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theskyisthelimit99

Cem120, hdx110 or other ie: ap900 used (11 edge + hyperstar + misc possible weight)

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Posted (edited)

I've decided i'm going big or going home on the mount, simply because i dont want to change things later on and more payload capacity the better (going on permanent pier, in nexdome, long term goal full automation)

I'm wondering of these choices or maybe another i havent considered, which would give me the least headache or tinkering needed. Which would do well with really long exposures (above 5 min?), though with a hyperstar most are 60 seconds, but if i later piggy back or side by side a larger refractor that could mean longer exposures there.

I dont intend to swap equipment in and out, i will probably be quite happy just doing hyperstar on this setup and planets and maybe some imaging without hyperstar at f7 for many years (given that SW PA weather sucks and we are lucky to get 40-50 good nights per year i think).

 

UPDATE: i've decided to go for the cem120, 10" pier and double plate system as of now.

 

 

So that said..
(originally i figured a cem60 would just make the cut at 45 lbs but i want growth and not to have to change things or create issues)

 

I guess a used (if safe to get used), ap900 (cp3?) would also be viable.

 

On the 120..

I've seen some reports of some issues with the cem120, often the RA worm needing changed i think? And other issues with stars being elongated, though i'm not sure if its directly related to the 120 mount itself, ie: this thread though most of it is beyond my current understanding.

 

Also, going to the ec version of the 120, well beyond my price gap, just curious if any real benefits for what ill be doing, which honestly will probably be short subs and maybe guiding later (i've read that if you ad guiding later its probably just as effective?).  I'm not sure its worth a 1500 price jump though, for my current needs anyway.

Any suggestions 
Thanks in advance


Here are some estimated weights i had figured (option b was drop back to a 9.25 to save some weight, but for planetary i really wanted that extra light power):

C11 setup with just hyperstar and maybe guiding (though not needed i dont think except for maybe planetary):

C11: 28lbs
9x50 finder: 1.5
3x barlow: 0.36
guide scope: 5
ccd for planetary: 1.5 (worst case)
Celestron focuser: 1.5 i think
Weight of dovetail? ?
missing things?: ??
filter wheel: 1.1lbs
Total: 40-42?

C11 with other options with side by side (likely wouldnt get to this for a long time):
c11 28lbs
9x50 finder: 1.5
3x barlow : 0.36
guide scope 5
ccd planetary : 1.5
celestron focuser: 1.5
dovetail and other side by side adapters: 10
piggy back mount or side by side mount?: 2
apo scope 120mm: 15?
apo guide scope on apo: 5
apo camera worst case: 3lbs
filter wheel: 1.1
apo focuser(electronic): 2-6?
misc adapters to fit 

Could be 81lbs here, i could see 60 eventually maybe (unlikely i'd ever have this complex of a setup)

Edited by theskyisthelimit99

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4 minutes ago, bottletopburly said:

There is a 11 inch celestron on sphock at the moment if it is of use to you https://www.shpock.com/en-gb/i/XRATO5GBL2jSLwQM/celestron-cgem-1100-telescope

 

ahh your in usa 

Thanks for the link, yeah i'm in the usa, i would have considered it, though primarily looking for the 11 edge (though i probably should entertain some larger meade f8 scopes, another story).

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Would a used ap900 with cp4 be considered a much better idea than even a cem120 here?  Im still a bit leary of going used especially if its older, but its my understanding that the update to cp4 can occur even on older setups.  Anything to ask or look for in this type of situation?

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It doesn't really matter which of the three you mention you choose, if performance is your major requirement. All are good solid mounts, all autoguide well. The 2015-on EQ8's/HD110's are better than the early mounts due to lower Dec backlash. The CEM ad AP mounts have spring loaded gears unlike the EQ8 which helps worm gear mesh clearance (i.e. backlash) control between summer and winter temperatures.

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5 minutes ago, tonyowens_uk said:

It doesn't really matter which of the three you mention you choose, if performance is your major requirement. All are good solid mounts, all autoguide well. The 2015-on EQ8's/HD110's are better than the early mounts due to lower Dec backlash. The CEM ad AP mounts have spring loaded gears unlike the EQ8 which helps worm gear mesh clearance (i.e. backlash) control between summer and winter temperatures.

What about differences in PE, ie: one rated at say 5 arcsec/pixel (i forget the data point) vs another like the cem120 at say 0.15..  how critical should i be in comparing those stats.. ie: for someone like me doing minor astrophotography or even mid duration subs 5-10 min, would such figures make much difference in the final images.. i dont understand these stats so i'm not real clear if there is an advantage.. ie: cem120EC vs even an ap900 used, let alone cem120 vs cem120ec

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All worm gear mounts of this class are pretty similar and better than 5 arcsecs peak-to-peak periodic error is typical. It doesn't make any real difference what the exact figure is, provided sensibly tuned autoguiding is being used. All will be reduced to 0.5" RMS on RA and a bit less on Dec, provided backlash is controlled. The EC mounts are a different animal, and essentially offer more linear RA or RA/Dec motion. But this is not a useful advance on open-loop tracking (no encoder/s) unless unguided imaging is a requirement and some mount modelling can be considered.

