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GavStar

Astro Physics 130GTX - First Light

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GavStar    767

Since I got the AP 130GTX it's basically been wall to wall cloud. However, the forecast seemed decent tonight. Looked out at 10pm and it was clouds again. But I thought as it's Friday I'd set the new scope up anyway and start it cooling down just in case.

At 11pm the clouds cleared and I had just over an hour before they came back again. It was enough though to get a nice first session in. First off was Jupiter since the GRS was visible. I used mark v binoviewers with 19 pans. GRS was very obvious, but not as red as I've seen it in the TEC recently. Also, at first, although I could see 11 regions, the detail was a bit fuzzy. I assume the scope was still cooling down (seemed to take longer than the TEC) as suddenly cloud details appeared and various features such as a large barge became clear. 

By this time the skies had cleared even further and stars had appeared all over. After having a great evening of observing in the iow a few weeks back it was shocking to see how bad the light pollution in SW London is. I decided to aim for some DSOs. First up was M13. The LP was so bad it took a while for my eyes to pick up the Keystone. In went an ethos 21 and m13 magically appeared through the whiteness. Best I've seen in my back garden. I moved to a Leica zoom to push up the magnification and at 160x individual stars appeared and it took on an appearance not too different from an open cluster at lower mag. I was impressed at how cleanly the stars resolved. A quick star test was excellent. In the iow I'd had an excellent view of the double double in the Tak FC100DF so I did a comparison. Not a fair competition but even with LP the AP gave a better split at a similar 160x magnification. The AP also split it very comfortably at much lower magnifications of around 50x. The views at 160x were very nice. The 4 stars had a crystal clear ball-like quality I just haven't seen before in any scope. Extremely comfortable split with clear blackness between the 'balls'. Unfortunately at this stage the clouds came in and I decided to pack up.

A few practical use points:

I prefer the feel of the feathertouch on the tec to the AP focuser. However with use the AP focuser got better and it does provide an easy sharp focus even with the f6.3 focal ratio.

Although not much lighter, the AP is much easier to mive around than the TEC.

On planets, so far the TEC has given me the best views but that's probably due to differing seeing conditions. Interesting that the GRS didn't appear that red in the AP compared to the TEC. Cool down seems longer in the AP vs the TEC.

On DSOs the AP gave a more pleasing image imo with very tight control of the star shapes.

A short but very enjoyable first light.

 

IMG_0759.JPG

Edited by Gavster
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John    17,048

Nice 1st light report Gavin :smiley:

Funny how these scopes we dream about, while being excellent, still have their quirks when you look at them critically :smiley:

I have a Feathertouch on the TMB / LZOS 130 and it's superb.

No surprise that the AP 130 delivers a better split of Epsilon Lyrae than the Tak 100 DL does but, IMHO, the Tak is still really amazing for a 3.9 inch :icon_biggrin:

I guess cool down comparisons are about oill spaced vs air spaced ?

All very good stuff - look forward to more reports :icon_biggrin:

 

Edited by John
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GavStar    767

Thanks John. The AP130 used to be fully oil spaced like the TEC but for some reason the new GTX is part oil spaced part air spaced, which may well be why the cool down seems longer to me.

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Stu    14,422

Great report Gavin :) 

I bet the views are amazing! In good conditions I think any of the top end fracs give the whole 'balls on velvet' experience (why does that sound so wrong? ;)), the Tak certainly does, but having that extra aperture along with the purity of a beautifully figured Triplet must just add that extra something!

Strangely I found GRS more muted last night so I do wonder if it was more the conditions than anything else? There was some high haze around at times which I thought had cleared but maybe not?

Lovely scope, I look forward to hearing more about it, and seeing it soon I hope :) 

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mikeDnight    3,554
1 hour ago, Stu said:

 

Strangely I found GRS more muted last night so I do wonder if it was more the conditions than anything else? There was some high haze around at times which I thought had cleared but maybe not?

 

Both myself and paulastro have noticed the seeing has been a little off over the last few days despite having a steady view. Our cars have had a fine covering of what appears to be dusty sand, which got us wondering if there's some Saharan sand in the atmosphere?!

Mike

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mikeDnight    3,554

I love the look and sound of your AP scope Gavin! Do you know if its oil spaced or air spaced?

Mike 

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Stu    14,422
20 minutes ago, mikeDnight said:

Both myself and paulastro have noticed the seeing has been a little off over the last few days despite having a steady view. Our cars have had a fine covering of what appears to be dusty sand, which got us wondering if there's some Saharan sand in the atmosphere?!

Mike

That would make a lot of sense Mike. The seeing was pretty steady but the colour in GRS definitely muted. Compared with other views this year it was very good but not up there with the best.

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GavStar    767
1 hour ago, mikeDnight said:

I love the look and sound of your AP scope Gavin! Do you know if its oil spaced or air spaced?

