Do I need a 5” ED doublet?

[IB20]

Having 76mm and 102mm “APOs”, how much benefit will I see if I acquire a 5” ED doublet?

How often do users take their 5” scopes out? How long do they take to acclimate and how affected are they by local or atmospheric seeing?

The scope in question is the Stellamira 125mm and so far the reports seem really good. It’s quite long at 1m extended but it seems extremely light compared to most other 5” OTAs. My longest scope is 820mm so I don’t think the length would surprise me. 

The thought of sitting in my garden looking at summer doubles with this scope is an incredibly enticing one!

 

 

 

[Mr Spock]

I use my 120 for solar only, the 4" being my main scope. Reports on the SL sound good though.
Here's my two so you can see a 100 v 120 size difference.

[IB20]

That looks huge! Is that 1200mm?

[Franklin]

My ED refractors are 70mm, 81mm, 102mm and 115mm, so the largest is only 4.5" not the 5" you're after. However, even just having 1/2" of more aperture than the 4" does make a noticeable difference, not just in the extra light grasp when observing faint fuzzies but extra resolution for planetary. The tube is a bit bigger and a touch heavier which does mean I use the 115 on the larger mount only, whereas the 4" and smaller scopes can do double duty on either the larger mount or the smaller ones for G&G sessions.

[IB20]

I don’t have a gng set up for the 4”, it currently sits on an AZ75 and 1.75” steel SW tripod which I’ll be upgrading to the Uni28. This will happen sooner if I decide not to get the 5”.  
It’s a two part carry as is, so having a 5” would make no difference in terms of set-up/tear down time…

[doublevodka]

Maybe this recent video will help? To my eye the smaller scope has the advantage, but then it is a Tak...

 

[dweller25]

The video does suggest the Tak is better but it was used an hour after the 125ED so Jupiter would have been higher and possibly the seeing was better.

[johnturley]

16 minutes ago, doublevodka said:

Maybe this recent video will help? To my eye the smaller scope has the advantage, but then it is a Tak...

 

I agree, based on the video files the advantage does seem to be with the Tak, would be interested to know how they compared visually.

Over the next few weeks (weather permitting), I hope to be able to do a few visual comparisons, on the Moon and Jupiter in particular, between my recently acquired Tak 100 DZ, and my ES 127 Refractor. I have rigged up my AZ-EQ5 mount in AZ mode so that both scopes can be mounted at the same time, making it easier to do the comparisons.

John 

[Mr Spock]

1 hour ago, IB20 said:

That looks huge! Is that 1200mm?

1000mm 

[The60mmKid]

I find the jump from 4" to 5" unquestionably meaningful. I find the planetary views, especially, far more engaging in 5" and larger scopes than in smaller ones. Of course, the performance improves on all objects, as one would expect. The "Everyone needs a 4" refractor" camp has many partisans, but I belong to the "Give me a lightweight 5" refractor or good 6" newtonian any day" camp.

Edited December 5, 2023 by The60mmKid

[IB20]

47 minutes ago, doublevodka said:

Maybe this recent video will help? To my eye the smaller scope has the advantage, but then it is a Tak...

 

Hmmm very interesting, the 125mm is certainly brighter. The Tak was also blessed with more interesting features at the time it was used and as @dweller25 suggests, altitude and or seeing may not have been comparable 60 mins apart but the Tak sure puts on a great show. 

Personally I wouldn’t view at magnifications the imagers use for planetary so I’d be keen to see comparisons at more usual magnifications too. 

[JeremyS]

The TSA 120 is a step up from the FC 100 and not that much bulkier.

A lot depends on your mount. The FC 100 just about works on a ScopeTech Zero.

[mikeDnight]

Cool down time seems to be around the same for my FC100DZ and my FS128 - around 15 minutes from a warm house into a cold winter night. I'm not sure how carbon fibre will affect that, but the FS128 is a tank by comparison and it doesn't have a problem. Perhaps being a doublet is more important than tube material.

