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Iscorama pre-36: very strange looking flares?


mdominic20
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I rented an Iscorama pre-36 to test out, and I noticed the flares were very strange.  There was a horizontal streak as expected, but the streak was surrounded by a bunch of criss-crossing lines at odd angles.  I found a video that showed the exact same thing i was seeing in my tests (starts at 2:07):  

 

At first I thought maybe it was an issue with the taking lens (I'm using Contax Zeiss lenses), but I tried several different lenses and they all flared with those weird surrounding lines.  I also tested my Kowa B&H with the same taking lenses and same setup, and it looked normal with just horizontal streaks.

Does anyone know what's causing these weird flares?  I'm pretty sure I've seen some flare tests with the Iscorama 36 and pre-36 that dont have this problem, so I'm a little confused what could be causing it.

If anyone has any insight please share!

 

 

 

 

 

 

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It is very common for the pre-36 to have these ‘square rainbow’ flares on the edge of the frame. They are caused by the rear element not having edge blackening, so it will catch the light and cause these flares when used with most ‘non factory’ taking lenses. The Isco taking lens that would have originally come with the iscorama has an internal baffle ring to eliminate this effect, so that there is the most basic solution to eliminate these particular flares...by using the factory taking lens.

The other solution is to use a thin nitrile rubber O-ring that can be installed to the rear of the iscorama to slightly ‘choke’ the light from hitting the rear optic edge that creates the flare. I have found this to be the best solution to use...as it also provides a thin rubber ‘bumper’ to the rear optic as a bit of protection when swapping out taking lenses. The thin rubber ring is simply attached to the optic rear edge with a small strip of electrical tape holding it in place from the outside edge (away from optic).

The rubber ring - when correct size and thickness, will not introduce any noticeable image vignette, as it will only block out the light from hitting the very edge extremities of the rear optic...and therefore eliminating the ‘square rainbow’ or diagonal line flares.

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Thanks Hans!  Very helpful information.  By the way, would this effect also happen with the 36 (single-coated version)?   I imagine it would, but the flares would be slightly further towards the edge of the frame since the rear element is larger?.  

I will give your o-ring solution a shot!

 

 

 

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I’ve not heard of the issue being present with regular 36 iscorama models, I believe the rear optics on those have blackened edges or are sufficiently shielded by the larger retainer assembly at the rear. The strange flare you mention is only a particular quirk of the pre-36 and (probably) the Cinegon versions.

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4 hours ago, HockeyFan12 said:

What is the diameter of the O-ring? 30mm I'm assuming?

I tried lots of different nitrile rings, all at different inner diameters and outer diameters...I still don’t know the exact size I used, since I ended up trying a load from an unmarked mixed bag until one or two worked. I think the quicker solution would be to buy a slightly larger than 30mm x 2mm or 3mm thick ring, measure it around the circumference of the rear optic edge...and then cut to size. Then apply a micro blob of superglue to join the ends of the rubber to make a ring with the exact inner diameter. Or buy a strip of the nitrile material and have lots of attempts to make the perfect sized ring that eliminates ‘square flare’, yet avoids added vignette : https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F120893807581

Hold the rubber ring in place by small strip of electrical tape around outside of rear optic housing, so it won’t shift position. As I mentioned before, it works well as an added ‘bumper’ to help protect the optic edge and face when positioning very close to a taking lens...as well as get rid of the nasty ‘square flare’. This solution works very well but may take 2-3 attempts to work out the ideal sized ring through a bit of trial and error. 

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5 hours ago, Hans Punk said:

I tried lots of different nitrile rings, all at different inner diameters and outer diameters...I still don’t know the exact size I used, since I ended up trying a load from an unmarked mixed bag until one or two worked. I think the quicker solution would be to buy a slightly larger than 30mm x 2mm or 3mm thick ring, measure it around the circumference of the rear optic edge...and then cut to size. Then apply a micro blob of superglue to join the ends of the rubber to make a ring with the exact inner diameter. Or buy a strip of the nitrile material and have lots of attempts to make the perfect sized ring that eliminates ‘square flare’, yet avoids added vignette : https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F120893807581

Hold the rubber ring in place by small strip of electrical tape around outside of rear optic housing, so it won’t shift position. As I mentioned before, it works well as an added ‘bumper’ to help protect the optic edge and face when positioning very close to a taking lens...as well as get rid of the nasty ‘square flare’. This solution works very well but may take 2-3 attempts to work out the ideal sized ring through a bit of trial and error. 

I have terribly shaky hands, but that sounds brilliant. Maybe I'll order a set from Amazon and just pick the best one. I suppose a bit large isn't a problem or does it need to be perfect?

Will this help at all with the corners getting bright when hit by a direct light? Seems like an internal reflection there, too, but I've seen this phenomenon even with Panavison C Series, I believe.

Those lens tests are a bit humbling. I like the Iscorama (it is stunningly sharp) but the others do have more character. 

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