Ways to avoid white Vignetting?

[Hans Punk]

You will need to go smaller with the ring - you will be surprised how narrow the diameter needs to be...it is trial and error. I can’t give an exact diameter since I’m away from my lens to check. You can use a thinner ring and cut to the perfect diameter (glue the two ends together with micro spot of superglue well away from the lens). You can then glue that smaller, thinner ring into the thicker outside ring that you already have. It is a bit tricky to explain with words, but the end result is a bit like a plug that is made from one larger diameter ring (like you already have) to fit flush around outside edge, with one smaller diameter ring that is glued to the inside of that ring that acts as the baffle/choke mask for the actual optic edge. From memory, finding one single ring that can be the ideal outer and inner diameter is pretty much impossible...so some experimenting with many combinations should be expected. As stated before, glue a few size options well away from the lens and leave to dry to disperse vapours before test fitting near the rear of the Isco. 

[mirekti]

I made it!!! ...almost

First of all, thank you, @Hans Punk There is no way I would have figured this out on my own. Adding a ring wasn't actually a desirable approach for me as it put Iscorama further away from taking lens' front element. I ended up buying some faux leather material which is rather thin, and instead of placing it on the back of Iscorama I put it on the lens itself. It is indeed a trial and error, and I came close, but need to figure out how to permanently add it to the lens so it doesn't rotate and I could get consistent results. As you will see in the picture the left bottom corner is not placed properly so I got some veiling glare, the right bottom corner is getting some vignetting. It seems there is a very thin line between veiling glare and vignetting.
What confuses me is that I actually see less vignetting too. The other day I posted a photo with Iscorama focused at 2m, and the corners were obviously dark. This is not the case anymore.

Photo 1 - Lens cover
Photo 2 - Veiling glare - > only visible in the bottom right corner (Is this coming from the opposite corner? When I full close the lens, only the opposite corner has no vignetting). Anyhow, even if it stays like this, I will not complain. This is much, much better than what I originally had.
Photo 3 - 35mm at f/2.8 x 0.7 Kipon focused at 2m -> vignetting is subtle and there are no hard cuts. I really like this side effect.
Photo 4 - 35mm at f/22 x 0.7 Kipon focused at 2m -> I know this will never be used, but it reveals the flaws in cuts I made.

 

 

[jaquet]

Sounded promising. But it seems to be more complicated.
I learned that adding a shape to the rear part of the Isco means adding a front iris to the taking lens.
Yes, it reduces the veiling glare/white vignetting but also adds a new shape to the bokeh! 

The white vignetting appears most when you open the iris to maximum.
It is produced by the edge of the Iscos's front lens element (i guess it's the second) and therefore just visible on the widest taking lenses only.

If the ring/shape or whatever you add to the Isco's rear part is smaller than the taking lens iris itself the shape is going to be your new iris.
That means your 1.4 lens is no longer a 1.4 lens any more but a 2.8 (depends on the diameter of the shape). The picture is getting darker and sharper (more depth of field). 
I made a rubber shape with a 15mm diameter hole which fits best to my Isco 36 (without vignetting). 

See the pictures below - with and without the rubber shape.
40mm 2.0 taking lens on a GH5s with Speedbooster XL (the widest you can go)
The flare pictures are made at 90cm close focus to show that it is not possible to avoid every white vignetting at this distance.
You can see that the overall bokeh and exposure has changed by at least 1 stop.

So at the end, is this mod useful? I don't think so …

… the Iscos overall performance and look is best at f4.0-5.6. At these iris settings the white vignetting isn't that prominent.
But if i had to shoot at night, wide open, facing a car's front light, on a wide shot, maybe I'd give it a try …

[Hans Punk]

A rear plug that effectively creates an aperture that is spaced away from the rear optic of the Iscorama will of course create an undesired effect. The rubber ring method however does not - because it is situated just on the very edge of the rear optic edge of the pre-36 that is collecting the light and causing the white vignette and square rainbow flare.

The rubber ring is acting as a pellicle/baffle, not as a mask or iris...it is a common method (with many vintage lens designs) to help clean up just the unwanted light and edge glow from an optic edge - that can otherwise introduce contrast drop and unwanted internal flares.

the only reason that the Isco-pre 36 may require such a pellicle/baffle ring - is when using the Isco on a non-factory taking lens (which most people these days are). The original 50mm Isco taking lens has a deep recess and edge baffle for the Isco rear built into its design, so does not exhibit the same amount of edge rainbow flare or white vignette.

 

[ponelli]

hello everyone -

i would like to share some informations with you:

i´ve got an isco pre36 lens. and i always had problems with these "undefined" flairs in case of straight spotlight into the lens.

the isco is based on a 35 mm nikon lens (aps-c sensor). i found a way to eleminate theses "false flairs", like hans punk described it:

i cut out masks with differnt innercircle sizes: from 17-30 mm (see photo) and found out that 21mm inner circle diametre is the perfect compromise between getting rid of the problem and not loosing to much light on the sensor.

here is a little trick: i found out that the old arriflex-lenscap from the bajonett mount (backside of the lens) fits perfectly on the pre 36. i screwed a hole with a diametre of 21 mm in ....here is the result:

 

 

[S.B. Goldberg]

Hello Anamorphic People,

We have the following problem with ghosting and would appreciate any help we can get. The problem is as follows: We are using a 2x Isco Ultra-Star Hd plus (the red one), with a 35mm taking lens on a GH5 (set to 4:3 anamorphic) with the intention of shooting 2.39. In addition, we have a Rectilux Hardcore DNA mounted to the front of the Isco. When there is light source in front of the lens (either a window, or just a light) we are getting the typical white ghosting talked about here. When there is no ghosting happening, the picture is great. The ghosting is for us a show-stopper -- we are not after glare of any kind, we want a clean picture with the anamorphic 2.39 picture ratio, bokeh and depth of field.

Does the method using the marker pen that is described above also work on the Isco Ultra-Star? If not, does anyone have any other suggestion for how to solve this? Any help is greatly appreciated.

Thanks in advance.

sbg