520 replies to this topic

[Erik Bakker]

I bought my first real quality scope in 1981, after dabbling with a tiny 40mm sub par “pirate” scope and nice 7x35 binoculars.

 

Enter my then new, made in Japan, 76 f/12 achromat. It’s color correction was quite good and it’s startest was, well, stunning. I then thought all “serious” telescopes would have that level of polish and spherical correction, just with (much) more aperture and/or better color correction. Boy was I wrong. It took me a long time to encounter scopes with similar high levels of polish and spherical correction, but with more aperture and less chromatic aberration. I am glad I kept my first real telescope. For the fond memories it brings. And for a reference startest in green light, even though that is in part because it’s maker had limited it’s effective aperture by placing first internal baffle too far forward. It also showed me my first solar eclipse and the impact of Shoemaker-Levy on Jupiter. It will go nowhere.

 

I also kept my my first 80mm fast wide field achromat, an ST80. A very portable scope in comparison to the 76mm f/12. Not as sharp, more chromatic aberration, less contrasty. But easy to take with me on a plane and onto a mountain top for stunning wide field views under very dark skies, outweighing it’s deficiencies, inluding field curvature. 

 

Both these scope easily spend over 99.99% of the time in their cases these days though.

[Sketcher]

"What should you expect, and not expect, from an achromat?"

 

I enjoy using achromats, so when I first saw this thread, yesterday, I started to make a reply.  But I quickly came to the same realization that Thomas came to, more or less summarized by this quote from Thomas:  "What should you expect from a car?"

 

I know what I can expect and not expect from my various achromats.  I can summarize in the same vague manner as the original question was asked:

 

One should expect a perfectly usable telescope within the limitations of the achromat's design, fabrication quality, aperture, and focal-ratio.  One should not expect an achromat to be an ideal telescope for all people and all purposes.

 

Note that in the above paragraph one could substitute any other telescope type for "achromat" in order to answer the same question for any other telescope type,

 

It's clear from other responses in this thread that some refuse to tolerate the limitations of achromat refractors, while others freely admit to the strengths of achromat refractors.

 

It boils down to personal "hang-ups" or prejudices (the glass is half empty); and personal abilities to see and make use of a telescope's actual capabilities without being overly distracted by the weaknesses (the glass is half full).

 

And again, this is all applicable to any telescope type.  There's not a telescope on (nor off) the planet that is without its own list of strengths and weaknesses.

 

But people tend to not be impartial.  When it comes to telescopes, some people become so defensive of one telescope type that they ignore that telescope type's weaknesses.  Then they turn around and concentrate on the weaknesses of other telescope types while ignoring the strengths of that telescope type.

 

A telescope is a telescope.  All have their different strengths and weaknesses.

 

If 25585 (the original poster) wants more specific responses, I suggest posing more specific questions -- with narrower specifics.

[Bomber Bob]

I am fortunate to have an excellent achromat built by Richard Day of Skylight Telescopes. It is 100mm f/10 with an outstanding Vixen objective. I use it frequently, though i have triplet and doublet apos. I have seen CA, but it is generally negligible to undetectable. It provides excellent, contrasty views with pinpoint stars and a flat field. I was tempted by the Altair Planeta, but I really can't see it supplanting my beloved achro. 

Ditto for my custom 1970s Dakin 4" F10.  The Lens is probably a Bausch & Lomb leftover -- a Baker Doublet with a 7mm band airgap.  OTA is very nicely machined, and features a scope within the scope baffling tube.  It competed well with my 1971 RV-6 on fine planetary detail; and, with my '58 Edmund 4" F15 on low false color.  It's not a light-weight 4" scope... For no-shake high power (80x / inch on Mars / Jupiter / Saturn), I used to put it on a Tak EM-1.  Now, it rides well on my Tall Pedestal Meade StarFinder EQ.

 

 

Outstanding Views, and Decent Imaging:

 

 

The Dakin is a Keeper.  [No, the Dakin can't beat my '88 Tak FC-100.  But it's such a finely-made achromatic old scope that it stays.]

