[codemonkey (Lee)]

I managed to get a brief first light with the new Skywatcher Esprit 120 last night. As I learn more, I'll update this thread.

The Focuser
First things first, the focuser. The focuser is a really big deal on an imaging scope, and it's almost always neglected. This usually results in the purchase of expensive aftermarket focusers. Honestly I don't understand why manufacturers do this; either ship it with a usable focuser, or reduce the price and ship it without one at all.

Skywatcher claim that the focuser fitted to these as standard will handle payloads of 5kg while focusing, and 10kg locked.

My imaging train consists of a SX Trius 674 CCD, Orion Nautilus electronic filter wheel (with LRGB, OIII and Ha filters) and a focal extender. I think I weighed it all at about 2.5kg once, either way, well under the 5kg limit.

On unpacking one of the first things I did was stuck my ccd/efw on the back of the focuser and see if it would hold it without any tension applied. It did not; it immediately began slipping. Adjusting the tension/locking lever enabled me to halt the slipping.

Speaking of the tension/locking lever, it's quite awkward. I've never used a focuser with this type of locking mechanism and I'm not sure why they did it. On the bright side, it does seem to (without significant scrutiny) enable locking without shift.

In the field I was able to focus the CCD using the coarse-grained focus knobs, however inward adjustment with fine-focus knob didn't seem to work very well due to insufficient tension. You could say that's user error. I found that adjusting inwards with the coarse-grained control, then backing it out with the fine-grained enabled me to reach focus, even if it was a bit fiddly.

Another review I've seen mentioned the focuser having a series of tension screws that can be adjusted to enable smooth focusing with heavier loads. I'll be looking into making this adjustment and I'll report back.

Now something happened with the subs that I took last night, and I'm not sure what it is so it'll need further investigation before I can reach a conclusion on the focuser. After a few subs the stars got noticeably bigger, the images softer and the FWHM went up significantly. This could have been focus slip, or it could have been caused by user/guiding error: I forgot to turn the power up on the dew heater on the guide scope which caused some guiding issues. The dew heater on the Esprit was turned up well enough and was dew free. So it's possible there was significant focus slip during the subs, even with the focuser fully locked. I'll report back on this after the next clear night.

At this point I think I'll be able to adjust the focuser so that I don't have to look into a Moonlite/Feathertouch, but I'm uncertain. As I said, I'll try to adjust it and report back.

The Optics
In the past I've owned a Saxon ED100 doublet, Skywatcher ED80 doublet, William Optics GT-81 triplet, and a GSO RC8. I've not owned any premium refractors and barely used the GT-81 which is the only other triplet that I've owned.

I currently use SGP for imaging and have been using their statistics module to aid in focusing lately. SGP provides you with a Half Flux Radius (HFR) of stars across the frame. I've assumed this to be an average, but I'm not sure if that's the case. Anyway, we can basically say that a smaller HFR = sharper image.

With the ED100 the smallest HFR I saw was 1.47px. Last night, with the Esprit 120, I saw a HFR of 0.89. Now there's multiple variables at play here so we can't say that all of this is due to the optics, but I think it's safe to say that a significant amount is.

Now of course this is a totally unfair comparison. The ED100 is a doublet costing less than 1/3 of the price of the Esprit 120. The thing is though, it's this difference that I was looking for, it was this that would justify the price to me. How would this compare to a Takahashi? Who's to say.

One thing to note is that this analysis was done with a 11mm diagonal CCD chip and no flattener. And as you will see in the attached mosaic generated by PixInsight's AberrationInspector, the stars look pretty good across the entire field. Of course if you put this on a full frame sensor or even an APS-C sized sensor I wouldn't expect results as good as this. Note that this was generated from a single 430s frame, which was obviously subject to guiding/tracking fluctuations.

Speaking of the flattener, mine was missing from the box. According to my retailer, this has been known to happen with some of the Esprits because the flattener was packaged separately in some cases. I believe that info came from the local Skywatcher rep.

I have seen complaints in the UK that the Esprit were no longer shipping with the flattener, but apparently they should still ship with it over here. Mine is supposed to be mailed out to me shortly.

Everything else
The lens hood is retractable, which may help with transport but probably nothing else. It does have a locking screw (I think two actually, but my memory's terrible so don't quote me on that) which means it'll always stay up. That's a nice touch; my older GT-81 doesn't have one and relies on the tube rings being pushed flushed to the back of the hood to keep it up.

The lens hood does move awkwardly and doesn't feel very professional when compared to the smooth movement of the GT-81. But eh, it does the job and will stay up so I suppose that's what matters.

The scope comes with nice CNC tube rings and a Losmandy-D style dovetail, both of which are a big step up from the lower-end scopes and very welcome additions.

The scope also comes with a nice road case, complete with two wheels on one end, although I'm not sure how they'll go on typical terrain.

Also included is a diagonal, eyepiece and right-angle finder. As I don't do visual at all, these accessories will stay in their original packaging, never to see the light of day. Given the target market for this series of scope is mostly imagers, I question the inclusion of these accessories; they could be sold as optional extras as I imagine lots of imagers, like myself, would eschew finders in favour of platesolving, and probably never stick an eyepiece to it.

Conclusion
So far I'm happy with my purchase. I think going from a doublet to a triplet was a worthwhile investment, but if I were not into imaging I may not have been able to justify the cost.

I expect to be able to adjust the focuser so that it's realistically usable. A shame it didn't come like that out of the factory. If I'm unable to do so I'll report back.

Overall the mechanics of the scope (lens hood, focusing tension lever) feel a bit awkward and I'd hoped for better, but it's not really unexpected.