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1 inch APO vs 12 inch SCT

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#401 Daniel Mounsey

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Posted 19 January 2018 - 02:23 AM

Yello, yea, somewhere we're crossing paths and wires. No offense ever intended.

I wasn't trying to say what I think you understand. Lol

I guess all Im saying, really, if we're perceiving color, then we are not observing Jove with low res, grey scale dark adapted vision. We are still firing hi res, color receptors and may have no need to reset our eyes with a bright light. Actually, it was a question. I've tried this technique and found it distracting. That's all.

Howver. I also take a break and have coffee, too. Esecially during a long session. It's relaxing. smile.gif

 

So it's basically this. The rods in the retina are the receptors in low light and are less sensitive to color. The cones are sensitive to colors but need higher light levels and the cones at the center result in the best sharpness. My own discovery of this effect occurred by accident after 10 minute coffee breaks in my brightly lit kitchen many years ago. Every single time I came back and looked into the eyepiece of any of my telescopes, I was absolutely stunned. The OP is about a 1" vs 12". This Will seriously help observers with larger 12" scopes where the brighter light of planets is very saturated and irradiation is severe. The smaller the aperture, the more discipline you need and this is probably what's happening since your Mak is only 6". The basic rule is "planets are bright enough" and here's exactly what it looks like when the effect occurs.

 

When you come out of the kitchen, the background is jet black as illustrated in the first image left. At this point, the effect is absolutely astonishing while viewing the planets because nothing in the background or around the planet is visible yet. Remember too that the colors we see on the planets are the fuel to the surface contrast. Light does not scatter or encroach into adjacent features. Instead, the edges around the planets including their features appear tack sharp and relatively filled with more visible surface color. As the eye begins to dark adapt (the enemy), the background starts to appear more like the center image. Notice how you begin to see more stars. Now imagine it's a Newtonian and there are diffraction spikes from the 4 vane spider. Because of the effect in the first image far left, your eyes are not dark adapted enough to see the diffraction spikes. But as they dark adapt, the fainter diffraction spikes become more and more visible. This starts to occur in just 30 to 45 seconds, so time is very crucial to get the best planetary views. By the time your eyes are dark adapted, the background becomes worse. Color Contrast starts to weaken, light around the planet is scattered and encroaches on adjacent features. The halo of scattered light around the planets also becomes completely visible and more annoying. 

 

Awwww, what a bummer. What should you do? Keep an 8.5x11 notepad with white paper next to you and shine a white light onto the paper and stare at it as much as possible and continue taking moments to look into the eyepiece. Doing so will help generate the effect you see in the left image. Remember that planets will always be bright enough, so dark adaptation is never needed nor wanted. You should keep white lights on around you at all times. I suggest white LED's and avoid red flashlights at all times as a source of light. LED's are extremely efficient and don't give off terrible heat currents near the telescope compared to conventional light bulbs. There's still another method you can use that works equally amazing. I also noticed it by accident at home as well as Charlton Flats during sundown. In this particular case, the background light is so bright, your eyes are unable to dark adapt. As a result, the background light completely hides any scattered light because the brighter planets don't have a dark background to see scattered light against. With larger apertures, diffraction spikes, halos and light scatter are completely invisible. But, as the sky darkens, scatter and halos become more and more visible and the enemy (dark adaption) resumes. 

 

Then one day I accidently stumbled on a quote by Master planetary observer John B. Murray that described exactly what I had been seeing. He said it best which I shared in an article in 2003 called "planetary eyepieces". "Sometimes it's the contrast of a dark sky and a bright disk that renders details difficult to see, and observations during bright twilight, when planets first become visible to the naked eye may show surface features much more clearly than against a dark sky.

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#402 Asbytec

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Posted 19 January 2018 - 03:37 AM

Thank you, Daniel. Normally when I grab a cup of coffee, the lights are out except for the TV. It's an old habbit.

So, not sure I've discovered this phenomenon. Folks talk about bright light and observing at dusk or dawn. So, there must be something to it.

"Sometimes it's the contrast of a dark sky and a bright disk that renders details difficult to see..."

Curious as to what's going on here, the physiology. I'll think it through trying to understand why this works. I trip myself up thinking twilight is a form of noise thus lower contrast. Weird.

