Viewfinder for homemade 6x12

[Fragomeni]

I'm getting ready to build a 6x12 camera and will use a 65mm Super Angulon as the lens. I'd like a viewfinder but would prefer not to pay the high price of a 612 finder like the Horseman or Linhof versions. I'm looking at two options that I'd appreciate some clarity on if anyone can help.

1. Masking an existing 65mm viewfinder
- My question here is, can I take an existing 65mm viewfinder, say for 6x9, and mask it to 6x12? Will this work or since it would already be framed for 6x9? Obviously I can't stretch the long side so this would involve a mask that reduces the short side to achieve the correct aspect ratio. Would this give an accurate representation of the image being captured?

2. Making a viewfinder using a peephole (for doors)
- What I've read is that you can take a door peephole and place a mask with the correct aspect ratio in front of it at a distance equal to the focal length. So in this case it would be a 2:1 mask placed 65mm in front of the peephole. Is this accurate and have people here found that this works?

Thanks for your help.

 

[Donald Qualls]

1. Masking an existing 65mm viewfinder
- My question here is, can I take an existing 65mm viewfinder, say for 6x9, and mask it to 6x12? Will this work or since it would already be framed for 6x9? Obviously I can't stretch the long side so this would involve a mask that reduces the short side to achieve the correct aspect ratio. Would this give an accurate representation of the image being captured?

Closer. If you get a viewfinder intended for a 65mm lens on 4x5 you can mask it top and bottom and use it on a 6x12 camera. As you note, one made for 65mm on 6x9 would be the right height, but wouldn't be wide enough horizontally. A door peephole lens wouldn't help you much; the ones I've used had an image so small it'd be like looking at a Minox film frame with your naked eye.

You'd be much better to simply make a no-optics frame finder. The simplest of these are a peephole in the plane of the film, and a frame the size of the film image frame in the plane of the lens. These are common on press cameras, and they work well because they automatically compensate for focus and for changes of lens (because the front frame moves further or closer, automatically framing the exactly field of view).

 

[Fragomeni]

Thanks for this info. Its very helpful. I just ended up finding a Fotoman finder for 65mm with a 6x12 mask so wont need to make one but this is still good info to have for my next project. Thanks again.

 

[europayer]

Hi Fragomeni and Donald Qualls,

I just found this thread and have a similar problem with a customised 35mm camera.
The camera has an altered film gate for 2:1 panoramic pictures. The lens is a 50mm.

All the panoramic viewfinders I found were for medium format so I wonder which focal length the 50mm would translate to.
The viewfinders I found were:
https://www.ebay.de/itm/Viewfinder-...ra-45mm-50mm-55mm-60mm-65mm-lens/173308787046
https://www.ebay.de/itm/Slip-in-28m...rmat-Lens-Rangefinder-Viewfinder/233274342394
and the mentioned Fotoman finder from the OP (but then I would need to know which mask to get).

Thanks in advance
Oli

 

[Donald Qualls]

Once again, the easy way is a no-optics frame finder -- a peephole at/above the film plane, and a 24x48 frame 50mm head of it. A 3D printer would make really short work of this kind of thing, BTW, but ten years ago I'd have gotten a short piece of PVC, a couple inches I.D., and cut the peephole and mask from caps, then fabricate a shoe foot some way to mount it.

You could buy a 28mm finder made to fit a Leica or Contax RF camera, and mask top and bottom to the correct aspect ratio, but that's likely to cost more than your camera project...

 

[ProfessorC1983]

I've found this to be a useful resource for optical viewfinder construction: Galilean Viewfinder Design — Panomicron

I'm currently working on a software tool that pulls the current stock of PCV and PCX lenses from Edmunds and Surplus Shed and uses the math on the above page to find appropriate viewfinder lens combinations for a given angle of view, then generates a 3D printable housing at the correct focal distance and masked for the specified frame shape. Will share on the forum here once I've verified it actually works in practice.

 

[Donald Qualls]

I'm currently working on a software tool that pulls the current stock of PCV and PCX lenses from Edmunds and Surplus Shed and uses the math on the above page to find appropriate viewfinder lens combinations for a given angle of view, then generates a 3D printable housing at the correct focal distance and masked for the specified frame shape.

