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Ceph and Cass

80ED v ZS71 - The shootout begins


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I've seen a few posts with people asking about & comparing the ED80 & the ZS71 for AP. So I thought I'd post up my impressions & findings as I test these out to determine the direction for my next imaging setup. I'm hoping that the ZS71 will have better star control than my much loved ZS66, which tends to show star bloat in RGB.

My last imaging session was nearly 4 months ago & whilst waiting for clear dark skies to return I've been collecting kit for next seasons rig. My plan is for a triple shooter and I've narrowed the affordable scopes down to 80ED's or ZS71's. Well, about 6 weeks ago I picked up a very clean, used ZS71 (2013), to compare with my 80ED and I just can't wait for dark skies any longer. So tonight I finally got back into the obsy and setup the 80ED & ZS71 side by side.

Pier mounted NEQ6

Each is fitted with an .85x reducer/flattener. This takes the 80ED down to f6.37 and the ZS71 down to a nice f4.7

The CCD's are Atik 314L+'s and (because it's still not astronomically dark here yet) I've fitted a Baader 7nm Ha filter in the train for the first image test.

I normally cool to -20c but it's warm tonight so settled for -10c

Guiding is with a 50mm finder/guider (SX CoStar) & PHD

Focused with Bahtinov masks

NGC6888 The Crescent Nebula

These are the first uncropped single 10 minute subs (taken at the same time under the same conditions) to roll out. No calibration, just an auto stretch in PixInsight. It gives you an idea of the field of view and the depth each scope allows for the same exposure time. I've probably got an hour or so's usable data with each one before the clouds have rolled in. I'll shoot some flats & bias later (I don't use darks with the 314's) & follow up with stacked versions. I think it might still be a few more weeks before I get to try RGB.

80ED

post-11176-0-47753000-1375493201_thumb.j

ZS71

post-11176-0-45142300-1375493224_thumb.j

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This is quite handy for me as well as i may be looking at a new frac myself soon.

The ZS71 seems to have more gassy data (if that's what it is ?) than the ED80 or is it because the ED80 is slightly a wider field ?

Nice shots for 10 mins btw.

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This shows the different focal lengths well. However, narrowband (as your post implies) is not a real test of the apo-dom of a scope. The real test will be RGB. I used to find that my Mk1 pre-CCD era Genesis (late eighties) was pretty well identical to a Tak FSQ in narrowband but, not surprisingly, was blown out of the water for CCD broadband, notably in blue.

This is a good test. It will produce o lot of interest, I think.

(Agree over the ZS66, too. Super for NB, bloatish in RGB. I still have mine.)

Olly

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  • 1 month later...

Well, a month on & I've finally got a bit more data to share. Not for want of trying.. :icon_geek:

Here are some LR & B on the Elephant (IC1396). I've yet to get a clear sky for G. I normally shoot sequential RGB so at least I get a full set but I only have one electronic FW at the moment, the one on the ED80 is manual & I want to capture both sets at the same time so they are under identical conditions.

L&B were captured on 03/09 & R on 04/09 I think the seeing was a bit better on the 4th so would have benefited the L&B better but beggars cant be choosers.

All at -10c using Baader filters. NO calibration, aligned & stacked in PixInsight, applied an automatic stretch using the ScreenTransferFunction & that's it. Just noticed looking at the R framing, the alignment of the minimount on the ZS71 was slightly out in my rush to beat the clouds. Yes.. if I were imaging this target "properly" I would have turned the sensors 45 degrees to frame the long side.

L is 6x600

B is 6x300

R is 8x300

I'll not comment on my interpretation of these so far just yet... I'll leave that for the more experienced of you :smiley:

Fingers crossed for some G soon so I can at least have a bash at putting it together. Any suggestions on targets & the way tests should be done welcome.

ED80 L post-11176-0-36829700-1378580239_thumb.j ZS71 L post-11176-0-45918400-1378580232_thumb.j

ED80 B post-11176-0-11428200-1378580237_thumb.j ZS71 B post-11176-0-91627600-1378580229_thumb.j

ED80 R post-11176-0-70459300-1378580241_thumb.j ZS71 R post-11176-0-69889500-1378580234_thumb.j

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Might have a problem. Managed to get some G tonight and just having a look at combining the RGB. Whilst the ED80 sets look normal the ZS71 don't. Looks suspiciously like the colour channels are wrong, I've a horrible feeling that running multiple instances of Artemis capture has caused a problem with the EFW2 filter selection. Not been a very good night.. it's the best I've seen this side of summer.. and no work in morning! So what happens.. lost 3 hours to what was a cold welded spacer/adapter coming loose & causing the CCD on the ZS71 to rotate.. must be due to the noticeable drop in temp tonight, an windoze deciding to lock up on the netbook. Now I find this.. sometimes I wonder why I bother :BangHead:

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Well, if the blues are blues and focus was good for both the ED80 is well ahead. Star bloat is far less. Some trace of the shape of a bright double is visible but is entirely absent form the WO.

