A super light 5" doublet apo - does one exist?

[Paz]

I've come very close to getting a 5" ish f7-f9 apo refractor a few times but each time have backed off after thinking about the reality of size/weight and that anything too big/heavy will end up competing with my VX14 and end up losing and gathering dust.

Thinking about it one can't do much do too much about the size but if the weight could be reduced to something I would consider easy to handle and which would be reasonable for an EQ5 / Skytee 2 type of mount so that I would not have to upgrade to a heavier mount I would be interested (I am averse to vibes so I would not like a scope that was pushing the limits of its mount).

I saw this carbon fibre scope from Explore Scientific that got me interested, with a weight of 5.2kg quoted on some retail sites that I assume that is just the OTA, I've seen weights of 6.4kg also quoted (including on the manufacturer's site below) that I assume would therefore include tube rings/dovetail/handle/findershoe type things.

Explore FCD100 127mm f/7.5 Carbon Fiber Triplet APO Refractor Telescope — Explore Scientific (explorescientificusa.com)

That kind of weight is getting into the right ball park, I wondered how much more weight would be saved if this was a doublet rather than a triplet and if there are any other options out there or developments pending? As well as the additional weight I am not sure I would want a triplet due to the longer cooling periods.

[John]

Many manufacturers weight quotes don't include tube rings, finder, dovetail, diagonal etc. It's worth checking if it's critical, to be 100% sure. My 130mm F/9.2 triplet weighs 9.3kg and that does include those accessories but it is not the lightest around (or the heaviest !).

Borg have the reputation of producing about the lightest refractors for their aperture class. I don't know if the 125mm is still made though ?

 

[Mr Spock]

The Skywatcher 120mm is listed as 5.13kg. The Tecnosky 125mm is 7.6 kg.

[Space Hopper]

I have a friend who's just got an Altair 125 doublet F7.8

So quite a long tube, and has a quoted weight of 8.3kg

https://www.altairastro.com/altair-wave-series-125-edf-f78-apo-w-large-m92-rp-focuser-454-p.asp

[Louis D]

I do have to wonder what makes refractors so much heavier than their Newtonian size equivalents.  Are two or three hunks of 5" or 6" diameter refractor glass that much heavier than one hunk of 5" or 6" mirror glass?  Is it that the refractor lens cell is much heavier than a Newtonian mirror cell?

[Naughty Neal]

What about the starfield 115 triplet APO F7 quoted on FLO as approx.4.2kg with rings and diagonal ?

Scrub that looks like it is 15lbs /6.8kg , the 4.2kg must be an error on FLO.

 

Edited May 5, 2023 by Naughty Neal

[Paz]

3 hours ago, Mr Spock said:

The Skywatcher 120mm is listed as 5.13kg. The Tecnosky 125mm is 7.6 kg.

 

2 hours ago, Space Hopper said:

I have a friend who's just got an Altair 125 doublet F7.8

So quite a long tube, and has a quoted weight of 8.3kg

https://www.altairastro.com/altair-wave-series-125-edf-f78-apo-w-large-m92-rp-focuser-454-p.asp

I looked for a long time at those 125mm scopes but thought them too heavy in the end.

[Elp]

I was gonna suggest Borg 107FL, they're pricey though.

Edited May 5, 2023 by Elp

[John]

I have just weighed my ED120 Pro at 6.4kg which includes 9x50 RACI finder, 2 inch diagonal, tube rings and a 250mm CNC Vixen-type DT bar. The focuser on the scope is a Moonlite CF dual speed though which might weigh a bit more than the stock focuser.

[fireballxl5]

This new Borg 125FL sounds interesting if,  likely,  expensive

 

 

[LDW1]

My 5" f6.6 scope and AZ5 mount weighed over 40lb, they definitely aren't gng !

[dweller25]

Hello @Paz

You have probably realised your true 5” Goldilocks scope does not exist ☹️

The closest would be a Skywatcher 120ED

The Takahashi TSA120 would be a little heavier but it does have a very good reputation 🙂

As mentioned above, Borg have a very light 125mm that’s due out soon, but I suspect it will be VERY expensive.

 

Edited May 6, 2023 by dweller25

[Nik271]

13 hours ago, Louis D said:

I do have to wonder what makes refractors so much heavier than their Newtonian size equivalents.  Are two or three hunks of 5" or 6" diameter refractor glass that much heavier than one hunk of 5" or 6" mirror glass?  Is it that the refractor lens cell is much heavier than a Newtonian mirror cell?

I believe that at 5 inches and above the Newts are just shorter and save weight on the tube. They can even be truss tube desigh like the Heritage, unlike refractors which have to have a tube to hold the focuser in good collimation with the objective. It's also very hard to make a well corrected 5 inch doublet refractror faster than F/7, whereas a Newtonian can be made at F/6 or even F/5 comparatively easer. So the Newts end up being much shorter.