Mike 

Mike, I don't understand all the details but one interface is Air spaced and the other one is oil spaced so it's a mix of both. Using both allowed AP to use all spherical lenses. But I guess with one interface being Air spaced I think the cool down is longer. This probably means more to you than me!

Pre 2016 the design (AP 130GT) was all oil spaced but with aspherical lenses.

Edited by Gavster
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Highburymark    929

Interesting report Gavin. I too found the GRS lacklustre on Friday evening with Tak FC-100. Slightly more defined with a Baader Neodymium filter.

But if you are getting any sort of star resolution in M13 with London light pollution, clearly the new scope is a gem. From where I am, M13 is an indistinct milky blur, even in a well collimated C8 Edge. 

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GavStar    767

Forecast looks clear this evening and grs is transiting from 9pm so am going to try to get both tec and AP out for a quick compare (children permitting!). I am also intrigued to see what m13 and the double double look in the TEC. Those ball shaped stars (in velvet!) I saw in the AP have made a real impression on me.

Edited by Gavster
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John    17,048

Additional aperture usually gives a better view of globular clusters. Whether 10mm is enough to see much difference will be interesting to find out :smiley:

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GavStar    767

So tonight was my first direct comparison of the TEC140 and the AP130GTX.

On Jupiter and M13 I couldn't see any noticeable difference. However on Epsilon Lyrae I'm sure I saw a difference. The split with the AP was just a bit easier and the stars a bit sharper. Seeing wasn't as good as the first light night but it was still good. 

It may be new scope bias - I really don't know. Possibly Stu will be able to see if I've got this wrong in a few weeks time...

The AP was also easier to manoeuvre and the stiffer AP focuser was helpful as the scope neared the vertical - I was having to use the focus brake on the TEC quite often.

At the moment I'm hooked!

(I was using same diagonal and Leica zoom to get similar magnifications)

Edited by Gavster
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John    17,048

You would have thought that the additional 10mm might have given the edge to the TEC140 on double stars ?

From what I've read, both objectives are of just about the finest optical quality that is available to the amateur :icon_scratch:

I suspect you are going to have to compare the two night after night on a really wide array of very challenging targets to reveal any meaningful differences, apart from the aperture.

 

Edited by John
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GavStar    767
3 minutes ago, John said:

You would have thought that the additional 10mm might have given the edge to the TEC140 on double stars ?

From what I've read, both objectives are of just about the finest optical quality that is available to the amateur :icon_scratch:

I suspect you are going to have to compare the two night after night on a really wide array of very challenging targets to reveal any meaningful differences, apart from the aperture.

 

John, you are probably right that there was no difference - also seeing was varying and maybe that's what I was noticing. I am loving the AP though!

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John    17,048

It's funny with scopes. Last year I bought 2 "dream" scopes, the Tak FC-100DL and the TMB / LZOS 130 F/9. They are both superb instruments and undoubtely the best scopes of their respective apertures that I've ever viewed though and arguably in the top few ever made at those apertures for amateur use.

You would have thought that the old, slightly scruffy gold tubed ED120 Skywatcher would have had it's marching orders ?. But no, I keep coming back to the Skywatcher of all things. I guess that it's the whole package that is "right" with that one which includes size, weight, ease of mounting, cool down, ruggedness as well as optical ability way above it's price band. Still trying to figure it out ..... :dontknow:

 

 

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surfindogg    165
On 15/05/2017 at 00:04, Gavster said:

At the moment I'm hooked!

 

That says it all. Enjoyed reading this. 

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Stu    14,422
On 15/05/2017 at 00:29, John said:

It's funny with scopes. Last year I bought 2 "dream" scopes, the Tak FC-100DL and the TMB / LZOS 130 F/9. They are both superb instruments and undoubtely the best scopes of their respective apertures that I've ever viewed though and arguably in the top few ever made at those apertures for amateur use.

You would have thought that the old, slightly scruffy gold tubed ED120 Skywatcher would have had it's marching orders ?. But no, I keep coming back to the Skywatcher of all things. I guess that it's the whole package that is "right" with that one which includes size, weight, ease of mounting, cool down, ruggedness as well as optical ability way above it's price band. Still trying to figure it out ..... :dontknow:

 

 

John, I think that's why the DC is such a great proposition. I do have envious thoughts about the probable higher quality of the DL, and whether I'm losing out in resolution to larger aperture, but as a combination of quality and useability the DC is hard to beat. That's why it is the scope I have used most and will be the one I hold on to as long as I can.

@Gavster, you basically have two lovely scopes which give you slightly different things, the 140 will ultimately give higher resolution views under ideal conditions but you will more easily be able to get the GTX to dark sites under fab skies. A very nice combo to have :) 

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Highburymark    929
5 hours ago, Stu said:

John, I think that's why the DC is such a great proposition. I do have envious thoughts about the probable higher quality of the DL, and whether I'm losing out in resolution to larger aperture, but as a combination of quality and useability the DC is hard to beat. That's why it is the scope I have used most and will be the one I hold on to as long as I can.