Olly

My fear too, so I shot some more B as well last night. Once I realised the CCD/FW had come loose & slipped I rechecked focus (using B/mask, still have to get Focusmaster working). Unlike with the ED80 the Baaders don't seem parafocal & B didn't seem to be quite focused.

Anyway, after sorting that the results initially look the same. Ill post them up in a bit. The other thing I'm wondering about is difference in speed as the ZS71 is much faster. I've been using the same times for both scopes. Would over saturation have a part to play in this?

Sent from my iPhone using Tapatalk - now Free

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Doh, not enough sleep.. I meant FocusMax before, Focusmaster works fine.

Yes, I probably have to get as close to comparing "apples" as I can. So, I'll need to find a way of calculating correct exposure times for each scope. Think I need to find a target that doesn't require a lot of time to prove this, otherwise it'll be next year before a decision is made!

I have to say, I "wanted" the ZS71 to shine through but the ED80 is a hard one to beat at this level. At the moment the (B)lues on the ZS71 are looking very similar to the ZS66. :sad: Now that doesn't mean it's no good, I love the wider FOV, I'm keen on NB (Astrodon 3nm keeps calling me :evil: ) & it's faster, so it may still be right for me.

The downside for the ED80 against the ZS71 is the speed and the stock focuser. I've been lucky having tweeked & fitted a focus motor to it it's now stable & holds focus night after night, (or maybe it's the speed/optics that are more forgiving?). My goal is choosing the right scope for a triple shooter, trying to fit 3 of these as opposed to 3 of the ZS71 is a bit more daunting, size & weight wise.

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I have the older ZS70 which performs fairly similarly. It’s been good for narrowband imaging particularly Ha and SII. I find OIII can appear a little bloaty.

RGB wise the results seem much the same as yours above. I'd also agree that "the Baaders don't seem parfocal". As an experiment, I’ve stuck a Baader semi-apo filter into the imaging train and that has helped tighten the stars somewhat.

Like you, I was rooting for the ZS71!! As you say the wider fov is great. I have been considering a double or triple imaging rig based on these ZS scopes.

It has been very useful to see the results of your experiment. Thanks.

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I have to confess that I was rooting for the ED80! I find WO an irritating manufacturer, intent on a pretty cosmetic finish at costs but with a record of getting lots of important things wrong, even grossly wrong. So there's my prejudice coming through!

Baader filters are parfocal. Of that I'm as close to certain as I can be. If you are refocusing for blue, for example, that is because the telescope is not parfocal with itself - ie it isn't apochromatic. The ED80, which I've never owned but which I've seen in action any number of times, is incredibly well corrected for a doublet. Is the Takahashi Sky 90 any better? That would be another good shoot out!

Olly

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Hehe.. send me a sky90 Olly and I'll let you know :grin:

I shot some NB into the dawn last night too, after faffing about about with this my soul needed feeding on what turned out to be the clearest night I've had since the end of last season.!

I'm also seeing the same on the OIII as the Blue. This is the same as the ZS66 really although It does look a bit tighter I cant be sure it's not my slowly improving processing skills that can account for it. :p

The Baaders are parfocal on the ED80 no doubt but it looks like the B & OIII on the ZS71 & the ZS66 need refocussing with them, so yes it's not the filters but the optics. I'm a bit disappointed really as I had high hopes, the feel, finish & speed offering of the ZS71 is really nice & lured me in... you'd approve of the R&P focuser at least Olly surely :grin:

So, I'm not sure there's another contender to beat the ED80 in speed & FOV then at this level.. maybe I have to look at it another way & swap the 3 x 314's for 460's :eek: ... she'll kill me!

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I bought the ZS70 2nd hand earlier this year to take to France during our summer holiday. It is an ideal size for travelling. Now home, it will come out occasionally but its not my main imaging scope...

As for rooting for either scope - really I'm happy to sit on the fence! I have an SW ED80 - it is a cracking scope that I'm very happy with. That is until some point in the future when I make the mistake of perhaps looking through a Tak (or similarly expensive brand).

In my previous post's quote, I meant that the lack of Baader filter parfocal-ness applied to the ZS70. Apologies if that was not clear, so: -

Baader filters are parfocal.

I agree, yes they are - just not in the WO scope - which is as you state, is entirely down to the scope. They are fine in my SW 200p and ED80.