 There's definitely a jump in performance visually between 4" and 5" as regards brightness and planetary detail, far more in fact than the difference between a 5" and a 6". Having said that, it should be remembered that there will almost certainly be a noticable difference between a FS128 and a StellaMira 125, just how noticeable I've no idea. Stick a binoviewer in that 125 and I bet you'll soon forget about any comparisons.☺️

Having said the above, the scope that's given me the greatest experience over time has to have been my FC100DC,  and that's because it was so easy to use and always punched above its aperture class, at times leaving me in awe. So ultimately if I were to choose just one great scope, I wouldn't go for a 5" apo, I'd go for a 4". But that's me, based on my experiences. 

Edited December 5, 2023 by mikeDnight

[IB20]

8 minutes ago, mikeDnight said:

Cool down time seems to be around the same for my FC100DZ and my FS128 - around 15 minutes from a warm house into a cold winter night. I'm not sure how carbon fibre will affect that, but the FS128 is a tank by comparison and it doesn't have a problem. Perhaps being a doublet is more important than tube material.

 There's definitely a jump in performance visually between 4" and 5" as regards brightness and planetary detail, far more in fact than the difference between a 5" and a 6". Having said that, it should be remembered that there will almost certainly be a noticable difference between a FS128 and a StellaMira 125, just how noticeable I've no idea. Stick a binoviewer in that 125 and I bet you'll soon forget about any comparisons.☺️

I’ve read a comparison between the FS128 and AT125EDL on CN. As ever with Tak scopes it’s eking out perfection against excellent in the FPL53/equivalent but by no means does the 125 leave the observer wanting!

[SCANS]

It isn't a question of need for me, but after seeing AstroLaVista's videos, I most definitely want one 🤤

What stuck me the most wasn't the sharpness of the Tak, it was how much brighter 125mm is vs 100mm. And since I'm not willing to pay for a Tak, the Stellamira is a very suitable alternative. In fact, considering how much I'm saving by not buying a Tak, one might say that I really should buy one regardless of want, or need 😁 

[dweller25]

10 minutes ago, SCANS said:

It isn't a question of need for me, but after seeing AstroLaVista's videos, I most definitely want one 🤤

What stuck me the most wasn't the sharpness of the Tak, it was how much brighter 125mm is vs 100mm. And since I'm not willing to pay for a Tak, the Stellamira is a very suitable alternative. In fact, considering how much I'm saving by not buying a Tak, one might say that I really should buy one regardless of want, or need 😁 

As a visual observer a bright but not sharp image would not work for me.

Best solution is a bright and sharp image 👍

Edited December 5, 2023 by dweller25

[Merak]

You can never have too many refractors......

[F15Rules]

I have the 5" Tak and have owned 2 superb Vixen 4" ED103s's.

I think the bottom line for me is this: if you can use the bigger scope for longer sessions, you will see very significantly more at 5" than 4". For example, the great Globular cluster M13 is very nice in the 4" during a quick 5 minutes look through the 4 incher. Individual stars can be picked out with mainly averted vision.

Observe the same object through 5" for 10-15 minutes and you see tthose stars with direct vision, and the longer you look, the more stars "pop out", greatly adding to the experience.

Ideally, I'd own one of each, but as I cant, I will keep the 5" for as long as my physical state allows it!

Dave

Edited December 5, 2023 by F15Rules

[Stu]

4 hours ago, JeremyS said:

The TSA 120 is a step up from the FC 100 and not that much bulkier.

A lot depends on your mount. The FC 100 just about works on a ScopeTech Zero.

That 120 is nice and compact isn’t it?

Amazing how big the FS-128 is compared with the FC-100 but it’s quite light so I find it manageable.

Dave is right about longer sessions. Most of mine are short, so the four inch suits these well. If I ever get more time, the 5” will get more use. Strangely the 8” f8 is quicker to get out if I don’t have time for the big Tak.

These pics show the impact of focal ratio on size. f6 for the LZOS and f8.1 for the Tak. I find the Tak much better balanced though as the lens is much lighter than the LZOS faster triplet.

