76 replies to this topic

[Scott in NC]

Now for part 2 of the telescope testing extravaganza from yesterday.  My friend with the TOA-130NFB also recently received an Agema SD 130. I was especially excited about testing this one, as I had never seen one in person, and this will be the first one to have the results of its DPAC testing reported here on CN. This is a 130mm f/8 fluorite apochromatic doublet, made by Eduard Trygubov (Agema Optics, Inc.) in Colorado. Unlike its predecessor 5" f/8 fluorite doublet, the venerable Takahashi FS-128, this scope incorporates a wide air gap to minimize spherical and chromatic aberration, much like Takahashi's triplet TOA series does. The fit and finish of this scope is immaculate, and it just exudes quality. The downside of that is that it's heftier than one would expect for a 5" doublet, weighing 9.5 kg (20.9 lbs.) according to the specs on the Agema website. I believe that may be for the OTA alone. In comparison, the FS-128 weighs 7.5 kg (16.5 lbs.). Once again I believe that's for the OTA alone. Regardless, its still a lightweight compared to the TOA-130,

Here's the scope set up on my friend's optical testing bench (his dining room table).

 

[Scott in NC]

And now on to the Ronchigrams.

 

[Scott in NC]

Spherical aberration is extremely minimal, with just a touch of over correction in blue.  Chromatic aberration is quite low for a doublet of this size, thanks to the fluorite element, wide air gap, and fairly slow focal ratio.  I see a tiny central peak and a small edge zone.  More puzzling to me is the "at focus" view, which isn't as smooth as I've seen with many of the other premium apochromatic refractors that I've tested. Perhaps this is a result of hand aspherization as opposed to strictly machine polishing?  Hopefully someone more knowledgeable than I about such things will comment. After nearly 2 years of doing DPAC testing, I'm still learning.

[Wildetelescope]

On the inside focus, I see what look like little wings at the ends of the outer bands.  I forget what contributes to that?     That surface is clearly not as smooth as your Tak.  Interesting results!

 

jMD

[Scott in NC]

On the inside focus, I see what look like little wings at the ends of the outer bands.

Good eye! That’s the small outer zone that I referred to. And on the outside focus view you can see it as inward-turning “wings.”

[scoale]

Thanks, again, Scott for an outstanding job.  And I love the side-by-side format of the intra/extra focal images.

 

A few comments:

• The surface irregularity observed in the null images is due to the aspheric.  I confirmed this with Agema.
• The weight of my Agema with rings, plates, finder, lid, and diagonal is 25.4 lbs.  For reference, my Stellarvue with same gear is 22.9 lbs (but I have a red dot on the SVX instead of a finder).
• As Scott mentions, build quality is superb, with lots of innovative touches.
• Focuser is a bit stiff, but I suspect that is due to newness.

Scope has seen first light in a three hour side-by-side with TOA 130 on Jupiter in 3/5 seeing.  I need more time under stars prior to communicating POV, but no initial concerns.

 

Star testing shows good spherical correction, little to no coma, some transient astigmatism at focus that is probably thermal related, a central zone, and outer zone.  The DPAC image confirms the outer zone.  Color in and out of focus appeared to be minimal.  Seeing was abysmal the night I star tested, so I used an artificial star at 135ft - which is a bit close.

 

Key question on outer zone is depth and width.  Star testing and DPAC are very sensitive and can pickup zones at 1/50 to 1/60 wave.  I'm not worried about central zone.

 

Sorry for the crude image format. 

Top row is with green filter on left and without on right.  Consistent with DPAC spherical results.

Next row is with green filter and a bit more defocus.

Next row shows central zone

Next row is a sample of in focus images I culled from a video I took.  Note intermittent astig, no coma.

Last image captures outer zone

 

Edited by scoale, 09 November 2024 - 09:50 AM.

[Scott in NC]

The surface irregularity observed in the null images is due to the aspheric.  I confirmed this with Agema.

