ZS66 vs C6

[Ags]

I had a good long look at Jupiter and Saturn last night with my Zenithstar 66, and the difference to the past few nights of observing with my C6 was quite striking. 

Firstly seeing seemed much more stable with the ZS66, a well known effect of small apertures. I will need to prove this with a side-by-side comparison of the two scopes on another clear night.

Secondly the contrast and color was much stronger in the refractor. For example, the SEB is faint in the C6 but plain as day in the ZS66. The GRS was visible last night but I  think the smaller scale in the refractor worked against it.

Thirdly I'm not sure the C6 has revealed much more detail. On Saturn, the ZS66 seemed to show better definition of the rings including shadows on the rings. I guess on a night of excellent seeing the C6 would pull ahead, but I don't exactly live on a mountain-top.

Finally, even when I pushed magnification to 0.5 mm exit pupil, floaters were less of an issue in the refractor than the C6. I wonder if this comes down to what photographers call bokeh - the smoothness of out of focus objects. Mirror lenses for cameras are plagued by very rough and intrusive bokeh because of their central obstruction while a good refractive camera lens can have much smoother bokeh. So maybe what troubles me with the C6 isn't just the floaters  but the noisy bokeh of the floaters?

I won't get rid of my C6 - it excels at deep sky and some kinds of doubles - but I am definitely saving up for a bigger refractor.

[dweller25]

Is your C6 wrapped with reflectix ?
I wrapped  my C6 with 2 layers and suddenly my “seeing” got better.

Edited August 30, 2022 by dweller25

[Ags]

No, but it is outside cooling for four hours. It is worth trying this however, if I can overcome my aesthetic objections!

I forgot to mention I was also observing with a GSO Wratten #8 filter last night, it certainly helped a lot with atmospheric dispersion.

[dweller25]

I know exactly what you mean, it does not look nice, but the increase in sharpness and contrast overcame my aesthetic objections 🙂

 

Edited August 30, 2022 by dweller25

[Ags]

That may help the seeing, but the points about contrast and floaters remain. 

Definitely looking at picking up a nice 90mm frac 😀... Just the right size for travel and enough to get decent magnification on the planets and splits on doubles.

[dweller25]

1 hour ago, Ags said:

That may help the seeing, but the points about contrast and floaters remain. 

Definitely looking at picking up a nice 90mm frac 😀... Just the right size for travel and enough to get decent magnification on the planets and splits on doubles.

I also like a nice refractor, or two 😁

[RobertI]

9 hours ago, Ags said:

I had a good long look at Jupiter and Saturn last night with my Zenithstar 66, and the difference to the past few nights of observing with my C6 was quite striking. 

Firstly seeing seemed much more stable with the ZS66, a well known effect of small apertures. I will need to prove this with a side-by-side comparison of the two scopes on another clear night.

Secondly the contrast and color was much stronger in the refractor. For example, the SEB is faint in the C6 but plain as day in the ZS66. The GRS was visible last night but I  think the smaller scale in the refractor worked against it.

Thirdly I'm not sure the C6 has revealed much more detail. On Saturn, the ZS66 seemed to show better definition of the rings including shadows on the rings. I guess on a night of excellent seeing the C6 would pull ahead, but I don't exactly live on a mountain-top.

Finally, even when I pushed magnification to 0.5 mm exit pupil, floaters were less of an issue in the refractor than the C6. I wonder if this comes down to what photographers call bokeh - the smoothness of out of focus objects. Mirror lenses for cameras are plagued by very rough and intrusive bokeh because of their central obstruction while a good refractive camera lens can have much smoother bokeh. So maybe what troubles me with the C6 isn't just the floaters  but the noisy bokeh of the floaters?

I won't get rid of my C6 - it excels at deep sky and some kinds of doubles - but I am definitely saving up for a bigger refractor.

