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Istar 5" f/8R30, first light

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#26 t.r.

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Posted 12 February 2013 - 01:37 PM

Yep on the Jupiter mags for detailed views...C80SS ~ 100x, TMB 92L & Tak Sky 90 ~ 155x, AP 130 ~ 220x, TEC 140 ~ 245x...on GOOD nights of seeing! For an average night I run the AP 130 @ 165x on Jove. ;)

#27 Gord

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Posted 12 February 2013 - 09:17 PM

I'll add that my experience is in line with Kevin's on those other targets as well. They take magnification much better than Jupiter. It seems Jupiter is more the odd-ball than any other as it takes really good seeing and big aperture to be able to push things.

Clear skies,

#28 mikey cee

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Posted 12 February 2013 - 11:42 PM

Tom I believe in what you're saying about the Istar quality. Scaling your 5" up to my 10" F/11 R30/35 I hardly ever go below 515x with my 65° plossls. Jupiter is actually still quite sharp at 685x with my 15mm plossls. At 815x with my VT 12.5mm orthos it really does begin to lose definition. Things that are linearly larger like the blue festoons become less distinct. At lower powers like 410x in my 25mm plossls the planet is so bright and contrasty sharp but to me the festoons are too small to see easily. This probably has more due to my eyesight becoming more used to the higher powers at 515x-685x. As far as I'm concerned the R30/35 lenses really excel. I'm as happy as a clam. :p Mike

#29 AlienRatDog

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Posted 13 February 2013 - 07:19 AM

Not to be a negative nancy but I noticed the Istar 127 R30 OTA is about $2k. What would be the advantage of this scope in comparison to, let's say, an Explore Scientific 127apo?

#30 tomharri

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Posted 13 February 2013 - 07:41 AM

You buy the lens for $700 and build your own tube assembly, my total cost is around $1000 and it is lighter than the way Istar builds them.

I build, therefore I am.

#31 Kunama

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Posted 13 February 2013 - 07:44 AM

Not to be a negative nancy but I noticed the Istar 127 R30 OTA is about $2k. What would be the advantage of this scope in comparison to, let's say, an Explore Scientific 127apo?


Build quality, the Istar is built to last a lifetime. But you do need to consider the size of the mount as the Istar is no lightweight.

#32 tomharri

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Posted 13 February 2013 - 10:08 AM

Mikey Cee: You must have excellent atmoshereics in Nebraska, way better than the eastern guys, or even me. I'm on the western side of the mountain from Portal AZ. Only had my 10" Zambuto newt up to 570x with a Pentax 2.5 XO. Something to be said about a longer focus scope. You don't need to peek thru a tiny lense to get high powers.

#33 t.r.

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Posted 13 February 2013 - 10:40 AM

Roland and I had an enlightening exchange over on the 'Mart awhile ago. I wonder if this R30 lens is indeed the C-e achro Roland discusses. The above reports sounds like it may be...

http://www.astromart...6701&poll_id...

#34 Gord

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Posted 13 February 2013 - 11:17 AM

Hi t.r.,

Thanks for the link to the discussion. However, these R30's are not C-e, they are F-e corrected (green/blue focus as opposed to the green/red C-e focus Roland is talking about). They are the opposite of what Roland discusses, at least as I understand what C-e means.

And that would seem to hold for his comment about Mars. Green and red are the primary colors for Mars, so an objective that lets red go out of focus is going to perform poorly. In this regard, I believe the classic archo's from IStar are closer to C-e than are the R30's.

Clear skies,

#35 t.r.

