In betweener

[Kobayashi Maru]

Hi all

I currently have a sw72ed and a 10' dob. seems like a nice complimentary pair. Visual only. Low tech mounts

I'm looking to start searching for my next scope. I have acquisition fever. My immediate reaction is a 5 inch apo/achro or a 6/8" mak/cass but as I'm relatively new to this game I'm not sure what would be a better fit. Anything up to Takahashi prices would work, although I assume that for visual I don't need perfect optics.

Any recommendations would be much appreciated.

 

 

[Kobayashi Maru]

Just found this thread on page two. Seems pretty close to what I'm doing.

 

 

Edited March 3, 2023 by Kobayashi Maru

[jetstream]

51 minutes ago, Kobayashi Maru said:

Anything up to Takahashi prices would work,

The TSA120 is a nice scope.

[Kobayashi Maru]

23 minutes ago, jetstream said:

The TSA120 is a nice scope.

A very nice scope. Does it being a triplet help visually? I'm not too concerned about weight, I have the 72ed for that, just wondering if the difference between a doublet and a triplet is apparent?

[jetstream]

20 minutes ago, Kobayashi Maru said:

A very nice scope. Does it being a triplet help visually? I'm not too concerned about weight, I have the 72ed for that, just wondering if the difference between a doublet and a triplet is apparent?

It can be... depending on the optics.

The very highly regarded Tak 100mm doublets are excellent visual telescopes, however some other doublets might not fare too well and be subject to sample to sample variation IMHO. Mind you its possible to get a "good one" . Maybe most are good, I dont know.

I do know that when you buy a Tak what I see in mine you will see in yours. My TSA120 is a superb telescope, my SW120ED doublet average. My older 90mm Stellarvue triplet is a vg scope but not in Tak territory contrast wise on the moon and planets.

Its said that refractors by nature are small telescopes, always will be small telescopes, regardless of aperture so it makes sense to buy the best you can afford.

If I had a choice in refractors and could spend on a 120mm triplet or get a 100mm Tak doublet for the same price, Id go for the Tak doublet.

Gerry

[Kobayashi Maru]

1 hour ago, jetstream said:

It can be... depending on the optics.

The very highly regarded Tak 100mm doublets are excellent visual telescopes, however some other doublets might not fare too well and be subject to sample to sample variation IMHO. Mind you its possible to get a "good one" . Maybe most are good, I dont know.

I do know that when you buy a Tak what I see in mine you will see in yours. My TSA120 is a superb telescope, my SW120ED doublet average. My older 90mm Stellarvue triplet is a vg scope but not in Tak territory contrast wise on the moon and planets.

Its said that refractors by nature are small telescopes, always will be small telescopes, regardless of aperture so it makes sense to buy the best you can afford.

If I had a choice in refractors and could spend on a 120mm triplet or get a 100mm Tak doublet for the same price, Id go for the Tak doublet.

Gerry

Thanks Gerry...that is quite an endorsement of the 100mm Tak. I imagine the TSA is amazing. I may have to start saving my pennies. 

[JeremyS]

Not too shabby, those Taks.

The FC100 DZ is super, but if you can stretch to a TSA 120 is even better of course. Remarkably compact too.

[John]

I have a Tak FC100, a Skywatcher ED120  and a LZOS 130 triplet. I am purely a visual astronomer.

The 130 performs just like a bigger version of the FC100 doublet - no false colour at, or either side of sharp focus and an ability to handle "stupidly" high magnifications with some ease. My Skywatcher ED120 is a good one and performs somewhere between the 2 although, as an F/7.5 doublet, it does show a little false colour either side of sharp focus around bright targets plus a small splash of it around Sirius and Venus at focus. My ED120 seems to have an excellent optical figure to the objective (just as important as false colour control IMHO) and the star test is as good as the more exotic refractors. The chinese ED120's can vary sample to sample as  @jetstream's example seems to show. Plus the stock focusers might not prove entirely satisifying.

My only word of caution is to be prepared for the step up in size, weight and mounting requirements if you choose to go above 120mm in aperture, even if a doublet, can be more than you might expect !

 

 

Edited March 3, 2023 by John

[Mr Spock]

10 hours ago, Kobayashi Maru said:

although I assume that for visual I don't need perfect optics

Completely the opposite  The better the optics, the better the view. Unless all you want is low power wide field.

