Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Refractors

Pages: 1 | 2 | 3 | (show all)
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Istar 5" f/8R30, first light
      #5666825 - 02/07/13 10:49 AM Attachment (187 downloads)

First the conclusion: AND IT'S GOOD. Almost equal to the Meade 5" f/9 ed apo of long ago. The bad news is everything is metric and its very difficult to use usa inch parts to make the 1/2 collimatable cell you get to fit a 5" or 6" Hastings pipe, unless you are a machinist or can get parts made at a reasonable (cheap) price.

The View: Popped in an eyepiece that gave 150x to find Jupiter and align finder, and thought OH-OH?! There was alot of blue fringing around Jupiter for such a low power. The Jaegers I've built previously had almost no blueing at low to medium powers, and they got progressively worse as you increased magnifications.

This R30 Istar gets better, less fringing, as you increase powers. At 200x the blue haze is about equal to a regular achromat. At last nights atmospheric limit of 250x with a 4mm Radian there was almost no blue haze around the edges of Jupiter. Can't hardly wait for a real steady night to see how much power this lens can handle. Who says you need an APO?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Kevin Barker
super member


Reged: 04/22/09

Loc: Auckland, NZ
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5667833 - 02/07/13 08:45 PM

Thank you for this report.

The scope does look well constructed, well done.

This is the second recent favourable report from an owner of an Istar Anastigmatic R30 lens.

Is it possible the eyepiece you used to achieve 150 power might have been a factor in the blue fringing you saw?

Also of note the objective is clearly quite massive judging from the point of balance of your ota.

Are you going to paint the ota?

Kevin

Edited by Kevin Barker (02/07/13 08:46 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: Kevin Barker]
      #5668115 - 02/07/13 11:33 PM

I took apart the lens to see if it would fit in a Surplus Shed cell, they are same diameter. No luck, the Istar lens is an incredible 1.5" thick vs. the SS at just under an inch. The 3/4" thick ring to mate the cell to the 5" tube just ads to the front heaviness. Might polish and leave tube bare aluminum, they sure look rough as delivered.

The blue haze decreased as the powers went up on Jupiter. At 250x there was very little blue, but the planet had a yellow-reddish cast that was faint but odd. Didn't seem to cloud out any details and I'm sure the scope will go above 300x when the atmosphere permits. When this next cold front passes will have to set it up next to the SS 5" just to see how much better it is than an ordinary achromat.

Feel sorry for the guys on the east coast of usa, no end in sight from winter, enjoy!


Post Extras: Print Post   Remind Me!   Notify Moderator  
zjc26138
Loved By All
*****

Reged: 02/24/05

Loc: Mingo Junction, Ohio
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5668201 - 02/08/13 12:39 AM

Thanks for the report. And congrats on the new scope!

Post Extras: Print Post   Remind Me!   Notify Moderator  
Kevin Barker
super member


Reged: 04/22/09

Loc: Auckland, NZ
Istar 5" f/8R30, first light new [Re: tomharri]
      #5668304 - 02/08/13 03:19 AM

My twin brother Phil Barker made an ota using a SS 5 inch f-9.4 lens last year. I have used it a couple of times and yes it is a good example of an achromat. He reckons it star tests OK and seems to have reasonable control of astigmatism or any major aberrations.

It is interesting your comment about Jupiter having a faint reddish/ yellow caste. Phil's SS lens shows Jupiter slightly yellow with a slight magenta residual CA. In my Zeiss it is pure white.

He had to tinker with the lens to get a decent image. It had a rubber ring which I think he removed it to add spacers. he also spend a bit of time getting good collimation.

It performs pretty good and is quite a light ota.

With Jupiter here in NZ's typical average seeing I tend to use lower power on Jupiter than you do. I find around 125 to 180 power is best for fine detail with most seeing we get here.

Phil( a South islander) has had his SS 127/1200 lens cranked up to 270 X or so on doubles and Saturn recently. He has not been successful splitting Sirius with this scope although I have been able to here in Auckland several times using a 130/1000 Zeiss apo.


