520 replies to this topic

[Mike W]

Here's an acromat. (10.75" Butler Clark at the old Yale obs.) It's listed in "Alvan Clark & Sons" 

 

 

Edited by Mike W, 24 March 2025 - 02:03 PM.

[Phil Cowell]

To stick to the topic. Disappointment of spending hard earned cash if it’s a large Achro. Having read many of your previous posts you have several fine scopes in your stable, The inherent CA is going to be an enjoyment killer. You’ll get some who will give methods like filters, masking etc but you have already progressed beyond that with what you have. You have much better scopes that cover the niche it would fill. If you were looking at a piece of history from a bygone era then I could understand it. Forget about imaging with one, star bloat is obvious due to the inherent design of a fast Achro. 
The other side is to reduce CA your going to have a long focal length along with additional cost required for mounting.

My guess is it would be a hanger queen after a couple initial setups.

Honest answer.
 

In respect of performance, what should you expect, and not expect, from an achromat?

 

Aperture and f-ratio will determine much, but what generally is allowable, given what achros are?

Edited by Phil Cowell, 24 March 2025 - 02:45 PM.

[kmparsons]

Here's an acromat. (10.75" Butler Clark at the old Yale obs.) It's listed in "Alvan Clark & Sons" 

 

 

post-16463-0-06188600-1458765176.jpg

Wow! By far the best view of Saturn I have seen was through the 13" Fitz-Clark refractor at the Allegheny Observatory. 

[saemark30]

I expect a lot better bang for the buck from a good achromat than a premium apo refractor especially anything larger than 4".

People buy achromats for the value they offer.

For powers under 100x or deep sky viewing they are more similar than different.

Edited by saemark30, 24 March 2025 - 02:53 PM.

[Tony Flanders]

Compared to the achromatic refractor design, the apochromatic refractor design has "no" optical or performance visual or imaging disadvantages.

This isn't a big deal, and it's not relevant if you believe that a doublet can be an APO. But triplets do have a significantly longer cooldown time than doublets. And of course they're heavier.
 

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.

You have a mighty casual attitude toward money. I think that cost is a really big deal, in more way than one. I'm willing to take my $100 (original cost) achromat places where I would be extremely reluctant to risk my $600 APO. And for most prospective beginners cost is a very big deal indeed.
 
I think that quite a significant fraction of all beginners would be best served by an old-fashioned 70-mm achromat. I would say 60 mm, because as far as aperture alone is concerned there's not that much difference. But for whatever reason I've found the average mechanical quality of 70-mm refractors better than 60-mm refractors, at very little extra cost.
 
What's not to like about a 70-mm f/10 achromat? Simple, almost instant cooldown, useful for terrestrial observing, generally quite good optical quality, easy on eyepieces, works well even with a fairly crude focuser -- as I said, ideal for beginners who don't want the size, weight, and cost of a more capable instrument, and don't want to worry about collimation.
 
I certainly agree that long-focus achromats with apertures bigger than 100 mm aren't very practical due to the size, weight, and cost of the mount. So yes, in that one particular niche you might argue that achromats are obsolete except for sentimental value.
 

Bottom line. The market has spoken.

Indeed. I'm quite sure that inexpensive achromats still outsell APOs by a factor of tens, hundreds, or maybe even thousands.

[Erik Bakker]

Over many years, I’ve logged hundreds upon hundreds of hours with a 266mm f/15 Alvan Clark achromat observing Jupiter, Saturn and Mars.

 

Chromatic aberration? Sure.

 

But most of all: stunning planetary detail on good nights.

 

[maniack]

Cost isn't the only advantage a short focal length achromat has. Weight is another significant difference. Part of this is due to the generally cheaper components that get mated to a achromat lenses. Part of that is due to apos being aimed at imagers who need bigger and more robust focusers etc. But part of it is you can't get apochromatic performance out of a doublet at something as fast as f/5.

 

Like Tony I took a $90 ST80 to Mexico over my >$400 AT7EDII. It was less of a risk (especially since I was staying at the beach and sand was a concern). But it was also a couple of pounds lighter, which helped in my backpack carry-on.

[Bomber Bob]

   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.

