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iStar Optical’s Phantom FCL 140-6.5 review


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iStar Optical’s Phantom FCL 140-6.5 review

 

Tested and written by Josef Ladra

(I have no financial or other interest in iStar Optical, its owner and employees. All tests were performed and described to my best abilities of a highly experienced amateur astronomer)

 

 

 

 

iStar Optical has been successfully manufacturing 127-250mm F5-F15 achromatic lenses for many years. These lenses are also purchased by various professional manufacturers of achromatic telescopes, as well as by amateurs who build refractors for themselves.

 

Technologically advanced achromats with the designations R30-T, R35-S, and R50-S (Anastigmatic, T-thick, S-slim) are also very well known because the optical design reduces chromatic aberration by 30-50% when compared to Fraunhofer’s conventional achromat designs. This is due to an improved false color correction due to incorporation of a dense flint (type of an ED glass) in the design.

 

H-Alpha (solar) 150 mm, 228 mm, and 250 mm lenses, which are used by solar observers and imagers achieve outstanding results, have also become very popular and successful on the global market.

 

Recently, iStar began to sell the long-awaited apochromatic telescope Phantom FCL 140-6.5 and has also designed a 170 / F7 model.

 

In the first series, the OTAs were manufactured with a standard tube length with matching 100 mm (4”) rack and pinion focuser with 80mm tube travel. This is a fairly common issue where a standard length of the main tube sometimes does not allow the use of some accessories with a longer optical path. Most manufacturers end up producing their telescopes with shorter tubes and then customers are forced to purchase an extension tubes of various lengths to remedy the problem. iStar approached this issue from a different angle. Even though iStar is still producing a certain number of telescopes with standard tube lengths, the second and latest series is being designed and produced with a removable (threaded) 80 mm rear section of the tube. By removing the rear section it is now possible to use the scope with all types of bino-heads (binoviewers), filter wheels + OAG, other specialized imaging equipment requiring longer back focus distance. For example, my own Baader-Zeiss Mark V binoviewer still have a 25 mm reserve in focus.

 

 

 

 

As can be seen in the next picture, with the OTA not shortened (the 80mm rear section attached), the telescope is slightly longer than the TEC 140 / F7. However, after shortening the tube by removing the rear 80 mm section, the Phantom is significantly more compact than the TEC 140. The Phantom focuser has 80 mm tube travel and has a rotary lock mechanism attached via M61 thread. Unfortunately, on one of two tested Phantom FCL 140-6.5 OTAs, this mechanism does not clamp the accessories 100% and tends to slip slightly from time to time. The mechanism is secured with several worm screws and is attached on a M63 internal thread into which other accessories such as a flattener/reducer (F/R), cameras, etc. can be inserted.

 

 

 

 

 

This is an illustration of how you can disassemble the rear section of the focuser for the use with other accessories.

 

 

 

 

 

I decided to compare the Phantom CFL 140-6.5 with the top-of-the-line TEC 140/F7, which was produced in the ED version, using FLP-53 optical glass manufactured in Ohara, Japan. Today it is produced in the FL version (CaF2). The TEC 140 refractor has an aplanatic three-element oil lens, which means that the lens behaves like a compact optical element with two optical surfaces. This offers an advantage in contrast, as it creates a minimum of reflections over the air-spaced triplet used in the Phantom, which has six optical surfaces. However, when observed, I did not find a difference in contrast in the image of the Phantom and TEC refractors. When I first looked at the diffraction pattern of the star Vega, it was immediately clear that the Phantom has a better color correction of the spectrum than the TEC, which was an unexpected surprise to me. I compared the in/out of focus star diffraction rings and both telescopes showed textbook set of concentric rings.

 

 

 

The diffraction pattern (IN/OUT) on Arcturus shows the slightly turned-up edges of this particular telescope lens, however, it is completely within the limits of high surface accuracy of RMS 0.024 and the resulting excellent Strehl 0.977.

 


Click on image to launch full-sized version in a new tab

 

The Ronchi test shows the Phantom has an excellent lens, and I have no reservations about that. The objective collimation was checked by the GMK collimator (Grzybowski) and shown to be practically perfect. The inside of the telescope tube is well blackened and there are no shiny reflective surfaces anywhere. The telescope has three knife-edge baffles mounted inside the tube.