Post Extras: Print Post   Remind Me!   Notify Moderator  
ValeryD
Vendor (Aries)
*****

Reged: 11/26/05

Loc: Kherson, Ukraine.
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5668305 - 02/08/13 03:20 AM

Quote:

I took apart the lens to see if it would fit in a Surplus Shed cell, they are same diameter. No luck, the Istar lens is an incredible 1.5" thick vs. the SS at just under an inch. The 3/4" thick ring to mate the cell to the 5" tube just ads to the front heaviness. Might polish and leave tube bare aluminum, they sure look rough as delivered.

The blue haze decreased as the powers went up on Jupiter. At 250x there was very little blue, but the planet had a yellow-reddish cast that was faint but odd. Didn't seem to cloud out any details and I'm sure the scope will go above 300x when the atmosphere permits. When this next cold front passes will have to set it up next to the SS 5" just to see how much better it is than an ordinary achromat.

Feel sorry for the guys on the east coast of usa, no end in sight from winter, enjoy!




Thanks for the report.


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: ValeryD]
      #5668407 - 02/08/13 07:23 AM

So is this an R30 design attribute that when you increase magnification, the CA decreases? How is this accomplished, because it defies what I know about achromats?

Post Extras: Print Post   Remind Me!   Notify Moderator  
johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Istar 5" f/8R30, first light new [Re: t.r.]
      #5668412 - 02/08/13 07:29 AM



Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: johnnyha]
      #5668493 - 02/08/13 08:50 AM

I'm just an assembler of premade parts. My previous build is the Surplus Shed 5" f/9.4. It tops out at 280x with a 4.3mm lens. If you go to a 4mm, the scattered purple haze starts obscuring planetary details. The 2 Jaegers at f/8.5 & f/10 previous to both these, topped out at 250x.

So $700 for the Istar lens is just what I was hopeing for- A new and improved Super Achromat.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5668503 - 02/08/13 08:58 AM

Tom,

Thanks for posting your experience. Do you have any of the other lenses (SS or Jaegers) to do a side-by-side comparison?

Thanks,


Post Extras: Print Post   Remind Me!   Notify Moderator  
RussD
member


Reged: 04/20/06

Loc: Minnesota
Re: Istar 5" f/8R30, first light new [Re: t.r.]
      #5669150 - 02/08/13 02:09 PM

This makes sense if the scope is corrected a toward the red end. The purple side of things are not as well corrected so you would see a lot of CA in blue/violet at low powers. At higher powers the CA in blue is still there and now very large, but it is really spread out over the whole image and is just not as noticeable. But it is there. At the same time the remaining error on the red side has been magnified at higher powers and becomes more visible giving the image a reddish tint.

Russ


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff B
Carpal Tunnel
*****

Reged: 12/30/06

Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5669391 - 02/08/13 04:43 PM

Quote:


...but the planet had a yellow-reddish cast that was faint but odd.




Not odd at all. Achromats act like yellow filters at high power. Airy disks will also look distinctly yellowish at high power and the slight redish tint may indeed suggest it's red lateral CA is less than the blue. In fact, if you let blue defocus enough, it puffs out to the point of being invisible since your spreading the same amount of energy over a much bigger area. Conversly, bringing the red focus closer to the yellow/green will indeed make it more visible as your concentrating the same red energy into a smaller area. Ironically, this combination gives the subjective impression of more CA in the red and less in the blue when, in fact, it's quite the opposite.

Jeff


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar 5" f/8R30, first light new [Re: Jeff B]
      #5670465 - 02/09/13 10:32 AM

Hi Jeff,

What you are describing sounds like the red is closer to the green focus with blue hanging out. That's seems to be opposite to what the R30 spot diagrams that IStar has shown where they have the red hanging out and the blue in tighter.

At the same time, the spots they have shown for their classic achros seem to show what you are describing. Mind you, those were shown for a 6" F8, no the 5".

Could it be that this lens is actually one of their classic achro's and not an R30? Or could the R30's be differently corrected at 5" vs. 6"?

Clear skies,


Post Extras: Print Post   Remind Me!   Notify Moderator  
Sean Cunneen
Let Me Think
*****

Reged: 08/01/07

Loc: Blue Island Illinois
Re: Istar 5" f/8R30, first light new [Re: Gord]
      #5671177 - 02/09/13 06:35 PM

I think we should all be patient and wait for the Op to post more observations before jumping to crazy conclusions about the R30design. Mikey Cee has posted his report on his R30 objective which does not rewrite optical theory.