Thanks for confirming this, Steve! And thanks for adding the star test images. Star testing is a powerful test method, and so is DPAC, but it’s great when we can put the two together and see how well the results correspond. I personally have a much easier time seeing zones and spherical aberration with DPAC testing, but I think star testing has more sensitivity for other aberrations like coma and astigmatism (not that any significant amounts were seen here).

[fate187]

Very very interesting Scott! Thank you very much. I think this is the first Agema Apo being tested with DPAC and published here on the forums.

Color correction is very good. I think for modern apos, thats not an issue. Especially with fluorite and such a talented optician.

That edge is likely only 1-2mm wide I would estimate. I have seen edges from as wide as 10mm down to some millimeters, so I can also judge their influence on the visual quality under the sky. This one should be no problem. But DPAC still shows it!

Also shallow central zone as noted by Scoale.

The surface/wavefront irregularisties are likely very shallow. As confirmed by Scoale these features are due to aspherisation. I have readily seen this in my CFF185 and 200 triplet apos in DPAC test. These have an aspherized element as well. Jeff B has seen this with the CFF160 as well.

 

 

 

Thanks, again, Scott for an outstanding job.  And I love the side-by-side format of the intra/extra focal images.

 

A few comments:

• The surface irregularity observed in the null images is due to the aspheric.  I confirmed this with Agema.
• The weight of my Agema with rings, plates, finder, lid, and diagonal is 25.4 lbs.  For reference, my Stellarvue with same gear is 22.9 lbs (but I have a red dot on the SVX instead of a finder).
• As Scott mentions, build quality is superb, with lots of innovative touches.
• Focuser is a bit stiff, but I suspect that is due to newness.

Scope has seen first light in a three hour side-by-side with TOA 130 on Jupiter in 3/5 seeing.  I need more time under stars prior to communicating POV, but no initial concerns.

 

Star testing shows good spherical correction, little to no coma, some transient astigmatism at focus that is probably thermal related, a central zone, and outer zone.  The DPAC image confirms the outer zone.  Color in and out of focus appeared to be minimal.  Seeing was abysmal the night I star tested, so I used an artificial star at 135ft - which is a bit close.

 

Key question on outer zone is depth and width.  Star testing and DPAC are very sensitive and can pickup zones at 1/50 to 1/60 wave.  I'm not worried about central zone.

 

Sorry for the crude image format. 

Top row is with green filter on left and without on right.  Consistent with DPAC spherical results.

Next row is with green filter and a bit more defocus.

Next row shows central zone

Next row is a sample of in focus images I culled from a video I took.  Note intermittent astig, no coma.

Last image captures outer zone

 

Scoale. In your star test images, which are inside and which are outside focus. Are these side by side?

An edge with a detrimental effect on visual quality would be visible with either a low contrast inside or outside startest with the other side being having nice contrast (rings can be easily distinguished).

 

 

[scoale]

Very very interesting Scott! Thank you very much. I think this is the first Agema Apo being tested with DPAC and published here on the forums.

Color correction is very good. I think for modern apos, thats not an issue. Especially with fluorite and such a talented optician.

That edge is likely only 1-2mm wide I would estimate. I have seen edges from as wide as 10mm down to some millimeters, so I can also judge their influence on the visual quality under the sky. This one should be no problem. But DPAC still shows it!

Also shallow central zone as noted by Scoale.

The surface/wavefront irregularisties are likely very shallow. As confirmed by Scoale these features are due to aspherisation. I have readily seen this in my CFF185 and 200 triplet apos in DPAC test. These have an aspherized element as well. Jeff B has seen this with the CFF160 as well.

 

 

 

Scoale. In your star test images, which are inside and which are outside focus. Are these side by side?

An edge with a detrimental effect on visual quality would be visible with either a low contrast inside or outside startest with the other side being having nice contrast (rings can be easily distinguished).

