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Telrad vs Celestron/Orion Red Dot

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#1 nikdangr

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Posted 19 February 2013 - 11:27 PM

What are the differences between those two finders in terms of usefulness in finding your way around the sky?

#2 herrointment

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Posted 20 February 2013 - 01:11 AM

One is easy to use and well made and the other is not.

#3 David Knisely

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Posted 20 February 2013 - 01:26 AM

What are the differences between those two finders in terms of usefulness in finding your way around the sky?


A Red Dot finder is simply a way to point the scope at something you can see or know the precise location of. You just put the dot over the location of the object and it should be at least close to being in the field of the main telescope. The problem is that in some star-poor areas, it can be hard to find that location precisely enough to put the dot right on it. The dot may also be big or bright enough to cover up the desired location.

A Telrad is way different. It is reflex-type finder which puts an unique three-ring reticle of adjustable brightness in the viewer's field. These rings are 0.5 degrees, 2 degrees, and 4 degrees in diameter on the sky, and are most useful, not just as a simple bulls-eye, but as a "pattern maker", for star hopping. By using overlays which resemble the Telrad's reticle pattern on star atlases, and centering the target object's chart location in the overlay, star patterns and alignments with the Telrad rings in the area around deep-sky objects can be worked out which can then be duplicated by looking through the Telrad at the night sky. The Telrad rings can also be used as measured "steps" in extended star hops. This can make finding even faint non-naked eye objects much easier than with the simple "dot" finders. Those people who insist on downplaying the Telrad's usefulness based on merely using the unit only as a "bull's-eye" centering finder like the "dot" sights do not really understand how to use a Telrad! It is the pattern making or stepping-off field size which makes it a truly valuable finding device for the telescope.

The Telrad is a bit bulkier than some of the simpler "dot" sights, but its low cost (less than many telescopic finders) and simplicity have made it very popular, especially among Dobsonian telescope users. For smaller scopes, another popular reflex finder is the Rigel Quickfinder, which is smaller and lighter than the Telrad. However, it only produces two rings in its window instead of the Telrad's three, and is a bit more fragile physically.

Below is an example of how the three rings of the Telrad are used to find an object that is far too faint to be seen with the unaided eye (in this case, the faint galaxy NGC 1272 which is one of the core galaxies of the Perseus Galaxy cluster Abell 426). Clear skies to you.

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#4 orlyandico

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Posted 20 February 2013 - 06:39 AM

the Telrad is also very good because you can "acquire" the reticle very easily and you can see this reticle even off-axis.

The Rigel is much worse in this regard; your eye must be positioned just right to see the reticle.

I suspect the various red dot finders are more like the Rigel.

Telrad all the way (I have two).

#5 Jon Isaacs

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Posted 20 February 2013 - 07:18 AM

the Telrad is also very good because you can "acquire" the reticle very easily and you can see this reticle even off-axis.

The Rigel is much worse in this regard; your eye must be positioned just right to see the reticle.

I suspect the various red dot finders are more like the Rigel.

Telrad all the way (I have two).


Telrads are a wonderful tool. They are not the most attractive piece of equipment but they are very effective and as you say, the reticule is much easier than the Rigel's, the 4 degree ring is very useful and the AA batteries last forever. I have a few myself.

I also have some red dot finders. Like the Telrad, the dot is easy to find, they have some parallax but it's within reason. I use red dot finders on telescopes that have wide fields of view, 3-4 degrees, the scope itself is a finder and it is possible, with reduced accuracy, to point the scope in a similar manner to the Telrad, gauging star fields rather than directly pointing at an object.

Jon

#6 nikdangr

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Posted 20 February 2013 - 07:53 AM

Well, I'm glad a Telrad is inexpensive. It sounds much more appropriate for my C90, and I'm sure I can get most of those dollars by putting my red dot on eBay. I like inexpensive mistakes. :rockon:

#7 nikdangr

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Posted 20 February 2013 - 07:56 AM

Is there a planetarium app for Android that will put the Telrad reticle on a selected object?

#8 Jon Isaacs

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Posted 20 February 2013 - 08:16 AM

Is there a planetarium app for Android that will put the Telrad reticle on a selected object?


Sky Safari had the capability to display the Telrad reticule. It can also be customized. There are three versions, the Basic, the Plus and the Pro. The Plus is $15, the Pro is about $40. Unless you are super serious and have a large scope, the Plus has about everything you need, the only difference is the size of the databases.

Sky Safari is an amazing program, it has features that few if any desktop programs have.

