80mm ED and 120mm ED or single 100mm APO?

[Moonshane]

I have been discussing this today a little with Stu and we have our own views but thought it would be interesting to gauge the wider view of SGLers.

I am lucky enough to have a Meade 80mm f6 triplet which I use for wide field and camping/caravanning trips as it's a small beast along with a Skywatcher 120mm f7.5 ED which is used mainly for planetary and doubles. Both are used for white light solar with a Lunt wedge. I also have aperture in the form of a 6" f11 dob for solar system / doubles and 12" / 16" f4 dobs for deep sky.

Having read all the recent talk of how good the Takahashi 100mm fracs are I have started to wonder if it's worth 'cashing in my (frac) chips' and buying a premium frac such as a Tak or Vixen 100 (used naturally). Finding one is likely to be an even bigger challenge than the decision but ignoring this, I'd welcome the views of owners of different fracs.

In the interim, Stu has kindly 'offered out' my 120ED with his 100mm Tak at SGLXI so I will hopefully get a chance to see them in combat. 

Any comments?

I suspect it's a difficult one to answer as I lose a bit of aperture and a bit of field at either end but perhaps the increased optical quality compensates for this a little?

[Peter Drew]

I took part in a "shootout" with MikeDnight and Paulastro using a Takahashi Sky90, Mike's Takahashi 100 and my Vixen 102mm Flourite. To my eye the image of the test object, Jupiter, looked excellent in each with very little difference in perceived detail. However, the biggest difference is with the observers, I will never be as good an observer as Mike or Paul and at my age my eyesight is not going to get any better. The overall result is that I need a little more aperture to keep up with them, in the circumstances a 4" refractor would not suit me for planetary observation although double stars would still be fine.

[Stu]

I did try a Sky 90 briefly, hoping that it would combine high power with widefield capability. The answer was it delivered on the high power, but to me the widefield view as not sharp enough over the field to be satisfactory.

I'm fairly sure the 120ED will 'win' in terms of resolution, but as a single scope the Tak is hard to beat. Hopefully we will get to see very soon!

[Moonshane]

Great point about visual acuity Peter.

[Moonshane]

One thing about resolution Stu (and possibly a driver of my thinking) is that I have resolution for those times when the seeing can stand it in the guise of my bigger dobs.

My thinking partly started last night when I noted that the 120ED provided distinctly better views than the 12" dob at lower powers when Jupiter was lower in the sky and in the murk, the classic 'cutting through the atmosphere' yet when the planet rose a little more, the seeing then allow the bigger dob to stretch its legs. As mentioned my wife would appreciate one less box in the office, especially one the size of the 120ED flight case! If I end up with a top class frac out of it then it's all good!

[John]

I have a very nice Vixen ED 102mm but the Skywatcher ED120 beats it, unsuprisingly.

Whether the optical finesse of something like a Takahashi can make up for the 20% aperture difference I don't know

 

 

[Stu]

46 minutes ago, John said:

I have a very nice Vixen ED 102mm but the Skywatcher ED120 beats it, unsuprisingly.

Whether the optical finesse of something like a Takahashi can make up for the 20% aperture difference I don't know

 

 

I doubt there is a huge amount of difference between your Vixen and the Tak John, and wouldn't claim that the FC-100 would beat a 120ED, but for a 4" scope it is pretty lovely.

[John]

I agree Stu - all the reports I've read on the FC-100 have been exceptional.

I'm in the same camp as Peter in that I want a bit more than 100mm of aperture so my 4" scope always seems to be my 3rd scope after my 12" dob and the ED120. The little Vixen can show more sky than either though so there are times when I'm very glad I have it.

 

[nightfisher]

I cant help as i dont (and probably wont ever) own an ED or Apo frac, but i agree with your thought train that you have the aperture for good seeing with the dobs and a Tak FC-100 would be a superb scope to own, but maybe another option would be to keep the 80mm sell the 120 and use the 6" f11 for higher res thus making space and harmony at home

[ollypenrice]

I heard a jeweller being interviewed on French radio a while back. He described his career (a mystery to me!) but when he started working at Cartier the boss looked at what he was doing and said, 'That's not Cartier.' Well, I'm going to say that the Sky 90 'is not Takahashi.' I don't think it was Tak's finest hour and it is well past its sell by date.

With refractors for visual use you are (or more accurately I am) into this strange thing of 'the exquisite view.' It tends to infuriate the Dob Mob and I fear the appearance of Swamp Thing, guns blazing, but I do have this refractors-for-visual passion which puts the 'more' behind the 'exquisite.'

I've said more than enough already to get me ridiculed. Have you considered looking for a Genesis? 4 inch aperture but enough FOV for the biggies like the Veil.  That really is a rich field killer and the older ones, which are not AP corrected well enough to pass CCD muster, are affordable.

Olly

[Stu]

52 minutes ago, John said:

I agree Stu - all the reports I've read on the FC-100 have been exceptional.