[jetstream]

4 hours ago, John said:

The chinese ED120's can vary sample to sample as  @jetstream's example seems to show

Rumour around the campfire is the the earlier Sw120ED's labelled "Pro" had some excellent optics. Mine goes 300x on lunar, about 265x on Jupiter. Its not bad ...until you look through something with truly good optics- and I'm fussy.

The 120mm's definitely need a heavier mount system, the 100's do not IMHO. I bought a moonlight focuser for it eventhough I had the stock one working not too bad.

Edited March 3, 2023 by jetstream

[Skyline]

My C100ED, has very favourable optics, seldom goes out for imaging.

But its a fantastic scope for visual, even @Grump Martian had a peek through it.

[John]

7 hours ago, jetstream said:

Rumour around the campfire is the the earlier Sw120ED's labelled "Pro" had some excellent optics. Mine goes 300x on lunar, about 265x on Jupiter. Its not bad ...until you look through something with truly good optics- and I'm fussy....

 

That would be the difference then - I'm not really fussy 😀

 

Edited March 3, 2023 by John

[Kobayashi Maru]

16 hours ago, Mr Spock said:

Completely the opposite  The better the optics, the better the view. Unless all you want is low power wide field.

My question was badly phrased. It’s more around whether a triplet or quadruplet makes a discernible difference. Seems like they may but with diminishing returns?
  

[jetstream]

@Kobayashi Maru Just had a stunning lunar session with the TSA120, seeing was pretty good allowing up to 375x, however most views were just under 300x. My 15" dob is a vg planetary scope but had thermal issues and the aperture was a bit much for the seeing.

I see you have a 10" dob- great scope- a 100mm frac will compliment it well. One thing- Ive noticed that the 120mm is more sensitive to mediocre seeing than the 90mm. Not sure how your seeing is where your located but if your seeing isnt good or better most of the time a 100mm would be the better choice IMHO.

Let us know what you decide to get 👍

Edited March 4, 2023 by jetstream

[Deadlake]

Triplets give better colour but at the expense of weight, which is the trade off you need to make. Also they can take a little while more to accilimate, but the 105 mm I have takes around 5 minutes and then is razor sharp. 
 

Much has been made of the TSA-120, and like many Japanese scope you get a very compact scope that is lightweight which I think cannot be over looked. 
 

Same time the ‘seeing’ does not make much of a difference between a 105 and 130 I have, but for a larger scope like the 10” then for sure that’s going to be a point.

I’d work out how you are going to mount the scope, once you go above 6-7 kg the options you have are going to be a step up in cost and also will remove flexibility. You might need to move the scope around the garden to dodge trees for instance.

[Stu]

12 minutes ago, Deadlake said:

but the 105 mm I have takes around 5 minutes and then is razor sharp

Presumably your scopes are kept somewhere cool Martin? A fast triplet takes longer than five minutes to cool if taken from a warm house.

12 minutes ago, Deadlake said:

Same time the ‘seeing’ does not make much of a difference between a 105 and 130 I have

Like Gerry, I see differences in susceptibility to seeing between 100mm and 130mm.

[Deadlake]

55 minutes ago, Stu said:

Presumably your scopes are kept somewhere cool Martin? A fast triplet takes longer than five minutes to cool if taken from a warm house.

Like Gerry, I see differences in susceptibility to seeing between 100mm and 130mm.

The 105 mm takes 5 minutes from a warmish garage to freezing to acclimate the 130 mm longer maybe 30 minutes.

As far as seeing, recently moved house. It’s 75 meters higher then last house and hidden behind a large hill, one of the highest in the southern downs.
 

Maybe the lower boundary layer turbulence does not effect so much when I view from the new house as much or maybe I’ve not been out as much, I’m picky on nights to view.

Although the new house is only five minutes from the old house it’s a noticeable step up in ‘seeing’ quality…

[Paz]

One thing I notice is that as you allude to they are best when they are complimentary to each other.

I looked at length at 120-130mm refractors as I was aiming for downsizing to just 3 scopes, a 72mm refractor for travel so that had to be small, a 14" reflector for epic sessions, so that had to be epic(!) and being big/heavy didn't matter, and a third scope in between.

I looked at some 120-130mm refractors in the flesh and was worried about their size/weight and that I might need a more serious mount and that setting one up would be in the same league of challenge as the vx14 in which case the vx14 would probably get used and the big refractor would probably not. So I thought longer about the point of a 3rd scope. In the end I decided it had to be a general purpose great grab and go scope, I e. did not have to be small but did have to be fast and flexible and l easy to set up so it filled a gap that didn't compete with the 72mm or 14" and I ended up with a smaller 3rd scope than I initially wanted.