I get ya.  Every so often, I'll set up my 100+ year old Mogey 3" F14:

 

 

Man!  Ole BB is getting old... Forgot that I'd made updated pix of it... Mercy!!

Edited by Bomber Bob, 24 March 2025 - 05:13 PM.

[Refractor6]

 Awesome condition for a old scope......

[Bomber Bob]

Thanks!  I had a local guy match the Mogey Grey & powder-coat it.

 

BEFORE RESTORE:

 

 

Took about a year -- off & on -- to get all that tarnish / corrosion off the all that brass.  No plastic on this antique.

Edited by Bomber Bob, 24 March 2025 - 05:21 PM.

[Refractor6]

Thanks!  I had a local guy match the Mogey Grey & powder-coat it.

     Good job...what's the story on the mount?.....thanks.

[Mike W]

     Good job...what's the story on the mount?.....thanks.

Looks like a meade starfinder 

[Bomber Bob]

It's an early 1980s Meade StarFinder -- made for their 6" to 10" SF Newtonians.  Simple, well-made, pretty accurate R/A tracking with no Wires -- battery pack is in the housing.  So... I bought 2, and left 1 on its 3' Short / Newt pedestal, and made a 5' pedestal for the Refractors & CATs...  Paid about $100 for each mount head, plus maybe $100 on the Tall pedestal...

 

I had way too many EQs in the shed, and started making Multi-Scope mounts -- modded them to accept dovetails...  (All my old mounts are pre- dovetail.)

 

For its age -- and uncoated optics -- the Mogey delivers good views to about 75x / inch with equally antique & uncoated eyepieces; with 1980s spectros Kellners & Plossls it performs much better...

Edited by Bomber Bob, 24 March 2025 - 05:34 PM.

[Sketcher]

For whatever reasons, some have been making contrasts/comparisons -- achromats with other telescopes (usually apochromats).

 

So, here are some specifics concerning my 130mm apochromat and my 152mm achromat:

 

Prices have all been adjusted from the respective purchase dates to 2025 dollars, with some minor rounding of the values.

 

First my 130mm apochromat:

Adjusted purchase price for OTA -- no tripod, no mount, no star-diagonal, no finder, but the price did include a case -- $6,250.

 

Adjusted Purchase price for my tripod and German Equatorial mount for my apochromat: $2080.

 

Total 5.1 inch apochromat cost (excluding finder and star-diagonal, but including case): $8,330

 

My 152mm f/6.5 achromat:

Purchase price for OTA -- including star-diagonal and finder, but without a case -- $1,000.

 

Adjusted purchase price for my tripod and German Equatorial mount for my achromat: $470.

 

Total 6-inch achromat cost (includes 2-inch dielectric diagonal and 50mm finder, but does not include a case: $1,470.

 

So, I paid 6,860 more for an apochromat that has 0.9 inches less aperture.

 

* * * * * * * * * * * * *

Sure, the apochromat produces higher quality views.  But how do the deep-sky views of the two telescopes compare?  (They're hardly different enough to matter to most observers).  And are the solar, lunar and planetary views $6,860 better with the apochromat? (That's a personal, judgmental question that some would answer with a "Yes", but I have no doubt that there are others who would answer with a "No".

 

And what about resolving double stars?  Believe it or not, the larger achromat is capable of splitting closer doubles.

 

The apochromat has a clear edge on low-contrast planetary detail, while the achromat has the clear edge on high-contrast detail.  In other words, there are areas in which the larger, but far less expensive achromat will excel -- a fact that many have either chosen to ignore or were unaware of.

 

* * * * * * * * * * * * *

These two telescopes were very different in cost, yet the less expensive achromat can still hold its own, and then some, in certain areas.  Both telescopes are "keepers" as far as I'm concerned.  I enjoy using both telescopes for what each is capable of.  And as others have mentioned, I have no problem using the less expensive achromat under conditions in which I would rather not expose my apochromat to.  That's a very real advantage that an achromat can have over an apochromat, and something that many have chosen to ignore.

