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iOptron CEM60, First Impressions

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#926 nickwv

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Posted 26 July 2014 - 10:04 AM

It's not really possible to rate a mount accurately in terms of capacity, because it's really down to torque acting on the mount. Torque is a function of weight / leverage and moment arm, and is dictated by the shape and length of the OTA - distribution mass etc.. If a manufacturer gave a torque rating in NM it wouldn't really mean anything, and no one wants to make torque calculations.

As a loose example, a long achromat sits very different to a stubby Cassegrain. They may weigh the same, but one will dampen a lot slower than the other if tapped, etc. etc. but it's a pointless discussion with so many OTAs. Every mount has its limits, accuracy levels, and it's price.

The payload quoted cannot take OTA shape into account, nor does anyone specify whether this is an imaging or visual figure (as Tazer pointed out). As payload increases, so tracking accuracy will deteriorate, so some consultation and assistance from the dealer is helpful.

We just checked this mount with our RC250-TT (v2) 10" RC, and there was no problem at 30lb) - but this is a compact OTA with a compact centre of mass. Also, we tried the Altair 130mm f7 triplet, and it was fine, but it weighs less and is shorter. Then we tried our RC300-TT and it was on the limit. I would rather wait for a larger CEM for that scope, (which we are still changing the design of anyway and doing a 14"), so it can wait.

Photovisions, as you say, you're conscious you're pushing the mount, and haven't decided whether to return or not, nor on what grounds it should be returned.

It may be an easily solved issue which will be evident on opening it, or you may just be pushing the mount beyond its torque limits.

If the mount is distributed by Altair, then we are happy to work with customers to resolve any issues, and this should the same with our advanced dealers.

I would be grateful if you contacted me by PM , and we talked you through a basic inspection to see what the issue might be, before we jump to conclusions. I would hope your dealer offered this.
 

#927 x6gas

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Posted 27 July 2014 - 06:19 AM

I completely agree Nick but that's why I think it was really unwise for iOptron to publicly state that the payload capacity of the mount is 60lbs for astrophotography. I don't think it would get anywhere near that even with a compact SCT... slewing with that kind of load is one thing but tracking and guiding quite another...
 

#928 Photovisions

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Posted 27 July 2014 - 06:15 PM

Nick
I have already gone through inspecting the mount and made sure everything is tight and balanced. I waited for Ioptrons approval before going ahead, so as not to void any warranty. Thus far, there has not been any improvement. I am able to roughly image with the mount, but its not right. I am getting guiding errors of around 0.5 arc secs, then every 4-5 corrections, over 1 arc sec, which is not really acceptable and results in elongated stars corresponding to the larger excursions. I believe this is related to the instability I am experiencing. PLease have a look at the 3 videos I have uploaded to Youtube:
https://www.youtube....EN-69jyYnIRE_zw

What I can't do is compare this directly to another CEM60 and others here have said something is not right.

My conclusion is either there is something wrong with the mount or it doesn't have the capacity to handle a 6 inch 13 Kg refractor. Hence I have considered returning the mount. Now it sounds like you have tried quite a large payload on your mount and I know others have tried a 6 inch refractor with comments of rock solid, so perhaps my mount is not right. I am now beginning to think there might be an issue with the main RA shaft/bearings being loose.

If I can get this mount to be much more stable, then I would gladly keep it, as I do like many of the features.
 

#929 akulapanam

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Posted 27 July 2014 - 11:45 PM

My question is if it can't handle a greater then 10" scope for astro photography then why buy it over a cgem dx? The polar scope and weight are nice but the cgem dx also has all the bugs out and with guiding can one tell the difference? I started a thread about this because the cgem dx is on sale and a couple cem60 features are really nice but I'm not sure I would see the difference?
 

#930 x6gas

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Posted 28 July 2014 - 01:29 AM

Owning both I can tell you that in my experience the CEM60 is an appreciable step up from the CGEM DX.
 

