Kodak Printing Ektar with and without the inner disk

alex ph · Joined: 16 Mar 2013 Posts: 1674

Kodak printing and enlarging Ektars are often praised for their sharpness. Many of them are not equipped with adjustable aperture and only have an inner metallic disk that serves as fixed aperture. This way the "real" speed of the lens is limited in the sake of better sharpness and contrast. I am always curious which kind of added value a suppression of those fixed stoppers might bring.

I already experimented with a tiny rarer version of highly common Kodak Enlarging Ektar 4.5/50 (London) which does not have an adjustable aperture but such an inner disk. This one was a Heliar type lens. And I was quite curious to see the difference with and without the disk, but did not manage to open the lens.

I got recently a more classic Kodak Printing Ektar 4.5/96 which must have a four glass design, while a Camerapedia page mistakenly attributes Heliar type to the whole Ektar range.

This lens is easy to disassemble, so I made an experiment to explore a possible gain.

After realizing a short series of test shots, I made four quick conclusions:

a) Overall sharpness predictably drops down when the inner disk is retreated.
b) Corners quite predictably degraded without the inner disk.
c) But... colours get warmer and more natural. Even if CA are more visible (slight purple fringing).
d) And shiny surfaces have a much smoother transition to shadow without the inner disk (see #2).

The last two points make me think the lens was still optimized for BW prints, where sensitively cooling the colours and making reflective surfaces shinier was less critical than sharpness.

#1 The test view taken with the inner disk followed by a direct comparison with and without the disk

#2 A 100% crop from the center of the image

#3 A 100% crop from a corner

#4 A 100% crop from the next shot centered and focused on the tree, auto-contrast is applied to lighten the leaves

#5 Another, closer test view

#6 A 100% crop from it

#7 A 100% crop from the lens without the inner disk. Unfortunately, the same scene with it got fuzzy handheld, so no good reason to include both

sergtum · Joined: 14 Nov 2016 Posts: 735

Blazer0ne · Expire: 2024-12-07

alex ph · Joined: 16 Mar 2013 Posts: 1674

Sergtum, Blazer0ne, glad you find that interesting.

Blazer0ne, I won't have the lens in my hands a couple of weeks more. In a "normal" assembly you find this lens and its closest relatives looking like that:

I borrowed this shot from a random ebay listing.

I could easily unscrew the front group and gett off the inner disk. Mine has a mark "44", while those ones on the ebay "38" and "41". Mine has just a larger hole. And that's now, looking at them, I start asking myself if those disks are really fixed "by design" or they are indeed simple and exchangeable drop-in apertures! If it is the case, then the "real" speed of those Ektars is f4.5 without any disk, and we find them second hand "closed", with an aperture disk that was the latest stop used.

That makes me feel stupid, I am pretty sure someone already explained all that in some post.

Blazer0ne · Expire: 2024-12-07

alex ph · Joined: 16 Mar 2013 Posts: 1674

Thank you for your kind words!

blotafton · Joined: 08 Aug 2013 Posts: 1633 Location: Sweden

Interesting lenses, are they yellow from thorium or is it just the light that makes it look that way?

alex ph · Joined: 16 Mar 2013 Posts: 1674

Mine is a bit yellow, not as strong as depicted in that shot.

Ernst Dinkla · Joined: 30 Nov 2016 Posts: 408

alex ph · Joined: 16 Mar 2013 Posts: 1674

Thank you for this additional info and for the precaution. I won't bring the lens in my pocket ! Smile

As far as I understand, the radioactive impact of such lenses is really minor in usual photography practice.

To my surprise, I found nothing specific about the habitual use of aperture disks in Printing Ektars. Well, the original intent of this post turned out finally not be that naive.