 

My smallest Outstanding Achromat is my '75 Tak TS-50 F14:

 

 

It's a 100x / inch high-res Tiny Tak -- runs out of light before going soft.  Trapezium views are... Tak Sharp.  It's my default Solar Scope.

 

In between the Dakin & the TS-50... a "new" 1980s KENKO A-80M F12.5:

 

 

It edged-out an Outstanding Celestron (V) Premium 80 F11.25 for low false color (Olympic Scoring), so I sold the C80P.  I'm still testing this Kenko, but so far, it's an 80x / inch on Jupiter & Mars.  And... the Kenko NES EQ it's on was made for this series -- about my only complete OEM Kit.  Most likely, it'll stay, even though my '84 FC-76 drinks its milkshake (after taking the lunch money)...

Edited by Bomber Bob, 23 March 2025 - 05:02 PM.

[fishhuntmike]

As a few have also shared ive found a few of mine (6" F5, 8" F5.9, 9" F7.7) useful to keep. CA ratios mostly look horrendous (all < 1). Who would want one? The one I abandoned was the 6" F15 (CA ratio 2.5). Why, because it couldnt compete with my 5" and 6" APOs. The others, especially the 8" and 9" just give me big smiles everytime I use them (I only use them at their lowest powers) where they give wonderful "4k" views like my 5-6" APOs but with more depth. My SCTs 5, 10 & 14" never did this. Its likely a premium well acclimated dob would too but I have never looked thru one. My 8" F5.9 is an amazing sweeper and I cant imagine not having it despite my other tools I have. The dob owners, or everyone for that matter who have looked thru it with a 31 nagler or 41 panoptic were impressed and many shocked by how something with CA ratio of 0.74 could present the universe so nicely. I dont use my achros for planets, the moon or even double stars. My APOs get those subjects.

I guess as many have figured out opinions are subjective. The more experience with a range of instruments and environmental conditions will produce stronger opinions. In my case I dont live in Florida or a place where the better seeing environment can shape ones opinion in a different direction. To me all that matters is I am happy.

Edited by fishhuntmike, 23 March 2025 - 05:35 PM.

[Bomber Bob]

What about The Clunkers??

 

Whew!!  Where to begin??  The cheap plastic Department Store scopes are an easy target, so I'll ignore those...

 

Among Classic Scopes, some have been disappointments -- usually unexpected.  For Starters...

 

BORG K10-76AB:  My 1st & only BORG is an F6.6 achro (cemented doublet).  Bright Views!  But... more false color than my older Mizar GT-80S F7, which also has sharper resolution at high-powers.  But... the BORG is about half the Mizar's weight.  It also features that BORG modular OTA (you can mix & match all kinds of stuff), AND a nice 4-slot Eyepiece Turret.  I may replace its achro with a BORG 77ED -- gotta read some more reviews first.

 

B&L / Bushnell Banner 1000:  This one makes No Sense.  B&L imported the exact same KENKO NES Series Scopes & Mounts as my A80M already posted...  Did Kenko send B&L the duds, or what??  NOTE to Pentax Fans:  The 1980s Pentax J Series use a lot of the same Kenko hardware -- and eyepieces.  My 1988 B1000 wasn't awful, but my 1978 Tasco (TOWA) 80 F15 had a much better Lens!!  I expected better from B&L...

 

Carton 60B:  Carton has mixed-opinions on the Classics Forum.  It's rumored that Edmund used Carton optics in their outstanding first-edition refractors.  But, quality on the 60mm lenses is all over the place.  This model had better quality Accessories than the Objective...  Views actually made me wince!  YET... my current 4" RFT is a converted to Astro Carton ZO-101 Monocular. 

 

IOW:  You never know til you buy...

 

About the modern China-made achromatics:  I've only tested a few of these.  2 were 102mm models from Bresser and Explore Scientific [Reviews on this Forum].  IIRC, both were acceptable (50x / inch); the Bresser had the better optics & overall build quality, though.

[25585]

Thank you all for your replies so far. 

 

There is only so much that can be written for a thread's title.

 

My best achromat is an 80mm F15, it is as good as my, much shorter EDs for that aperture, a TV 85, and an 80mm Equinox.

 

I try Baader semi-apo filters & fringe-killers, which make some difference, but nothing really helps a ST-80.
 

[CHASLX200]

Thank you all for your replies so far. 

 

There is only so much that can be written for a thread's title.

 

My best achromat is an 80mm F15, it is as good as my, much shorter EDs for that aperture, a TV 85, and an 80mm Equinox.

 

I try Baader semi-apo filters & fringe-killers, which make some difference, but nothing really helps a ST-80.
 

Here was my best.

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[Sketcher]

I purchased a 6-inch f/6.5 achromat 10 years ago, despite having a 5.1-inch apochromat that I purchased 30 years ago.  I put that achromat to use on planets precisely because of the overwhelming consensus on CloudyNights that such a telescope is useless for planetary observations -- due to its strong chromatic aberrations (CA).  And yes, that achromat does indeed have strong CA when it comes to sufficiently bright objects:

 

 

 

 

Is such a telescope the best choice for visual planetary purposes?  Certainly not, if one has access to better telescopes for that purpose, but that doesn't make it useless for such purposes.

 

For low contrast planetary detail, yes, that telescope takes a serious "hit".  But for high contrast detail that telescope will resolve to the theoretical limit of a 6-inch aperture.  I can identify each of Jupiter's Galilean moons by their different apparent sizes or by their different colors (if one foregoes the use of filters) with that very same 6-inch f/6.5 achromat.

 

While the moon is loaded with visible details, the dark (black) shadows that one sees with most telescopes are replaced by deep blue shadows with my 6-inch f/6.5 achromat -- if one looks closely enough -- not that it really matters all that much in one's ability to see the (high contrast) details.

 

For visual deep-sky observing most would be hard pressed to notice the effects of the CA until one gets to resolved globular clusters where the otherwise pinpoint stars become a tad bit fuzzy due to the large number of overlapping (faint, as in individually invisible) CA induced stellar halos.

 

I expected the CA to cause issues when observing the Pleiades nebulosity, but the tell-tell shape of the Merope Nebula still came through with the large, fast, achromat.  But how much of the glows around the other bright stars was nebulosity and how much was CA?  That I was unable to determine with any degree of certainty, but based on my observations with other telescopes, I would give it being mostly actual nebulosity as the more likely reality.

 

Still, I enjoy using that achromat, along with my other achromats.  Furthermore, I even enjoy taking notes on the CA and studying ways of reducing its negative effects.  I can even enjoy the added colors that it provides around objects such as Venus!  Speaking of which, I've also recorded in my sketches the rainbow-colored diffraction spikes that my 12-inch reflector put around Venus when that planet is observed high in a dark sky.  Achromat refractors don't have a monopoly on instrumentally induced color around bright objects -- surprise, surprise, surprise for those who use reflectors with diagonals held in place by spiders.

 

Anyway, that's the short story for one of my achromats -- the one with the strongest CA.  It's still one of my favorite telescopes to use -- seriously!  I don't personally find that achromat's CA to be so bad that I'm no longer able to enjoy using it.  But I'm very aware that for many others, that amount of CA is unacceptable.

 

Achromat refractors are achromat refractors.  If one can't accept them for what they are, one is free to look elsewhere for a telescope that better pleases them.  I seem to have a soft spot in my heart for all telescopes -- even achromat refractors  .

 

P.S.  I've also enjoyed using and documenting the performance of a very low-quality singlet refractor.  Like I said, I have soft spot for all telescopes.

[gnowellsct]

I've owned many, many achromats. Nearly all were purchased used via Craigslist, a few via CN and AM.

Jon

You've owned many and yet they've all managed to find their way into other houses, which is exactly the point I made in my first sentence.

It kind of reminds me of my wife and potatoes. When she was growing up she had to eat potatoes with nearly every meal. They made her sit at the table until she was done. Today if you ask her if she likes potatoes she says she likes them fine and they are great for soups and stews. she just doesn't eat them. Ever.

Talking about the greatness of the achromats you've had in the past and yet somehow they have found new homes is a bit reminiscent of how she talks about potatoes.

The spindly Little monkey Ward Japanese 60 mm I have down in the basement is, as I recall, f/11 and the color correction is quite good. I've never seen false color in it.

The tripod isn't bad but it isn't exactly good either. The system was designed around 0.965 eyepieces and focuser.

I wanted to use it with modern 1.25-in eye pieces and purchased a very nice aftermarket focuser. Well that was fantasyland. You don't take a rig like that and put on an aftermarket focuser and then drop a 10 mm XW into it and expect it all to hang together.

It was engineered to a certain spec and I exceeded the spec. I wasn't particularly fond of the 0.965 eye pieces. You could get an adapter for 1.25 in, I did get one, But the OEM focuser could not handle something like a 24 pan. That's when I decided to try a replacement focuser.

But instead it destabilized the whole apparatus. That's when I thought well what I really need are a couple of rings and a vixen dovetail and... That's when I remembered I had a vixen SD81s f / 7.7 with impeccable optics and color correction and that maybe I should take a deep breath and think things through before I spent more money on the 60 mm.

It is fun to mess around with these things but I figured out other astronomy stuff to use my Astro budget. The 60 mm is pretty much an abandoned project.

Other achromats have come in and gone out.

Achromats have a big fan base and we're in the refractor section so it behooves me perhaps to praise the refractors I do have and refrain from criticizing the ones I no longer have. But they are part of my overall refractor experiences.

Greg N

[Phil Cowell]

Based on my experience with the three I've owned I would expect an achromat to find another house to live in.


Greg N

I agree, but I’d never forgive myself inflicting them on anyone. Have two left and they live in a dark closet. Took them out to get a picture of them for the post a picture of your refractors thread then put them away again, where they won’t be causing any harm to anyone.

[Tony Flanders]

We're all saying much the same thing, but I'll try to be terse:

 

An achromat can deliver either a color-free image with a long f/ratio or an ultrawide true field of view with a short f/ratio, but unlike an APO it can't provide both in the same instrument.

 

Aside from color fringing, good achromats still have the high contrast characteristic of refractors. And it's very easy to make a good, small achromat, so you can get one pretty cheap.

 

Achromats work quite well in small apertures; old-fashioned 60-mm f/10 achromats are generally very cheap, have reasonably big true fields of view, and often have superb optical quality. But once you get much above 100 mm, the choice between false color and wide field of view becomes pretty stark, and the physical size tends to become problematic.

[Erik Bakker]

Excellent summary Tony!

[gnowellsct]

I agree, but I’d never forgive myself inflicting them on anyone. Have two left and they live in a dark closet. Took them out to get a picture of them for the post a picture of your refractors thread then put them away again, where they won’t be causing any harm to anyone.

If you really want to neutralize them you have to land fill them. Sitting in your closet they are outwaiting you, against the day that you croak. They will migrate to the Goodwill or the kids down the street that your heirs pass this stuff on to.

I have my share of Astro junk. Very strikingly when I visited Lord Rosse's telescope in Ireland they had an attached museum. It was full of HIS astro junk.

Greg N

[bobhen]

"What should you expect, and not expect, from an achromat?"

 

One should expect a perfectly usable telescope within the limitations of the achromat's design, fabrication quality, aperture, and focal-ratio.  1. One should not expect an achromat to be an ideal telescope for all people and all purposes.

 

2. A telescope is a telescope.  All have their different strengths and weaknesses.

 

1. One should not expect an achromat to be an ideal telescope for all people and all purposes.

 

Well, no telescope can be the ideal telescope for "all" people and "all" purposes. That statement has nothing to do with the achromatic refractor design. It has more to do with the various needs of people and their observing and imaging interests. The same could be said of the SCT or the Newtonian.

 

I think the correct comparison is between the achromat and the apochromat. Of course, even an apo cannot be the perfect telescope for all people and all purposes. But the point is, the apochromatic refractor design lends itself to be and do "many more things" and do them "better" for both the visual observer and the imager than does the achromatic design. 

 

2. A telescope is a telescope.  All have their different strengths and weaknesses.  

 

Again, no telescope design is perfect and it's true that all telescopes have different strengths and weaknesses. But the point is, that compared to the achromatic refractor design, the apochromatic refractor design has "no" optical or performance visual or imaging disadvantages. Whereas, the achromatic design has many disadvantages that are all well known. The only advantage the achromatic design has is a cost advantage. But when we consider the cost of a mount to mount achromatic refractors with long FLs and in sizes above 4-inches, that cost advantage becomes much less and might disappear altogether. 

 

Bottom line. The market has spoken. And today, with evermore reasonably priced apos to choose from, the achromatic refractor has gone the way of the typewriter. Sure, some still love their IBM Selectrics but the vast majority today use word processors; for the simple reason that word processors have so many more advantages. The same goes with apos versus achromats. Compared to the achromat, the apochromat has far too many observing and imaging advantages for the achromat to ever be the popular choice that it once was.   

 

Bob

[Jon Isaacs]

You've owned many and yet they've all managed to find their way into other houses, which is exactly the point I made in my first sentence.

 

 

If you really want to neutralize them you have to land fill them. Sitting in your closet they are outwaiting you, against the day that you croak. They will migrate to the Goodwill or the kids down the street that your heirs pass this stuff on to.

I have my share of Astro junk. Very strikingly when I visited Lord Rosse's telescope in Ireland they had an attached museum. It was full of HIS astro junk.

Greg N

 

Apparently the difference between you and me is that I am able to appreciate basic achromats for what they can do and I find homes for them with others in need of a good telescope.  I have a number of very good telescopes that I use on a very frequent basis.. Something about living in the southwest... However, I can still appreciate and enjoy a basic achromat. If I couldn't, I would be very, very disappointed in myself.  

 

The reason I give away telescopes is because they are good telescopes deserving of a home where someone appreciates them, uses them..  It's not just achromats I give away.   A couple of years ago, I gave my William Optics 80mm Megrez II FD (FPL-53) to a long time because I just wasn't using it. That is not the only ED/apo I have given away. 

 

The key to using any tool is to use it for the appropriate task.  There are "junk" telescopes out there, plastic lenses, singlets.  But the typical Synta-Skywatcher achromat is a decent telescope with decent optics, workable focuser etc.  Part of being a skilled observer is choosing the appropriate telescope for the object(s) of interest.  And part of being a skilled observer is making the most of the equipment you are using.  

 

I always keep in mind, my equipment is better than I am. Someone else with my equipment, they could see more than I can.  My goal is not the have the best equipment, it is to be the best observer I can be.  I admire and respect those who are highly skilled observers, it's not their equipment..  Sketcher, he and I have different strategies and goals but he is a highly skilled observer who makes the most of his equipment.  I admire and respect that.

 

Jon

Edited by Jon Isaacs, 24 March 2025 - 08:38 AM.

[Phil Cowell]

Might use the celestron yard cannon as an urn.

 

If you really want to neutralize them you have to land fill them. Sitting in your closet they are outwaiting you, against the day that you croak. They will migrate to the Goodwill or the kids down the street that your heirs pass this stuff on to.

I have my share of Astro junk. Very strikingly when I visited Lord Rosse's telescope in Ireland they had an attached museum. It was full of HIS astro junk.

Greg N

[nicknacknock]

OK folks,

 

Let’s get back on track and stick to the topic, cheers!

[saemark30]

I wouldn't pass up a chance to view through master crafted Alvan Clark masterpieces such as the great 24" Lowell, 36" or 40" Yerkes achromatic refractors.

Or a Zeiss 12" F15 achromat for that matter.

Well polished and figured glass will yield loads of detail on the planets.

The observers from the past used Wratten filters to enhance planetary detail.

[kmparsons]

I agree, but I’d never forgive myself inflicting them on anyone. Have two left and they live in a dark closet. Took them out to get a picture of them for the post a picture of your refractors thread then put them away again, where they won’t be causing any harm to anyone.

Just curious. What are the two despised achromats? Maybe you could inflict them on me. 

[Refractor6]

Nice to know the achromat hate lives on some 20 years later on CN as predicted in my earlier post....if you have one you don't like here's an idea... pass it along to someone to enjoy and use and rid yourself of it or better yet let others who still use them enjoy theirs in peace...amen.

[gnowellsct]

Apparently the difference between you and me is that I am able to appreciate basic achromats for what they can do and I find homes for them with others in need of a good telescope.
Jon

??? I've never tossed an achromat. Not yet anyhow. I've sold a couple.

Greg N

[bobhen]

Nice to know the achromat hate lives on some 20 years later on CN as predicted in my earlier post....if you have one you don't like here's an idea... pass it along to someone to enjoy and use and rid yourself of it or better yet let others who still use them enjoy theirs in peace...amen.

I think the word "hate" is rather strong. No one hates achromatic refractors any more than they hate dial phones or cars that you have to crank to start or typewriters. It's just that a better refractor design has come along that offers many more advantages than the achromat. One can still make a call on a dial phone or write a letter with a typewriter or start a Model T using a crank. And one can still look at the heavens using an achromat. But like those other outdated technologies, there' now a better refractor design that offers more advantages for the observer and the imager than does the achromat. 

 

Below is my $59 Celestron 4" achromatic OTA that I gifted to my niece. There's no question that having that telescope is better than having no telescope. But there's also no question that having a 4" apo would be an even better telescope to own and observe with and image with.

 

Bob

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[Sol Robbins]

Here's a sketch I made of a well placed Saturn I made a while back using my Skywatcher 6" f/8 achromat refractor on a good night. Details are embedded in the sketch The 3 Venus sketches are a progression using the 6" achromat refractor followed by inserting CED-1 & CED-2 star diagonals to show a comparison. Venus is a harsh test for a scope..

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Edited by Sol Robbins, 24 March 2025 - 01:03 PM.

[Refractor6]

   My point is under my dark skies my two 20+ year old achromats still provide me very enjoyable visual observing sessions like they did when I first purchased them....neither are relics or extinct in my view. In fact for their intended use both provide even more satisfying views in the light pollution free location they currently reside.  It just rubs me the wrong way when folks talk land fill and urns for scopes that could be happily used by others instead.

 

 I trade off between a excellent 120 F/7.5 ED for planet season {which is just winding down} or a 127 F/6.45 achromat using the same mount when open clusters and the summer milky way shows up late in the night sky at present. In the summer my 152 F/8 achromat is out most nights covering a wide variety of objects I love to observe and I don't feel one bit like I'm missing out on anything by just using this and my other achromat by choice for visual observing from my location.

[Mike W]

I think the word "hate" is rather strong. No one hates achromatic refractors any more than they hate dial phones or cars that you have to crank to start or typewriters. It's just that a better refractor design has come along that offers many more advantages than the achromat. One can still make a call on a dial phone or write a letter with a typewriter or start a Model T using a crank. And one can still look at the heavens using an achromat. But like those other outdated technologies, there' now a better refractor design that offers more advantages for the observer and the imager than does the achromat. 

 

Below is my $59 Celestron 4" achromatic OTA that I gifted to my niece. There's no question that having that telescope is better than having no telescope. But there's also no question that having a 4" apo would be an even better telescope to own and observe with and image with.

 

Bob

She looks happy! My first scope was a Jason under the Christmas tree. I mapped the moon with it for the science fair, girl with a Unitron 114 won! She sketched double stars. I eventually won -made a draw bridge with an erector set. (remember those?)