How to make lens caps (for TCs) slightly tighter?

[masayoshi]

I recently bought MC-20, and wanted to exchange/remove MC-14/MC-20 as quickly as possible in the field. I got this dual mount m43 lens holder (GoWing), and tested last week for birding.
Rear side of the lens (TCs in my case) is mounted on this device (with a lock), so I can carry two TCs on a strap. The problem was, the cap on the other side is a little loose so it fell in the bush several times. If I loose them, I need to buy and it's kind of expensive FWIW, because it's a special design cap to accommodate the protruding part of the TC's front element.

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I tried 3M Scotch tape and GAFFE tape around the rim, and it's kind of working, but it doesn't look excellent. Do you have any other methods to increase the tightness of the lens cap?

 

[PakkyT]

Just a thought. I wonder if anyone has reversed engineered that cap for use on 3-D printers. It might be too specialized but I have seen people make replacement parts for a lot of stuff that they can now 3-D print. If there is such a beast, someone who knows how could take the design and push the tolerances of the job onto the slightly larger size so it is a tiny bit oversized and really tight when mounted.

Another thought is to get a regular body cap and cut the middle out of it for the bump and if the body cap is much tighter, then glue on a cap over the cut out (plastic easter egg half, large plastic bottle cap like on a gatorade bottle, etc.)

 

[masayoshi]

Actually, I thought about 3D printing myself too, but I don't have.
It's possible to have a design, with which locking pin locks the cap, isn't it?

 

[PakkyT]

I am fairly sure you could print something with the locking tabs. (I edit my post with another idea if you didn't see it when replying to the first part).

 

[PakkyT]

Here is a bodycap 3D print page...
https://www.thingiverse.com/thing:2911408

We have a 3D printer at my work. When I get in tomorrow I will have to ask if the CAD file from this page is easily modifiable.

 

[oldracer]

The first thing I would try to do is to center-punch a few dimples on the cap's mating surface. This raises a little ring of displaced material around the dimple, increasing the pressure/friction. I would use what is called a "jump punch" aka "automatic center punch." This is a lot easier than having three hands to hold the cap, a punch, and a hammer. Also much more controllable. If this is feasible you can just add dimples until you get the amount of friction you want.

 

[PakkyT]

The first thing I would try to do is to center-punch a few dimples on the cap's mating surface.

I think the problem is that there won't be a place to put the punch without breaking off a tab. If I am thinking about this correctly, what he needs to modify is not a lens caps but a body cap that allows for the TC's protruding bump. So basically his two sided device has two camera body mounts. You can then mount lenses onto it like you would on your camera. If he instead mounts his TC then what he has on the other end is another camera body mount but with an element protruding.

So looking at one of my body caps I see this...

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Yellow arrow points at the tab that needs to be thicker but where is need to be thicker is under it, or inside the channel as pointed into by the green arrow. Or shown here by another green arrow...

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One option is to get a tooth pick and smear a bit of epoxy that dries hard dabbing in on the bottom surface (base of the little green arrow in second photo), let it dry and see if it works. If you have too much, then a little sanding/filing until it fits but tightly. Don't put it on the little tab because when you try to file it you might snap it off.

 

[masayoshi]

Thanks for chiming in, for seemingly a 'minor' problem!
Here's a picture of 'interim' solution (two pieces of black GAFF tape make friction between the cap and mount larger), but the tape tends to come off after a while, and also leaves some adhesive on the lens mount.

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Thanks @oldracer for the idea of punching a dimple, but as you can see, the place the mounting lock goes in is a deep hollow (indicated by the pink circle), and cannot make a dimple. So, unless we design something with 3D printing where the locking pin goes into it, I have to modify either the thickness of the tab or the thickness of the rim (where I have tape right now).
Thanks @PakkyT for the idea, I think making the tab thicker is a great idea, if I'm skillful enough to dab small amount of epoxy. If you have 3D printing, and possible to design/fabricate a m43 lens cap (actually body cap) that won't fall, I would be the first buyer!

 

[barry]

I'd think doing the punch dimpling on the outer edge would be an option.

 

[PakkyT]

I'd think doing the punch dimpling on the outer edge would be an option.

Ah ya, maybe. You mean coming in from the side and punching the edge of the tab (rather than top or bottom)? Might help.

Thanks for chiming in, for seemingly a 'minor' problem!

