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Achro to Apo Upgrade Advice

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#1 barsuda

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Posted 21 January 2020 - 11:26 PM

Achro to APO upgrade advice.

 

Life and local sky conditions have resulted in my grab-and-go refractors being what I use 90% of the time. (The C8 hardly makes it out of the door these days). I do visual observing, wide field, almost entirely DSOs. My grab-and-gos are 2 Meade Infinity scopes, 80mm f5 and 102mm f6, both upgraded with 2” dual speed crawfords. I recently acquired a older 90mm f5.5 StarSky (re-branded Long Perng) “semi APO” and noticed the 90mm has somewhat sharper views than either of the Meades. As a result I am looking at upgrading at least one of my grab-and-gos to an APO.

 

My primary question is, in these aperture and focal lengths, what image quality differences have others experienced when moving from an Achro to an APO? 

 


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#2 mikeDnight

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Posted 22 January 2020 - 12:38 AM

The sharper stars you noticed are almost certainly due to better colour control and better glass types. In scopes of equal aperture and focal length, APO's tend to offer fainter stars at the limit of visibility and somewhat brighter DSO's due to greater light through put - superior glasses. Id be looking for a doublet rather than a triplet, and one that preferably uses fluorite in its objective, so FPL53 fluorite glass, or Fluorite crystal.


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#3 clusterbuster

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Posted 22 January 2020 - 01:37 AM

I have an Orio 80mm ED APO that I use basically as a grab n go, I think it gives very nice views, The Lunar views with the Binoviewers are fantastic,

 Mark



#4 SeattleScott

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Posted 22 January 2020 - 02:15 AM

Comparing a 4” ES AR102 with an Orion 100ED:
Under 100x, bright stars and planets suffered a bit in the achro. Pleiades was a little cleaner in the Apo. But on DSO and fainter stars there really wasn’t any clear difference.

Over 100x:
Planetary is clearly superior in the Apo. DSO are pleasing in the achro, but when compared side by side, you can see they are softer in the achro.

Comparing 100ED to Vixen ED103S:
No significant difference in views at low to medium power, other than the Vixen is less prone to glare from bright light sources outside the field of view (presumably due to superior baffling). At high power, the Vixen had a slight advantage in planetary contrast. Definitely noticeable though. Generally I felt I can push the Vixen to 300x but I felt the Orion topped out at 200x (still not shabby). Also the Vixen had negligible lateral color, although the Orion didn’t have much either, so kind of splitting hairs here. Worth twice as much (or more)? YMMV.

There were a few advantages the Vixen had not related to quality of the view. Better focuser, better balanced, which results in improved ergonomics and less issues with scope hitting tripod, two finderscope bases, significantly slower (better for imaging or wide field views), carry handle, etc.

So there you have it, definite improvement in the Apo particularly for medium to high viewing and lunar/planetary. The difference between a mass produced Apo and a Japanese Apo were more subtle, but basically the Chinese Apo was good, and worked well up to its rated maximum useful magnification. The Vixen was clearly a step above in optics and build quality, but the Orion is good enough that even a perfect Apo won’t be a substantial improvement.

Scott
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#5 junomike

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Posted 22 January 2020 - 04:01 AM

IME an apo of equal size offers cleaner views and usually can obtain a higher magnification as well.

Worth it IMO.


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#6 erin

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Posted 22 January 2020 - 07:52 AM

Just to add to what everyone else has said, my favorite thing about the ED glass is that you can take the scope out, point it at high and low magnification objects and everything will look great. I thought I could get by with one scope for wide views and another for planets and doubles. Nope. One scope that does it all is awesome.


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#7 Jon Isaacs

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Posted 22 January 2020 - 08:26 AM

I recently acquired a older 90mm f5.5 StarSky (re-branded Long Perng) “semi APO” and noticed the 90mm has somewhat sharper views than either of the Meades.

 

 

Realistically, the 90mm F/5.5 Starsky is almost certainly an achromat and the difference you are seeing is due to the fact that it is just a better quality achromat than your Meades. Experience has taught me that "semi-apo" generally means it's really an achromat. 

