40 replies to this topic

[moshen]

A local CN member reached out to me to DPAC his Stellarvue SVX127D. It was purchased and picked up April 2022, but was in storage and I was the first to unwrap it. Impressions of the build quality and fit and finish is excellent. It has removable sections to shorten the tube for binoviewing as well as a Feathertouch focuser. I put it up against my 6" flat and a 200LPI ronchi.

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Edited by moshen, 16 May 2023 - 05:36 AM.

[moshen]

Taking a look at the supplied interferogram we see a good correction and strehl, tested in red. Also visible is a center hill and a ring zone, these will be very visible in 200 LPI DPAC but we see from the inteferogram the hill is only 1/75 wave high in red, or 1/64 wave in green.

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[nicknacknock]

Moshen,

 

I look forward to your incoming posts in this thread, but somewhere along the line, I would appreciate it if you could comment on what the impact would be if this was masked down to 125mm.

 

I notice the edges are kinda "rough" (even though we are down to a ridiculously low wavefront as is). This seems to be a great scope, but I am just wondering what difference those 2mm would make.

[Maciek_Cz]

Nicknacknock, the answer is simple, Strehl equals almost 1

[moshen]

DPAC results. I use a 200lpi ronchi and it's more sensitive than a 133lpi ronchi. Keep that in mind when comparing with other DPAC results. It turns out that this sample is slightly undercorrected in red and best correction is in yellow-green (I use a led that peaks at 557nm).  In the interferogram (that was done with Stellarvue's Zygo and red laser) I believe the undercorrection in red can be seen in the profile - the edge and center are slightly raised.

 

In green it essentially nulls out and I don't see any edge issues.

 

This is a f/8 doublet and the white LED images shows color correction is very good.

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[moshen]

The 'knife-edge' view shows a relatively smooth surface with the center and ring zone visible. These features match Stellarvue's supplied Zygo surface plot and if I'm reading the plot correctly the center zone is only 1/75 wave in red, or 1/64 wave in green. The ring zone is even smaller than that.

 

The white LED again shows color correction to be very good.

 

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[moshen]

Star Testing

 

Seeing was not the best but inside & outside patterns were white with no color that I could see. The doublet does very well here. The patterns on both sides of focus looked identical at first pass and confirmed what DPAC tests show. Over time I could tease out subtle differences such as the inner zones and a slightly brighter outer ring on the inside focus. I've never seen a perfect star test, I can always tease out differences in diffraction patterns with a bit of time but my goal here was to identify any issues not seen in DPAC.

 

Since seeing was not great, I set up an indoor star test to look for astigmatism or collimation issues under high power.  With a 3mm eyepiece (338x) I could see a perfectly centered airy disc with one diffraction ring and no astigmatism or other apparent issues.

 

Overall I think the owner has an excellent scope. While we know Stellarvue tests and nulls in red light, we can see here that this sample is actually slightly undercorrected in red and that happens to place the best correction in yellow-green.

Edited by moshen, 16 May 2023 - 05:28 AM.

[fate187]

Is the center zone a prominent feature in all chinese fabricated doublets? This was also seen in Jeff's SW150EDs right.

[Wildetelescope]

Machine polishing.

Jmd

[Maciek_Cz]

Great results.
Ronchi screen 200 lpi is very sensitive.
AOS gives Strehl ~0.994 in red (zones not included, SA only).

[Eddgie]

It is good to see that the supplied wavefront analysis was easily confirmed by the DPAC test. 

 

The SV127D was one of the two Apos I considered buying and while I did not go with the SV127D, I had high confidence that the optical quality would be at the top end of what money can buy. 

 

Nice to see such superb optical quality and at $3K (With the SV focuser), this is probably one of the best deals in the high end Apo world. 

Edited by Eddgie, 16 May 2023 - 09:23 AM.

[Jeff B]

A very nice objective Moshen.

 

I see those small circular machine polish center zones way more often than not.  No big deal in reality but they jump out in DPAC, which is why it's such a powerful tool.

 

Are the individual color images derived from the white light images?

 

Well done.

 

Jeff

[Bikeboy60]

I love my SVX127D.  Pinpoint stars.  Perfect star test.  Lately I have been enjoying splitting binaries and observing globulars.  Last fall the planets had breathtaking detail.  Vic has done a wonderful job with these scopes.

 

I encourage you all to look through one if you get a chance:-)

 

Keep Looking Up,

Bob

Edited by Bikeboy60, 16 May 2023 - 11:58 AM.

