Long Perng 90 APO incoming!

[Ags]

You don't hear much about these scopes but I have been hovering over the buy button for a while, and finally committed today.

It's a 90 mm f5.6 FPL51 doublet. I hope the chromatic aberation is reasonably controlled as the FLP51 is paired with a Lanthanum element. In a former life, this scope was the very fashionable Megrez 88.

I'm not expecting Takahashi levels of correction but if it's not good enough... the delivery van goes two ways. I have bought a Celestron prism that reportedly cleans up the CA in the Megrez 88 at least.

What I like about the scope is the reasonable weight (3.3 kgs), 41 cm transport length, and wide 500 mm focal length. I can see it being used multiple ways:

- air travel to dark skies

- doubles, I prefer views in a refractor to my SCT, but my ZS66 is a bit aperture limited, and fainter components just can't crawl out of the light pollution

- solar with a herschel wedge or Quark (I should be able to get a full disk with a combo Quark and 3x telecentric extender).

- as an RFT 'sweeper'

- I love planetary views through a 66mm APO so I am hoping an extra inch of aperture will be even better (CA worries aside...)

If the LP90 doesn't work out, I'll be getting an Evolux 82.

Edited October 16, 2022 by Ags

[cajen2]

14 minutes ago, Ags said:

You don't hear much about these scopes but I have been hovering over the buy button for a while, and finally committed today.

It's a 90 mm f5.6 FPL51 doublet. I hope the chromatic aberation is reasonably controlled as the FLP51 is paired with a Lanthanum element. In a former life, this scope was the very fashionable Megrez 88.

I'm not expecting Takahashi levels of correction but if it's not good enough... the delivery van goes two ways. I have bought a Celestron prism that reportedly cleans up the CA in the Megrez 88 at least.

What I like about the scope is the reasonable weight (3.3 kgs), 41 cm transport length, and wide 500 mm focal length. I can see it being used multiple ways:

- air travel to dark skies

- doubles, I prefer views in a refractor to my SCT, but my ZS66 is a bit aperture limited, and fainter components just can't crawl out of the light pollution

- solar with a herschel wedge or Quark (I should be able to get a full disk with a combo Quark and 3x telecentric extender).

- as an RFT 'sweeper'

- I love planetary views through a 66mm APO so I am hoping an extra inch of aperture will be even better (CA worries aside...)

If the LP90 doesn't work out, I'll be getting an Evolux 82.

I'm sure that if the glass in the Evolux was any better than FPL 51, SW would loudly trumpet it in the specs. I wouldn't mind betting that the CA in the Long Perng is better corrected. It looks a good scope.

[Ags]

I am hoping this ends my scope-buying ways. The ZS66 for photography, the LP90 for visual, and the C6 for solar system imaging.

Edited October 16, 2022 by Ags

[cajen2]

45 minutes ago, Ags said:

I am hoping this ends my scope-buying ways. The ZS66 for photography, the LP90 for visual, and the C6 for aolar system imaging.

How many people have said this? Then you spot a scope that looks like just what you need.....😄

[Ags]

To avoid confusion, I should add that the OTA comes in two flavors - an ED/RFT version with regular glass and lanthanum, and an APO version with FPL51 and Lanthanum. @ONIKKINEN has the RFT version. 

There are one or two threads about these scopes on CN, but they seem to mix up the two versions.

[Ags]

34 minutes ago, cajen2 said:

How many people have said this? Then you spot a scope that looks like just what you need.....😄

I've said it a lot of times, so I know what I am talking about 😀

[Mr Spock]

Nice looking scope 👍 It's so cute! 😜

[Ags]

It does look a bit "Disney" in that photo 😀

All my scopes are cute: ZS66, C6, now the LP90.

Busy rethinking my eyepiece case...

Hopefully this arrives in time for my trip to rural Wales at the end of the month.

Edited October 16, 2022 by Ags

[badhex]

You pulled the trigger! Good work, I remember you mentioning a while back that you had been mulling it over. Looking forward to first light. 

[Ags]

I'll post my thoughts over the next few months on this thread. It's hard to judge the first few nights...

[ONIKKINEN]

I have thoroughly enjoyed the cheaper version of this as an RFT type scope. Interested to hear how well your better one handles the targets the scope really isn't suited for: Jupiter and Lunar for example.

Mechanically the included 2'' to 1.25'' clamp ended up being of poor quality in mine. Same story as the recent thumbscrew thread pointed out. Its made of some kind of mystery metal and the threads are difficult to tighten all the way, i replaced mine with a clicklock and life has been good with the scope ever since.

The thought of upgrading to the better version did cross my mind several times, especially with Lunar and Jupiter stuff, so your experiences with the scope may have expensive collateral damage if it ends up being great 😆.

[Ags]

I suspect Mars will be the toughest test as I understand these scopes are less well corrected in the red spectrum. I am certainly hoping for some monster Jupiter views! I'm not expecting or tolerating obvious color fringing, let's hope the false color is subtle.

Edited October 16, 2022 by Ags

[ONIKKINEN]

1 hour ago, Ags said:

I suspect Mars will be the toughest test as I understand these scopes are less well corrected in the red spectrum. I am certainly hoping for some monster Jupiter views! I'm not expecting or tolerating obvious color fringing, let's hope the false color is subtle.

Have not seen a peep of interesting detail on Mars with mine, but it is still just a tiny red blip at max usable magnification. There is a red fuzz at one side of focus that turns into green fuzz at the other, so you are probably right in the red correction department. Yours will be much better, at least would expect it to be.