 

* * * * * * * * * * * * *

Some may consider the above comparisons to be unfair on the grounds that my apochromat is one of the more expensive apochromats (for its aperture) that has hit the market.  But I would reply with the same "logic" that so many have used against achromats:  But look at the superior optical quality of the apochromat.  If, to a certain degree, it's a good thing, then it's an even better thing if one chooses to use an even higher quality apochromat.  Many apparently think nothing of spending double, or even triple the money in order to gain relatively small, but nevertheless real advantages in one's views of certain objects.

 

Well, not everyone is able to fork out that much additional money in order to acquire a more or less "perfect" apochromat -- especially in consideration of how much one is capable of seeing with a somewhat less capable achromat at a significantly lower cost.

 

The comparisons I've made are accurate as well as justifiable.  Justifiable if for no other reason than that these are two actual telescopes that I own and use.

 

P.S.  That part highlighted in red above is very important for some of us.  It's very important to me considering how I use and care for my equipment under my, sometimes harsh, environmental conditions.

[Refractor6]

   Great post Sketcher....  I think with the latest trends towards imaging which seems to be the main focus of the sales market at present is that many have forgot the ability of the performance achromats can deliver for pure visual observing even the larger aperture ones.

 

Performance is pretty strict for folks doing long exposure ca free imaging understood but that doesn't apply the same for visual observers at the eyepiece of a achromat.

 

Since I took my forum break and came back posting about achromats again this has been the point I've been trying to get across...don't confuse to two disciplines under the same conversation since it doesn't really apply to visual use only of a achromatic refractor.  If you know what a achromat can do and chase down targets that are presented well within it limits all is good in my book.

[Phil Cowell]

I take it you also have an AP130GTX as well. Mine is in an imaging configuration. The OP if you look at his previous posts also has high end APO’s as well. Including scopes by Takahashi TV etc which was why I stated he would be disappointed with an Achro. A bit of research helps when replying.to a question to provide a hopefully targeted answer to the OP.

 

For whatever reasons, some have been making contrasts/comparisons -- achromats with other telescopes (usually apochromats).

 

So, here are some specifics concerning my 130mm apochromat and my 152mm achromat:

 

Prices have all been adjusted from the respective purchase dates to 2025 dollars, with some minor rounding of the values.

 

First my 130mm apochromat:

Adjusted purchase price for OTA -- no tripod, no mount, no star-diagonal, no finder, but the price did include a case -- $6,250.

 

Adjusted Purchase price for my tripod and German Equatorial mount for my apochromat: $2080.

 

Total 5.1 inch apochromat cost (excluding finder and star-diagonal, but including case): $8,330

 

My 152mm f/6.5 achromat:

Purchase price for OTA -- including star-diagonal and finder, but without a case -- $1,000.

 

Adjusted purchase price for my tripod and German Equatorial mount for my achromat: $470.

 

Total 6-inch achromat cost (includes 2-inch dielectric diagonal and 50mm finder, but does not include a case: $1,470.

 

So, I paid 6,860 more for an apochromat that has 0.9 inches less aperture.

 

* * * * * * * * * * * * *

Sure, the apochromat produces higher quality views.  But how do the deep-sky views of the two telescopes compare?  (They're hardly different enough to matter to most observers).  And are the solar, lunar and planetary views $6,860 better with the apochromat? (That's a personal, judgmental question that some would answer with a "Yes", but I have no doubt that there are others who would answer with a "No".

 

And what about resolving double stars?  Believe it or not, the larger achromat is capable of splitting closer doubles.

 

The apochromat has a clear edge on low-contrast planetary detail, while the achromat has the clear edge on high-contrast detail.  In other words, there are areas in which the larger, but far less expensive achromat will excel -- a fact that many have either chosen to ignore or were unaware of.

 

* * * * * * * * * * * * *

These two telescopes were very different in cost, yet the less expensive achromat can still hold its own, and then some, in certain areas.  Both telescopes are "keepers" as far as I'm concerned.  I enjoy using both telescopes for what each is capable of.  And as others have mentioned, I have no problem using the less expensive achromat under conditions in which I would rather not expose my apochromat to.  That's a very real advantage that an achromat can have over an apochromat, and something that many have chosen to ignore.

