The SkyWatcher 90 Backpacker on the moon and some birds
March 2, 2012Fate smiled on me yesterday and early this morning, and I was able to get some pictures with the SkyWatcher 90 mm Backpacker. If you’re impatient you can scroll to the bottom of the post for the photos.
I should stop here and say that I ultimately intend to test the whole kit–scope, mount, and accessories–as a system, because whether you use it as-is or mix-and-match components, it is sold as a system and is at least theoretically supposed to function as one. However, between teaching, taking a statistics class, and wrangling ostriches, I just haven’t had time to mess with the mount. My primary concern has been to assess the optical quality of the scope–and now I actually have some information.
I got in a brief observing session between responsibilities yesterday afternoon. I was plinking around the yard, looking at birds. For these observations I started out using the included 90-degree prism diagonal and 25mm Plossl eyepiece. I first looked at a couple of obvious birds silhouetted against the sky in treetops, and they looked fine. Then I went after one hidden in the leaves and branches of one of my neighbor’s trees, and in those dimmer conditions I noticed something unnerving: the eyepiece view was very soft and didn’t snap to focus, as if I was observing with a very short focal ratio scope like an Astroscan. Also, there was some ghosting of the image in the eyepiece, and the edge of the image was poorly defined. In short, it was very, very different from the crisp, sharp, detailed images that Maks are renowned for, and not in a good way. I was just having a “Hey, what the–!” moment when I remembered where I had seen these kinds of problems before: in scopes using cheap prism diagonals instead of mirrors.
Without moving the scope, I went to the garage and pulled the Astro-Tech dielectric diagonal off my Apex 127, and swapped that out for the prism diagonal. I held my breath as I put my eye back to the eyepiece–were the problems all in the diagonal, or had I gotten a lemon of a scope?
Sweet relief–even in the dim light amongst the leaves and branches, the view was razor-sharp and contrasty. It was like someone had run a very good image-sharpening algorithm on the eyepiece view. Suddenly details that were invisible before were popping out all over the place. Leaves that had been too fuzzy to invite close inspection were etched with delicate networks of veins. The whole view just looked more real.
I decided then that I would try to find out just how good or bad the prism diagonal is, and under what conditions.
After that quick peek I didn’t get another chance to use the scope until about 10:00 last night. The first quarter moon was still fairly high in the west, but the seeing was not good. The air just roiled over the moon, and every star I looked at scintillated with fast-moving rays of light. Not good conditions for testing a new telescope, because it’s hard to push the magnification up and tell if the results you’re getting are because of the scope, the seeing, or both. But I went ahead and put the scope through it’s paces anyway. The thing about seeing is that from time to time it does settle down a bit, at least momentarily, and in those instants the amount of additional detail that is visible is sometimes shocking. So the longer you look and the more patiently you observe, the more likely you are to catch those rare moments of steadier air and see something really remarkable.
For eyepieces I used a 32mm Sirius Plossl from Orion and the 12.5mm and 6.3mm SkyWatcher Plossls that came with the scope. I took all of the pictures in this post afocally with a Nikon Coolpix 4500 hand-held to the 32mm Plossl, and with the camera optically zoomed enough to eliminate any vignetting.
The moon looked surprisingly good with the Astro-Tech diagonal in place. It was fairly swimming in the turbulent air, as if being viewed under a thin stream of moving water. But if I focused on a particular crater or feature for the space of a minute or two I would catch a patch of calmer air and see perhaps double the detail in those brief glimpses. Small craters that were otherwise just spots would pop into focus with dark rims and bright floors. The 12.5mm eyepiece had tighter eye relief than I am used to in that focal length; I have long-ish eyelashes and they were occasionally brushing the eye lens, something I don’t remember ever happening with the 12mm SkyWatcher Plossl that I got with Shorty Long, my 80mm f/11 achromat. That 12mm looks identical to the Orion Sirius line, whereas the eyepieces that came with the Backpacker have smooth silver barrels and no rubber eyecups, so even though they are both branded SkyWatcher they might have somewhat different guts. Also, I’ll have to look more closely the next time I’m out, but the 12mm felt like it had a narrower apparent field of view than the 32mm, which shouldn’t be possible if they are both Plossls, which typically yield a 52-degree apparent field. Could be that the short eye relief was playing tricks on my perceptions. Anyway, with the 12.5mm EP in the scope was working at 100x and I was still seeing plenty of few detail in the still moments.