[John]

I have a couple of 4 inch, a 4.7 inch and a 5.1 inch refractors. All pretty good performers. The 4's and the 4.7 get used a lot and ride on the same class mount. The 5.1 inch needs a stronger mount and does not get as much use. There are noticeable differences in the performance levels of each aperture although they are not striking I would say.

I probably only "need" one of the above but, hey, it's fun to own telescopes - I'm an amateur astronomer 😁 

The 125mm ED doublets do seem to offer a lot of refractor aperture for their weight and cost 👍 

[Peter Drew]

After all my years in astronomy I'm still puzzled by the hype surrounding Takahashi telescopes as an OTA.  Granted the performance is legendary but this is due to the excellence of the Canon made objective, so shouldn't Canon deserve the accolades?.  In reality, what is Takahashi's contribution to the hype? a fairly ordinary looking tube assembly, yukky colour (ymmv) and a so-so  focuser which those who can still afford it replace with something better.  Wouldn't another telescope, say an Askar, with the same Canon objective, be a better telescope overall? or are Canon objectives available only to Takahashi ? I'm not knocking refractors, I have at least 20 including 7 150's and a 220.   🙂   

[Cjg]

9 hours ago, IB20 said:

Having 76mm and 102mm “APOs”, how much benefit will I see if I acquire a 5” ED doublet?

How often do users take their 5” scopes out? How long do they take to acclimate and how affected are they by local or atmospheric seeing?

The scope in question is the Stellamira 125mm and so far the reports seem really good. It’s quite long at 1m extended but it seems extremely light compared to most other 5” OTAs. My longest scope is 820mm so I don’t think the length would surprise me. 

The thought of sitting in my garden looking at summer doubles with this scope is an incredibly enticing one!

 

 

 

An Altair 125 EDF owner here. 

Yes, an appreciable advantage over my 92mm Stowaway, but ....the extra length, weight etc means that I have to use a much bigger / heavier mount, so if you already have a mount capable, then the only thing stopping you, really, is the weather and how many clear nights you have in your part of the world to use it. 

I've put off investing in a harmonic drive mount for my 125 as the weather has gotten worse each year, with fewer opportunities to get out for a few hrs. The recent @FLO pricing of their 125 in Carbon Fibre is a bargain.

Good luck,

Chris

[IB20]

The AZ75 holds 15kg on each saddle depending on length of OTA. It should handle it relatively comfortably, I’d imagine? 🤷🏼

What do other members mount their 5” scopes on?

[Paz]

My main refractors are a TS Photoline 72mm f6, Altair Starwave 102mm f7, and Strlla Mira 125mm f7.8 doublet apos.

The 72mm is used for travel and Ha solar. It doesn't get used much at home as it is just as fast to set up the 102mm or 125mm.

I got the 125mm this summer and since then my 102mm has not been used other than to do a comparison.

I was in the market for a 5" for a few years and always held back due to weight of them meaning too much vibes on a Skytee 2 or EQ5. I am not going to go for anything that needs a bigger heavier mount. Then the SM125 appeared at a weight that meant it was a goer for me.

The SM125 is fine for me on those mounts. It makes no difference time wise if I am carrying out any of those 3 scopes, so the big one gets picked.

I have intended to do comparisons with a C8 but have not felt like taking the C8 out yet since the SM125 arrived, as the C8 is more of an undertaking to set up and more specialist and complicated to use.

I see a noticeable benefit going to 5" from 4" but whether that is worth the cost and slightly extra strength needed to set it up is a personal thing. The 5" is longer and heavier and a bit more to handle but it's within my current abilities.

[John]

2 hours ago, Peter Drew said:

..... are Canon objectives available only to Takahashi ? I'm not knocking refractors, I have at least 20 including 7 150's and a 220.   🙂   

Canon (Optron) also made objectives for the Vixen fluorites when they were being produced.

I'm not sure that they make the non-fluorite Takahashi objectives 🤔

Edited December 5, 2023 by John