Large Format DOF adapter + PD170 at DVinfo.net

Chris Knight · October 28th, 2006, 10:23 PM

My parents used to be photographers, so we've got a bunch of interesting things for me to mess with in our basement (I'm 17, so I still live with my parents), one of them being an old Large Format 5 X 7 View Camera.

I was messing around with it today trying to convert it for my PD170. It has some amazing DOF, I can tell you that much. Right now I need to get a plain matte ground glass for the thing, and make a trip to home depot to ghetto rig a support system. Right now I just put my camcorder and the view camera on seperate tripods, line them up, and wrap some black cloths around the thing.

I did some test shots in my room, and then a few outside. There seemed to be some hotspot and vignetting, but that may have been a function of the fact that this thing needs a LOT of light. My room isn't all that bright and it was overcast with a setting sun when I was outside.. If that was't it I should probably get a fresnel of some sort, right?

The strange thing about the hotspot is that it doesn't appear when viewing the focusing screeen with your eyes from under a black cloth, the picture looks perfect. But the camcorder vignettes and hotspots. Also, the hotspot / vignette moves around with the camera if I zoom in a little and pan across the focusing screen. This differs from how my first AGUS35 style 35mm adapter worked, where the hotspot and vignetting were a problem with the ground glass.

I also need to devise an effective way to eliminate as much of the light loss as I can...

Hopefully it will be nice and sunny tomorrow, so I can see what this thing is capable of and get some good test shots.

Rolland Elliott · October 28th, 2006, 11:44 PM

most large format lenses do not have an aperture bigger than f/4. Compared to a f/1.4 lens that is 3 stops of light which is basically 1/8th the amount of light most people are using here.

The lens could even be a f/5. 6 lens which means your light leve would be 1/16th of most DIY 35mm adapters.

Given the cheap cost of a 50mm 1.4 lens of $30 or so on www.keh.com you may find it better use of your time to get something a bit more compact to play around with.

Peace, Rolland

Chris Knight · October 29th, 2006, 04:44 PM

Yeah, you're right. My lens is a f 5.6, which explains the heavy vignetting.

What I don't get is why the image is projected perfectly on the focusing screen, but when viewed on the camera there is heavy vignetting. Can someone explain this to me?

Chris Barcellos · November 6th, 2006, 12:33 PM

Quote:

Originally Posted by Chris Knight

What I don't get is why the image is projected perfectly on the focusing screen, but when viewed on the camera there is heavy vignetting. Can someone explain this to me?

I've just been working with this in the last month, trying to put together my own DIY adapter. I ve tried static, and I am currently working on the Redrock Micro DIY Project that I bought last year.

I notice the same thing. My conclusion is that when we are looking at the image projected by lens on the ground glass, the lens is directly behind it, and creates a secondary light source. If you have a projector, you can hang a sheet in the middle of the room, and project an image on the sheet. You can go to the other side, and see the image on the sheet. But if the sheet is thin enough, and you stand directly in line with the projector and the image, you will also see the light from the projector.

That is why you seem to have to zoom in more than the size of a 35mm frame to avoid vignetting, I think....

October 28th, 2006, 10:23 PM	#1
Chris Knight Regular Crew Join Date: Sep 2006 Location: Hyde Park, New York Posts: 53	Large Format DOF adapter + PD170 My parents used to be photographers, so we've got a bunch of interesting things for me to mess with in our basement (I'm 17, so I still live with my parents), one of them being an old Large Format 5 X 7 View Camera. I was messing around with it today trying to convert it for my PD170. It has some amazing DOF, I can tell you that much. Right now I need to get a plain matte ground glass for the thing, and make a trip to home depot to ghetto rig a support system. Right now I just put my camcorder and the view camera on seperate tripods, line them up, and wrap some black cloths around the thing. I did some test shots in my room, and then a few outside. There seemed to be some hotspot and vignetting, but that may have been a function of the fact that this thing needs a LOT of light. My room isn't all that bright and it was overcast with a setting sun when I was outside.. If that was't it I should probably get a fresnel of some sort, right? The strange thing about the hotspot is that it doesn't appear when viewing the focusing screeen with your eyes from under a black cloth, the picture looks perfect. But the camcorder vignettes and hotspots. Also, the hotspot / vignette moves around with the camera if I zoom in a little and pan across the focusing screen. This differs from how my first AGUS35 style 35mm adapter worked, where the hotspot and vignetting were a problem with the ground glass. I also need to devise an effective way to eliminate as much of the light loss as I can... Hopefully it will be nice and sunny tomorrow, so I can see what this thing is capable of and get some good test shots.

October 28th, 2006, 11:44 PM	#2
Rolland Elliott Regular Crew Join Date: May 2003 Location: Charlotte, NC 28273 Posts: 108	most large format lenses do not have an aperture bigger than f/4. Compared to a f/1.4 lens that is 3 stops of light which is basically 1/8th the amount of light most people are using here. The lens could even be a f/5. 6 lens which means your light leve would be 1/16th of most DIY 35mm adapters. Given the cheap cost of a 50mm 1.4 lens of $30 or so on www.keh.com you may find it better use of your time to get something a bit more compact to play around with. Peace, Rolland __________________ Rolland Elliott

October 29th, 2006, 04:44 PM	#3
Chris Knight Regular Crew Join Date: Sep 2006 Location: Hyde Park, New York Posts: 53	Yeah, you're right. My lens is a f 5.6, which explains the heavy vignetting. What I don't get is why the image is projected perfectly on the focusing screen, but when viewed on the camera there is heavy vignetting. Can someone explain this to me?