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Upgrading the diagonal - tangible benefits?


newman

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Hi everyone, I've been wondering about a possible diagonal upgrade on my 120/1000 Sky-Watcher achromatic refractor. I bought it recently and even though I'm quite happy with my first scope, there's always room for improvement :hello2:

The scope came with a 2" 90deg diagonal - this thing:

1z2mxdx.jpg

It has no markings on it and I was unable to find specs on it online. I'm guessing they're not putting premium equipment like this with the scopes so it's probably one of those standard 91% reflectivity ones SW bundles as stock with certain scopes. I'm wondering if I would see a tangible benefit from an upgrade to something like this?

GSO 2" 90-deg 99% Quartz Dielectric Mirror Diagonal for Refractors

The local store has these in stock. According to the specs it's a 2" quartz dielectric diagonal with 99% reflectivity. Assuming my current diagonal has 91% reflectivity, my newbie logic tells me that I should get 8% more light to the ep with that diagonal? If so, this would (again, noob logic) give me somewhat brighter images of DSO's?

What I'm interested in are opinions of astronomy enthusiasts here - would such an upgrade produce a visible difference in DSO brightness, for instance? Would it be worth the money or should I just prioritize other stuff, like better ep's than the scope came with (which I do plan on getting, too)? I'm mainly trying to work out an upgrade priority list. So far I thought I'd upgrade the big stuff first (diagonal, steel tripod for the mount to reduce vibration, ra/dec motors, telrad..) and then move on to eyepieces since there's so much choice one could spend a lifetime upgrading his ep collection.

Another noob question: does using a 2" diagonal + 1.25" adapter + 1.25" ep's give me any degradation in image quality because an adapter is being used? I'm guessing no but I would like to confirm this.

Thanks in advance!

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Hi newman, fellow noob and evostar 120 owner here :hello2: I was considering upgrading the stock diagonal to a wo model, but from what i could gather from sgl members discussing this is that theres minimal differance so I decided to wait and concentrate on something that will most definatly improve the views, namely ep's(the basic ones that come with the scope are god awfull compared to the models i upgraded to). Will defo upgade in the future though just for the build quality if nothing else, im sure I read on here that its worth upgrading if you plan on using huge 2" eps(wouldnt want some cheapo diagonal hitting the floor and taking your lovely new 2" 38mm wide angle ep with it).

This is second hand knowledge though so might want to see what someone who has actually made the change has to say about it.

One thing I can recommend doing from personal experiance is regreasing the focuser on the evostar 120, made a big differance for me, much smoother now.:D

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First off, as the 'quality' of gear improves so does the price but not in strict proportion as I'm sure you have already found out. As the diagonal forms an important role in transferring light from the objective to the eyepiece, it's important that its reflectivity is as good as you can get it. Now I will express a personal viewpoint which others might well disagree with. I believe it is worth getting a dielectric type simply because this coating will allow you to clean it without damaging the surface (reflectivity) and also because a proven 99% WILL be better than 91% but not such a difference that will have all your neighbours banging on your front door to beg for a glimpse of Saturn! I guess what I am saying is that at least by owning a dielectric version you will at least know that any problem with resolving details will not fall at the foot of this part of the light path and so it must be something else like the collimation or quality of eyepiece. I would add that I have a Williams Optics version which appealed to me because it was constructed in part from carbon fibre and so appealed to me aesthetically but its quality is no better or worse than any other similar dielectric. So fashion aside, buy the cheapest one and that will be fine and you would have to own an expensive refractor to really see any difference and even then it would be small.

The smaller 1.25 adapter makes no difference to quality of image. The 2" facility is really for larger eyepieces 32mm, 40mm that also have greater fields of view like 80 or 100 degrees.

