PDA

View Full Version : Meniscus coverage taken out of barrel



renes
26-Sep-2011, 10:52
Just short qustion: does the coverage of meniscus lens increases when it is used taken out of the barrel? I have heard something like that today. Normaly the coverage reduces when the aperture is opening and increases when it's closing.

Stephane
26-Sep-2011, 11:55
Yes, the coverage increases when out of the barrel. This is because the barrel causes some vignetting.

renes
26-Sep-2011, 13:24
Thanks Stephane.
Have you noticed is it significant coverage increase or minor?

Stephane
26-Sep-2011, 13:48
Significant. I felt there was no coverage limit ;)

I can check later how much (in day light). I'll try from the shortest FL I have (140mm?) on 8x10 focused at infinity and tell you tomorrow evening.

You can also try on your side with whatever you have, so we can compare the results...

Mark Sawyer
26-Sep-2011, 18:59
Keep in mind that as you progress outwards farther from the center, the image will degrade significantly. Illumination does not mean useful coverage. But the loss of image quality may be acceptable, even desireable, for those who know how to use such things.

Jim Fitzgerald
26-Sep-2011, 19:06
So, I'm going to ask the dumb question that I hope someone else out there is curious about. What exactly do you mean when you say " taken out of the barrel" Does this mean you have one piece of glass and you glue it to a lens board. I know I'm not the brightest guy around but this is confusing to me.

Stephane
26-Sep-2011, 23:16
Some of us have iris clamps, so you just unscrew the rear element and fix it on the iris clamp. No glue. No tape.

Jim Fitzgerald
27-Sep-2011, 06:50
Some of us have iris clamps, so you just unscrew the rear element and fix it on the iris clamp. No glue. No tape.

Okay, thank you! Now it makes sense. With all of this out of the barrel, uncorked, etc,etc all it is is just like when Mark took the .99 cent magnifying glass and glued it to the lens board. Now I've got it.

Stephane
27-Sep-2011, 10:31
the 150mm covers 8x10, or at least illuminates the gg.

renes
27-Sep-2011, 11:31
the 150mm covers 8x10, or at least illuminates the gg.

Thanks. That's significant :)

I am fitting two Lancaster meniscus (WA 4" and 6") to the shutters and will check how much the coverage will differ comparing to the barrel mounting.

Emil Schildt
27-Sep-2011, 14:10
fun to try and use...

I wonder how much my 600mm will cover..... ;-)

cdholden
27-Sep-2011, 18:05
I picked up a Lancaster meniscus as a project that I've still not done anything with. When I unscrewed the lens element from the body, I found it will fit into the back of one of my pre-drilled boards... maybe some silicone or RTV to hold it in place and I'll be set. And yes, the iris clamp would work too.