#931 whwang

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Posted 28 July 2014 - 04:22 AM

Hi,

I just had two nights in the field with my CEM60EC. Here are my "first impressions" (despite that this thread already has 47 pages).

I put TAK Epsilon 180ED (f=500mm) on it. In addition, there is a small guide scope and a piggy-back camera. The main imaging camera is Canon 5D2 (6.4 um pixel), so the pixel scale is 2.6 arcsec. The entire system is quite heavy. To balance, it requires 19 kg of counterweight, putting at the very bottom end of the shaft. This should give you some idea about the loading.

The first thing I tried is unguided tracking. On Vega (Dec=??), it can do 3 minutes of unguided tracking. The stars start to show elongation along RA when exposure is longer than 4 min. On an equatorial star, the max unguided exposure reduces to 2 min. However, on longer exposures on the equatorial star, the elongation is not exactly along RA. There is a Dec component. So at least part of the elongation is caused by polar alignment (see below). It is even possible that a large fraction of this elongation is caused by the polar alignment, since a misaligned polar axis can also produce RA elongation.

I only use the polar scope for the alignment on Polaris, based on the position indicated by the hand controller. I use the latest versions of the HC firmware. One thing I notice is that earlier in the night, the HC tells me a position of (roughly) 11hXXm, r = 42.X. Later in the night, when I checked it again, the position becomes something like 8hXXm, r=38.X. This is strange, since the distance of Polaris from the pole should be fixed. I first guessed this has something to do with the atmospheric refraction. However, since we see an up-side-down image in the polar scope (is this right?), the 8hr one should have a larger r than the 11hr one, if this is caused by the atmospheric refraction. Can someone tell me why r changes?

Of course, when you see elongated stars and have doubts on the polar alignment, the next reasonable thing to do is to try drift alignment. I didn't bother, primarily because I want to spend more time on imaging. A secondary reason is that I feel it is quite difficult to fine-adjust the polar axis. Both for the elevation and azimuth directions, once they are locked, it will be very difficult to change it. And if I loosen the lock and adjust the alignment, the alignment will change again once I lock it. The locking and adjustment mechanism of the polar axis of CEM60(EC) is by far my largest complaint. It is far more difficult to use comparing to my other mount (TAK EM-400). If find adjustment cannot be done easily and quickly, drift alignment is not too attractive to me.

After spending roughly half hour on the above unguided test, I decide to guide all the way in the remaining part of the two nights. Just like Paul showed us, the mount has no problem at all when guided. But this is not really the reason I got this mount. For its price, I don't have super high expectation on it, but I do hope I can push for 4 minutes of unguided exposures routinely on equatorial regions. It looks like this will definitely require good polar alignment. I appreciate any suggestions on how to do this very quickly in the field (including how to smoothly operate the polar adjustment mechanism of CEM60). It remains to be seen whether 4-min unguided exposures can be achieved if very good polar alignment can be made.

Cheers,
Wei-Hao
 

#932 tazer

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Posted 28 July 2014 - 09:08 AM

Both for the elevation and azimuth directions, once they are locked, it will be very difficult to change it. And if I loosen the lock and adjust the alignment, the alignment will change again once I lock it.


My mount didn't ship with nylon washers so alignment for me was rough initially. Once I received the washers it got easier. I'd just start off with everything tight enough that I couldn't easily force an alt/az motion. Next I'd back off the knobs a quarter turn so that turning the alt/az knobs was possible though there was still lots of resistance. Once alignment was finished, I'd tighten it back up a quarter turn and found little to no alteration of my polar alignment.

Also, if you're not in an obs and you want to do 5 minute unguided exposures then drift aligning is the way to go. Even if you're guiding for 5 minute exposures drift alignment is important. Bring your laptop with you and use PHD2's polar alignment routine, it's pretty slick.
 

#933 whwang

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Posted 28 July 2014 - 09:31 AM

Hi Tazer,

Thank you for the suggestions. I did not get the nylon washers either. I will try to find ones. I just switched from PHD to PHD2 and I also noticed there is a polar alignment function. I will give it a try once I can see stars again. We are cloud out today.

