Foggy images with enlarger lenses

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Freak
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Foggy images with enlarger lenses

Post by Freak »

Hello everybody,
i was trying for the first time the componon 28/f4 witn my Canon 60D at around 3.5:1 of magnification and also less.

The problem I found are the images affected form some fog. I used a cutted glass of polystyrene (which gave me excellent results with the canon 28mm f/2.8 pankake) and also with some other material. I tried to flock the extension tubes, to fit an hood on the lens with the flock material but nothing changed.

The pictures I made without diffuser were not affected by this problem (loss of contrast?), so I don't think it's a problem of the lens but of the lights bouncing inside of it.
Tomorrow I'll try to build a conic hood, let's see what happen. I got this problem also with a pentax 50 f/1.7 reversed.

IMG_0067milk-min.jpg

rjlittlefield
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Re: Foggy images with enlarger lenses

Post by rjlittlefield »

With a DSLR, the first thing to do when you have fog is to remove the camera body, place your eye behind the optics in the same place that the sensor would normally be, and look around. Chances are that you'll see rings of light around the lens. Those will be reflections from the inner walls of tubes, fittings, and sometimes the insides of lenses. In any case, every place there's a bright ring, that's a place that has to be either flocked so it won't reflect stray light, or masked/baffled so that stray light cannot get to it to reflect.

See for example the discussion and illustrations at viewtopic.php?t=35350 .

Sometimes the best mask/baffle is a hood on the front of the lens, but that's a tradeoff against working distance. If you want to go with a hood, consider making an inverted cone -- wide at the lens and narrowing to just enclose the actual subject. See for example viewtopic.php?t=424 , first panel, lower left.

--Rik

Freak
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Re: Foggy images with enlarger lenses

Post by Freak »

Thank you Rik for answering and for your precious advices. Very helpful and informative.

Yes, I flocked the extension tubes nad now I tried to make it better (I flocked also the flange with the bajonet). Anyway I had the problem also without extension tubes.

But I got the real improvment when I tried with a little cone hood. The image came much better. The problem, how you said, is with the working distance, it has been not so easy to make it :D

20210218_191116 (1).jpg
But, is it normal to fit an hood like this? I mean, everybody who have these componon lens need to build it ?

Thanks a lot.

Daniele

rjlittlefield
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Re: Foggy images with enlarger lenses

Post by rjlittlefield »

Freak wrote:
Thu Feb 18, 2021 11:29 am
But, is it normal to fit an hood like this? I mean, everybody who have these componon lens need to build it ?
I have no experience with any Componon 28mm f/4. I do not see any mention of hoods in Robert Otoole's test report at https://www.closeuphotography.com/4x-lens-test-part-3 .

Have you done the test that I suggested, to remove the camera body and simply look into the optics, with your eye at the same position that the sensor would be, as illustrated at viewtopic.php?t=35350 ?

Whenever you are getting fog due to stray reflections, that test should tell you where the reflections are coming from.

Some lenses have built-in rings with shiny sides that can reflect light coming from far off center. Those rays can be blocked by a hood like you have. Sometimes they can also be blocked by a simple baffle of black paper, placed just behind the lens, with a hole just large enough for the aperture that you want to be shooting at.

--Rik

Freak
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Re: Foggy images with enlarger lenses

Post by Freak »

Dear Rik,
from this post, thanks to your explanations and advices I have learnt something very important about light reflection.
rjlittlefield wrote:
Thu Feb 18, 2021 5:23 pm
Have you done the test that I suggested, to remove the camera body and simply look into the optics, with your eye at the same position that the sensor would be, as illustrated at viewtopic.php?t=35350 ?
Thank you to have reminded me because it has been an important lesson. In this way you can really understand from where the reflection come from :D

circle_01.jpg
I took this pic with my phone, you can see clearly the ring. I used 60mm extension tubes

circle_02.jpg
The same subject from a prospective different a bit

buffle.jpg
Here I fitted a baffle on the back of the lens, as you suggested here:
rjlittlefield wrote:
Thu Feb 18, 2021 5:23 pm
Sometimes they can also be blocked by a simple baffle of black paper, placed just behind the lens, with a hole just large enough for the aperture that you want to be shooting at.
No more rings and reflections.



Finally I have taken the shoot of the same bug I posted at the beginning, a substancial improvement here. I fitted 2 baffles behind the lens with no hood. I tried also with the hood as I shown in the previous pic and I got an extra improvement of about 10%, maybe less, but you have to fight with it because of the little work distance

2_buffles_no_hood.jpg

So, I realized the reflection came from inside the lens, on the back, as you said here
rjlittlefield wrote:
Thu Feb 18, 2021 5:23 pm
Some lenses have built-in rings with shiny sides that can reflect light coming from far off center.
Or maybe the reflection come from the side of some element with no coating ? #-o

I took these shoot just as they came out from my camera, without any post production. The same, I didn't take any importance to the deep of field and the stacking.

Thank you again Rik for your help !

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Re: Foggy images with enlarger lenses

Post by rjlittlefield »

Freak wrote:
Fri Feb 19, 2021 2:56 pm
Or maybe the reflection come from the side of some element with no coating ?
I assume you mean the lateral sides, where the lenses were edged. That's definitely possible. Componon's are designed to be used as enlarging lenses. When used for that purpose, the metal plate that holds the film also blocks any light reaching the lens except from inside the frame to be imaged. In effect, the film holder also serves as a very tight-fitting lens hood. That, plus the lens aperture, prevents any light from reaching the sides of lens elements and bouncing around to make fog. So, the manufacturer had no reason to blacken the edges of lens elements or to add internal baffles to prevent fogging. The need for extra baffling is introduced when the lens is repurposed for use in a situation where there's lots of light coming in from outside the frame.

I'm glad to see that all is well now.

--Rik

Freak
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Re: Foggy images with enlarger lenses

Post by Freak »

rjlittlefield wrote:
Fri Feb 19, 2021 5:26 pm
I assume you mean the lateral sides, where the lenses were edged.
Yes, right.

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