Sky Safari for the Android

A Telrad is pretty big, about 8 inches long, mounting one on a C-90 is possible but something of a stretch.

Jon

#9 orlyandico

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Posted 20 February 2013 - 08:35 AM

one nice thing about the Telrad is that it attaches with double-sided tape (so long as you have the base). it's easy to remove the Telrad base from a scope - just use floss to cut through the double-sided tape. Then clean up the adhesive residue with Simple Green.

The telrad is accurate enough that if I put a star at the center of the smallest circle (which is 0.5 degree I think?) it will be in the FOV of my C9.25 with a 15mm-range reticle eyepiece. Very handy when doing the GoTo align...

#10 nikdangr

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Posted 20 February 2013 - 08:59 AM

Is there a planetarium app for Android that will put the Telrad reticle on a selected object?


Sky Safari had the capability to display the Telrad reticule. It can also be customized. There are three versions, the Basic, the Plus and the Pro. The Plus is $15, the Pro is about $40. Unless you are super serious and have a large scope, the Plus has about everything you need, the only difference is the size of the databases.

Sky Safari is an amazing program, it has features that few if any desktop programs have.

Sky Safari for the Android

A Telrad is pretty big, about 8 inches long, mounting one on a C-90 is possible but something of a stretch.

Jon

They've got an adapter at ScopeStuff that will slide right into the existing female dovetail on the C90. It'll look dorky but it's shorter than the OTA and the eyepiece is far enough back so I won't bump my forehead on the Telrad. The female dovetail on the scope will only hold a couple of inches of the adapter at the back end, but at 11 oz. that shouldn't be a problem. If it is, I can make a spacer that will friction fit between the adapter and OTA at the front end.

Thanks for the tip on sky Safari. I'll definitely check that out.

#11 spencerj

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Posted 20 February 2013 - 09:17 AM

I love the Telrad. It is so easy to use, very accurate and very durable, but for a small OTA like the C90 it is not a good fit.

Hanging something as large as a Telrad off some kind of adapter just doesn't sound like a good time. The best way to mount a Telrad is with the double sided tape directly on the OTA. That just will not work well with the C90.

I usually use my 90mm Apex for quick views of bright (easy to find) objects like the planets, the moon, double stars and bright DSO's. For that kind of application, the Telrad's great features are not very useful--especially when you consider the mounting difficulties. For my Apex 90, I use a simple Stellarvue red-dot finder (not sure if you can get those any more). Outside of that, I think the multi-reticle finders are a good choice. They are a little more expensive, but very well made.

#12 Jon Isaacs

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Posted 20 February 2013 - 10:26 AM

Outside of that, I think the multi-reticle finders are a good choice. They are a little more expensive, but very well made.



I have one of those Multi-Reticle finders, it sure looks a lot nicer than the standard red dot but it's not dim enough, the only reticule that has a chance of being dim enough is the red dot... The $25 OPT red dot is about as effective.

Jon

#13 nikdangr

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Posted 20 February 2013 - 01:18 PM

Got the red dot batteries from Amazon. The red dot finder I bought off eBay doesn't work. So...I'll try the Telrad when I get it and if it doesn't work out, I'll save it for a future scope and buy a new red dot finder.

#14 spencerj

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Posted 20 February 2013 - 03:00 PM

I have one of those Multi-Reticle finders, it sure looks a lot nicer than the standard red dot but it's not dim enough, the only reticule that has a chance of being dim enough is the red dot... The $25 OPT red dot is about as effective.

Jon


They are a bit brighter than my old Stellarvue red-dot finder. I am surprised so many vendors sell them as premium RDFs. I have never been too bothered by the brightness, because I use mine in my suburban backyard to point at reasonably bright objects or for aligning my Sky Commander.

Jon,

I looked at the OPT site. For $25 they still have the Stellarvue F1 finder listed. I would love to get another one of those, but I suspect "back ordered" means "gone forever". Was that the one you were talking about? Or was it the $27 RDF that has the exposed battery? I have two of those in a junk drawer somewhere. They were cheaply made and just stopped working after a month or two. I thought the first was a fluke so I bought the second. Didn't want to buy a third so I picked up the multi reticle with the bright dot that everyone sells.