[mikeDnight]

20 hours ago, Paz said:

I've come very close to getting a 5" ish f7-f9 apo refractor a few times but each time have backed off after thinking about the reality of size/weight and that anything too big/heavy will end up competing with my VX14 and end up losing and gathering dust.

Thinking about it one can't do much do too much about the size but if the weight could be reduced to something I would consider easy to handle and which would be reasonable for an EQ5 / Skytee 2 type of mount so that I would not have to upgrade to a heavier mount I would be interested (I am averse to vibes so I would not like a scope that was pushing the limits of its mount).

I saw this carbon fibre scope from Explore Scientific that got me interested, with a weight of 5.2kg quoted on some retail sites that I assume that is just the OTA, I've seen weights of 6.4kg also quoted (including on the manufacturer's site below) that I assume would therefore include tube rings/dovetail/handle/findershoe type things.

Explore FCD100 127mm f/7.5 Carbon Fiber Triplet APO Refractor Telescope — Explore Scientific (explorescientificusa.com)

That kind of weight is getting into the right ball park, I wondered how much more weight would be saved if this was a doublet rather than a triplet and if there are any other options out there or developments pending? As well as the additional weight I am not sure I would want a triplet due to the longer cooling periods.

 I suppose it depends on how far do you intend to carry it?  If you can cope with a 14" Dob, I can't imagine the weight of a 5" refractor putting you off. The weight of my FS128 and its heavy Celestron G11 mount and tripod never seemed much of a problem to take on field trips. I'd just load it into my car and off I'd go. Now if I needed to take it on a bus, then there'd be a problem.

Me and my youngest on a field trip to observe the Transit of Venus 2004. (An image very kindly enhanced from a blurred old photo by Louis D)

 

Edited May 6, 2023 by mikeDnight

[LDW1]

That photo is 19 yrs. ago as we age our muscle mass is not quite the same, when it comes to even 40+ lbs of weight, the enjoyment will / does change and I am not a weak guy. If the OP is over 50 lets say, as with looking through scopes at club meetings, they should try lugging some of these larger scopes back and forth to get a feel. They aren't lite when you are stumbling around in the dark, lol !   PS:  There are no lite, capable scopes 5" or over, just ask the mounts, lol !

[Paz]

4 hours ago, mikeDnight said:

 I suppose it depends on how far do you intend to carry it?  If you can cope with a 14" Dob, I can't imagine the weight of a 5" refractor putting you off. The weight of my FS128 and its heavy Celestron G11 mount and tripod never seemed much of a problem to take on field trips. I'd just load it into my car and off I'd go. Now if I needed to take it on a bus, then there'd be a problem.

Me and my youngest on a field trip to observe the Transit of Venus 2004.

Nice photo, I  would have liked to have seen that transit!

The challenge is that how much I use a scope depends on the relationship between how good the views are and the time and effort required to set up and take down. I think of there was a 5" that my EQ5 could handle and that was a doublet so that cool down was quicker I could use that pretty much as easily as I use a 102mm f7 refractor currently.

The vx14 basebase is about 20kg including the motorcycle battery I have nestled in it for power. The ota is well over 20kg including the Dob mount rings , ota extension and ota reinforcement that it has. I've set this up up to a hundred yards from the car at meets in the past although I don't think I could carry it that far any more, but I usually just observe from home. I'm about to have a  heart procedure that might mean a step change in what I can handle but hopefully I'll still be good to set up my scopes.

[LDW1]

52 minutes ago, Paz said:

Nice photo, I  would have liked to have seen that transit!

The challenge is that how much I use a scope depends on the relationship between how good the views are and the time and effort required to set up and take down. I think of there was a 5" that my EQ5 could handle and that was a doublet so that cool down was quicker I could use that pretty much as easily as I use a 102mm f7 refractor currently.

The vx14 basebase is about 20kg including the motorcycle battery I have nestled in it for power. The ota is well over 20kg including the Dob mount rings , ota extension and ota reinforcement that it has. I've set this up up to a hundred yards from the car at meets in the past although I don't think I could carry it that far any more, but I usually just observe from home. I'm about to have a  heart procedure that might mean a step change in what I can handle but hopefully I'll still be good to set up my scopes.

You won't be able to lift more than 10 lb. for about 3-4 months after that the sky will be the limit or your muscle strength. There is no cool down, basically, in a refractor in comparison to the other types of scopes.

[Deadlake]

I'd start researching a light AltZ harmonic mount. The HAZ31 plus a carbon tripod (combined weight around 5.5 kg) makes a 130 mm grab n go.

See:



Not my scope, but I understand the tracking and stability is so similar to a Panther you would go with the weight saving every time.

The AP130GTX is around 9 kg, and the scope I have in mind a 130 LZOS is around 11.k kg, but I understand from other scopes used on the mount that the HAZ31 can accommodate that.

I would estimate the combined weight of the above scope, mount and tripod is around 15 kg.

