12 replies to this topic

[Joe G]

An astro buddy stopped by yesterday and brought his assortment of refractors to test.  I have never looked through this scope.  It gets nice reviews here I believe.

 

The build quality seems great.  The price is amazing.

 

And here are the DPAC tests of the optics.

 

Edit:  I only ran the AOS program on the intrafocal images.

 

Green:

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Edited by Joe G, 16 April 2023 - 02:07 PM.

[Joe G]

Red:

 

 

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[Joe G]

Blue:

 

 

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[Joe G]

White:

 

 

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Edited by Joe G, 16 April 2023 - 03:46 PM.

[Joe G]

Please ignore the "white light" strehl calculation.  Need to ask Maciek about what that means.

 

Edit:  I deleted the "white" AOS evaluation. 

Edited by Joe G, 16 April 2023 - 03:47 PM.

[CHASLX200]

Looks good. My 130 was good, just too heavy for a G8 mount.

[PhotogTom]

Since I have one of these AT130EDT's, it is good to see that it appears, in my lightly-educated opinion, to be pretty decent. Certainly above what its price might imply. 

[Scott in NC]

Nice work, Joe.  I see mild SA (undercorrection) in green, with a greater degree of undercorrection in blue, and mild overcorrection in red.  There may be some surface roughness and a couple of mild zones (one closer to the center, and another near to the edge).  Overall this isn't bad though, and I suspect that this scope gives nice views. 

[Eddgie]

This looks like a quite excellent telescope for an ED triplet.

 

The ED glass is more of an issue than the optical figure. There is only so much you can do with FPL-51 or FK-61 and being optimized for red comes at the expense of some meaningful SA in blue. It appears that imaging is driving design today (and since so many people do image, that makes sense) so some blue performance is sacrificed for the improvement in infra-red, and for imaging, optimizing in red or close to red is the best call. 

 

Had this scope been made with FPL-53 or other SD glass, the blue and green performance would be greatly improved, but there is zero wrong with the optics here.  This scope is design limited, not optical quality limited. Very impressive for such large, fast, and inexpensive instrument. 

[jlecomte]

Related: See my post on the AT130EDT longitudinal chromatic aberration study:

https://www.cloudyni...tic-aberration/

Yes, it is a great scope for the price. Far from perfect, but possibly one of the best value refractors out there.

[Joe G]

Yeah, so this was a friend's scope.  I tested it but never looked through it visually.  The Ronchi's look nice.

 

But despite that, how do owners view it for visual and/or AP. 

 

It seems jlecomte suggests that there are errors, as described.

 

I believe this scope does not use FPL 53 or equivalent for the ED element.  I have the WO FLT 132 which does.  Have not noticed issues with color fringing visually or for AP.

 

But what I muster about is the difference in glass types.  Folks here often say that FPL 53, FPL 51, etc don't matter as much as mating elements, design, polish, etc.

 

Yet the Ronchis above look really good.  My personal experience is FPL 53 elements tend to be better despite my last statement.

 

So why the reason for really nice Ronchis for this scope, but still some false color.  Are the Ronchis not picking up subtle differences between the glass types?

 

Just curious and not an optics expert.

[davidc135]

Yeah, so this was a friend's scope.  I tested it but never looked through it visually.  The Ronchi's look nice.

 

But despite that, how do owners view it for visual and/or AP. 

 

It seems jlecomte suggests that there are errors, as described.

 

I believe this scope does not use FPL 53 or equivalent for the ED element.  I have the WO FLT 132 which does.  Have not noticed issues with color fringing visually or for AP.

 

But what I muster about is the difference in glass types.  Folks here often say that FPL 53, FPL 51, etc don't matter as much as mating elements, design, polish, etc.

 

Yet the Ronchis above look really good.  My personal experience is FPL 53 elements tend to be better despite my last statement.

 

So why the reason for really nice Ronchis for this scope, but still some false color.  Are the Ronchis not picking up subtle differences between the glass types?

 

Just curious and not an optics expert.

 

The Ronchi would be testing for spherochromatism ie spherical aberration for each colour which is very good in this case. It doesn't test for longitudinal chromatic error ie variation in focal length for each colour which would show as false colour. That long. chr. error could be 1/2000 f.l in an achromat, 1/5000 say in ED and perhaps 1/10000 f.l in an apo.

 

If the Ronchi grating was at exactly the same position for each colour there might be a slight difference in the number of bands, I'm not sure. I'll look at some of Jeff's tests.

 

David

[Jim in PA]

 

I believe this scope does not use FPL 53 or equivalent for the ED element.  I have the WO FLT 132 which does.  Have not noticed issues with color fringing visually or for AP.

 

But what I muster about is the difference in glass types.  Folks here often say that FPL 53, FPL 51, etc don't matter as much as mating elements, design, polish, etc.

I'm under the impression that the AT130EDT uses FK-61 as the ED element, not sure what the mating elements are.  At any rate the ED element performance should be similar to FPL-51.

 

I use the AT130EDT visually, I can't see any longitudinal color at 228x, which is as high as I've ever tried to go.  But I can certainly see it with an unfiltered color camera.  I was using an ASI224MC to take some DSO happy-snaps (quick 5-10 minute stacks) last year.  I've tried the same thing with my AT60ED, and it shows the same sort of blue star bloat.  The 60mm ED doublet has a combo of FPL-53 and Lanthanum elements.  I can also detect a bit of CA in the 60mm visually, I'd say that the AT130EDT performs better visually when it comes to controlling CA.

 

Julien's spectrograph (linked to in post 10 above) indicates some longitudinal CA should be visually detectable at around 420nm, maybe even higher.  I was going to try a brute-force visual test on Venus with a Baader 495 long pass filter but I've not had the opportunity to try it yet.

 

EDIT:  PS, Nice work on the DPAC by the way, thanks for posting it.  I was wondering if DPAC would show any color error in blue after Julien had posted his spectrograph results.

Edited by Jim in PA, 25 May 2023 - 07:03 AM.