Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_christmas_presents.thumb.jpg.587637e0d01baf4b6d21b73610610bbb.jpg

Size9Hex

ED frac... what size to go for?

Recommended Posts

Wanted to ask for some advice on a possible purchase please, assuming I get permission from the boss...

My main scope is a basic 10" dob, supported by a 72mm ED frac. Since getting the frac, the dob hasn’t appealed as much for doubles, lunar and planetary despite usually (but not always) showing more detail. So I’m looking for a bigger ED frac with more horsepower.

Current thinking is that a 120mm (ish) would be manageable and a worthwhile step up  from the 72mm. But for planetary in particular, would it be worth going bigger, with 150mm being probably the upper limit?

I guess I’m trying to balance performance (especially planetary) vs. hassle. A smaller scope might mean a bit more budget for something other than a basic model. But if a 150mm is capable enough to become the planetary scope of choice (rather than the 10" dob) then it’s tempting. Or is this just aperture fever? Either way, a new mount would be needed, with intention to dual mount with the 72mm.

All comments, advice and opinion really appreciated. Thanks!

Edited by Size9Hex

Share this post


Link to post
Share on other sites

I think to some extent a 120mm Ed is a great Goldilocks scope. It's not huge and has good aperture without being in any way cumbersome. I'd think a 150mm would be a lot more of a challenge.

  • Like 3
  • Thanks 1

Share this post


Link to post
Share on other sites

For double stars, lunar and planetary viewing as a main requirement, a 150mm Maksutov would be worth considering. Easier to handle, cheaper by far and nearer to being an APO than any ED refractor. It would fit nicely between your 72ED and the 10" Dob.    😀

Edited by Peter Drew
  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites
4 minutes ago, Peter Drew said:

For double stars, lunar and planetary viewing as a main requirement, a 150mm Maksutov would be worth considering. Easier to handle, cheaper by far and nearer to being an APO than any ED refractor. It would fit nicely between your 72ED and the 10" Dob.    😀

Thanks Peter, that’s a really useful suggestion. I didn’t say above, but one use would be solar white light, but I did wonder if a smaller frac with a larger mak would be a good combo, and then I realised I was getting ahead of myself already planning scope n+2 😆. Food for thought though.

Share this post


Link to post
Share on other sites

yes agreed the ed120 would hit the spot, there a fine scope which wont break the bank, ive had a few 150s over the years but there monsters which after a while ive pass on which is hard with me being hoarder. for me 120mm is the sweet spot. goodluck ,  charl.

  • Thanks 1

Share this post


Link to post
Share on other sites

Hi Paul,

I asked a similar question a few weeks ago in the beginners section although mine was a more generic and got some great answers from the guys on here.

For myself and answering maybe the portability question as well, I feel something in the 4 to 5 inch zone is the Goldilocks scope I would use the most for visual. Easy to set up and use with an alt/az mount.

TS Telescope do some great scopes as do Altair Astro around the F6 to F7 range. I always find the Sky watcher scopes a bit to long in focal length for me at F9 as I’m more of an all round guy, but if planets and the moon are what you like they will be right up your street.

Also factor in a decent mount for visual something like a sky watcher 2 or similar which would allow dual mounting 2 scopes at the same time.

  • Thanks 1

Share this post


Link to post
Share on other sites

 

Hello

I would go with a 120ed.  A good 120 ed is difficult to beat IMO. You still have great portability for the average Joe ,fine to handle in regards set up time and effort, and cool down time not excessive ( and you don't have to splash out on a heavy duty mount). But a 120ed is a great aperture to deliver some great views. Also a big plus there are some top quality 120ed on the market for sensible money. And I have added binoviewers on my 120ed , and a real worthwhile investment. Great for Luna IMO.

 

Hope this helps ☺🔭

 

  • Thanks 1

Share this post


Link to post
Share on other sites
18 minutes ago, xtreemchaos said:

yes agreed the ed120 would hit the spot, there a fine scope which wont break the bank, ive had a few 150s over the years but there monsters which after a while ive pass on which is hard with me being hoarder. for me 120mm is the sweet spot. goodluck ,  charl.

Thanks Charl, that’s really useful feedback that the 150s have come and then gone. I guess not worth it despite the extra horsepower.

  • Like 1

Share this post


Link to post
Share on other sites

This is an excellent thread topic.    Good to hear experienced observers and imagers giving advice.  It's sooooooo easy to succumb to APERTURE FEVER !!

  • Like 1

Share this post


Link to post
Share on other sites

Another vote for the ED120, can be mounted on an EQ5 or an AZ4 mount to give a borderline grab and go setup.

I was looking at an ED150 a few months ago then saw a photograph of one next to an ED120, those things are huge and a large part of the attraction of a refractor for me is ease of use

  • Thanks 1

Share this post


Link to post
Share on other sites

Paul, the 150mm are worth if you have one in a obsy, but there huge and heavy and catch the wind with having a heavy lens and dew sheild the size of a small dustbin. i find the 120mm much kinder in every way. charl..