 

Hi, Michael.  Thank you for sharing your experience and expertise.

 

The star test images are side-by-side with left outside and right inside - but the fact that you asked is a good indicator.  Contrast is a bit stronger inside of focus, with outside contrast improving, but not quite reaching, inside definition as scope settles.  To be clear, rings are readily seen outside of focus.

 

Agree with your points on DPAC/star test sensitivity on zones.  I did send Lana at Agema a note to see if she could provide any insight on depth and width.

Edited by scoale, 09 November 2024 - 10:17 AM.

[fate187]

Scoale, thank you for clarifying. With that being said, these inside and outside focus images look good! I have seen the effect of large edges...

Also at focus there is probably no "junk" around the central airy disc (thats how Jeff B would call it). Another indicitor for a negligible edge effect in the visual quality.

[Jeff B]

Well done Scott and Scoale!  I'm soooo envious.

 

The effects on star test SA at 135' distance depends on your star size but for the purpose of ferreting out coma and astigmatism, it should be fine even with a 100 micron star.  But, if you can, putting a barlow over the star will help too, though it will dim the star.

 

Thermal transient coma and astigmatism can be vexing.  One moment "Oh, nice!".  The next moment "Ok, wait a second...".  But for me, that's because I'm being especially and specifically picky during star testing which is always done at Chaz high powers.

 

Catalin confirmed to me too that the "orange peel" texture on some CFF objectives is from the hand generated aspheric.

 

Scott, I notice the Agema white images are "warmer" than those of the 130 TOA.  Is the TOA just that freaking good & neutral, or did you change something in your test/capture/processing chain?

 

And Scoale, you mentioned you spent time comparing the Agema and the TOA visually on real stuff.   Sooooo..... 

 

Well done and thanks for posting!

 

Jeff 

[Scott in NC]

 

Scott, I notice the Agema white images are "warmer" than those of the 130 TOA.  Is the TOA just that freaking good & neutral, or did you change something in your test/capture/processing chain?

 

Jeff, I think that effect is real. It makes sense to me that an extremely well corrected triplet like the TOA should be a little cooler than a doublet of similar focal ratio, no matter how well corrected. The one thing that did change though is that the batteries for the rheostat that controls the intensity of my LED light started to run out halfway through the testing period and had to be replaced, but I’m not actually sure when in the testing period that actually occurred. It might not have actually happened until I finished testing both of these scopes. I don’t think that made a difference in the warmth of the Ronchigram images, as any of them that were too dark got reimaged.

 

So the bottom line is that, yes, I really do that the TOA is “just that freaking good & neutral.”  It’s over the top as far as color correction goes for a refractor.

[davidc135]

It'll be interesting to compare the heavens side by side, this objective and the near perfect TOA, in excellent conditions. Going by the Ronchi images the TOA edges it with it's smoother wavefront but could it make any difference in practice, at high power?

 

I think that faint zones and surface roughness happen when an optician does an imperfect job although, as ever, tiny departures should be kept in proportion. But it's possible that performance is sensitive to errors of 1/50th wave roughness. Still, probably hard to see.

 

David

Edited by davidc135, 09 November 2024 - 01:42 PM.

[peleuba]

On the inside focus, I see what look like little wings at the ends of the outer bands.  I forget what contributes to that?     That surface is clearly not as smooth as your Tak.  Interesting results!

 

Good eye! That’s the small outer zone that I referred to. And on the outside focus view you can see it as inward-turning “wings.”

 

An artifact like this can sometimes be caused by diffraction, but this in instance I think its in the glass.  Notice the the infocus image which is analogous to a Foucault test when testing a parabolic (Newtonian) mirror.  You want this outer ring to be balanced ie. same brightness around the circumference of the lens (or mirror).  I took Scott's image and marked it up with arrows to high light the difference in brightness.