Andy

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I bought the ZS70 2nd hand earlier this year to take to France during our summer holiday. It is an ideal size for travelling. Now home, it will come out occasionally but its not my main imaging scope...

As for rooting for either scope - really I'm happy to sit on the fence! I have an SW ED80 - it is a cracking scope that I'm very happy with. That is until some point in the future when I make the mistake of perhaps looking through a Tak (or similarly expensive brand).

In my previous post's quote, I meant that the lack of Baader filter parfocal-ness applied to the ZS70. Apologies if that was not clear, so: -

I agree, yes they are - just not in the WO scope - which is as you state, is entirely down to the scope. They are fine in my SW 200p and ED80.

Andy

Yes, it's ideal for travel, I can't see me wanting to part with it unless I'm financially strapped. However, I'm set on putting the triple shooter together & right now I'm thinking if SW put R&P focuser's on the ED80's I don't think anything would touch them for miles. Perhaps the next step up being Borg & then Tak?

Probably the morale of this story is a single "quality" scope is within financial reach and is great if you have decent skies. If you're in the UK & you want to get your data within one season.. you need to compromise or take the hit... kidney anyone.. :eek:

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Yup.. been thinking about this overnight. I reckon the way forward with the multishooter is to find a quality well corrected scope of similar FL/FOV to cater for the B & OIII. Then use the "budget" scopes to cover the rest.

I feel another thread coming on..

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There is something incredibly nice about the using the Tak Baby Q and knowing that any errors are your fault. :grin:

Olly

Not me you need to convert.. If only you can convince my financial controller :embarrassed:

I've been doing some sums with the current CCD's I have & out of the ED80, ZS71 that I already have... the next possible step up maybe being Borg and the pipe dream Tak... :grin:

Resolution wise.. (arc secs per pixel) with the 314L+'s , the ED80 looks like the best match if I understand this correctly?

314L+ & ED80 + .85 FR/FF = 2.6 arc secs /pp

314L+ & ZS71 + .8 FR/FF = 3.9 arc secs /pp

314L+ & Borg77ED @ f4.3 = 4.03 arc secs /pp

314L+ & FSQ85 + .73 FR/FF = 4 arc secs /pp

Anyhow, I also shot some NB with the ZS71 the other night so thought I'd add it to the thread so it's NB performance can also be seen.

My HST palette processing skills are still firmly in their infancy but here's 6x900 Ha, 6x900 SII & 5x900 OIII

The heart of IC1805

post-11176-0-88632700-1378840589_thumb.j

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There are maybe a couple of OTAs you havent considered. For the 314 pixel size, I think 400mm is as low as I would dare (3.33 /pp) - which is the focal length of the long awaited (and STILL waiting) Espirit 80ED. Or, you can plump for a reduced 80/480 which gives 3.46.

Either way the next step has to be at least f5, otherwise youre not really gaining much over what you have now. Im pretty much in the same situation in regard to researching any potential replacement for the 80ED (had to whisper that in case it hears me!) :)

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Well, yes I had thought about them but the Esprit is still an unknown quantity, the reports of the one that "seems" to have been let loose in Canada hasn't got off to a good start & gone quiet. The 80/480 had too many reports about pinched optics in the cold... I'm not taking a lucky dip there. So I hadn't brought them up, but you are right they deserve to be mentioned and I am secretly hoping the Esprit delivers as it's the only thing I can think of that may save me from getting a kicking from the other half if she catches me drooling over Taks again :shocked:

I've been playing with the limited subs I've managed to get so far with the ED80 & ZS71 and I can't quite put my finger on it but the ED80/314 combination looks "sweeter" to my eyes even in NB. Can't quite put my finger on it but I prefer it even though I wanted to like the ZS71's wider FOV. I'm tempted to get another anyway & run a dual shooter till the Esprit gets a decent outing at least.

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I was asked about the ED80 I'm using for this. So to clarify I'm comparing the Skywatcher 80ED (Blackdiamond) and the William Optics Zenithstar ZS71 (2013)

Now, another scope that's come up in discussion is the Equinox 80 (£520). As far as I know it uses the same optics as the SW80ED I'm using but has a shorter FL of 500mm & f6.25. Looking around it seems the reducer of choice is the Televue TRF2008 (£235) taking it to f5. with the 314L+ its about 3.3 Arcs Per Pixel. A possible contender?

Now.. I've not got any more RGB yet but here's the processed HST from the ZS71

post-11176-0-79572800-1379154648_thumb.j

HA from the 80ED

post-11176-0-31701900-1379154651_thumb.j

And the 80ED overlay so you can see the difference in FOV

post-11176-0-50282900-1379154646_thumb.j

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