AstroTim

I don’t have experience of the Astro Fi 125, but have a C5. The OTA does look to be the same. The mount and tripod are obviously different to the SE, and possibly where some cost has been saved (no handset, and the tripod looks lighter). Also, the accessories are different compared to the 5se, mirror diagonal instead of prism, and Kellner eyepieces, rather than 25mm Plossl. I think the C5 OTA on its own was actually supplied as a spotting scope bundle, so came with some accessories (eyepiece, right image finderscope, and right image diagonal) and possibly a bag, which might account for the higher than expected price (or at least some of the additional cost), although could be wrong there. Tim

Hi Rob, I don’t have an exact figure, and it’s a while since I tried to estimate it, but recall it being between 200x and 210x i.e similar to a 10mm in cyclops mode (I have a non-stock diagonal which increases the light path too). As mentioned on a previous thread, I use the barrel from a barlow to extend the light path a little further, and this gets me to what I would estimate to be a little over 225x, which is more than I have achieved in cyclops mode. I probably can’t pick out any more detail through the bino than in cyclops mode, but find it easier to observe, and therefore the detail is seen more easily. I’d say it’s a similar effect to what you observed between your scopes, where the clarity in cyclops mode appears to vary more than in bino mode. Tim

I have tried a moon and sky glow filter and it can tease out a little more detail on occasion (although possibly just when the moon is nearby). I also find that I achieve more magnification when using the Binoviewer with the C8 (Binoviewer with 20mm eyepieces and 1.6x nosepiece barlow is the max I’ve managed), hence my earlier question. I’m beginning to wonder whether it is down to the light being split in the Binoviewer, resulting in less glare from the surface at the higher magnification and therefore more detail visible than in cyclops mode. I am hoping to get hold of a variable polariser at some point to see if dialling down the surface brightness might increase the magnification and detail achievable. Tim

Hi Rob, thanks for the magnification info. No need to spend time measuring, I was only after a rough idea to compare to what I’m achieving through my scope, which seems to be similar. I have seen much higher magnifications being reported with a C8 but have never managed to anywhere near myself. We must have similar local seeing conditions! Tim

Interesting report. I have a C8 myself but have been wondering how the views from a 4” refractor might compare. Did you try the Binoviewer on the C8 to see how that configuration compares too? What sort of magnification were you able to achieve in the C8, and was that similar to what you could achieve in the 102? I seem to be struggling to get much above 226x (9mm eyepiece) with mine in cyclops mode, and only a little more with the Binoviewer (maybe 250x). Tim

I think it’s certainly worth trying the Binoviewer out with your existing barlows (and single eyepieces) before shelling out on additional eyepiece pairs. With an SCT, the Binoviewer has an effect on the final magnification so you will get a different magnification than when using the same eyepiece and barlow in cyclops mode. Swapping a barlow out is a little quicker than two eyepieces. You can also add extensions to tweak the magnification a little. I’ve have used a standard barlow with the lens cell removed in order to give a little more magnification (and to fit any filters to in order to save swapping them between nosepiece / eyepieces).

I don’t know how they compare to the Hyperions, but I’ve been very happy with the supplied WO eyepieces when used in an f10 SCT.

While I have often read advice that you should only ever tighten the collimation screws, I’m not convinced by it myself. The mirror sits on a central pivot. If you keep tightening all of the screws it will eventually deform the pivot or backplate. There are a few examples of this happening. Obviously, if you keep slackening all three screws, the mirror will eventually detach from the holder and drop into the tube, and I think that’s where the only tighten rule comes from. I’ve not had to collimate an SCT many times, as despite being carried out every time I use them, mine have kept their collimation after I’ve done an initial collimation. I start by tightening all the screws up. When I then need to make a collimation adjustment, if the screw I need to tighten is already tight, I slightly loosen one or both of the opposite screws and then tighten the desired screw. Afterwards I nip the other two back tight. I only turn the screws a fraction of a turn at a time and at no point do I loosen all three screws. After each minor adjustment, all three screws are tight before I recheck the collimation. Because of this, I think the risk of completely loosening the mirror is minimal. In terms of the rotating secondary, and I’m not familiar with your generation of C8, so double check before you remove anything, but i think you need to tighten that up from the back of the corrector plate i.e. from the inside of the scope. I think the secondary shroud on the inside of the scope screws onto the secondary holder, sandwiching the corrector plate between them. Modern C8’s have a nut on the inside of the bolts that hold the front corrector plate housing on (which will fall into the tube if you loosen them), so you would need to remove the corrector from the housing to get to the inside. However, it’s worth checking as I know some of the Celestron SCT’s don’t have nuts on the inside so in theory you can remove the entire housing, tighten up the secondary holder, and refit without having to remove the collector itself. You would just need to make sure you mark the orientation of the housing with the tube so that you don’t rotate it when refitting.

