Nexstar 5i - First Impressions

[seiko]

As some may know I opted to go with a Nexstar 5i based on my previous ETX90, Nexstar 8i and CPC800 experience. Ultimately I wanted a more portable Grab and Go, fast and quiet slewing that I'd use more than the 8i due to to the ease of portability and more than the ETX due to more aperture.

As always, I was on a real tight budget so couldn't really afford the 6 or 8 SE variants and felt lucky when I stumbled on Dhind's "As new" stock of old 5i's. For those that don't know the 5i, it shares the same mount as the larger 8i which is still the fastest and quiestest of the Celestron mounts including the newer 6SE/8SE.

The scope arrived and as promised all items where in perfect condition. The corrector plate was a little dusty truth be told but I've left it as is as it certainly not hampering viewing?

I'm still saving for a powerTank but having tested the scopes slewing using a new set of batteries all appears well. The 5i/8i mount really does have a great slew speed and equipped with the older american motors is thankfully much quieter.

So onto the important part, optics, over the last few weeks many forum memebers have given great advice on the strengths and weaknesses of the grab and go goto scopes and having understood the 5i with it's 40% central obstruction would restrict contrast I was a little concerned especially as a scope with such a small aperture runs up against the ETX125 and smaller refractors. Well last night provided the first true clear sky in which I was able to view the moon and Jupiter using the standard 25mm plossl.

Firstly the good news, the moon looked great, very sharp, bright and compared with my other scopes perfectly adequate.

Alas, then came jupiter. oh dear, all I can say is that in my humble opinion the 5" SCT really struggles. Jupiter appeared as a small round white ball. No contrast at all, no bands no hint of colour! I could clearly see 5 pin pricks of light as the moons but overall I'm convinced my old ETX 90 provided better views? I know my 8" obviously did but I'm currently still in shock as to how white the planet looked? Not even a hint of Jupiters belts? is this really what a 5" SCT will do to planets with its central obstruction?

I appreciate the 25mm plossl is for all intended purposes the wrong tool for the job as it doesn't have the magnification to view Jupiter clearly but as I said, I'm convinced that my ETX90 and it's stock 26mm plossl came out on top in contrast and sharpness?

Am I missing something or did I just loose the ability to enjoy planetary viewing?

[seiko]

Had another chance to put the 5i through its' paces last night and I'm pleased to say that seeing conditions really helped the little scope perform very well.

Jupiters primary bands were clearly visible and other fine details. I think the only real missing item was any hint of colour but overall I was really pleased.

I'm not sure if this is even possible with the stock 25mm plossl but at very clear times I could make out what appeared to be a small round shadow, bottom right of the planet that naturally aligned with one of it's moons positions, the moon nearest to it on the right? Was this a moon shadow or simply a flaw in the optics?

Either way, fast, quiet slewing, super portable and clear optics!

[seiko]

Thought I'd post another update on the little 5i's performance and alas it's still not looking good.

I'm still without a Goto controller so there are a limited number of things I can find/view. M13 has been on my list for awhile and after 5 minutes of slow slewing on a diaganol line between Zeta and Eta I finally managed to get it in the eyepiece. Unfortunately using the stock 25mm the image was so dim and unresolved I almost wish I hadn't. M13 just so happened to be one of the last objcets I looked at through both my 8i and 800CPC using their stock eyepieces and boy was it nice. I remember over multiple nights seeing the mass of pin point of lights and thinking wow. I even showed the wife who too was taken aback as it really did look like many of the pictures we'd seen in books.

Last night however with plenty of transparency, steady seeing conditions, a stock 25mm plossl and the 5i I could hardly make out m13 at all. Very dim, no real dots of light and even after 30 minutes of viewing the scope simply hadn't revealed anything more.

With a hand controller and zoom eyepiece still to purchase at some point I'm now really considering my next steps carefully.

Will an eyepiece (15mm) that effectively matches the 81x of the default one on the 8i help the 5i when viewing M13? It'll obviously be dimmer but will it resolve the image into pin points of light as opposed to the dim smudge it appeared like last night?

If not then I think the journey with my 5i might be coming to a quicker end than I really wanted?

Finally, a few additional details that might help

1) the scope does appear to be colliminated. Star tests look absolutely text book.

2) I live in small town light poluted area although last night the sky really had a large number of stars on show,

3) The moon had yet to make an appearance.

4) Focus did appear to be fine.

5) Stock 25mm plossl used.

6) I'm no star navigator but I'd bet my house and everything in it that I was indeed looking at m13. Starry nights helps there

7) Imagine was very dim, no genuine pin pricks of light. more like a smudge with the occasional detail in the center.

8) The scope had indeed cooled for 30 minutes before viewing began.

Potentially an obvious question but is this what a 5i will do under these conditions because compared with the 8 it falls massively short?

[Doc]

You cannot really compare a 8" and a 5" for comparison. The extra 3" of aperture will show alot more thats for sure but your 5i should show quite alot of detail in M13.

