Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4450
Loc: Inner Solar System
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I've seen ad copy from Meade touting the UHTC coatings as increasing light transmission so much it's like adding 1" of aperature.
I know this is probably obvious to everyone, but no coatings are going to make a 12" scope perform like a 13" scope. The corrector plate sucks up a lot of light. A plate with normal coatings will let through, say, 85% of the light. (I'm making these figures up to illustrate my point). This gives a 12" SCT the same light collection ability as a 10.2" mirror. Say the UHTC coatings allow 93% of the light through. This makes it equal an 11.1" mirror. Presto - an extra inch. But, it's an inch less taken away - not an inch added. To Celestron's credit, I haven't seen them use the "added inch" ploy.
I'm just pointing this out for the benefit of anyone who might misinterpret the ad copy, which is certainly worded to make you do so.
On the other hand, SCT's are what they are, and the UHTC coatings do give you that extra benefit. Just don't be surprised when your 12" SCT isn't as bright as your buddy's 13" newt.
- Rick (a happy Meade SCT owner)
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- Rick
14" LX200GPS
8" Meade 826C
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Joseph Gillman
Carpal Tunnel
Reged: 12/06/05
Posts: 2358
Loc: Boothwyn, PA
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A 13 (or 12) inch Newt well most of them, are not f/10 either. That is a big factor in "how bright" it is. If you put a focal reducer on your SCT you are adding more glass elements to take away light throughput so it's not an ideal situation either.
Joe (a happy Meade SCT user)
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Meade RCX400 30cm --
People dont like when I stick up for Meade but they're just jealous of my RCX 
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JerryWise
Postmaster
Reged: 12/26/03
Posts: 7008
Loc: Lexington, SC
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I have a LX200 14" UHTC that is as bright as a 13.65 inch OTA.
(It's PopEye. It has 5 square inches missing from the chipped primary. Works great.)
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Jerry
LX200ACF 14", Tak FS 152 & TOA 150
AP-1200 & Mach1
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4450
Loc: Inner Solar System
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Quote:
I have a LX200 14" UHTC that is as bright as a 13.65 inch OTA.
(It's PopEye. It has 5 square inches missing from the chipped primary. Works great.)
As bright as a 14" newt without a corrector plate would be? How do you calculate that? I'm certainly not an expert, but I don't see how that could be.
Do you call it PopEye because it has a "squinky eye"?
- Rick
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- Rick
14" LX200GPS
8" Meade 826C
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4450
Loc: Inner Solar System
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Quote:
A 13 (or 12) inch Newt well most of them, are not f/10 either. That is a big factor in "how bright" it is. If you put a focal reducer on your SCT you are adding more glass elements to take away light throughput so it's not an ideal situation either.
Joe (a happy Meade SCT user)
Well, sure. I meant "all else being equal", if the only difference were the presence/absence of a corrector plate.
But, if you take a fast newt and an SCT (same size), and use the appropriate eyepiece to bring them both up to the same magnification, I'm thinking the image in the newt will be brighter. I've seen this in an 8" f6 newt alongside a C8. The difference was subtle, but there.
- Rick
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- Rick
14" LX200GPS
8" Meade 826C
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Mark Costello
Pooh-Bah
Reged: 03/08/05
Posts: 1037
Loc: Matthews, NC, USA
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Hmmmm. Good refractors supposedly are much better than even 93%. I'm wondering don't the CAT makers coat the corrector plates with the same coatings the refractor manufacturers use for their lenses? If not, why not?
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Mark Costello
Matthews, NC
Wife, son, three daughters, two dogs, ... and
Souped up & Tuned Burgess 102mm refractor on a CG5 & Celestron 7X35's
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JerryWise
Postmaster
Reged: 12/26/03
Posts: 7008
Loc: Lexington, SC
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Quote:
Quote:
I have a LX200 14" UHTC that is as bright as a 13.65 inch OTA.
(It's PopEye. It has 5 square inches missing from the chipped primary. Works great.)
As bright as a 14" newt without a corrector plate would be? How do you calculate that? I'm certainly not an expert, but I don't see how that could be.
.........
Rick, where'd the Newt come from?
The LX200 14" went from an effective diameter of 14" down to a 13.6276 diameter OTA by virtue of the loss of a 3 x 5 inch chip out of the primary mirror. Figured by pi x radius squared - 15 square inches.
I should have said "a LX200 14 UHTC that is as bright as a 13.65 inch LX200 UHTC". Sorry.
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Jerry
LX200ACF 14", Tak FS 152 & TOA 150
AP-1200 & Mach1
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smooth
super member
Reged: 10/30/06
Posts: 135
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Not sure how helpful this will be but here:
http://www.astrosurf.com/legault/obstruction.html
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4450
Loc: Inner Solar System
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Quote:
Quote:
Quote:
I have a LX200 14" UHTC that is as bright as a 13.65 inch OTA.
(It's PopEye. It has 5 square inches missing from the chipped primary. Works great.)
As bright as a 14" newt without a corrector plate would be? How do you calculate that? I'm certainly not an expert, but I don't see how that could be.
.........
Rick, where'd the Newt come from?
The LX200 14" went from an effective diameter of 14" down to a 13.6276 diameter OTA by virtue of the loss of a 3 x 5 inch chip out of the primary mirror. Figured by pi x radius squared - 15 square inches.
I should have said "a LX200 14 UHTC that is as bright as a 13.65 inch LX200 UHTC". Sorry.
Hi Jerry
The newt is a 1988 Meade 826c, which I had resilvered in the early 90's. The C8 (an old orange one) belongs to a buddy of mine. The 826c is a very good scope, they were using their "research grade" mirrors in them at the time. But I was surprised at how close the image in the C8 was to the Meade. Not as bright, but just about as sharp.
I think my original meaning is being lost here. I just didn't want anyone to think that their 10" LX200 was going to perform like an 11" telescope because the coatings were "like adding an inch of aperature". Rather, the coatings are like subtracting an inch less than would otherwise be the case.
- Rick
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- Rick
14" LX200GPS
8" Meade 826C
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Gama
Vendor (Gama Electronics)
Reged: 08/23/05
Posts: 688
Loc: I come from the land downUnder
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What i think your not seeing, is that when they are refering to an extra inch of aperature, this would refer to the same telescope optic setup, e.g another Cat.
So they are saying an 8" f10 LX200 with UHTC will give the same light output as an 9" f10 SCT without UHTC.
This was a big argument some time back, plus (For the Oldies like me who remember) also some many years ago, they also fought over the fact Meade uses an "Oversized Primary" which gives a wider field blah blah.. compared to other manufacturers (Which then was really only Celestron).
The whole deal with coatings is very valid. If the coatings were not there, then you would have more light reflected then passed thru.
Mirror coatings are also similar. The higher reflectivity the brighter the image.
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Rick Woods
Post Laureate
Reged: 01/27/05
Posts: 4450
Loc: Inner Solar System
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Quote:
So they are saying an 8" f10 LX200 with UHTC will give the same light output as an 9" f10 SCT without UHTC.
That's probably a better way to put it.
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- Rick
14" LX200GPS
8" Meade 826C
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Gama
Vendor (Gama Electronics)
Reged: 08/23/05
Posts: 688
Loc: I come from the land downUnder
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Meade always have to be vague.. RCX anyone..
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