115 replies to this topic

[Jon Isaacs]

A 4" Apo won't go any deeper than a 5" Newt. It might be a touch sharper on planets. It will be lower maintenance. But it won't be much different on DSO. 

 

A much bigger change would be an 8" Dob. That would be more of a dramatic difference. 

 

I have owned a number of 130mm F/5 Newtonians.  

 

That really depends on the particular 130mm F/5 Newtonian.  If the optics are of good quality, if it is properly collimated and has fully cooled, then it might give a 4 inch apo/ED a run for it's money viewing the planets.  At this point, it's not clear what the 130mm F/5 we are dealing with it.  Is it Celestron with a spherical mirror?  Some of them do have spherical mirrors.  Cool down, even in San Diego's mild climate, that takes a hour to be more or less cooled down.  And collimation....

 

A 100 mm apo, it does not have these issues. You take it outside, it will be immediately giving you very good views, nearly it's best and soon enough it will be giving you the best.

 

I own both 80mm and 102mm apo/ed refractors.  For the planets and general all around observing, the 102s are more satisfying.  

 

An 8 inch or 10 inch Dob is more capable but comes with it's own hassles.  I love my Dobs but if I lived in London, I would probably spend most of my time with a 4 inch or 5 inch refractor.

 

Jon

[Sebastian_Sajaroff]

On Solar System and doubles the incremental move from 80 mm apo to 100 mm is quite noticeable

[skysurfer]

Visual only ?

Keep the 80mm and get a Skywatcher Heritage 130mm f/5 tabletop Dobson. With simple DIY you can make a nount adapter to mount the OTA on your mount.

[Arkade]

Visual only ?
Keep the 80mm and get a Skywatcher Heritage 130mm f/5 tabletop Dobson. With simple DIY you can make a nount adapter to mount the OTA on your mount.

I have the skywatcher 130p (its a parabolic 650fl on an az5 mount) i used it last night, had it out for an hour or more and was suprised how good it was as havent done that long before

[Arkade]

I have owned a number of 130mm F/5 Newtonians.

That really depends on the particular 130mm F/5 Newtonian. If the optics are of good quality, if it is properly collimated and has fully cooled, then it might give a 4 inch apo/ED a run for it's money viewing the planets. At this point, it's not clear what the 130mm F/5 we are dealing with it. Is it Celestron with a spherical mirror? Some of them do have spherical mirrors. Cool down, even in San Diego's mild climate, that takes a hour to be more or less cooled down. And collimation....

A 100 mm apo, it does not have these issues. You take it outside, it will be immediately giving you very good views, nearly it's best and soon enough it will be giving you the best.

I own both 80mm and 102mm apo/ed refractors. For the planets and general all around observing, the 102s are more satisfying.

An 8 inch or 10 inch Dob is more capable but comes with it's own hassles. I love my Dobs but if I lived in London, I would probably spend most of my time with a 4 inch or 5 inch refractor.

Jon

It is the skywatcher 130p which is parabolic mirror and 650 fl. It comes collimated from factory, it is weird as skywatcher have made these so it has a fixed plastic seal which cant be opened on the back where collimation screws usually are. The only thing you can access is 2nd mirrior.

I used it last night,left it out for over an hour and was amazed by views

[Jon Isaacs]

It is the skywatcher 130p which is parabolic mirror and 650 fl. It comes collimated from factory, it is weird as skywatcher have made these so it has a fixed plastic seal which cant be opened on the back where collimation screws usually are. The only thing you can access is 2nd mirrior.

I used it last night,left it out for over an hour and was amazed by views

 

I am glad you got some good views.  The collimation thing on those scopes is a compromise but as long as you are not using a coma corrector and things are not too far out, collimating with the secondary is doable though not optimal.

 

Sounds like you are on your way with the "little guy."  I used call mine, a "half pint" 10 inch Dob...  

 

Jon

[mikeDnight]

Hi
I was wondering if anyone has an 80mm apo and also a 100mm and if there is a big, noticable difference.

( I have looked and on numerous stores, they have all dropped the price on this skywatcher. Does this usually happen? Anyone know why? As this happened with starsense a few months ago. It was £200 for a few weeks and now it is back to £280)

I have a 80/560mm apo from starfield and have just seen Skywatcher Evostar 100 ED DS Pro on sale with a focal reducer, 2 inch diagonal, rings and mounting plate, a finderscope, 28mm eyepiece, reduced from £945 ($1179 us dollars) to £729 ($910 usd)

This is a large scope 900mm fl, f9 but has a focal reducer also.