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Posted 13 February 2013 - 11:47 AM

That clears it up! So, the opposite...now the question...WHY? If planetary detail is mainly in the red/green channel as Roland confirms, why, why, why let the red go out?!?! The only reason to do so is to preserve star color information (blue)and grab up the visual primary of green I suppose...so technically, the standard c-f achromat is still going to perform better than this R30 lens for planetary. Let me ask it this way, what is the R30 supposed to accomplish, what is its virtue? Maybe that will make it crystal clear... :grin: Is it simply to reduce/eliminate the defocused blue CA one sees and trade it for defocused red which the eye is less sensitive to? To me, that tradeoff is not worth the price of giving up the red channel information if I use the lens for planetary. What am I missing?

#36 Gord

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Posted 13 February 2013 - 12:39 PM

That clears it up! So, the opposite...now the question...WHY? If planetary detail is mainly in the red/green channel as Roland confirms, why, why, why let the red go out?!?! The only reason to do so is to preserve star color information (blue)and grab up the visual primary of green I suppose...so technically, the standard c-f achromat is still going to perform better than this R30 lens for planetary. Let me ask it this way, what is the R30 supposed to accomplish, what is its virtue? Maybe that will make it crystal clear... :grin: Is it simply to reduce/eliminate the defocused blue CA one sees and trade it for defocused red which the eye is less sensitive to? To me, that tradeoff is not worth the price of giving up the red channel information if I use the lens for planetary. What am I missing?


Ding! Ding! Ding! Ding! I think we have a winner!! :lol:

Seriously though, I believe it is just that. The secondary color is less obvious, so it must be better, right? To Roland's comments (and other ones made in the other color correction thread), it very much looks to be a marketing exercise. People seem to be getting conditioned to "CA is BAD!" and must be avoided. We see it all the time in the kinds of discussions and questions asked. So you can see how it could be appealing to have someone present an option for less CA.

But as seems to be coming up with more discussions around this, things just aren't that simple. Tom's own experience here with the SS lens that shows more traditional CA, but showing better detail is a good example. You can't just look at it in a simple "I see less CA, so it must be better".

Anyway, I look forward to more user reports, especially on side-by-side tests to get a really good picture. And on the alternate side, where are these alternate correction designs excelling. Double stars have been mentioned, and thinking about it the moon would seem like a good target as well.

Clear skies,

#37 t.r.

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Posted 13 February 2013 - 01:00 PM

...Yep , yep. I too look forward to more reports, always good to read what others are experiencing and add it to the CN collective knowledge base. I still believe, if a manufacturer tried a C-e design and admittedly let the blue go out of focus, even though the CA would be more obvious, the planetary detail (red/green) would be enhanced thus producing an improvement over either the R30 or standard Fraunhofer for planets. For stellar it would be nasty! :rainbow: But that would truly be a change and an improvement in achro design strictly for the planetary observer...a dedicated achromat "Planet Killer"!!! Just look at the pic of Jupiter in the C-e that Roland posted on that A'mart thread. There is more blue CA halo yes, but look at the enhanced belt definition! It makes the low contrast detail pop out! If you really study the images, the C-F achro image is blurry in comparison. But you would have to contend with that blue halo in the C-e. My :penny: :penny:

#38 Kevin Barker

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Posted 14 February 2013 - 12:29 AM

Tim, Gord et al
The old Zeiss AS lenses were supposedly CDe corrected. They also used a special short flint glass as well which reduced secondary spectrum by 40 % or so for KZF6 and BK7(from memory)

I think planetary observers would love a scope with this type of correction if it did have significant benefits.

I would love to know definitely the glass types Istar are using, it is relatively straight forward to calculate the amount of secondary spectrum. Do they sit amongst normal glass types. Recently there are suggestions on another thread that Chinese do not have access to short flint and /or it is too expensive.

Also if they are not using special glass of some sort for the R30/35 etc lenses why are they using so much glass. They are truly very massive. The 250 mm version is close to 14 kg. The 127 mm R30 has more mass than a fast 6 inch standard Crown Flint.

Surely they could achieve different correction than C F if that is just what they are doing without all of the trouble of a massive lens.