 

 http://www.longperng...?act=view&no=25

 

A good achromat is nothing to shake your head at as you have found out. 

 

Others have described what they see, stars are sharper, the planets are crisper.  At high powers, there will be a noticeable difference in the star quality.  

 

Since your emphasis is on deep sky, faster is better than slower, you get a wider field of view.  I think the Astro-Tech AT-102ED sounds like a good fit.  It's F/7 so it's not super fast but it does offer quite wide fields and very good if not perfect color correction.  

 

At $600, it's quite a deal.  

 

https://www.astronom...ractor-ota.html

 

I had the very first AT-102ED ever.. this is my review.. That was 12 years ago, the new ones are better.

 

https://www.cloudyni...h-at102ed-r1690

 

Astro-Tech is the brand name Astronomics uses for it's scopes and eyepieces.  I do have an association with Astronomics, we all do.. Astronomics sponsors Cloudy Nights, they have done so for 15 years.. without them, you and I wouldn't be talking about telescopes.

 

Jon


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#8 Phillip Creed

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Posted 22 January 2020 - 08:32 AM

+1 on Jon's advice.  The AT102ED is a steal if you're looking for a good visual ED doublet that provides plenty of reach under dark skies and good lunar/planetary/double star performance.

Clear Skies,

Phil



#9 k5apl

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Posted 22 January 2020 - 08:36 AM

Lot of good advice in the previous posts.  I really am partial to refractors and owned many through the years:  Many achro's and many apo's.  When upgrading to an apo, I would consider:

1.  My observing preferences- high power or wide fields or both

2.  Preferred objects- determines the aperture

3.  Sensitivity to chromatic aberrations- color on objects, especially high power

4.  Type of mount-  solid or will you need a new mount?

5.  Cost-  what is your budget?

 

I sure haven't looked through all the wonderful scopes that you can choose from in today's marketplace, so my experience is limited in that regard.  For an economy scope, I have viewed through the 'Skywatcher type' 100ED

refractor and was very impressed.  For portability, I liked the Astro-Tech 80mm triplet.  If I was going to buy a

scope that I haven't used, but has received very good reviews, I would buy the Astro-Tech 90mm triplet.

 

My recommendations are for what I think are low cost, good telescopes.  If you want to move up to a larger refractor in the future, you can sell these with a minimum loss.  And, if you are like most of us, you will want to move up to a larger scope. But, if you want to go 'bigger' and have the budget, then I highly recommend the

TEC 140.  I owned one for years and it hit the sweet spot for my observing of deep sky and planets.

 

You are going to get many opinions, and many of those are valid.  Its hard to go wrong in today's marketplace.

BTW really good scopes are available on the 'used' market too.  I wish you success.

 

Wes


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#10 clearwaterdave

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Posted 22 January 2020 - 08:37 AM

For me I see the difference.,and I like the ED views.,but.,I just picked up an Orion 120/f8.3 achro.,the views are very nice.,I paid $150+25 for driving to meet me closer to my home.,I put a gso2spd focuser on it so add another $100.,Also it came with a mount and tripod.,Now I just looked at the ever popular SW120ED.,Here at Astronomic's it sells for $1900+.,I'm not sure of what it will sell for used.,.but at the new price it's over 10x the price I payed for the Orion.,For me.,I'm not sure it would be worth it.,I bought the AT102ED on sale for $500.,I bought a Celestron Omni102AZ for $170 w/ tripod and mount.,Yes the AT is better in most ways.,and I like it more.,In this case the price difference was exceptable to me.,but I already had a mount for the AT so no extra cost to get started using it.,

  What I'm saying is for each of us there is a point where the price versus performance will become a deciding factor as for how much to up grade.,The jump in price between a 102ed and a 120ed is a lot.,for me anyway.,good luck with your choices.,


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#11 kmparsons

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Posted 23 January 2020 - 12:43 PM