I'm in the same camp as Peter in that I want a bit more than 100mm of aperture so my 4" scope always seems to be my 3rd scope after my 12" dob and the ED120. The little Vixen can show more sky than either though so there are times when I'm very glad I have it.

 

That's a very good point John. One scope I really regret selling is my Astrotech 106mm triplet. It had a 690mm focal length, at f6.5, just that little bit faster than the Tak and a proper triplet Apo at that. It also had a nice flat field, so even with a 31mm Nag in it gave lovely views, sharp to the edge. It's only downside was it was heavy, and so would not have been at all happy on the photo tripod and Giro-WR setup I use for the Tak.

I think I've been searching for a replacement ever since, something capable of widefield and high power views. The Tak is pretty close, but actually your Vixen is a little faster so has that advantage. Not having seen them side by side it's hard to know how they really compare though.

[John]

I've never looked through a Tak or any really top brand refractor to be honest with you so I've not had the opportunity to compare the views that my fracs put up with them. I tend to get drawn to aperture at star parties so miss out on the chance to look through smaller but top quality instruments.

I enjoy the views my scopes give and they seem to be reasonably well regarded in reports so I've been happy with them. I could also afford them, which helped a lot with the justification

Having been in the hobby quite a long time now I tend to feel, if I'm going to invest a lot in a scope, that I'd like something that will show me something that I've not yet seen, rather than slightly more polished versions of things that my current scopes can already show me.

But this is Shane's thread not mine and I'm very interested in his thinking, rather than my own

 

[Piero]

7 hours ago, Moonshane said:

I am lucky enough to have a Meade 80mm f6 triplet which I use for wide field and camping/caravanning trips as it's a small beast along with a Skywatcher 120mm f7.5 ED which is used mainly for planetary and doubles. Both are used for white light solar with a Lunt wedge. I also have aperture in the form of a 6" f11 dob for solar system / doubles and 12" / 16" f4 dobs for deep sky.

Hi Moonshane,

I haven't watched through any of your scopes or a tak, so mine are just thoughts. Maybe I am too naive but I wonder how much competitive the SW 120 is against your dob OO 6" f11 on solar system / doubles. As far as I can tell the latter beats the former possibly like a triplet 150 would beat a SW120! If so, the real unique benefit in having the 120mm would be for high mag solar observation.. As you go camping / caravan by car, you can also have a little bit more than an 80mm, and a 100mm f6-ish would still do a wonderful job on wide field. Plus I would expect it to work very well on Solar too. 

In my opinion a 100 F6-ish would get more use that your combined 80-120 as it would become your grab 'n' go telescope for travelling, solar, wide field, and why not planetary too if you don't have much time for cooling down one of your newtons properly. 

Whereas this 100mm should be a Takahashi, a Vixen or a Tele Vue, I cannot attempt to answer. As they are very expensive and difficult to find, possibly looking through one of them would be ideal so you can see whether for you it is worth the price. 

Piero

[Moonshane]

Cheers all. Every viewpoint is valuable to me and I am really warming to a Tak but would be a big decision.

I think the genesis et al have a rear doublet like a petzval?  This would rule out solar with a wedge unfortunately,  one of the main uses.

 

[swamp thing]

4 hours ago, ollypenrice said:

With refractors for visual use you are (or more accurately I am) into this strange thing of 'the exquisite view.' It tends to infuriate the Dob Mob and I fear the appearance of Swamp Thing, guns blazing, 

Nah! I love you really  Olly 

 

[mikeDnight]

4 hours ago, Moonshane said:

Cheers all. Every viewpoint is valuable to me and I am really warming to a Tak but would be a big decision.

I think the genesis et al have a rear doublet like a petzval?  This would rule out solar with a wedge unfortunately,  one of the main uses.

 

I've had three Taks to date, the first a FS128, which was big for a 5" frac and it needed at least a GM8 to mount it well. I then bought a FS152, which was even more massive and required a G11. They were both superb instruments but the bigger they became, the less I used them. Eventually I sold the 152 after my back gave way as I was lifting it onto the G11, which was mounted on a pier in my garden, and stood about 7 feet off the ground. At the time I took planetary observing really seriously and preferred looking directly through the refractor.

I decided I wanted to get a scope that would be more of a pleasure than a chore to use, so foolishly I believed the advert in S&T that stated "It Is What You Want It To Be"! and bought a NP101. It was a beautiful rich field refractor but it wasn't pure like the Tak's, and its planetary performance was not in the same league. I sold it a year later!

Enter the ED120! I bought a 120ED Pro which was an excellent all round performer. I later part exchanged it for an Equinox 120ED, as paulastro assured me that the writing on the lens cell travelled all the way through the tube just like Blackpool Rock. I think he lied! However I used the ED120 for six years or more before Tak reintroduced fluorite into their scopes. Eventually I just had to have one.

On the first night I looked through the FC100D I knew I'd made the right decision. In side by side comparison with the120 ED the Tak was noticeably better at revealing planetary detail on Jupiter, so much so in fact that I actually exclaimed WOW! as I saw the intricacy of the belts in the Tak. Despite the greater theoretical resolution of the 120 ED, it didn't reveal the same level of detail. It wasn't that the 120 was a poor scope, it was superb, and had on many occasions whopped the socks of much larger scopes on the moon and planets; but the little Tak just had defining ability and a vibrance that, although subtle, was not evident in the ED.