I guess my exit pupils are such that my "disc" is not terribly bright...but the sky is darker save for some atmospheric scatter. (Nice night when it's not). I dunno...

But, yea. We want to avoid dark adaption. If we are dark adapted, Jove is too dim to work with, I suppose.

Edit: I do understand how radiance of a bright image can inhibit detection. My answer has always been a smaller exit pupil.

Edited by Asbytec, 19 January 2018 - 03:50 AM.


#403 yellobeard

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Posted 19 January 2018 - 05:14 AM

"planetary eyepieces". "Sometimes it's the contrast of a dark sky and a bright disk that renders details difficult to see, and observations during bright twilight, when planets first become visible to the naked eye may show surface features much more clearly than against a dark sky.

Now thats exactly what I already noticed years ago, but mostly, the sky here was not yet at ease during those 'mid twilight' moments.
But in theory, think about this:

If you observe for example Jupiter during twilight, the light coming from the atmosphere is between you and Jupiter, bringing down the contrast inevetably!
So, even if, with that in mind, we still have a better contrast (and color) perception, than we really are on the right track with our tendency to NOT want the dark adaption during observations of at least the higher luminance planets!

And Asbytec: For me there is a logic in choosing 'the killing of dark adaption' over a smaller exit pupil: In my case, a smaller exit pupil causes impurities in my eyes to compromise the image! Thats why I like bino viewers so much.
Also, in my experience, making jupiter bigger, in my case with sometimes 900-1000x magnification, makes me feel having a problem with details getting too far apart from each other.. I don't know if I'm on the right track with this, but seems to me that with 600-700x in my 16", details are much better 'overviewable?'.. But the fact about the impurities in my eyes also can be a problem there, so I'm not quite sure..

Well, the positive is: We have a whole new year to try things in the field, and discuss our findings..

Edited by yellobeard, 19 January 2018 - 05:34 AM.


#404 Asbytec

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Posted 19 January 2018 - 06:20 AM

Yello, sure. Impurities in our eye can be a problem. Viewing the moon at small exit pupils, especially, they can be a chore to move them out of the way. I dont "notice" them as much on Jove at 240x 0.6mm exit pupil. Jove is just on the verge of being too dim and it is too dim at 0.5mm. To my knowledge, I've never sketched a floater. :lol:

But, I still perceive color, somewhat subdued, so I know my color receptors are firing and high res is still possible. Image scale is conducive to bright low contrast detail.

Yea, I dunno. What works, I guess. :)

Interestingly, at 700x in your 16", were both operating at 0.6mm "overviewable" exit Pupil. I cannot get to the equivelent of 900x through your 16". That's ~0.4mm exit pupil and a very dim image for me.
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#405 yellobeard

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Posted 19 January 2018 - 08:20 AM

What the blieb...you are right!! I didn't even notice myself that 700x already gives some 0.6mm exit pupil in my 16"...

Point is, apparently, the 16" tends to be a very "forgiving" telescope.. Easily going over the 500x mark on Jupiter, I never had the same feeling with any of my other scopes, well, the watercooled 31cm newtonian comes close, with perhaps my two modified C11's.
With high efficiency coatings, the total transmission of the 16" SCT definitely is far above the 90% mark..
And then there is the 17% (diameter) total obstruction, also pushing up contrast somewhat (in theory)

And, I provided the 16" with very low surface roughness optics, which drasticly loweres the scatter losses..

Edited by yellobeard, 19 January 2018 - 08:35 AM.


#406 Asbytec

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Posted 19 January 2018 - 09:35 AM

Yello, yea I have no doubt your scope's optimizations allow you to squeeze a little more from it working at smaller exit pupils. :)

I'm not sure what my MCT throughput actually or might be. The optics appear fairly smooth and zone free in the star test (other than overcorrection). Likely less than your 16".

I've seen stars down to the theoretical limit, for sure, and dimmer magnitudes listed at different wavelengths. So, its confusing, but I imagine its at least ok.

Edited by Asbytec, 19 January 2018 - 09:38 AM.


#407 Daniel Mounsey

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Posted 20 January 2018 - 08:47 AM

Norme, 

Curious, what kind of magnifications do you find yourself using in your 6" Mak for Jupiter?


