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Stratis

iOptron CEM60 vs CEM40 Mounting Holes

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Hi all,

Coming back to astro after a long break, many ups and downs :) 

I recently hauled my trusty CEM60 out of limbo and realised I'd like to shift to a smaller mount, as I have never come near the incredible weight limits on this mount for imaging or visual. The new CEM40 really looks perfect in most regards, so I am hoping that will serve as my new main imaging mount. I image with apo refractors, from a 7kg 115mm TS triplet down to a little WO Megrez 72 at only 2kg on an AstroTrac, with both DSLR and QSI 583wsg (so about 2kg camera package). My greatest imaging load has never exceeded 12kg.

I already have an amazing Avalon T-110 T-pod underneath the CEM60, with an iOptron adapter atttached, this one in fact: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10799_Avalon-T-Pod-110-130-Adapter-Kit-for-iOptron-iEQ45-and-CEM60-Mounts.html

This adapter has the central peg for iOptron, plus mounting holes set around the perimeter for the alignment pegs. The adapter has two sets of two threaded holes; the first set is 130mm apart across the centre, and fits the CEM60 perfectly. The second set is 120mm apart across the centre, and I think is meant to fit the smaller iOptron mounts like the iEQ30. 

So the £1400 question; can the adapter accept a CEM40 mount? Can the two threaded holes set 120mm across the centre mate with the CEM40? If anyone has any info on the absolute mounting hole arrangements for the CEM40 alignment pegs it would really help :) 

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Best to email ioptron support with that question as reports suggest that the cem40 has its own mounting setup.

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Its all in the manual: -

https://www.ioptron.com/v/Manuals/7400_CEM40_Manual.pdf

" STEP 2. Set up tripod The tripod top is 120 mm in diameter with 2x M6 holes 103 mm apart for mounting. Two additional M6 holes are for the Alignment Peg (the one on top of a leg is for high latitude use; the other one between two legs is for low latitudes). Thread the Alignment Peg into the correct M6 hole. Insert the Accessory Tray through the center rod and secure the setup by tightening Locking Knob from underneath."

HTH

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Posted (edited)

Hi Stratis,

Is this what you want to load on a CEM 40 ?

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p3041_TS-Optics-PHOTOLINE-115-mm-f-6-96-Triplet-APO-with-2-5--RP-focuser-1-11.html

If yes, I do not recommend to go down to a CEM 40.

Weight is not everything. Moment arm is more important then total weight ...

There is a big difference between a cylinder 40cm long weighing 7 kg or a cylinder 100cm weighing 7 kg. Both have the center of gravity in the middle but the moment arm exert totally diferent forces on the mount if 40cm or 100cm at the same weight ...

You can test it your self. Take a 40 cm long stick and move it rotational back and forth and take a 100cm long stick and do the same ...

regards Rainer

Edited by Rainer

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I have that telescope and i am also thinking about cem40 and i believe that you are wrong

If you balance it correctly, then only thing that matters is a mass of an object, it is the same if you have an object that is 100cm long or 200cm long if the weight is the same

That optical tube is 6.4 kilos, mount the guidescope, camera, filterwheel..... and you are well beneath the 18 kilos that mount can handle, just balance it carefully

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Posted (edited)

No he's not wrong, but maybe more details would help.

It's why you have the crazy 1/2 and 2/3 rule that's outdated but keeps being repeated. All the rule does is helps beginners avoid being overly ambitious and end up discouraged.

Now I am no fan of Astro-physics for various reasons but even they have admitted their payload rating isn't the simple old dogma of "it's premium so it's imaging payload" by publishing a diagram for the mach2 showing what the limits are based on OTA dimensions. Go check it out if you want but basically longer the tube the less it can hold, and the wider the tube the less it can hold. So even though the mount claims 75lb of payloads it only can achieve it if the diameter of the OTA is around 8 inch. Sobering news actually for anyone considering a so called premium mount. Btw please never use the word premium again here, it's uniquely useless in providing any useful information. All it does is divided people by implying some is more equatorial than others (if you are confused about this joke, go read up on animal farm :) ).

The reason why dimensions and moment matter is this:

http://web.mit.edu/4.441/1_lectures/1_lecture5/1_lecture5.html

Boil it down and it's basically about leverage, longer arm the more force applied at the other end.

One thing to also note is that longer the OTA the more the ends of the OTA move in an arc for a given rotation at the pivot. It's actually the related physics for moment arm/leverage but it also means that for a given tacking error the impact is greater for a larger OTA. And if you think about it this is spelled out also in image scale calculations, with different implications depending in relation to moment arm forces and the mount ability to resist the force.

Edited by cotak

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On 16/05/2019 at 04:26, Stratis said:

Hi all,

Coming back to astro after a long break, many ups and downs :) 

I recently hauled my trusty CEM60 out of limbo and realised I'd like to shift to a smaller mount, as I have never come near the incredible weight limits on this mount for imaging or visual. The new CEM40 really looks perfect in most regards, so I am hoping that will serve as my new main imaging mount. I image with apo refractors, from a 7kg 115mm TS triplet down to a little WO Megrez 72 at only 2kg on an AstroTrac, with both DSLR and QSI 583wsg (so about 2kg camera package). My greatest imaging load has never exceeded 12kg.

I already have an amazing Avalon T-110 T-pod underneath the CEM60, with an iOptron adapter atttached, this one in fact: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10799_Avalon-T-Pod-110-130-Adapter-Kit-for-iOptron-iEQ45-and-CEM60-Mounts.html

This adapter has the central peg for iOptron, plus mounting holes set around the perimeter for the alignment pegs. The adapter has two sets of two threaded holes; the first set is 130mm apart across the centre, and fits the CEM60 perfectly. The second set is 120mm apart across the centre, and I think is meant to fit the smaller iOptron mounts like the iEQ30. 

So the £1400 question; can the adapter accept a CEM40 mount? Can the two threaded holes set 120mm across the centre mate with the CEM40? If anyone has any info on the absolute mounting hole arrangements for the CEM40 alignment pegs it would really help :) 

Hi Stratis,

Any news about your project about downgrading from CEM 60 to CEM 40 ? 😲

Rainer

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