Edited by Sean Cunneen (02/09/13 07:05 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: Sean Cunneen]
      #5671315 - 02/09/13 07:49 PM Attachment (27 downloads)

Sorry for the delay, but we've had a bit of weather here in the Arizona desert- 40mph wind, rain and snow, watch out you eastern guys, more winter coming at you!

So took the time to touch up paint the interior and get my monster alt-az mount to hold the Surplus Shed 5" f/9.4 along side the Istar for same time comparison.

When doing the site tube alignment, you know how you see the 2 circles around the peep hole when it is not aligned. One circle is red, the other blue in the R30. That's not normal.
2nd look will be sunday nite, should be clear and cold. Later, Tom.


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5673215 - 02/10/13 10:37 PM

Istar 5" vs. Surplus Shed 5" f/9.4 on Jupiter 2nd Light

One of those cold, clear, very little air movement nights where it seems magnifications can be unlimited. The R30 topped out at 340x with a 3mm radian. The SS at 300x with a 4mm Radian. By topping out mean going any higher resulted in a loss of details.

150x R30 7mm, ss 8mm-a little more blue haze in R30, almost none in ss.

200x R30 5mm, ss 6mm- blue about same in both, still real sharp/distinct detail, moons more evident as discs- ganymede largest, callisto kinda dark, io&europa about same.

240x R30 4.3mm, ss 5mm- R30 almost no blue, in ss blue haze starting to be objectionable, still good clear defined details both.

This is where I swapped over to the Televue/Pentax case of lenses, previously was using ortho-plossls.

300x R30 3.5mm, ss 4mm, R30 is showing a definite yellow tint, more so than ss which has a little. Also R30 is starting to show more blue hazing around planet than at 250x but it is nothing compared to what shows in ss.

340x R30 3mm Radian- I'm out of eyepieces, can't go higher, but this is probable limit since planet is yellowing more and blue haze is increasing. ss will not take 3.5mm XW, just too much power.

Only just above freezing here, took an hour and a half, so that's all for tonight.


Post Extras: Print Post   Remind Me!   Notify Moderator  
bremms
Carpal Tunnel
*****

Reged: 08/31/12

Loc: SC
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5673264 - 02/10/13 11:00 PM

Tom, That sounds good. I talked to Istar for a good bit about the R30. They said it will have the correction of a standard crown flint lens with an f ratio 30% longer. 5" F8 R30 should be as well corrected as a 5" F 10.4. My issue is the weight of the lens. I was looking to get a 6" R30 but it weighs over 10 lbs!!

Post Extras: Print Post   Remind Me!   Notify Moderator  
Kevin Barker
super member


Reged: 04/22/09

Loc: Auckland, NZ
Re: Istar 5" f/8R30, first light new [Re: bremms]
      #5673299 - 02/10/13 11:34 PM

Tom
Thank you for the report.

Were Jupiter's subtle belt and zone details any better at a magnification (150-200X) in the R30 or SS lens?

Also were there any features on jupiter visible in one scope which were not visible in the other?

Kevin


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: Kevin Barker]
      #5673567 - 02/11/13 07:20 AM Attachment (22 downloads)

Hate to say it, but thought the regular achromat was better under 200x, everything seemed more sharply defined, better contrast.

From 225 to 275 is where the Istar really performed because of less color scattering. This wasn't the red spot side and how well the spot shows and its wake really separates the average scopes from the best. Just judging from the ripply belts, they both showed about the same details.

You can see from my scope pic they are front heavy, mount a bigger finder. Add the stick on lead car wheel weights, did that on a dob when I got the box side height wrong. There is more going on here than just blue fringe reduction. The optical quality is clearly better than any of the achromats we have used before in these f/ratios.

A small cold front is going to zoom by monday, tuesday should be good, going to do all the doubles around orion's belt. More later.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5673678 - 02/11/13 09:30 AM

Hi Tom,

Thanks for the report. I think those powers are into empty magnification, at least in terms of Jupiter. It's a target I find that seems to top out at quite low power relative to some other cases (doubles, etc.). At this size and focal ratio, I would think 150x is as high as new details are likely to be seen. Under rare conditions, things may hold up ok at higher powers, but more likely details will be lost.

