Zenithstar 73- Are these stars bloating or I'm too picky again? - Forums

Topic starter

Aug 13, 2023 · Edited: Aug 13, 2023

I recently aquired a W.Optics Zenithstar 73. I have the Flat73 adjustable flattener with it.
This is my 2nd W.O. telescope so far, my first one was the 61, sold it after a year due to not liking how the stars looked like (pinched optics)
Now, it looks like I am either too picky and got spoiled by Newtonians, or this telescope is bloating the stars.
I took 5-10-15 second subs, all guided, focused with EAF.

The EAF cannot get better stars than 4.10 HFR. I tried several runs, it always arrived to the same focal point with a .97 score on the hyperbola curve.

The camera is QHY183C which has a UV/IR glass.

It actually doesn't matter what length of subs I do, even a 2 second sub shows enormous stars (according to me).

Tell me if this is typical image for this scope or it has collimation issues or something else?

See this sample 15 second image, auto-stretched by AsiFitView, I used 0 gain to avoid any gain-related over saturation or bloating.

I also stacked 300 of these subs but the results were rather disappointing with huge stars and looking over exposed, although with 15 second subs with 0 gain the histogram looked good.
Object: Double Cluster in Perseus.

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andrea tasselli

Frequent contributor

Aug 13, 2023

From what I can see the image isn't colour calibrated and you should do that before drawing a final judgement. This said yes they look distinctively bloated as the colour correction of these refractors isn't that great, especially when coupled with the field flattener.

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Frank Szabo

Topic starter

Aug 13, 2023

andrea tasselli:
From what I can see the image isn't colour calibrated and you should do that before drawing a final judgement. This said yes they look distinctively bloated as the colour correction of these refractors isn't that great, especially when coupled with the field flattener.

*It's just one raw .fits file saved as a .jpeg. I didn't think I had to color correct a single sub to figure out if the stars are bloated or not.

andrea tasselli

Frequent contributor

Aug 13, 2023

It is good practice do just that since the right colour balance will affect how bloated the stars will look.

Guiem Kimi

Aug 13, 2023 · Edited: Aug 13, 2023

I had bloated stars in the blue channel with my TS Optics Photoline 130 (even though it is an APO triplet and it was re-collimated at the factory). The Astronomik L3 luminance filter improved that blue channel quite a lot (I was using the L2, which I use with other scopes and works like a charm)

As they state in their website:

L3 filter is designed for users of refractors with a less-than-perfect colour correction and in combination with the new Deep-Sky RGB filters, the L3 filter will minimise the problem of bluish halos around stars.

So, after going from L2 to L3, the results were much better for that scope. I can provide some subs that I took with the two filters in order to see the differences.

Guiem.

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Joe Linington

Aug 13, 2023

I agree with the above. I use the Astronomik L3 in my FPL51 doublet (SVBony SV503/102ed) and it improves the blue halos a lot compared to my ZWO or SVBony UV/IR filters.

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Frank Szabo

Topic starter

Aug 13, 2023 · Edited: Aug 13, 2023

I don't think I have a blue halo problem. I am aware what blue halos with FPL51 and PK glass, this is FPL-53. My Svbony 80mm has blue halos and much much smaller stars, (despite the blue halos) despite being half the cost of this telescope.
I also have the final image (300 subs) and the stars are enormous and that's color corrected.
I expect more from a $800 telescope (plus $200 for the flattener), otherwise I'm just gonna stick with Svbony for $500. This supposed to be an upgrade, but so far it's a downgrade for more money.

I also searched around astrobin for this telescope and I see much smaller stars from users. I also watched Astrobackyard who did a testing on this, and he is doing like 3 minute subs. Mine bloats at 2 seconds.
I'm asking for a replacement , since only bought this 2 weeks. ago.

At the meantime I'm back to my Newtonians.

Final image (photometric color corrected)

Image done with 80mm Svbony:

enta

Aug 14, 2023

Looks like bloated stars tbh.
Never been super satisfied with my Zenithstar 81, here's a image I took with it
But I've never seen stars bloating much with my scope, used a generic flattener and the L-Extreme in that pic.
I think for the money it's a nice light scope.

Idk how experienced you are, but maybe it's not a scope issue you got there.

Frank Szabo

Topic starter

Aug 14, 2023 · Edited: Aug 14, 2023

Looks like bloated stars tbh.
Never been super satisfied with my Zenithstar 81, here's a image I took with it
But I've never seen stars bloating much with my scope, used a generic flattener and the L-Extreme in that pic.
I think for the money it's a nice light scope.

Idk how experienced you are, but maybe it's not a scope issue you got there.