 

* * * * * * * * * * * * *

Some may consider the above comparisons to be unfair on the grounds that my apochromat is one of the more expensive apochromats (for its aperture) that has hit the market.  But I would reply with the same "logic" that so many have used against achromats:  But look at the superior optical quality of the apochromat.  If, to a certain degree, it's a good thing, then it's an even better thing if one chooses to use an even higher quality apochromat.  Many apparently think nothing of spending double, or even triple the money in order to gain relatively small, but nevertheless real advantages in one's views of certain objects.

 

Well, not everyone is able to fork out that much additional money in order to acquire a more or less "perfect" apochromat -- especially in consideration of how much one is capable of seeing with a somewhat less capable achromat at a significantly lower cost.

 

The comparisons I've made are accurate as well as justifiable.  Justifiable if for no other reason than that these are two actual telescopes that I own and use.

 

P.S.  That part highlighted in red above is very important for some of us.  It's very important to me considering how I use and care for my equipment under my, sometimes harsh, environmental conditions.

Edited by Phil Cowell, 24 March 2025 - 09:19 PM.

[Mike W]

I take it you also have an AP130GTX as well. Mine is in an imaging configuration. The OP if you look at his previous posts also has high end APO’s as well. Including scopes by Takahashi TV etc which was why I stated he would be disappointed with an Achro. A bit of research helps when replying.to a question to provide a hopefully targeted answer to the OP.

The OP knows the answer, he's just bored with the weather like the rest of us. (He's been on C/N for years) Has a Televue Genesis that is basically a wide field acromat. Relax and stop being a self promoted moderator.

[maniack]

The OP if you look at his previous posts also has high end APO’s as well. Including scopes by Takahashi TV etc which was why I stated he would be disappointed with an Achro.

Disappointment occurs when expectations don't meet reality. I have a couple of apos but I'm not disappointed in my 90mm SV48p, nor was I disappointed with the ST80s I had. I knew what to expect and the performance met my expectations.

 

I was disappointed in the AT80ED I bought, after being told here that FPL51 is good enough for visual. In the case looking at Jupiter my expectations were not met.

 

 

A bit of research helps when replying.to a question to provide a hopefully targeted answer to the OP.

Looking at older posts is a bit much. I look at the poster's signature and location, and that's about it. In any case it's fair to take the question at face value and provide an answer that will at least be helpful to others who come across the thread.

[Phil Cowell]

No one is self promoting but differing opinions are allowed are they not? The OP has a Tak FC 100DL and has had/has other Taks the comparison to a fast Achro would be underwhelming based on the achro’s poorly controlled performance. 

The comment is based on having 4 of the same scopes the OP has. The TV Genesis is a piece of TV history.
 

The OP knows the answer, he's just bored with the weather like the rest of us. (He's been on C/N for years) Has a Televue Genesis that is basically a wide field acromat. Relax and stop being a self promoted moderator.

Edited by Phil Cowell, 24 March 2025 - 11:54 PM.

[Refractor6]

 Speaking of big visual use achros.... here's a couple up today in CN Classifieds......

 

 Same look from maker Jinghua as my Antares 152 F/8 evaluation sample from 2005

 

https://www.cloudyni...atic-refractor/

 

 and this...back in the day these Antares 152 F/ 6.5 refractors disappeared from the local astro shop soon as the new shipments came in to Sky Instruments {Antares}...amazing price for this early 6" sample:

 

https://www.cloudyni...atic-refractor/

 

 

[Phil Cowell]

Disappointment occurs when expectations don't meet reality. I have a couple of apos but I'm not disappointed in my 90mm SV48p, nor was I disappointed with the ST80s I had. I knew what to expect and the performance met my expectations.

 

I was disappointed in the AT80ED I bought, after being told here that FPL51 is good enough for visual. In the case looking at Jupiter my expectations were not met.

 

 

Looking at older posts is a bit much. I look at the poster's signature and location, and that's about it. In any case it's fair to take the question at face value and provide an answer that will at least be helpful to others who come across the thread.

I did give an answer that might indicate another viewpoint to others. Have a C6R sitting in a closet because of its CA and other aberrations it’s a valid answer Have have an ST80 which was also not worth using with just general poor quality and again too much CA to my eye. The OP has a Tak 100DL as do I so expectation based on comparison with the 100DL the Achro is going to be unimpressive. Unless the OP is looking for the telescopic equivalent of a burner phone for a leave behind on vacations or high risk observing areas.

