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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, jimegger and 18 others like this


46 Comments

Photo
ISTAR Optical
Jan 12 2022 05:18 PM

Are  Istar's lens and OTA made by Istar?

I know the other APO similar to Istar Phantom  140.

These refractors seems twin...

Hello,

please see previous post by Psion. It explains quite nicely. 

Hello,

please see previous post by Psion. It explains quite nicely. 

Has the Phantom's lens 3 ED elements? 

According to Psion's review, it seemed that Phantom 140APO have 1 FPL53 class + 2 other ED class lenses in the cell.

Yes Phantom is triplet (1+2 lenses) and in the review you can read "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."

I can attest to the quality of iStar's optics.  I built a scope last year using this lens.

More detail can be found at seriousastronomy.com.

 

Cheers,

 

Ted White

Great to see a quality product not made in China. Hopefully it's a success. I have an ES FPL53 140MM f/6.5 Triplet on order. How does the ES compare with the Phantom? 

Unfortunately I don't know anyone who can compare these telescopes side by side, otherwise it's just conjecture.

    • VincentJC likes this

ISTAR,

 

Is the Phantom 140 part of your new "Super APO" design referenced above, or will there be another scope available soon?

I just ordered the 140. The web site said they had these scopes in stock. I have heard that before. I hope it’s true. I am really looking forward to getting this scope!

 

Those are some really nice images!!!!

Photo
ISTAR Optical
Feb 15 2022 08:50 PM

ISTAR,

 

Is the Phantom 140 part of your new "Super APO" design referenced above, or will there be another scope available soon?

Hello Stephen,

yes, all these new scopes produced since 2011 are part of the Super Apo design. We are not planning any other telescope line. 
actually, the latest design variation is superior to all of the previous models. We have achieved a stunning fully corrected F/6 system both in 204mm and 175mm aperture class. I don’t know of any competition offering such fast systems in this aperture range. 
 

    • Jon_Doh likes this

Hello Stephen,

yes, all these new scopes produced since 2011 are part of the Super Apo design. We are not planning any other telescope line. 
actually, the latest design variation is superior to all of the previous models. We have achieved a stunning fully corrected F/6 system both in 204mm and 175mm aperture class. I don’t know of any competition offering such fast systems in this aperture range. 
 

This looks promising for the 170mm lens.

I was a little concerned about the halos in the images, the minor ones not so much, but the larger one associated with the bright star made me think of the Antlia filter line.  I suppose there are a number of filters that could be tested to mitigate halos, also processing of course to which I know nothing.  However, I have seen demonstrations of the effectiveness of an Antlia filter suppressing halos and the results were impressive.  Has anyone else considered this filter as a candidate for testing with the Istar 140?

Photo
denis0007dl
Apr 06 2022 04:41 AM

Excellent report!

 

What is fantastic there, besides excellent optics, is that telescope tubus can be shortened, and binoviewers users can reach focus without using need of using any GPC etc!

I just purchased an iStar Phantom FCL 140mm (5.51") f/6.5 refractor telescope this month, April 2022.  I'm so glad I did!

 

I am getting older, and I can no longer comfortably lift and mount a traditional f/12 refractor of this aperture.  The iStar Phantom 140mm telescope is shorter, lighter, and much easier to mount, and offers me even larger aperture than I had before (old telescope was a 127mm f/12).

 

The Phantom's super apochromatic corrected lens is a delight to view through.  I enjoy studying the moon.  On lunar images, the contrast and detail are astounding.  I tried several of my orthoscopic eyepieces, and saw no limit to details my eyes could discern.  So just for fun, I used a 2x Barlow and my shortest 4mm orthoscopic eyepiece (Magnification = 2* 910/4 = 455x).  The image was still clear to the finest details.  It seemed unbelievable.  Also one of the first things I noticed right from the beginning of viewing, was the colour purity of the image compared to my old telescope. It just was so refreshingly pure.  I can't describe it better with any other adjective.

 

The spring weather in southern Ontario has not been night sky friendly, and seeing conditions had lots of turbulence, 3-4 out of 10 is how I rated the atmosphere.  I managed to

take a quick image through this telescope with eyepiece projection to my cheap grainy webcam. It is a screen capture on a laptop limited to 1366x768 pixels, no filters, no processing, just a single frame shot.  You can see there are details in the shadow of the crater still wanting to be pulled out by a better image capture device.  When viewing directly with eyes, there seems to be no breakdown of the image no matter what eyepiece I used!