 

Agree Stu. But doesn't the DL have basically the same optics (and aperture) as the DC? Just a longer tube and hence f/l? I presumed resolution would be broadly similar once the different magnifications are accounted for? 

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Stu    14,422
34 minutes ago, Highburymark said:

Agree Stu. But doesn't the DL have basically the same optics (and aperture) as the DC? Just a longer tube and hence f/l? I presumed resolution would be broadly similar once the different magnifications are accounted for? 

Not sure, I thought I read that the optical figure was more accurate?

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Highburymark    929
33 minutes ago, Stu said:

Not sure, I thought I read that the optical figure was more accurate?

Just checked - and yes, the DL is identical to the DF/DC bar the focal length. 

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John    17,048
16 minutes ago, Highburymark said:

Just checked - and yes, the DL is identical to the DF/DC bar the focal length. 

I think the DL has a slightly tighter spot diagram, whatever that means. Probably more to do with the different focal ratio rather than differnt figuring quality though.

The official blurb at the launch said this (Google translated from the original Japanese, so blame that !):

"In recent years of refraction telescope, but Photo visual system short focus apochromat has become the mainstream, it is the emergence of these and differing length personality focus two ball fluorite apochromatic telescope FC-100DL.
FC-100DL in the FC type which arranged the street flow light lens of the name behind, worthy of long focal refraction of f / 9.0, chromatic aberration, you get high spherical aberration less contrast image. Specifically, halo is approximately 40% reduction of the g-line against FC-100D of f / 7.3 (purple), and has realized the 97.5 percent of about 4% increase in the Strehl ratio that indicates the high magnification performance. (Data calculated)
This aberration data is almost the same number as the three pieces ball apochromat, coma is coupled with stable image plane of the zero, I think that you understand that it is a telescope that has a high-eye viewing performance."

 

 

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Highburymark    929
59 minutes ago, John said:

I think the DL has a slightly tighter spot diagram, whatever that means. Probably more to do with the different focal ratio rather than differnt figuring quality though.

The official blurb at the launch said this (Google translated from the original Japanese, so blame that !):

"In recent years of refraction telescope, but Photo visual system short focus apochromat has become the mainstream, it is the emergence of these and differing length personality focus two ball fluorite apochromatic telescope FC-100DL.
FC-100DL in the FC type which arranged the street flow light lens of the name behind, worthy of long focal refraction of f / 9.0, chromatic aberration, you get high spherical aberration less contrast image. Specifically, halo is approximately 40% reduction of the g-line against FC-100D of f / 7.3 (purple), and has realized the 97.5 percent of about 4% increase in the Strehl ratio that indicates the high magnification performance. (Data calculated)
This aberration data is almost the same number as the three pieces ball apochromat, coma is coupled with stable image plane of the zero, I think that you understand that it is a telescope that has a high-eye viewing performance."

 

 

Thanks John. That's cleared that up then. 🤔

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mikeDnight    3,554
14 hours ago, John said:

I think the DL has a slightly tighter spot diagram, whatever that means. Probably more to do with the different focal ratio rather than differnt figuring quality.

Specifically, halo is approximately 40% reduction of the g-line against FC-100D of f / 7.3 (purple), and has realized the 97.5 percent of about 4% increase in the Strehl 

 

 

Hi John,

My late friend Phil was obsessed with comparing spot diagrams of various designs of telescope. He spent a lot of his time over many years designing many different kinds of telescope. From what I remember about the spot diagrams he showed me, if a telescope keeps its natural aberrations within the Airy disk, it is essentially perfect. Most telescopes come nowhere near this kind of perfection, though Apo refractors tend to be among the best. Often the aberrations between similar scopes such as the DL and DC, though being noticeably different on paper, still come close to, or within the confines of the Airy disk and so both scopes will offer essentially the same level of performance, or at least it would take a very expert eye to notice any real difference in image quality. For a 6" achromat to give a perfect image it would need to have a F ratio of around F25, yet at F15 it performs stunningly, so it illustrates how forgiving the visual view is. SCT's produce very poor spot diagrams and this is quite noticeable in the star image produced, where the star never quite seems to snap into focus, yet the SCT remains popular. As you pointed out, focal length does play a part. Short F ratio Newtonians suffer from numerous destructive aberrations outside the Airy disk, where as, long focal length Newts have very tightly constrained aberrations and deliver near perfect images. It seems to me that we're all so easily distracted by graphs, spot diagrams and Strehl that we forget the most important factor which Gavin touched on when he said he's "Loving" his AP130. ❤💜💛

Mike

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Davey-T    9,000

Theory is all well and good but as has been mentioned while it's nice to have a top of the range scope 99% of the time it's advantages are destroyed by the conditions :hmh:

Dave

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