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T-Rex vs. DM 6

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#1 la200o

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Posted 17 October 2012 - 11:51 AM

Anybody ever done a head-to-head? Or had 'em both? Your thoughts about one vs. the other?

Thanks,
Bill

#2 Tamiji Homma

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Posted 17 October 2012 - 03:34 PM

Hi Bill,

I have both T-REX and DM-6 and use them side-by-side.

In terms of capacity and stability, given the same steady tripod, DM-6 may have a little edge over T-REX when you go to 7" f/8 refractor. Up to 6" f/8, both T-REX and DM-6 perform equally well.

5" f/7 on DM-6 and 6" f/8 on T-REX and MN-86 on DM-6

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Tammy

#3 la200o

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Posted 17 October 2012 - 05:39 PM

Tammy,

Beautiful! I like the slo mo cables on the T-Rex. Do they work well?

Bill

#4 Mkofski

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Posted 17 October 2012 - 06:07 PM

What tripod is that on the right n the first picture? Is it as stable as it looks?

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#5 Tamiji Homma

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Posted 17 October 2012 - 06:32 PM

Beautiful! I like the slo mo cables on the T-Rex. Do they work well?


Yes, they work well. I have two different length cables. When cable becomes long, it creates lag. So if you go alt/az up/down/left/right, you feel more lag when you reverse direction. Maybe more stiff cable would help but it would not be easy to handle.

If you are tracking specific target, you go on the same direction. The lag isn't a big deal.

Your arms feel a little sore next day after a few hours of manual tracking, though. It is actually quite workout, believe or not :)

Tammy

#6 Tamiji Homma

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Posted 17 October 2012 - 06:41 PM

The tripod is Tall Tripod by Joe Castoro at Binoscope.com. I bought the tripod for 60lb 6" binoculars originally.

You can read about it here.
http://www.binoscope...ino.htm#tripods

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Tammy

#7 Ira

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Posted 18 October 2012 - 03:39 PM

I have a T-Rex. Like it alot, except manual tracking is a hassle after you've gotten used to a driven scope. Since I've gotten my iOptron MiniTower Pro working, I've all but abandoned manual tracking. Only use it as a backup now if the MiniTower fails.

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#8 johnnyha

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Posted 18 October 2012 - 04:36 PM

Tammy how does the T-Rex compare to the DM6 with regards to changing out heavy eyepieces and how smooth are the movements? With my DM6 I can change out a 31T5 or 21E no problem without losing the target. I also find the DM6 has no need for slo mo cables, I just move the telescope by hand and its *perfectly smooth* at over 300X.

#9 Tamiji Homma

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Posted 18 October 2012 - 05:38 PM

Tammy how does the T-Rex compare to the DM6 with regards to changing out heavy eyepieces and how smooth are the movements? With my DM6 I can change out a 31T5 or 21E no problem without losing the target. I also find the DM6 has no need for slo mo cables, I just move the telescope by hand and its *perfectly smooth* at over 300X.


Hi Johnny,

What scope did you put on DM-6 with Nagler 31T5/Ethos 21? FS-152?

Are you saying that ALT axis stays put when you remove 31T5 or Ethos 21 from focuser so that you can put other eyepiece back in focuser without any rotation on ALT axis?

My DM-6 can not do that. T-REX can't do that either.

For example, with TMB 130SS f/7 with 31T5/Baader MaxBright diagonal, distance from scope weight center to eyepiece is about 19 inches, 31T5 is about 2.2lb. That's a lot of moment, I mean big unbalance, isn't it?

Your DM-6 does not rotate at all with such force? You may have tighten DM-6 ALT disk much harder than mine but that's a lot.

Regarding smoothness of T-REX movement, it is as smooth as DM-6 as far as I can tell. You can track at 300x without slow motion with T-REX as well.

Tammy

#10 johnnyha

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Posted 18 October 2012 - 06:31 PM

Thanks for the answer Tammy. Yes absolutely with the FS152, easily - I have the DM6 tightened per the manual, so that I can add or remove a 31T5 without the scope moving at all - and a touch more for good measure. Works beautifully. I balance the tube near the midpoint of COB with the 31T5 at 60 degrees but with a bit more weight forward. Also per Tom Peters' preference I keep the az pretty tight, we had a long phone conversation about it. He has said on Yahoo too that people tend to keep their DM6's way too loose, especially in az - he prefers it tight and I agree. I cranked alt and az down and I love it. They should not be where you can move it with the touch of a finger, that's not the concept. Motions are still completely smooth and easy. I can move the target anywhere within the FOV, even an ortho, fluidly. Tighten it down in alt and az Tammy, and let me know what you think. When it's tightened down a bit, the heavier the eyepiece the more fluid the movement.