I'm not sure how much things are improved for this F8 version, but I know IStar recommends only 0.25D for their faster ones (F5 and the big 200mm F6), which is only around 50x max. I'm sure on your's it's probably in the 1D range (so 127x). 150x would seem very likely and as you have shown, it will still work at 300x and I'm sure do well on doubles.

I think I goofed on my initial interpretation of your and Jeff's comments. If you are seeing a blue halo, then as Jeff was saying this would mean more focused blue and in agreement with the spots I've seen where red hangs out (and would be less visible). So that sounds in like it matches up with the design.

On the SS lens, is this one of those that came in the plastic cell? Were those coated?

Do you have access to a prism diagonal? This was brought up in the other color correction discussion and I've found some interesting info on the Astro-Foren site that Mr. Rohr has done and it shows improved focus of the red to end up with a better balance. I'm wondering if you would see an improvement of the image through this lens.

Thanks,


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: Gord]
      #5673852 - 02/11/13 11:14 AM

How do you tell if coated/uncoated? When light is reflected off lens front there are no colors, just natural reflections. The SS was from last batch with the all aluminum collimatable cell. Tried a prism 90 in SS with no changes I could see. When Istar says their lenses have collimatable cell, was expecting both sides like the SS came with. But no, you have to source your own tube to cell connection.

Empty magnification? Put a coin 6' away from your eyes. How much detail can you see? Now hold that coin as close to your eye as possible. See the difference? Quality accurate optics can make as much power as the sky will allow. You need to separate the details to clearly see them. Mars is the best example of the need for alot of powers.

The Istar 5" has the perfect range of powers/quality that can be used around here, 200-300x. Though it does seem kinda pricy at $700 vs. $200 for the Surplus Shed one, of which there may be no more cause the Lens Description with the out of stock label is gone from his site. Oh well, things can't last forever.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5674841 - 02/11/13 09:35 PM Attachment (24 downloads)

Hi Tom,

Here's a picture of a couple of lenses and differences in coatings. One has the common broad-band multi-coatings (the green), and the other seems to have none (both are IStar lenses). I believe your IStar is the same as the achro in this image. The other possibility is MgFl which have a kind of purple/violet color to them.

Sounds like your SS may be uncoated.

On the optimum magnification, how much more detail are you seeing at 200x (or 250, 300) vs. at 150x on the surface of Jupiter? Things like the sizes of the disks of the moons will benefit from higher powers if the seeing and optics will support it, but details in the banding are usually lost if overpowered. Eddgie could explain the why better in terms of the MTF relationship, but I know that brightness is a component and when you go to those higher powers in a small scope, the exit pupil gets very small and contrast suffers.

Clear skies,


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: Gord]
      #5675654 - 02/12/13 11:35 AM

Even Jupiter is so small at 150x. It is much easier to see the details at 250x which the Istar can support but is near the limit of the SS achromat. Yes, 300+ power is a bit much for a 5" but in the Istar it is able to do this with an atmosphere that cooperates.

Takahashi states you can use 100x per inch in their scopes, This 5" looks able to do 60x per inch without the image fuzzing up.


Post Extras: Print Post   Remind Me!   Notify Moderator  
johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5675716 - 02/12/13 12:12 PM

But for many planetary aficianados, anything beyond 30X per inch is empty because no more details can be seen, the image is only physically larger. The larger the image gets beyond that, the more "grainier" it becomes. I have a magnificent 6" APO and anything beyond 200X for planetary is just too dim for my taste. Yes the scope will handle more, but that does not change the exit pupil.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Kevin Barker
super member


Reged: 04/22/09

Loc: Auckland, NZ
Re: Istar 5" f/8R30, first light new [Re: johnnyha]
      #5675835 - 02/12/13 01:14 PM

Johnny
I agree with your and Gord's magnification comments.

I usually view Jupiter somewhere from 125 to 170 X in My 130 mm apo. At 200 X subtle detail is not normally improved but I have had a couple of rare occasions when it did show a bit more detail.
For my little AS80/840 Zeiss achromat 100-140 is the range that seems to work on Jupiter. The 0.6-0.8 mm exit pupil range seems to work best from my experience.

I also had an APQ100/1000 for ten years, this worked well in the 125-166X range on Jupiter. I never had a night when 200 X worked better.