#15 nikdangr

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Posted 20 February 2013 - 03:21 PM

Is this the red dot Stellarvue you're talking about? Seems to be available.

http://www.stellarvu...ot_finders.html

The multi-reticle Stellarvue is available in a dimmer version for an extra $20 over the brighter one.

http://www.stellarvu...cle_finder.html



#16 nikdangr

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Posted 20 February 2013 - 03:28 PM

Post deleted by nikdangr

#17 nikdangr

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Posted 20 February 2013 - 04:00 PM

Boy, is this fun. Got the Porta Mount today and because the C90 gets turned 90 degrees to fit in the dovetail, the location of the base for the old finder scope is unusable. So I guess I wait and see if the Telrad will work with the two-sided tape. I should have seen this coming.

More minor is the fact that the focus knob is now right behind the eyepiece. Not a showstopper, just less than optimal.

#18 Raginar

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Posted 20 February 2013 - 04:44 PM

Telrad works great with doublesided tape. ONly way I've ever attached one to my mount.

#19 cloudmagnet

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Posted 20 February 2013 - 04:48 PM

I have both- the Telrad is on my DOB, and the Orion Red Dot is on my RA88 Binocs. I find that each is well suited to their purpose.

#20 Jon Isaacs

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Posted 20 February 2013 - 08:57 PM

Or was it the $27 RDF that has the exposed battery? I have two of those in a junk drawer somewhere. They were cheaply made and just stopped working after a month or two. I thought the first was a fluke so I bought the second. Didn't want to buy a third so I picked up the multi reticle with the bright dot that everyone sells.



When I bought it, the "RDF" from OPT was $25. I have had a few, never had one fail, I let them go when I ship out a scope that needs a finder. I have had this one more than a year, it's the only finder I use on Multiple scopes and I have been through one battery but otherwise it's been a good performer. I have had others, all have been reliable for me.

I use Telrads on my larger scopes, the RDF otherwise except for a Multiple Reticule Finder on one scope.

Jon

#21 spencerj

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Posted 21 February 2013 - 09:23 AM

Boy, is this fun. Got the Porta Mount today and because the C90 gets turned 90 degrees to fit in the dovetail, the location of the base for the old finder scope is unusable. So I guess I wait and see if the Telrad will work with the two-sided tape. I should have seen this coming.


Amateur Astronomy is full of fun surprises. This won't be the last. Just take them in stride. Learn and move on. The Telrad will be a bit big on the scope, but it will work.

#22 csrlice12

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Posted 21 February 2013 - 11:26 AM

Couldn't you reposition the focuser to compensate for the 90* mounting difference? Also, while the Telrad is about half the size of the scope, and it will look unique (in astronomy we prefer the word unique to weird), but as the mount can handle the weight, it shouldn't be a problem. Try to mount it as far forward on the tube as you can, and rebalance the scope (if you mount it towards the diagonal end, you could bang your head on it, not good). The problem is, where do you mount the actual finderscope. While Telrads are good, they are really meant to be used in conjunction with a regular finderscope. The telrad gets me into the ballpark, the finder shows me home plate....

#23 nikdangr

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Posted 21 February 2013 - 11:54 AM

Couldn't you reposition the focuser to compensate for the 90* mounting difference? Also, while the Telrad is about half the size of the scope, and it will look unique (in astronomy we prefer the word unique to weird), but as the mount can handle the weight, it shouldn't be a problem. Try to mount it as far forward on the tube as you can, and rebalance the scope (if you mount it towards the diagonal end, you could bang your head on it, not good). The problem is, where do you mount the actual finderscope. While Telrads are good, they are really meant to be used in conjunction with a regular finderscope. The telrad gets me into the ballpark, the finder shows me home plate....

Can't move the focuser. It's an internal mechanism on the C90.

I'm looking at a number of options for getting a finder mounted where I want it (preferably the Telrad, but that may change).

1. Two sided tape
2. Clamshell rings on the tube
3. Remove the current finder mounting plate and see how deep I can get with sheet metal screws in a new location. The plate sits on a poly plastic ring at the back end of the OTA, so there's more depth to work with than just the metal OTA. I have to check with Celestron first and make sure the plate was originally installed with screws and not bolts. I'd hate to have nuts rattling around inside the scope.

Correction: I thought the ring was poly without having looked closely at it. It's actually aluminum.

#24 edwinh

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Posted 21 February 2013 - 12:35 PM

Is there a planetarium app for Android that will put the Telrad reticle on a selected object?


I just found this one called "astro tools" if you want something free - it has a telrad circle you can turn on or off. Wasn't aware of it earlier... can't comment on the app's usability yet.

#25 SteveG

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Posted 21 February 2013 - 01:07 PM

On my Vixen Porta, I just flipped the head and mounted my RDF on the mount. I had to drill & tap 2 small threads.

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