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Thread: Noob Loupe Questions - Focusing v Slide, Magnification

  1. #1

    Noob Loupe Questions - Focusing v Slide, Magnification

    I apologize if this has been covered, but I did not find it with a search. I have recently purchased, and am eagerly awaiting, a new Intrepid 4x5 gen 3 camera. I am amassing the accoutrements necessary to use the camera when it arrives. I have 5.5 film holders (11 shots as 1 slide is cracked) and a Nikkor-W 150/5.6 lens on the way. Now I am looking at loupes.

    I have a 8x loupe that I have used for years to view slides on a light table. I have read some things that indicate this may not be the right tool for focusing a view camera. I donít want to get tools I donít need, but I also donít want to shoot several frames to figure out that I donít have the right tool.

    I have seen sone loupes that allow you to focus the loupe. That seems weird as it appears that you are focusing two things against each other, but, if that is the right tool, once explained, it should make sense.

    I appreciate your input on this issue & in helping a LF noob out.

  2. #2
    Jim Jones's Avatar
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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    A focusing loupe is convenient because it can always be focused exactly on the ground glass image. However, using a loupe that must manually be focused on the GG while one is focusing the camera becomes instinctive. Inexpensive loupes may not have the optical performance of better ones, but they have long sufficed for me. If they clearly resolve the grain of the GG, they are good enough.

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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    With a GG focusing loupe you remove the lens of the camera, you point the camera to a well illuminated area and then you focus the loupe until the grains in the Ground Glass are perfectly sharp.

    With this procedure the loupe is adapted to your sight. This is the Pro way.

    With a regular loupe without focusing feature you can do the same, making a diy spacer that separates the loupe from the ground glass in the same way for the optimum distance. This is what I do.

    Or, less convenient, you can tilt a bit the loupe every time you focus until you see the grain sharp and at the same time you try to see if the image is in focus. It can be done in this way and you would also get perfect focus, but it requires playing care, it takes more time and, I reiterate, it's way less convenient. This is how I started.

  4. #4

    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    Thanks for the responses. I will see how the loupe I have works. If I need to shim it, I will give felt pads a try as they won’t scratch the glass.

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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    Quote Originally Posted by Shutterbug57 View Post
    Thanks for the responses. I will see how the loupe I have works. If I need to shim it, I will give felt pads a try as they wonít scratch the glass.
    A shim is nonsense, especially on the Agfa type loupe which is not a shining example of optical quality. Especially the Chinese made on. The Spanish ones were a little better.

    First, a clear sided Loupe is for prints, nor slides or focusing. Those type loupes require opaque sides.
    Secondly, you need to focus on the grain side of the gg, not the top of the system. For that you need a focusing eyepiece. During the course of time, be it a day, a week, a month or years, your eye will change, a shim does not. A focusing eyepiece does!

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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    Quote Originally Posted by Bob Salomon View Post
    A shim is nonsense, especially on the Agfa type loupe which is not a shining example of optical quality. Especially the Chinese made on. The Spanish ones were a little better.
    Besides, how could a felt pad serve as a useful shim is beyond me. It has no dimensional stability - the more your press it, the thinner is the shim.
    If you insist on using your Agfa loupe, turn it the other side out and focus with it with a free hand. It will be more difficult to use but you will not be dependent on a wrong thickness shim. Then go and buy yourself a focusing loupe.

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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    An 8x loupe is fine for some. Others prefer a 4x to 6x loupe. We are all different. The focusing loupe is the best.

    Try out your loupe. This will tell you plenty.

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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    I use a cheap thread counter. It works so well, I can't imagine any advantage to using a more expensive one.

    Here's my problem with a focusing loupe. Unlike a piece of film, your eyes can focus themselves. So you don't need to focus the loupe on the front of the ground glass, because your eyes can do that. And unless you keep your eye at the exact same distance every time you view through the loupe, it's focus will change too. Just like how if you raise or lower your enlarger's head, it changes the focus as well as the size of the projected image. So unlike a camera lens on film, you've got two competing and constantly changing variables. Therefore, focus just need to be within a usable range, and not precise. Maybe if my near vision was bad, I'd find a use for a focusing loupe (to help compensate for that). But with my good near vision (and terrible far vision), pretty much any magnifying glass works just as well as any other.

    And my real world experience backs this up. I've never had focusing issues using the super cheap 8x thread counter. Plus I like how it folds up small, and is easily and cheaply replaced should I lose or damage it.

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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    Quote Originally Posted by jim10219 View Post
    I use a cheap thread counter. It works so well, I can't imagine any advantage to using a more expensive one.

    Here's my problem with a focusing loupe. Unlike a piece of film, your eyes can focus themselves. So you don't need to focus the loupe on the front of the ground glass, because your eyes can do that. And unless you keep your eye at the exact same distance every time you view through the loupe, it's focus will change too. Just like how if you raise or lower your enlarger's head, it changes the focus as well as the size of the projected image. So unlike a camera lens on film, you've got two competing and constantly changing variables. Therefore, focus just need to be within a usable range, and not precise. Maybe if my near vision was bad, I'd find a use for a focusing loupe (to help compensate for that). But with my good near vision (and terrible far vision), pretty much any magnifying glass works just as well as any other.

    And my real world experience backs this up. I've never had focusing issues using the super cheap 8x thread counter. Plus I like how it folds up small, and is easily and cheaply replaced should I lose or damage it.
    Providing that your thread counter isn’t grossly defective it is focused on the surface that you have placed it on. With a camera that can be very far away from the surface that the image is being formed on, the grain side of your gg.

    A focusing loupe is focused on the grain of the gg, not the top of the gg or on top of the Fresnel screen, if it is on top of the gg.

    Yes, your eye changes during time, but once the loupe is focused on the grain of the gg it stays focused on the grain, unless you replace the gg/fresnel. But if your eyes change the loupe can alw@ys be readjusted.

    Your thread counter or an Agfa loupe can not be adjusted other then by your changing the distance between where you hold it!

    Lastly, a proper focusing loupe has an opaque barrel to eliminate stray light and maintains maximum contrast to your eye to make focusing easier. Your thread counter or any loupe with a clear barrel, or anytime you have clear space between your loupe and your gg you will induce flair from extraneous light and reduce that contrast!

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    Re: Noob Loupe Questions - Focusing v Slide, Magnification

    Quote Originally Posted by jim10219 View Post
    I use a cheap thread counter. It works so well, I can't imagine any advantage to using a more expensive one.

    Here's my problem with a focusing loupe. Unlike a piece of film, your eyes can focus themselves. So you don't need to focus the loupe on the front of the ground glass, because your eyes can do that.
    No, they cannot. If your loupe is not correctly focused on the plane that needs to be in focus, your eyes cannot correct for that. Why? Simply because if your loupe sends the incorrect picture to your eye any focusing in your eye cannot compensate for the lost optical information of the first optical system that sends the picture (fuzzy one) to your secondary optical system (the eye). What you say is completely wrong from the optical point of view.

    Were it as you say, we could easily focus a non sharp negative in the printing optical system to get somehow a sharp print - and we all know, it is not possible. Only digital system can do such a trick, the human eye cannot.

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