Nice!!

 

[Fragomeni]

Returning here with a related question. I sorted out my original use case but have now found myself right back around to where I started in a way. Im working on a 612 again and I ended up with a Horseman Universal Finder with the 6x9 mask that I was going to use for a 6x9 project. I like the finder and decided it would be nice to use on 612 which put me right back to where all this started. Since it has a 6x9 mask, I can’t simply mask it off top and bottom like I could with a 4x5 mask, which was the solution last time per Donald’s wisdom (thank you Donald). Now, the Horseman Universal Finder mask is reflective and allows you to see beyond the frame (the masked off area is darker but translucent when viewed through the finder). If this were a 4x5 mask, I’d expect to be able to mask it top and bottom to get to 612 again but what I’m finding is that the 6x9 frame is working very well but I’m confused about the focal length settings on the finder (it’s working well because the right and left boundaries of the finder beyond the 6x9 frame match 612 pretty perfectly so it’s actually very easy to frame for 612 using the 6x9 frame and looking just beyond the right and left edges of the frame to see the extra that 612 would see in both sides). The Horseman Universal Finder is multi-format, having focal length settings for 6x9 and 4x5. When I put the ground glass on the camera to compare ground glass and viewfinder images, the view on the ground glass matches the view in the finder with the focal length set for 4x5, not 6x9. When setting the same focal length for 6x9, the magnification doesn’t match what the lens is seeing on the ground glass. I’m perplexed. That’s probably a little unclear so let me offer this example to clarify:

With a 135mm lens on the camera, the image framed on the ground glass matches what I’m seeing in the viewfinder with the focal length selector (magnification) set on 135mm for 4x5. However, when I set it to 135 for 6x9, the finder magnification is greater (more zoomed in) than what is seen on the ground glass. I think I’m overthinking this and confusing myself. Why am I seeing different magnifications in the finder when viewing the same relative focal length for the formats?

 

[reddesert]

A 135mm lens on 4x5 has a much wider field of view than a 135mm on 6x9. When you set the finder to 135mm for 6x9, the field of view should match what you see in the central 6x9cm (really 56x84mm) of the ground glass. I think you've managed to confuse yourself. The finder is labeled for the actual focal length of the lens, just use that.

 

[Fragomeni]

Yea, this is where my being lazy just creates problems. It was brilliant to think I could accurately compare ground glass and viewfinder images…handheld. I just put it on a tripod and the focal length for 6x9 matches. Thank you for being my voice of reason here.

 

[wiltw]

Hi Fragomeni and Donald Qualls,

I just found this thread and have a similar problem with a customised 35mm camera.
The camera has an altered film gate for 2:1 panoramic pictures. The lens is a 50mm.

All the panoramic viewfinders I found were for medium format so I wonder which focal length the 50mm would translate to.
The viewfinders I found were:
https://www.ebay.de/itm/Viewfinder-...ra-45mm-50mm-55mm-60mm-65mm-lens/173308787046
https://www.ebay.de/itm/Slip-in-28m...rmat-Lens-Rangefinder-Viewfinder/233274342394
and the mentioned Fotoman finder from the OP (but then I would need to know which mask to get).

Thanks in advance
Oli

Use format vertical dimention to ratio lens FL, to calculate equivalence (same FOV)

1. 50mm FL = 24mm frame height * 2.08 (135 format)
2. 116mm FL = 56mm frame height * 2.08 (medium format)
3. 35mm FL = 24mm frame height * 1.46 (135 format)
4. 82mm FL = 56mm frame height* 1.46 (medium format)

This (#3 vs. #4) demonstrates how the 135 'normal' is actually OVERLONG for the format, compared to medium format frame, and why many famous film photojournalists prefered to shoot with 35mm FL on their 135 format rangefinder bodies.

 

[monopix]

I have a spreadsheet that calculates angle of view for different lenses on different formats. It might help. You can download it from here:

https://drive.google.com/file/d/0B4...bm8/view?resourcekey=0-Z021jIrbXldKvqoq9vSq6w

Horizontal angle of view of 65mm lens on 6x12 = 85 degrees. 35mm equivalent = 20mm. So a 20mm (or 21mm) finder made for 35mm film would work masked top and bottom.