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Info required on a replacement Apo lense

Rob

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orion f6.3

orion f6.3

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I am thinking of upgrading my scope (Revalation 80mm) if i put the APO WO kit (inc 1:10 micro focuser) on my scope (£350) + scope price (£250) total £600. How will it differ from the new APO Revalation 80mm now offered by Telescope House for £399 inc 1:10 micro focuser? Is the upgrade lens that much better that the new APO Revalation? or should i sell the none APO Revalation and buy the new one? Orion f6.3

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russ

russ

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Not totally unchartered. These new batch of scopes do not have the same quality lens as the Synta ED80 or the WO Zentihstar ED. The Synta and WO both use FPL53 glass which performs as near dammit to Calcium Flourite. FPL51 glass which the Astronomica and Revelation 80ED's use have marginally lower colour correcting performance. Which means you may see a hint of false colour, although probably not for visual, but almost certainly for CCD imaging.

Hence why the WO scopes cost that much more and the Apograde kit is the price it is. It also makes you realise what a stonking deal the Skywatcher/Orion ED80's are.

I copied this piece from a review on CN:

With an ED scope like this, one always wonders just what ED glass is used. The ED (extra dispersion) glass (also referred to as SD – special dispersion) and it’s mate are largely responsible for color correction. If you take Calcium Fluorite (CaF2) to be the ultimate abnormal lens element, then the next runner up (and it would be a close one) would have to be a glass in the same category as O’Hara’s FPL-53. Glasses are referred to by their catalog numbers which differ between manufacturers. In this article, I refer to glasses available from O'Hara, but most of these have close analogues from other manufactures. You should also realize that a glasses dispersion properties are described by its abbe number. For reference, CaF2 has an abbe number of about 95, while FPL-53’s a mere 94.99, FPL-52 comes in at about 90, and FPL-51 at around 81.5. Comparing apos to apos - ie doublets to doublets, and triplets to triplets - the better the dispersion numbers (abbe number), the better the you correct false color when placed with an appropriate mating element. (TMBs new brick design is aparrently something a little different, but that falls outside the scope of this article.) Glasses with higher abbe numbers typically allow for better color correction, but as you can imagine the price of the glass typically falls as its abbe number decreases. A halfway educated guess tells me that this probably isn’t an FPL-53 doublet (like Orion’s ED80) as the cost is just a bit too low. Looking at other offerings in the same price bracket, I’d probably guess the ED glass to be something similar to FPL-51. Technically, this means color correction probably won’t be quite as good as on the FPL-53 models but for the visual observer this will only be a small drawback. Chromatic aberration (false color) should be fairly well suppressed given the overall design of the scope.

Read the full review here:

http://www.cloudynights.com/item.php?item_id=1467

Russ

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russ

russ

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Hi Gordon, Ric will have to answer that question but i'm guessing yes it's FPL51. But It sounds as if a visual astronomer would not notice the difference anyway. Which makes the Revelation, Moonfish, Astronomica and Astro-Tech all stonking good deals.

Perhaps an astrophotographer may notice the difference.

Russ

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russ

russ

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Hi Gordon,

It seems the Synta ED's are the only sub £500 scopes to use FPL53. Even the William Optics Zenithstar 80 ED II uses FPL51.

Been trying to find out about the new Meade Series 5000 ED Apo's. They use a glass called FCD1 ED. Which, after doing some digging on the web, again is lower spec than FPL53. In fact it's a first generation ED glass used in the original Meade Apo doublets. Here's a quote from the review:

The design specs say it uses FCD1 which is basically a first generation ED glass of the same type used in their original apo doublets (which they also advertised as having no color error, and which they said would easily beat any triplet because triplets don't cool down because of the third element). At f6 and F7.5 this glass will either have some leftover color or it will have high sphero-chromatism at the ends of the spectrum, resulting in slightly soft images with respect to higher end designs using FPL53 or fluorite. Of course, the people which they aim this product at will not be all that picky, so they may indeed have a winner, if the price is right.

So the Synta ED's really are a true bargain and absolutely the closest you'll get to a full monty Apo in the sub £500 bracket. Plus at £295 delivered for the ED80 Pro 1, it's actually sub £300.

Russ

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GordonCopestake

GordonCopestake

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You are right of course, the optics on the ED80 are fantastic for the price. But the focuser needs replacing with a decent rotating 10:1 crayford, and to be honest i just dont like the tube hehe. If i could have the ED80 optics in the WO tube for the same price as a moonfish 80ED i'de be a happy bunny. I think im going to go with the moonfish anyway though. I doubt i'll notice too much difference between the FPL51 and the higher FPL53. Although I know for a fact that they will introduce something the day after i've brought it thats even better and i'll kick myself (again)

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russ

russ

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I think you'll be over the moon with the Moonfish....probably the one i should have gone for too!

You are right about the Skywatcher paint schemes. The light blue metallic makes it look very 'Toys'r'us'. And the gold is just awful.

Russ

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Rob

Rob

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I think you'll be over the moon with the Moonfish....probably the one i should have gone for too!

You are right about the Skywatcher paint schemes. The light blue metallic makes it look very 'Toys'r'us'. And the gold is just awful.

Russ

Gold bling scope... really don't like it. Well only time will tell on everything in the market right now. To clarify then, WO APO flourite upgrade is 53 glass?. Maybe time may reduce the cost... then we will all be happy :D

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Rob

Rob

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Hey, have faith Gordon... the retail world will always bow down in the end!. The market is filling up with 60/80/90mm (WO has a new 90 coming) apo's so hang in there!

I am! :D :D

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russ

russ

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The Apograde is a fully fledged TMB designed Flourite, so is definitely worth the asking price. Quick calculation:

Antares Sentinel 80 from SnS for £180 delivered

William Optics Apograde 80 with dual focuser for £350 delivered

Sell the Antares lens cell to someone with a Skywatcher ST80 for £30

Total cost £500 for a TMB/WO 80mm Flourite :D

Now why didn't i work that out 2 weeks ago :?

Russ

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russ

russ

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It's the same when you upgrade the Sentinel/Revelation. As you say, they are f6. The Apograde is an f6.8 lens. WO provide a 2" extension tube to account for the extra outward focuser travel needed.

Russ

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GazOC

GazOC

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I didn't know the apo upgrade was longer again than the Sentinel. Not far off the size of a Celestron ED.

I'm disappointed those Meade 5000s will use the cheaper glass, maybe they think a triplet design will work - the old Meade ED were doublets

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russ

russ

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There's quite a discussion on Astromart about the Meade's. It seems people are a little disappointed like you by their choice of glass. There's also concern that the previous 127ED was okay but not brilliant. It was plagued by collimation issues and very poor performance if the collimation wasn't spot on. Also concerns about the triplet design and whether they can pull it off.

Only time will tell. The fact Meade keep putting back the shipping date doesn't inspire confidence.

Russ

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