Flip without prism?

Michael Maier · January 29th, 2006, 05:59 AM

Quote:

Originally Posted by Wayne Kinney

Actually, there is potentially less distortion from the flip version. Most if not all barrell distortion from the letus or SG35 for that matter comes from the PCX lens inside. On the flip version, you are increasing the length of the light path and as a result, you dont need such a strong PCX, a PCX with a longer focal length can be used to give the same level if corrrection to vignetting. This gives you almost unnoticable distortion and much less chromatic abberation.

Your correct about the extra light loss, but im sure that is an exceptable sacrifice for better image quality.

But then again, with a flip version using 4 mirrors, there are more things that can potentially go wrong, dust being 1 of them.

Does the Letus use 4 mirrors?
Considering what you are saying about the PCX and distances, a shorter adapter like the MPIC should have a lot of distortion, but it doesn't. So I’m not sure I understand it.

Wayne Kinney · January 29th, 2006, 06:38 AM

Yes the letus flip uses 4 mirrors.

Regarding Dan's adapter, he is probably using something different to a PCX lens, hense his high price.

Michael Maier · January 29th, 2006, 07:55 AM

So I would think an adapter without a PCX would be the best. Ben Winter mentioned something about not using a PCX in his Letus with an interscreen didn't he?

Wayne Kinney · January 29th, 2006, 08:10 AM

Yes, the beattie uses a fresnel lens, apparently.

Michael Maier · January 29th, 2006, 09:25 AM

So the beattie seems to be the bet set up. I wonder why adapters are not using it. If it needs no PCX and probably no achromat (didn’t Ben say he could use it without one as well?) it seems the way to go to me.

Wayne Kinney · January 29th, 2006, 09:38 AM

Only experiementation can tell.

Lots of opinions about the use of fresnel's. Some say they loose resolution and the 'rings' appear in the image, especially with HD footage. I know Steev used a beattie in his adapter, weather the fresnel was attached or not I have no idea.

Dennis Wood · January 29th, 2006, 09:59 AM

Dan is able to use the MPIC on a GS200 without an achromat...but it has a min focus distance of 1.6 inches...so a 24x36mm will fill a 4:3 frame from this cam at that distance.

I believe Ben is using the achromat to address slight vignette on his GL2 with his Beattie mod'd Letus.

Here's my 2c on the adapters based an a whack of reading...and a lot of experimentation (although none personally with a Beattie)

The only downside I can see of a vibrating Beattie is that you have 0 control over the diffusion surface, squirmy grain (Letus has it too), and have a need to tightly control motion. A medium format lense system with a larger Beattie, vibrating, would be the bomb IMO. The spinning GG systems have .5 to 1 f/stop greater light loss, are larger, but will accomodate higher shutter speeds (depending on GG), and will allow "tunable" bokeh.

Pick yer poison.

Alain Bellon · January 29th, 2006, 11:48 AM

A fresnel lens just acts as a PCX lens. The Beattie has a fresnel with a focal length around 120-150mm (depending on the screen).

So the Beattie is using a PCX, but in the form of a fresnel (I would assume this is to increase the light transmission since fresnel lenses are very thin).

Regular focusing screens use normal PCX lenses and show no distortion.

Wayne Kinney · January 29th, 2006, 12:05 PM

Alain,
Any experience with fresnel type lenses? I was just wondering how it effects resolution. I may try it out for fun.

Michael Maier · January 29th, 2006, 12:08 PM

Quote:

Originally Posted by Wayne Kinney

Alain,
Any experience with fresnel type lenses? I was just wondering how it effects resolution. I may try it out for fun.

I heard the MPIC uses a fresnel screen and it looks nice in the resolution department. Dan even has some rez chart shots.

Alain Bellon · January 29th, 2006, 01:03 PM

The only experience with fresnel lenses I have comes from larger projection setups where the fresnel is just used to condense light from a bulb, so I do not know how it would affect an actual image.

Theoretically, there should be no loss in resolution provided that the fresnel has very thin grooves. But fresnel lenses can have much more distortion than a regular lens.

I really think an aspherical lens should be the best solution with regards to coma and spherical aberration (or perhaps an achromatic condenser?), but I am waiting on some lenses. (plus this isn't the topic of this thread :) )

Daniel Apollon · January 29th, 2006, 01:06 PM

Classical fresnel lenses, as described by Alain have a regular pattern. It is possible to imagine fresnel structures with local random orientation, thus bringing them closer to ground glasses.

