122 replies to this topic

[Jeff B]

So here are the basic DPAC  OUCH!  I mean, double pass results.  Put the cursor over them to read their titles.

 

 

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[fishhuntmike]

Looks like a keeper!!!

[dryfly]

Pretty **** good.

 

Mike

[mblack]

beautiful scope :-) easy to say as it’s not mine, but I wasn’t really thinking test results would be in doubt.

 

just needs a sticker like this ; )

 

 

 

[Dean J.]

Yuri and company sure make nice scopes.  

[Paul Morow]

Wow, that's amazing!

 

Definitely the absolute best blue DPAC I have ever seen.

 

I would guess the images are going the be very cool. Not just cool, but wicked cold images. Absolutely no warmth to the images at all.

 

If one uses the instrument on a hot summers night your eyeballs might get frostbite.

 

I definitely want to experience some views through a Yellow Submarine someday.  

[RichA]

These tests are appreciated and in-case anyone needs a reference scope to compare all the rest to, when it comes to CA control, SA control and smoothness of figure, I nominate this one:

 

https://www.cloudyni...3#entry13152804

[Jeff B]

My take is that in double pass, this is an overall excellent sample.

 

Best correction seems to be in green.

 

Secondary spectrum is really very low as judged by the lack of red/blue color fringing around the bands in the white light images.  Spherochromatism is similarly very well controlled with only very mild over correction in blue and a little more under correction in red with both colors well under the diffraction limits for their color. 

 

The edges are very good with only minor, very narrow, regional indications of jogging/hooking/rolling.  There is that small edge sector at the 7 o'clock position with a mild under corrected jog or "tail wagging" in the line shadow but it is small, covering only a small sector of the edge.  You can clearly see that small sector in the at focus image above and the one below.  Similarly, you see the small line shadow disturbances at the 2 o'clock position are associated with a localized polish feature as well.  I've seen this before on some other objectives.

 

There is no readily seen circular zoning, and if there are any, they are broad and very mild.  The ubiquitous small center zone from machine polishing is "missing". 

 

Overall polish is very good IMO, especially considering how difficult it is to get a smooth polish on a large FL element.  There is some structure, some of it medium scale in size, but it is random and low in level with smooth transitions.  Similar shots from a TMB/LZOS and an AP 175 EDF are attached for comparisons.  I suspect this will be a low scatter objective with very white stellar cores at high power.

 

I saw no signs of astigmatism when slowly sweeping from one side of focus to the other.

 

Jeff

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[Scott in NC]

Nice work, Jeff!

[Yu Gu]

Beautiful sample! not to mention that DPAC test is more sensitive at F11

[Yuri]

My take is that in double pass, this is an overall excellent sample.

 

The edges are very good with only minor, very narrow, regional indications of jogging/hooking/rolling.  There is that small edge sector at the 7 o'clock position with a mild under corrected jog or "tail wagging" in the line shadow but it is small, covering only a small sector of the edge.  You can clearly see that small sector in the at focus image above and the one below.  Similarly, you see the small line shadow disturbances at the 2 o'clock position are associated with a localized polish feature as well.  I've seen this before on some other objectives.

 

There is no readily seen circular zoning, and if there are any, they are broad and very mild.  The ubiquitous small center zone from machine polishing is "missing". 

 

Jeff

- Thanks Jeff for your tests. I have seen everything you showed above, and as being a very good "as is", it required only 4 minutes of my touch-ups¹...

Whatever is left is caused mostly by the inhomogeneity of glass.

The amplitude of surface errors  for all 4 finished sets is <20nm.

RMS of the wave front for all 4 objectives is in range 0.010÷0.012.

 

 

 

¹ The meaning of this is simple -  your "YS" optics was done by Gabrielle !
 

[Jeff B]

- Thanks Jeff for your tests. I have seen everything you showed above, and as being a very good "as is", it required only 4 minutes of my touch-ups¹...

Whatever is left is caused mostly by the inhomogeneity of glass.