I don't know what your budget is, but for wide-field views of DSOs, I would strongly recommend the AT 92 f/5.5. I have had one for about six months, and have been deeply satisfied. I live in the badly light-polluted suburbs of Houston, but my views of the brighter DSOs have been great. In the summer, I got very good views of M7, M6, M8, M20, and M22. In winter, the Orion nebula is beautiful as well as the Hyades, Pleiades, and the Perseus Double Cluster. If you could get it to a dark sky site, I think you would get glorious views. It is optically and mechanically excellent, and its compact size makes it highly portable. If the $1800 price tag is a bit steep for you, I would endorse the advice of others and consider the AT 102, at about a third of the cost. I do not own one, but my experience of other AT products gives me confidence to make the recommendation. 


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#12 MalVeauX

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Posted 23 January 2020 - 01:52 PM



Achro to APO upgrade advice.

 

Life and local sky conditions have resulted in my grab-and-go refractors being what I use 90% of the time. (The C8 hardly makes it out of the door these days). I do visual observing, wide field, almost entirely DSOs. My grab-and-gos are 2 Meade Infinity scopes, 80mm f5 and 102mm f6, both upgraded with 2” dual speed crawfords. I recently acquired a older 90mm f5.5 StarSky (re-branded Long Perng) “semi APO” and noticed the 90mm has somewhat sharper views than either of the Meades. As a result I am looking at upgrading at least one of my grab-and-gos to an APO.

 

My primary question is, in these aperture and focal lengths, what image quality differences have others experienced when moving from an Achro to an APO? 

Your 102mm F6 achromat will have very similar, if not nearly equal performance on deep space objects (referring to nebula, galaxies, etc, things that are not bright point light sources or solar system objects). The aperture gives you the light collection. Getting a same aperture ED/APO scope will not really change how nebula and galaxies look in that sense. What will change however, in an ED/APO is the CA on bright subject matter such as stars, clusters, solar system objects, where the CA masks detail and reduces contrast. It's not a magic bullet. A same size aperture ED/APO will not make DSO brighter. And if you're into DSO, aperture is what matters for light collection (a smaller aperture with best glass ever will not show a nebula better, it will lose light). So while I would normally say a 102mm F7 Astrotech (or equivalent) would be an excellent 4" ED frac grab & go, it will really not do much for DSO viewing compared to your current 106mm. If you are interested in seeing brighter nebula and stuff like that, not bright objects, more aperture would be more beneficial. Also, most globs/clusters are better in larger aperture, not just having better glass, and these fast achromats don't show severe CA at low power on these objects. So really, I would likely look at something like a 120mm F5 or even 150mm F5 achromat (or just get a 6 inch reflector really.... F5~F6) if DSO is your thing. ED/APO correction is a lot more important on brighter things.

 

Unfortunately the moment you get into 120mm+ aperture ranges on ED/APO's, they require significant mounts to handle them, they're big heavy scopes, even the fast ones. So grab & go sort of goes away there.

 

Biggest grab & go ED frac is likely going to be the 102mm F7 flavors. But again, aperture for aperture, you're not gaining anything there. You would have better views of bright things though. But nebula aren't going to be better. Also the 102ED F7 will have a little CA still unfortunately, it's not an APO.

 

For cost, the alternative really is a 150mm F5~F6 reflector. No CA. More aperture over a 4" scope so everything will be brighter (and will be equivalent in many ways to a 5" frac).

 

If you still want a ED/APO, a doublet with FPL53 glass will be virtually CA-free for visual use and ideal there.

 

Here's my 120mm F5 achromat and 80mm F7.5 ED (FPL53) side by side. The ED80 is better on planets, solar, lunar, some brighter stars, etc, no visible CA. But the 120/5 achromat eats the ED80's lunch on DSO like M42, M13, galaxies, etc. Aperture just brings in more light to see things that are faint and fuzzy. ED glass is great on already really bright things where the CA from the achromat masks detail and/or robs contrast. I like both. But for DSO I choose the 120mm aperture each time. Similar sized scopes.