[moshen]

A very nice objective Moshen.

 

Are the individual color images derived from the white light images?

 

Well done.

 

Jeff

 

Thanks Jeff. I used LEDs with peaks at 470nm, 557nm, and 640nm for the color images.

[ken30809]

A very nice objective Moshen.

 

I see those small circular machine polish center zones way more often than not.  No big deal in reality but they jump out in DPAC, which is why it's such a powerful tool.

 

Are the individual color images derived from the white light images?

 

Well done.

 

Jeff

How does this objective compare to the SVX127D that was DPAC'd a few weeks ago?

[Scott in NC]

How does this objective compare to the SVX127D that was DPAC'd a few weeks ago?

Upon first glance, they look pretty close, but I'll go back and look at the images that I took of that scope and give my opinion later tonight.

[nicknacknock]

How does this objective compare to the SVX127D that was DPAC'd a few weeks ago?

Ken,

 

I try to keep this list updated so that all can reference to it. Has both tests there. Hope it helps!

[ken30809]

Ken,

 

I try to keep this list updated so that all can reference to it. Has both tests there. Hope it helps!

Thanks Nick (and Scott),

That is well organized and allows for easy side by side comparisons.

[Maciek_Cz]

I started analyzing ronchigrams. In the AOS version without zones and edges, the results are as follows:
red ~0.994, green ~0.994, blue ~0.968.
I remind you that these results apply only to spherical aberration!
Thus, the specimen studied by Moshen is significantly different from that examined by Scott.

Edited by Maciek_Cz, 17 May 2023 - 05:09 AM.

[ken30809]

I started analyzing ronchigrams. In the AOS version without zones and edges, the results are as follows:
red ~0.994, green ~0.994, blue ~0.968.
I remind you that these results apply only to spherical aberration!
Thus, the specimen studied by Moshen is significantly different from that examined by Scott.

Yes, there will always be variations among specimens due to variations in the figuring process, environment, testing, etc.

 

Sorry, did not intend to get off of the topic of Moshen's testing. Thanks all.

[Maciek_Cz]

Yes, there will always be variations among specimens due to variations in the figuring process, environment, testing, etc.

Sorry, did not intend to get off of the topic of Moshen's testing. Thanks all.

Remember the one Scott analyzed was 1/4 lambda in blue and 1/6-1/7 lambda in green. The one from this thread is above 1/10 lambda in each color.

[edinorcal]

Big thanks to Moshen for taking up a meaningful chunk of his time to DPAC, star test and evaluate my SVX127D,  and to Maciek for analyzing the results in his AOS software. Although I had a department store refractor over 50 years ago and even tried to grind my own glass, I'm once again a virtual beginner in AA, and I depend on the community here to help guide me in my decisions, It's a great resource that provides both an objective means of testing an OTA and the the subjective experience of fellow owners, and I really appreciate everybody's input.  Moshen mentioned that someone asked for the serial number of the lens. It is Serial # 41.

[ken30809]

Big thanks to Moshen for taking up a meaningful chunk of his time to DPAC, star test and evaluate my SVX127D,  and to Maciek for analyzing the results in his AOS software. Although I had a department store refractor over 50 years ago and even tried to grind my own glass, I'm once again a virtual beginner in AA, and I depend on the community here to help guide me in my decisions, It's a great resource that provides both an objective means of testing an OTA and the the subjective experience of fellow owners, and I really appreciate everybody's input.  Moshen mentioned that someone asked for the serial number of the lens. It is Serial # 41.

It's a very nice scope. Congratulations.

[Bikeboy60]

Big thanks to Moshen for taking up a meaningful chunk of his time to DPAC, star test and evaluate my SVX127D,  and to Maciek for analyzing the results in his AOS software. Although I had a department store refractor over 50 years ago and even tried to grind my own glass, I'm once again a virtual beginner in AA, and I depend on the community here to help guide me in my decisions, It's a great resource that provides both an objective means of testing an OTA and the the subjective experience of fellow owners, and I really appreciate everybody's input.  Moshen mentioned that someone asked for the serial number of the lens. It is Serial # 41.

Looks like our scopes might be from the same batch:-) I have SN43.  I have really enjoyed my SVX127D.  I am strictly a visual observer.  I hope you get a lot of enjoyment from it.  Bob

[iseegeorgesstar]

Thanks for posting this. I've had my eye on this scope for a while as I have the 4" version of this scope and often wonder if the extra bulk is worth the extra inch in aperture.