35mm Adapter Condenser | Shedding some light
- Thread starter Dingles
- Start date
not sure how or why that would help...
I believe Vignetting is caused by uneven light dispersion from the (SLR 35mm) lens when it hits the ground glass. The problem has to be corrected before the image hits the gg, so the PCX lens would have to be in between the SLR 35mm lens and the ground glass to prevent/correct the vignetting.
Once it appears unevenly on the GG, I don't think you can then optically correct it properly between the GG and the videocam. You can only then eliminate it by zooming in more on the GG so the vignetting won't be videotaped by the videocam.
I'm not even sure why there is a vignetting problem, unless it is in the nature of the GG to display the image incorrectly. If the SLR lens is the proper distance from the GG, then the image (at least 24mm x 36mm of it which is the size of the film which would be normally exposed in place of the GG) should have no vignetting at all in that area. After all, the print pictures from your 35mm camera don't exhibit vignetting. Again, perhaps the nature of the GG itself causes improper light dispersion that results in vignetting, where filmstock doesn't.
I believe Vignetting is caused by uneven light dispersion from the (SLR 35mm) lens when it hits the ground glass. The problem has to be corrected before the image hits the gg, so the PCX lens would have to be in between the SLR 35mm lens and the ground glass to prevent/correct the vignetting.
Once it appears unevenly on the GG, I don't think you can then optically correct it properly between the GG and the videocam. You can only then eliminate it by zooming in more on the GG so the vignetting won't be videotaped by the videocam.
I'm not even sure why there is a vignetting problem, unless it is in the nature of the GG to display the image incorrectly. If the SLR lens is the proper distance from the GG, then the image (at least 24mm x 36mm of it which is the size of the film which would be normally exposed in place of the GG) should have no vignetting at all in that area. After all, the print pictures from your 35mm camera don't exhibit vignetting. Again, perhaps the nature of the GG itself causes improper light dispersion that results in vignetting, where filmstock doesn't.
I'm not sure why that helps either ( it seems to increase the magnification), but here is a thread that go over the setup with footage. I also think the quility and grain and diffusion of the GG has a lot to do with vignetting. Film is essentially smooth and light sensitive and my guess is it acepts the full range of light coming in...
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I've done some tests with a PCX lens with a focal length of 100mm. Putting in front of the GG seems to change the distance needed between the GG and the lens...Placing it in front of the achromat further magnifies the image...that is why the guy on the forum was seeing reduced vignetting and hotspotting...it was due to the extra magnification. I am going to do some further testing with the lens in front of the GG. I want to see if the GG will have to be positioned closer or further fron the 35mm lens.
twocik23
Veteran
"I'm not even sure why there is a vignetting problem, unless it is in the nature of the GG to display the image incorrectly. If the SLR lens is the proper distance from the GG, then the image (at least 24mm x 36mm of it which is the size of the film which would be normally exposed in place of the GG) should have no vignetting at all in that area. After all, the print pictures from your 35mm camera don't exhibit vignetting. Again, perhaps the nature of the GG itself causes improper light dispersion that results in vignetting, where filmstock doesn't."
There's two parts to this problem, the back-end and front-end (flange distance, and magnification distance).
Think of two halves,
- Distance from Lens to GG (flange distance)
- Distance from GG to Camera (magnification distance)
One of the most common problems is that the flange distance isn't set properly, which this can be hard if your system isn't machined. The other half can be from many others things not being set properly. To answer your question, it could be from the GG to camera. If the achromat/macro isn't strong enough, you'll will also introduce vignetting from that. To compensate this you'll need to add more space or find something a little stronger.
Another can be caused from the GG housing or as simple as a Step down ring.
Hope that helps.
There's two parts to this problem, the back-end and front-end (flange distance, and magnification distance).
Think of two halves,
- Distance from Lens to GG (flange distance)
- Distance from GG to Camera (magnification distance)
One of the most common problems is that the flange distance isn't set properly, which this can be hard if your system isn't machined. The other half can be from many others things not being set properly. To answer your question, it could be from the GG to camera. If the achromat/macro isn't strong enough, you'll will also introduce vignetting from that. To compensate this you'll need to add more space or find something a little stronger.
Another can be caused from the GG housing or as simple as a Step down ring.
Hope that helps.
PappasArts
Veteran
I believe the PCX lens is more about getting rid of the hotspoting isn't?
Ted Ramasola
Veteran
A slight confusing element here, i think the diagram is wrongly illustrated, the light arrows coming out of the 35mm lens should point inward not outward. in fact it converges to a point then flips upside down before hitting a focal plane. The light concentration is at center then falloffs to the sides, thus the so called vignette.
I agree with twock , that if the elements are correctly positioned;ie; lens flange to GG+ gg to cam lens, there wont be a need for pcx.
I agree with twock , that if the elements are correctly positioned;ie; lens flange to GG+ gg to cam lens, there wont be a need for pcx.
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Posted a new article on PCX lenses as Condensers in a 35mm Adapter
http://35mmadapter.blogspot.com/2008/09/condensers-revisited-some-new-light-on.html
http://35mmadapter.blogspot.com/2008/09/condensers-revisited-some-new-light-on.html
Tim Joy
Veteran
I used a PCX lens that I took out of an old SLR lens, (a 135mm if I remember correctly) and put it in between the microX flip and the GG. Worked like a charm to get rid of hotspotting, and without zooming into a smaller area. (I had it right up close to the GG)
I tried it both with the convex side facing the GG and the flat side facing the GG but didn't really notice a difference. Is there a correct way?
It seems to me, that all the adapters that have a condeser lens, do not have issues with hotspotting, but ones that go straight from the GG to the macro (redrock) do. Some people call it vignetting, but I think it must be hotspotting, because it happens even when zoomed in past 35mm SLR frame size. If you look at the projected image on the GG with your eye, it's even with no hotspot.
Also, when I tried a less-diffuse GG, the hotspotting is MUCH worse without a condeser lens. So, using a condenser lens allows you to use a less-diffuse GG, decreasing the light loss. Yes?
It is my feeling that the problem lies AFTER the GG, so putting a PCX lens between the 35mm lens and the GG is the wrong approach.
I tried it both with the convex side facing the GG and the flat side facing the GG but didn't really notice a difference. Is there a correct way?
It seems to me, that all the adapters that have a condeser lens, do not have issues with hotspotting, but ones that go straight from the GG to the macro (redrock) do. Some people call it vignetting, but I think it must be hotspotting, because it happens even when zoomed in past 35mm SLR frame size. If you look at the projected image on the GG with your eye, it's even with no hotspot.
Also, when I tried a less-diffuse GG, the hotspotting is MUCH worse without a condeser lens. So, using a condenser lens allows you to use a less-diffuse GG, decreasing the light loss. Yes?
It is my feeling that the problem lies AFTER the GG, so putting a PCX lens between the 35mm lens and the GG is the wrong approach.