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I have a somewhat unique question here, and I haven't been able to get a clear answer elsewhere. There is a question with a similar title, only with the camera and lens terms swapped. My question is different, in that I really do need to know how much weight a Canon white telephoto prime L series lens can handle on its mount.

I am looking to use a particular CCD camera with my 600mm f/4 L II lens, and probably with a 300mm f/2.8 L II lens in the future. The camera with all the various accessories attached may weigh in at about 6lb, maybe more. The heaviest DSLR camera with accessories that I've been able to identify weigh in at around 4lb.

I just need to know what the acceptable limits are. Once the camera is attached, it won't really be touched or moved or anything like that...it will only track, with the lens, on an equatorial tracking mount for astrophotography. If the mount cannot handle 6-7lb of weight, then I think I'll need to figure out some kind of custom support rig, so the entire weight of the camera is not hanging off the mount alone.

UPDATE:

I use a custom rig to attach my lens and a guidescope to my mount. This is what I use:

enter image description here

So the weight of the entire system will not be hanging off the tripod foot on the lens. Actually, the tripod foot is not used at all...the lens is supported in both the front and the back by scope rings, attached to a large Losmandy D-type dovetail at the base, and a Vixen V-type dovetail at the top, for both support and accessory attachments.

The entire weight of the camera will really be hanging off the lens mount. It will usually not remain in the orientation you see above...that is the park position in polar alignment pointing at Polaris (well, the NCP). The mount will reorient the setup to point wherever I want it to in the celestial hemisphere, and then track my object across the sky throughout the night. So the force of gravity on the camera will change, frequently sometimes, and as the mount tracks.

Maximum tracking speed is about 3.5 degrees per second...not terribly fast. Normal tracking rate is sidereal, extremely slow (it matches the rotational speed of the Earth...so, extremely slow. :P) It moves pretty smoothly, comes to a stop slowly. There shouldn't be any jerking actions...unless I experience a pier crash, where the scope or camera run into the pier or tripod the mount sits on.

UPDATE 2:

Here is an example of the size of the camera:

enter image description here

It is largish, maybe about the size of a 1D X. However, that is not its total size. It will also be used with a filter wheel, which is actually larger in area than the camera, and offset down from the center of the camera a bit:

enter image description here

enter image description here

The trick here is getting the camera supported...despite the filter wheel. More so than that...I need to be able to rotate the lens with the camera in order to properly frame my targets. So the filter wheel won't necessarily always be hanging over the camera down towards the ground...it could be pointed to the side, up, at a 45 degree angle or anywhere really.

...hence the reason I am wondering whether the lens mount can handle it on its own, safely, without any risk. I can't risk this lens, so if there is any risk, then I'll probably have to build some kind of support rig for the camera.

  • Just commenting as it doesn't qualify as an answer: when going hiking, if I loose the balance 2 out of 3 I end up supporting on my lens... – motoDrizzt Apr 25 '16 at 20:50
  • Similar to the above but not a real answer; people using those on monopods with the sports cameras like 1Dx often put quite a bit of weight on the camera just for steadiness, one arm out front, the other pulling down a bit on the camera. Not like putting their weight on it, but certainly another few pounds to brace the whole setup. Similarly speedlight mounts with modifiers like a better beamer probably come close to the other 2 pounds you've identified. I think you're worrying for nothing on the pro lenses. But that's opinion not fact. – Linwood Apr 25 '16 at 21:01
  • I would say this question is related and has an answer which I believe is highly relevant. – Octopus Apr 25 '16 at 22:45
  • I have entered the retro-engineering mode with Catia, and should have some result this weekend :) – Olivier Apr 27 '16 at 18:49
  • Thanks for the link, Octopus. It is relevant...sadly, it also does not provide any actual specification. ;p I need an actual value, and it seems manufacturers are VERY unwilling to actually provide one. Liability issue, I assume...meh. Does anyone know if they really do intentionally build in extra support for small forces from dropping, etc.? – jrista Apr 28 '16 at 4:13
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It's not just the weight of the camera that's a concern, but the torque that it will apply to the mounting ring on the lens (and in the camera, of course).

Torque is turning force, and it's calculated by multiplying force (weight, in this case) by distance from the center of rotation. So, if we guess that your camera is 4" deep from the mount to the back of the camera so that the center of mass is about 2" from the flange, and that the camera weighs 7 lbs, the torque at the mount would be around 14 in-lb. That's probably comparable to an EF 70-200 f/2.8 being mounted with no support: that lens weighs around 3 lbs and is about 8 in long, giving a torque of around 12 in-lb.

