Working Distance, focal length

[AdamR]

Hi all,

I'm looking to reverse a lens on another to achieve 2:1 magnification (starting with a 50mm reversed on a 105). Does anyone know the formula for the working distance of this setup?

Ultimately my parameters are the following: need 2:1 reproduction (image on sensor is twice life size) and 10-20 inches of working distance between my subject and the front of the lens.

Would a 2x teleconverter work on a 1:1 lens whose closest focusing distance is around my desired working distance?

I'm not too worried about light loss or cost of purchasing additional equipment.

Thanks!

p.s. all equipment is Nikon, F-mount

[PWhite214]

I looked on the internet and did not find any info on what the actual working distance will be with any reversed lens combination. I have some reverse rings on order planning to experiment with different lens combination's. My best advice, try it and see. Post the results, we might all get together and make a reference table if we can't curve fit a formula.

phil

[LeeR]

I used to have a ring that would allow me to reverse my lens and attach it backwards to my camera. While I don't have a formula, I can tell you that with the 50mm lens I was a LOT closer than 10 inches, more like 2 to 3 inches and magnifcation was close to or greater than 1:1. Also, DOF was extremely small.

[PWhite214]

Yes, with my 50mm lens reversed directly to the camera, the working distance is very short. I need to take time to try the 28mm, so I can see what difference. I do not have any experience with lens reversed on another lens, so I will try it as soon as I have the ring. I will have to use a 70-200mm on the camera, with a 50mm reversed. I can see the eventual need for more rings. They are very inexpensive, but take a long time to come from Asia.

Have fun,
Phil

[PWhite214]

I finally received my reverse rings. I used a 50mm lens reversed on a 70-210mm Minolta lens, set at 100mm. It does give a magnification of 2X, but the working distance is about 1.5". I have no idea how you might get a 10" minimum working distance.

I used a tripod, macro slider and flash to get this shot. I will have to try focus stacking next.



Phil

[AdamR]

That's a cool looking shot! I received the Novoflex bellows this week and reversed a 50mm lens on it. This gave adequate working distance (about 2 inches). I figured out how to make 2 inches work as working distance. The application for this is actually for the lab I work in. We've got a high speed camera, Photron APX and we're trying to take high speed images of a very small object... Since things are moving quickly, focus stacking isn't feasible for this application. Thank you all for your help!

[wulf]

What sort of depth of field do you need to get? I think that is likely to be a challenge - as you get closer, the DoF rapidly gets smaller.

How was the 2:1 requirement arrived at? Off the top of my head, I think my D40 has a sensor which is about 23mm across. If I can get a 1:1 image, that means 1mm in real life will be represented by about 110px (very rough figures!). That is actually pretty detailed - not quite microscope levels but still a good deal of magnification. Depending on the resolution of your screen, that could give an effective magnification of 20x or larger while still appearing sharp.

That may not be enough for your particular purposes (I'd love to hear more about what you are attempting to capture) but is ample to reveal aspects of the natural world that are effectively invisible to the naked eye.

Wulf

[PWhite214]

I looked at the EXIF data on the shot posted above. The zoom lens had slipped out to 135mm so the actual magnification is 2.7X. I had tried to hold the lens at 100mm with a piece of painters tape, but guess I knocked it loose during setup. When I made the working distance measurement the lens was securely set at 100mm.

Phil