I put the 6.3mm EP in just for the heck of it. I wasn’t expecting much, both because of the punk seeing and because that magnification–200x–ought to be pushing on the edge of what this scope can do. A commonly used rule of thumb is that a good scope should be able to handle 50x per inch of aperture. At 3.5 inches, any of these 90mm Maks ought to be good up to at least 175x. But I have to point out that the 50x/inch “rule” is often broken and not only by premium scopes. David DeLano has had his 114mm reflector up to 400x (89x per inch), and the other night I took my Apex 127 to 514x (103x) to split a close double star that was not split at 257x. I’ll just note that those are both relatively long focal ratio scopes, about f/8 for David’s reflector and f/12 for the Apex, and maybe that has something to do with it; such gently-tapering light cones are certainly easier on eyepieces and so on. Anyway, at 200x with the 6.3mm EP I was still getting glimpses of considerable detail. I can’t say for certain because of the lousy seeing, but I think this scope can handle 200x. I hope I get a still night soon to test that.
Okay, so far so good with the Astro-Tech diagonal. I swapped it out for the stock prism diagonal and went back to the 32mm Plossl. YUCK! I almost could not focus my eye on the moon, because there was a moon-sized ghost image floating around in the field of view that looked like it was probably some kind of reflection of the primary mirror or maybe even the corrector. It was a big white donut with a dark hole in the middle, anyway. I’ll stress that this ghost image or whatever it was was not there with the Astro-Tech diagonal. I have never seen anything quite like it before, and given the controlled conditions of time, place, observer, scope, and eyepiece, I feel confident blaming the prism diagonal.
I tried the two other eyepieces. The ghost didn’t show up in either of them. The 12.5mm was merely okay, producing a slightly softer view in the prism diagonal than in the Astro-Tech. The 6.3mm was very noticeably softer; this time going from 100x to 200x looked and felt like empty magnification.
I also looked at Belelgeuse and Mars with all combinations of diagonals and eyepieces. Betelgeuse was sparkling in the Astro-Tech diagonal, but at least the scintillating rays of light were sharp. In the prism diagonal it was a fuzzy mess. Betelgeuse was down near the horizon, though, and Mars was very high, so I hoped to see at least some detail on good old Barsoom.
Mars really required the 12.5mm EP; at 39x it was a bright orange BB, too small to see detail on, and at 200x it was a big orange smudge. At 100x with the prism diagonal I could only suspect the polar cap, and that might have been because I knew it was there to be seen. I had started that run with the Astro-Tech, and in steadier moments the polar cap was a well-defined white patch with a hair-fine black border. In brief flashes I also saw dark markings on the face of the planet’s disk. So despite the lousy seeing, the little scope lived up to the Maksutov reputation as a fine planetary instrument.
I did see some off-axis glare from Betelgeuse and Mars, but only in the 32mm Plossl. I am going to do some more testing to see if that is a scope issue or, as I suspect, an eyepiece issue. Also, getting the scope on target using the 8×20 straight-through finder was not difficult but it was uncomfortable, and usually required me to move my chair, squat behind the scope, and go back and forth between sighting down the tube and squinting through the finder. It’s doable, it’s just not fun, and something like a 6×30 RACI should be a high-priority upgrade if you get one of these.
This morning before work I got some photos of neighborhood birds, using both the Astro-Tech dielectric diagonal and the prism diagonal that came with the scope. Be aware that that both my camera and my photographic method are primitive. The camera is a 4-megapixel job more than a decade old now, and while its rotating barrel design is convenient for digiscoping, it just can’t keep up with the better modern cameras. Also, hand-holding the camera to the eyepiece means that I’m usually the most mobile link in the system, so any fuzz or blurring in the photos is possibly caused by my minuscule shakes rather than by the optics. To try to eliminate that factor as best I could, I took several exposures of each target and picked the sharpest from each set for the comparison images. In all of the comparisons between diagonals, the photo through the prism is on the left, and the dielectric photo is on the right. Other than having been put into the same image for comparative purposes, the photos are completely unprocessed: no sharpening, no levels or curves, no rotation, and I didn’t even flip the photos through the star diagonal, which are reversed left-to-right. Click each image for the original, full-resolution version.