Cheers,
Wei-Hao
 

#934 mikeyL

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Posted 28 July 2014 - 10:17 AM

Wei-Hao,

I have had good luck using Alignmaster software to refine the polar alignment that you get using the polar scope. There is a free fully functional download that is good for 30 days. After that it costs 14 euro ($19 US) to buy. It picks pairs of stars to slew to, then after you have corrected their location to the center of your camera or crosshairs on your eyepiece, it gives you a calculated PA error and then moves the star off in each axis (ALT and AZ) one at a time and you adjust closest to center mechanically. Then you can iterate through again if you wish, using the same or a different pair of stars. If your initial alignment is close enough to get the stars at least in the FOV then an iteration takes 5 mins or less. On a typical night of setting up from scratch I can routinely get to an arcminute or less in each axis (as reported by Alignmaster) in 2 to 3 iterations taking not much more than 30 minutes worst case.

It seems both faster and easier than drift aligning to me and seems to do the trick. The only issue can be whether you have enough visibility to find any of the suggested pairs of stars from your location. I think though that there is even a way to specify your own stars to be added to the built in list.

ML
 

#935 tazer

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Posted 28 July 2014 - 04:09 PM

Wei-Hao,

PHD2 drift alignment is great. If you're connected via ASCOM it'll identify where your mount is pointed and, when you tell it to, it'll slew to the appropriate area of the sky for that step of alignment. A couple of tips that may help out:

1) Be sure when drifting in AZ that instead of slewing to 0,0 (meridian offset in degrees, declination offset in degrees), which is the default, that you slew to the west of the meridian. I found that with the CEM60 it would start off on the east side of the meridian and then meridian flip to the west after a minute or two.

2) Your initial error will be very obvious as the trend line will have a very sharp angle (up or down.) Hit adjust, make an adjustment and then hit drift and wait a minute to see what effect it has. If it reduces the angle of the trend line, keep making small adjustments until it's near flat. Keep in mind that periodic error will be a large part of your trend line error at this point. To get a true assessment of your alignment error you'll have to let it drift through a full worm period (5 minutes) and gauge the trend line then. Of course if you have an EC version with realtime PEC running then this will be less of a problem, though not non-existent.

After one session of drift aligning with this tool with my former CEM60 PHD2 was reporting that I was within 1', or less, of the pole. With the nylon washers and Paul's PTFE tape under the mount base tip, you should be able to make really fine adjustments and perhaps get your alignment even more precise.

Please report your experience once those clouds clear!
 

#936 x6gas

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Posted 29 July 2014 - 01:42 AM

Also note that the Alt adjuster knob has holes machined into it so that you can use the stainless steel rod to make fine adjustments with the locknuts almost fully tight.

I don't think this is mentioned in the manual.
 

#937 orlyandico

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Posted 29 July 2014 - 01:57 AM

periodic error should not affect azimuth alignment (DEC drift) since PE causes up-and-down movement in RA.

one trick that I use on my (non-CEM60) mount is that the azimuth adjuster knobs have precisely 3' / ridge and the altitude has 3.875' / ridge. So once my polar alignment tool of choice (I use PEMPro) says I'm off by say 8' east, I can dial in the precise amount by counting ridges on the knobs.

I have yet to do this for my other mounts but it should be possible as well.
 

#938 whwang

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Posted 29 July 2014 - 09:10 AM

ML, thank you. I will give it a try once I have a chance to put the mount under stars.

tazer, thanks for the PHD2 tips.

The tests I made two days ago was the last time I can use the mount in Taiwan. I am moving to the Big Island in two weeks and will bring the CEM60EC with me. Hopefully the light pollution there is small enough so I can make all the tests in my yard, and bring it to the mountain for real things. It will take some time before I have something more to report, but I believe it will be exciting news for every one.

Cheers,
Wei-Hao
 

#939 snowllama

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Posted 29 July 2014 - 03:26 PM

Oh, if you think the az adjustments are easy now, put four pieces of PTFE Tape (Teflon) on your tripod/pier surface and see how incredibly smooth it is. I used 3.5 mil PTFE tape, 1/2" wide and the result is just amazing.