A couple of exceptions are Mars and Saturn. I have used using higher mag to see the smaller detail in Mars. Possibly the contrast is different and also the damn planet is usually so small. I have used smaller exit pupils around 0.5 mm (250-260 X) on these targets. Sometimes even higher but not to gain anything.

The bright moon can usually take a higher magnification than Jupiter does. I guess the contrast here is also very different. Seeing smaller craterlets easier for my eyes sometimes requires 200 +.

Tighter and difficult doubles however can benefit from extreme mag 40-50X aperture in inches. Seeing dependent.

I would expect a good 5 inch achromat would operate best in the 125-170 X on Jupiter.

Both of Tom's scopes seem to be working well, the differences seem minor. The length of the tubes and mass of the lenses/ota seem to be the main differences.

Kevin


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: Kevin Barker]
      #5675878 - 02/12/13 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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar 5" f/8R30, first light new [Re: t.r.]
      #5676607 - 02/12/13 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,


Post Extras: Print Post   Remind Me!   Notify Moderator  
mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Istar 5" f/8R30, first light new [Re: Gord]
      #5676820 - 02/12/13 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. Mike

Edited by mikey cee (02/12/13 11:44 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
AlienRatDog
Carpal Tunnel
*****

Reged: 07/15/05

Loc: Ann Arbor
Re: Istar 5" f/8R30, first light new [Re: mikey cee]
      #5677114 - 02/13/13 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?

Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: AlienRatDog]
      #5677147 - 02/13/13 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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Kunama
professor emeritus


Reged: 10/22/12

Re: Istar 5" f/8R30, first light new [Re: AlienRatDog]
      #5677149 - 02/13/13 07:44 AM

Quote:

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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: Kunama]
      #5677342 - 02/13/13 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.

Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5677387 - 02/13/13 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.com/forums/viewpost.asp?forum_post_id=606701&poll_id...


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar 5" f/8R30, first light new [Re: t.r.]
      #5677475 - 02/13/13 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,


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: Gord]
      #5677533 - 02/13/13 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... 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?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Gord
Carpal Tunnel
*****

Reged: 01/06/04

Loc: Toronto, ON, Canada
Re: Istar 5" f/8R30, first light new [Re: t.r.]
      #5677619 - 02/13/13 12:39 PM

Quote:

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... 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!!

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,


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: Gord]
      #5677649 - 02/13/13 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! 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

Post Extras: Print Post   Remind Me!   Notify Moderator  
Kevin Barker
super member


Reged: 04/22/09

Loc: Auckland, NZ
Re: Istar 5" f/8R30, first light new [Re: t.r.]
      #5678651 - 02/14/13 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


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: Kevin Barker]
      #5678813 - 02/14/13 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!


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5678906 - 02/14/13 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!


Post Extras: Print Post   Remind Me!   Notify Moderator  
johnnyha
Postmaster
*****

Reged: 11/12/06

Loc: Sherman Oaks, CA
Re: Istar 5" f/8R30, first light new [Re: Kevin Barker]
      #5678978 - 02/14/13 08:59 AM

Quote:

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?


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: johnnyha]
      #5678990 - 02/14/13 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!!! 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


Post Extras: Print Post   Remind Me!   Notify Moderator  
tomharri
sage
*****

Reged: 09/19/08

Loc: USA
Re: Istar 5" f/8R30, first light new [Re: t.r.]
      #5679046 - 02/14/13 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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
t.r.
Post Laureate
*****

Reged: 02/14/08

Loc: Upstate NY
Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5679330 - 02/14/13 12:13 PM

Quote:

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.


Post Extras: Print Post   Remind Me!   Notify Moderator  
stanislas-jean
Carpal Tunnel


Reged: 10/22/08

Re: Istar 5" f/8R30, first light new [Re: tomharri]
      #5680676 - 02/15/13 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


Post Extras: Print Post   Remind Me!   Notify Moderator  
mikey cee
Postmaster
*****

Reged: 01/18/07

Loc: bellevue ne.
Re: Istar 5" f/8R30, first light new [Re: stanislas-jean]
      #5683247 - 02/16/13 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!! Mike

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | (show all)


Extra information
36 registered and 48 anonymous users are browsing this forum.

Moderator:  Scott in NC, FirstSight, panhard, star drop 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 3502

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics