92 replies to this topic

[CHASLX200]

I have a Meade ACF mush dog. Will not resolve the double double. Both my NP-127 and Tak FCT-125 are freaky sharp, with the Tak just a bit ahead. My C-11 seems to be average, but aperture wins so it is overall the sharpest once cooled down in good conditions.

SCT's are the worst. They all vary from any year from 1965 to now. Anyone saying they never had a bad  1 lies or knows no better.

Edited by CHASLX200, 09 March 2025 - 06:32 PM.

[ccwemyss]

My Tasco 9TE-5 wasn't sharp. Tons of CA. The Edmund Deluxe Space Conqueror was sharp when collimated. A 1982 C8 was never very sharp. It got shipped across the country a coupe of times, so it may have gotten misaligned and I didn't know enough at the time to check it, but collimation didn't help, and it was built during the Halley run-up. I sold it to buy the Questar, which was a big improvement. My wife's Astroscan is mushy. 

 

The AP 6"f9 is freaky sharp. and will go to 600X in good seeing, as are the Pentax 85 and 100. The C11 at school (s/n 4) is freaky sharp. My C14 was close when I got it, and not so close after Celestron fixed it, so I need to really work on tuning the alignment. The early Unitron 142 was mushy until I got a replacement objective and cell from Johann. 

 

Among the loaners, the HOCs are close to freaky sharp (Selsi 247, ATCO 1254, especially). The others are sharp. I haven't actually used the Tasco 7Ts, but should check them out myself. The students seem to like them. 

 

Chip W. 

[Defenderslideguitar]

+.It is easier to count the good sharp ones    "Freaky Sharp"  I have come to like this term alot

Can you define Freaky Sharp?  I say it is hard   but it reminds of what Supreme Court Justice Potter Stewart said about Pornography....."I can't define  it      But I know what it is when I see it"  

Pushing aside the fact that Justice Stewart seems to admit looking at it way back then   ....

 

I know Freaky Sharp when I see it.......now anyway    after having most excellent and a few sub bar scopes

 

Freaky Sharp    look that up and you see       the AP 6 inch F 12  Starfire     and these others

                                                                        Tak FS 128  ..Tak FC -100 ..Tak FC -76

                                                                        (Red F-model)

                                                                        C-102 FL  Vixen 80mmFL Pentax 75

 

  Mush Dog   -  Sub Par                                   Early non-Tri-color Sandcast C-8 another C8 and                                                                           a  Towa

 

Really Good non Freaky sharp scopes           C-102 achro   great views  C-80  1984 Meade                                                                               LX2    U-140 

Edited by Defenderslideguitar, 09 March 2025 - 09:33 PM.

[starman876]

the reason why I posted this is because I have learned that if you look through a scope at the wrong time you do not get a favorable impression even if it has great optics.  Could not be aligned properly  and there is more to alignment then just making sure the secondary looks like it is centered in an SCT.   Could be not be  temperature acclimated,  seeing could really be bad or maybe it just not focused just a tiny little bit to see really fine detail. 

[tturtle]

I have 2 classic Vixen refractors at both ends of the spectrum. One is an 80mm f11 that I cannot get a sharp image out of to save my life. Newton rings off center, mushy star test and noticeable color. I’ve tried many things to get it right to no avail. The second Vixen is a 102mm (or 100mm?) f13 and is just the opposite. I bought it cheap as an orphaned doublet and cobbled an OTA together to see whether it was worth building a serious OTA around it. I guess I’ve looked at the moon hundreds of times in my life and when I viewed it with this lens at >300x the images (with binoviewer) were absolutely mesmerizing - the sharpest I have ever seen and totally without false color. All my other scopes are between these two extremes and mostly at the good end. 

[Terra Nova]

SCT's are the worst. They all vary from any year from 1965 to now. Anyone saying they never had a bad  1 lies or knows no better.

Totally agree! Never had one that I liked much. My old 1990s 10" Meade was the best and it went downhill from there. About all I can say is they're short, fat, and compact so the aperture to OTA length ratio is nice but other than that, meh.

[deSitter]

I have a Meade ACF mush dog. Will not resolve the double double. Both my NP-127 and Tak FCT-125 are freaky sharp, with the Tak just a bit ahead. My C-11 seems to be average, but aperture wins so it is overall the sharpest once cooled down in good conditions.

I would try centering the corrector plate and then do a complete collimation. Getting the corrector directly in front of the mirror is critical.

 

-drl

[starman876]

I would try centering the corrector plate and then do a complete collimation. Getting the corrector directly in front of the mirror is critical.

 

-drl

I wonder how many SCT's suffer from this issue?  

[starman876]

Had way more good than bad.

Really, from your comments in the thousands of posts you have made it always sounded like you had a lot of bad scopes.  

[deSitter]

I wonder how many SCT's suffer from this issue?  

I have seen countless times where a good design is poorly assembled. The cells on SCTs - at least the ones I know - are very sloppy and use cardboard (!) compressive rings to fix the corrector.

 

Since there MUST be some QA control over how the correctors are made, they cannot be bad in proportion to the reports of poor performance. Yes there are examples of master blocks just wearing out. But making a corrector is a machine process, which can be monitored. I doubt the glass changes much.

 

I mean them minimum you should expect is 1/4th wave. That's enough at 8" to make excellent views.

 

-drl

[deSitter]

I have 2 classic Vixen refractors at both ends of the spectrum. One is an 80mm f11 that I cannot get a sharp image out of to save my life. Newton rings off center, mushy star test and noticeable color. I’ve tried many things to get it right to no avail. The second Vixen is a 102mm (or 100mm?) f13 and is just the opposite. I bought it cheap as an orphaned doublet and cobbled an OTA together to see whether it was worth building a serious OTA around it. I guess I’ve looked at the moon hundreds of times in my life and when I viewed it with this lens at >300x the images (with binoviewer) were absolutely mesmerizing - the sharpest I have ever seen and totally without false color. All my other scopes are between these two extremes and mostly at the good end. 

That's interesting - I have the same 80mm f/11 Vixen (Celestron) and the performance is just fantastic.

 

I think I would replace the aluminum spacers. Use 0.004" sticky backed foil. You can get it in craft stores. Forget about Newton's rings! They tell you nothing. Rotational arrangement of the lens elements - change it in increments of 1/8th turn and do repeated tests. Just assemble it with your fingers to make this go fast. You can clean it up later.

 

-drl

[Rick-T137]

I have seen countless times where a good design is poorly assembled. The cells on SCTs - at least the ones I know - are very sloppy and use cardboard (!) compressive rings to fix the corrector.

 

Since there MUST be some QA control over how the correctors are made, they cannot be bad in proportion to the reports of poor performance. Yes there are examples of master blocks just wearing out. But making a corrector is a machine process, which can be monitored. I doubt the glass changes much.

 

I mean them minimum you should expect is 1/4th wave. That's enough at 8" to make excellent views.

 

-drl

All of the SCTs I've had have used cork shims to center the corrector plate in the cell. Mind you, there were all from the mid-80's to the early-90's. Dunno what they are using these days...

[Kasmos]

Totally agree! Never had one that I liked much. My old 1990s 10" Meade was the best and it went downhill from there. About all I can say is they're short, fat, and compact so the aperture to OTA length ratio is nice but other than that, meh.

A couple of days ago I came across what I believe was your C8 refurb.

 

Is this the same person?    

https://www.cloudyni...t-c8/?p=8472023

[starman876]

All of the SCTs I've had have used cork shims to center the corrector plate in the cell. Mind you, there were all from the mid-80's to the early-90's. Dunno what they are using these days...

I have seen popsicle sicks, cork and RTV.  Wonder why the corrector gets cloudy on the inside 

[CHASLX200]

Totally agree! Never had one that I liked much. My old 1990s 10" Meade was the best and it went downhill from there. About all I can say is they're short, fat, and compact so the aperture to OTA length ratio is nice but other than that, meh.

You got that right. And we got someone that post on here saying they never had a bad scope. SO that would be a lie. or they don't know jack about optics.

 

As many as i have had you will have a few bad 1's.

 

My rating system is easy.

 

Past nuts insane freaky sharp means when you look thru a scope at Jup the image knocks you out of the seat and you say WOOOOOWWWWWWWWW the detail snaps to life.

 

Freaky sharp means the image is alive with detail and you have a top made optic.

 

Very good means the image is very nice and the scope it doing it's job bob but could be better.

 

Good to so so means the image is ok to good but lacks that snap and pop on Jup as details just kinda show but no real life to them.

