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Kodak Printing Ektar with and without the inner disk
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PostPosted: Mon Jul 29, 2019 6:22 pm    Post subject: Kodak Printing Ektar with and without the inner disk Reply with quote

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


PostPosted: Mon Jul 29, 2019 6:45 pm    Post subject: Reply with quote

Like 1


PostPosted: Mon Jul 29, 2019 8:37 pm    Post subject: Reply with quote

This is very interesting. Thanks for sharing.

In photo #3 the chimney vent metal fittings, I can see coma has grown and astigmatism is now showing up quite pronounced. This area of interest would probably substitute a star chart or pin hole test. I guess this is expected from a faster lens.

Would it be possible to share a before and after photo of the lens aperture opening?


Like Dog


PostPosted: Mon Jul 29, 2019 9:02 pm    Post subject: Reply with quote

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.


PostPosted: Mon Jul 29, 2019 10:09 pm    Post subject: Reply with quote

No reason to discount the effort.

Surely there was some gratification in proving the results first hand, and sharing!

Like 1 small


PostPosted: Mon Jul 29, 2019 10:12 pm    Post subject: Reply with quote

Thank you for your kind words!


PostPosted: Mon Jul 29, 2019 10:30 pm    Post subject: Reply with quote

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


PostPosted: Mon Jul 29, 2019 10:35 pm    Post subject: Reply with quote

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


PostPosted: Tue Jul 30, 2019 1:17 pm    Post subject: Reply with quote

alex ph wrote:
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.


That (vintage) lenses get warmer when opened up is quite common, I would not make assumptions on Color vs B&W.

Given the sample photo's of the four 113's the manufacturing indicated by the the first two characters (around 1960) put them in the likely thoriated lens category, Kodak lenses even more than other brands. If so a UV treatment can help to improve the image quality. The 96 4.5 is in the list here: https://camerapedia.fandom.com/wiki/Radioactive_lenses

However the reproduction ratio they were designed for was probably 1:4 or similar. Not optimal in a test like shown.

Met vriendelijke groeten, Ernst Dinkla


PostPosted: Tue Jul 30, 2019 7:22 pm    Post subject: Reply with quote

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.


PostPosted: Wed Jul 31, 2019 11:37 am    Post subject: Reply with quote

alex ph wrote:
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.


It is not the radioactivity I worry about but the fact that the optical properties of that kind of lenses deteriorate over time by the decay. Changes in the glass itself happen, not just the discoloring. Both can be cured to an extent with UV treatment.

I guess the choice of aperture discs depends on the use of the lens. If speed of the process is more important than image quality a wider opening will be used. That can also relate to the intended magnification factor of the device it is used in. Small differences in the disk openings could be an indication of calibration purposes for the disks. Although I think it is easier to calibrate on the illumination source in the equipment.

Your test shows enlarged crops of the image. I guess you made more images, each one focused per plane of the crop. Made for flat field, the lens may have some curvature at longer distances but not that much to create the same resolution at the building and tree at the edges as it did on the roof in the upper center.

Met vriendelijke groet, Ernst Dinkla


PostPosted: Wed Jul 31, 2019 11:52 am    Post subject: Reply with quote

Ernst Dinkla wrote:


It is not the radioactivity I worry about but the fact that the optical properties of that kind of lenses deteriorate over time by the decay. Changes in the glass itself happen, not just the discoloring. Both can be cured to an extent with UV treatment.




Apologies for butting in Ernst, but do you have a reference or link, so I could read more on glass deterioration due to radioactivity? I knew, as you say, that the discoloration reduced a lenses optical performance, but I had no idea that changes in the glass itself occurred.


PostPosted: Wed Jul 31, 2019 1:38 pm    Post subject: Reply with quote

Sciolist wrote:
Ernst Dinkla wrote:


It is not the radioactivity I worry about but the fact that the optical properties of that kind of lenses deteriorate over time by the decay. Changes in the glass itself happen, not just the discoloring. Both can be cured to an extent with UV treatment.




Apologies for butting in Ernst, but do you have a reference or link, so I could read more on glass deterioration due to radioactivity? I knew, as you say, that the discoloration reduced a lenses optical performance, but I had no idea that changes in the glass itself occurred.


I had no idea either but after reading this thread and some searching on the internet it is quite plausible;
https://www.dpreview.com/forums/post/58177318

F centers is the key word here.
https://en.wikipedia.org/wiki/F-center

On refraction changes;
https://akademiai.com/doi/abs/10.1007/BF02034800?journalCode=10967

And I also think that there are way more lenses affected than the usual lists show. Yellowing not always as visible as in the worst cases. I subject all my vintage lenses to UV cures now and I am thinking of getting one of those diode based radioactive measuring tools to get better information which ones were actually radioactive.

Met vriendelijke groet, Ernst Dinkla


PostPosted: Wed Jul 31, 2019 3:14 pm    Post subject: Reply with quote

Thanks Ernst. That's much appreciated Like 1 .


PostPosted: Thu Aug 01, 2019 1:54 am    Post subject: Reply with quote

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.


PostPosted: Thu Aug 01, 2019 11:11 pm    Post subject: Reply with quote

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.


PostPosted: Sun Aug 04, 2019 1:52 am    Post subject: I have a 113mm. It's radioactive Reply with quote

[quote="Ernst Dinkla"][quote="Sciolist"][quote="Ernst Dinkla"]…

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