 

 

 

 

The next was a photographic test, showing stars without chromatic aberration, and how big of a field of view can Phantom actually produce (the full resolution image must be opened in a new window). I took the first cropped image with an APS-C format using non-modified SONY A7SII (pixel size 8.4 μm). It can be seen that near the corners, the stars are beginning to have an elliptical shape and being slightly out of focus that is expected from a very fast APO triplet. However, the specially designed Starizona Apex ED-L reducer / corrector (R/C) designed for APS-C sensor, or WO flattener 68III for Full Frame, fully remedies this issue (Starizona is currently testing their brand new FF (Full Frame) field flattener matched to the Phantom FCL 140-6.5. These new units should become available for sale by early 2022). Other universal field flatteners/reducers can also be used. There is absolutely no chromatic aberration visible on white stars. Unfortunately, I took tests in the MSA 20.4 area, so I used a SkyTech QuadBand filter on some images, which turned out to be inappropriate because it creates a visible halo around the stars. There was also a considerable amount of moisture in the high layers of the atmosphere.

 

 


Click on image to launch full-sized version in a new tab

 

 

Following images were taken using ASI071MC camera (4.78 μm pixel) with and a QuadBand filter from SkyTech. 

 

 


Click on image to launch full-sized version in a new tab

 


Click on image to launch full-sized version in a new tab

 


Click on image to launch full-sized version in a new tab

 


Click on image to launch full-sized version in a new tab

 

 

In the next series of tests I performed observing the sunspots, and here again the Phantom proved to be practically flawless. Image reproduction of the spots, granulation and foculae, all in great contrast, everything as it should be with a high-quality refractor.

 

Next, I observed Jupiter and Saturn, attaching Zeiss Mark V binoviewer without power-mate and Nagler 5 mm eyepieces. The image quality was excellent with great level of contrast. When observing stars, globular clusters and DSOs with the Panoptic 24 mm eyepiece, the stars retained perfect image quality all the way to the very edge of the field of view. Absolutely comparable image quality with my TEC 140.

 

Conclusion:

From what I was able to see, I conclude that the optics belongs to a Super APO class, which is highly suitable for both visual observing and astrophotography. Unfortunately, I have to state that the TEC 140 lost in the direct side-by-side chromatic aberration comparison test, otherwise the TEC is practically perfect from the optical point of view. The Phantom FCL 140-6.5 is, therefore, a great all-round refractor, and the manufacturer has promised to remedy the minor mechanical issue with the amount of “grip” of the rotary lock. Therefore, iStar Optical can be congratulated on a very well made optical instrument.

 

Technical specification of the telescope:

 

Lens diameter: 146 mm (class FPL-53 (Hoya FCD100) + 2 x ED glass) FMC layers on glass-air surfaces

Clear aperture: 140 mm

Focal Length: 910 mm (F/6.5)

Theoretical max. Resolution: 0.8 "

Focuser: 100 mm (4.0 ”) with reductions to 2” and 1.25”, with rotary locking system

telescope length (retracted): 826 mm

Tube diameter: 144 mm

Back Focus: 138 mm

Focuser tube travel: 80 mm

Dovetails: Losmandy 300 mm & Vixen 300mm (each scope is supplied with both)  the Vixen dovetail serves as a handle 

Fully Retractable dew shield  with lock

Weight: 10.1 kg (including CNC machined tube rings and dual dovetails

Guaranteed minimum Strehl: 0.90

Guaranteed minimum PV: lambda 1/5

Manufacturer's website: Istar-Optical.com


  • Bob Campbell, Gregory, weis14 and 13 others like this


28 Comments

Excellent review and direct comparison!

    • Maximus001 likes this
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Stargazer3236
Dec 02 2021 02:21 PM

Too bad it wasn't cheaper, but alas, that's what you pay for excellence!

Too rich for my blood. Sticking with my cheap by comparison TV85.

Great review, really nice scope and great shots. Thanks for the side by side comparison. It is definitely a game changer in the APO market and really the price is reasonably for what the performance is. 

Great review! I actually read it before I did mine (yours was the one I was referencing). I agree the Phantom 140 f/6.5 delivers great performance especially given the price of competitors that it beats or equals.

CS!

That is one extremely impressive refractor!

Thank you for your review.  The 140 is becoming the sweet spot for refractors it seems and now there are a lot of excellent offerings in that category making the decision of which 140 refractor to buy more difficult.  

Photo
Christine_Z
Dec 06 2021 01:15 PM

Thank you for the review...A 140 that can be reduced to f/4.2 that's kinda really appealing for smaller format cameras and EAA

I would like to see a side by side comparison between the AP Gran Turismo, Takahashi has TOA-130NS and the iStar Phantom FCL 140. The first two are 10mm smaller and over $2K more expensive.

    • Navy-Jim and ddouble518 like this

Thank you to all. It would be nice comparison, it's a pity AP Gran Turismo and TAK TOA is out of stock.

How about showing the wave front error profile, strehl ratio, and Ronchi on the TEC you used?  If it showed more CA, it would help to understand why.  Does not appear to be any quantative data to support the observation.  