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Posted (edited)
3 hours ago, tonyowens_uk said:

All worm gear mounts of this class are pretty similar and better than 5 arcsecs peak-to-peak periodic error is typical. It doesn't make any real difference what the exact figure is, provided sensibly tuned autoguiding is being used. All will be reduced to 0.5" RMS on RA and a bit less on Dec, provided backlash is controlled. The EC mounts are a different animal, and essentially offer more linear RA or RA/Dec motion. But this is not a useful advance on open-loop tracking (no encoder/s) unless unguided imaging is a requirement and some mount modelling can be considered.

Ok, i think that makes sense to me at least.

Yeah then im guessing going for the ap900 probably wont benefit me, at least not in the medium term.

The ap900 in question is around 6500 (vs 4k for the cem120 new).  The person says its a cp2 upgraded to cp4, gave me the serial number as well.  Comes with the cp4 controller, hc, cw shaft and 20lb weights, 18lb and 10lb weights and another 7lb one.  Has the saddle and polar scope too along with the software licenses.. not real sure on the age, comes with a custom grease kit to regrease.  I guess on paper it sounds good, the seller is reputable.

I could probably still do just as well going hdx110 i would imagine if not the cem120 

 

 

Edited by theskyisthelimit99

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19 hours ago, theskyisthelimit99 said:

I've seen some reports of some issues with the cem120, often the RA worm needing changed i think? And other issues with stars being elongated, though i'm not sure if its directly related to the 120 mount itself, ie: this thread though most of it is beyond my current understanding.

Hi,

There are quite a lot of CEM 120 already in the wild as far as I know. If you just look at that thread to which you have posted a link then you should read the Google Group messages and get a better picture of what is discussed there.

Quote

often the RA worm needing changed i think?

You think ... Where did you read that ? Please, guesses and assumptions are the parents of Gossips ...

You will not get happy as there is one think, some are testing new things for iOptron, see the infamous link you posted, and other happily imaging ...

Do yourself a favor as you are biased and scared about problems with the CEM 120 and go for other alternatives you can go with 10micron, Astro Physics, Paramount, ASA all " Premium " mounts ... OK they cost the double or the triple but you will be happier 🤔

Just an honest tip. I have seen people so scared after reading all sort of problems and without having tried anything they bought the alleged troublemaker mount and never got Happy ...

Believe you Brain will betray you ...

best regards Rainer

 

 

 

 

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16 minutes ago, Rainer said:

Hi,

There are quite a lot of CEM 120 already in the wild as far as I know. If you just look at that thread to which you have posted a link then you should read the Google Group messages and get a better picture of what is discussed there.

You think ... Where did you read that ? Please, guesses and assumptions are the parents of Gossips ...

You will not get happy as there is one think, some are testing new things for iOptron, see the infamous link you posted, and other happily imaging ...

Do yourself a favor as you are biased and scared about problems with the CEM 120 and go for other alternatives you can go with 10micron, Astro Physics, Paramount, ASA all " Premium " mounts ... OK they cost the double or the triple but you will be happier 🤔

Just an honest tip. I have seen people so scared after reading all sort of problems and without having tried anything they bought the alleged troublemaker mount and never got Happy ...

Believe you Brain will betray you ...

best regards Rainer

 

 

 

 

Look i'm sure these are isolated instances, however if you dig around you will find plenty of discussion on these and the issues "some" have had, its not gossip, unless they are making up stories or dont know what they are dealing with.

I know someone first hand that went through several cem60's before they had one that worked and from another forum someone directly i spoke to that went through three of the cem120's.   I also have talked with folks that have the 120 and no issues and love it.  Take it with a grain a salt here.

No one is trying to spread gossip here, but merely trying not to end up with a $4000 brick or go through the pain of repeated swaps if thats really what it takes to get a good one.

 

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15 hours ago, tonyowens_uk said:

All worm gear mounts of this class are pretty similar and better than 5 arcsecs peak-to-peak periodic error is typical. It doesn't make any real difference what the exact figure is, provided sensibly tuned autoguiding is being used. All will be reduced to 0.5" RMS on RA and a bit less on Dec, provided backlash is controlled. The EC mounts are a different animal, and essentially offer more linear RA or RA/Dec motion. But this is not a useful advance on open-loop tracking (no encoder/s) unless unguided imaging is a requirement and some mount modelling can be considered.