Ernst Dinkla · Joined: 30 Nov 2016 Posts: 408

Sciolist · Expire: 2021-04-16

Ernst Dinkla · Joined: 30 Nov 2016 Posts: 408

Sciolist · Expire: 2021-04-16

Thanks Ernst. That's much appreciated Like 1

.

jamaeolus · Expire: 2015-08-20

If you think about it its obvious that the radioactivity is changing the optical properties of the glass. Our weak inefficient optical sensors (eyes) can readily see it. I am sure that with high tech sensors you could really get to the nuts and bolts of the changes Exactly in what ways and how much is likely a PHd thesis for some intrepid optics physicist candidate.

alex ph · Joined: 16 Mar 2013 Posts: 1674

Ernst, thank you for the interesting remarks. Later I'll test my copy in close field with and without the disk, to see if the difference is less in astigmatism in the corners.

RichA · Joined: 17 Feb 2011 Posts: 55

[quote="Ernst Dinkla"][quote="Sciolist"][quote="Ernst Dinkla"]â€¦

About 6000 counts per minute 1 inch from the rear lens surface with a geiger counter.

alex ph · Joined: 16 Mar 2013 Posts: 1674

Here is some update:

The lens with the inner disk inside (marked 44)

Without the disk

Without, a lens-through view

alex ph · Joined: 16 Mar 2013 Posts: 1674

And here are some more test shots in close field, as suggested by Ernst. I was glad to find difficult light conditions, the lens properties are in some way better observable.

#1 Without the inner aperture disk on Sony A7

#2 With the inner 44 disk on Sony A7

#3 Without the inner aperture disk on Sony Nex

#4 With the inner aperture disk on Sony Nex

In both cases the difference visible in large distance shots is predictably confirmed, wide open the lens shows more CA and glow.

Just to have a scale for comparison, here is the same scene taken on Nex with Meyer Helioplan 4.5/75 (uncoated) wide open

alex ph · Joined: 16 Mar 2013 Posts: 1674

The final test which does not fit a usual set of comparisons. Although seeing the easiness of unscrewing the front group and eventually changing the inner fixed aperture disk, it seemed to me a curious one.

I asked myself what is the margin of tolerance for inter-glass distances of such a lens that might be easily unscrewed and recomposed. What if someone does not "close" the lens well enough? Does it impact dramatically its performance? And, accidents apart, might it be used for purpose, as in some old brass lenses, to make for example soft effect?

Here is a test answer. First of all, the test scene on the whole, taken with Nex

And here is a line of 100% crops I took from the upper left corner, without post-processing, as the center part of the image does not show that visible difference.

Click on the image to see it full size.

To tell the truth, the results are rather puzzling for me. First, it seems to be more about colour abberations than sharpness. Then, unscrewing the front group almost fully, I got a better result than unscrewing it at half. How does it expalin? And what should be done to the lens to get a clearer soft-effect? Anyway, it is quite a fun to tease the lens in such way. It gives more open questions than predictable results.

Ernst Dinkla · Joined: 30 Nov 2016 Posts: 408

Possibly coincidence but a recent similar thread on adjusting element distances of enlarger lenses for infinity is here; https://www.dpreview.com/forums/post/63025308

I suspect in your case, widening the space between elements may have have flattened the focal field for longer distances.

alex ph · Joined: 16 Mar 2013 Posts: 1674

What a coincidence, Ernst! Thank you for the link. I haven't seen this thread. Besides there is a thread on this forum about enlarger lenses at infinity that I equally ignored. Even though I never experimented an "awful" IQ with enlarger lenses at long distance close to infinity. But this might be because I have never got my hand on EL Nikkor...

If I understand right your idea on dpreview forum, you suppose that recessing the front group may flatten the optical field of the lens. My experiment goes in the contrary direction: I unscrewed the front group, so that it goes further from the focal plane. Besides my result is not consistent, as the last test series testimony: putting the front group further turns the image quality better, i.e. closer to the "normal" glass position, other than unscrewing just slightly. Maybe to get a more consistent result I need simply to repeat the test a couple times more.

Ernst Dinkla · Joined: 30 Nov 2016 Posts: 408

alex ph · Joined: 16 Mar 2013 Posts: 1674

Ernst, interesting information and reflections! I will experiment more with unscrewing, unfortunately not in the sense you suggest, as it requires lathe work on the barrel. If you do some experiments with your lenses, please share the results.

I remember having crossed some sources about this lens, some saying Heliar type, some others Tessar. In the final count I made a conclusion that it is most probably the Tessar one.