The FS152 fluorite doublet is a *perfectly* balanced tube to begin with compared to say a grossly front-heavy TOA130 triplet, I think this helps a lot.

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#11 la200o

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Posted 18 October 2012 - 09:04 PM

Johnny,

That is a beautiful set-up. And I must say, the ability to change heavy eyepieces without losing the target sounds wonderful to me.

Bill

#12 johnnyha

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Posted 19 October 2012 - 12:55 AM

Thanks Bill, with the recent addition of the FT 3543 I feel like I finally found the magic combination. :cool:

I have actually removed the MkV binos loaded with Brandons, changed the glasspath quickly, and put them back on without losing the target.

#13 JMW

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Posted 19 October 2012 - 10:07 AM

I own the DM-6 and DM-4. I use the DM-4 when portability is the most important factor. I use the DM-6 for when I want the scope to not move between eyepieces. That is with my SV115T20. My TEC 140 APO only gets used on the DM-6. My C11 EdgeHD also works great on my DM-6.

My setup looks close to Jonny's. My DM-6 is on top of a Losmondy extension on top of the Planet tripod. I love if for public outreach. I never fear it being around the public in this solid setup.

Jeff

#14 Tamiji Homma

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Posted 19 October 2012 - 10:52 AM

The FS152 fluorite doublet is a *perfectly* balanced tube to begin with compared to say a grossly front-heavy TOA130 triplet, I think this helps a lot.



Hi Johnny,

I think that weight balance of FS-152 made it easer as you said. I can try grossly front-heavy 6" f/8 to see if I can do that or not? :)

Tammy

#15 jmiele

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Posted 19 October 2012 - 02:07 PM

I haven't had a T-Rex but can't say enough good things about the DM-6. I've had everything from an FSQ, TOA150 to Mewlon 300CRS on mine. And the fit and finish are excellent as well..

Best, Joe

#16 johnnyha

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Posted 19 October 2012 - 04:01 PM

Hi Johnny,

I think that weight balance of FS-152 made it easer as you said. I can try grossly front-heavy 6" f/8 to see if I can do that or not? :)

Tammy


Yes I think you should still be able to do that with your grossly, obscenely front-heavy triplet, Tammy. :grin: Here is the section from the manual that describes initial setup:

Best balance (Altitude axis)
Balance should be performed first with the telescope set up with no eyepiece (worst case light), then again with the heaviest eyepiece (worst case heavy).
The Disc Mount will handle approximately 21/2 pounds’ weight difference. The weight spread can be larger or smaller depending on the weight, length of the telescope, the height the heaviest eyepiece is above the center of gravity, and the highest power being used. My 5.5” diameter, f-7, 24lb., refractor works well when adjusted with a 0-21/2 pound differential. The movement at 250 power is still smooth.


Here is another shot, where the FS152 is balanced for a 31T5... just mess around with balancing the scope and tightening up the nuts until you can take the eyepiece out and stick it back in without the scope moving. I also found the 8" long Eagle pier extension has more torsional stability than the DM6 extension, which helps in az especially. When your setup with a couple long extensions maybe that is also contributing to the movements you were reporting in az.

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#17 Tamiji Homma

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Posted 19 October 2012 - 09:53 PM

Here is "grossly, obscenely front-heavy triplet" balance with ES9-120 :)

I did tighten ALT disc so that scope didn't turn when I removed ES9-120, whose weight is 1,294 gram. I wasn't able to try it this evening. It is dense fog here :(

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#18 johnnyha

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Posted 19 October 2012 - 09:57 PM

Sweet! Yeh it's foggy in Sherman Oaks too. ;)

#19 Ira

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Posted 20 October 2012 - 09:31 PM

I don't have any problems with balance changing out heavy eyepieces with my T-Rex and a 5" f6 APO. Never loose the object because of that. The T-Rex has axle locks that really hold it in place, even when severely unbalanced.

/Ira

#20 mistyridge

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Posted 20 October 2012 - 10:29 PM

I have a DM6 and use a variety of scopes on it, including A SV115T20, C-8Edge HD and C-9.25 Edge HD. I find it get more use than my Losmandy G11. I use the Losmandy tripod with 12" extension.






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