Discovery RFT90


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Discovery RFT90
This is the same as the Orion Short Tube 90. I got it 3 weeks ago (today 12/22) but the weather has been so bad, that I really have not wrung it out. I brought it outside a few days after I got it and again last night. I was not dark enough for a star test. Here is what I discovered thus far.

3.5" clear aperature with some lens coatings (light green) and tube baffles. Comes with: OTA, 45 erect image diagonal, 2 brand X Plossls, a brand X barlow, an EQ mount that converts into a table mount, 6x30 finder. Promised moon filter was missing, but I already had one. The whole thing fits in a case about twice as thick as a brief case. It will fit in an overhead airline bin, but not under the seat. The case is not padded enough to allow airline lugage handlers to have it.

The mount is adequate, but a bit wobbly. Any sturdier and it would not be so portable, so it is a trade-off. It helps not to extend the last section of leg and view seated. The quick-release attaching mechanism is not very sturdy, but adequate if you rubber-band the release lever in the shut position. (I think I will replace that.)

With supplied EP and diagonal it gave a nice view of M31 with the entire thing in view. With the supplied barlow, it gave adequate views of Jupiter and Saturn (the seeing was not particularly good). Later, with a gibbous moon up and a thin cloud cover it revealed some luminous fuzziness at Orion's Nebula. The moon was pretty sharp. Last night it was pretty clear for awhile with no moon. Also, I replaced the 45 diagonal with an Orion mirror diag. and used my 25mm University orthos. I could not find Andromeda (my roof was in the way), but the double cluster was very pleasing. Orion's Nebula and its whispy structure were obvious as were dark spots in the nebula. Some fuzziness could be discerned around Pliedes, though the stars were sharp and without any chromal aberrations. Stars arrear as sharp pin-points. No apparent diffraction. These observations were made in my somewhat light polluted backyard.

I am taking this scope to a very dark site over Christmas and we will see how it does. It seems to work pretty well considering I am used to using an 8" Dob. If you get one, replace I diagonal immediately. I cannot figure out why they put a 45 terrestrial viewing diagonal on an EQ mounted scope. The supplied EPs are not bad, but if you have better ones handy, you ought to use them. Also, you may decide that the EQ mount is not worth the trouble and get a big camera tripod instead. The field of view is very wide and apparent movement of stars is not very quick.

I will write again when I have had a chance to really use it in a dark place.
rah4@hotmail.com

Overall Rating: No Vote
Weight: <none>
Date:
By: Anonymous (xxx.xxx.205.173)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=40217


Discovery RFT90
The Little Scope that Could

I wrote the previous review. Since then, I have tested it at a dark sight in western Massachusetts. It was bitterly cold, so I did not stay out long.

First, a correction. I mentioned that the mount's quick-release was a bit unstable. I discovered that the cause was some of the screws not being tight. Once tightened, it was good.

Nice view of M31 again. Both companion galaxies were visible and a large extent of the disk. Orion's Nebular was clear with extensive whispy. Using a 32mm Sirius Plossl, nearly the entire "sword" was visible. Moving to a 12.5mm ortho, the four stars of the Trapizium were distinct. It was apparent that the four stars were not exactly the same color.

On a different and soupier night, Jupiter and Saturn gave nice images through the Celestron Ultima Barlow. (In the future, I might use the supplied 2 element Barlow just because it is a little lighter.) Some detail on Jupiter's disk was visible, more than just the two obvious bands. Could see Titan and one other fainter moon. A 12.5mm ortho and Barlow is probably the magnification limit of this scope.

I do not know how this scope compares to others of its size since I have never had a thousand bucks to drop in a Televue Pronto, therefore, I have no basis for a numerical rating. Nevertheless, this scope works. I do not know how a very technical test would rate the lenses, but that are surely good enough for anything I am going to do. I find the supplied EQ mount to be awkward, but I am not used to using one. Also, its weight (about 5 lbs for the head) renders the tripod top heavy. I am going to construct an alt-az mount similar to the one described in the Oct.2000 S&T. This will save overall travel weight and make the mount more convenient for me. I have also added a Rigel Quickfinder. (The supplied finder and its mount require about ten minutes to attach with a screwdriver.) I agree with other reviewers of this scope (under the Orion Short Tube 90 title) that to bring out its full potential, the diagonal needs to be replaced almost immediately.

In conclusion, for its size it is an entirely satisfactory telescope, far superior to anything you can find at the mall.

rah4@hotmail.com

Overall Rating: No Vote
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Date:
By: Anonymous (xxx.xxx.206.102)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=40218