TEC 140 ED (not FL) has significant more chromatic aberration because of used glasses - K10/FPL53/BK7 and RC index is 0.9, while RC index of Phantom is 0.6. Simply put, Phantom uses a better combination of glasses and modern optical design. You can see Airylab test, this TEC is little bit worst than my TEC.

Photo
ISTAR Optical
Dec 12 2021 02:25 PM

I would like to see a side by side comparison between the AP Gran Turismo, Takahashi has TOA-130NS and the iStar Phantom FCL 140. The first two are 10mm smaller and over $2K more expensive.

Hello, I am so confident about the modern design, quality of optical glass and superior quality of iStar's Phantom FCL 140-6.5 Super APO triplet that I would welcome such direct side-by-side comparison and testing. I am quite sure that our new APO triplet will either match or exceed the quality of all comparable models using comparable optical design (a triplet, regardless if air spaced, cemented or oil spaced).

 

best regards,

 

Ales

    • sonny.barile and StarAlert like this

Ales, congratulations on what appears to be a top tier scope.  Can you elaborate on why, given the degree of confidence you have in how your scope would compare to AP/Tak/Tec, etc., the strehl guarantee is only 90%?  Thank you. 

The standard Strehl value has Istar from 0.96 to 0.98. The manufacturer only guarantees a minimum value 0.90 in all circumstances.

 

Generaly - The acceptable level of wavefront aberrations is  value of 0.80 Strehl is conventionally used to define an optical system as “Diffraction limited”, as we know.

Photo
Hobby Astronomer
Dec 24 2021 08:37 PM

Very nice review with lots of detail.

 

Have to ask this most important question when a review is offered...

 

Do you own this scope? Will this be your primary imaging telescope going forward?

 

Again thanks for the work putting this together.

Thank you! No, the tested Istar telescope was my colleague's telescope, I have a TEC 140ED. A lot of people usually tries to praise their own technique, this is not my case. I have many telescopes and not one of them is primary for imaging.

Sharpstar (& rebranders) sell a fast 140mm double ED triplet. The Istar seems similar...

Yes, Sharpstar has 140 / 6.5 like other manufacturers (CFF, TS-Optics, ES and etc.), but that's a different lens design and glass than iStar. Anyway, I'm a little disappointed with the Sharpstar Hypergraph8, it's a bad telescope. I've seen bad primary mirrors and the image quality isn't very good. Much better are Hypergraph6 and 130 (Hyperbolic mirrors) IMHO.

Are  Istar's lens and OTA made by Istar?

I know the other APO similar to Istar Phantom  140.

These refractors seems twin...

Are  Istar's lens and OTA made by Istar?

I know the other APO similar to Istar Phantom  140.

These refractors seems twin...

iStar lens are made by them. I build a custom telescope using the iStar 140mm f6.5 APO lens, the same one used in the Phantom 140, and I am extremely happy with the performance of the lens. It is consistent with the review on this thread.

iStar has a proprietary and original optical design and there is no identical optical design from any other manufacturer. In this time has new optical design for 200 mm F6 Super APO and prepared also FF/APS-C reducer for F3.9!

Photo
ISTAR Optical
Jan 12 2022 05:08 PM

I would like to see a side by side comparison between the AP Gran Turismo, Takahashi has TOA-130NS and the iStar Phantom FCL 140. The first two are 10mm smaller and over $2K more expensive.

Hello,

a new customer from Poland is going to do side by side comparison with 3 or 4 similar models by Takahashi, APM, CFF and AP from what he said. They have their nation wide astro meetings coming up this spring and that is where all these scopes will be in one place. So Im curious about the outcome myself but if I had to bet, I think Phantom 140 will end up as a virtual tie or even above the image quality of some of these comparable models. 

I will ask him to post his review on CN.

Photo
ISTAR Optical
Jan 12 2022 05:11 PM

Ales, congratulations on what appears to be a top tier scope.  Can you elaborate on why, given the degree of confidence you have in how your scope would compare to AP/Tak/Tec, etc., the strehl guarantee is only 90%?  Thank you. 

Hello,

Psion's response to your question is spot on. I would write exactly the same. 

Photo
ISTAR Optical
Jan 12 2022 05:17 PM

Sharpstar (& rebranders) sell a fast 140mm double ED triplet. The Istar seems similar...

Yes, and so it Takahashi TOA-130NFB. This is an idea that will be copied by others.

Ive heard from one or two other people about this company and I can assure you and others that iStar has absolutely no affiliation with Sharpstar.

 

To stay ahead of the curve we just finished a new revolutionary Super APO design that will outperform everything else on the market as of now. Im thinking about filing a patent on this idea, if possible. It would be worth it. 



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