Edited by Phil Cowell, 24 March 2025 - 11:36 PM.

[Sketcher]

I take it you also have an AP130GTX as well. Mine is in an imaging configuration. The OP if you look at his previous posts also has high end APO’s as well. Including scopes by Takahashi TV etc which was why I stated he would be disappointed with an Achro. A bit of research helps when replying.to a question to provide a hopefully targeted answer to the OP.

Mine's an older version of the AP130.

[Sketcher]

   Great post Sketcher....  I think with the latest trends towards imaging which seems to be the main focus of the sales market at present is that many have forgot the ability of the performance achromats can deliver for pure visual observing even the larger aperture ones.

 

Performance is pretty strict for folks doing long exposure ca free imaging understood but that doesn't apply the same for visual observers at the eyepiece of a achromat.

 

Since I took my forum break and came back posting about achromats again this has been the point I've been trying to get across...don't confuse to two disciplines under the same conversation since it doesn't really apply to visual use only of a achromatic refractor.  If you know what a achromat can do and chase down targets that are presented well within it limits all is good in my book.

Of course, I've been posting from a strictly visual point of view.  One conclusion that one might be able to draw from that price vs. performance comparison is that for visual observers who are willing to tolerate an achromat refractor's CA, achromats can be real bargains in the refractor world.  I don't foresee them becoming obsolete any time soon.

[Jon Isaacs]

No one is self promoting but differing opinions are allowed are they not? The OP has a Tak FC 100DL and has had/has other Taks the comparison to a fast Achro would be underwhelming based on the achro’s poorly controlled performance. 

The comment is based on having 4 of the same scopes the OP has. The TV Genesis is a piece of TV history.
 

 

Share our own experiences, our own opinions, that is what the OP asked about.  The OP does not need to be educated.  

 

The question is what should you expect and not expect..  For example, you should expect to see coma in an F/4 Newtonian without a coma corrector but you should not expect to see a purple halo around a bright star.  In an ST-80 with a 2 inch focuser and a 31mm Nagler, you should expect to see significant field curvature but very little chromatic aberration. Add a TSFLAT2 and most of the field curvature will disappear.  You should expect to see a 6.0 degree field that is quite bright.. 6.2 mm exit pupil at 13x...  

 

Pretty awesome for viewing Barnard's loop.  With a 3.5mm Nagler pointed at Jupiter, the chromatic aberration will be quite apparent and the view will be limited.

 

I distinguish between being able to see aberrations and being bothered by those aberrations.  Learning to see means learning to identify aberrations.  But it is my choice whether or not I am bothered by them or merely acknowledge them.  Realistic expectations are the key to satisfaction. 

 

"Blessed are those with low expectations for they are seldom disappointed."   Tony Hillerman

 

Beginners mind... 

 

"Shoshin (Japanese: 初心) is a concept from Zen Buddhism meaning beginner's mind. It refers to having an attitude of openness, eagerness, and lack of preconceptions when studying, even at an advanced level, just as a beginner would."

 

https://en.wikipedia.org/wiki/Shoshin

 

Optical perfection is not necessary to joyfully observe the universe. 

 

Jon

[bobhen]

   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.

Okay, you enjoy using your achromats. So what. People still enjoy driving their Chevy Corvairs. And the Corvair is well known to be one of the worst cars ever made. Heck, there are even Corvair clubs. But the fact that you enjoy using your achromats does not make them better refractors or better tools in which to enjoy the heavens than the more advanced apochromatic refractors. Logic dictates that you would get even more enjoyment by using a better tool.

 

Granted, this is a hobby. And folks can use whatever they want and whatever they like. But enjoyment cannot really be quantified. But performance can be. And if you are talking about pure performance and only performance, then the achromat falls behind. You might not "feel" like you are missing out, but when it becomes to pure performance, of course you are.

 

In the end, enjoyment from a hobby is probably paramount. But let's not confuse "enjoyment" with "performance". One can certainly derive enjoyment from using and inferior instrument. But one cannot deny, that when it comes to "performance", compared to the apochromat the achromat is the inferior instrument and the inferior design.

 

Bob