 

Lack luster means the image is not so hot and the scope has fair to poor optics.

 

Mush dog- mush monster and or Mush bucket means very bad optics were nothing forms a clean image. Jupiter will mush in and out of both sides of focus and never snap chaps.

 

This only counts for collimated- cooled scopes and not any pinched optics or bad seeing. Seeing has to be 8+ for my rating system.

 

So out of all the scopes i have had the avg fall into the lack luster to very good range. The APO's all fall into the top ratings but also vary a tiny bit. But don't count the Meade 7" ED as it was in the worst of the worst due to the cell not the lens.  All my high end Dobs gave the best planet images by far with OMI- Terry O , Zambuto and a Galaxy mirror.  My 18" Tectron fell into the mush dog rating thanks to a bad Nova 18" F/5 blank where planets would mush around focus and never snap.  The Tectron scope itself was very good and smooth.

 

SCT's by far got the lower ratings with around 6 being well past Avg and were super good.  Never had a old school slower Newt let me down. All fast Newts made in the 70's and 80's that i had were a sea of coma and much monsters as that pre Nag and Paracorr days. All older school better built Fracts were also super good.  Maks are another story as all my bigger Maks were not so hot. 7" Q a flop, 8" Intes could not be collimated but i think would have been fine and a SW180 Mak while better than SCT's was nothing that threw me back in the seat while two 125 ETX that have that perfect snap and contrast. Just also used a Intes 703 that was also very good but seems to be toe to toe with the SW703 that had a big C/O.

 

 

Never owned a RC or Cass as any i have used were not so hot.

Edited by CHASLX200, 10 March 2025 - 07:11 PM.

[CHASLX200]

I would try centering the corrector plate and then do a complete collimation. Getting the corrector directly in front of the mirror is critical.

 

-drl

Well i never gave that any thought back then. Just collimated. I am not tearing into a SCT other than i have removed a few correctors to clean.

[CHASLX200]

I wonder how many SCT's suffer from this issue?  

Must be over 75% gent. As out of around 65 i have had only 6 got top ratings and most were in the good to lack luster range. Only 5 i have seen hit the total mush monster rating.  A friends mint 1982 C11 and a gray 2004 C8 i had and three 2045's.

 

You all gotta remember these scopes are made for a cheap price and can't expect Tec like images or AP. Then ya got a image robbing big C/O and the corrector itself is the killer.

[CHASLX200]

Really, from your comments in the thousands of posts you have made it always sounded like you had a lot of bad scopes.  

Naw only 5 super bad SCT's a Meade 7" ED and a mushy Comet catcher and catcher JR that would never come to focus.  Mounts are another matter.

[CHASLX200]

All of the SCTs I've had have used cork shims to center the corrector plate in the cell. Mind you, there were all from the mid-80's to the early-90's. Dunno what they are using these days...

The cork was bad on my mushy orange 1980 C14.

[CHASLX200]

That's interesting - I have the same 80mm f/11 Vixen (Celestron) and the performance is just fantastic.

 

I think I would replace the aluminum spacers. Use 0.004" sticky backed foil. You can get it in craft stores. Forget about Newton's rings! They tell you nothing. Rotational arrangement of the lens elements - change it in increments of 1/8th turn and do repeated tests. Just assemble it with your fingers to make this go fast. You can clean it up later.

 

-drl

Never ever had a bad Vixen anything. Not sure if Vixen made the comet catcher JR.  Two 4.5's and two 6's on the P and SP mounts were super sharp. All fracts perfect.

[CHASLX200]

I have seen popsicle sicks, cork and RTV.  Wonder why the corrector gets cloudy on the inside 

Out gas i guess like the glass on the inside of a car.

[starman876]

You guys were right. I guess I have enabled the monster.

[starman876]

Out gas i guess like the glass on the inside of a car.

Most compounds like silicone outgas when they cure. 

[starman876]

Never ever had a bad Vixen anything. Not sure if Vixen made the comet catcher JR.  Two 4.5's and two 6's on the P and SP mounts were super sharp. All fracts perfect.

Anything Vixen has always been good.   There neo series was hit and miss⁹

[starman876]

The cork was bad on my mushy orange 1980 C14.

Cork was ok as long as one did not take the corrector out.  If it was dried up it would come apart in pieces.