Negative reproduction

[Boris Mirkov]

Hello everybody,
I've bought some time ago a Paterson negative reproduction bellow (I think that's the name) but I can't seem to get a full zoom of the negative on it! On the other side of the bellow is Canon 350D (1.6x crop) and when I manage to focus on the negative, it is a center crop of a complete 36x24. I tried with 29mm, 35mm and 50mm lenses, considering that I tried the 50mm backwards also. I know that the first slider (with the lens on it) is for zooming and the second one is for focusing, but that knowledge doesn't help me much because I can't get a decent focus except on that one focal length where I have that center crop...
Any thoughts on resolving this issue?

 

[Ian C]

The bellows unit forces the lens to be positioned some minimum distance forward of the usual position on the camera.

The problem is: the lens is too far forward to give you the more modest magnification that you require. The minimum magnification produced by the 50mm lens on the bellows unit is too great and can’t be modified.

That means that you can’t use the bellows unit to obtain the lower magnification needed with a 50mm lens. You might be able to focus a longer focal length lens on the bellows unit.

You can get the magnification needed with a dedicated macro lens. This allows the lens to extend forward sufficiently to focus the subject (the negative). In this case you wouldn't be using the bellows unit.

I believe that the “film” you’re using has a 14.8 mm x 22.2 mm image rectangle. So the greatest magnification you can tolerate is about 0.6x to produce the largest possible image of the 24 mm x 36 mm negative onto your “film.”

With a 50mm macro lens you’d need about 213 mm from subject to image planes and the lens needs to be extended about 30 mm forward of its infinity position.

Another possible solution is the use of dedicated Canon extension rings to position the lens forward sufficiently to focus the 50mm lens at the distances noted above. The combination of the extension rings and the helicoids extension needs to sum to about 30 mm to focus a 0.6x-magnification image.

 

[Boris Mirkov]

OK, so first of all thank you Ian for your reply.

I've tried what you said for the extension rings (in my case, not Canon but Paterson M42 extension rings). I can say that this has only made it zoom in closer to the negative. Tried several combinations, all resulting the same. More rings - more zoom. I can't seem to find the right focal range, when I'm searching for it (by moving the sliders), I can only find one "working" focal range and by "working" I mean the only distance where I can find sharp image.

I believe it's the lens that is not fit for this hell's device (duh), but cannot seem to be able to find one. I know it is some macro lens like you said in the previous post but I don't have anything longer than 50mm on M42 screw. I'm willing to purchase one but not willing to experiment with my low budget wallet.

I'm going to upload some photos to try and explain the problem more specificaly.


Thanks again for the help.

 

[John Koehrer]

I think you're way beyond the extension you need. Especially with the bellows extended as far as in the picture.
With a 50mm lens 1:1 magnification is a total of 100mm from the film to the optical center of the lens. By the same token,
the subject would also be ~100mm from the front of the lens.
1) set the bellows so the diaphragm is 100mm from the film plane.
2) adjust the slide so it's ~100mm from the diaphragm of the lens. The diaphragm is typically considered the optical center.
If you can't close the bellows tight enough, you're going to need a longer focal length lens.

The first shot in post #3 looks like it should be close, can the bellows be closed any tighter? Once it's tight, slide the slide back & forth until you get focus.

The second shot with the additional extension tube gives a much greater than 1:1 magnification something like 2:1 or greater.

Most folks that want an accurate 1:1 mag will as above set the extension first and then adjust location between the camera and subject second.
crop factor will have no bearing on the actual focal length of the lens, it's a fixed value.
The standards are used interchangeably, not focus, zoom. when you have set the magnification you want either adjust the top rail or the slide back & forth until you get your focus.
If you're trying to copy a 24X36 frame to fill the sensor you're going to need a longer lens to get the entire frame. 100-135mm?
Got a friend you can borrow a lens from?