Over the last year the FC100 has almost never failed to impress me with its planetary performance. It takes power well, so well in fact that I've been able to use X474 on Venus and the moon, and have razor sharp, colour free views. 

On DSO's, the fluorite lens seems to perform well beyond its aperture class, as I've been able to detect the subtle nebulosity around the Pleiades like I've never seen in any scope irrespective of aperture. The flame nebula and IC434 extending down from Alnitak could be detected without the use of a nebula filter. Binary stars are great to observe in the FC and somewhat difficult targets like the E and F stars in the trapezium become observable with careful study on a steady night.

The FC100D is a great scope that punches well above its weight, but it's not immune to bad seeing, and it is still subject to the laws of physics. With good eyepieces and good diagonal though it will revitalise your observing as it is so lightweight and easy to mount and makes for a great grab and go set up. For many it would be all the telescope they'd ever need.

Mike

[ollypenrice]

12 hours ago, Moonshane said:

Cheers all. Every viewpoint is valuable to me and I am really warming to a Tak but would be a big decision.

I think the genesis et al have a rear doublet like a petzval?  This would rule out solar with a wedge unfortunately,  one of the main uses.

 

Yup, I'd forgotten that. It also rules out oil spacing, I think.

Olly

[MartinB]

There is another factor to consider, one that moves into the realm of emotion over logic (never to be dismissed), pride of ownership connects directly to the visual cortex and significantly improves acuity.  Never to be dismissed!

[Moonshane]

cheers guys. Great posts from Mike and Martin.

11 hours ago, mikeDnight said:

Over the last year the FC100 has almost never failed to impress me with its planetary performance.

which begs the question......when did it not and why?    I presume seeing was the culprit?

Is the D bit important or is it just a larger format focuser? Personally I'd think I will only use 1.25" eyepieces with this scope but maybe it's worth having the option?

Looking forward to (I hope) a look through Stu's over the SGL weekend in comparison with my 120ED.

[Stu]

28 minutes ago, Moonshane said:

cheers guys. Great posts from Mike and Martin.

which begs the question......when did it not and why?    I presume seeing was the culprit?

Is the D bit important or is it just a larger format focuser? Personally I'd think I will only use 1.25" eyepieces with this scope but maybe it's worth having the option?

Looking forward to (I hope) a look through Stu's over the SGL weekend in comparison with my 120ED.

The D is the standard focuser Shane, there is another variant with a larger format I think, can recall the suffix though.

I confess I've never used the original focuser on mine, I stuck a FeatherTouch on it straight away. If buying used the focuser is something to look at carefully though. I think Tak focusers are ok if used for visual. Once you let though brutes over in imaging at them, they tend to develop image shift which is not something I can deal with. As new, and well maintained though I think they are fine. Mike still uses the original I think.

I do try to be realistic about the views through mine.  I know it cannot change the laws of physics, but it is very nice ??

EDIT the DC is the one with 1.25" focuser, the DF has the 2"

[Stu]

I can see there is a member of the dob mob infiltrating a refractor thread. Steve probably thinks it's discussing finderscopes ??. I'm sure you could happily got an FC-100 to your dob Steve, great combination ??

[swamp thing]

 

Sadly I cannot afford one Stu  
TBH if I had that sort of money I'd buy a Nikon 300mm f2.8 prime lens instead. Now that is an APO I'd buy tomorrow.
 

[John]

There was a very similar thread on the CN forum in 2014. There might be some comments worth reading in there:

http://www.cloudynights.com/topic/480560-premium-100mm-apo-or-sw-120-apo/

[DirkSteele]

Very interesting thread.  I think most are aware of what scopes I own and while you would have to pry my LZOS made triplets from my cold dead hands before I would let them go, I have been very impressed with the image thrown up by my two small Taks (the FS-60 and FC-76, the 76 in particular).  The clarity and contrast is exceptional. I would love to be able to compare triplets of the same aperture and fabrication quality to find out if that is down to less glass (or crystal in the case of the Fluorite elements) in the light path, or the lower scatter characteristics of the Fluorite, or perhaps a bit of both.

 

The one that has me very excited is the TAX FC-100 DL which is the f/9 version.  Ian King had one on his stand at Astrofest and for a few moments I really thought about before I remembered I already have seven scopes!  Fortunately a couple of hours later someone bought it so I could not change my mind! 

 

 

[Mark at Beaufort]

I have enjoyed reading this thread and to be honest I always wanted a high quality APO - Takahashi or TeleVue. At the moment I have a 102mm Astro Tech ED doublet with a Starlight Feathertouch focuser and I love it. I quite fancy comparing my Astro Tech with Stu's Takahashi or Shane's 120ED at SGLX1 but my worry is my scope will be blown out of water and I will get frustrated and end up buying a better frac.