Laowa RF 100mm for Canon - Confusion over proper exposure + 1 more question

11 months 3 weeks ago #753130 by MikeSD
Question 1:
I have a Canon R7 camera and found a used Laowa RF 100mm (for Canon), in mint condition.  Couldn't resist picking it up, for only macro photography use.

But I'm confused about how I can know the exposure is correct. This is a fully manual lens. There are no electrical contacts, so the camera can't know the aperture settings.  it does see the light change, when the ring is turned.

There should be some way inside the viewfinder to know if my exposure is correct.  I have tried AV, fixed iso, and let the camera pick the shutter. That works but I have no indication, if the exposure is correct.  In using it this way, I do see the shutter change as I change the app ring, but at some point the pics become under or over exposed.

I've also tried AV, Auto ISO, and just let the camera choose shutter and iso.  But I'm not a fan of letting the ISO just float.  I have it limited to 3200 or 6400, just so it doesn't go to high ISO.f

Shutter Priority is useless, since the camera can't control the aperture

So, my question is, what is the best/proper way to use the Laowa RF 100mm, to get the shot, with the correct exposure? And how will I know, looking in the viewfinder.

2nd Question

Not so important but I'd like knowing.  This lens is advertised as having 2x magnification for macro.  I have no clue how to use this or what that even means.  The manual is useless.  Normally, using a macro lens, you just focus on the close object and take the picture.  If I want a larger image, in the frame, I just move closer, But this lens, I have to do exactly the same thing.  I was kind of thinking this meant I could take a 1 to 1 macro, and then just switch to 2x to get a larger image, without moving.  No way to do that.  I still have to move.

I'm guessing that this simply means it's possible to get larger than life size, on the frame.  Correct? What's confusing is the instructions say;
1) Set the magnification, then
2) change the focus
This sounds like two operations, but both are done with the same ring, I think, so why two steps. Step 2 undos what was done in step 1.  Very confusing.

Anyone understand this?  Is there some super secret trick, to actually make a selection of magnification?


11 months 2 weeks ago #753136 by Screamin Scott
As to your second question, when you set the magnification factor, you move the camera to and fro in order to achieve the desired focus. As for your first question, I shoot Nikon and Olympus and have no knowledge of Canon's ways, so I'll let a Canon shooter answer that one.

Scott Ditzel Photography

Photo Comments
11 months 2 weeks ago #753140 by MikeSD

Screamin Scott wrote: As to your second question, when you set the magnification factor, you move the camera to and fro in order to achieve the desired focus. As for your first question, I shoot Nikon and Olympus and have no knowledge of Canon's ways, so I'll let a Canon shooter answer that one.

Yeah, that's kind of what I figured.  Thanks

For the first question, for Canon users, this is what is confusing.  The camera has zero way of knowing the f-stop selected on the lens. And the aperture is not controlled, so it's stopped down. The camera shows F00.  And the camera uses some method of determining exposure. Typically you choose the f-stop, in aperture priority, and the camera does the rest.  But the camera is assuming a canon lens with lens open, and a known f-stop.  On the Laowa, the lens is not open.  So how can it calculate the shutter and/or ISO, if it doesn't know the f-stop.

I did do a test in aperture priority, and as I changed the f-stop, the shutter did change, but I don't know if that gets correct exposure for all cases.

If it does at all, I'm assuming it's just by monitoring the light coming in, through whatever f-stop is set. If that's the case, one could just monitor the exposure index and set aperture or shutter or ISO, until it's zero. But I'm not sure.

Anyone know?




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