 

48625898061_5e8d92b648_c.jpg

 

Very best,


Edited by MalVeauX, 23 January 2020 - 02:10 PM.

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#13 Scott Beith

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Posted 23 January 2020 - 05:52 PM

I wrote this review quite a few years ago.  In it I discuss the optical performance difference between two of my personally owned scopes.  One was an 80mm f/6 achromat and the other was an 80mm f/7 ED doublet.

 

It might answer some of your questions on expectations of performance.

 

https://www.cloudyni...on-deluxe-r1741


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#14 barsuda

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Posted 24 January 2020 - 12:54 PM

Your 102mm F6 achromat will have very similar, if not nearly equal performance on deep space objects (referring to nebula, galaxies, etc, things that are not bright point light sources or solar system objects). The aperture gives you the light collection. Getting a same aperture ED/APO scope will not really change how nebula and galaxies look in that sense. What will change however, in an ED/APO is the CA on bright subject matter such as stars, clusters, solar system objects, where the CA masks detail and reduces contrast. It's not a magic bullet. A same size aperture ED/APO will not make DSO brighter. And if you're into DSO, aperture is what matters for light collection (a smaller aperture with best glass ever will not show a nebula better, it will lose light). So while I would normally say a 102mm F7 Astrotech (or equivalent) would be an excellent 4" ED frac grab & go, it will really not do much for DSO viewing compared to your current 106mm. If you are interested in seeing brighter nebula and stuff like that, not bright objects, more aperture would be more beneficial. Also, most globs/clusters are better in larger aperture, not just having better glass, and these fast achromats don't show severe CA at low power on these objects. So really, I would likely look at something like a 120mm F5 or even 150mm F5 achromat (or just get a 6 inch reflector really.... F5~F6) if DSO is your thing. ED/APO correction is a lot more important on brighter things.

 

Unfortunately the moment you get into 120mm+ aperture ranges on ED/APO's, they require significant mounts to handle them, they're big heavy scopes, even the fast ones. So grab & go sort of goes away there.

 

Biggest grab & go ED frac is likely going to be the 102mm F7 flavors. But again, aperture for aperture, you're not gaining anything there. You would have better views of bright things though. But nebula aren't going to be better. Also the 102ED F7 will have a little CA still unfortunately, it's not an APO.

 

For cost, the alternative really is a 150mm F5~F6 reflector. No CA. More aperture over a 4" scope so everything will be brighter (and will be equivalent in many ways to a 5" frac).

 

If you still want a ED/APO, a doublet with FPL53 glass will be virtually CA-free for visual use and ideal there.

 

Here's my 120mm F5 achromat and 80mm F7.5 ED (FPL53) side by side. The ED80 is better on planets, solar, lunar, some brighter stars, etc, no visible CA. But the 120/5 achromat eats the ED80's lunch on DSO like M42, M13, galaxies, etc. Aperture just brings in more light to see things that are faint and fuzzy. ED glass is great on already really bright things where the CA from the achromat masks detail and/or robs contrast. I like both. But for DSO I choose the 120mm aperture each time. Similar sized scopes.

 

Very best,

Thanks for your post.

 

I would certainly agree with you that for DSO work aperture is king. I particularly like your comparison of your ED80 and 120mm f5 and how the120/5 “eats the ED80’s lunch on DSOs” :) I suspect that the efficiency of EDs glass makes better use of the available photons, but will not compare with the more than doubling of photons of the 120mm.

 

My current 102mm achro, with an OTA dressed weight of about 10 lbs, has been about at the practical limits of my heavier grab-and-go mount. Tube leverage on that mount has limited maximum controllable focal length to about 600mm. I recently acquired a better fluid head for the mount that will up the maximum OTA dressed weight a few pounds. This should  make a 120mm f5 achro doable for grab-and-go, but as you said, not enough to handle the extra weight of a 120mm ED/APO.

 

I will certainly be watching for a light, good quality 120mm f5 achro to fill the maximum aperture/grab-and-go OTA spot.