Just for the heck of it, (I'm trying to be sure that I'm not just seeing things), I imaged the same object last night with the Svbony 80ED, which supposed to be an inferior scope, as far as optics. Not in this case.
The stars look more rounded (even with not so great guiding) and this is actually a 30 second exposure (same camera, same 0 gain same offset) and even the scope is faster (F5.6 vs F5.9). So faster scope/ longer exposure should make the stars even bigger on a scope that has obvious chromatic aberrations due to lesser quality glass (PK) doublet.
Here is a 30 second sub with the same camera (QHY183C) and Svbony 80ED, again just autostreched and saved as .jpg- no color correction. Now, this has CA, and that's expected. And yet the stars are much smaller and more pinpoint. The Zenithstar should be beating this by all means, and it probably would if it was calibrated the right way from factory, that's why I wrote to the seller yesterday, I'm still within the return period.

enta

Aug 14, 2023

Really weird, always thought highly of WO, let me know what they are saying when they get back at you

Marc V

Aug 15, 2023

Hi All,

Interesting exchange... I also possess a ZS73, and like @frankszabo75 I find my star "big"... At first I thought it was just me... LOL may be it is not...

Clearsky

Sean Mc

Aug 15, 2023

I returned two flt91’s before going with a different brand. From all the posts I’ve read in various places, you can get duds from ANY manufacturer. Right or wrong, I now look at spot diagrams and go from there.

enta

Aug 15, 2023

Damn, maybe WO is not what I thought it is.
I went with Explore Scientific now and I'm very happy with my new scope, but I heard bad quality control from ES as well.
Guess you're never safe, unless you buy really high end stuff like taka or tec etc.

stuffedcrust21

Aug 15, 2023

Not sure if this will be relevant for you but worth a try

Ivan

Aug 15, 2023

They look like the stars from my z73. I always wonder as well why my stars are so bloated looking, especially compared to other, faster, bigger light gathering scopes. Even when I shrink them, they just never look as good as other folk's stars.

Elmiko

Aug 15, 2023

I think the stars look pretty good. It could also be seeing or sky transparency.

dkamen

Aug 15, 2023

Hi,

If you ignore the bigger stars for a moment and focus on the tiny ones, I don't think the Svbony is sharper. Quite the opposite. And the ZenithStar reveals visibly more (and sharper) tiny stars, despite the shorter exposure and the shorter focal length. It also renders the differences in apparent magnitude more clearly.

This is especially evident if you zoom 2x1:

I think the only reason your bigger stars are blown is the ZenithStar's clearer glass, which is letting too much light through (perhaps also your seeing was less than ideal). IOW it's a feature, not a bug. You could simply stretch the stars less aggressively. If you are taking photos of nebulae, just use a good star mask to process stars and nebula separately.

Cheers,
D.

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Karl Theberge

Aug 15, 2023

Personally, as soon as I get my RC6 going, im done with my ZS73 and any other WO scope.

I was diseapointed with it, most people I know where diseapointed too. Their flattener reducer is a piece of garbage like no other.

I would rather go with a Svbony telescope that perform better for cheaper. So far WO only offer "bling bling" look telescope with 1mm more aperture (on paper).

Joe Linington

Aug 15, 2023

Hi,

If you ignore the bigger stars for a moment and focus on the tiny ones, I don't think the Svbony is sharper. Quite the opposite. And the ZenithStar reveals visibly more (and sharper) tiny stars, despite the shorter exposure and the shorter focal length. It also renders the differences in apparent magnitude more clearly.

This is especially evident if you zoom 2x1:

I think the only reason your bigger stars are blown is the ZenithStar's clearer glass, which is letting too much light through (perhaps also your seeing was less than ideal). IOW it's a feature, not a bug. You could simply stretch the stars less aggressively. If you are taking photos of nebulae, just use a good star mask to process stars and nebula separately.

Cheers,
D.

I will agree that the small stars are tighter in the WO 73 but the SV503/80 shows more and dimmer stars in both samples, as it should with a larger aperture.

dkamen

Aug 15, 2023

Joe Linington:
Hi,

If you ignore the bigger stars for a moment and focus on the tiny ones, I don't think the Svbony is sharper. Quite the opposite. And the ZenithStar reveals visibly more (and sharper) tiny stars, despite the shorter exposure and the shorter focal length. It also renders the differences in apparent magnitude more clearly.

This is especially evident if you zoom 2x1:

I think the only reason your bigger stars are blown is the ZenithStar's clearer glass, which is letting too much light through (perhaps also your seeing was less than ideal). IOW it's a feature, not a bug. You could simply stretch the stars less aggressively. If you are taking photos of nebulae, just use a good star mask to process stars and nebula separately.

Cheers,
D.

I will agree that the small stars are tighter in the WO 73 but the SV503/80 shows more and dimmer stars in both samples, as it should with a larger aperture.

It depends I guess, look at the three stars at the bottom left, they are a smudge in the svbony image. In other parts it does show more stars. But keep in mind the exposure is double.

dkamen

Aug 15, 2023

Karl Theberge:
Personally, as soon as I get my RC6 going, im done with my ZS73 and any other WO scope.

I was diseapointed with it, most people I know where diseapointed too. Their flattener reducer is a piece of garbage like no other.

I would rather go with a Svbony telescope that perform better for cheaper. So far WO only offer "bling bling" look telescope with 1mm more aperture (on paper).

Hi Karl,

Obviously I am wishing you otherwise, but there is a very strong chance you will find out that a RC6 can disappoint you in an enormously more diverse number of ways that a Zenithstar 73 (or any 3" refractor for that matter). Also, I do not see how one can replace the other, the FOV of the RC is many times smaller, they are not meant for the same targets.

Cheers,

Dimitris

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