Cheers...Paul


Paul,

Are you using a PTFE tape with adhesive on one side ? If not how do you attach the tape to the tripod base?

Thanks,

Fred
 

#940 Astronewb

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Posted 29 July 2014 - 08:29 PM

Oh, if you think the az adjustments are easy now, put four pieces of PTFE Tape (Teflon) on your tripod/pier surface and see how incredibly smooth it is. I used 3.5 mil PTFE tape, 1/2" wide and the result is just amazing.

Cheers...Paul


Paul,

Are you using a PTFE tape with adhesive on one side ? If not how do you attach the tape to the tripod base?

Thanks,

Fred


Yes Fred, the Teflon tape is self-adhesive and adheres quite well. I just put four or five strips along the outer circumference of the tripod/pier and trim the curved edges with a razor knife.

Posted ImageTeflon Tape on mounting surface by Astronewb2011, on Flickr

Oh, on EQ mounts it's only necessary to tighten the Az lock(s) enough to keep the mount flat on the tripod base, like a quarter turn at most. Any more torque just adds to your grief when trying to adjust in azimuth. Oh the CEM I can loosen the locks and just finger tighten them without any tipping of the mount when balanced. Adjustments with the PTFE tape are like moving air.

Cheers...Paul
 

#941 nickwv

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Posted 30 July 2014 - 07:35 AM

Hi there, I found a new CEM60-EC image from UK Customer Phil Shepherd, who reports that he was using a Starlight Xpress H16, with an 8" RC, the Altair 60mm Miniguider Barlowed at 2x, and a Lodestar camera.

The target is NGC6888 and it's a stack of 5x 20 minute exposures in HA, posted here:

http://ukastroimagin...p?topic=60768.0

For those of you who aren't UKAI members, I also attached the image file to this post.

Best, Nick

PS: Edited post - it's a CEM60-EC not a CEM60!

Attached Files


 

#942 tazer

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Posted 30 July 2014 - 08:20 AM

Good catch orly. I wasn't saying exactly what I was thinking. When you start your PHD2 drift align and your polar alignment error is greatest, you'll see both DEC and RA with steep trend lines. Once you're finished polar aligning the DEC trend line should obviously be flat, but the RA trend line may not be due to periodic error. If you wait the full worm period it should flatten out nicely (if you're interested in doing so.)

Nick, good picture but it would be nice to see an unguided image at that focal length. Hopefully one will turn up soon.
 

#943 nickwv

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Posted 30 July 2014 - 08:45 AM

Hopefully someone might try it, but I think most imagers I speak to feel it's lot less effort just to use an autoguider. They seem to think it compensates for minute polar alignment errors, atmospheric refraction, camera / OTA flex in realtime. This is probably why most customers who are imaging at longer FL prefer to guide. Still, it will be interesting to see if someone tries to buck the trend - and for how long they can manage it!
 

#944 snowllama

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Posted 30 July 2014 - 10:52 AM

Thanks Paul,

The information and photo are very helpful.

Fred
 

#945 Astronewb

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Posted 30 July 2014 - 01:05 PM

with an 8" RC, the Altair 60mm Miniguider Barlowed at 2x, and a Lodestar camera.


That's an excellent stacked image for 20 minute Ha subs. So barlowed, the 60mm is 450mm? Very nice results.

Phil mentioned that his guiding was nudged about every 5 minutes by guiding? Do you happen to know his guide software and the guide parameters he was using?

Regards...Paul
 

#946 Astronewb

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Posted 30 July 2014 - 01:15 PM

Nick, good picture but it would be nice to see an unguided image at that focal length. Hopefully one will turn up soon.


Tazer, here's an unguided image from the CEM60EC with only a polar align and Two Star align. It's 'only' 270 seconds, I was seriously fighting cloud cover with a thunderstorm rapidly approaching last month. Ota was the AT6RC at 1370mm.