Fascinating report! I found similar when comparing my 102ED refractor and my C8 on Mars a couple of years ago, although the smaller scope had binoviewers. The full report is here for your interest. I also tried my ZS66 with binoviewers on Jupiter and was suitably amazed at the detail it showed. 🙂

[Stu]

I can generally only agree with the comments about the capabilities of nice apo refractors 😀👍. I’m very partial to them myself, particularly my two 4” fluorites the unmentionable T** and Vixen FL102S. They tend to present stable views that stand careful observing to draw out the detail. I find them more restful if you like, vs the ultimately more detailed but less stable views from larger scopes. The latest Starfield 102mm f7 scopes seem to be a perfect balance of price vs performance, and hopefully open this up to a lot more people.

Over the years I’ve posted a few things which may be relevant and/or informative.

The first two here relate to the kinds of detail visible under good conditions in a 4” scope:

 

.....and finally, just something a little contradictory 😜. Refractors perform very well in varying conditions, but a decent larger aperture scope will pull away under good and excellent seeing. This was a report on observing Mars near opposition through my Vixen Fluorite and Orion Optics 8” f8 1/10th wave dob. As you will read, the Vixen barely got a look in as the detail visible in the 8” was substantially better and more rewarding. I do think that SCTs can suffer compared with, say, a long focal length newt of similar aperture. Collimation errors and cooling issues given the extra pass down the sealed tube account for a lot of that I think.

Those are my thoughts anyway. Everyone needs a 4” apo doublet 👍👍

Stu

[JeremyS]

5 hours ago, dweller25 said:

I also like a nice refractor, or two 😁

Or eight 🤣

[Ags]

I am hoping to get out again tonight to try 0.5 mm exit pupil on Saturn, I only discovered the very small exit pupils were viable in the refractor when Jupiter was up and Saturn had drifted behind Tower Block C due south of me.

Edited August 30, 2022 by Ags

[JeremyS]

12 minutes ago, JeremyS said:

Or eight 🤣

I should add that by no means are they all Taks.

Only seven are.

[Ags]

Saturn has been duly observed at 125x, or 0.528 mm exit pupil, using a Speers WALER 4.9 mm with 1.6x extension tube. The ZS66 blows away (not that phrase!) the C6 on Saturn. Clearly visible in the little frac: Cassini Division, the ring passing in front of planet, traces of surface detail, planet's shadow on the rings. I must say I am happier looking through a telescope that I feel is overperforming rather than one that seems to be doing the opposite. Also, absolutely no traces of floaters in the frac - I am sure they were there but indistinguishable from the seeing ripples.

Two hacks I am using to boost the refractor's performance: a celestron prism diagonal to reduce the residual CA of the scope (it really does work - on the right scope!) and a Wratten #8 to tame the atmospheric dispersion.

[dweller25]

I just came in from looking at Saturn at x150 in a 4” refractor and the view was very unstable, soft and low contrast. I could see some surface banding but could not see the Cassini division at all. I seem to have dreadful seeing where I live 😕

[Ags]

It is very low, not a good decade for Saturn viewing...

[RobertI]

21 hours ago, Ags said:

Saturn has been duly observed at 125x, or 0.528 mm exit pupil, using a Speers WALER 4.9 mm with 1.6x extension tube. The ZS66 blows away (not that phrase!) the C6 on Saturn. Clearly visible in the little frac: Cassini Division, the ring passing in front of planet, traces of surface detail, planet's shadow on the rings. I must say I am happier looking through a telescope that I feel is overperforming rather than one that seems to be doing the opposite. Also, absolutely no traces of floaters in the frac - I am sure they were there but indistinguishable from the seeing ripples.

Two hacks I am using to boost the refractor's performance: a celestron prism diagonal to reduce the residual CA of the scope (it really does work - on the right scope!) and a Wratten #8 to tame the atmospheric dispersion.

Interesting to see the ZS66 outperforming the C6 so much on Saturn. I also use a prism diagonal on my ZS66 and I haven't noticed any CA at all - it might be there if I were to look really hard, but if it's not obvious and is not interfering with the observing, then it's effectively absent for me! I find orange and red stars stand out really nicely with this scope, perhaps the 'semi-apo' glass helps there.

[Ags]

I too have noticed the ZS66 shows reds and oranges very well.