Services For Re-cementing A Doublet in 2021? DIY?

justtorchit · Joined: 12 Oct 2009 Posts: 269 Location: St. Louis, MO

I came into a rather rare fisheye lens for my Bronica SQ system (the PS 35mm f/3.5) at a fairly good price given it's rarity. Unfortunately the price was a result of some mild haze or separation in the rear optical assembly. I opened it up and the issue is between two bonded elements. It's enough that strong highlights, such as a setting sun, in a certain part of the frame, does affect the final image (some veiling, lack of contrast).

As a DIY'er, and having read a lot of these posts, I can see lots of info from photographers and astro folks who heat their doublets up in the oven (or toaster oven) and have in some cases reported getting rid of the issue then and there. More commonly, they're merely doing this to separate the optics. Then using solvent to clean them entirely. And either re-cementing with balsam or UV-cured optical adhesive (like Norland NOA 63). I have a very rudimentary understanding of this process, but did go down the path of considering purchasing the NOA 63, a UV lamp, and a V-block to hopefully separate and re-cement my doublet. Heck, because I love this stuff, I even checked out Opto-Alignment's youtube videos on their optical benches and wondered "How much do those cost...."

But given the rarity of the optic, again, I have held off, still searching to see if there are any services out there who still do this. I am located in the US. Has anyone done this at all? Have any recommendations? I reached out and did get one response from Duclos Lenses. They put the repair in the ballpark of $1000 (also aware it could be well over the value of the lens). I see some broken links on past posts of similar nature though indicating the previously recommended services no longer exist.

The last option is just live with it, perhaps until a better copy comes along. I really just enjoy fixing things and would love to get this back to original spec.

D1N0 · Joined: 07 Aug 2012 Posts: 2491

You would probably need an optical bench in order to reliably recement lenses like it is done here: https://www.youtube.com/watch?v=cl6K-EXPILo

eggplant · Joined: 27 May 2020 Posts: 516

As always, you should join the learn camera repair Facebook group, because there are countless discussions and examples on doing this, what not to do, how much will it cost to do a better job etc.

I'll copy from one of the comments I found particularly illuminating:

white paper on cementing doublets from one of the larger precision optics shops in the US: https://www.photonics.com/images/Web/WhitePapers/53/Assembly_Method_Considerations_for_Cemented_Assemblies.pdf
Keep in mind that Optimax usually works to a higher level of precision (and cost!) Than typical consumer photographic equipment.
Excellent results can be achieved with an air bearing and a <$100 mechanical test indicator like you'd find in any machine shop. And the air bearing is probably overkill. A precision ball or roller bearing would likely work.
It all depends on how sensitive the design is to the doublet assembly tolerance. Unfortunately this is difficult to estimate without the full prescription of the lens.

justtorchit · Joined: 12 Oct 2009 Posts: 269 Location: St. Louis, MO

John Shriver · Joined: 24 Dec 2009 Posts: 192

Eric Hendrickson (pentaxs.com) re-cemented the doublet in the short-mount 100/4 Bellows Takumar for me. I don't know if he'd consider working on a Bronica lens element. I don't know how fancy his centering setup is.

guardian · Joined: 18 Mar 2009 Posts: 1749

RokkorDoctor · Joined: 27 Nov 2021 Posts: 1268 Location: Kent, UK

This is likely a modern lens cement which won't come apart unless heated to high temperatures or soaked for a long time in something nasty like methylene chloride. Traditional Canada balsam on older lenses does melt at much lower temperatures, but no chance that will have been used in a Bronica PS lens.

I would say you will likely pay less for another copy of the PS 35mm compared to having it repaired for you. I have no experience with Bronica lens repairs, so I don't know if the doublet was edge-ground to fit the cell precisely post-centering (likely though), in which case a V-block would suffice for adequate alignment when cementing (assuming you maintain exactly the original rotational alignment of the flint & crown).

Another obvious DIY route would be to see if you can find a cheap 35mm PS with damaged front optics/shutter and use that as a donor for the rear optics, assuming you know how to re-collimate Bronica PS lenses.

justtorchit · Joined: 12 Oct 2009 Posts: 269 Location: St. Louis, MO

John I may reach out to Eric and just see what he says. Can't hurt! Thanks for all the input so far.

marius.zaech · Joined: 27 Jan 2021 Posts: 53 Location: Switzerland

Idk if he can or will touch this lens but I've had a lens recemented from a guy in Taiwan once, and it turned out perfectly fine (The lens was a Contax 28-85mm).

I think it's worth writing him a mail. Waiting times for the repair might be long (3+ months) though.

http://lens-cla.blogspot.com/p/blog-page_19.html

Gardener · Joined: 22 Sep 2013 Posts: 950 Location: USA

Lightshow · Joined: 04 Nov 2011 Posts: 3669 Location: Calgary

For alignment, a V-block with an end plate(3 adjacent surfaces on the inside corner of a cube) made out of hardwood should be an inexpensive project to make a useful tool that will hold the elements reasonably close to their optical centres assuming they were manufactured properly, and have enough exterior surface to self align when placed in the V-block, most doublets I've seen would have enough surface in contact with the V-block to not have any issues with finding alignment.

