Idea for high magnification lupe for digital view camera

**atorger** · 29-May-2012, 06:21

I have a Linhof Techno digital view camera and made the discovery that 6x or 10x lupes is way too low resolution to maximize ground glass capability and focus precision. The 6x lupe tradition is obviously for 4x5" not for 36x48mm digital backs. Using a 1:1 macro lens on a Canon 5D mark II to look at the ground glass with live view I see more detail and considerably better precision in focusing can be achieved than with my 10x lupe.

For the 36x48mm area the ground glass shows detail corresponding to about a 18 megapixel sensor, and I've calculated that about 30x magnification would be suitable for critical focusing.

Here's a photo with 100% crops http://torger.dyndns.org/temp/dwcf-fs.png showing the groundglass as the 5D sees it at roughly 4000 ppi and the resulting 33 megapixel picture. With the 10x lupe I can barely see that there are numbers on the slanted ruler, but I can definitely not read them.

Has anyone experimented with higher magnification on the ground glass and have tips of what to use? I'm thinking of a high quality 25x pen microscope, not sure if it will work though.

**dh003i** · 29-May-2012, 12:01

I had a pen microscope from Edmund Scientific. It was garbage.

What I have been using for aerial focusing with 4x5 and 8x10 on clear parts of the glass is a 20x Belomo Jewelery's loupe. These aren't very expensive and work well.

The downside is that you need to move them back and forth to find the plane of focus (you don't place them on the GG). The nice thing is that you can look at the edges of the GG sideways for brighter viewing.

**Bob Salomon** · 29-May-2012, 12:41

The problem is the grain of the ground glass. As magnification goes up so does the size of the grain, making it tricky to see the detail. That is why Linhof keeps their gg focusing loupes to less then 6x.
Are you focusing the eyepiece of the loupe on the grain side of the gg before focusing? That can make a big difference in what you can discern.

Even the focusing magnifier that Linhof offers for the M679/Techno backs is just 3x magnification.

**atorger** · 30-May-2012, 01:38

As you can see in the linked photograph (in the original post) of the ground glass it is a bit of a myth that the grain cannot handle large magnifications. Starting to see grain is not the same as stopping to see detail. With 10x those numbers on the ruler cannot be read, while it is clearly readable on the high magnification photo. I've tried it and it works excellently, but it is not exactly practical to use a Canon 5D with a macro lens as a loupe :-)

That Linhof does not provide adequate magnification solutions for their GG is simply a large mistake. Many digital users get Arca-Swiss RM3Di, Cambo Wide, or ALPA (pancake cameras) with helical focus and focus on distance since they can't trust the ground glass, and the #1 criticism of digital view cameras is lack of focus precision. With proper magnification that would be different. It should be said though that in practical situations the 10x precision is often good enough, when you tilt for example there is rarely need of the exact precision as when focusing on a flat object.

Thanks for the jewelery loupe tip, I'll look into that!

**dh003i** · 30-May-2012, 07:55

Originally Posted by atorger

As you can see in the linked photograph (in the original post) of the ground glass it is a bit of a myth that the grain cannot handle large magnifications. Starting to see grain is not the same as stopping to see detail. With 10x those numbers on the ruler cannot be read, while it is clearly readable on the high magnification photo. I've tried it and it works excellently, but it is not exactly practical to use a Canon 5D with a macro lens as a loupe :-)

That Linhof does not provide adequate magnification solutions for their GG is simply a large mistake. Many digital users get Arca-Swiss RM3Di, Cambo Wide, or ALPA (pancake cameras) with helical focus and focus on distance since they can't trust the ground glass, and the #1 criticism of digital view cameras is lack of focus precision. With proper magnification that would be different. It should be said though that in practical situations the 10x precision is often good enough, when you tilt for example there is rarely need of the exact precision as when focusing on a flat object.

Thanks for the jewelery loupe tip, I'll look into that!

Just be warned the jeweler's loupes can be frustrating, because you can't "place them on the ground glass" and calibrate a focus point. Every time you focus, you must make sure your jewler's loupe is focused on the ground glass. They are pretty cheap and readily available in the higher magnifications.

http://www.google.com/search?q=20x+l...tbm=shop&tbo=u

I have the Belomo one.

A solution to the problem of having to move your hand/fingers with the loupe back and forth every time to find the right focus distance is to tape a shim onto the loupe (dimes or nickles may do). 20x is a high enough magnification to focus on the aerial image if you have a ground glass with a clear spot for aerial focusing (make sure you're focused on the grain too, or on the reticle, as when looking at the aerial image, you can focus on any image-plane).

**atorger** · 31-May-2012, 01:59

Thanks for the reply.

I actually use some of my loupes without the skirt to tilt it, so then it becomes much like a jewelry loupe.

I'm also thinking about going crazy and try to adapt something like this: http://www.youtube.com/watch?v=NEbS0-CwRs4 that is a portable USB microscope with LCD screen. I would be interesting to see if it works... then focusing with the camera in awkward positions would be possible too.

The greatest challenge for these microscopes would probably be the weak light from the ground glass, don't know if they are light sensitive enough.