The biggest difference you could make to DSO brightness is to observe from as dark a sight as possible. Flocking the inside of the tube won't improve contrast but will help prevent it diminishing. I guess the Skywatcher is already baffled and painted black which will probably suffice. Better eyepieces will also 'maximise' and that is the key word here the quality of image that the objective lens has mustered for your eyepiece. Good quality eyepieces will through coatings and design, certainly help maintain and assist with providing a sharp image from the light be sent down the tube of your scope. As said at the beginning, prices far outstretch the advantages gained and it must be remembered that the available field of view, the sharpness of stars across this whole field, eye relief etc all help to construct the final price which could pay for advantages that might be of little relevance to your observing and therefore your wallet. The eyepieces that are supplied today bare very little resemblance to the jam jars that used to be supplied many years ago and certainly will keep you going until you decide what your want to observe or focus on in the longer term.

Lastly, I would suggest getting a Telrad as part of your upgrading as there are relatively cheap and make finding objects a lot easier than a finder that provides a view that is back to front and upside down. A RA motor will allow you to stare all night without touching the scope which as I'm sure you're aware induces vibrations and will certainly make focusing easier as you will have one less thing to keep adjusting to secure pin point images. All the above is my personal view and as I said others might disagree. In the end, it's down to personal preferences and how you observe.

Clear skies

James

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Thank you both for the info. Right now it's looking like I might postpone upgrading a diagonal in favor of things which will provide a bigger difference. As for cleaning a non-dielectric diagonal, I own an air compressor and an airbrush used for model kit painting - I frequently use an empty airbrush hooked up to the compressor to dust off certain things that are either too sensitive or hard to reach by hand/cloth. I believe cleaning a regular diagonal this way would probably work well - since you don't touch the actual mirror with anything but air.

I'm already planning on getting a Telrad, after comparing it with a Rigel Quickfinder and a similar Celestron system (forgot the name) it seems like the best option for me. After 8 dark nights in a row testing the scope I realized full well what the benefits of a non-mag sight like that would be. I also plan on replacing my straight-through 9x50 finder scope with a 90deg prism one. Trying to look down the finder scope when the refractor is pointed upwards near the zenith is almost impossible - a 90deg amici prism would work wonders there. Also already got the Ra/Dec motors planned as well as a steel tripod upgrade for my mount.

Keano, nice to meet a fellow sw 120/1000 refractor owner! Could you pm me (or just post here) what ep's did you get? I still only have what came with the scope and while I did look at some possibilities, the opinion of someone who has the exact same scope and already got some ep's for it would be very valuable, indeed.

Thanks!

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Hi newman and thnx jbm1165 for the info on the diagonals saved me some ££'s :D, newman the ep's i upgraded to were the celestron x-cel 5/10/25mm I was amazed at the differance build wise compared to the basic ep's supplied with the scope (mine were the sw 10mm and 25mm) there big and they just look a better quality overall. As too the veiwing differance I thought it was a very noticable differance,things seemed clearer and sharper and there much more comfortable to use (i'd imagine that to be the eye relief).Overall im very pleased with them,also just recieved a tmb design 7mm which im chuffed with as it only cost £41 delivered and it seems to a very nice ep, not as flashy as the x-cels but i'll happily take perfomance over a paintjob any day:).

P.s I wear glass's so eye relief is important to me in an ep which is the reason I went for the x-cels (it didnt hurt they were on offer from flo as well), tbh if it wasnt for me wearing specs I probably would have went with the sw super plossls as I doubt i'd notice the differance between a decent plossl and something crazy expensive like a nagler. As with most things though your milage might vary so take all this with a pinch o salt, anyways I hope you get as much enjoyment from your scope as I have from mine.:hello2:

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Oh I already got loads of enjoyment from my scope :hello2: The local vendor has something that's tempting despite the hefty price - here's a link to it (considering a 16mm variant). An eyepiece like that in an f8.3 scope would probably get a lot of use - provided it's as good as advertised...

Anyway, thanks for the info!

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They look like clones of the William Optics UWAN's and Skywatcher Nirvana's. The Nirvana 16mm costs around £145 / 160 Euros in the UK so the price is a little high but not outrageous.

Designing and building a well corrected eyepiece with an 82 degree field of view is not going to be cheap unfortunately. A Nagler, which would perform little or no better in your scopes would cost over £100 more.

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