plano convex dilemma

Dizkoteck

Dizkoteck

Well-known member
Hey guys,

Im on my way to make my third and hopefully last design 35 adapter. However, Im having a little dilemma with PCX lenses and its positioning inside the adapter. Okay, heres the deal

I read somewhere here a long time ago that the PCX lens should be between SLR lens and GG, but right next to GG.

Now Im reading that it should be between DVX and GG. Someone also mentioned sandwiching two together.

Can you guys point out which one is the better or correct option and why?
 
I have tried about every way, but have had the best results with the plano (flat) side as close to the GG as possible (or against) and the convex side facing the 35mm lens.
 
snodart said:
I have tried about every way, but have had the best results with the plano (flat) side as close to the GG as possible (or against) and the convex side facing the 35mm lens.
Click to expand...

This setup will change the properties of the 35mm lens, and depending on the FL of the PCX will actually widen the DOF produced by the 35mm lens. It also results in a smaller then 36x24mm projection onto the GG.

Please experiement, Dizkoteck, but I think generally the best setup is flat side against GG, between GG and camcorder.
 
Wayne Kinney said:
This setup will change the properties of the 35mm lens, and depending on the FL of the PCX will actually widen the DOF produced by the 35mm lens. It also results in a smaller then 36x24mm projection onto the GG.
Click to expand...

Wayne, I'm not sure that the properties would be changed since the GG captures the light rays before they reach the focal point of the plano-convex lens. I can see how there would be problems if the GG was to be outside of the focal point of the lens. This of course would flip the image though and force the GG to be pretty far from the plano-convex lens.

plano-convex_lens.jpg


Technically, when using the plano-convex to collimate light then it should be as you have described, with the convex side toward the DV cam and the plano side toward/at the GG. With my set up though, this caused a hot spot from the 35mm (50mm FL) aperture at f/11 and up.

Can you tell us the FL of the plano-convex in your design?

The image on the GG does become smaller when placing the convex side toward the 35mm lens and the plano side toward the GG, but depending on the FL of the plano-convex and its distance from the GG, the change in size is normally minute.

Wayne, I'm going to flip my plano-convex again and compare once more to make sure that I'm not crazy. I will post the comparison if you like Dizkoteck.

Dizkoteck, here are some links that are both helpful and confusing.

link 1
link 2

EDIT: fixed dead link
 
Here is an example of the hot spot (it is not the sun) that occurred with the convex side facing the DV cam and the plano side at the GG.

hotspot.jpg
 
Thanks for the grab. Hotspot in this case is a combination of condenser lens strength, GG diffission and distance from GG to camcorder. Its finding the right combination but looking at your grab, I would say your GG is not diffussing enough.
 
Wayne Kinney said:
Thanks for the grab. Hotspot in this case is a combination of condenser lens strength, GG diffission and distance from GG to camcorder. Its finding the right combination but looking at your grab, I would say your GG is not diffussing enough.
Click to expand...

Thanks Wayne. In the case of the grab above, turning the convex side toward the 35mm lens helped a little (I am going to retest this again though with your advice). I also increased the distance a touch, which made a huge difference. I also agree that the GG might not be diffusing enough. I am going to test some GG's today that aren't so fine.

The 35mm lens (FL 50mm) in the grab was at f/22 by the way.
 
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