Is this the sort of bracket you are after (mini dovetail bar)? https://www.ebay.co.uk/itm/SVBONY-Bracket-Base-42mm-UNC-1-4-20-Dovetail-Mount-Optical-Telescope-Finderscope/362517375434?hash=item5467b829ca:g: I have seen the mini dovetail bars sold separately. Tim

it might be down to the way your scope focuses. An SCT focuses by moving the primary mirror. This in turn changes the focal length of the scope. The focal length in the specification (and used in the FOV calculator) is just a nominal value. Depending upon which diagonal and eyepiece (and any other component) you attach, you will need to move the mirror by differing amounts in order to bring the image to focus (as well as how far away the target is). That will change the actual focal length away from the value used in the FOV calculator, and your actual view will be different to the calculator view. Tim

I use either skyalign (choose any 3 bright stars, spread some distance apart, but no need to know their names, and the Mount will try and work out which ones they are and align), or solar system align (not as accurate but ok if looking for easily identifiable or large targets, such as planets). I know a lot of people favour one of the two star methods, but I’ve never tried them so can’t comment. Any of the methods should allow you to accurately track a chosen object for quite some time, at least an hour. If you search the forum, or web, there will be plenty of guides and tips for improving Goto accuracy with nexstar mounts. Without following the tips the Mount will likely lose some accuracy in it’s alignment every time you slew to a new object, which will be fine if you are only looking at a couple of objects in a given session. You can correct the alignment if that happens but the tips are designed to minimise the need. I happily used the Mount for some time without delving into backlash settings and the like and it might be worth waiting until you are more familiar with the mount before starting to tinker with the config. Tim

A very common mistake that affects the tracking of the Mount is to enter the date incorrectly. The Mount requires the date to be entered in US format I.e. month/date/year, so yesterday would have been 10/09/20. The other common error is to enter the wrong time zone (Universal Time for the UK) and daylight savings settings (“Standard Time” If you enter the time as GMT, or “Daylight Saving” if you enter the time as displayed on your phone, until the clocks next go back). Tim

Screenshots from the Pro version

The option I set was “with Surface Labels”, although I know you said you tried the other options too. Which SkySafari version are you using? I have the Pro version but the labels are also available in the Plus version according to the developer web site. If you don’t have one of those versions then the Pro and Plus versions are frequently on offer, so worth waiting a few weeks if currently full price. Tim

You can configure SkySafari to show feature names Settings->Display Options->Solar System Then you can toggle on/off Surface Labels in the Planets and Moon section Mars Mapper is another useful tool http://www.nightskies.net/mars/mars.html Tim

I think you would need exceptional seeing to be able to use a 5mm (406x magnification). The maximimum I’ve achieved is 250x but then I don’t live in Abu Dhabi. My point about the barlow (combined with the zoom) is that it would allow you to try those shorter focal lengths without investing a lot of money upfront on eyepieces that you end up not using. Once you know which focal length(s) work best for the sky conditions you have access to, then you invest in a quality eyepiece (or eyepieces) to suit your needs. The barlow might still be useful to fill in the gap, or extend into the less used lengths. As long as you get a half decent barlow, I don’t think it will degrade the view that noticeably on an f10 SCT.

Most of my observing to date has been of the planets. I have the Baader zoom (8-24), however, my most used “cyclops” eyepiece is an X-Cel LX 9mm. The 9mm seems to hit the sweet spot for my sky conditions and therefore I tend to go straight for that rather than the zoom (which gives similar quality views). You could go with an 8-24 zoom and use that to work out where your most used focal length would be, and then buy a good quality eyepiece at that length if you feel you need to. You could also add a 2x barlow to use with the zoom (at say its 14 or 12 setting) to give you a little more magnification for when the seeing is particularly good. That would save purchasing a dedicated 6mm or 7mm that would then get little use (unless one of those happens to be where your sweet spot lies). By far the best purchase I’ve made is the William Optics Binoviewer. Binoviewers don’t suit everyone however, but I find that mine give me much better views, and more comfortable viewing, than any of the single eyepieces I own (none of which are high end eyepieces). The 20mm eyepieces and 1.6x barlow nosepiece that come with the Binoviewer work well for the planets and lunar. I haven’t tried the matching 2x barlow nosepiece so not sure if it would give too much magnification. I can’t really advise on eyepieces for deep sky objects, as I haven’t done enough of that type of viewing yet. You would probably want to look at a 2” diagonal and then maybe something like a 35mm OVL Aero ED eyepiece. That’s certainly what I’m considering.

