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07-03-2016, 08:12 PM   #1
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Plastic jars as lens cases for manual focus lenses

Perhaps others would be interested in the results of my mini-project to make lens cases for my old manual lenses, most of which I did not receive with original cases. I did receive the original case with my K35, but it's a little large, it wouldn't protect the lens particularly well against desert dust and ocean spray, and it would probably age much faster in my custody. So not only did I hope to replace the missing cases, I wanted to improve on them.

After looking at many specifications of plastic bottles and contacting manufacturers that did not provide adequate specifications, I purchased several plastic jars from United States Plastic Corp ( These jars are durable PETE with 70/400 threaded finishes, in particular items 066843 for the 6 ounce jar and 066844 for the 8 ounce jar. I also used polypropylene lids, item 066338, but most any 70/400 lid should work.

The 6 ounce jar is not quite big enough for my K35 or A35 (same size; I have both). With the front cap on but rear cap removed, it fits snugly with the front up, but I wanted to avoid any mechanical force on the aperture lever projection on the back of the lens. Therefore I carefully heated the bottle with a heat gun (my first try destroyed a bottle with too much heat) and smashed down the two high spots on the bottom of the bottle with a hunk of metal I happened to have:

The smashing action necessarily warps the plastic so that the bottom of the jar is no longer round, but the K35 and A35 fit comfortably. However there is still no room for the rear cap.

The 8 ounce jars seem to be a much more useful size for my K28, K55, and A50 macro, which fit well when both front and rear caps are attached. Here is my K28 next to my only point of reference, the K35 case.

The 8-ounce jar is slightly smaller in height and diameter compared to the K35 case, and I expect the K28 case would be larger yet. Also notice the EPDM foam tape weatherstripping:

There is room for improvement here as well, since a snug fit would probably be about 5mm thick of EPDM foam tape, whereas the product I used here is 3.2mm or 1/8 inch. As it is the lenses move around about 5mm laterally. I used MD All-Climate Rubber Window Seal.

The neck of the 8 ounce jar, unlike the 6 ounce jar, was too small for the lenses to fit. It required about three minutes working with 60-grit sandpaper to allow the lenses to pass through. Quite snug!

There is also room for improvement in perhaps gluing the rear cap to the lid, which would reduce the parts count and perhaps the time required to swap lenses. However those rear lens caps don't stay on very well, and I can easily imagine opening the lid of the jar with the lens barely attached, inviting an accident.

For all the photos here, don't blame the poor colous and blown-out highlights on Pentax gear; I used an old Canon for reasons I don't need to go into.

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07-03-2016, 08:59 PM   #2
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Low cost, seems to work, great idea!
07-04-2016, 02:28 AM   #3
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I am cringing while looking at the pictures of lenses sitting on their mounts, without a rear cap...
07-04-2016, 05:40 AM   #4
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Stubby holders

cooler shop

07-04-2016, 07:13 AM   #5
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QuoteOriginally posted by pepperberry farm Quote
I am cringing while looking at the pictures of lenses sitting on their mounts, without a rear cap...
For that reason the 6 ounce jar may be too small, but there is room to put foam on the bottom so that there is no pressure on the aperture lever projection. There is plenty of room in the 8 ounce bottles for foam on both ends, between 5mm and 10mm depending on the lens, and I will do it before they travel any bumpy roads.
07-04-2016, 08:56 AM   #6
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Well done. Consider adding this project to the permanent Articles section.

Pentax Articles | Pentax K-5 | Pentax K-r | Pentax K-x -

I like the idea of the rear lens cap attached to the jar cap. That provides for a more universal application of caps vs. lenses given different sized jars and it avoids 'custom' cushioning for lenses by isolating the lens within the containers.

As for security for the lens cap attachment, I've found judicious application of 'bumps' of silicone sealer can provide a secure friction fit for problematic bayonet threads.

See-through cases make weather-proof lens ID easy!

Affixing caps to the bottom of a shelf provides for efficient 'bat-cave' storage.
07-04-2016, 09:14 AM   #7

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Anything sealed like that I'd throw in a desiccant pack or two -- airtight keeps out moist air, but also traps it -- give it somewhere to go.

07-04-2016, 11:01 AM   #8
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Nice. Those remind me of the cases that Minolta Bellow macro lenses came in. The cap had an incorporated rear cap in them. I would get a bunch of the cheap counterfeit Pentax AF lens caps from eBay and cut a hole in the bottle cap the size of the center portion. Install the lens cap from the inside and glue the lip that covers the contacts. Then use the caps as the base as the Minolta cases do.

Last edited by Not a Number; 07-04-2016 at 11:37 AM.
07-04-2016, 11:41 AM   #9
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looks good! and though maybe this is just me but I'd be a little concerned about the storage condition, i.e temperature and possibility of condensation building up but I'm not a scientist so...
07-04-2016, 11:46 AM   #10
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In Texas condensation is always a concern. Yes desicant packs for sure.
07-04-2016, 11:51 AM   #11
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I often visit humid environments, but I never stay there long enough for mold and mildew to develop. If you live in a humid area and you don't use desiccant, I agree that storing lenses in a vapor-proof jar is probably asking for trouble.
07-04-2016, 11:54 AM   #12
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If you turn the plastic jar over - lid side down - the hanging-by-a-thread issue with the rear cap goes away.

Glue the rear cap to the inside of the lid.

Store: Attach your lens to the glued rear cap. Place a small color-changing dessicant pack next to the lens. Screw the entire jar onto the lid. Store lid-side down.

Use: Unscrew the entire clear plastic jar with the lid side down, then remove your lens from glued rear cap. Throw the dessicant pack on the upside-down lid. Screw the entire jar on until returning the lens.

You could even label your plastic jars since the beauty ring is covered by the lens cap, or leave the lens cap off, stored in the jar.

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