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Disassembling the Sony FE 135mm F/1.8 GM (lensrentals.com)
167 points by luu 73 days ago | hide | past | web | favorite | 33 comments

> There’s also a bit of glue, or possibly just sealant, around the second group, too. Since the element fell right out once the screws were removed we’ll go with sealant, since that sounds better than ineffective glue.

"The element fell right out" is one of the reasons I've never considered trying to peek inside a lens.

I had a Canon EF 17-35/2.8L (on which I got a really good deal used, because the model is known to be a bit soft, and IIRC parts were no longer available). I banged it at an event (a July 4th exhibition of the ship USS Constitution), the hood didn't soften the impact enough, I held my breath and didn't look at any exposed entrails. I sent it to Canon, with an explanation to the effect of "the front fell off", along with monetary tribute. The lens came back not only repaired perfectly, but calibrated to what might've been better than new. In my living room is a poster-sized print of a crowd photo taken with this lens, and all the great happy facial expressions reacting to something happening are clear and sharp.

I love people/street photography, would you mind sharing the poster?

I was actually personally very averse to doing street photography, but there seemed to be a fuzzy overlap with photojournalism. In my rules for myself, the difference was when newsworthiness trumps privacy/imposition.

This particular image was when I was learning photojournalism, had just left practicing fluffy stuff at a street fair (e.g., visually appealing image of vendor making candied popcorn), and the crowd I was in suddenly parted, to something newsworthy, and muscle memory kicked in.

I didn't try to publish it, because it turned out to involve a celebrity (who I didn't recognize until a real photojournalist told me), and I had a rule against shooting that, but it was a happy enough image that I had a print made for myself.

As an FYI for anybody getting ready to take apart their own lens to repair it, be aware that Japanese made lenses frequently use JIS screws [0], not Philips. If they aren't super tight, you can get away with using Philips, but you wouldn't want to make a regular thing of it.

I've had a no-name 28mm lens apart a couple of times to clear oil off of the aperture blades. The old manual everything lenses are relatively straightforward to get apart. Be aware of the minuscule ball bearing that engages the detents in the aperture ring. It's spring-loaded, which might be obvious to you, but wasn't to me the first time I took the lens apart.

[0] https://en.wikipedia.org/wiki/List_of_screw_drives#JIS_B_101...

> It's spring-loaded, which might be obvious to you

In my experience it's never "obvious" until it flies across the room :D

I assume everyone who ever took a manual lens apart has at least one lens with a cine-style aperture ring... that is, without detents.

If you enjoyed this, you'll probably also really enjoy the video teardown of the Sony OSS 16-50mm kit lens. It's cool for two reasons — one is that it's a zoom lens, but the really awesome part is that it has an optical stabilization element. There's also a bit more focus on the electronics and motors.

https://petapixel.com/2016/02/09/this-teardown-of-a-sony-e-m... (blog bait summary — but with a bit more text)

https://www.youtube.com/watch?v=g9umAQ1-an4 (the actual video)

Regardless of weather sealing lenses will get dusty if they breathe. If any outside lenses move the internal volume of air must change and that means air is being exchanged with the outside.

Do they at least have filtered air vents? Most hard disks (the non-helium-filled ones) are very carefully sealed except for a single vent that has a big filter on it.

Dust in a lens isn't a big problem. It really doesn't effect the image quality [1]. They had another tear-down to remove a fly from Canon 70-200mm [2], and it didn't make difference until stopped down.

1: https://www.lensrentals.com/blog/2011/08/the-apocalypse-of-l... 2: https://www.lensrentals.com/blog/2019/04/removing-fly-from-w...

I don't think that necessarily implies that the inside will get dusty. For example, if the air intake had a HEPA filter with a sufficient lifetime, only particles smaller than the filter's rating would be able to enter the body of the lens.

I suspect this is design tradeoff.

First, hepa filters tend to block flow of air A LOT. Lens designers strive to get lenses to focus as quickly as possible. Any blockage of air would necessarily make it very difficult for the lens to breathe quickly.

Second, dust particles in the lens do not affect the image nearly as much as you would think they do. Just look at this pic: https://www.lensrentals.com/blog/2008/10/front-element-scrat...

If there was no exchange it would create a pressure differential. I don't know how large it would be or if it'd matter though, but if it weren't large enough to overpower the mechanism or make it difficult to use, it could avoid purposely exchanging air.

