Last updated: 15 March 2002
Sent: Saturday, March 9, 2002 11:55:08 From: firstname.lastname@example.org (DC) I recieved the Shutan part # 5956290, called the SCT adaptor. This was ordered to see if I could use the Celestron f6.3 corrector and the Shutan SCT adaptor to widen the ETX field and reduce the focal length. The test was done on a standard 90mm ETX tube assembly (the spotter) and was placed on a Celestron G5 german EQ mount. (This same mount is available from ORION under a different name, called the EQ 2). I actually am doing all of this to widen the field of view on the ETX 90 to be used as a guidescope for my LX200, and the problem was to find a guidestar you need a wide field, bright stars, but the ETX being a MAK is often too dark with a 9mm eyepice and those glowing red dual crosshairs on the MEADE illuminated & adjustable reticle eyepiece! But as this combination worked so well, I wanted to share it with ETX users as it is also a visual dream come true. Keep in mind, the whole assembly sticks out about 3.5 inches from the back of the ETX tube, so it probably will not clear the ETX 90 forks! But being careful, it can still be used except at zenith. As I do not have a digital camera to attach to the scope for a star test and photos, I can tell you the view is crystal clear, with little diffraction problems. Maybe in the future I can send you scans done from my OM-1 35mm at a later date, but there was no clear skies for this test on the date of this article. The Shutan ETX SCT adaptor ring fits well. The included Shutan info says to NOT tighten it too much. It appears that if you did, these things can stick and getting them loose is a problem. Also it is possible to break the ETX metal thread loose from the plastic housing. (Hear that MEADE?). But I see not problems for a careful user of this part. The corrector is a Celestron f-6.3 field widener, or a focal reducer used for SCT photos work. They work well on any SCT and MEADE also makes a similar version. I have tried both and they seem identical in every way, so both are good. It weighs about 6 ounces. The Shutan SCT adaptor weighs about 6 ounces, and then you have to add a visual back, a star diagonal and of course an eyepiece. But the total weight is about 1.2 lbs. This may be too much for a ETX on the To Go mount, but maybe not. As I do not own a full To Go ETX, I do not know. OK, here we go. The test for a wider field was done using a MEADE 25mm plossel, a 45 degree upright star diaonal (So I could read measurements on a yardstick at 21 feet). I sat the ETX tube with the complete widener assembly attached and looked at a yardstick exactly 21 feet away. The standard ETX at f-13.5 showed 3.5 inchs in the eyepiece across, and the widened filed showed a full five inches! As the corrector is called a f-6.3 field corrector, that means it converts a SCT f-10 to f-6.3. This in percentages is a 63 % reduction in focal length, and a 37% wider field on any SCT. The ratios are the same on the ETX. The formula came out yielding a new ETX ratio of Focal Length 787mm, at f.8.7. The field of view is 37% wider, and power is reduced 37% accordingly. And again the actual yardstick measurement at 21 feet was f-13.5 = 3.5 inches, and f-8.7 = a full five inches! Much wider! A success! Upon doing the SAME TEST using a Celestron G5 SCT f-10 tube, it's field of view at 21 feet was FOUR inches (no corrector). So this makes the ETX a wider field than any SCT at F-10 and the estimate of focal ratio is really about f-8.7.
The cost are.. Shutan SCT adaptor $36 plus shipping. Celestron F 6.3 corrector $119 (shop around!) An SCT visual back ring (price unknown) An SCT star diagonal (about $49 bucks) and use youe existing eyepieces... So for around $200 bucks you can do all of this, a bit pricy. You can go the other way and order a more lightweight field widener, I understand some are out there in the form of a reducing star diagonal, but this way you can use SCT parts, and that means I can attach my OM-1 35mm camera using the OM-1 T bracket ring or do whatever I need to do! While I was not rigged for astrophotos at the time of this article as seeing was not good enough, I did get to look through passing clouds and got a clear view of Saturn and Jupiter. They of course seem smaller, as the power is reduced, but the field of view was much wider! ! Clean and crisp and full contrast views with perfect all the way to the edge focus.Putting on a Televue 11mm, the rings if Saturn showed the Cassini division clearly and bands on Saturn and 3 moons. Jupiter looked as good as in the regular ETX and better than my LX200! I add that an ETX Tube only is front heavy. Adding all this gear balances it almost perfectly, so for ETX tube owners, this is the way to go! It makes you a real nice 90mm APO f-8.7 refractor like scope! There was no visual distortions I could find. Perfect focus just as the regular ETX we all love to use! I am well pleased I did all of this, but as I already had all parts except the Shutam SCT ring, the conversion only cost me $42 with shipping. Shutan shipping cost was over $6 bucks..a bit high, but it came fast and well packed with a Shutan catalog. The guy at the store could not find the part number. But just tell them it is an ETX -SCT adaptor ring, they know what to ship. Hope this helps someone, and please tell people who wish to use the ETX as a guidescope about this. Anyone wishing more info write me ( I may be slow getting back as I have to work and all that stuff). Dan Callahan email@example.com The Springfield Astronomical Society
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