The amplitude of surface errors  for all 4 finished sets is <20nm.

RMS of the wave front for all 4 objectives is in range 0.010÷0.012.

 

 

 

¹ The meaning of this is simple -  your "YS" optics was done by Gabrielle !
 

You are welcome Yuri and thanks for an excellent telescope.

 

Your direct "manufacturer's comments" are most appreciated, helpful and adds directly to our understanding.

 

So Gabrielle is an optician too?  How cool and well done.

 

Jeff

[CrazyPanda]

These tests are appreciated and in-case anyone needs a reference scope to compare all the rest to, when it comes to CA control, SA control and smoothness of figure, I nominate this one:

 

https://www.cloudyni...3#entry13152804

Wow...

 

I'm blown away by how well corrected and how smooth that sample is.

[Dean J.]

- Thanks Jeff for your tests. I have seen everything you showed above, and as being a very good "as is", it required only 4 minutes of my touch-ups¹...

Whatever is left is caused mostly by the inhomogeneity of glass.

The amplitude of surface errors  for all 4 finished sets is <20nm.

RMS of the wave front for all 4 objectives is in range 0.010÷0.012.

 

 

 

¹ The meaning of this is simple -  your "YS" optics was done by Gabrielle !
 

Well done Gabrielle!

[peleuba]

Definitely the absolute best blue DPAC I have ever seen.

 

And, notice how the red and blue are almost equally opposite one-another in correction.  This is a by product of the scope being best corrected for green (green/yellow) light.  This is why nulling in green matters.  It allows for near equal and opposite correction at the far ends of the spectrum.  In this sample, the blue is slightly over corrected and "balanced" (like a see-saw) with the red being under corrected.  In other words the small amount of spherochromatism is balanced between red and blue.

[slavicek]

And, notice how the red and blue are almost equally opposite one-another in correction.  This is a by product of the scope being best corrected for green (green/yellow) light.  This is why nulling in green matters.  It allows for near equal and opposite correction at the far ends of the spectrum.  In this sample, the blue is slightly over corrected and "balanced" (like a see-saw) with the red being under corrected.  In other words the small amount of spherochromatism is balanced between red and blue.

This is doublet f/11. So, in theory, one can make a triplet of even better correction of blue/red or a triplet of the same blue/red correction but of shorter focal ratio, like f/7-8?

Basically, I am wandering "why triplet" ?

Just curious.

[CrazyPanda]

Doublets are lighter and at this aperture, it's going to be hard to get really good color correction at F/7 or F/8 in a triplet. I feel like a lot of triplet designs tend to push the focal ratio too short just because they can. Takahashi solves this by using two ED elements and gives nearly perfect color correction, and even then the TOA 130 is F/7.7, not F/7 like a lot of 130 triplets are.

 

I think the whole point of this scope is to use a doublet but leverage a long focal ratio to minimize color error. I wish more doublets did this to be honest.

 

But I agree that a triplet at F/11 or maybe going down to F/10 would have allowed basically perfect correction. But whether that's worth the extra cost and weight is hard to say. This scope would put up fantastic views as is.

Edited by CrazyPanda, 02 August 2024 - 12:51 PM.

[Jeff B]

slavcek and CrazyPanda, check out case #28 here:

 

https://www.telescop...m#extraordinary

 

on Vlad's excellent site.  Whether or not one can see the improvement associated with the slower doublet is an excellent question. Now, talking to Yuri, he felt the doublet had exceptionally pure and clean star images.  He made no comments to me about comparisons.

 

If someone wants to float me their TEC 160FL, F7 for a solid month, I'll gladly take up the challenge.  I think such a direct comparison would be quite valuable to this community.  

 

But I do have my older TEC 160ED, F8, which has some of the smoothest, best corrected in green/yellow, set of optics I've run across.  It is one of my "Reference" scopes.  It "misses" slightly in the blue but is an exceptional visual scope with no visible, to me, coma or astigmatism at over 400X.  

