Dedicated Jupiter Refractor?

Any suggestions for a dedicated Jupiter refractor, longer focal length for larger image scale, and aperture under 4" for portability?

New or used made in the last 10 years or so....

Thanks

Tom

Takahashi TSA102 or FS102
Vixen 102 Fluorite

I think much under 4" is wasted on Jupiter --
the visible detail drops pretty fast below 4" or 5".

Achromats have a lot of trouble with Jupiter -- theres
a lot of blue light. I'd stick with APOs.

Try the FC-100 or FS-102 or their equivalent from other makers. With the Taks, one can add a 1.6x extender making it essentially an F/12.8. Like many others, I prefer long focal length refractors for planetary work. Since there are but few long FL APOs, using the Tak extender solves the problem rather elegantly. Fabulous images of Jupiter and more detail than one would expect from a small scope. Jupiter and Mars are challenging targets and a large scope helps in pulling out great levels of detail.

If you really want to stay under 4", the FS-78 is a fabulous little scope and does a surprisingly good job on the planets for a 3" scope. A Televue 85 falls into the same category, superb image, a bit more resolution and still very light. I am sure there are other superb 3"s out there, but I feel uncomfortable recommending scopes I have not actually used.

I agree with the comment about using an APO, no disrespect for large achromats, but both planets were challenges for the 6" and 8" achros I owned as color is present. It is not a huge problem, but an APO puts that same light back into the image and improves planetary detail. Of course, a Newtonian does as well and an optimized planetary reflector is a hard scope to fault.

This is definitely not what you want to hear, but here are the facts;

Portable is hard to define, it varies from person to person, but using your stated benchmark of 4” refractor for size and portability, if I waned a portable instrument for Jupiter, something that that can do justice when it comes to showing the low contrast features of this planet, I would consider a cat, a 7” Mak Cass with small co or Mak Newtonian, the MC would be more portable.

With a 4” or smaller refractor, preferably an apo, the small exit pupil needed to achieve a decent power will add exit pupil’s diffraction effects & reduce the contrast to a point where the instrument will not produce much detail, perhaps with the exception of the two major equatorial belts.

I routinely use a 155 apo for Jupiter, that is when I am too tired to carry less portable but larger reflectors and the first thing that I notice is how limited the 155 aperture is for capturing difficult detail.

This is an argument that I always lose, those who view Jupiter with 4” apo’s tell me how wonderful and detailed the image is, I suppose that depends on your experience and the expectations, if what you see in a 4” refractor is good enough then you are in business, but once you get a taste of what is possible with a 6” refractor or equivalent Mak then perhaps you will give this a bit more thought.

Vahe

While the views of Jupiter are nice with a quality 4" apochromat, and I've often been surprised at how much detail is visible, I find the aperture quite limiting for planetary observing. My long used 8" f/8 Newtonian was a far more capable planetary instrument and I would certainly aim for a quality 6" or larger instrument for serious Jupiter observing.

Clear skies, Alan

Jupiter at the eyepiece offers a huge and impressive disk compared to other planets, this makes it a very interesting object to view in any small telescope, even a 3.5” Questar will give you a spectacular view of this planet.

That is the easy part, now try to extract low contrast surface detail from this large disk and you will be faced with formidable challenges, this is where you will need aperture and IMHO a quality 6” is the starting point, not ideal, but just the starting point.

And also remember that whatever that you get will also be used for Mars and Saturn this coming season.

Vahe

Dont have a suggestion......given your specified limitation of UNDER 4" since I wouldnt use anything less than 4" for serious observation of Jupiter. However if you are willing to go to 4" then I would suggest the FL102S Vixen if you see one available. For the $$ you wont find a better option. The FS102 Tak would also do the trick, and so would the Celestron 4" Flourite although I dont recall the exact model it is.

Thomas Wos said:

Any suggestions for a dedicated Jupiter refractor, longer focal length for larger image scale, and aperture under 4" for portability?

New or used made in the last 10 years or so....

Thanks

Tom

Thomas Wos said:

Any suggestions for a dedicated Jupiter refractor, longer focal length for larger image scale, and aperture under 4" for portability?

New or used made in the last 10 years or so....

Thanks

Tom

Sky-Watcher "Pro Series" ED100.
It's under 4" (3.94") :-)
Very light weight for it's aperture.
Longer focal length (f/9, 900mm).
Added bonus-- it's quite inexpensive.

I can see how going to a larger aperture, while theoretically offering some benefit, might not be such a great deal under less than optimal seeing conditions. That's my situation, unfortunately. Most nights, the air is rather turbulent and Jupiter doesn't look any better in a bigger scope. The 4" size seems to be a sweet spot under those less-than-ideal circumstances.

Tom,

I think a little more definition of what you mean by "portable" would be useful to understand to better hone a recommendation. By my own standard, if you are talking about taking a quick 30 minute jaunt in the back yard to view Jupiter then for me a 4" is actually too big for that, at least an f/8 like I have.

I have both a 102mm and 80mm APO and for those quick looks where I don't plan on being outside more than an hour, the 80mm often wins...even for Jupiter. So if this is the type of portable you mean, then by all means the smaller the instrument's physical size all the better so I might start considering something like the TMB92SS, TMB80SS, APM 80/480, etc. I would also probably put a binoviewer on it as your brain lets you see more with two eyes so helps overcome the limited aperture. Or, if you have the time and money, get on the list for the TEC110 if one still can for a nice ultra-short and convenient larger aperture scope.

btw, when using the smaller apertures, especially the 80mm class, I find top notch eyepieces really make a noticable difference for planetary...so something like TMB Supermonos, ZAO-IIs, Pentax SMC Orthos, etc. really let you squeek out the last bit of performance from these smaller apertures and I find it is quite worth it. All this is getting expensive though :-/

If ultra small size is not necessary, then I'd say try to get above the 4" mark a little, like with the new TEC110 already mentioned as a potential, or the new TSA-120 which is only a few incehes longer than the TSA-102. These 10 to 20 more mm of aperture will make a difference, especially on Jupiter. If your seeing conditions are usually very stable then the 3-4" class should do well, otherwise a little larger aperture and resolution will be appreciated if the seeing is often not so great as I think you mentioned. Caution though that getting up over the 4" mark means instruments will need a little cool down time for optimum performing. My 4" works pretty good right out the door, but it's at the limit I feel and larger glass may have more noticable immediate thermal issues.

Good luck,
-Bill