The moon last night. The view through the dielectric diagonal was markedly sharper and more contrasty, and these unprocessed photos, taken just minutes apart, bear that out. The full-resolution dielectric photo shows a very thin line of purple chromatic aberration around the limb of the moon, but I couldn’t see it at the eyepiece despite being on the lookout for it.
This fellow was sitting a tree that I have paced out at about 70 yards from my driveway. Again, the dielectric photo (right) has better contrast, and look at the difference in the color of the background sky. This is the same bird and I took the photos about 2 minutes apart.
This dove was quite a bit farther way. I haven’t paced it out, but this powerline must be well over 100 yards from my driveway. Notice the scale of the bird in the photos and the pronounced drop-off in detail compared to the little songbird above. Detail is probably a wash here, but the dielectric photo has better contrast and again the background sky is more blue.
One more point to make is that I hardly ever post raw images. Almost every photo can benefit from a little processing with Unsharp Mask and Curves (I use GIMP, which is free–see details on what I do to each photo in this post). Here are the best dielectric photos of the moon and the songbird, with the unprocessed photo on the left and the lightly processed version on the right (this time I did rotate the moon and flip it to its correct side).
So, what did I learn from all of this? The SkyWatcher 90 Backpacker is a decent little scope. I couldn’t see any optical problems, and I was impressed to see details on Mars at 100x with the included 12.mm Plossl and the Astro-Tech diagonal. Views of birds are as good as those I used to get with my Orion Apex 90. But the supplied diagonal is not good, and really limits the views the telescope is capable of providing. If you get one, replacing the diagonal with even an inexpensive mirror diagonal should be a top priority. Let me put in a plug here for the Astro-Tech dielectric diagonal. It consistently throws up a great image–it’s the diagonal I used when taking the Apex 127 to 514x for that double star split–but at $69.95 for the 1.25″ version it is no more expensive than some ‘entry-level’ mirror diagonals.
The supplied prism diagonal does have one potential use: if you have an old binocular laying around, you can disassemble it and use one of the objective lenses to make a proper finderscope, and if you include the diagonal it could even be a RACI. Mounting a bigger homemade finder to the scope will take some ingenuity, but I figure anyone who likes to tinker enough to build a finder in the first place can be trusted to come up with a mount as well.
So I now feel confident enough to recommend the scope, at least, although the mount is still a question mark and the diagonal and finder are troublesome (as expected). I don’t know how the scope performs compared to the Celestron C90, which is also on sale, because I haven’t had the chance to test them side-by-side. But with a little luck I may get that chance soon.
Hopefully this weekend I’ll have time to get the mount up and running. Stay tuned.
10 Minute Astronomy 
Since I almost exclusively use prism diagonals on my refractors, I’m going to have to go back and compare them to mirrors again. From my original testing, I actually think the view is better, and that there is less CA, with the prisms, but then again, I also have more expensive prism diags than came with the scope you are testing (one is a StellarVue).
However, the other night I had some rather yucky views of both Jupiter and Venus. I was blaming it on the EP I was testing (6.3mm), or possibly the seeing, but it could have been the prism diag, and if so, it likely was not cooled down at all, and may have even had some fogging on it. I’d never thought about the prism needing to cool down, but in the GS, it’s probably the one part that could use some equalizing this time of year.
The EP I was testing was a SkyWatcher 6.3mm, though it isn’t smooth sided and has an eye guard (maybe SkyWatcher is running out of EPs to ship with the closeout scopes). I had the same experience you had with the 12mm. I had to get close enough that my eyelashes touched the EP to get a decent view. But, once I did that, I think I had a full 52* FOV and had that “falling into the EP” type feeling. I just didn’t like the fact that the EP was getting eyelash oil on it!
David
From my original testing, I actually think the view is better, and that there is less CA, with the prisms, but then again, I also have more expensive prism diags than came with the scope you are testing (one is a StellarVue).
Yeah, I think that is really important. I’m not claiming that all prism diagonals are bad–or I have, I probably shouldn’t have, since StellarVue, TeleVue, etc. put out some high-end ones to go with their apo refractors for daytime use. But the ones shipping in the case with these Synta Maks are at the completely opposite end of the quality spectrum.
