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View Full Version : Advise and info on Goerz Dagor 12" coatings, IC and focus shift



Tim V
23-Feb-2018, 21:18
Hi all,

I've come into possession of a non-gold dot / rim C. P. Goerz Dagor 12", AM Opt. Sn. 7705** (in Ilex 4 shutter), which indicates it was made somtime between 1945–48.

I have a few questions with regards to this version of the lens, and was wondering if people may be able to help answer them.

Firstly, I'll attach photos of the front and rear elements which have quite a bit of mottling on the lens coating. Viewed straight on it's not really visible, but viewed from the side at a particular angle it's very obvious. Do people think this will affect its performance too much? I'm suspecting not, but thought I'd ask to see what people think. I'll be shooting BW.

Also, with regards to this era of the 12" Dagor, I'm wondering what people have found with regards to focus shift when focusing wide open then stopping down to shoot. I'll be shooting mostly up around f32/45, where I guess focus shift will be less obvious, but I'd like to get info on how to predict its behaviour if I choose to shoot wider in some situations. With lenses that exhibit it a lot, I'm guessing it's best for focus at f8/11? And if I'm focusing at mid-distances, I'm wondering how much it'll rear its ugly head anyway?

Lastly, is it fair to say that the IC is quite large, upto 85, but that for good corners and even illumination it's best kept below 70?

Thanks again for the info, it's a good community of people and knowledge here!

Tim

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Bernice Loui
24-Feb-2018, 12:08
Appears this Dagor is in a Ilex shutter. Are the shutter speeds accurate enough and the shutter functioning properly?
If yes, then simply make some images with this Dagor and go from there. Don't be overly concerned with coatings. Shade the lens (dark slide works) before making the exposure.

Focus shift, focus on an item at full aperture, then stop the lens down to say f16 or smaller aperture then check focus at the same item and note what comes into apparent focus relative to full aperture. IMO, focus shift of a Dagor is not that big a deal and can-does vary with the individual Dagor.


Enjoy,
Bernice

Tim V
24-Feb-2018, 14:36
Thanks,

Yes, it's in Ilex #4 shutter. Speeds seem accurate and all looks to be working as it should. I've given it to a friend who has a device that can measure the exact speeds against the marked speeds.

I'm interested in the focus shift issue as I've experienced it with Leica lenses and it was a pain in the neck, but never suffered it with LF lenses. Part of the reason I'm asking here is because my camera is away getting repaired and I'm waiting for a lens board to arrive from SK Grimes, so I can't test anything! The wait is painful!

The other reason I'm asking is because there is so much conflicting or confusing information regarding these lenses that it's hard to determine what one is actually buying or dealing with. E.g. IC specs seem different depending on who you are talking to – seems though that common opinion puts the usuable IC for good corners for enlargement at a max of 70.

With regards to the coatings, I've never shot with a lens of this vintage before, save for an old 50mm Leica collapsible Summicron of around the same era. I loved that lens; the flare and the contrast were kind of special, the front element was pretty average in condition with cleaning marks and tiny defects, but I can't remember it having the same kind of mottling on the coating.

I'm so used to using new digital RS lenses on my Leaf Credo 60 digital back that this is kind of new territory for me. With 4x5" I used the same two lenses for 10 years and never strayed from the known, but with 8x10" I want to be a bit more experimental.

Thanks again,

Tim

LabRat
24-Feb-2018, 16:54
My AO Dagors are uncoated, and I find that they behave very well, and the (lack of) coating was never an issue, so give 'em the tests, and enjoy...

Good Luck,

Steve K

Greg
24-Feb-2018, 17:22
I use a 14” f/7.7 GOERTZ DOUBLE-ANASTIGMAT (Dagor formula) on my 11x14. I normally stop down to f/45 or f/64. Focus shift has never been an issue for me to deal with. But if there is any focus shift, my stopping down so far I think would probably negate this factor. Read somewhere in the past that focus shift could be cancelled out by using a filter over the lens... Wratten #12? I believe, but I just don't see the logic behind this "solution". In the 1980s, I used a 240mm Dagor on my 8x10. Now it did display some focus shift "on a test bench" but in practice when shooting in the outdoors was not a factor.

Luis-F-S
24-Feb-2018, 17:52
From the Serial # this lens is likely uncoated, unless it was coated later; not that it should make any difference. If the bloom bothers you, you can have it cleaned. Again, no difference. I've never noticed focus shift on any of my dozen or so Dagors, just focus wide open and slowly stop down and see if the image focus shifts. I doubt it will or that you will notice it. Quit reading and just take pictures with it! This ain't a Leica!

Bernice Loui
25-Feb-2018, 10:43
Dagor has essentially four glass to air interface surfaces, this will have lower inherent flare simply due to the limited number of glass to air interface surfaces.
Compare this to the vast number of optical elements in a modern zoom lens where coatings make these complex optical designs possible.

Many decades ago, got a uncoated Zeiss Planar process lens. After two sheets of film, it was gone on to another owner due to the horrid flare-low contrast problem. These were among the first Gauss lens designs produced and they had serious problems due to the number of glass to air interfaces. It was not until the science and technology of optical coatings advanced enough to reduce the serious internal reflection problems.

Optical glass "blooming" is how the entire science and technology came to be. It was observed many decades ago that old lenses with blooming produced higher contrast-better images. This got the optical folks wondering why this happened and eventually resulted in the world of optical coatings.

Better to not worry or be overly concerned about this techno stuff and get to know the personality of a given lens and how they produce images on film. This is what really matters. This techno stuff is often a distraction from what really matters, the goal of expressive image making.


Bernice

Tim V
26-Feb-2018, 11:36
Hi guys,

Thanks for the help. I plan on shooting with the lens a lot, regardless of the coatings etc., so no dispute from me there!

I didn't know that you could get the bloom cleaned off. Who performs such a service? I doubt very much I'll have that done, but I'm interested to know as thought it was impossible.

Thanks again,

Tim

LabRat
26-Feb-2018, 13:20
Hi guys,

Thanks for the help. I plan on shooting with the lens a lot, regardless of the coatings etc., so no dispute from me there!

I didn't know that you could get the bloom cleaned off. Who performs such a service? I doubt very much I'll have that done, but I'm interested to know as thought it was impossible.

Thanks again,

Tim

I have also read in several old texts to never remove the bloom on old lenses, as they are crude coatings... (Usually oxides of lead or other compounds used in the glass making that oxidize over very long times...)

One might be able to re-oxidize these glasses by fuming elements in the fumes of Liver of Sulfur for some weeks until they start reflecting a spectra...

Steve K

Luis-F-S
26-Feb-2018, 13:27
"Liver of Sulfur" and throw in a couple of newt's eyes into the caldron for good measure. Just use the lens as it, it should be just fine. If you love it, you may wish to trade it in years down the road and get a more recent one (say 50 yo instead of 70 yo) in a newer shutter.

Lightbender
2-Mar-2018, 11:47
I've had a couple of plate f6.8 dagors.
I found focussing at f6.8 to have a noticeable amount of focus shift. But there was a wide variety of dagors and they were made over a long period of time, so results may vary. If you have some focus shift then just focus all f8 and that should solve the problem.

Tim V
2-Mar-2018, 22:30
Thanks again for all the comments.

I think that's what I'll do: focus at f8 and just see how it goes. My camera is stuck in Italian customs on its way back to Gibellini for repair and modification, so I'm still not able to try the lens out regardless...

In the meantime I'll continue dream about using the damn camera and lens. I miss the meditation when in the field!