 

Stating the obvious, the lens has some medium scale roughness when compared to some other "peer" refractors but I'd only caution that DPAC is very sensitive to this and that its appears twice as bad in the photos as it is in "real life". 

 

Nice job.  Nice scope.

Attached Thumbnails

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Edited by peleuba, 09 November 2024 - 01:43 PM.

[Erik Bakker]

Scott and Steve,

 

Wonderful to see that you DPAC’ed the Agema SD130 doublet and shared the results here. And the additional startests, comments and insights by Steve add to the understanding of the behavior of the optics in this scope. In instruments with very wide air gaps and hand aspherization, additional phenomenon can be seen compared to others that do not have those attributes.

 

The somewhat rough biscuit structure at best focus and the significant difference in contrast between the black Ronchi bands and the red, green, blue and white backgrounds in the inside- and outside focus Ronchi test images are not what I prefer to see  in a high end refractor for low contrast planetary observations. On the moon and double stars, that is less of an issue for me.  Color correction looks very fine, a superb result in a 130mm f/8 doublet.

 

To see the same knowledgable and open minded people without a commercial bias DPAC and star test two random samples of 130mm refractors under very similar conditions is very much appreciated! It is a pleasure to read you comments on these two telescopes, including the others you’ve tested in that way in the past.

 

Thank you both so much  

[Erik Bakker]

A thing that is also of interest for observing the planets and other objects requiring high powers, is how these instruments and their optical corrections and -qualities change with time under actual cooling conditions under the night sky.  

 

For some scopes, cooling temperatures have a very benign, mild effect on behavior and optical performance, resulting in already quite good planetary images before they reach their optimum visual high power performance when fully acclimatized.

 

Others need all the time they can get to come close to thermal stabilization before they start to perform well, until that moment they are almost unusable above 100x.

 

Depending on climate and telescope storage, that can mean many hours of low power deep sky observing, before the planets are worth closer scrutiny at 200x.

 

Any comments on that behavior for the SD 130 and TOA-130?

[scoale]

I'm hesitant to share my initial impressions on my side-by-side comparison observing Jupiter through the TOA 130 and Agema 130 because the impression is informed by one session with 3/5 seeing.  That said, a few folks have asked, and the weather forecast is going to preclude further side-by-side opportunities for some time, so here goes:

 

The conditions were stable, high 60s temps, Jupiter @ 45 to 60 degrees altitude, Jupiter at 46", and 3/5 seeing.  Red spot beginning to emerge near end of session.  I ran out of gas before transit.  Both scopes cooling for several hours (and, again, stable temps).

 

Power used was 208x for Agema and 200x for Tak.  Eyepiece used was a 5mm Delite. Diagonal was Baader BBHS mirror. Image held together in both scopes when bumping power to 250x, but no additional detail was resolved, and view was appreciably dimmer.

 

In summary, the comparison was inconclusive.  There was no difference in detail resolved, no distinguishable difference in color (surprisingly), and no certain difference in contrast.  There were two times that I thought the TOA might have been sharper, but I couldn't definitively confirm.  It was a best view was the last view situation.  Given the seeing, I tended to spend a decent period of time at each scope waiting for a moment of sharper seeing before switching.

 

Detail resolved included north and south equatorial belts, north and south tropical zones, the north temperate belt, festoon activity in the equator, a partial south temperate belt, shading in the north polar region, some wrinkling in the south polar region, and the red spot when it emerged at the limb.  I was not able to detect any ovals in the north or south polar regions.

 

Subtle color differences are difficult to judge, at least for me, when moving from scope to scope.  I am confident the differences in belt, zone, festoon, and polar region color were not distinct - but that's as far as I could judge on this night.

 

Contrast on both scopes appeared fairly sharp - relative to the seeing.  Again, if my life depended on it, I would give a slight nod to the TOA - but I simply could not say with certainty.

 

All of that said, I tend to formulate my opinion about a scope over time, and I'll probably have a stronger point of view at the end of this year's planet season.