On one hand, I don’t think anyone who does any homework is getting duped, because Every. Single. Review. of these little scopes says to ditch the prism diagonal and the tiny finder. On the other hand, there’s something odd about the scope business that a very high-quality optical instrument is somehow more marketable with accessories that degrade its performance in obvious, non-trivial ways, than it would be with high-quality accessories or just as a naked tube (which is in fact how the larger Mak tubes are usually offered, if not bundled with large, expensive mounts). It mainly bothers me to think that people who haven’t read around about them much might blame the poor performance on the scope rather than the accessories. Which would be a shame, since the scopes themselves are usually good to excellent.
Matt,
Ouch. I was about to order one of these, but have now hit the brakes as it seems I would need to pony up another 70 bucks immediately. What is your best guess about the C90’s diagonal? Same thing? Also, it is a 45 degree angle, so you would probably have to replace it anyway, so suddenly Great Deal becomes Sorta Good Deal. I would like a 90mm Mak but am now consigned to floating around in the Sea of Indecision. Also eager to hear your thoughts on the motorized operation of this scope.Keep us apprised. This is excellent stuff.
Doug
I think vendors think they have to compete on the check-off list, so the more accessories, the better. And often, it’s the comparison of the accessories that one does when deciding on a scope.
I’m guessing that the diag you have is pretty much sealed up. It would be interesting to see how it’s made on the inside. Either the prism is not well coated, or the inside of the diag is not flat black, would be my guess from your description. This would be especially annoying on brighter objects. You might try testing it on the something less bright to see how they compare.
David
I was about to order one of these, but have now hit the brakes as it seems I would need to pony up another 70 bucks immediately. What is your best guess about the C90′s diagonal? Same thing? Also, it is a 45 degree angle, so you would probably have to replace it anyway, so suddenly Great Deal becomes Sorta Good Deal.
Hi Doug, I haven’t used the C90, but as it is a Synta-made scope, my guess is that its supplied 45-degree diagonal is the same as the one that ships with Orion’s Apex 90, in which case you would definitely want to replace it.
I was thinking that if the Orion StarMax 90 Tabletop came with a mirror diagonal that would put it in the lead over both the C90 and the Skywatcher 90. And the brief description of it on Orion’s website says it includes a “90° mirror diagonal for comfortable night sky viewing”. HOWEVER, on the Specs tab below the diagonal is described as “1.25” 90° Prism Star”, in which case it is probably the same as the one that came with the Backpacker. So we’ve got a problem, or rather Orion does, in that their own material says the diagonal is a mirror in one place and a prism father down the same page! I’m going to send them an email and see if we can find out which it is.
Anyway, to get back to your question. On one hand, to get the full benefit of the optics on any of these little Maks–or even to be able to tell how good the optics actually are–you will need a better diagonall. On the other hand, there are options that are less expensive than $70. ScopeStuff has a 90-degree mirror diagonal for $32 plus $5 shipping, here, and Agena Astroproducts has a Celestron 90-degree mirror diagonal for $30 with free shipping, here. Finally, I see on the Cloudy Nights Classifieds that Sheldon (MASILMW) has a 90-degree mirror diagonal for $8 shipped, here. He sells a lot of stuff at close to wholesale prices. I’ve bought a bunch of gear from him and it’s always been good quality and he’s very easy to deal with.
So there are diagonal options under $70, which is good, because you really, really need to budget for one if you’re considering one of these little Maks.
Matt,
You are a certifiable treasure trove for total tyros such as myself! I learn so much from your in-depth replies, including this one. Hard to believe that one can get a mirror diagonal for 8 bucks, yet there it is. I just registered on CN and as soon as it goes through, I will order that diagonal just to have that one piece already in place when I pop for a Mak. I noticed the same discrepancy on Orion’s Web site, re the conflicting descriptions of exactly what kind of diagonal comes with it.
So it seems that with the mirror diagonal, your Skywatcher Mak delivers clean, crisp images, hence still something for me to consider. But I have also read great things about the C90, including Ed Ting’s 3 scope shootout where the C90 held its own against the Questar. So I may be leaning in this direction now. I think another poster here (Terrance?) is about to do a first light report with his C90, so I will keep my eyes open for it.
