'd be able to come up with a suitable interface for the cell. Too bad, though, about the weight; the C6-R is already kind of top heavy...

#12 Rusted

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Posted 19 March 2013 - 08:49 AM

The color has never bothered me much. I spend most of my time with DSO's and trying and trying to see nebula's from my light poluted back yard in LA. The lens upgrade for me is to get the best view I can get without having an APO. My lens I think is just average because Ive looked through some scopes that had better pin points than mine and most of them werent APO's, they were just good quality scopes and I figure I have a tube why cant I just get a better lens.

John


I wonder how much you would really gain from a "better" lens on DSOs under heavy light pollution?
A good filter may actually be more useful.
With a new lens you might only gain on planetary/lunar detail when the seeing permits.
A new lens may be more "sexy" but I'd invest first in a taller, rock solid base for your mounting.
So you can sit perfectly comfortably while viewing the zenith through a good star diagonal.
Then use an adjustable height observing chair.
Or lean, facing a stepladder, to view at lower altitudes.
A rock solid view is a better view. Comfort makes a huge difference to how much you can actually see.

Work on maximising contrast.
If the nearby moon or a planet shows a glow long before you get them in the field of view then your contrast can be improved.
The dewshield is usually far too short on most commercial refractors and they often have poor light absorbing paint.
Particularly at glancing angles.
This just funnels stray light into your field of view.
Your dewshield wants to be about 2.5-3 times aperture and preferably much larger than the aperture.
I wrap stiff, black plastic or black foam around the existing dewshield.
Both types are just taped into a tube and held in place by friction.

Sensitivity to chromatic aberration is a personal and often age-related factor.
I find it is also highly seeing related.
Seeing false colour is not a competitive sport. ;)

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#13 rboe

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Posted 19 March 2013 - 09:13 AM

A light haze removed all false colour that I could detect on Jupiter using my SS 127mm. :) Alas; not exactly the optimal solution.

After all the money and time spent on my 127 I'm both seduced by the 152 and unwilling to part with the 127. :p

Nice setup there Rusty. :bow:

#14 john@dps

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Posted 19 March 2013 - 09:28 AM

Rusted, its interesting that you talk about seeing glow before you get to an object and i can see alot. I thought that was normal for scopes. I can see brite dso's even before i get to them, so thats not right I take it. I have the stock C6R dew sheild that I thought was ok, so I should get a longer shield? This is the first time I've heard anyone take about seeing glow before seeing the object, the moon and jupiter are really bad in my scope, I can see where they are way before I get to them.

John

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#15 herrointment

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Posted 19 March 2013 - 10:08 AM

That dew shield is a boat anchor. I get glow prior to bright objects also, and he's spot on about changing that out. Foam works great.

Fun looking set up you've got there.

Ron, someday I'll build my tapered tube 127....but the other six scopes all want attention and I don't think they are going to like the 10" F8 I might be bringing home .

#16 herrointment

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Posted 19 March 2013 - 10:17 AM

Stupid question time, John.

Have you checked collimation?

I ask because my C150, which had been shortened by a previous owner, needed a serious filing job to get the focuser in the right position.

#17 john@dps

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Posted 19 March 2013 - 11:24 AM

Im in the process of trying to get a chelshire I beleive they call it, and find or borrow a laser to check the JMI focuser

#18 buddyjesus

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Posted 19 March 2013 - 11:59 AM

a collimation was necessary on my scope and it greatly reduced my soft focus problems that I thought was due to secondary spectrum. good advice above.

#19 plyscope

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Posted 19 March 2013 - 03:51 PM

Here's an older article that might be useful.

web page

#20 Jim Curry

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Posted 19 March 2013 - 07:56 PM

John
I have both 4" & 6" f/12 Istar lenses. They both star test at 1/6 wave and are advertised at. 93 strehl. The f/8 at. 90. If that's better than your current lens it makes sense to make the upgrade. Assume Color to be the same.
Jim

#21 bremms

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Posted 19 March 2013 - 08:20 PM

Truth is a perfectly corrected 6" F8 starts off with a poly Strehl of lower than .70 there is also some higher order SA that needs aspherical surfaces to correct. I'm just saying at F8 a 6" achromat has inherent issues. One that is "better" may not give that much improvement.

#22 plyscope

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Posted 19 March 2013 - 08:55 PM

You are right Marc, I enjoy a 6"f5 and f15 but for different targets and magnifications.

I've not owned a 6" f8 however you can be inspired by Leslie Peltier (author Starlight Nights) who did years of valuable observations with 6" f8 refractor including comet discoveries and thousands of variable star observations.