With photography and equipment it is the little things that can make the difference between enjoying it and being frustrated. It is like a car. You can get the best engine, all the upgrades, auto everything and every sensor known to man, but if the radio controls are awful or the cup holder placement is weird (both that you use more than any other feature on the car) it can really effect your enjoyment of using the car.

possible to design/fabricate a m43 lens cap (actually body cap) that won't fall, I would be the first buyer!

Ya let me check what we can do and I will get back to you.

 

[barry]

Ah ya, maybe. You mean coming in from the side and punching the edge of the tab (rather than top or bottom)? Might help.

Hi, I mean the outer edge of the cap where @masayoshi shows he taped... I think it'd have friction with the face of the mount/TC.

 

[Harvey Melvin Richards]

A lot of my caps are ABS plastic. ABS is very easy to solvent weld (use MEK or ABS glue). It would be easy to shave some ABS off of another cap and use it to build it up. An easy test is to put a drop of solvent somewhere unobtrusive and if your finger or glove sticks to it, it will be solvent weldable.

I broke the inner finger on my Oly 8 mm and I glued it back on with solvent welding. This was over a year ago and it still is attached.

 

[Hendrik]

I wouldn’t be confident that a little extra friction will be sufficient under all circumstances. How about putting some filling in the channel (meant to avoid the locking pin) with a filled epoxy and drilling a hole to allow the tc’s locking pin to do its job on the front cap?

 

[ac12]

Yellow arrow points at the tab that needs to be thicker but where is need to be thicker is under it, or inside the channel as pointed into by the green arrow. Or shown here by another green arrow...

View attachment 762624

One option is to get a tooth pick and smear a bit of epoxy that dries hard dabbing in on the bottom surface (base of the little green arrow in second photo), let it dry and see if it works. If you have too much, then a little sanding/filing until it fits but tightly. Don't put it on the little tab because when you try to file it you might snap it off.

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I see two options with one method.

Either do as Pakky said and thicken the tab, or in a variation of Masaaki's method, thicken the cap, but use epoxy instead of tape.

CLEAN the tab, cap, so there is no oil or soap.
Them mix a small bit of epoxy and smear it on with a toothpick. You need very little, just in a few spots.
- If too tight, file with a needle file or finger nail file.
- If too lose, put another smear of epoxy, to make it thicker.

This is very similar to how I take up the slop in loose pens where the section is too loose in the barrel/body.
Instead of epoxy, I put a smear of shellac. And same routine, as above test for fit and file/sand or put another smear to make it thicker.

While you could use shellac, I don't think it will stand up to repeated wear that the cap will be subject to.

 

[ac12]

Another idea is to put a "cap keeper" onto the cap, and attach the string to one of the rings on the holder.
But I do not trust the 2-way sticky foam on some of the 'cap keepers,' as mine loose their grip after a bit. I would take off the foam, clean the keeper, then use silicon adhesive to "glue" the keeper to the cap.

 

[Ross the fiddler]

Why don't you just buy 41mm Inside Dia. 'O' rings? It can be fitted into the body cap well as well as cutting into segments to fit into the lens caps (with a spot of silicon glue).
https://www.ebay.com/itm/1-4mm-Cros...hash=item1cd09f4932:m:mWO9-mxZwO7iAkSFJiwF-4w

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Here is another seller with some other technical details in the UK. https://www.bearingstation.co.uk/Products/O_Rings/Nitrile_O_Ring_Metric/25mm_-_49.99mm/OR41X4

 

[Ross the fiddler]

I've ordered the above O rings to try myself but they may take a few weeks to get here though.

 

[masayoshi]

Thank you all for various ideas!
I actually like the cap keeper idea by @ac12 since I have Dremel drill and can make tiny holes through the protruding part of the cap. Then I can connect the cap to the D-ring of the GoWing device, using strap cord or something I can get in Joann Fabric.

With photography and equipment it is the little things that can make the difference between enjoying it and being frustrated.

Yes! I had to spend more than 15 min around the bush I thought I lost the cap, and I got at least 5 mosquito bites because of that. If it's a regular lens cap, I know I can get one really cheap (I have many spares), so I can let go, but TC's cap is $10 a piece.

 

[masayoshi]

I've ordered the above O rings to try myself but they may take a few weeks to get here though.

Thank you. The width of the hollow part I indicated with a pink circle in my image is actually 4mm, so it could work really well. The only concern is the depth is 3.7mm, so the O ring could protrude 0.3mm, and that could be too much, and too tight. Shaving off 0.3mm of silicone will be very difficult.

 

[retiredfromlife]

I've ordered the above O rings to try myself but they may take a few weeks to get here though.

Let us know how it works out, could be a good cheap solution