One other question. I noticed in your piece on your first Mak, I think an Orion 102mm, that you had it mounted on Orion’s tabletop EQ mount. This is the one I was thinking about getting should I opt for the C90. How did you find that it worked as a Mak mount? Stable? Easy to get around on? I would definitely want a tabletop mount, and this looks like a solid one.
Thanks, Matt. Looking forward to your report on the motorized Skywatcher mount.
Doug
I noticed in your piece on your first Mak, I think an Orion 102mm, that you had it mounted on Orion’s tabletop EQ mount. This is the one I was thinking about getting should I opt for the C90. How did you find that it worked as a Mak mount? Stable? Easy to get around on? I would definitely want a tabletop mount, and this looks like a solid one.
Well, your preferences may be different from mine, but I hated that tabletop EQ mount. And I’ll explain why.
First off, I’m an alt-az guy, not an EQ man. I know that there are some people who find EQ mounts more intuitive than alt-az, but I’m not one of them. I don’t mind nudging a scope in two dimensions to stay on target.
BUT if I am going to use an EQ, I need to be able to move all around it. EQ mounts put scopes at odd angles, and for things like sighting through finders you need to be able to get around the scope in three dimensions.
Put the EQ mount on a tabletop and you’ve just lost that ability. You can’t get underneath it. I’ll give an example. Unless you buy some tube rings and a dovetail plate, the little Maks attach to the EQ mount with their built-in dovetail plates. That means that the finder might end up on top of the scope, beside the scope, or even underneath the scope, depending on the angle of the scope. If the finder is underneath the scope, it can be physically impossible to move your head between the scope and the table to peer up through the finder. You might be able to scoot the mount to the edge of the table to get enough headroom to find stuff, but probably not without throwing off the alignment. And you’ll have to scoot it to another edge of the table when you want to look at an object elsewhere in the sky.
The Tabletop EQ mount I had was solid enough for either the 90mm or 102mm Maks, it was just a huge pain in the rear to use. IF I was going to use an EQ mount, it would be for a big scope that I will have out for a long session, and it will be a full-size tripod- or pier-mounted rig that I could move all around, and ideally the scope would be in tube rings so I could rotate the tube and keep the finder at a convenient spot. IMHO–and again, other people may feel differently–an EQ mount just doesn’t fit the grab-n-go spirit of these little Maks, and the top of a table is an incredibly inconvenient place to put an EQ mount.
I was going to say that if you want a light manual alt-az mount for a Mak, just get the Orion StarMax 90 Tabletop. But I just found out from playing around with the SkyWatcher Backpacker mount that it CAN be used manually. And, like the Orion tabletop mounts, it can be placed up on a tripod. So I think the SkyWatcher package wins on functionality, even though the diagonal is lousy.
Great stuff, Matt!
As for mounts, I have no preferences as I have almost no experience, and hence know only what I can glean from reading. I have read that EQ mounts are good at what they do, but are hardly user-friendly. But I had no idea they could present the problems you describe. Yikes! Definitely not for me. Many thanks for the explicit heads-up on that sucker. Color it: AVOID.
Had it not been for your blog, I would have likely ended up with one of these with all the attendant headaches and ended up returning it. I do though definitely want a tabletop mount for whatever 90mm Mak I get. I found a couple online for about $40 that look decently substantial, BUT if the motorized mount on your new Skywatcher can be manually moved alt-az style, then this would be ideal. Can you tell me more about how you move it manually? Or . . . does it just move in a more-or-less standard alt-az manner if the motor is turned off? If so, it would be a mount similar to that of the Orion StarMax tabletop, correct? That is, a kind of “half Dob”. If so, all I would need to do is add a mirror diagonal. When you get time, please fill me in more on the manual operation of the SkyMaster. Thanks, Matt. You’re a terrific resource. Your astro knowledge and passion both come through strongly.
Btw, I order all kinds of stuff from Amazon. So if I go to your blog, click on the “Amazon” in blue I see there, it will take me directly to Amazon and whatever I order from them will credit something back to you. Do I have that correct? Doesn’t just have to be scope stuff? If so, I will access Amazon this way each time I buy something,
Doug
Can you tell me more about how you move it manually? Or . . . does it just move in a more-or-less standard alt-az manner if the motor is turned off?