This is making me think twice about adding motors to my AZ100. 

[LDW1]

49 minutes ago, Deadlake said:

I'd start researching a light AltZ harmonic mount. The HAZ31 plus a carbon tripod (combined weight around 5.5 kg) makes a 130 mm grab n go.

See:



Not my scope, but I understand the tracking and stability is so similar to a Panther you would go with the weight saving every time.

The AP130GTX is around 9 kg, and the scope I have in mind a 130 LZOS is around 11.k kg, but I understand from other scopes used on the mount that the HAZ31 can accommodate that.

I would estimate the combined weight of the above scope, mount and tripod is around 15 kg.

This is making me think twice about adding motors to my AZ100. 

At low powers probably but at higher powers when you really want to make the 130 or higher scope zing, I don't think so unless you don't mind waiting for the shaking to subside. This is from my personal, actual experiences, I hate to underestimate the actuality to a fellow astronomer. A 130 or larger is / are a big heavy scope ! My Porta II 's don't cut it and my AZ5 with the 1 3/4-2" ss legs is okay, when it gets in to those size refractors an AZ mount at a decent price are hard to find !

Edited May 6, 2023 by LDW1

[Deadlake]

1 hour ago, LDW1 said:

At low powers probably but at higher powers when you really want to make the 130 or higher scope zing, I don't think so unless you don't mind waiting for the shaking to subside. This is from my personal, actual experiences, I hate to underestimate the actuality to a fellow astronomer. A 130 or larger is / are a big heavy scope ! My Porta II 's don't cut it and my AZ5 with the 1 3/4-2" ss legs is okay, when it gets in to those size refractors an AZ mount at a decent price are hard to find !

It's all in the tripod, the super mount tripod used above can take 150 kg, an alternative would be a Planet of TPod tripod which are also very rock solid.

The above works at 200x with no wobbles and great tracking.

As I stated it's hard to tell the difference with a Panther mount.

Edited May 6, 2023 by Deadlake

[Elp]

Or a Berlebach Uni/Planet. Very excellent.

Edited May 6, 2023 by Elp

[mikeDnight]

4 hours ago, Paz said:

Nice photo, I  would have liked to have seen that transit!

The challenge is that how much I use a scope depends on the relationship between how good the views are and the time and effort required to set up and take down. I think of there was a 5" that my EQ5 could handle and that was a doublet so that cool down was quicker I could use that pretty much as easily as I use a 102mm f7 refractor currently.

The vx14 basebase is about 20kg including the motorcycle battery I have nestled in it for power. The ota is well over 20kg including the Dob mount rings , ota extension and ota reinforcement that it has. I've set this up up to a hundred yards from the car at meets in the past although I don't think I could carry it that far any more, but I usually just observe from home. I'm about to have a  heart procedure that might mean a step change in what I can handle but hopefully I'll still be good to set up my scopes.

An ED120 immediately comes to mind. They really are excellent and could be carried comfortably by an EQ5. I've had three of them and they've shown me many amazing sights. I rarely go on field trips these days but generally prefer to observe from home. Before I built my observatory I decided to sink a pier into my lawn with my mount permanently attached. That simplified matters, as I only needed to carry my tube assembly and eyepiece case outside. I used a canvas garden chair cover to cover the mount and its electronics, which at the time was a Losmandy GM8. In the five years I used that set-up the electronics and mount never once got wet. It also made packing up, when I was tired and frozen, and the scope was caked in ice easier.

  

Edited May 6, 2023 by mikeDnight

[LDW1]

I didn't realize the OP has unlimited cash for some of these mounts being mentioned ! My apologies.

[LDW1]

4 hours ago, Deadlake said:

I'd start researching a light AltZ harmonic mount. The HAZ31 plus a carbon tripod (combined weight around 5.5 kg) makes a 130 mm grab n go.

See:



Not my scope, but I understand the tracking and stability is so similar to a Panther you would go with the weight saving every time.

The AP130GTX is around 9 kg, and the scope I have in mind a 130 LZOS is around 11.k kg, but I understand from other scopes used on the mount that the HAZ31 can accommodate that.

I would estimate the combined weight of the above scope, mount and tripod is around 15 kg.

This is making me think twice about adding motors to my AZ100. 

What combined weight of 5.5 kg ( 11 lb ), I must have missed the combo, what scope ? Your definition of grab n go must be a lot different than mosts ?

Edited May 6, 2023 by LDW1

[Deadlake]

7 hours ago, LDW1 said:

What combined weight of 5.5 kg ( 11 lb ), I must have missed the combo, what scope ? Your definition of grab n go must be a lot different than mosts ?

That was for the mount and tripod, I have manual mounts like a ScopeTech Zero and tripod that weigh more. Such is progress. 
 

Put what scope you want on it, but for a lighter setup the reduction of weight in the mount and tripod is what I’d look to reduce.