One specific lens causes redness!

[wgerven]

Hello everybody!
I am new to the forum and hope that I will be able to contribute my equal part in the future! However, right now I need your help with something strange.
A week ago I decided to pick up my old camera again, a Ricoh KR-5 Super. I like the manual labour it involves very much! Anyway, I also have some lenses for it, however one of them is causing me trouble, which I don't know how to interpret..
The lens is a Rokinon 28mm 1:2.8 MC lens. I found out that the aperture blades are stuck, and thus I wanted to clean them this weekend. Nevertheless, I took some pictures with it, adjusting my shutter speed just to largest aperture setting. However, when comparing to the results of my other lenses, this single lens really causes quite a "reddish" tint to the pictures that were taken with it! It is quite subtle though, but the white of the clouds is definitely different between lensen. One might say the pictures look a bit sepia, or have "funky" colors...!

Is there somebody who can point out to me what could be the source of this problem? The lens is actually in very good (external) condition, and I would say just by looking at/through the lens I couldn't tell any obvious source. Can it be related to the fact that the apperture is currently not working? Must something be mis-aligned? It's very weird (to me).
I would really appreciate any help!
Best regards,
Willem.

 

[BrianV]

Can you post an image of the lens, looking through the elements.

 

[wgerven]

Hi Brian, thank you for your reply! Unfortunately I have not the possession now over a digital camera, so I can only satisfy you at this point with images taken with my webcam:

I am sorry for the low quality, but I hope it might tell you something. Today I want to go and clean the aperture blades. (Can't that have something to do with it? That the exposure of the film is weird and that this machine in the lab does some kind of "auto-correcting"?) I somewhere have the feeling that the redness of the pictures is related to the poor exposure the camera now does, as the aperture is stuck. But I cannot substantiate this, that is why I post here, as maybe someone has experience with this..
To be more specific: The right picture is a good working 50mm, the left picture is the 28mm acting strange. Both picture were taken with more or less the same ambient light, shortly after each other.

Thanks for your help, thoughts or suggestions!
Cheers,
Willem.