 

iStar Phantom FCL 140mm f/6.5 super APO refractor
 

The build quality and finish of the telescope are first class.  The fact that it is shorter and lighter than traditional achromatic refractors, has a double mount that can be used as a carrying handle for us older astronomers, yet offers a super apochromatic corrected lens at a price that is lowest on the market for this aperture of telescope, makes it the best telescope value on the market as far as I'm concerned.

 

Boris D.

Toronto, Canada

    • denis0007dl and lwbehney like this

I have had my Phantom 140mm out a few times for some imaging since I got it. It seems to do a really good job. I am looking forward to using it a lot more after galaxy season. 

I did image M51 with it. I didn’t get good focus on it so I wasted a few hours of data, but it still looks pretty good if I don’t zoom in at all. 

 

M51 RGB session 1 St

 

UntitledUntitledUntitled 2
 
Istar 140

 

 
The moon is the first image I tried with my Istar Phantom and I did get this one with decent focus.
    • ArizonaScott and denis0007dl like this

   A very good review and comprehensive test , which I'm reading a bit late in the game. A bit pricy, but what can you expect from this class of scope. Nate Goodman  (Nato). Salt Lake, Utah.

4500 dollars is a lot of money but isn’t bad at all for such a large triplet. 

I got out to a dark site last night and did some imaging with my Istar 140mm Phantom. I think I am going to be very happy with this scope. 

Seeing was good and my auto guiding was just so so, but I manage to get some sharp photos with my new scope.

 

m51B RGB session 1 St
 
M13

 

    • ArizonaScott and denis0007dl like this
m45
 
I thought I would add one more image I have taken through my Phantom scope. The longer I use it the more I like it. 
Photo
ISTAR Optical
Nov 05 2022 03:59 PM

I just purchased an iStar Phantom FCL 140mm (5.51") f/6.5 refractor telescope this month, April 2022.  I'm so glad I did!

 

I am getting older, and I can no longer comfortably lift and mount a traditional f/12 refractor of this aperture.  The iStar Phantom 140mm telescope is shorter, lighter, and much easier to mount, and offers me even larger aperture than I had before (old telescope was a 127mm f/12).

 

The Phantom's super apochromatic corrected lens is a delight to view through.  I enjoy studying the moon.  On lunar images, the contrast and detail are astounding.  I tried several of my orthoscopic eyepieces, and saw no limit to details my eyes could discern.  So just for fun, I used a 2x Barlow and my shortest 4mm orthoscopic eyepiece (Magnification = 2* 910/4 = 455x).  The image was still clear to the finest details.  It seemed unbelievable.  Also one of the first things I noticed right from the beginning of viewing, was the colour purity of the image compared to my old telescope. It just was so refreshingly pure.  I can't describe it better with any other adjective.

 

The spring weather in southern Ontario has not been night sky friendly, and seeing conditions had lots of turbulence, 3-4 out of 10 is how I rated the atmosphere.  I managed to

take a quick image through this telescope with eyepiece projection to my cheap grainy webcam. It is a screen capture on a laptop limited to 1366x768 pixels, no filters, no processing, just a single frame shot.  You can see there are details in the shadow of the crater still wanting to be pulled out by a better image capture device.  When viewing directly with eyes, there seems to be no breakdown of the image no matter what eyepiece I used!

 

 
 

The build quality and finish of the telescope are first class.  The fact that it is shorter and lighter than traditional achromatic refractors, has a double mount that can be used as a carrying handle for us older astronomers, yet offers a super apochromatic corrected lens at a price that is lowest on the market for this aperture of telescope, makes it the best telescope value on the market as far as I'm concerned.

 

Boris D.

Toronto, Canada

That is very impressive. Thank you so much for sharing with everyone here on CloudyNights.com.

Photo
ISTAR Optical
Nov 05 2022 04:01 PM

 

 
 
I thought I would add one more image I have taken through my Phantom scope. The longer I use it the more I like it. 

 

Jeff,

 

could you do me a big favor and send this image in full resolution to our graphics guy Petr in Europe petr@istar-optical.com together with basic info about your set up, time sequences, filters used (if any), etc.. I would like to post this image on our website, it is a quite nice one. If you have other images in high quality, please share with us. Thank you,

 

Ales

Jeff,

 

could you do me a big favor and send this image in full resolution to our graphics guy Petr in Europe petr@istar-optical.com together with basic info about your set up, time sequences, filters used (if any), etc.. I would like to post this image on our website, it is a quite nice one. If you have other images in high quality, please share with us. Thank you,

 

Ales

I can do that, Ales. 

 

Jeff



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