Vignetting with SLR wide angle lens and condenser
 

Alright, i decided to upgrade my static adapter with a new condenser, because i noticed that when i put my 35mm lens on my old 35mm slr camera, i was getting a wider area of view then i was getting with my camcorder because i had to zoom in too far to not get vignetting. well, i thought, "hey, if the image on the viewfinder in the SLR camera is what it should look like, then perhaps they got the right type of condenser in there i need. and it was. i took apart the junker and got out a really nice PCX condenser. It measures 36mm by 24mm. just like those nikon type d sizes. anyways, when its set up in the adapter and with a slr lens on front, and looking into it with just my eye. i can see no vignetting. its really cool, because the 36 by 24 area is perfectly lit, then you see the the image turn dark on the other gg off the edges. so you know the frame is lit.

anyways, how come when i put my 1.7 50mm m42 mount lens on, i wont get any vignetting, but when i put my 28mm 2.8 lens on. i get slight vignetting in the corners. i realize the diamter of the lens is differnt. why is this though. how can it be fixed, and is it normal?

Well, that 28mm is pretty wide, which may be contributing to the vignetting problems. That would be my first guess, especially since it isn't happening on the 50mm.

What kind of camera did you pull the focusing screen out of? I'm curious as those Nikon D screens are dang hard to come by.

Well, i pulled the focus screen out of an old Yashica camera. the focus screen is of no real use because it has a big circle in the middle. but the condenser that it butted against it is really nice. it is a perfect film frame size and in theory, i should be able to combine with a ground glass of my choice.

thanks

Damn! I moved a month ago and threw away my donator SLR. Do alla SLR-cameras have condensers, even those Nikon cameras that you can replace the focusing screen on?

yes, most slrs have a focus screen and condesner combo, if you take it out, you can seperate the 2 easily. sorry for the loss buddy. anyone have any answers to my orginal question. I measured the light hole diamter on the back of my lenses. (sorry, i dont know what to call it.) anyways, the hole on the back of the lens where the mount is is . the 50mm lens measures at a 25mm diameter of glass on the backside. while the 28mm lens measures at a 14mm diameter of glass on the backside. its a pretty big difference in diamter. but i am guessing thats how they're meant to be. the 50mm has a 25mm backside, while the 28 has a 14mm backside. half the focal size of the lens. makes sense. but it creates a bad vignetting. and i love my 28mm lens, i just cant think why it would vignette. it seems i have a pretty bad hotspot also. could this be a factor of not enough diffusion? thanks

The reason is the light rays from 50mm lens to the GG is more straight to the GG compare the 28mm. The condenser does bend the light rays on the 50mm but not powerful enough to bend the light rays of the 28mm. There are 2 solutions here. Move the camera further from the GG or get a stronger condenser, hope this helps.

Quyen

thank you Quyen!

i had bought this condenser a while back,
http://www.surplusshed.com/pages/item/l3385.html

and it kinda works,(the sucker is freakin huge) but i have to zoom in too far even with it, and my 50mm lens ends up looking like a 80 and my 28mm looking like a 50mm anyways. so i get the undesired telephoto. when i took out the condesner from my old slr camera, it was the perfect film stock size and seems to light everything well and keeps the orignial perspective that was shown in my cameras viewfinder. but i am still a little weary about using it with wide lenses. Is there a stronger condenser that you have found which keeps the focal properties correct, and frame size correct, without having to zoom past the required 35mm by 24mm frame? if so, could you tell me what type and where you purchase it from? thank you so much for any help. if parts you use are under secrecy, i totally understand and respect that also.