I am sure there is an expert or two out there who can enlighten us all. Valery etc

I would not say conclusively from reading this interesting comparison of two 5 inch scopes whether R30's are better or worse with respect to planetary observing. The earlier comments about lower power could be due to cooling issues of the more massive lens. And even there what was better, same etc

More reports with different/same lenses will however start to help ascertain some certainty one way or the other.

I reckon an interesting comparison would be two Istar f-8 lenses of the same aperture, one an achromat and one R30. Of course I am assuming the normal achromat is corrected to C F??

I still suspect the R30/R35's's use slightly different glass types.

Are we comparing different levels of CA or different wavelength points of correction ??

Kevin

Kevin

#39 tomharri

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Posted 14 February 2013 - 06:12 AM

The only reason I started this thread was because there was no information out there about the Istar R30. Figured to start with a small scope just to see, then move up the ladder to the most I could handle/afford.

First objective has been accomplished. These lenses are a step above a regular achromat. I feel sorry for you armchair observers. Winter must really be brutal back east. But it sounds as if your atmosphere never really steadies up the rest of the year.

MOVE! The country is pretty much the same from sea to shining sea. During my military career seen pretty much all of it and decided the west was the best. Then you got Florida. If it hadn't been for that shark attack while kayaking, would probably be there.

Put down your musty/dusty books on theory and get out there and do something real. This is beginning to seem like Galileo vs. the Pope, or a good old fashioned witch hunt. Anything new is VERBOTEN!

#40 t.r.

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Posted 14 February 2013 - 07:46 AM

Tom, you seem to be taking things personal and becoming defensive for NO reason. No one here is attacking you, your observations, Istar, the R30 lens or the like. When manufacturers remain tight lipped as to what their latest creation involves it creates speculation. They could end it easily by providing details, but most choose not to and allow the customer to sift through truths, half-truths and even lies to draw a conclusion about the product. This thread isn't even a spirited debate yet, so relax a little. Nothing new is VERBOTEN...but it does bring about intelligent discussion on whether it has anything "new" to offer. If it does, it will stand up to a little scrutiny. ;)

The reason the lens doesn't show CA in your observation is two-fold IMHO. First, it is correcting the blue to focus, taking what you can see easily and replacing it with defocused red, which you can't see. That red channel does however, contain planetary information that is sacrificed! This explains why the SS standard achromat lens showed a better image. Second, you are magnifying to a point where the image is stretched and the color error left over drops below the point of perception. The same thing happens in observing reports of the Short Tube 80 on the moon in particular, which I have seen for myself (I do leave my armchair from time to time to actually observe ;)) when folks magnify over 100x or so with it, the CA "goes away" because the image is enlarged(stretched) and dimmed to a point where that defocused light drops below visual perception. But, it is also in the realm of "empty" magnification and most objectives will begin to break down in contrast. Hence, NO FREE LUNCH. There is nothing magical to the attenuation of the CA in this case, it doesn't happen by lens design, glass used or a "new" breakthrough. It simply comes down to trade-offs, but one must choose them wisely! For myself, thanks to this thread and a better understanding, I can cross the R30 off my list and go back to the standard C-F achromat design from Istar or D & G for consideration and simply filter it selectively. Thank you for starting it!

#41 johnnyha

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Posted 14 February 2013 - 08:59 AM

Also if they are not using special glass of some sort for the R30/35 etc lenses why are they using so much glass. They are truly very massive.


...so they can then market a normal lens set as the"special new lightweight version? :question: :lol:

#42 t.r.