Discovery RFT90
I agree with the comments of the previous reviewer (rah4@hotmail.com). I like the packaging in a sturdy travel bag. I found tha the counterweight on mine was not nearly enough to balance the OTA. To give you an idea of how much additional weight is required, I had to hang a Pentax 7x50 binocular, in it's case, on the other counterweight to get it to balance. Since the binoculars fit in the carry bag of the scope, I may continue to use them a counterweight when I travel, instead of adding another heavy weight to the bag that only serves as a counterweight.
I, also, found that my quick release latch has the tendency to loosen. Since there is no lock nut on it and it can not be fully tightened ( then the lever would not move) loosening is inevitable. Also, the square plastic mounting block on the tube needs to be tightened firmly and the scope should be moved by pushing on the declination slow motion control handle not the tube to prevent this block from looosening.
When I first used the scope the equatorial head was very loose and sloopy and after some use the declination brake stopped working properly. I dissasembled the head and found both brakes work by tightening a screw directly against a piece of tan colored plastic. The pressure from the steel screw had crunched through the plastic and was gouging the aluminum of the rotating declination casting. To fix this, I broke a 1/2"X1/2" piece of hacksaw blade off (it was the quickest, easiest piece of thin metal to fashion to the right size in my workshop)and placed inside the eq. head for the screw to push against and placed a thick piece of cardboard on that to apply friction to the rotating aluminum shafts. Then, the inner fixed steel declination shaft, which was very loose, was tightened with an allen wrench and the rest assembled with all the nuts and bolts tightened to give free motion without play. After this, the equatorial head is much steadier and smoother and works fine. The tripod, though, is not very steady if the center shaft is extended. Like the former reviewer, I always observe with it unextended to maximize steadiness. This means sitting or kneeling on a chair for most observing.
Optically, I wasn't expecting much from such a small achromatic refractor of such short focal length. My main scope is a homemade 16" dob using Obsession's design and parts, and a Meade mirror. I bought the 90mm scope for three reasons. I travel a lot every summer and miss being able to look at the sky through a scope, wanted a large finder for my 17.5" Discovery Truss tube Dob, that was ordered and now received, and the scope was very cheap (I've spent almost as much on a single Nagler eyepiece as many of us have done, so how critical can you be). So, I was pleasantly surprised at how much I could really see with it. I don't use the stock eyepieces. I checked them out and they are usable and aren't bad but I have better ones with wider fields. Also, the 45* diagonal is useless for astronomy, so replace it immediately unless you have a chiropractor on retainer.To obtain high powers, I placed a long, standard 2X Meade barlow before the diagonal( to be able to bring to focus, don't fully insert). This gives you more than the 2X, maybe around 3X(I don't have any 2.8x, 3X or higher barlows on hand.If you do, use them.)If you want even higher powers, use another barlow after the diagonal.Then maybe you will get 6X but with more image degradation. When looking at Jupiter using a Celestron 7.5 Ultima and the barlow before the diag., maybe around 200X, I am able to see the shadows of moons passing over the surface as a small black dot. I've counted 5 dark bands on the surface with hints of detail in the bands. At least, the bands aren't completely homogenous in width and density. Of course, Jupiter is surrounded by purple haze as expected. Saturn is very nice with no purple haze, with Cassini's division, shadow on the surface from the rings and surface shading apparent. Having said this, I didn't get this for a planetary scope and the views don't come close to the ones in my 16". The thing this scope really shines doing, is giving very pleasing wide field views of star clusters. The stars are very sharp tiny pinpoints and I don't notice any color problem except on the brightest objects. Blue and yellow double stars are blue and yellow. In a dark location, the Orion Nebula is very large and beautiful, as though any scope. The four trapezium stars are easily seen. I have looked, but have not seen the E and F stars from my city home ( Riyadh, Saudi Arabia, A city of 4 million) which are often easily seen in my 16", so will try from the dark, desert sky.
Comparison to other scopes its size? As I said I bought it for use as a finder and I already have a Lumicon 80mm on my 16". I figured that the price for the 90MM wasn't too much more and you get a rack and pinion focuser(the Lumicon only has a ,IMHO, useless helical one), plus the additional aperature. Optically, the Discovery is much superior with much less color (chromatism), sharper pinpoint images and the abilty to take higher powers.
I, like the previous reviewer, don't have any several thousand dollar APO to compare it to. This makes it hard to give any meaningful numerical rating. I'd give the tripod a below average or fair rating. I cannot think of when I would ever use the short tabletop legs that are supplied, but they should be quite steady (or as steady as the table they are set upon) as they are short,solid, heavy lengths of steel. The equatorial head, after adjustments and modification to the brakes an ok, usable ratings. The optical tube assembly and optics, considering the price and design, F5.6 and achromatic, a very good rating. The packaging, an excellent rating. And the price, an excellent rating. The Barlow is as sharp as my Meade. The eyepieces, Ok and usable, if that is all you have at first, The finder, ok, since the main scope is capable of such low powers and can be a finder itself, and last, but least, the diagonal, totally useless, unless you want to watch birds (although, I have never used the scope in the daytime, so I can't even attest to this).
A great, easily transportable, low maintenance (as compared to a reflector) scope for a beginer or child with adult help. My 3 1/2 year old enjoys looking though it. It is VASTLY superior to any 60mm department store scopes. I have one of these that I bought for a guide scope years ago to compare it to. It is fun to use and very quick to set up and take outside for a quick look. It does well what it is designed to do, and that is, to give sharp low power wide field view, to be easily tranported and, obviously, to be economical. And, as a bonus, it also has some high power capability. I would not be embarrassed to give as a gift,although the declination and RA locks must be modified as soon as possible before the plastic brake is destroyed and damage is done to the aluminum castings.
Hope this review helps.
Bob Parks at arielb3@yahoo.com

Overall Rating: No Vote
Weight: <none>
Date:
By: Anonymous (xxx.xxx.19.155)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=40219


Discovery RFT90
For the price (clearance: $159.00 directly from Discovery) it can't be beat. It came with 25mm, 10mm, 2x barlow, table top tripod, field tripod, EQ mount, and carry-all bag. The optics are excellent with very little aberration. The 2x barlow is worthless, but the other two lenses actually give very good viewing. The focuser was broken during shipment, but Discovery replaced it immediately -- good service. The EQ mount is not as smooth as it could be, but otherwise I have been quite pleased.

Overall Rating: 9
Optics:9 Mount:7 Ease of Use:8 Value:10
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.36.65)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=184289

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