I have been wanting a new scope, was thinking a 150mm achro, but now this has come up at around the same price.

Would you guys get a 100mm if you had an 80mm? Also, side question, is a 100mm apo better than a 150mm achro ( im guessing no as for dso, the achro wins)

Thank you everyone

Unless its purely brighter deep sky youre interested in, a 100mm apo will do better all round as a high quality general observing instrument. My 100mm apo destroyed my 150mm F10 achromat on the moon and planets, and even gave it a run for its money on brighter dso's. I'd take a 100mm Apo any day over most other scopes as it really does punch above its aperture class.

 

Here's my 150mm F10 and it looks impressive, but its images were not nearly as pure, sharp, and contrasty as my 100mm apo.

 

I've been using a 100mm apo for 10 years this coming March and the100mm is my most used scope ever over my 45 years in the hobby.

[Arkade]

Unless its purely brighter deep sky youre interested in, a 100mm apo will do better all round as a high quality general observing instrument. My 100mm apo destroyed my 150mm F10 achromat on the moon and planets, and even gave it a run for its money on brighter dso's. I'd take a 100mm Apo any day over most other scopes as it really does punch above its aperture class.

Here's my 150mm F10 and it looks impressive, but its images were not nearly as pure, sharp, and contrasty as my 100mm apo.
20220408_104954.thumb.jpg.93e8c5ab749830526035013acb0a0942.jpg

I've been using a 100mm apo for 10 years this coming March and the100mm is my most used scope ever over my 45 years in the hobby.
IMG_5971.JPG

Yeah, i find my 80mm apo beats my 130mm newt on everything, as the contrast and crispness of moon and planets is something else.
The newt is very good as i saw last night but doesnt have that wow factor
Beautiful takashai..i think my 80mm apo starfield will be okay for now

[SeattleScott]

The newt will be better on galaxies and globs. The Apo will do well on planets and open clusters.

[areyoukiddingme]

There are a lot of considerations to take into account.

 

Refractors do not scale well when it comes to weight/ergonomics when related to the aperture.

 

My 80mm apo weighs in a hair over 5lb, whereas my Televue 101 weights about 12lb, albeit with a more impressive build.

 

If my goal was to keep a small refractor for grab and go, as well as pairing with a larger SCT or reflector, I might be inclined to go with the 80.

 

If my plan was to have the small refractor as a high use scope, and grab-and-go weight was not a particular concern, then I would go for the 100mm.

[Jon Isaacs]

The newt will be better on galaxies and globs. The Apo will do well on planets and open clusters.

 

Collimated and cooled, a good 130 mm F/5 Newtonian can outperform an 80 mm APO on the planets.. 

 

Jon

[SeattleScott]

Collimated and cooled, a good 130 mm F/5 Newtonian can outperform an 80 mm APO on the planets..

Jon

Agreed

[Russell Swan]

If seriously interested in deep sky, at a minimum 6” of aperature and preferably 8 or 10” is what you need for a satisfying experience, especially so in light polluted skies. Anything less is a compromise for other consideration such as portability and quick setup. Grab and go. However, aperature wins. 
 

No one amateur scope is ideal for everything. Apocromats for optimum contrast and fine detail. Large reflectors or folded optic scopes for deep sky reach. Having both in the arcenal is ideal. Also, goto or push to for deep sky in heavily light polluted areas is nearly essential these days. 

[vtornado]

I think the 100mm frac is a nice step up from the 80.   Also in my budget, the 100ED is the largest affordable ED (120 too much)  So if the goal is to own the biggest ED affordable refractor then the 100 is it.   However ...  I no longer consider a 100 grab and go.  This varies from person to person.   If I had a permanent pier, or a roll out of the garage dolly, didn't have to deal with stairs and snow,  things would be different.

[gnowellsct]

I consider the difference between 81 and 92 mm to be noticeable. And 130 mm is more noticeable still.

Difference between a C8 and a c 9.25 is also noticeable. But if you repeatedly observe next to the c 9.25, as I do, since I have a friend who has one, that doesn't mean you're going to dump the C8. I like my C8.

