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- Annals of the Deep Sky, Volumes One and Two
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- Optolong LRGB Filter Testing and Comparison with Baader LRGB Filters
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CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
Meade DS 90EC (90mm f/11.1 Achromatic Refractor with Autostar)
The DS 90EC is one of many "go to" telescopes currently in the market. I found it to be a descent entry-to-intermediate level telescope with surprisingly good optics and a good value considering the price.
Having been absent from the hobby for more than 10 years, I recently got bitten by the bug again. Since I live in a moderately light polluted suburban area, I decided to concentrate on planetary observing and thus a refractor seemed like the instrument of choice. Also, upon reading about the new "go to" instruments now available, I could not help but at least try one out. This is my fourth telescope, the others being another refractor and a couple of reflectors, and comparisons will be mainly based on my experience with these as well as observations with popular eight inch catadioptric instruments.
The DS 90EC optical tube contains a doublet objective lens that appears to be multi coated. The tube incorporates 3 baffles to control stray light. The focuser is a plastic unit that exhibits smooth tracking and includes a locking screw. It is unusual for me to see so much plastic in a telescope but, it appears to be of a high quality, in fact all the plastic parts could pass for metal at first glance. The finder scope is a simple 6 x 30 unit with a plastic objective. Its mounting is plastic and it is very easy to secure and adjust the finder.
The alt/az mount is also plastic and incorporates hook-ups for the computer controls as well as connections for the electric motors and batteries. The standard electronic control is a hand held unit that slues the telescope at the push of a button with 4 different speeds available, it also controls the optional electronic focusing motor. I purchased the optional Autostar controller that is needed for "go-to" capability.
The tripod is of light weight aluminum with rubber tips that contact the ground and do a descent job of damping vibrations.
Two eyepieces (Meade MA 25mm and 9mm), are included, as well as a 90 deg. star diagonal.
I have read several reviews regarding Meade DS telescopes that were much less than favorable. I do not know if the quality of all DS models is the same, or if the reviews were written by inexperienced users, or maybe I got lucky and got the only scope that has been relatively trouble-free. One must also consider the price paid for such an instrument and temper ones expectations accordingly.
I only use the scope from my backyard so I have no reason to take it apart and all the transportation involved takes it just a few feet from where it is stored. The tripod is rather delicate but more than adequate for my purposes. It is definitely not something to be taken out on field trips, unless it were properly encased. With the legs fully extended vibrations typically damp-out in about a second and a half, but anything more than a light breeze will produce too much vibration for comfort. However this hardly ever presents a problem from my backyard. The whole assembly is light enough to carry around for short distances.
The operating instructions are fairly complete and walk the owner through assembly and setup. The electric motors must be "trained" prior to first use. This is a simple procedure covered in detail. Observing setup and alignment take less than 5 minutes. The autostar computer displays the simple instructions and they become routine after a couple of times. One thing that is not given enough emphasis is to make sure that the mount is level. Failure to do this will cause inaccurate alignment and also poor tracking. The problem is that there is no way to indicate if the mount is level. I solved this by buying two bubble levels and taping them to the mount. Total money spent: $1.75. Two other things also increase alignment accuracy; one is to point the telescope at true north as closely as possible and the other is to use stars that are far apart. I always use Polaris as one of my stars for alignment.
After alignment is complete, all there is to do is select an object from the menu and press the go to button. The telescope automatically slues and tries to center the object in the field of view. If care is taken during alignment, pointing accuracy can be fairly good and the desired object will fall within the low power field of view more than 90% of the time. Some nights, every object I selected was found on the first try. For one used to star hopping I find that very impressive. And observing is a lot more fun than spending time finding the desired object.
The optical performance was complete surprise to me. My crude star test shows symmetric diffraction patterns inside and outside of focus. The airy disks present the starry/spiky pattern associated with optical aberration, but this does not seem to be a problem. The stars appear as distinct pinpoints across most of the field of view and they easily snap into focus. The big surprise was the relative absence of false color. Hardly any is present on bright stars at low to medium powers and very little is present on the moon and the sun when viewed with Baader safety film. A slight blue haze is observed on one edge of Mars, but it is much less pronounced than I have observed with other refractors and certainly less than I expected. I guess the relatively high focal ratio of 11.1 makes a difference in these days of "fast" refractors. I have spent many hours observing Saturn and have experienced my best views of that planet so far with detail comparable to that on amateur CCD images as seen in popular astronomy magazines. For some reason, Saturn exibits the least amount of false color. Jupiter is quite impressive, but I am still waiting to catch it on a really good-seeing night. It is noteworthy to mention here that I use a Meade series 4000 Plossl 9.7mm eyepiece with a Meade shorty barlow for 222x. Very steady and dry atmospheric conditions here in Arizona permit this level of magnification on a consistent basis. I consider this level the maximum but also the optimum for observing fine detail. The standard 9mm eyepiece included with the telescope is almost useless because of its small exit pupil and lack of eye relief. The 25mm EP produces good sharp images at low magnification or medium magnifications when coupled with the barlow lens.