Edited by Daniel Mounsey, 20 January 2018 - 08:47 AM.


#408 Asbytec

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Posted 20 January 2018 - 09:24 AM

Norme,
Curious, what kind of magnifications do you find yourself using in your 6" Mak for Jupiter?

40x per inch at 240x, Daniel. Used to do the more traditional 30x per inch, but find it more productive up a little higher at 0.6mm exit pupil. You?

On my way home from a Boy Scout out reach. Seeing was amazing. Quick check of collimation on defocused Sirius showed a rock steady pattern. So sweet.

Edited by Asbytec, 20 January 2018 - 09:27 AM.


#409 gnowellsct

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Posted Yesterday, 01:06 AM

One of the issues about the master and corrector roughness is that some SCTS were produced with this issue for thirty or 40 years till the manufacturing process was modified in the 00s, if memory serves. But that doesn't stop the lore.

#410 CHASLX200

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Posted Yesterday, 06:25 AM

One of the issues about the master and corrector roughness is that some SCTS were produced with this issue for thirty or 40 years till the manufacturing process was modified in the 00s, if memory serves. But that doesn't stop the lore.

And don't forget master blanks wearing out. So maybe the C8's from 1972 to 75 were the best.  Then whenever Celestron made  a new master blank then the optics were good again for a few years.



#411 luxo II

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Posted Yesterday, 07:27 AM

Norme, 

Curious, what kind of magnifications do you find yourself using in your 6" Mak for Jupiter?

If seeing permits, I'll push my Santel MK91 to 450X which is X2 per mm of aperture, or 0.5mm exit pupil.

 

One thing I have noticed particularly on star clusters is that collimation is utterly critical...  When it arrived the scope had a very a slight misalignment - close enough that at 300X I thought it was 'OK'. But not perfect.

 

Finally I pulled out the tools last Saturday and got the collimation spot on, and Lord-oh-my-Lord, what a difference. Nice concentric bulls-eyes at 450X, everywhere.

 

By way of example... start with 400X on the Trapezium in Orion. E and F for me stand out very easily, yet with the collimation just slightly off they were much harder. Next, turn to Sirius, and the Pup. With the scope properly collimated the Pup is an easy target with its current separation. With the collimation off just a tad, it was a far harder target.

 

Jupiter, Mars and Saturn should be awesome later this year.

 

But this is no run-of-the-mill SCT...


Edited by luxo II, Yesterday, 07:40 AM.

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#412 Asbytec

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Posted Yesterday, 07:39 AM

Luxo, concentric bull's eyes. Yes. Nice. Mine is always collimated well, too. :)



#413 luxo II

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Posted Yesterday, 07:49 AM

So maybe the C8's from 1972 to 75 were the best.  Then whenever Celestron made  a new master blank then the optics were good again for a few years.

 

Nope... the production quality at that time was very variable. I bought an orange C8 from the late 70s, very poor optically and wouldn't form a recognisable Airy disk.

 

At that time I belonged to a large society where it was quite usual to see perhaps 10 C8's onsite at an observing night, and a few years later the first of the Meade 8" SCTs appeared. Of the C8's it was evident that several were like mine - quite poor optically - and just one was what I regarded as quite good in comparison to a tradition old-school 8" f/8 Newtonian.

 

The orange 1970s C8s had an RA drivetrain that was best described as "agricultural".

 

The early Meade 8" SCTs had better optics and better mechanicals, though the electronics without exception had a very short life. Most were de-forked and remounted, or trashed.


Edited by luxo II, Yesterday, 07:50 AM.


#414 luxo II

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Posted Yesterday, 07:52 AM

Luxo, concentric bull's eyes. Yes. Nice. Mine is always collimated well, too. smile.gif

Ok.. try Trapezium E and F.

 

Then Sirius and the Pup. Ask a second observer to verify. A 130 APO will be struggling to do that. A 180 APO might.

 

Then say how many stars you can make out in the trapezium (there are more), and your scope details.


Edited by luxo II, Yesterday, 07:57 AM.

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#415 yellobeard

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Posted Yesterday, 08:08 AM


So maybe the C8's from 1972 to 75 were the best. Then whenever Celestron made a new master blank then the optics were good again for a few years.

Nope... the production quality at that time was very variable. I bought an orange C8 from the late 70s, very poor optically and wouldn't form a recognisable Airy disk.
I have seen a few mint C5's an C8's from that time, some only needed some re-collimation, but overall, they were exellent on optical quality.

Remember: When you buy a scope from that early period, you never know what life it had, and who messed with it..So you cannot, certainly not from one particular case, ever say something about the average quality of those Celestrons from the 70's.. For that, you need to test some 20 or more scopes from that time, and be sure that they are nicely collimated, and untouched in the past.

.

Edited by yellobeard, Yesterday, 08:11 AM.


#416 Asbytec

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Posted Yesterday, 08:11 AM

Sure. If you're asking me. I see E and F trap readily at higher magnification. Normally they come and go with the atmospheric conditions. One night, however, they were bright steady tiny pin points. Quite a sight. Cant say Ive seen G or H Trap, but I have kept an eye out in case.

A real challenge, in my view, is to count white ovals in Joves southern hemisphere. They are small, low contrast detail and telling about contrast (and seeing). Over time, I've managed 5 of the 9 or so ovals. I still remember catching the first one. Gosh, they are tiny. :)

Three years ago the Pup was a real challenge. It took quite an effort just to glimpse it. Not easy at all. Back then, folks were reporting it easy in 4" refractors.

But, yea actual visual observations are a great way to compare. The problem with a second opinion is asking my inexperienced wife to see what I see. :)

Edited by Asbytec, Yesterday, 08:18 AM.


#417 TG

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Posted Yesterday, 03:44 PM



The roughness comes from the material they use to polish the correctors surface.
I test the roughness in schmidt corrector plates by putting them in a scope with very low roughness optics, and in autocollimation (double pass)

But also, if roughness is revealed during testing of a existing SCT, that roughness is very very likely comming from the schmidt corrector, as that corrector is the only optical element that undergoes a different way of polishing.
I never found mirrors in SCT's that have unaccepable roughness, roughness in tests always came from the schmidt corrector's

Also, I noticed a very wide variety in the amount of roughness in the many SCT's that i tested so far, factory tolerances?? I don't know. But I have seen many of the shelf scopes that were very bad, and a very few that were exellent! The remaining scopes tested somewhere inbetween those two extremes. Where the exellent ones come from, and what the difference in the polishing process was, that they underwent? I wish I knew..

I have four of those exellent 'of the shelf' scopes, that I decided to not need to modify.. A C90 (newest model) a 1974 orange C5, a new model C6, and a 1974 orange C8.. They all give a very smooth perfect test image when put in front of my 18" flat collimation mirror.
Ok, the C90 is a Maksutov, so a bit less valid in the schmidt corrector issue..

I would assume the material they use to polish the correctors is a polishing compound on a pitch lap. What polishing compound they use I don't know, but it's probably the same one used to do the mirrors and secondary, so no reason the material used would cause it.

Just putting the corrector in a mirror and secondary jig and testing it doesn't reveal roughness. Maybe an inaccurate figure. Rohr has done a lot of SCT testing and he does find rough primaries. That's easy to do and photograph with a Focault test. Anyone can do it. It's is in Texereaux's book. I don't know another test for surface roughness on flat or convex optical surfaces.
Here is a quote from Roland Christen...

"None of the commercial SCT manufacturers grind the corrector plates. They simply polish the bent plate flat. The process is very fast using plastic high speed polishers.

"How fast is this process? When Criterion (Bausch&Lomb) was making the correctors for their 8" SCTs, it took all of 17 seconds to fully polish out each corrector surface."

Rolando

Bob
I have two things to offer:

1. Roland was talking about B&L, presumably when they had just acquired Criterion. He also worked at B&L so we can take his statement at face value. However, Criterion SCTs are the worst SC telescopes -- no, actually just the worst telescopes -- ever made. Whatever they were doing didn't actually result in a functional telescope so extrapolating from what Criterion was doing to Celestron/Meade is nonsensical.

2. Here's a quote from a Celestron employee "MM" who actually did the work of making correctors. Note the text in bold. So much for Roland's 17 seconds.

RP: Were you making them one at a time?

MM: No. We had maybe five 8-inch blocks, maybe five 5-inch blocks, a Schmidt
Camera block, and 1 or 2 10-inch blocks. They were all in a row, and you would lay
down a fresh set of blanks and start grinding and polishing them, one right after another.
It took about five hours to make a corrector, starting with heavier grits, then finer and
finer, then polish it out, and that would take 2 or 3 hours, then we'd flip it over and finish
it.


The above quote is from Robert Piekiel's (RP above) book, "Celestron: The Early Years".

Tanveer.

Addendum: there's also a scan of actual Celestron handbook pages relating to the polishing of a C14 corrector plate in the Piekiel book. Its grind and polish time is 1.75h on one side and 1.5h on the second. In addition there is other prep work, edging, etc. which makes the above 5 hour number completely believable. For copyright reasons, I can't provide the scan but it's in Ch. 69 of the book.
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#418 CHASLX200

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Posted Yesterday, 06:54 PM

 

So maybe the C8's from 1972 to 75 were the best.  Then whenever Celestron made  a new master blank then the optics were good again for a few years.

 

Nope... the production quality at that time was very variable. I bought an orange C8 from the late 70s, very poor optically and wouldn't form a recognisable Airy disk.

 

At that time I belonged to a large society where it was quite usual to see perhaps 10 C8's onsite at an observing night, and a few years later the first of the Meade 8" SCTs appeared. Of the C8's it was evident that several were like mine - quite poor optically - and just one was what I regarded as quite good in comparison to a tradition old-school 8" f/8 Newtonian.

 

The orange 1970s C8s had an RA drivetrain that was best described as "agricultural".

 

The early Meade 8" SCTs had better optics and better mechanicals, though the electronics without exception had a very short life. Most were de-forked and remounted, or trashed.

 

Every orange Celestron i owned was so so at best.  One very bad C14 , 6 or 7 lack luster later 70's and early C8's and a few later 70's and early 80's C5's that were ok to somewhat good.  Then a friend had a 1982 C11 that was the worst by far. Never owned any of the pre 1977 with the holes in the forks Celestrons so i can't judge them. Did have a insane sharp 1984 black C8 that was one in a million.  Out of around 60 SCT's only 5 stand out as very good to super. I have a pre 1975 small round base C5 coming soon and maybe a so called hand picked early 70's C8 that is said to be unreal.

 

This is what the seller says.

 

I have a Sandcast C8 with exceptional optics, the scope as a whole is in 90% clean condition.  When I pulled the Mirror to re-lube it there were instructions written with Celestrons Black felt tip marker, on the back of the primary...
                                                                       STATING
                                           "Strip and recheck, inside sales, Leo Henzel".


Edited by CHASLX200, Yesterday, 06:56 PM.


#419 Mitrovarr

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Posted Yesterday, 08:02 PM

 

 

So maybe the C8's from 1972 to 75 were the best.  Then whenever Celestron made  a new master blank then the optics were good again for a few years.

 

Nope... the production quality at that time was very variable. I bought an orange C8 from the late 70s, very poor optically and wouldn't form a recognisable Airy disk.

 

At that time I belonged to a large society where it was quite usual to see perhaps 10 C8's onsite at an observing night, and a few years later the first of the Meade 8" SCTs appeared. Of the C8's it was evident that several were like mine - quite poor optically - and just one was what I regarded as quite good in comparison to a tradition old-school 8" f/8 Newtonian.

 

The orange 1970s C8s had an RA drivetrain that was best described as "agricultural".

 

The early Meade 8" SCTs had better optics and better mechanicals, though the electronics without exception had a very short life. Most were de-forked and remounted, or trashed.

 

Every orange Celestron i owned was so so at best.  One very bad C14 , 6 or 7 lack luster later 70's and early C8's and a few later 70's and early 80's C5's that were ok to somewhat good.  Then a friend had a 1982 C11 that was the worst by far. Never owned any of the pre 1977 with the holes in the forks Celestrons so i can't judge them. Did have a insane sharp 1984 black C8 that was one in a million.  Out of around 60 SCT's only 5 stand out as very good to super. I have a pre 1975 small round base C5 coming soon and maybe a so called hand picked early 70's C8 that is said to be unreal.

