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Direct Drive Mounts for 30-40 Kg Astrophotography

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#1 ispybadguys

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Posted 20 September 2021 - 11:07 PM

Are there other direct drive mounts like the PlaneWave L-300 or Alcor DirectDrive Nova 120 Mount? I read on a telescope network site that they removed guide scopes from their L-300 mounts.

 

Thanks

 

Kurt 


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#2 psandelle

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Posted 20 September 2021 - 11:17 PM

Are you looking just for direct drive mounts, or mounts that can do consistent unguided imaging?

 

Paul


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#3 ispybadguys

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Posted 22 September 2021 - 11:26 AM

My dream would be 10 minute subs at 2541mm (CDK 12.5) unguided. Avoiding worrying about worm gear issues is a bonus. I was looking at one of these networked telescope sites, that I can't seem to find again, that had some L-300s, AP's, and others. They said they removed all guide scopes from them because they weren't needed. I could also mount my FSQ on the mount with the CDK.

 

Kurt


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#4 ispybadguys

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Posted 22 September 2021 - 11:34 AM

I just noticed that you have the Rainbow Astro RST-135. What do you think of that? Is it ASCOM only?


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#5 555aaa

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Posted 22 September 2021 - 12:41 PM

Yes there are.


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#6 psandelle

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Posted 22 September 2021 - 12:48 PM

10Microns do not need their worm gears adjusted, and they'll give you 10 minute subs unguided (the 2000 should be fine for that weight, I think the 1000 is stretching it) no problem. I've used the 1000 unguided over the years and LOVE it. APs with absolute encoders should do it. ASA no longer makes smaller mounts (their smallest holds 100kg), but they are wonderful for unguided, too.

 

The RST-135 won't hold the CDK 12.5, but the 300 will, but neither will do unguided. Great little mounts and a DREAM if you're strictly mobile as they're so light, but something like a 10Micron is still the better mount if pure portability is not your #1 variable.

 

Paul


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#7 ispybadguys

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Posted 22 September 2021 - 07:33 PM

Paul

 

Thanks for the info. The 2000 looks to be a little over $15k. I am trying to find out of the L-300 needs the wedge or if it can drive my Nightcrawler. It would be $10K without the wedge.

 

Kurt


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#8 psandelle

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Posted 22 September 2021 - 09:23 PM

I do like the L-350’s, but I’m strictly mobile, so it’s a no-go for me. grin.gif

 

I hope some of the Planewave owners can jump in here, as they’d know. Or, just call Planewave! Nice people.

 

Paul



#9 andysea

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Posted 22 September 2021 - 11:03 PM

I believe Planewave sells a rotator that can be used with the L-350 in alt-az mode. However I don't know how one would take flats. The Planewave mount looks like a bargain for what it can do.



#10 ispybadguys

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Posted 23 September 2021 - 06:41 AM

Paul

 

The Planewave guys are great! I have pestered Bill Dean with many emails when I was trying to figure out if I could get an OAG in the short back focus of the reducer. Bill told me that it would need to be in the Nightcrawler's ASCOM driver. I did see the following in the PWI Manual "Leveling the azimuth base when using third-party derotators (Optec, Moonlite, etc) is important to prevent errors". Bill was not aware of anybody using the NightCrawler only the Optec. I needed to use Kstars so I went with the Moonlite. It is a fantastic piece of hardware.

 

I knew the CDK was big but it is hard for me to appreciate it from an image on the web. When I hefted it onto the mount I knew I was not going to any dark site with it. I was trying to catch some photons last night. I had set the system up on my roof deck and carrying the telescope up the spiral staircase was fun. The Planewave guys thoughtfully put a sturdy handle on the back of the CDK. I got focused with very sharp stars around 1.6 pixels HFR on the Sony's 3.76um pixel. I noticed when I pointed it the polar alignment changed by a large amount. My guess is that this is due to some flexing of the tripod or the deck itself. For some locations this was 10 or 20 arc-minutes. I am waiting on a shaft extension to better balance the RA but clearly the setup is not going to work. I'll take it down today and set it on the ground and see how that performs.

 

Can you explain your comment on taking flats? I have been using the NM but skies for flats. With an AZ/EL mount I think I could put a panel on the telescope base and point at it.

 

Kurt


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#11 schellaj

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Posted 23 September 2021 - 11:05 AM

Just to be the devil's advocate here, but why do you (or anybody) "need" to do unguided imaging. Guiding is relatively easy (tho a bit more expense) and can only improve the tracking. Long focal length imaging certainly make is worth guiding.  If you can do 2 minute exposures unguided and get small stars then you can do 120 minute exposures with guiding (just to throw out a big number).

 

Maybe it's just me. I just truly don't understand. 

 

Jason


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#12 psandelle

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Posted 23 September 2021 - 12:47 PM

Just to be the devil's advocate here, but why do you (or anybody) "need" to do unguided imaging. Guiding is relatively easy (tho a bit more expense) and can only improve the tracking. Long focal length imaging certainly make is worth guiding.  If you can do 2 minute exposures unguided and get small stars then you can do 120 minute exposures with guiding (just to throw out a big number).

 

Maybe it's just me. I just truly don't understand. 

 

Jason

Well, at the very least, options: with absolute encoders you can do "unguided" (really "predictive" guiding, since it's tracking mathematically rather than optically and you don't throw out subs like someone who gets a good PA and hopes for the best), as well as guiding (with vaguely a touch every-so-often, like 10, 15 seconds), so you have a choice. As was shown with 10Micron's data, up to a certain focal length, you get better numbers unguided than guided with their mounts and algorithms/encoders (custom). And if you're strictly mobile like me, it's one less scope (unless you OAG)/camera/USB cable to worry about (or go bad, which, out in the middle of nowhere means no imaging). I never understood why people didn't want the choice in their mount of being able to do both. And, I think guiding is easy, too, but it has it's downsides as well.

Now, you say "need", and that's open to interpretation. None of us "need" any of our gear grin.gif, but having the option to do "predictive" guiding is fantastic and going unguided can be a solution for various situations.

 

Paul
 


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#13 555aaa

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Posted 23 September 2021 - 01:31 PM

Guiding is worse than unguided because the guide star position is noisy and so you are just injecting that noise into the drive system and telling the mount to sped up by a bunch and then slow down a bunch and then speed up again when
you should just as well leave alone.
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#14 ispybadguys

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Posted 23 September 2021 - 05:38 PM

Jason

 

In my case the back focal length of the CDK with the reducer is too short to get an OAG in there and with a focal length of 1677mm with the reducer is kind of long for your average 240mm guide scope. I just tried the Sagitta OAG last night with the unreduced 2541mm focal length and the stars I could see had an SNR of 12 at 15 seconds integration time. This strikes me as that there is something wrong but IDK what. The OAG Stalk is fully extended and I can see a slight shadow on the FPA. That is driving my interest and then of course the bragging rights on CN that I did a hour long exposure unguided cannot be understated.

 

Kurt



#15 rockstarbill

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Posted 23 September 2021 - 06:23 PM

Just to be the devil's advocate here, but why do you (or anybody) "need" to do unguided imaging. Guiding is relatively easy (tho a bit more expense) and can only improve the tracking. Long focal length imaging certainly make is worth guiding. If you can do 2 minute exposures unguided and get small stars then you can do 120 minute exposures with guiding (just to throw out a big number).

Maybe it's just me. I just truly don't understand.

Jason


Guiding is very problematic at times. Eliminating guiding if done properly should improve image quality. No one thinks it's hard. It's not. It's brain dead simple to do. That's not the point at all though.


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