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Istar 5" f/8R30, first light

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#1 tomharri

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Posted 07 February 2013 - 10:49 AM

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?

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#2 Kevin Barker

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Posted 07 February 2013 - 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

#3 tomharri

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Posted 07 February 2013 - 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!

#4 zjc26138

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Posted 08 February 2013 - 12:39 AM

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

#5 Kevin Barker

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Posted 08 February 2013 - 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.

#6 ValeryD

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Posted 08 February 2013 - 03:20 AM

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.

#7 t.r.

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Posted 08 February 2013 - 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? :john:

#8 johnnyha

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Posted 08 February 2013 - 07:29 AM

:gotpopcorn:

#9 tomharri

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Posted 08 February 2013 - 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.

#10 Gord

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Posted 08 February 2013 - 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,

#11 RussD

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Posted 08 February 2013 - 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

#12 Jeff B

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Posted 08 February 2013 - 04:43 PM

...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

#13 Gord

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Posted 09 February 2013 - 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,

#14 Sean Cunneen

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Posted 09 February 2013 - 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.

#15 tomharri

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Posted 09 February 2013 - 07:49 PM

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.

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#16 tomharri

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Posted 10 February 2013 - 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.

#17 bremms

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Posted 10 February 2013 - 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!!

#18 Kevin Barker

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Posted 10 February 2013 - 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

#19 tomharri

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Posted 11 February 2013 - 07:20 AM

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.

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#20 Gord

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Posted 11 February 2013 - 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,

#21 tomharri

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Posted 11 February 2013 - 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.

#22 Gord

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Posted 11 February 2013 - 09:35 PM

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,

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#23 tomharri

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Posted 12 February 2013 - 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.

#24 johnnyha

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Posted 12 February 2013 - 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.

#25 Kevin Barker

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Posted 12 February 2013 - 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






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