Even so, I'd want to support the camera for two reasons:

  • Safety. You don't want to take chances with a lens that costs $11K.

  • Stability. Putting a relatively heavy, unsupported object on the end of the lens will shift the center of mass of the whole system. Even if the mount itself is fine, expecting a rock solid connection to the equatorial mount through just one point might be asking too much of the lens' tripod foot. Connecting both camera and lens to a support system will help eliminate unwanted movement.

In the movie industry it's common to use a rail system as a chassis to assemble lens, body, and other camera components into a single unit. There's lots of good info online for DIY rail systems.

I just need to know what the acceptable limits are.

Reach out to Canon. If you're not already a Canon Professional Services member, you should be with a lens like that, and the CPS folks will be able to find out for certain whether you're pushing your luck with a 7 lb camera or if you're completely within bounds.

Reach out to the camera manufacturer. The thing you really care about is whether it's safe to mount the camera and filter wheel on your expensive lens -- you don't need to know about the actual limit so long as your use comes in under the limit. Considering that the manufacturer designed the camera to use an EF mount in the first place, they've probably done some research on the subject and may even have licensed the use of the EF connector from Canon, in which case they may have access to Canon's specifications for the hardware. At any rate, they should be able to tell you if it's safe to let the mount support the camera or if you need to provide additional support of some kind.

  • I agree with this answer, and I also think it will come down to the structural integrity of the camera and the lens as well. You can have the exact same mount holding together a lens and a cardboard box. What will give? It will be the box. – Octopus Apr 26 '16 at 20:37
  • Re: the lens that costs $11K. The lens costs that much, but replacing the bayonet mount at the back of the lens doesn't cost anywhere near that much. In that regard I'd be more concerned about damage to the mounting flange on the camera. Tweaking that too far can exceed the ability to repair it. – Michael C Apr 27 '16 at 2:13
  • I don't mount the lens at one point. I built a custom rig to mount both the 600mm lens and a guidescope and camera. See my question edit for a photo of the rig, and more. – jrista Apr 28 '16 at 4:03
  • Regarding CPS...I would love to be a member...however as far as I know, in the US, they require that you be a full time working photography professional in order to join. I have been published, twice, in magazines coming out next month and the month after...but that would only make me semi-pro, and a baby semi-pro at that. I don't think I qualify for CPS, despite the lens. – jrista Apr 28 '16 at 4:14
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    If you have the equipment that gives you enough points for whatever tier you're interested in they'll let you join without proving anything with regard to your source(s) of income. You do have to check a box on the registration that says something to the effect that you do professional work. The way it is worded covers the pro-bono work I do for non-profits, which is my primary photographic activity these days. – Michael C Apr 28 '16 at 4:58
3

Using Catia (Mechanical engineering software), I tried to answer your question by retro-engineering the canon parts.

I found a 3D model of a canon lens from grabcad.com and isolated the lens mount geometry. I compared its dimensions to the ones of my lenses and found them accurate enough. On the following view, you can see the lens mount.

Catia lens mount model

I used brass as a material (Young modulus = 1,31 10^11 N/m2, elastic limit = 3,5 10^8 N/m2), as cited here : http://photography-on-the.net/forum/showthread.php?t=1118809 (you can find information about dimension too).

Then I applied a surface load representative of a force of 100 Newtons, so about the weight of a 10 kg body hanging vertically from the lens mount (considered as fixed, as if the lens is looking toward the sky). I set the surface connecting the screws to the body as anchor points.

As expected, higher constraints (effort) are found on the screw fixations.

Catia Von Mises Results global

Catia Von Mises Results local

As you can see, with a 100 N load, the Von Mises criterion stay under 9 10^7 N/m2, which is under the elastic limit of the brass (about 3,5 10^8 N/m2).

This is good news, it means that your lens mount will not break and that you won't stress the material above its elastic limit. Moreover, you have a safety factor of about 4.

With a load of 5 kg (50 N), the maximum constraint is about 4,5 10^7 N/m2, about 8 times less that the elastic limit.

Given the geometry, this constraint will probably go up if your lens is horizontal because only 1 or 3 fixations will work on traction. I will make a second simulation to look at this case (maybe this weekend if I have time).

2

The 1D Mark II was 55.5 oz. The 5D Mark III + BG-E11 grip + 2 LP-E6N batteries is about 59 oz. The heaviest flash Canon has sold in the recent past is the 600EX-RT which is 18.5 oz with batteries installed. The WFT-E8A is another 1.35 oz. Add that up and you're at 79 oz. which is about 17 oz. less than a 6 pound CCD camera.