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Posted 14 February 2013 - 09:13 AM

Just FYI, Royce has had a variation on the achromat for some time using a Barium crown glass instead of Bak7. It is said to reduce secondary spectrum by about 15% and can be visually appreciated. The lens is also oil-spaced resulting in two air-to-glass surfaces. To me, this is a true "new" offering, even though it has been around a while and was actually conceived years ago by another well know optician. It is an improvement on the fraunhofer design, whilst preserving what a C-F correction provides. Interestingly enough, years ago I tried to commission Rob to make me a 7" F/12 C-e corrected achromat discussed earlier in this thread. He wouldn't do it. Said that it would be great at planetary, but nothing else and wouldn't want his name attached to it!!! :lol: He said that his design hit a sweet spot as a planetary scope at 7" F/12 with the Barium...I may have to revisit this.

http://www.rfroyce.com/refobs.htm

#43 tomharri

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Posted 14 February 2013 - 09:47 AM

I don't care how they are made or what they are made from. That's all private information, company secrets. All I care about is how it performs. And the 5" R30 performs very well to my expectations and usage.

Sure a regular achromat 'may' be better under 200x, kind of hard to quantify what you are seeing sometimes. But where I spend the most time is over 200x, and the R30 is clearly better than an achromat here.

Yes the first versions are kind of weighty, but it looks to me as if they are addressing the issue with a thinner and even better performing 2nd version. Kinda like the motorcycle you are buying today is inferior to what's coming next year. Is this marketing? Buy the variation that best suits you, or sit on the fence and wait forever for the perfect 'one'. Don't denigrate the company for not replying to your every whim.

#44 t.r.

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Posted 14 February 2013 - 12:13 PM

Sure a regular achromat 'may' be better under 200x, kind of hard to quantify what you are seeing sometimes. But where I spend the most time is over 200x, and the R30 is clearly better than an achromat here.


THIS is a very valid point and one that begs for more reports to confirm or deny!!! If others can confirm this, then the R30 has its merits and truly does offer something "new" over the standard achromat...higher obtainable magnification without a reduction in low contrast planetary detail! ;) I will say this, the design choice is counterintuitive to enhancing planetary detail, but alas, Istar is very good at thinking outside the box and offering new concepts with products like Raycorr, the TCR and these lenses.

#45 stanislas-jean

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Posted 15 February 2013 - 04:36 AM

If this design, visually well seen, helps to diminish the blue hapo at high power, at the opposite it should reinforce a red brown halo around brilliant planetary disks.
I own a 150mm F10 istar classic that works already very fine.
In the blue area, the documents brought by T.R. is intereesting for showing the lacks at the ends of the visual spectrum: blurring in deep blue and so in red channel for classic achromats.
The 150mm istar get against already some improvements where:
- in blue channel we can go from the W80A filter to the W38A filter,
- in red channel the W29 filter is very well workable.
I think the R30 design has less spherochromatism in red channel and globally the CA curve is shifted to the red channel portion.
This represents a good optimisation for the Halpha field where the spherochromatism is well improved.
Personnally this my feelings about.
I owned also a 1529 model antares refractor, 152mm and 990mm focus length, where the effects can be similar.
Improved in blue fields (the W80A filter well workable, the W38A too limited) with anyway the blue halo more confidential than a classic doublet, but in the red fields the red-brown halo is present. The front lens has also an aspheric surface on the outside part created by a soft different curvature (well accessible for making this evident at a ronchi and 13lp/mm grating). Also a matter of spherochromatism result.
Here a F6.5 the istar F10 being on a step above for contrast images.
But we are far from an apo.
The istar works well on Mars with 300-375x without filter, 200x on Saturn, Venus in daylight without blue halo at 150x, Jupiter at 150-165x. The same characteristics on the 1529 but with light coloured filters.
There was some istar doublets with lanthanum glass having say 25-30% less CA, where this is now? Was interresting with regards the costs and performance.
Stanislas-Jean

#46 mikey cee

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Posted 16 February 2013 - 11:08 AM

Well I just finished looking at Damian Peach's double transit of Jupiter. Judging from the pinkish orange of the GRS and GRS Jr. my 10" R/11 R30/35 leaves absolutely nothing to be desired in color or contrast. Glad I made the plunge into R30/35 land instead of waiting around for others to be the guinea pigs!! :smirk: Mike






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