 

I'll eventually get around to this direct visual comparison, but only after I have wrung out the F11 for a while, which will be reported here.  For now, you will have to chew on the double pass comparison.

 

Jeff

 

 

 

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[Jeff B]

I am a little surprised nobody has commented on the comparison above.

 

They are really very similar overall.  

 

Like the 160FL F11, the "old" 160ED is, as Paul says, an impeccably well balance design, centered on the green/yellow.  The red and blue line shadows smoothly bend in opposite directions by an almost equal amount. 

 

The 160ED's wave front in green is very smooth and uniform, a bit more so than the FL.  But even though double pass clearly shows that, the differences on an absolute basis, are very, very small in magnitude, and IME, will be completely invisible in actual use.  

 

The 160ED does have a little more secondary spectrum and red/blue spherochromatism than the 160FL F11 which I see as a warmer tone to the white light image and more blue fringing at the line tips and lines creeping in at the edges.  However, I have always found the 160ED, like my 140ED, to be rather "neutral" in color tone at the eyepiece.

 

So, I am looking forward to an eventual comparison between them.  However, it seems I will have some decent weather over the next several days and I plan to take advantage of them to do some looking through the GS...Gold Submarine.  

 

So, more later.

 

Jeff

 

PS, I'm serious about someone sending/bringing me their TEC160FL for testing and comparisons.

 

Jeff

[Scott in NC]

These tests are appreciated and in-case anyone needs a reference scope to compare all the rest to, when it comes to CA control, SA control and smoothness of figure, I nominate this one:

 

https://www.cloudyni...3#entry13152804

Yep…that’s one of my favorites!

[Tamiji Homma]

Hi Jeff,

 

 

So, I am looking forward to an eventual comparison between them.  However, it seems I will have some decent weather over the next several days and I plan to take advantage of them to do some looking through the GS...Gold Submarine.

I am also preparing for the second light.

 

It is warming up here so I hope marine layers stay in Pacific ocean.

If weather permits, I can try before Sunday morning sunrise. 

 

I see Orion in low sky, Jupiter, Mars and Aldebaran triangle at good elevation around 5am PDT.

 

I am experimenting ADC.  I think this is the best configuration.

 

OTA -> Astro-Physics Maxbright -> ADC -> Baader MarkV -> eyepiece.

 

This setup yields around 300x.

 

 

Looking forward to reading your first light.

 

Tammy

[Jeff B]

Yours too Tammy. 

 

Is that the actual focus position for that stack?  The GS does have a bunch of back focus.

 

Jeff

[drprovi57]

Hi Jeff,

 

I am also preparing for the second light.

 

It is warming up here so I hope marine layers stay in Pacific ocean.

If weather permits, I can try before Sunday morning sunrise. 

 

I see Orion in low sky, Jupiter, Mars and Aldebaran triangle at good elevation around 5am PDT.

 

I am experimenting ADC.  I think this is the best configuration.

 

OTA -> Astro-Physics Maxbright -> ADC -> Baader MarkV -> eyepiece.

 

This setup yields around 300x.

 

 

Looking forward to reading your first light.

 

Tammy

Great setup -can you let me know what ADC are you using?

 

Thanks

Jason

[Tamiji Homma]

Yours too Tammy. 

 

Is that the actual focus position for that stack?  The GS does have a bunch of back focus.

 

Jeff

 

Yes, it is the position focused to infinity.  Using diagonal is part of extension tube makes the whole OTA length short

 

This is when ADC is placed in front of Baader T2 diagonal.

 

 

Tammy

Edited by Tamiji Homma, 03 August 2024 - 11:29 AM.

[Jeff B]

Someone wrote to me say they felt the 160FL F11 was under corrected in green.

 

I said no, not really, but that small bit of local under correction at 7 o'clock can give that impression.  It's more of an illusion I have seen before.

 

The attached green images have that 7 o'clock section masked off.  Pretty neutral.

 

Same thing with my former APM/TMB 175 F8, again, seeming under corrected.

 

Jeff

 

 

 

 

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