By the sound of it contrast is the problem. Have you tried a better eyepiece or maybe a better corrected diagonal.

Are your seeing conditions OK.

Are you sure your collimation is spot on. I have never owned a SCT so cannot really help much more.

[seiko]

Thanks doc,

I only have the standard plossl at the moment so is difficult to know if that's the culprit. I'm convinced the views are darker than they should be though? Almost as if the scope has a slightly darker greener tinge to the image than it should?

Collimination looks fine, star test rings look very symetrical. It's just the image appears dim and greenish.

[sxinias]

Alas, then came jupiter. oh dear, all I can say is that in my humble opinion the 5" SCT really struggles. Jupiter appeared as a small round white ball. No contrast at all, no bands no hint of colour! I could clearly see 5 pin pricks of light as the moons but overall I'm convinced my old ETX 90 provided better views? I know my 8" obviously did but I'm currently still in shock as to how white the planet looked? Not even a hint of Jupiters belts? is this really what a 5" SCT will do to planets with its central obstruction?

Something is amiss. I have a vintage Meade 2045LX3 102mm SCT which is not known for its stellair optics and doesn't have the modern coatings scopes have today. I can clearly see the two cloud bands on Jupiter using a 25mm eyepiece even in the horrible seeing conditions we have at the moment. This was not the case at one time .... the culprit being poor collimation.

I also have a Celestron C6S 150mm SCT, a tad bigger than your 5SE but the same tube as the 6SE. It has even a larger central obstruction than your 5 inch SCT ..... 13.9% vs the 5SE's 12.6% area wise. With the 6 inch SCT, the details of Jupiter are much clearer and defined than the 4 inch SCT .... more details on the pole areas, details in the two cloud bands, a glimps at other bands, and once in a while on a rare night with decent seeing the "red spot".

Don't know about the 5SE but with Celestron's 6 inch SCT, the diagonal is reportedly not that great. I had severe image shift with mine when I rotated the diagonal so I generally used the diagonal from my older Meade SCT. One day I felt a rattle in the C6S's diagonal. Opened it up and the mirror was loose. Celestron uses double side tape to mount the mirror. The cause of my image shift was immediately apparent. The double sided tape was folded over in one corner which destroyed the mirror's alignment. I removed all the tape then used super glue to fix the mirror to its backing plate. Works great now.

Again, something is amiss. You should be able to see something inbetween what I described for the 102 and 150 mm SCTs.

Sxinias

[sxinias]

If your scope is properly collimated, perhaps you did not wait long enough for the 5Se to stabalize thermally. One thing with my 102mm Meade SCT is that it does not perform very well until it has equalized its temperture. If I took it outside at the moment, Jupiter would most likely be a white dot. After sitting out for a half hour or so, the temperature inside and out will equalize and the scope will perform and I will see details of Jupiter. Temperature equalization is not as big an issue with refractors like your 90 mm ETX. It was with your 8 inch SCT but it would probably show some details with unequalized temperatures however would perform far better after temperture equalization.

Sxinias

[John]

I think something must be amiss with your N5i as well. I used to have a Nexstar 5 (your scopes predecessor) and it was great for it's aperture. M13 for example showed brightly with stars resolved well into the cluster although not right across the core as an 8" scope is capable of. I was observing from a moderately light polluted back garden.

I've owned 2 C5's and a C8 and the one lesson I learned from this was that SCT's need to be in really good collimation to perform as well as they can. Even small collimation errors can have a substantial impact on resolution and contrast.

John

[seiko]

Thanks, yes so far the views are very dim. I've asked for some advice from Dhinds where I purchased the scope and so far they are simply unsure what the problem could be? I plan to try again on M13 tonight to confirm that it is in fact a very greenish blob.

To answer a few questions above, the scope had cooled for more than an hour when I viewed M13. In terms of checking colimination, star tests do seem to be very good and Chris from Dhinds aka telescopes plus has confirmed he did indeed check the scope before shipping.

Overall, I'm really struggling now as the scope is clearly struggling but why is another question? Standard plossl, diaganol or coatings?

[Doc]

Just out of curiosity how are you checking your collimation? what tools are you using?

[steve_bham]

I have a nexstar 5, and the views through a 25mm plossl are very bright if im honest, not looked at m13 but the 1st night out with it was pointed at saturn and was a very clear and bright view.

Do you have a barlow? are you going to Salisbury

[seiko]

For collimation I'm simply looking at the rings on a defocused star. Both inner and outer focus.

Alas I dont yet have any other eyepieces. The plan was to pick up a decent zoom but having been so disappointed with the 5i I'm not sure now.

The views are just too dim on M13 although Jupiter was ok, just nothing special.

Of course in the back of my mind is the fact that I could just have too high expectations but my real feeling at the moment is M13 should appear as a series of white star dots and not a very faint greenish smudge?