* with fringe killer, otherwise would be purple on the other side of focus

Edited October 16, 2022 by ONIKKINEN
filter

[Ags]

Are you using a prism diagonal with the scope - they seem to help with red correction.

[ONIKKINEN]

14 minutes ago, Ags said:

Are you using a prism diagonal with the scope - they seem to help with red correction.

I have a a TS mirror one, this one: https://www.teleskop-express.de/shop/product_info.php/info/p1771

Might be worth a try with a prism one then? I could use another diagonal to convert an old guide scope to a right angle finder so wouldn't be a waste. I suppose i could also test straight trough without a diagonal, should remove any possible diagonal issues. Ill try that on the next clear night to see if i spot a difference.

[Ags]

Apparently the cheap Celestron prism is the best. It works in my ZS66: with a mirror diagonal, there is red and blue fuzz either side of focus,  and with the prism the fuzz stays white.

Trying straight through won't help. You need the prism to introduce mild CA opposite to the scope CA.

Edit: the reason the Celestron prism is preferred is it (reportedly) uses cheaper glass that causes a stronger CA shift.

Edited October 16, 2022 by Ags

[Louis D]

Looks like a slightly bigger version of my Astro-Tech 72ED.  I use mine for all of my indoor eyepiece testing, so you've probably already seen plenty of those images. 😁

Even with my new Planetary II 2.5mm eyepiece, red/green fringing on the planets was very muted.  I was able to discern low contrast details, and high contrast images like the moon and Saturn's rings looked fantastic and color free.

Since your scope will be faster and larger in aperture, the color correction will be slightly worse.  I would hope the lens figure is just as spot on as mine is.

[Louis D]

You're going to want to attach the dovetail foot to a longer dovetail bar to achieve balance.

The R&P focuser should be a nice upgrade from my AT72ED.  Its focuser slips under heavier loads at high altitude pointings despite increasing the tension on the focuser set screw.

[Ags]

Yes it looks similar to the AT72 or indeed my ZS66. Compared to the AT72, the 90 seems to add lanthanum glass, so maybe it won't be too far behind in CA terms.

Besides, i have a magic diagonal 😀

[Ags]

Still waiting for the scope... In the mean time, I am plotting the next steps of my setup. I want to replace my Berlebach Report 112 with a taller 312, and likewise upgrade the AZT6 mount head with a Mount Zero. Also thinking about getting a Baader T2 prism and bolting it to a TSFLAT2 flattener, but of course I need to see if the curvature of the LP90 bothers me first.

I can't do without a finderscope, but 50mm can be a bit of an overkill. Now I am thinking the Askar FMA135 might do the job - its a 30mm aperture lightweight and would do double duty as an imaging scope on those dark sky trips. I said my scope buying days were over... But I wonder if it has the backfocus for an amici prism.

Assuming it is good, I am thinking the Svbony 3-8 56° zoom could just live in the focuser - it would get wide enough for most DSOs and zoom in close enough for doubles and planets. But that eyepiece is not released until the end of the year... maybe. The other eyepieces that seem ideal for the new scope are my ES82 6.7 mm and ES68 20 mm.

[Ags]

Apparently the scope arrives on Friday, and the internet says Saturday is clear. Testing targets:

Epsilon Lyrae - expecting a clean, easy split.

Albireo - expecting good, pure colors.

Ring nebula - a side by side comparison with the ZS66.

Mars - will the scope cope with a very red target?

Double Cluster - it is always "wow" but will the LP90 be more wow than the ZS66?

Pleiades - ditto.

Jupiter - more color, more resolution? Any fringes?

Vega - check for CA...

Polaris - is the companion easily spotted, unlike the ZS66?

Also: compare mirror vs prism diagonal.

 

[grjsk]

Looking forward to read your notes on the new scope. I have a 72mm doublet myself, and I am contemplating a slight upgrade. The obvious choice would be a 80mm f7 (fpl53), but a 90mm triplet has also crossed my mind. A 90mm ED would be a perfect option (if it performs): bigger than the 80 doublet, but lighter and cheaper than the triplet.

[F15Rules]

On 16/10/2022 at 22:10, Louis D said:

Looks like a slightly bigger version of my Astro-Tech 72ED.  I use mine for all of my indoor eyepiece testing, so you've probably already seen plenty of those images. 😁

Even with my new Planetary II 2.5mm eyepiece, red/green fringing on the planets was very muted.  I was able to discern low contrast details, and high contrast images like the moon and Saturn's rings looked fantastic and color free.

Since your scope will be faster and larger in aperture, the color correction will be slightly worse.  I would hope the lens figure is just as spot on as mine is.

I like Astro Tech gear but they aren't common over here in the UK..

I have a very nice 2" Dielectric Diagonal which I bought from someone in France a few years back, and it's very sharp.

Are Astro Tech just a reseller, or a marketing arm of a company like Long Perng?

Dave

Edited October 20, 2022 by F15Rules
Photo added

[Ags]

Old vs new... scopes always look smaller on the internet!

It is a solid thing, pure neutronium. Long Perng probably make battleships and tanks on the same production line. I thought I wasn't going to attach the handle but I have changed my mind - when I figure out how to attach it.

Lovely big lens 😀

It's somewhat heavier than the ZS66, but I think you get a lot more glass for the weight.

The focusser feels very nice.

The dew shield is nice and deep.

Edited October 21, 2022 by Ags

[grjsk]

Lovely!