Edited by xtreemchaos
  • Thanks 1

Share this post


Link to post
Share on other sites
21 minutes ago, Neil27 said:

I always find the Sky watcher scopes a bit to long in focal length for me at F9

The 120ED is f7.5, so has a very useful 900mm focal length.

I'm with the others, 120ED is a great scope, and one you will use frequently because it is still relatively lightweight and portable. No need for a dramtically bigger mount, but you could put it side by side with the 72ED on something like an Ercole.

Great for doubles, lunar, planetary and brighter DSOs, even faint ones from a dark site. They are quick to cool too.

  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites
15 minutes ago, Timebandit said:

 

Hello

I would go with a 120ed.  A good 120 ed is difficult to beat IMO. You still have great portability for the average Joe ,fine to handle in regards set up time and effort, and cool down time not excessive ( and you don't have to splash out on a heavy duty mount). But a 120ed is a great aperture to deliver some great views. Also a big plus there are some top quality 120ed on the market for sensible money. And I have added binoviewers on my 120ed , and a real worthwhile investment. Great for Luna IMO.

 

Hope this helps ☺🔭

 

Thanks, it definitely does helps (as do all replies so far). That heavy duty mount you mention is something I’ve thought of. Looking at the weight of the 150mm and mount, it’s a case of setting everything up and there it stays, which is maybe ok, but a 120mm could be set up then moved across the garden on the spur of the moment when Jupiter of whatever appears from behind a hedge.

Share this post


Link to post
Share on other sites
6 minutes ago, xtreemchaos said:

...and dew sheild the size of a small dustbin. i find the 120mm much kinder in every way. charl..

That may be well be the quote that decisively steers this one...! 🤣

Edited by Size9Hex
  • Haha 1

Share this post


Link to post
Share on other sites
14 minutes ago, Craney said:

...  Good to hear experienced observers and imagers giving advice.  ...

Agreed. This is a great forum. Huge thanks to everyone who’s replied so far and added their knowledge and experience. Really appreciate it.

Share this post


Link to post
Share on other sites
6 minutes ago, Stu said:

The 120ED is f7.5, so has a very useful 900mm focal length.

I'm with the others, 120ED is a great scope, and one you will use frequently because it is still relatively lightweight and portable. No need for a dramtically bigger mount, but you could put it side by side with the 72ED on something like an Ercole.

Great for doubles, lunar, planetary and brighter DSOs, even faint ones from a dark site. They are quick to cool too.

The 100 ED is F9 though ...... 😉

Yep another vote for the 120 ED it’s on my short list as well, although I just love the portability of the 4 inch as well. Tough choices my friend, tough choices 👍😉

  • Like 1

Share this post


Link to post
Share on other sites
1 minute ago, Neil27 said:

The 100 ED is F9 though ...... 😉

Yep another vote for the 120 ED it’s on my short list as well, although I just love the portability of the 4 inch as well. Tough choices my friend, tough choices 👍😉

Yes, am aware of that. The 120ED which we had been talking about is the odd one out in that sense, I've no idea why but it does make it a very versatile scope.

I love my 4" too, but I think in this instance a larger aperture makes sense.

  • Like 1

Share this post


Link to post
Share on other sites
13 minutes ago, Stu said:

The 120ED is f7.5, so has a very useful 900mm focal length.

I'm with the others, 120ED is a great scope, and one you will use frequently because it is still relatively lightweight and portable. No need for a dramtically bigger mount, but you could put it side by side with the 72ED on something like an Ercole.

Great for doubles, lunar, planetary and brighter DSOs, even faint ones from a dark site. They are quick to cool too.

Thanks Stu, useful comments. You mention dark sites. When I consider the 150mm, it’s hard to picture it ever going to a dark site, whereas the 120mm probably would.

Share this post


Link to post
Share on other sites

I have found around 100mm deliveres the greatest discriminations between star colours 🔭

Edited by Pig
  • Like 2

Share this post


Link to post
Share on other sites

There can be a big jump in performance from 4" to 5", but there isn't the same jump in performance from 5" to 6" as far as planetary is concerned. To get a truly meaningful jump in performance over a 5" refractor you'll likely need to be looking at 7" +.

I made the mistake a few years ago of selling my 5" Tak to buy a 6", but the bigger refractor didn't show me anymore than the smaller 5". What happened in my case was that I had to buy a much heftier mount, ( the eq6 in the attached photo was nowhere near good enough to carry the 6" Tak). My Losmandy GM8 was equally incapable of carrying the 6", so I had to buy a G11. The consequence being that I used the 6" far less as it was more hassle, and I found myself looking for excuses why not to observe.

An ED in the 4" to 5" range can be a wonderful lunar and planetary scope, that will give some incredibly sharp, contrasty views. The relative lack of resolution in these smaller refractors, is in my view, more than compensated for by the high definition they give, often leaving much bigger telescopes standing. Their portability and ease of use is another major benefit. These scopes don't generally need hefty mounts and they cool rapidly (15 mins for a doublet) on most nights, so you may find yourself doing a lot more observing, as short sessions are so rewarding.

Several of my associates who are very keen lunar and planetary observers use 4" ED apo's as their main work horse, as they seem to be relatively unaffected by seeing, and they are easy and comfortable to use.