Having the Autostar capability motivated me to seek views of the deep sky objects on the database which constitute the entire Messier catalog plus the brightest NCG and Caldwell objects, solar system objects and even some artificial satellites. Again I was pleasantly surprised. Open clusters are now a favorite. It sure is great not having to hunt for them or wonder if you are in the right area. Night adaptation goes a long way in improving the level of seeing in a 3.5 inch instrument, especially when looking at nebulas such as the dumbbell or ring, (the ring shape is clearly visible even at the lowest power). The Orion nebula shows good detail and the trapezium is easily resolved at 40x. Moon images are sharp and contrasty with little color showing only near the edge of the disk. The internal baffles do a good job suppressing stray light. I have taken pictures of the sun (while using safety film), by simply pointing my digital camera at the eyepiece with good results.
Taking advantage of the potential for rich fields of view with refractors, I purchased a wide angle eyepiece and it revealed the main flaw in the optical path. And that is the star diagonal, the edges of which exibit considerable aberrations. A new Tele Vue diagonal is on order and I can't wait to see the improvements.
All in all I am very impressed with this telescope. The ease of operation motivates me to use it a lot, and I spend much more time observing than searching for objects. It is still rather fragile (especially the tripod), but it is an order of magnitude better than the entry-level scopes of a decade ago, and almost an order of magnitude cheaper than the "go to" telescopes of that same time.
Update to Meade DS 90EC Report (02/14/02)
As I mentioned before, the ease of use and portability of this telescope motivates me to use it a lot, and I have. Even though now I also own a larger telescope, the DS 90EC is great for a quick observing session, also aided by its shorter cool down time. Over the past months, I have been able to make many more observations to present on this review.
First of all, a correction is in order. The 9.7 Plossel and barlow combination offer 206x, not 222x as previously stated. A more thorough star test has confirmed that this optcs' sample is very good. I feel that the telescope is capable of more than the 206x and I have tried 309x, which is possible by placing the shorty barlow in front of the star diagonal. Even on very good nights this has turned out to be too much as the image definitely breaks down at that magnification, even during excellent seeing conditions. However, 206x is already pushing it for this aperture and I am very happy to be able to obtain such good images at that magnification.
The Tele Vue Star diagonal helped quite a bit but with a caveat. I only ran into problems with the supplied star diagonal when using a wide-angle eyepiece or at very high powers where imperfections in the mirror were notable. It was perfectly fine for mid and low power viewing. The Tele Vue seems to be flawless and provides a distortion-free and also slightly brighter image. It also costs $75.00 so it is a big addition for a relatively inexpensive telescope. A definite must have on the other hand is a set of color filters for the planets. For example, the #8 yellow filter increases contrast in both Jupiter and Saturn while also suppressing the false color. And for the price, it is a good investment.
I finally caught Jupiter on a steady night and the detail was very good. The Great Red Spot was clearly visible as well as other cloud detail. Several satellite and shadow transits have also been observed with great results. The more I observe in different conditions, the more I have come to realize what a big effect the atmosphere has on image resolution as well as in false color. There is much less color when the air is dry. Again, here in Arizona it is easy to get spoiled by excellent seeing conditions.
I have not encountered any other problems with the telescope. The electronics are really quite good and once you learn all the tricks of the Autostar system, it works pretty well. There are many resources available for Autostar users. In fact the backlash compensation and tracking works better than that of my bigger "go-to" telescope. The only computer crashes I have experienced were related to low battery power. Batteries last about 5 hours of continuous use and I use the rechargeable NiH type. My only Autostar complaint is that this unit has a relatively small object database. However, there is space for 200 user-defined objects and these can be changed at any time. Care must be taken to make sure the electronic cords do not wrap around the mount during slewing.
My new scope came with a 40mm Plossel eyepiece that when used with the 90EC produces a very wide field of view. All of the Pleiades fit in the field for a stunning sight that is impossible to reproduce in my bigger scope. With a Lumicon UHC filter the large extent of the Orion nebula can be really appreciated. This filter darkens the background sky enough to produce an improvement in the image even though the 90mm aperture is small.
Again I recommend this telescope to anybody on a low budget. The accessories can be added with time. The optics are reasonably good and there is the optional magic of Autostar.
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