There are always better telscopes but it can be fun and satisfying to make the most of the one you have.

#23 john@dps

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Posted 19 March 2013 - 10:25 PM

To continue my scope issues,

I dont know what mine lens specs are, however I did get a cheshire eyepiece today and what I found out baffles me. When I first put it in, the baffle rings and lens were not centered in the eyepiece hole.

With the telescope in the home position I loosed all 6 screws, 3 on the tube and 3 on my JMI EV-1 focuser. I then moved the rear of the focuser to the left and all the baffle circles then centered with the lens. The part that baffles me is when I rotate either the focuser or the 90 off of the home position all the baffles and the lens shift off center again really badly, I mean the breaks between the baffles on the left in the eyepiece have large spaces and the baffles on the right are almost in line with each other. It doesnt matter which way I turn the focuser or 90 the lens and baffles are off on the left and almost in line with each other on the right!!!! I know there is no imagine shift in the 400$ JMI EV-1, and there is no play in it in any way shape or form, so the miss alignment has to be coming from the tube or adapter, but the holes have almost no adjustment. If I adjust the view out of the home position so the baffles and rings are closer together and then turn the focuser or 90 back to my main viewing position the chershire is off again.

I dont get, if the view is straight from the home position, then why is the focuser off when I rotate it. Some would say that if it is aligned in the right spot, then that should be good and dont mess with it anymore, but I didnt buy a 600$ scope and a 400$ focuser so I could only view in one position and not to mention that if the focuser isnt aligned in all positions then there has to be something really wrong and I'm sure my views are not right even with everything lined up in the home position, which I have thought all along.

Its clear Im going to have to have it looked at, but any thoughts would really help me. Maybe just to understand why it can be right in one position and wrong in all the other ones.

John

#24 john@dps

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Posted 20 March 2013 - 12:02 AM

Another update, what I was given was not a cheshire eyepiece they gave me a collamating cap, and by looking though it, is when I saw non centered baffles and cell. I did have the 90* in the focuser which I now am thinking was not right, I didnt try without the 90*, and didnt try to rotate the focuser without the 90 in. So everything Ive done maybe all wrong :question: I think I just need to have someone that knows what there doing look at it before I pass a point of no return. :bawling:

#25 Rusted

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Posted 20 March 2013 - 03:02 AM

It is rather difficult to understand from your description but it sounds as if your Cheshire may not be properly aligned.

Let's try a dirt cheap, simple and foolproof test of focuser alignment:

Find a perfectly straight tube about a foot long which fits nicely in your focuser.
Something like 2" plumbing pipe is perfect if your focuser will take 2" EPs.

Roll your bit of tube on a flat surface (glass table?) to check it is dead straight.
It will bump as it rolls if it isn't dead straight.
Discard and find another piece if it bumps at all as it rolls.

Use a compass to mark two card circles. One to fit at each end of your alignment test tube.
*BLEEP* through the compass holes with a small knitting needle onto a suitable surface to make the holes a bit larger.
Now cut out each circle carefully with scissors.
Tape each of them absolutely central on each end of your test tube with thin Cellotape.
Thick tape won't go in the focuser.

Roll the tube on your test table to check the holes aren't eccentric.
The holes MUST roll perfectly true without any wobble. This is vitally important to the accuracy of your alignment test!
Peel off and adjust the circles, if necessary, until they roll perfectly true.

Now you can wrap a bit of tape around the middle of your test tube to stop it falling into the OTA!
You couldn't do this before now or the tube wouldn't roll straight on the table.

Without the safety tape your test tube might hit the back of your objective lens if you point the OTA vertically downwards!
If it doesn't break anything it will still be hard to get the test tube back out of the OTA without removing the objective in its cell.

Now set the OTA horizontal on your mounting, fit your test tube and clamp it GENTLY.
Make sure there is a bright surface, or the sky, behind the focuser end.

Go round to the other end of your telescope and look through the objective lens.
The two holes in the card circles will only be visible as a single bright spot when your eye is directly on the axis of your test tube pinholes.

Hopefully this alignment will be dead on the centre of your objective lens.
You can even fit cotton or nylon Cellotape crosshairs across the lens CELL if you want to be super accurate. But NOT on the glass itself!

If the visible bright spot is not aligned with the middle of your objective lens then you may have to adjust the focuser/main tube adaptor.

You can use the alignment test tube for checking the accuracy of rotation on your focuser too.

Keep the test tube somewhere safe for when you feel things are off-line again.

Sorry about all the words but it is vital to get this test tube right.
A bent or badly made alignment test tube will give a completely false idea of focuser alignment.
As will a badly fitting (sloppy) test tube in the focuser.






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