Shorter lenses or reversing a lens give a greater than life size reproduction. Oops that's the wrong way. =)

 

[Boris Mirkov]

So I tried what you said, but the bellows won't come any closer. It actually is very close but still a significant part of the frame is out.

Just called a friend, he will look for his Pentacon 135mm, guess I'll test it a few days and I'll some back with the results.

Thanks again, folks.

 

[Boris Mirkov]

I'm just thinking, the closest focusing range of the 135mm i something over 1 meter. If the back slider can't compensate for that, I'm not sure if testing is necessary. Am I right or dead wrong?

 

[Ian C]

You can’t use the bellows. They place the 50mm lens too far from the camera.

The flat mounting surface of the lens (in normal forward facing configuration) needs to be approximately 30mm forward of the lens mount on the camera. Even with the bellows completely collapsed, the lens looks to be further forward than 30mm. That will prevent focusing at the magnification you need.

By reversing the lens, its optical center might be placed further forward than you suppose. The optical center of the lens might very well be significantly different that the apparent geometric center of the lens.

You need EXTENSION RINGS ONLY—NO BELLOWS. This should place the lens in the correct position to focus with the magnification you require. The camera will have to be supported on a tripod.

Can you measure the distance from the lens mount surface on the front of the bellows unit to the lens mount surface of the camera?

If we know that then we can calculate which focal length lens (in forward-facing position) will attain focus at the 0.6 magnification on the bellows unit that you need. Without knowing the position of the optical center of the lens, we can’t calculate this if the lens is reversed.

Bellows units are useful, but they’re practical only for relatively high magnification work. That bellows + the 50mm lens give more magnifcation than the approximately 0.6X magnification you require.

 

[John Koehrer]

I think Ian and I somewhat share the idea here, we just use different approaches. I'm a hobbyist and don't mind fiddling with this stuff and he's a pro and time is money to him.

When you say a portion of the frame is out. Do you mean it's not on the sensor and you get only the center of the slide, the edges spill over it?
I think that's because you're photographing a 24X36mm slide onto the smaller sensor. So you're actually making a REDUCTION of the slide
You can see this difference comparing a slide to the sensor you're copying to.

Again, I think you need a longer lens to reduce the coverage at the sensor. Whether you use rings or bellows, the effect is the same but
with the rings you're at a fixed magnification and with bellows you can change the magnification pretty much seamlessly.
With the bellows closed It will be less than 1m and as you move the lens and body apart it will focus more and more closely. The same rule applies to the FL fo this lens as to the 50mm. At 1:1 the total extension of the lens will be 2X it's focal length or 270mm for your 135mm lens. Taking a SWAG somewhere around 175mm extension should be in the ballpark. Whether the slide holder will still mount to the bellows is another question
I'd set the lens up on the bellows(@~175mm) and take a page from a book or one of the slides you're copying and move it back and forth until it's in focus. That will show the very approximate distances you need.

These formula may help determine actual precise values for your project. Don't be surprised if you come up with some weird focal length lens as an answer but it should get you close. Or not! I just move stuff around 'til I get sort of what I want. Easier for me to do than tell you how to do it.
Anyway:
lens focal length= Image size X lens to subject distance/ subject size---------*This determines the focal length of the lens needed*

This one gives the image size you want on the Sensor:
Image size= lens focal length X subject size/lens to subject distance..............

 

[ic-racer]

When doing a reduction like that, the lens, of course, needs to be closer to the camera film plane than the subject. You should be able to use that 50mm lens, just focus at the 'other' focal point, the one with the lens closer to the camera. The image below shows an enlarger, but the principle is the same for your bellows setup:

 

[John Koehrer]

His bellows doesn't compress far enough. Ian suggested extension tube(s) and Boris may have a short one.

 

[ic-racer]

His bellows doesn't compress far enough. Ian suggested extension tube(s) and Boris may have a short one.

Ok. I was going by image 2 in the OP. If the camera was in focus in that picture then it looks like there is enough room to focus on the other point.