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    h2ikxf's Avatar
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    Default Some observations on the installation of a Telrad



    Thoroughly disgusted with the stock 6 x 30 finder scope that came standard with my Celestron OMNI XLT 102 Refractor I decided to replace it with something else.

    There's plenty of choices out there in right angle finder scopes, reflex sights, laser pointers, etc... but I settled on a Telrad. Why the Telrad over anything else is a subject for another posting. For this posting I wish to provide some insights for the benefit of others in the mounting of the Telrad.

    One of my disgusts with this finder scope is the height between the telescope body and the center of the eye piece. Putting a crick in your neck when using it was going to be a recurring annoyance. The centre of the objective lense for the finder scope whilst seated in it's riser is 3 3/4" (9.525 cm) from the body of the telescope. Clearly I needed to get some more height.

    Researching the Telrad I learned that the distance between the telescope body and the glass viewing window of the Telrad is: 4" (10.16 cm). Hmmm... very close to the stock Celestron finder scope. Luckily Telrad has optional 2" (5.08 cm) and 4" (10.16 CM) risers available.

    BE FORWARNED. If you intend to use these risers you should know that their height has been mis-stated in the sales literature. I point this out not to quibble over it but simply to make people aware of it. The stated heights of 2" (5.08 cm) and 4" (10.16 CM) represents the height of the posts between the upper and lower mounting plates of the riser. Each plate (lower and upper) is an additional 3/16" or a total additional height of 3/8". Thus the ACTUAL height of the risers are 2 3/8" (6.03 cm) and 4 3/8" (11.11 CM).

    When you add the riser between the Telrad and it's mounting base the overall height from the telescope body to the centre of the looking glass would be 6 3/8" (16.19 cm) and 8 3/8" (21.27cm) respectively. On my telescope it has nearly doubled the height from the stock Celesctron finder scope.

    Some people have observed that they don't like the "look" of the Telrad mounted on a refractor as it appears to ungainly. HA! The overall difference in height when mounted is negligible on a 4" telescope on a 6" or 8" even less. The relative shape is a 2 x 2 profile on a riser. Even if you were to mount it on a 2" telescope it would not look ungainly since the relative sizes are similar. If it appeared as anything --relative to a 2" telescopes tube size -- it would be as a carrying handle or the handle grip on a rifle. One couldn't describe this as ungainly or aesthetically unpleasing. Now if I had purchased a 6 x 50 right angle finder scope and mounted that on my telescope THAT would look ungainly to the point of being ridiculously outlandish. So, if anyone has thought about using a Telrad on their refractor I say give it a go. The worst that could happen is you find yourself with a Telrad that you can use on your 10"+ reflector you already have or will be purchasing in future.

    Now on with the mounting of it.

    Some suggested mounting it as near the end of the OTA as possible. I found through experience this past week this is a bad idea. When you are seated and looking up the length of the tube toward the Telrad's glass view finder the farther the device is from your eye the larger the concentric rings become. So much so that the middle ring (of the three reticle rings) fills the glass view finder from edge to edge both vertically and horizontally. Moving the Telrad so that it's more centered in the length of the OTA ended up having the outermost ring filling the glass view finder edge to edge. Interestingly, placing the back-end of the Telrad's base up against the plate where the stock Celestron view finder was mounted (on top of the focuser housing) produced the best results. In that position the distance between the glass view finder and where my eye would be when I looked up from the telescope's eye piece in the star diagonal ended up being 7". The three reticle rings were centered within the Telrad's glass view finder with plenty of room on all sides.

    Now that I found where to mount the Telrad I had to decide how. Do I drill holes and mount the Telrad or do I use the sticky tape on the back of the Telrad's mounting base? Neither option thrilled me. The former would savage the resale value and looks should I (or the next owner) choose not to use the Telrad anymore. The latter would be a serious pain in one of two ways. In the best case scenario I would need to put new sticky tape on the Telrad's mounting bracket and the telescopes paint job would be marred. Worst case scenario, I would manage to snap the aged plastic of the Telrad's mounting base requiring the purchase of a new one and savage the paint job on the telescope. I decided to try the suggestion of another forum member to use velcro straps. The kind without the sticky-tape backing obviously. Viola! It worked like a charm. A word of caution though to those who also use this solution. The velcro will secure the Telrad to the telescope, however, if you should "bump" or "jar" the Telrad more than slightly it will move on you a bit. The movement isn't serious -- unless your "bump" is -- but it is there. It won't affect the Telrad's use to center on objects so you won't have to re-orient the Telrad's reticles in the glass view finder but it will shift it from where you had it on the telescopes body.

    I've only ONE complaint with my Telrad. Two days of use and the reticles brightness control knob is either off, at 75% brightness through to 100% brightness. Anything below 75%... zilch. I have to contact the seller and arrange for a return goods exchange. Isn't that something? You finally get it sorted and BOOM the thing goes south on you.
    =========================================
    Planisphere: Guide to the Stars (ISBN: 1928771033)
    Celestron SkyMaster Binoculars 20x80
    Celestron Omni XLT Refractor 102mm f/9.8 CG-4 Equatorial
    Nikon D3000 DSLR

    =========================================

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  3. #2
    LouP's Avatar
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    Quote Originally Posted by h2ikxf View Post
    I've only ONE complaint with my Telrad. Two days of use and the reticles brightness control knob is either off, at 75% brightness through to 100% brightness. Anything below 75%... zilch. I have to contact the seller and arrange for a return goods exchange. Isn't that something? You finally get it sorted and BOOM the thing goes south on you.

    Same thing has happened to mine. I am suspecting that this happens with anything less than fully charged batteries. I doesn't really bother me as I can still adjust the brightness down so it's dim enough for me. It's just that the range on the switch has now moved to the "bright" end for me where before it was more toward the off position (if that makes any sense).

    LouP

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    MarkM's Avatar
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    Quote Originally Posted by h2ikxf View Post

    I've only ONE complaint with my Telrad. Two days of use and the reticles brightness control knob is either off, at 75% brightness through to 100% brightness. Anything below 75%... zilch. I have to contact the seller and arrange for a return goods exchange. Isn't that something? You finally get it sorted and BOOM the thing goes south on you.
    Yep, that is faulty. Mine smoothly dims as the lever is rotated. Sounds like you learned a lot though--thanks for sharing your knowledge with us.
    Location: 30° 19' N; 97° 54' W; elev 248 meters; yellow/green zone; NELM 5.7
    Instruments: Obsession 15" Dob; Orion XT8i; 2" refractor (Galileoscope); Televue EP arsenal; Bushnell 7X50 binos
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