From the little I’ve read, the original and LX versions are very similar in observable visual performance. The original has 2 ED elements that the LX lacks, but also has a narrower field of view. The 8SE is the same optical tube as the other Celestron 8 inch SCT models, of the same generation, just a different colour. There will be some differences from one generation to another. Mine is a couple of years old, but I don’t think much has changed for some years. I think the XLT coating might have been the last change made. In theory, your f5 scope will be more sensitive to the quality of the eyepiece than your f10 8SE. I don’t have much to compare my LX eyepieces to other than the Baader zoom which I find gives similar views for a given focal length. If your zoom is giving good views at 10mm or even 8mm then that would suggest that it isn’t down to seeing conditions and the 10mm X-Cel should perform well too. The 5mm and 3.5mm won’t work well in the 8SE as they would give 406x and 580x respectively. For comparison, I can rarely get above 226x. While there are various rules of thumb for the maximum useable magnification, taking in different seeing conditions, you are probably looking in the ballpark of 240x for the 8SE. Could you see any detail on Mars with the 10mm X-Cel? How did the view differ to the Zoom at 8mm?

To clarify, I was referring to the X-Cel LX range in my post above. I didn’t realise there was an previous X-Cel eyepiece range (with a 10mm). Unfortunately, I don’t know how the X-Cel and X-Cel LX eyepieces compare so my comment regarding the LX and Baader zoom might not apply to the older X-Cel.

The 9mm X-Cel is my most used eyepiece with my C8 (not that I have many to choose from) and I am able to achieve a good focus. I also have the Baader zoom and would say that they provide similar views. I struggle to get a sharp image at focal lengths below 9mm. Are you sure it’s a 10mm X-Cel as I thought the range was 7mm, 9mm, 12mm? Tim

Thanks @Don Pensack. That’s useful to know. Tim

Thanks @Louis D. I’ll give that a go. I hadn’t really noticed that one barlow had required an inward focus change and the other an outward one, but think I do recall that being the case. I guess any movement of the mirror is going to change the focal length and therefore the resulting magnification. That makes it difficult to determine what magnification you are going to get with a given combo of barlow, bino, and eyepiece. I was trying to find a barlow + bino + eyepiece combination that would give me around x160 as that’s about the max I can typically use. I know a x2 long barlow is slightly too much, but I’m hoping a x2 nosepiece barlow (is this the same as a shorty?) might just work, as it will require more inward focus, shortening the focal length. Tim.

Hi @Don Pensack, Out of interest, how did you calculate that approximation? I have a C8 and have also been trying to work out the effect of various barlows and a Binoviewer. Given that you have to adjust the focus when adding a barlow (not sure if it’s inward focus or not) and that this in turn will alter the focal length of the scope (due to the mirror moving?), does that mean that a 2x barlow will not actually give a 2x magnification when used in a C8? I think I’ve also observed a difference between a nosepiece barlow vs the same magnification normal barlow, which I wasn’t really expecting, but maybe one of them is poorly specified. Regards, Tim

Thankyou for posting your at the eyepiece sketches. They are a great insight into how you produce your wonderful drawings. I have tried sketching the Orion Nebula on a couple of occasions before, but they didn’t turn out well (and that’s being polite). Making separate sketches or outlines of different features and details and then combining them later indoors, while still fresh in the mind, sounds obvious to me now, but had never occurred to me before, so I’m inspired to give it another go. Tim

Interesting event, although just been checking on SkySafari and wasn’t it Europa that was being eclipsed at that time? I was actually observing Callisto transiting Jupiter at around the same time, but didn’t realise that Europa was also being eclipsed, and would soon emerge, so missed it completely. I will have to look out for it another time. I only knew about Callisto because I could see a dark dot on Jupiter and (after checking for debris on the eyepiece) went inside to look up what it could be (which probably coincided with when Europa emerged). Tim