Aardappeltaart
Posts: 141
Joined: Wed Mar 02, 2016 11:32 am

Max weight for lenses

Wed Aug 05, 2020 5:22 pm

Is there an official max weight for the screw mount of the HQ camera?

I'm trying out some old Tokina glass lenses, and the mount seems to be OK carrying a 13cm 600gr 80-210 zoom lens.

But it does look painful. :o

Should it be OK?

aBUGSworstnightmare
Posts: 2326
Joined: Tue Jun 30, 2015 1:35 pm

Re: Max weight for lenses

Thu Aug 06, 2020 8:10 am

you should mount your lens, 600g is a lot of weight ..
Are your lenses C-mount? What do you use and how about resulting image quality?

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Location: ZZ9 Plural Z Alpha, aka just outside Cambridge.

Re: Max weight for lenses

Thu Aug 06, 2020 8:15 am

If at all worried, then mount the lens and let the module float on the back, as shown with the huge Canon lens in the original blog post.
Software Engineer at Raspberry Pi Trading. Views expressed are still personal views.
I'm not interested in doing contracts for bespoke functionality - please don't ask.

Aardappeltaart
Posts: 141
Joined: Wed Mar 02, 2016 11:32 am

Re: Max weight for lenses

Thu Aug 06, 2020 8:53 am

Yes, I would mount my lens that way if it had a tripod mount, it doesn't.
https://www.pentaxforums.com/userreview ... 0-5-6.html

At the moment I'm using a mount c - Pentax K bajonet adapter, an example with a Pentax 35mm lens (reversed)
https://dev.webonomic.nl/macro-photogra ... d-lens-iii

Using a full frame lens adds a 5.6 factor, so practically it is a ~400-1200mm. :D

Focusing is hard.

And portability with al the cables attached is an issue. I would love uvc gadget support for raspistill, for the moment only the webcam functionality works.

Wanting to achieve something like:
viewtopic.php?t=272658&start=175#p1699738

Probably the best thing then is to buy another adapter with attached tripod mount, the lens doesn't really support a tripod mount ring, because every part is moving or sliding. Or 3D print an adapter, if I recall correctly some have done that.

The HQ mount does feel sturdy I must say.

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HermannSW
Posts: 3216
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Location: Eberbach, Germany
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Re: Max weight for lenses

Thu Aug 06, 2020 10:40 am

Off main topic:
Aardappeltaart wrote:
Thu Aug 06, 2020 8:53 am
Focusing is hard.
Using cheap 28BYJ48 stepper motor superglued to microscope allows for 4.4µm/step with half-stepping:
Image

This allows very fine adjustment with Raspberry microscope:
viewtopic.php?f=43&t=210605&p=1704040&h ... e#p1704040
Image

Using raspistill's "--focus" feature allows to make focusing with microscope really easy.


For your lens you would need some band around focus ring and motor shaft of stepper motor, and fixate the stepper motor relative to the lens somehow. If you go that route, focusing should not be a problem anymore with your lens.


P.S:
I am currently working with DRV8834 stepper motor driver that allows 1/32-stepping -- that would allow 16× fine adjustments per step ...
https://stamm-wilbrandt.de/en/Raspberry_camera.html
https://stamm-wilbrandt.de/en#raspcatbot
https://github.com/Hermann-SW/raspiraw
https://github.com/Hermann-SW/Raspberry_v1_camera_global_external_shutter
https://stamm-wilbrandt.de/working_with_FPGAs

JovianPyx
Posts: 132
Joined: Fri Nov 20, 2015 9:34 pm

Re: Max weight for lenses

Thu Aug 06, 2020 3:05 pm

I was also concerned about lens weight as I have a collection of Contax lenses from the film days. These include a 135 mm and a doubler lens. I use the setup to do astrophotography, so the camera is mounted on a german equatorial mount. Looking at the camera board, there are just two small screws that hold the board/camera to the tripod mount, so the tripod screw is quite a bit heavier than the small mounting screws. I'm not saying it will break. I just decided to err on the side of caution. I also plan to use the HQ camera with 2 telescopes I have, but the telescope will hold up the camera and won't need the optical bench parts.

I found what I term "optical bench parts" online which were not terribly expensive. These consisted of two 12 inch aluminum alloy hollow rods, an aluminum alloy mounting block with tripod hardware and another block that has an adjustable lens cradle attached. These parts were all designed specifically for cameras and lenses. Both blocks have holes for the rods and locking clamps so that the blocks can be separated as required by lens length. I mount the camera on the tripod block, move the cradle under the lens and lock it in place. I also bought a camera cable extender connector so that I have a short cable from camera to extender board that is never removed and the long cable (I use 1 meter) from the extender to a Pi 4. One of the reasons I wanted to support the lens is that the equatorial mount moves.

Aardappeltaart
Posts: 141
Joined: Wed Mar 02, 2016 11:32 am

Re: Max weight for lenses

Fri Aug 07, 2020 10:19 am

Thanks all for your inspirational remarks.

Actually I'm planning to try the classic `bag of rice`, and see how that works out in the field. Probably biggest challenge to get the horizontal level right.

My plan: bag of rice, mini spirit level, battery-pack, get both the FoM value and a screenshot in an API over Wifi from the Zero to my phone. Ready to go!

IIRC HermannSW has described somewhere in his great attributions how to get the FoM value over SSH, will look it up.

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