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05-18-2019, 07:46 AM   #1
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How much lens weight can a 645 camera box tolerate without distortion?

In another thread, johnha wrote, in part:
QuoteOriginally posted by johnha Quote
For just one lens I'd go for the 55-100 zoom, although heavy and bulky.
Yes it is certainly heavy. I just did a quick "fish scale" weighing. The 645 400mm weighs about 1.7 kg with bag and comes with a support foot. The 67 55-100mm zoom weighs about 1.5 kg (with adapter and bag) and might have a commensurate turning moment at the camera flange. The c.g. is definitely under the lens.

I've only tested this zoom handheld, so the lens was supported. I have not yet tested it with the camera base mounted on a tripod.

Anyone have a risk/no risk perception/experience with respect to camera box distortion using the 67 zoom on either 645 camera without providing some lens assembly support?

Thanks

05-18-2019, 11:56 AM   #2
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I don't have anecdotal experience but my perception considering the age of the 645, the relative weight of both the lens and camera here, I would provide lens-camera support so it's not even a worry when I'm out in the field. I can just imagine shooting on safari, bouncing around with the lens/camera/mono or tripod and the strain that would put on the mounts. Okay, no safari, just a walk in the woods and moving 20 yards with everything over my shoulder....

Here is one solution, although I am certain there are less expensive alternatives:
Sirui VP-350 Telephoto Lens Support Quick Release Plate SUVP350
05-18-2019, 12:00 PM   #3
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The 6x7 55-100 weighs about 1.2kg without the adapter. The 645D & Z have magnesium shells with aluminium chassis's, both are much better built than the 6x7 bodies. I haven't owned 645 film bodies so can't comment on them.

It's likely the adapter would fail first but I doubt it would be a problem (you may need a good tripod head though).

A more practical problem may be the 95mm filter thread, not many filter systems are economical at those sizes.
05-18-2019, 01:12 PM - 1 Like   #4
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Let me tailor my question a tad -- my concern was not with the lens ripping off of the adapter or the adapter ripping off of the camera shell. I was firstly concerned about distortion of the camera frame such that the focus was no longer uniform over the focal plane, and secondly concerned about the distortion becoming permanent (metal distorted past its yield point). These concerns could also apply to the lens, adapter, or camera flanges. There will, of course, always be distortion in reaction to a load. If distortion is only a minuscule fraction of the depth of field and recoverable when the weight is removed then there is no problem.

Transport while mounted would be a problem as noted above, but I likely would never be in that configuration.

The Sirui or similar supports have potential, but unlike most long telephotos, the 55-100mm doesn't really have any fixed surface to tie down to a support, or even to rest on a support. Maybe a Teflon or polypropylene pad could be used to allow rotary motion of the focus ring. Adjustment finesse to just take up the weight might be a challenge. Hmmmm.

Anyway, thanks alex645 for pointing me in this direction, and johnha for relieving part of my concern.

05-19-2019, 12:02 AM   #5
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QuoteOriginally posted by kaseki Quote
I was firstly concerned about distortion of the camera frame such that the focus was no longer uniform over the focal plane, and secondly concerned about the distortion becoming permanent (metal distorted past its yield point). There will, of course, always be distortion in reaction to a load. If distortion is only a minuscule fraction of the depth of field and recoverable when the weight is removed then there is no problem.

Anyway, thanks alex645 for pointing me in this direction, and johnha for relieving part of my concern.
I have no doubt that Pentax engineers took this all into consideration when designing that lens. However, depending on usage and age, everything will fatigue and in some cases recover, bend, or break. Breaking of course is an extreme that in this scenario would only happen upon severe impact.

Permanent distortion due to metal bending in the lens mount, I believe, would not occur unless there was repeated and prolonged abuse, undue force, and impacts. IF you think you will be subjecting this set up to that possibility, and no bracket currently exists, there are a growing number of 3D makeries that are beginning to make single rather complicated metal pieces. The school where I teach has this technology and the potential for solutions like this one are real.

Summary: Should you worry? Yes, if the camera is mounted onto a helicopter or off-road vehicle, etc. No, if you're using the camera and lens for "normal" studio or field photography with no intention of bricking it.

Note: I'm a photographer; not an engineer.
05-19-2019, 06:51 AM   #6
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QuoteOriginally posted by Alex645 Quote
I have no doubt that Pentax engineers took this all into consideration when designing that lens. However, depending on usage and age, everything will fatigue and in some cases recover, bend, or break. Breaking of course is an extreme that in this scenario would only happen upon severe impact.
...
Thanks for the confidence inspiring words. I would note that in my case your first sentence should be reversed to read: the 645Z would have to have been designed to support the heaviest not separately supported 67 lens. In any case, the assembly seems stiff enough. To beat this subject to death, a means of totally fixing the camera body (or the lens) would be needed to measure any effect of flexure, likely also requiring a floated optical bench and Nikon autocollimator. I think I'll go with the flow of the myriad of 645x users who successfully use this lens, apparently without secondary support.

With respect to the Sirui, it is not clear that it would adapt well to this particular configuration. Better may be the Manfrotto 293 counterpart as it seems more adjustable in height and uses the same QD mounts as I use, but even it would require some machining because it is too long at its shortest setting.
05-20-2019, 09:38 AM   #7
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My 67 300mm M* has a weight mass of about 1.8kg and my P67 body is plenty strong to hold it cantilevered off the mount. But I'd never shoot it that way. If handhold, I'd have one hand under the lens. And if on a tripod, I'd use the lenses mount. I wouldn't be too worried about it.
05-20-2019, 05:29 PM   #8
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Thanks everyone. I stand free of further concern on this topic.

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