This lens, same as (for example) the SELP18105G (E-mount APS C 18-105mm/f4 Power Zoom) is fixed-length, meaning there is nothing moving on the outside.

Except for the autofocus mechanics of course. Those move around before every shot...

GP meant that while doing so, the physical length of the lens doesn't change, and I assume that means the amount of air inside remains the same.

Couldn’t you make a lens with a vacuum inside?

If the lens does not breathe there would be no advantage (it can just be airtight without being vacuum) and if the lens breathes (ie changes internal volume) it means the motor would have to work against atmospheric pressure which would be extremely difficult in a lens to do reliably.

Counter question: Why not fill lenses with Nitrogen? I know outdoor cameras CCTV cameras do this (more so to prevent condensation from internal moisture).

You'd still have to compress the nitrogen going one way to zoom, and pull the nitrogen against air pressure going the other way. Focus motors powerful enough to do that, plus including movable airtight seals to keep the nitrogen inside, would make the lens a serious chunk bigger, heavier and more expensive.

The dust that gets inside from breathing while zooming rarely affects image quality to any meaningful degree. Excessive humidity can lead to fungus growing on the glass though, which really can ruin your contrast. It's normally good enough to keep your lenses in a box with some silica desiccant during summer to prevent that.

It's pretty hard to make a vacuum with moving parts included in the wall of the chamber. The better your vacuum seal, the harder it'll be to move the lens elements and vice versa.

And if the seal fails then you'll get a lot of dust inside.

That was a fun read. I enjoy reading tear-downs like this, even if the fault was something they weren't able to fix.

I also like it that Sony was cool with them doing this.

Despite Sony's insistence on DRM they make some very repairable hardware. For instance, it is dead easy to replace the controller switches, battery, and other parts on the Playstation Vita where the flex cables are very well routed.

In general I've found electronics from the major Japanese companies easy to open, well labeled, and designed in a logical manner.

The PlayStation Portable was equally he say to work on, replacing any component was super easy. And to a very large degree repairing the PlayStation 4 is also pretty easy, of course most components are soldered on the motherboard but if you only needed to replace the fan or the the power supply that's very easy to do.

Nice writing, and very educational for someone who never had reason to take a lens apart. Explains part of why they're so expensive! :)

I think it's a bit more glue than I like, but still reasonably serviceable for something with small parts in a restricted space. About on par with a Toshiba laptop, not as good as a Thinkpad (based on my experience with now outdated hardware repairs).

I love the Lensrentals teardowns! I just finished reading this teardown of a then-flagship Sony camera that was exposed to saltwater.


Or if you're a Nikon fan, here's their teardown of a Nikon flagship a year later. Note that this camera wasn't suspected of exposure or abuse, so not really a comparison but I'm fascinated by how modern pro cameras are built, their weaknesses, and how they may or may not be serviceable.


wrt. casing at least Nikon's pro offerings were always top notch in terms of body ruggedness etc., although up to 2008 or so they did have occasional issues with the rubber coming off at the edges. Some problems with chemical resistance as well. Newer models use a different, notably stronger adhesive. Fewer problems wrt. chemicals it seems, too.

I once had to open an old 24mm Pentax lens that my parents handed down to me when I started photography. The aperture was stuck due to some old grease, and with that the lens barely unusable. The fix was pretty easy, and the whole process of understanding all the tiny mechanics of a lens were a lot of fun, but at the same time it was incredibly stressful to have those optical elements so exposed.

I couldn't image doing the same thing with a current lens that also has all those electronics in there.

I just disassembled (and didn't bother putting back together) a Sony 16-50mm f/3.5-5.6, the build quality here seems to be better. That was a lot of plastic and parts didn't really "click" in place so much as "mashed in there." I've had to replace this lens twice already (and it's only a very, very part-time camera for me); I am significantly less careful with my Nikkor equipment and never had any issues there.

The Sony camera stuff is really built like tanks and can pack a load of abuse. Thanks for the submission, that explains the "why" :)

I found this disassembly very interesting. Thanks for posting.

I've taken a lot of stuff apart in my days, but never an expensive camera lens. I've owned, just off the top of my head, a 70-200 f/2.8, 50 f/1.8, 85 f/1.8, and a 105 f/2.8 macro lens back in the day when digital was just starting to catch on.

There are times where I miss photography...I always assume I'll get back into it at some point.

Great read - I'm excited for the Sony 35mm 1.8 teardown.

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