Posted Image270sec_unguided_cem60ec by Astronewb2011, on Flickr

With a drift align long exposures at longer focal lengths should not be an issue for an experienced amateur astrophotographer. I really don't know of any that don't autoguide anyway?

Regards..Paul
 

#947 OzAndrewJ

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Posted 30 July 2014 - 06:47 PM

Gday Nick

Hopefully someone might try it, but I think most imagers I speak to feel it's lot less effort just to use an autoguider. They seem to think it compensates for minute polar alignment errors, atmospheric refraction, camera / OTA flex in realtime.



Just for interest i have attached 2 unguided data plots done by Alfred and Whichway in the earlier days. These plots were initially done to investigate the very slow /long term tracking performance vs the high freq SDE ripple that fed out of them.
You will note that the tracking clearly has better performance in certain regions.
The guess here was that the motor feedback loop appears to work well ( based on how regular the SDE is ), so are the long term errors due to flexure etc, or minor manufacturing tolerances in the etching of the encoder itself????
Either way, guiding would be needed in some positions of these traces.

So question for Paul.
When you opened the unit to refix the encoder disk, is the disk ALWAYS locked in a constant position relative to the dovetail head???
If so, you should be able to recreate logs like this by doing say three sessions where you always start at the same "HA"/DEC and collect an hour or so of data.
ie the encoder should retrace the same range for each run.
If the three logs show a common shape, then its more likely to be encoder variations, and you will know what sky regions will track better than others unguided.

Andrew Johansen Melbourne Australia

Attached Files


 

#948 Astronewb

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Posted 30 July 2014 - 09:12 PM

So question for Paul.
When you opened the unit to refix the encoder disk, is the disk ALWAYS locked in a constant position relative to the dovetail head???


Hi Andrew,

The disc is always supposed to be locked..:) Mine is now.

And for your information, my current mount is the one (second one) that Whichway beta tested. So it is quite possible he had the same issue when he tested the mount?

Since I reported the issue with the encoder, iOptron has changed the mounting method of the encoder in the CEM60EC and increased its retention. iOptron is a company that is not afraid to change what is not working or designed incorrectly (unlike some car companies).

I have imaged 300 seconds unguided with nothing more than a polar align and 30 minutes guided at 1370mm with round stars so I'm quite satisfied with the results from the mount.

And, in response to user requests, iOptron will be issuing a new set of Ascom drivers shortly for beta testing that will allow multiple connections at one time and a new control panel interface. If the new Ascom drivers work as well as the recent firmware releases, that should make a lot of users very, very happy.

Cheer...Paul

The
 

#949 OzAndrewJ

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Posted 30 July 2014 - 09:27 PM

Gday Paul

And for your information, my current mount is the one (second one) that Whichway beta tested. So it is quite possible he had the same issue when he tested the mount?



Not sure i understand what issue you mean here, as he had several??
Whichways data is the brown plot, and shows the tracking spikes he was getting, ( that i believe was fixed by newer boards/ firmware ). Alfreds data never showed them??
Both datasets show the SDE that will only affect the much longer FL imaging.
What i am trying to show here is that there may also be small errors in the etching of the encoder itself that may introduce very slow deviations in tracking that may or may not affect the results when imaging "unguided".
Its all down to where you image relative to where the woofs are for the given encoder ( if indeed the woofs are encoder based )
Either way, the errors are so slow that guiding will easily fix them, just it needs to be taken into account if trying for unguided.

Andrew Johansen Melbourne Australia
 

#950 orlyandico

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Posted 30 July 2014 - 09:51 PM

20 minute guided subs is all well and good, but I'm pretty sure the non-EC can do that.

If the default answer is "I'll be guiding anyway" then what is the point of the encoder?

That said, I think the non-EC is a pretty good deal for those who want to step up from the CGEM/Atlas class and don't want to spend for a Gemini 2 G11 or something even more expensive.

The EC version... I continue to struggle to see its value if you're going to be guiding anyway.
 






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