RokkorDoctor · Joined: 27 Nov 2021 Posts: 1268 Location: Kent, UK

FYI,

An update on this thread; I also own this same lens from new (Bronica PS 35mm f/3.5 FISHEYE) which I haven't used for quite a while. Checking mine this morning it has the exact same problem as the OP.

This was a later lens addition to the PS line, I bought mine long after Bronica had been taken over by Tamron. All my older PS lenses show no signs of any issues with the cement used. I wonder if they used a bad batch of optical cement or had some cleaning issues; they were financially struggling at the time...

Anyway, from looking at the lens there is no way of knowing if the issue is with the cement itself or whether there is an issue with the cement having attacked the actual glass.

I could try re-cementing with Canada balsam, but I fear this modern cement will require (substantial) heat to remove. Plus I have the same issue with a doublet deep inside the front cell, which means having to take all the elements out of that one too (not accessible from the back of the front cell).

Maybe this one will need to go for spares Sad

stevemark · Joined: 29 Apr 2011 Posts: 3754 Location: Switzerland

RokkorDoctor · Joined: 27 Nov 2021 Posts: 1268 Location: Kent, UK

visualopsins · Expire: 2025-04-11

Wealth here: https://www.optical-cement.com/

Including:
https://www.optical-cement.com/cements/chart.html
https://www.optical-cement.com/cements/decementing/decementing.html
https://www.optical-cement.com/cements/manual/manual.html#anchor1332722
https://www.optical-cement.com/cements/products.html

RokkorDoctor · Joined: 27 Nov 2021 Posts: 1268 Location: Kent, UK

Thanks visualopsins;

I was already aware of these links. Their de-cementing agent is furfuryl alcohol. I don't think they can send that to the UK and I have no idea where to get that here. Summers list a representative in the UK, but that representative makes no reference whatsoever to Summers optical products. Besides, I have neither the industrial ventilation setup required nor desire to work with that stuff at 340F Wink

I may try the usual de-bonding by careful slow heating to a high temperature. Apparently the residue left on the lenses should then be removable after soaking in acetone (I thought it wasn't).

The traditional way of heating doublets is by placing on a heavy metal plate which is then gradually heated from underneath with a gas burner. Perhaps a temperature controlled heat gun should work as well; I have a digitally controlled one which can be controlled in 10 degree Celcius steps. Using that (not directly pointed at the lens) and gradually increasing the temperature should avoid any temperature shocks.

After all that it may still turn out to be the glass and not the cement that has gone hazy Sad

RokkorDoctor · Joined: 27 Nov 2021 Posts: 1268 Location: Kent, UK

Update:

Today I examined the rear doublet on my PS 35mm (rear cell, nearest doublet to aperture, lenses 7, Cool

, and tried to separate it.

My findings:

The flint is about 90 microns greater in diameter than the crown lens. The two mechanical lens centers are about 25 microns displaced, i.e. there is a "step" between the edges of the crown and flint of 70 microns on one side, 20 microns on the other. This is the result of the in-factory centering applied to the doublet.

Use of a plain V-block is therefore not going to result in good alignment. Additional shim needs to be applied to the V-block to offset the crown approximately to the same factory-applied offset. About a 50 micron shim applied to both surfaces of the v-block will be appropriate, i.e. at a 45 degree angle to the main axis of displacement, together with appropriate alignment of crown and flint.

There was some anecdotal evidence on the web that a Bronica GS-1 PG 50mm lens had a doublet cemented with Canada balsam that was separated successfully. That was a potentially much earlier production run, this PS35mm lens was a late addition to the PS lens lineup. Still worth trying though.

I marked the lenses for later re-alignment, and I scraped the lens blackening out of the chamfer. I then carefully heated the doublet to 150 degree centigrade (plenty for CB softening) , with zero effect. There was no softening of the cement at all, which confirmed my suspicion that these later Bronica lenses no longer used Canada balsam as a cement.

Currently the doublet is sitting in a bath of acetone, which I will give a couple of weeks to see if there is any visible progress on edge softening of the cement used. TBH, I am not hopeful and fear that only application high heat will separate them.

Methylene chloride can only be ordered here upon proof of professional use, qualification, training, a declaration of use and proof of safety controls, and a copy of a photo ID of the relevant company director, so that rules that out...

Paragon19 · Joined: 26 Dec 2021 Posts: 45

RokkorDoctor · Joined: 27 Nov 2021 Posts: 1268 Location: Kent, UK

justtorchit · Joined: 12 Oct 2009 Posts: 269 Location: St. Louis, MO

Wow, thanks all for the additional info in this thread. Very helpful. RokkorDoctor, sorry to hear you're seeing the same issue with your lens! I did find a clean copy (pay for it though). I shot the clean copy beside the hazed copy and found that, while the haze definitely affects image quality, I must say I didn't find it nearly as bad as I anticipated. Again though, it's there. And I am one of those people that, once I know that, I can't help but think about it when using it.

Thanks so much for all the info here. I had read some of the few re-cementing forum posts out there and I can't say I came across any info as plentiful as you all have shared hear (regarding dangers of cracking your lenses when heating, how some adhesives may not even respond to heat, etc.) So I will be staying away from attempting anything with this optic. It's functional so I just as soon leave it for someone who may be less concerned about the haze.

It's a very cool lens, though! I've been really enjoying it.

RokkorDoctor · Joined: 27 Nov 2021 Posts: 1268 Location: Kent, UK