 

R



#15 barsuda

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Posted 24 January 2020 - 07:06 PM

There have been many good replies in this thread that have given me lots to think about. I realized after reading various perspectives that my question was not so much about achro to ED/APO, but rather what in general does better primary glass buy experiencially. Over the last year I went through the process of upgrading to premium eyepieces and my conclusion after that was, I wish I had done so much sooner! “Better glass” in the eyepieces made for a much better observational experience and I suspect that better primary glass will prove likewise.

 

It is unfortunate that OTAs are not as convenient to buy used and try them out, the way you easily can with eyepieces. However I have had a lot of good suggestions here on what to look for in a used ED/APO OTA,  80 to 90mm, f5 to f7. I will get some experience with better primary glass  in my smaller grab-and-go and see what works.

 

Thanks everyone for the suggestions thus far :)
 
R


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#16 Jeff B

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Posted 24 January 2020 - 11:15 PM

"Realistically, the 90mm F/5.5 Starsky is almost certainly an achromat and the difference you are seeing is due to the fact that it is just a better quality achromat than your Meades. Experience has taught me that "semi-apo" generally means it's really an achromat.

http://www.longperng...?act=view&no=25

 

A good achromat is nothing to shake your head at as you have found out."

 

Boom, what Jon said.  I'll take, and have taken actually, a good quality achromat over a poor quality "APO" any day. 

 

But there are also some very good quality 4" ED doublets out there as well and that would be my recommendation too if you can afford them and find a good one.  Otherwise, it sounds like you have an excellent 90mm RFT.

 

Jeff

 

Edit:  BTW, getting good quality eyepieces was a very smart move IMO.  Your 90mm F5.5 is what is called an aplanat design, meaning it is corrected for spherical aberration in green but, importantly,  it is coma free as well.  This means eyepieces like the Televue Panoptics, and the APM Ultra Flats will give you just beautiful, low power views with star images that are sharp, even out close to the eyepiece field stops.  

 

Jeff


Edited by Jeff B, 24 January 2020 - 11:25 PM.

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#17 barsuda

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Posted 25 January 2020 - 04:33 PM

"Realistically, the 90mm F/5.5 Starsky is almost certainly an achromat and the difference you are seeing is due to the fact that it is just a better quality achromat than your Meades. Experience has taught me that "semi-apo" generally means it's really an achromat.

http://www.longperng...?act=view&no=25

 

A good achromat is nothing to shake your head at as you have found out."

 

Boom, what Jon said.  I'll take, and have taken actually, a good quality achromat over a poor quality "APO" any day. 

 

But there are also some very good quality 4" ED doublets out there as well and that would be my recommendation too if you can afford them and find a good one.  Otherwise, it sounds like you have an excellent 90mm RFT.

 

Jeff

 

Edit:  BTW, getting good quality eyepieces was a very smart move IMO.  Your 90mm F5.5 is what is called an aplanat design, meaning it is corrected for spherical aberration in green but, importantly,  it is coma free as well.  This means eyepieces like the Televue Panoptics, and the APM Ultra Flats will give you just beautiful, low power views with star images that are sharp, even out close to the eyepiece field stops.  

 

Jeff

Interesting point about the 90mm Starsky (Long Perng) being a "aplanat" design. I had never heard of this term before and had to read up on it. It was also amusing in that I had the 90mm out last night, before I read your post, and the 24mm Pan got almost all of the focuser time. Very pleasing views indeed. Can't say I have ever used a APM Ultra Flat but I do have the 18mm on my wish list.

 

Down the road I can't say with any certainty what scopes will occupy my observing time. However I suspect, barring a full fledged observatory appearing in my yard, that a couple of good quality achros will be high on the list of what I most use.

 

R



#18 John Huntley

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Posted 25 January 2020 - 04:44 PM

The ED doublets that I've owned have tended to have a better figured objective than the achromats and through this seem to deliver better views at high magnifications than achromats of a similar specification.

 

This applies to chinese refractors mostly but I have also owned Japanese made refractors and found a similar, albeit more subtle, difference.


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