In the world of refractors, particularly under 4 in ches, jumps of 1/2 in do count for something IME. But it's not quite the same thing as the differences between a C8 and a 9.25 or a 9.25 and a c11. In the latter cases you are doing with different scaled versions of the same scope built with the same materials.

With refractors you can have all kinds of things going on. Achromatic versus apochromatic versus ED, doublets versus triplets, focal ratio which we care about because it impacts color control importability, and so on. I do think there are some refractors slightly smaller than some bigger refractors which outperform the bigger scopes.

Greg N

[gnowellsct]

A few years ago my 130 mm triplet apo was trounced by a 10-in and a 12-in Newtonian from skywatcher.

[Brent Campbell]

Considering you question.  About four years ago I was using an orion express 80 F/6 "Semi APO" (the same as the Antares Sentinal).  Before that I was using a Celestron Firstscope 80mm F11 (miss that one sometimes).  I came across a deal for a Stellavue Access 102mm F/7 which included the case and a field flatner for photography (which I don't use).   The same scope can be purchased now as the Astro Tech 102 EDL.  

 

I am so glad that I did that purchase.  I have a DOB and an SCT for larger things, but the 102 MM APO is just PERFECT.  It is a noticiable step up in light gathering from the 80 mm.  My 80 mm scopes always seemed to run out of light which dimmed their magnification.  The Stellarvue doesn't have that issue.  This weekend I had it up to 285 X and the image was solid the scope could have taken more if I had more barlows.  The F7 focal ratio gives the scope a very wide field.  

 

How many more nice things can I say about my 102 mm?  Once I strated using the 102MM Apo the 80mm never got used again and was sold.   

 

I am going to say one thing.  Team this refractor with a larger SCT or reflector and you have an unbeatable pair.

[gnowellsct]

What exactly is a semi-apo. An achromat by another name? Maybe they stretched the focal length by 25 mm? Or enlarged the internal baffle to reduce the effective aperture?

Greg N

[gnowellsct]

Or does it mean that if you espy a certain aberration, they respond, "Aha!  We told you it was a semi-apo.  Not our fault."

[gnowellsct]

achromatic: = color free

apochromatic: = "this time we mean it"

 

So the semi-apo is kinda sorta color free?  Or perhaps they only "sort of mean it"?

[maniack]

What exactly is a semi-apo. An achromat by another name? Maybe they stretched the focal length by 25 mm? Or enlarged the internal baffle to reduce the effective aperture?

Greg N

Typically a doublet with ED glass in the FK61/FCD1/FPL51 class. Much less false color compared to a standard achromat, but still visible compared to a reflector or a true apo.

[Bearcub]

What is your tripod and mount?

 

What are main things you dislike so far, just be as honest as you can. You might not figure out what you want, but you will figure out main dislikes, and those could allow you to understand what exactly can improve those.

[Jon Isaacs]

What exactly is a semi-apo. An achromat by another name? Maybe they stretched the focal length by 25 mm? Or enlarged the internal baffle to reduce the effective aperture?

Greg N

 

In the case of the Sentinel, the Orion Express as well as the original William Optics Megrez, it was just another name for an achromat but a nice one.

 

Jon

[Jon Isaacs]

Typically a doublet with ED glass in the FK61/FCD1/FPL51 class. Much less false color compared to a standard achromat, but still visible compared to a reflector or a true apo.

 

That was not the case with the Orion Express etc.  They were not FPL-51 class doublets.

 

I defer to Roland Christen as to what is what.  In this Astromart thread, Roland calls a FPL-51 doublet an ED-Doublet APO.  What he calls a Semi-Apo is an combination that provides 1 part in 3400 longitudinal chromatic error, that's twice the error an FPL-51 doublet.

 

https://astromart.co...orite-etc-54455

 

Jon

Edited by Jon Isaacs, 28 January 2025 - 09:56 AM.

[Brent Campbell]

What exactly is a semi-apo. An achromat by another name? Maybe they stretched the focal length by 25 mm? Or enlarged the internal baffle to reduce the effective aperture?

Greg N

Marketing term.  The lens had ED glass but not good enough ED glass or a long enough focal ration to make it a true apo.   I beleive the Celestron ED 80mm APOs came out about the same time and they had a Focal ration near 7.   It was a good scope just not a great one.