Bronica Lens Separation

[Danner]

Just put together a Bronica GS-1 kit (body, WL finder, film back, 65mm and 100mm), Everything is in wonderful conditions, but the 100mm/3.5 lens has "balsam separation" in the rear cemented lens group. It looks like a rainbow ring around a clear central region. I knew this when I bought it, at a bargain price. I will be running some HP5 through it this weekend to see how it functions, and hope it performs well at f8-f16. But I was wondering if others have shot lenses with separation, and how this affected (ruined?) the lens' performance. Also, whether it gets worse over time, etc.

Thanks for your thoughts.

 

[Don_ih]

Separation has the potential for greater impact in the rear element, especially at wider apertures. You would really have to test it to see how bad the impact is. If enough of the centre is clear, you're in luck - if not, the image will get distorted in some way (maybe blurry). As for whether or not it will get worse - if subjected to high or low temperatures, it's likely. It may stay exactly as it is forever, though.

None of the separated lenses I own have any impact on the image - but all of mine are in the front element group and very peripheral.

If you can buy an example with a wrecked front element, you could sway out the rear elements. You'd have to assess if it was actually correct after that, though, as there could be variations. (Probably are variations)

 

[petrk]

I own the 65mm for GS-1 with separation on about 60% of the area of the rear element (was advertised as for parts or repair) an cannot say it has any negative impact. Glad I bought it!

 

[Danner]

Encouraging news, thank you both. I will shoot the proverbial brick-wall test tomorrow, and see how the negatives print. Fingers crossed, and I will post results...

 

[petrk]

Make some shots against a strong light source, like sun, or of a very contrasty scene to see eventual ghosting, or a light scattering. If there is no such issue and there are no blurred details, you are fine.

Edit: or point the camera towards a bulb in a light and check if you can see the light bulb filament sharp on the screen. No need for wasting the film.

 

[Danner]

Everything looks fine in the WL finder, and I just took it outside and pointed toward the sun. Did not notice anything nasty in the finder. I'm optimistic :^)

 

[btaylor]

I have had similar hit or miss effects with separation. As others have chimed in, shoot with it and see- optimism!

 

[Maris]

It could be that there are only two 100mm f3.5 lenses for the Bronica GS-1 with balsam separation in the rear group because I've got the other one. The concentric rainbow stripes are very visible and closely spaced indicating that the separation is bigger than minimal BUT I can't see any effect in the images this lens produces. I use this lens for landscapes with the compendium lens shade on the front and well stopped down. Maybe that helps.

 

[Danner]

@Maris: You pretty much exactly described what my lens looks like. And then, inside the concentric rings, the central portion of the lens is crystal clear. I'm going to use the word "confident" that this lens is gonna be usable at f8 and tighter, which is fine by me. I'll keep an eye out for a replacement, if one turns up somewhere.

Bummer, my B&H order with 10 rolls of HP5-120 didn't make the schedule today, fingers crossed for tomorrow. I have not shot a single frame with this beast yet. I'm keen to do so.

 

[itsdoable]

Lens separation, by itself, will only reduce the contrast of the lens, it does not typically change the resolution. It's like having a spot that is not anti-reflection coated, so you get some transmission losses, and those losses can reflect back and forth causing some loss of contrast. However, if you get fungus growing in the separation, then that's a different story, but even then, it primarily affects contrast and transmission.

The Bronica GS1 lenses use Canadian Balsam, and are relatively easy to disassemble and re-cement.

 

[Danner]

Shot a roll of FP4 (XTOL 1:1) and printed to 8x10. Brick wall test (low contrast) all the images look sharp from corner to corner at f3.5 through f11. The attached image is a high contrast scene shot at f8, printed to 8x10 and scanned on a flatbed at 300dpi. Note that the scan came out darker/contrastier than the actual print.

I'm thinking this lens is just fine and I'm gonna shoot it without reservation.

Thank you for all your comments.

- Dan

 

[craigclu]

Odd... I've noticed other comments about their 100's. I bought some GS-1 gear some years back with 2 100's and one had separation. I had assumed it was damage by impact but perhaps this optic is prone to this? Here's my bad one:

 

[Danner]

Good job getting a clear picture of it.

Shopping the GS-1 system last couple months, about 2 out of 3 100m have separation. Japan pretty much has them all, and they keep the prices up there (compared to the ETR and SQ systems). BTW, the 150mm has no cemented elements, so they are all good to go.

Curious if yours has noticeable image degradation, and whether you are shooting it currently?

 

[craigclu]

Good job getting a clear picture of it.

Shopping the GS-1 system last couple months, about 2 out of 3 100m have separation. Japan pretty much has them all, and they keep the prices up there (compared to the ETR and SQ systems). BTW, the 150mm has no cemented elements, so they are all good to go.

Curious if yours has noticeable image degradation, and whether you are shooting it currently?

I've never used it as I had the good one. Can't imagine it working very well, though.

 

[moto-uno]

Imagine and reality , if possible take a few pics and post them here and see if anyone can find the difference ? Peter

 

[Danner]

Imagine and reality , if possible take a few pics and post them here and see if anyone can find the difference ? Peter

Side by side pictures for comparison would be interesting to see.