January 29th, 2006, 06:38 AM	#17
Wayne Kinney Major Player Join Date: Jun 2005 Location: Brighton, East Sussex, UK Posts: 938	Yes the letus flip uses 4 mirrors. Regarding Dan's adapter, he is probably using something different to a PCX lens, hense his high price. __________________ Thanks, Wayne.

January 29th, 2006, 08:10 AM	#19
Wayne Kinney Major Player Join Date: Jun 2005 Location: Brighton, East Sussex, UK Posts: 938	Yes, the beattie uses a fresnel lens, apparently. __________________ Thanks, Wayne.

January 29th, 2006, 09:38 AM	#21
Wayne Kinney Major Player Join Date: Jun 2005 Location: Brighton, East Sussex, UK Posts: 938	Only experiementation can tell. Lots of opinions about the use of fresnel's. Some say they loose resolution and the 'rings' appear in the image, especially with HD footage. I know Steev used a beattie in his adapter, weather the fresnel was attached or not I have no idea. __________________ Thanks, Wayne.

January 29th, 2006, 12:05 PM	#24
Wayne Kinney Major Player Join Date: Jun 2005 Location: Brighton, East Sussex, UK Posts: 938	Alain, Any experience with fresnel type lenses? I was just wondering how it effects resolution. I may try it out for fun. __________________ Thanks, Wayne.

January 29th, 2006, 01:06 PM	#27
Daniel Apollon Regular Crew Join Date: Oct 2005 Location: Norway & France Posts: 50	Fresnel lenses Classical fresnel lenses, as described by Alain have a regular pattern. It is possible to imagine fresnel structures with local random orientation, thus bringing them closer to ground glasses.

January 29th, 2006, 07:55 AM	#18
Michael Maier Trustee Join Date: Apr 2005 Posts: 1,269	So I would think an adapter without a PCX would be the best. Ben Winter mentioned something about not using a PCX in his Letus with an interscreen didn't he?

January 29th, 2006, 09:25 AM	#20
Michael Maier Trustee Join Date: Apr 2005 Posts: 1,269	So the beattie seems to be the bet set up. I wonder why adapters are not using it. If it needs no PCX and probably no achromat (didn’t Ben say he could use it without one as well?) it seems the way to go to me.

January 29th, 2006, 09:59 AM	#22
Dennis Wood Major Player Join Date: Mar 2005 Location: Ontario, Canada Posts: 916	Dan is able to use the MPIC on a GS200 without an achromat...but it has a min focus distance of 1.6 inches...so a 24x36mm will fill a 4:3 frame from this cam at that distance. I believe Ben is using the achromat to address slight vignette on his GL2 with his Beattie mod'd Letus. Here's my 2c on the adapters based an a whack of reading...and a lot of experimentation (although none personally with a Beattie) The only downside I can see of a vibrating Beattie is that you have 0 control over the diffusion surface, squirmy grain (Letus has it too), and have a need to tightly control motion. A medium format lense system with a larger Beattie, vibrating, would be the bomb IMO. The spinning GG systems have .5 to 1 f/stop greater light loss, are larger, but will accomodate higher shutter speeds (depending on GG), and will allow "tunable" bokeh. Pick yer poison.

January 29th, 2006, 11:48 AM	#23
Alain Bellon Regular Crew Join Date: Jan 2005 Location: LA Posts: 130	A fresnel lens just acts as a PCX lens. The Beattie has a fresnel with a focal length around 120-150mm (depending on the screen). So the Beattie is using a PCX, but in the form of a fresnel (I would assume this is to increase the light transmission since fresnel lenses are very thin). Regular focusing screens use normal PCX lenses and show no distortion.

January 29th, 2006, 01:03 PM	#26
Alain Bellon Regular Crew Join Date: Jan 2005 Location: LA Posts: 130	The only experience with fresnel lenses I have comes from larger projection setups where the fresnel is just used to condense light from a bulb, so I do not know how it would affect an actual image. Theoretically, there should be no loss in resolution provided that the fresnel has very thin grooves. But fresnel lenses can have much more distortion than a regular lens. I really think an aspherical lens should be the best solution with regards to coma and spherical aberration (or perhaps an achromatic condenser?), but I am waiting on some lenses. (plus this isn't the topic of this thread :) )