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

[Franklin]

I think an ED120 on an EQ5/Skytee type mount is about the limit for GnG but I still wouldn't be happy with it. I have a 115 which weighs in at 6.2kg with all the gear on and although it is usable on the GP2(similar specs to EQ5) it is much more stable on the SXD2(similar specs to HEQ5).

A true 5" refractor is a big scope and to get the best out of it should really be mounted on something that's capable of handling it. What I've found over the years is that it pays to ignore the published specs from mount manufacturers and keep the load well below their supposed capacity rating. That way the mount is not stressed and can easily hold the scope steady, even at high magnification. Trying to achieve focus at high powers when the scope dances around every time you touch the focuser or the wind blows is an exercise in frustration.

 

[LDW1]

7 hours ago, Franklin said:

I think an ED120 on an EQ5/Skytee type mount is about the limit for GnG but I still wouldn't be happy with it. I have a 115 which weighs in at 6.2kg with all the gear on and although it is usable on the GP2(similar specs to EQ5) it is much more stable on the SXD2(similar specs to HEQ5).

A true 5" refractor is a big scope and to get the best out of it should really be mounted on something that's capable of handling it. What I've found over the years is that it pays to ignore the published specs from mount manufacturers and keep the load well below their supposed capacity rating. That way the mount is not stressed and can easily hold the scope steady, even at high magnification. Trying to achieve focus at high powers when the scope dances around every time you touch the focuser or the wind blows is an exercise in frustration.

 

Hopefully by now the OP gets the idea about a super lite but stable 5" combination !   GnG won't happen unless you are Hurcules, lol !

[Paz]

Thanks for the replies there's a few lines of enquiry there I will look into.

Thinking about the heaviest scopes I've used on an EQ5 myself to date these are a ST120 that weighs in at 4.9kg including dovetail, rings and a chunky dual speed focuser, to which would be added finders, eyepieces etc. I've also used a C8 which weigh in at 5.6kg just with its dovetail, that would then have a 9x50 finder, chunky dual speed focuser, diagonal, eyepiece, sometimes binoviewers, sometimes dovetail counterweights, dew shield, etc so maybe 2-4kg more on top of the ota.

Both of those have been ok with me, a typical 5" apo seems to be about 2kg heavier than the c8 like-for-like plus being longer. I could perhaps add some weight to the st120 and see how the good or bad the vibes are when it's commensurately heavier (but noting it is shorter).

The sky watcher ed120 does seem to present well when you look its mix of aperture, weight, quality, and being a doublet, I keep coming back around to that (and the carbon explore scientific scopes) at the moment.

Edited May 7, 2023 by Paz

[mikeDnight]

1 hour ago, Paz said:

Thanks for the replies there's a few lines of enquiry there I will look into.

Thinking about the heaviest scopes I've used on an EQ5 myself to date these are a ST120 that weighs in at 4.9kg including dovetail, rings and a chunky dual speed focuser, to which would be added finders, eyepieces etc. I've also used a C8 which weigh in at 5.6kg just with its dovetail, that would then have a 9x50 finder, chunky dual speed focuser, diagonal, eyepiece, sometimes binoviewers, sometimes dovetail counterweights, dew shield, etc so maybe 2-4kg more on top of the ota.

Both of those have been ok with me, a typical 5" apo seems to be about 2kg heavier than the c8 like-for-like plus being longer. I could perhaps add some weight to the st120 and see how the good or bad the vibes are when it's commensurately heavier (but noting it is shorter).

The sky watcher ed120 does seem to present well when you look its mix of aperture, weight, quality, and being a doublet, I keep coming back around to that (and the carbon explore scientific scopes) at the moment.

The triplet may be appealing, but from experience I had in side by side comparison between my friends Meade 127mm ED triplet, which was a very nice scope, and my Equinox 120ED doublet, the triplet always took 45 mins to cool, compared to 15 mins for the doublet. Both were beautiful performers when thermally stable.

[LDW1]

2 hours ago, Paz said:

Thanks for the replies there's a few lines of enquiry there I will look into.

Thinking about the heaviest scopes I've used on an EQ5 myself to date these are a ST120 that weighs in at 4.9kg including dovetail, rings and a chunky dual speed focuser, to which would be added finders, eyepieces etc. I've also used a C8 which weigh in at 5.6kg just with its dovetail, that would then have a 9x50 finder, chunky dual speed focuser, diagonal, eyepiece, sometimes binoviewers, sometimes dovetail counterweights, dew shield, etc so maybe 2-4kg more on top of the ota.

Both of those have been ok with me, a typical 5" apo seems to be about 2kg heavier than the c8 like-for-like plus being longer. I could perhaps add some weight to the st120 and see how the good or bad the vibes are when it's commensurately heavier (but noting it is shorter).

The sky watcher ed120 does seem to present well when you look its mix of aperture, weight, quality, and being a doublet, I keep coming back around to that (and the carbon explore scientific scopes) at the moment.

120 is not 5" and carbon doesn't reduce weight by that much considering the extra cost. We can't have it all !  I had an ST 120 it's a different scope. Good Luck !

[John]

1 hour ago, mikeDnight said:

The triplet may be appealing, but from experience I had in side by side comparison between my friends Meade 127mm ED triplet, which was a very nice scope, and my Equinox 120ED doublet, the triplet always took 45 mins to cool, compared to 15 mins for the doublet. Both were beautiful performers when thermally stable.

The ED120 doublets have been known to show less CA than some lower cost 127 triplets.