 

This is what the seller says.

 

I have a Sandcast C8 with exceptional optics, the scope as a whole is in 90% clean condition.  When I pulled the Mirror to re-lube it there were instructions written with Celestrons Black felt tip marker, on the back of the primary...
                                                                       STATING
                                           "Strip and recheck, inside sales, Leo Henzel".

 

Have you tried many SCTs from more recent times? A lot of people say the quality of the new scopes is much more consistent, with most of them coming in at decent at least.



#420 CHASLX200

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Posted Yesterday, 08:11 PM

 

 

 

So maybe the C8's from 1972 to 75 were the best.  Then whenever Celestron made  a new master blank then the optics were good again for a few years.

 

Nope... the production quality at that time was very variable. I bought an orange C8 from the late 70s, very poor optically and wouldn't form a recognisable Airy disk.

 

At that time I belonged to a large society where it was quite usual to see perhaps 10 C8's onsite at an observing night, and a few years later the first of the Meade 8" SCTs appeared. Of the C8's it was evident that several were like mine - quite poor optically - and just one was what I regarded as quite good in comparison to a tradition old-school 8" f/8 Newtonian.

 

The orange 1970s C8s had an RA drivetrain that was best described as "agricultural".

 

The early Meade 8" SCTs had better optics and better mechanicals, though the electronics without exception had a very short life. Most were de-forked and remounted, or trashed.

 

Every orange Celestron i owned was so so at best.  One very bad C14 , 6 or 7 lack luster later 70's and early C8's and a few later 70's and early 80's C5's that were ok to somewhat good.  Then a friend had a 1982 C11 that was the worst by far. Never owned any of the pre 1977 with the holes in the forks Celestrons so i can't judge them. Did have a insane sharp 1984 black C8 that was one in a million.  Out of around 60 SCT's only 5 stand out as very good to super. I have a pre 1975 small round base C5 coming soon and maybe a so called hand picked early 70's C8 that is said to be unreal.

 

This is what the seller says.

 

I have a Sandcast C8 with exceptional optics, the scope as a whole is in 90% clean condition.  When I pulled the Mirror to re-lube it there were instructions written with Celestrons Black felt tip marker, on the back of the primary...
                                                                       STATING
                                           "Strip and recheck, inside sales, Leo Henzel".

 

Have you tried many SCTs from more recent times? A lot of people say the quality of the new scopes is much more consistent, with most of them coming in at decent at least.

 

Not really.  Maybe a few made after 2005.  The hit and miss is not as bad since the mid 90's.  Meade seemed to hit it good in the mid and late 90's while no Meade i owned made in the 80's seemed to be that good.



#421 Mitrovarr

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Posted Today, 12:15 AM

That's interesting. I've heard mostly good things about more recent SCTs. What everyone seems to say is that before Halley things were scattershot, with some great and some terrible and some in between. During the Halley era things were mostly bad, with some scopes being nearly unusable. Then, everyone steadily improved until the present day, when most SCTs made are pretty solid.

 

Of my three SCTs, I have one Dynamax (as bad as everyone says it is), a Meade 10" from the early 90s (fairly serious spherical aberration, I think, based on the star test, but otherwise pretty good) and a Celestron 6" from the 2000s (pretty good, nice symmetrical star test, works at powers its aperture says it should work at).



#422 Peter Besenbruch

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Posted Today, 12:50 AM

That's interesting. I've heard mostly good things about more recent SCTs.

I have been "hearing mostly good things about more recent SCTs" since the late 80s. That doesn't make it true. The fact is, Celestron and Meade disn't just churn out turkeys for Halley. They did it pre-Halley, and post-Halley and well into our century. I have heard the story that they "were bad a few years ago, but now they are better" far too often to believe any of it.



#423 Mitrovarr

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Posted Today, 01:16 AM

Oh well. Not much else to do if you want an SCT. Most of the other options are ridiculously expensive and some of them aren't reputed to be completely reliable either. I mean, a lot of them are so stupidly erxpensive you could buy like 3-4 Meade or Celestron SCTs, keep the best one, throw the rest in the trash, and still not spend as much.




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