Back to the ap900 possibility, I did find out that the one in question is from the year 2000, he claims never an issue with it, no noises or anything along those lines, however he's never greased it or had to.  I dont think the price was flexible, if it were it might be a consideration, though the age concerns me.  Does anyone know how long these can last (for that one its already at 19 years)?

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18 minutes ago, theskyisthelimit99 said:

however if you dig around

Hi,

I do not need to dig around. I am a memeber of the CEM 120XXX Google Group since day one so I know from first hand what is going on and BTW I do own two, yes TWO, CEM 120EC2 mounts ... and I know from first hand how they work.

If you are not sure better do not buy a CEM 120XXX. 

Rainer

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I also know someone who purchased the cem60ec directly from iOptron, and was having issues with guiding. They waived his return date so he can have enough time to determine what's what before he decides big he'd just get another cem60 instead.

While their customers service is not perfect it is quite good for a mass market company. Yes it's not a luxury experience but at least they are responsive.

All those scare stories are overblown in their magnitude. It's not like AP and Bisque doesn't have users who receive bad copies. There even a YouTube video of someone who got a new ap1100 with a floppy DEC. In the end it was fixed but if you think the expensive brands are perfect you could find the truth to be very different.

Too often the story line with expensive mount is that the QA is better, but other then finding a very frank large volume reseller who is willing to talk, we'll never know if that's true. Often to me it appears the way they gain their reputation is to change double what other costs then replace broken stuff with no questions asked. Which makes people feel better but doesn't help tell anyone if the quality is actually better.

This hobby sometimes feel like there's more hearsay than facts.

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Well i was able to find the hole pattern and the rough estimate on the height of the cem120, i'm definitely on the cem120 bandwagon, but i should probably get my pier created (10-12" sonotube) prior to ordering so i have a way to get it connected and tested (or after the nexdome arrives)

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They also sell a a perm aluminum pier if you don't want to pour so much concrete. For me I had the 24" 4' concrete base done and mounted a skyshed pier on-top. This way in theory the building can be converted to a regular shed by removing the pier and closing the pier hole.

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On 11/07/2019 at 17:57, cotak said:

They also sell a a perm aluminum pier if you don't want to pour so much concrete. For me I had the 24" 4' concrete base done and mounted a skyshed pier on-top. This way in theory the building can be converted to a regular shed by removing the pier and closing the pier hole.

Yep I was considering the steel pier option because I may move one day. I'm trying to save coin though so probably sticking with concrete if I can figure out where to get material for the pier adapter that will be above the 12 inch round concrete pier

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Getting a custom metal pier is usually not that bad. Once you consider the potential cost of injury moving heavy bags of mix and such. The ioptron Alu piers are also quite reasonable.

Alternatively a tripier on a concrete floor works ok too.

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On 13/07/2019 at 14:37, cotak said:

Getting a custom metal pier is usually not that bad. Once you consider the potential cost of injury moving heavy bags of mix and such. The ioptron Alu piers are also quite reasonable.

Alternatively a tripier on a concrete floor works ok too.

Any concerns with vibrations with the metal pier route?  Either way quite a few bags still needed for an 18 to 24 square footer 

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Posted (edited)

You can fill in the inside of a metal pier with sand to help make it as heavy as a concrete pier if you are worried.

Local post diggers would come with an auger and mix the cement for you for a few hundred dollars. I worked the math and it wasn't that far from renting and mixing myself so I just contracted that out.

Edited by cotak

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Posted (edited)
19 hours ago, cotak said:

You can fill in the inside of a metal pier with sand to help make it as heavy as a concrete pier if you are worried.

Hi,

It is not about weight but about stiffness and I guess there is a lot of info in the WWW in order to compare concrete stiffness and steel pipe or tube stiffness

Rainer

Edited by Rainer

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On 14/07/2019 at 21:41, cotak said:

You can fill in the inside of a metal pier with sand to help make it as heavy as a concrete pier if you are worried.

Local post diggers would come with an auger and mix the cement for you for a few hundred dollars. I worked the math and it wasn't that far from renting and mixing myself so I just contracted that out.

I checked around on just having the cement delivered, the best i can find is $280 for a 1 yard minimum (should be just under 1 yard), which isnt a bad price being as i'd pay around $220 for lowes to deliver everything inclusive of a mixer rental.  So ill probably do this option, but i imagine i just wheel barrow it from the street, so they probably wont help.

 

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I paid 400 CAD for 4x 8 inch piers for the observatory building, and 1x 24 inch pier which is the base for the metal pier. This includes augering. I just had to supply the tubes, rebars and brackets. Now the concrete on the top of one of the piers was questionable but they did a repair on it and it's ok for now. With a more reliable contractor I think it would be the easiest way to do it without risking your back.

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