The SW 120ED, either the DS Pro version or the Eqinox version, is in my view one of the best refractors currently available. There is minimal CA but it is certainly not objectionable, and can only be seen around the brightest objects. There is probably more CA introduced into a system by some wide angle eyepieces than by the excellent objective lens. I've owned three 120ED's and all were consistantly good. (I would certainly not worry about going for Takahashi or any other high end brand if I were on a budget. There's hardly a hairs breadth between the SW ED's and the high end refractors in planetary performance)! 

All the refractors below are superb lunar and planetary scopes. All cool rapidly and deliver breathtakingly razor sharp views, but choosing one that is easily carried out and back in again can greatly enhance your observing enjoyment.

FS152 apo doublet. ( Heavy and very expensive, requiring a heavier mount than the inadequate EQ6 shown)

DSC_0483a.jpg.f2ade1303846ca5f4a6a5851bd462466.thumb.jpg.4b475c131b9d6bdd0c018ddf4138d540.jpg

 

FS128 apo doublet. (Very expensive but just portable, still required a hefty mount to do it justice

247260070_2019-01-1212_39_03.jpg.238d79e4348037985db173e8701dbe2e.jpg

 

Equinox 120ED apo doublet.  (Superb value. Performs way beyond expectations! Can be mounted on a GP, Eq5, AZ4 etc)

294830465_2018-01-0523_31_53.thumb.jpg.377dc55a0168a84f575fa8c04d8b9aa3.jpg

 

FC100DC apo doublet. ( A bit pricey but a stunning performer, punching well above its aperture class! Easy to transport and very light, enabling it to be carried by most mounts)

1700123019_2018-01-1110_42_01.thumb.jpg.32b1c17fa1e23a8581e358c99a443d17.jpgmsg-41880-0-76686800-1428934447.thumb.jpg.98a05437aa2eea0b46bfda4923fdd27b.jpg

 

Edited by mikeDnight
  • Like 4
  • Thanks 1

Share this post


Link to post
Share on other sites

Funny how things develop!  I too was planning on an ED120 to replace the Startravel - but the ST is OK (not the best optics or focuser) and gives nice wide views, so I've decided to hang on to it and go smaller with an ED80 Apo.  I shall use it (amongst other things) as a guide for the wider ap  8" SCT without the GoTo mount.

And when I want even more ap, I can haul the Dob out.

Best of all worlds!

Doug.

  • Like 2

Share this post


Link to post
Share on other sites
1 hour ago, mikeDnight said:

There can be a big jump in performance from 4" to 5", but there isn't the same jump in performance from 5" to 6" as far as planetary is concerned. To get a truly meaningful jump in performance over a 5" refractor you'll likely need to be looking at 7" +.

I made the mistake a few years ago of selling my 5" Tak to buy a 6", but the bigger refractor didn't show me anymore than the smaller 5". What happened in my case was that I had to buy a much heftier mount, ( the eq6 in the attached photo was nowhere near good enough to carry the 6" Tak). My Losmandy GM8 was equally incapable of carrying the 6", so I had to buy a G11. The consequence being that I used the 6" far less as it was more hassle, and I found myself looking for excuses why not to observe.

An ED in the 4" to 5" range can be a wonderful lunar and planetary scope, that will give some incredibly sharp, contrasty views. The relative lack of resolution in these smaller refractors, is in my view, more than compensated for by the high definition they give, often leaving much bigger telescopes standing. Their portability and ease of use is another major benefit. These scopes don't generally need hefty mounts and they cool rapidly (15 mins for a doublet) on most nights, so you may find yourself doing a lot more observing, as short sessions are so rewarding.

Several of my associates who are very keen lunar and planetary observers use 4" ED apo's as their main work horse, as they seem to be relatively unaffected by seeing, and they are easy and comfortable to use.

I have had a different experience to Mike. 

I have 100mm, 130mm and 160mm APO refractors. For me the 160mm is a noticeable jump over the 130mm and very significant jump over the 100mm. Examples objects are plato’s Craterlets and the trapezium (which should really called the hexagon in the 160mm 😀).

In terms of portability and mounting requirements the 100mm is definitely easier and can be mounted on a light mount such as the az gti. I find the 130mm needs a much sturdier mount which also works very well with 160mm. Part of this is due to the relatively fast f7 ratio  that the 160mm has which results in a shortish tube (100mm) and hence short moment arm.

I’m much less experienced than Mike so I think I’m less able to tease out fine detail in smaller scopes. I need all the help I can get!! I’ve generally found the 160mm not to be much affected by seeing either.

 

Edited by GavStar
  • Like 3

Share this post


Link to post
Share on other sites

30mm "jumps" are not effectively linear, the 30mm jump from 100mm to 130mm is less in increased area compared to the jump from 130mm to 160mm.     😀

Share this post


Link to post
Share on other sites

Yes, but proportionally 100 to 130 is a bigger jump than than 130 to 160.

Share this post


Link to post
Share on other sites

I would go with a 5" class refractor

something between 125-150mm

  • Thanks 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×

Important Information

By using this site, you agree to our Terms of Use.