The above is just my own story and everyone would have different choicesabput a good mix of scopes that would work best,  but the thing that helped me was considering scope purpose again in detail and seeing if that helped to solidify a choice.

Regarding your starting point a challenge you have is that a 10" dobsoinian is a great visual scope and so anything else is going to have to have a specific advantage over that to make you motivated to use it once the novelty has worn off.

Edited March 4, 2023 by Paz

[ollypenrice]

TEC 140. Superbly built, wonderful views, corrected for visual (but a stunning imaging scope with the dedicated flattener.) A really great scope entirely free of Hospital Green and flashy red anodising!  (Yikes, I hope Jeremy doesn't read this...)

lly

[Mr Spock]

A TEC is considerable better than some others mentioned. However, good luck in finding one used, or, you could join the long list of deceased on the waiting list for a new one 😜

[dweller25]

Curved ball time…..

You may want to consider a Takahashi Mewlon 180 🙂

 

Edited March 4, 2023 by dweller25

[Stu]

56 minutes ago, Deadlake said:

The 105 mm takes 5 minutes from a warmish garage to freezing to acclimate the 130 mm longer maybe 30 minutes.

Interesting. Matthew puts it at 30mins for the same scope from warm house to cool outside.

Triplets will take longer to cool than a doublet of similar aperture due to the extra glass, and while the lens in the 105 is very thick and heavily curved, cool down time is good, taking about 30 minutes to produce excellent images after moving from a warm house to cool viewing location.

http://alpha-lyrae.co.uk/2014/01/01/the-apm-tmb-105-f6-2-triplet-apochromatic-refractor/
 

I wonder what is different about yours?

[Deadlake]

51 minutes ago, Stu said:

Interesting. Matthew puts it at 30mins for the same scope from warm house to cool outside.

Triplets will take longer to cool than a doublet of similar aperture due to the extra glass, and while the lens in the 105 is very thick and heavily curved, cool down time is good, taking about 30 minutes to produce excellent images after moving from a warm house to cool viewing location.

http://alpha-lyrae.co.uk/2014/01/01/the-apm-tmb-105-f6-2-triplet-apochromatic-refractor/
 

I wonder what is different about yours?

It’s coming from a garage, not quite same temperature as outside. For instance metal of an AZ100 will be cold to the touch as will metal handle of scope and FT focuser. So still some acclimation but not much. 
The only time the scope spends in the house from the garage is to put on a finder scope, so not much time for it to warm up. The phenolic tube is not a great conductor of heat.

The night I took it out was also not relatively cold, i.e no frost in the tube like this

 

 

Still on that night maybe 25 minutes for it to settle down. Again a phenolic tube.

The phenolic tube is a very good insulator making it maybe harder for a thermal gradient to form. Might help???

Edited March 4, 2023 by Deadlake

[Stu]

7 minutes ago, Deadlake said:

It’s coming from a garage, not quite same temperature as outside. For instance metal of an AZ100 will be cold to the touch as will metal handle of scope and FT focuser. So still some acclimation but not much. 
The only time the scope spends in the house from the garage is to put on a finder scope, so not much time for it to warm up. The phenolic tube is not a great conductor of heat.

The night I took it out was also not relatively cold, i.e no frost in the tube like this

 

 

Still on that night maybe 25 minutes for it to settle down. Again a phenolic tube.

The phenolic tube is a very good insulator making it maybe harder for a thermal gradient to form. Might help???

Ah, so not a warm garage but a cool garage, makes a big difference. The only reason I’m being specific about this is so people don’t have an expectation that a fast triplet will cool in five mins.

[Deadlake]

32 minutes ago, Stu said:

Ah, so not a warm garage but a cool garage, makes a big difference. The only reason I’m being specific about this is so people don’t have an expectation that a fast triplet will cool in five mins.

Doing a Google around this there is a huge range of cooling times for the same scopes, and even then if nighttime temperature is changing this has a large effect too. 
 

The other item to remember is the phenolic tube thermal expansion will result in better focus compensation than using an aluminium tube. Also apparently zero tube currents.

Back to the OP, I was going to suggest a 115 mm triplet is the best compromise between weight and performance, it has just that little more aperture and keeps the weight around 6-7 kg so no expensive mount.