 

***BTW, another comparison I am interested in is how these scopes will compare to my Mewlon 210.  My Mewlon has never lost in a side-by-side on Jupiter to any 5" to 5.5" refractor I have owned (but it's nervous, because a TEC 160fl is on order).

Edited by scoale, 09 November 2024 - 02:41 PM.

[Erik Bakker]

A wonderful and balanced report with your first impressions Steve, look forward to your future findings!

[scoale]

 

The somewhat rough biscuit structure at best focus and the significant difference in contrast between the black Ronchi bands and the red, green, blue and white backgrounds in the inside- and outside focus Ronchi test images are not what I prefer to see  in a high end refractor for low contrast planetary observations.

 

 

 

Hi, Erik.  Thank you for your kind comments.

 

I share your dislike for any surface roughness, but I know it comes with the territory with hand aspheric.  My bigger concern is probably the outer zone - pending more info on depth and width.

[scoale]

An artifact like this can sometimes be caused by diffraction, but this in instance I think its in the glass.  Notice the the infocus image which is analogous to a Foucault test when testing a parabolic (Newtonian) mirror.  You want this outer ring to be balanced ie. same brightness around the circumference of the lens (or mirror).  I took Scott's image and marked it up with arrows to high light the difference in brightness.

 

Stating the obvious, the lens has some medium scale roughness when compared to some other "peer" refractors but I'd only caution that DPAC is very sensitive to this and that its appears twice as bad in the photos as it is in "real life". 

 

Nice job.  Nice scope.

Hi, Paul.  Thanks for sharing your knowledge.  The outer edge is my only real concern.  That said, Agema shared with me today that the outer zone is 2mm wide and 1/6 lambda.

Edited by scoale, 09 November 2024 - 04:11 PM.

[Scott in NC]

Thanks for sharing that info from Agema, Stephen. That bit of data will be good to know for future reference when trying to interpret Ronchigrams on other scopes. That small amount really doesn’t sound bad at all to me. Would I like it be less? Sure. But would I find this disturbing? Absolutely not.

[betacygni]

I’m showing my ignorance here, but why is the surface roughness not a significant concern? I might be inventing this memory, but I seem to recall the Zambuto website having had on it an incredibly smooth DPAC image of their mirrors’ near perfectly smooth surface. I’d assume this was Carl saying something positive about the DPAC result of their mirrors, unless mirror and refractor DPAC results are apples to oranges.

Is there something inherit in the Agema design (or refractors in general) that makes this of no consequence? Then why is it being tested? To the relative layperson such as myself it looks horrendous as compared to the concurrent TOA DPAC thread’s smoothness results.

Edited by betacygni, 09 November 2024 - 05:29 PM.

[Scott in NC]

Ryan, I really have no answer to your question. I've had the same concern, but know better than to guess at things of which I have no knowledge. It would be great if someone who was actually knowledgeable about optics fabrication could offer their insights.

[davidc135]

Having made a number of objectives and plenty of deeply aspheric lens surfaces by hand, I'm sceptical of a manufacturer's claim that the roughness has anything to do with aspherics, as if this is the result that you should expect.

It's not easy to make a surface like that and makes me think of polishing happening too quickly or action being too aggressive, but that's guesswork.

 

I could be wrong, as amateur experience doesn't always necessarily relate to the professional world. If it came about by hand figuring in combination with a machine spindle, it's speculation as to why the result isn't optimal.

 

If Tak had made this lens, would there be a cause for discussion?

 

When a maker gives an explanation as to why something that's probably trivial turns up at focus in a bench test, there can be a bit of gloss or spin.

 

But the bottom line is; how does it compare with the best? The early signs in post 17 seem to be very well.

 

David

Edited by davidc135, 09 November 2024 - 06:51 PM.

[25585]

I have so far not been convinced the TOA is not king of the 130s.