The EF mount should be able to handle that, but you might be approaching the design limits. It's interesting to note that the EOS C100 + battery + grip comes in right around 51 oz. - just less than the same weight of most of the 1-series bodies and the grip is designed and wired to accommodate a boom microphone which would add another few ounces.

It would probably be safer to use a rig that supports both the lens and the camera. However, if the manufacturer sells the camera with no fittings for support of any kind beyond the mount interface, which in this case is a Canon EOS EF mount, then it would seem at the least they are confident the mount can handle the stresses put upon it by the use for which the camera is intended.

  • FYI, this particular camera does not have a tripod mount. It is a scientific imaging camera designed for microscopy, medical imaging purposes, astrophotography, etc. It is quite large...I'll see if I can get some images added to my question to demonstrate the size of the camera, size of the filter wheel, and the odd conundrum it presents to supporting the camera. – jrista Apr 28 '16 at 4:18
  • Surely it has some sort of fittings for attaching it to support stands of some type or another? – Michael C Apr 28 '16 at 4:53
  • No fittings of any kind. It is primarily intended to be attached to a telescope, so the only point of attachment is the opening to the sensor. On a regular telescope, you would usually use a minimum of a 2.5" (63.5mm) focuser, but if not a 3" or 3.5". Those are more heavy duty and stable, with high rigidity and they are designed to handle loads of 8lb up to 30-40lb. The Canon lens mount in it's total size is comparable to a 2.5" focuser, it's just that it's capacity is totally unrated (officially), and the mount is usually bolted onto the lens, rather than being like a solid focuser drawtube. – jrista Apr 28 '16 at 16:21
  • If the manufacturer sells the camera with no support points other than the EOS mount, then it would seem they are confident the EOS mount can handle the stresses placed upon it for the use for which the camera is designed. – Michael C Apr 28 '16 at 17:38
  • The manufacturer sells the camera with a 68mmx1 threaded mount. It is adaptable to just about any configuration by using adapters. The camera can be used bare, or with a filter wheel (few different options there), with a third party filter wheel (even more options), with an off-axis guiding port adapter, as well as with adaptation (with or without a filter wheel) for the EOS EF mount, Nikon F mount, M42 mount, etc. I don't think Moravian has actually done any confidence testing with their EF mount option, though. – jrista Apr 28 '16 at 19:30
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I don't have the answer for you but the answer is maybe obvious : if it were a classic mechanical problem, I would say that the lens capacity shouldn't exceed the capacity of the body (using no lens collar):

  • If you body can support a 2 kg lens on the body mount, then the same weight is supported by the lens mount ;
  • If your lens comes with a collar for your tripod, it's probably safe to say that your body isn't designed to support the lens weight for long (even if using a collar has probably more to do with torque and [camera+body] stability).

So a safe limit should between the 70-200 f/2.8 (1.3 kg) and the 300mm f/2.8 (2.5 kg) : you can probably attach a 2 kg CCD on your lens (the best solution being of course attaching both lens+body on a specific support).

  • Weights on both ends of the mount would be additive. – Octopus Apr 25 '16 at 22:18
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    @Octopus Why would they be additive? If the heavier of the two is supporting the combination then it isn't exerting any force on the mount in the same way that a lens not attached to a camera is putting zero stress on the bayonet mount of the lens (assuming it isn't sitting balanced on the mount end of the lens). – Michael C Apr 26 '16 at 2:18
  • @Oliver - All variants of the EF 70-200mm f/2.8 have been supplied with a tripod collar. The EF 70-200mm f/4 variants are not supplied with tripod collar, but the lenses are designed to accept optionally available ones. The same is true with the EF 200mm f/2.8 - tripod collar not supplied but optionally available. The 40 oz Ef 180mm f/3.5 L is also supplied with a tripod collar. – Michael C Apr 26 '16 at 2:55
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    @Michael, well you can look at it from the pov of do i mount the lens and support the camera or other way round, but in reality it is the torque load put on the mount from both sides. its not a static system it needs to hold up under the stresses of being lifted and moved around as well. its not just a question about supporting weight, its about total load on the mount. – Octopus Apr 26 '16 at 16:36
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    Slewing at 3.5º/second is not really considered "moving around" the same way running down a sideline to get to the other end zone during the timeout between quarters, or grabbing the tripod by the legs and hauling @$$ with the whole rig over your shoulder when mamma bear thinks you're a threat to her cubs, or even doing a tracking shot on a dolly and a set of rails is considered "moving around." – Michael C Apr 28 '16 at 5:11

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