You just grab it and point it. I discovered this on accident when I put the scope on it. But it makes some sense of what the manual says now. The manual says NOT to move it manually, but that is after you’ve got the tracking engaged. I saw that and thought it meant you can’t move it manually at all. But looking at the manual now I see that you are supposed to move it manually to get it aligned with north and possibly also to set the latitude. So as long as you don’t have it turned on, you can use it just as you describe, as a “half Dob”. And I think it will be excellent in that mode because it is so solidly built.
If so, all I would need to do is add a mirror diagonal.
Yep. And you would probably find it easier to use with a 6×30 RACI finder, but it is at least usable with the included 8×20 straight through. At least that finder doesn’t impair the views through the scope, which the prism diagonal does.
When you get time, please fill me in more on the manual operation of the SkyMaster.
I’ll try it out this weekend, maybe tonight, and let you know.
Thanks, Matt. You’re a terrific resource. Your astro knowledge and passion both come through strongly.
Thanks kindly! I’m glad you’re finding it all useful.
Btw, I order all kinds of stuff from Amazon. So if I go to your blog, click on the “Amazon” in blue I see there, it will take me directly to Amazon and whatever I order from them will credit something back to you. Do I have that correct? Doesn’t just have to be scope stuff? If so, I will access Amazon this way each time I buy something,
Yep, that’s all correct. You or anyone else can bookmark this link and use it to access Amazon, and when you do it won’t cost you a cent more, but I’ll get a little referral fee each time you buy something–books, lawn mowers, toilet paper, MP3s, whatever. My plan is to use those referral fees to try out more entry-level astro gear so I can review it here. If I can point people to good gear, and they go to Amazon through this site to buy it, then hopefully I can get enough referral fees to find more good gear to recommend, and perpetuate the cycle.
I’ve never said so explicitly because I haven’t talked about the Amazon Associate program much, but I won’t recommend gear that I don’t believe in just to try to earn referral fees. If something sucks, I’ll say so. And I will keep pointing people to good gear and good deals at other sites, not just Amazon. The Astro-Tech dielectric diagonal is a good example. It’s not on Amazon, and it’s not the cheapest mirror-type diagonal available, but I think it’s a great piece of equipment and a tremendous deal.
Link is bookmarked.
Quick final question: Do you think that the $8.50 mirror diagnonal from Sheldon is the equal of the Astro-Tech one for $35? Seems unlikely, but you had good things to say about Sheldon’s gear.
Doug –
Don’t sweat the diag issue too much. Most scope packages cut corners in some way. Most of the cost goes into the scope itself, though there are ways to cut costs there, too. Next is the mount, and a lot of times the scope is undermounted. Next are the EPs, which are usually good enough to get a person started, but won’t be used in the long run. If anything else that’s included is of good quality, it’s gravy. Everything that is included with this package will get you started. The diag is the first thing to replace. The next is the finder, which could actually be replaced with a Red Dot Finder instead for a reasonable price.
As for the cost of the A-T diag, I’m actually ordering one to compare it to the prism diags I have. Even on the Astronomics site, the comparable diags are $140 and $190, so this one is a true bargain.
David
Thanks, David. Good stuff to know,. I already have an Orion StarBlast 6, but want to add a Mak and the SkyWatcher set up Matt just got looks like the one. That, or the C90. Still have to think this through more. Either way, I will need to get a mirror diagonal and Matt suggested several good ones.
Doug
Do you think that the $8.50 mirror diagnonal from Sheldon is the equal of the Astro-Tech one for $35?
Sheldon seems to have a line on some made-in-China gear at prices close to wholesale. Maybe $8.50 is what Jinghua charges Meade. I honestly don’t know. I have one of Sheldon’s eight-dollar diagonals floating around here somewhere, and although I’ve never put it head-to-head with the Astro-Tech dielectric, I’ve never noticed any problems with it, either. Remember, the prism diagonal that came with the scope is so bad it was causing obvious problems with the image even at the lowest useful magnification. I don’t know if the eight-dollar mirror diagonal will be as good as the more expensive ones–for one thing it is probably a few percent less reflective than a dielectric–but I’m pretty sure it will blow the doors off the included prism.
Thanks, Matt. I am ordering one from Sheldon today. At 8 bucks, how can you go wrong?
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