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View Full Version : What would I get if I put a 90mm front and 180mm rear together?

bmgmusic
6-May-2002, 15:46
Do I still have a 90mm wide angle meanwhile the bellow length at infinite become s 180mm?

Jerry Flynn
6-May-2002, 16:56
Assuming you could actually do this, you'd get an entirely different focal length in between the 90 and 180. This is how covertable plasmats work - like the Protars and pre "Symmar-S" Symmars. However, the elements in those lenses were designed to work together. I'm not an expert in optics, but I don't think you can take any old set of cells like from a Super Angulon and a Symmar and put them together and get someting that works.

RichardRitter
6-May-2002, 19:15
Why not try it and let us all know how it works out. You may have something that could be the new fad in photography.

Bill C
6-May-2002, 20:29
Aaron, the general rule with combining lenses is that powers add, where "power" is a measurement of the same general type as diopters.

Assuming that when you say a "90mm front", you mean you are using a lens that functions as though it has a 90mm focal length, etc, combining the two should give you roughly a 60mm focal length. I say roughly, because the general rule I gave assumes that there is no distance between the two lenses. More than likely, you will have SOME distance between them which will weaken (I think) the effect slightly, so focal length is probably slightly greater than 60mm.

FWIW, the calculation I used is: new_fl = 1/(1/fl_front + 1/fl_back).

Also, I don't think anyone could say for sure what the final image quality or size of the image circle would be. Have fun experimenting.

paul owen
7-May-2002, 03:19
One, crazy, mixed-up lens!!!! Give it a try - Good luck!!

Dick Roadnight
7-May-2002, 18:20
What do you want it to do?

I think that if you stack an entire 90 reversed on the front of a 180, you get a 2X macro lens, without needing a great deal of extention.

bmgmusic
8-May-2002, 02:03
I'm trying to figure out a way to use my wide angle LF lens on Mamiya RZ.

Wayne_6692
8-May-2002, 07:07
You'd be better-off asking that on a Mamiya board. You probably can do it by pre-releasing the camera's lighttrap and mirror, then using the lens's shutter. You'll need extra extension though if you want to focus closer than infinity. You'll need to rig-up the lens solo - as someone else pointed out, a 90 in front of a 180 gives you a 2x microscope.

bmgmusic
8-May-2002, 12:03
For wide angle <100mm, RZ body is already too thick.

Wayne_6692
9-May-2002, 08:37
Oops - been a while since I owned my RB, I guess anything shorter than 127mm is a retrofocus design. Other than using a Mamiya lens I don't see another alternative. You might check backfocus specs on the large format 90mm lenses to see if there's one out there that will work, but they're probably all within a mm or two of each other.

Jason J.
10-May-2002, 02:18
I think it was sally mann who was experimenting with taking old and broken lenses and using them to make new 'frankenstein' lenses. Her photos using these 'homemade hybrid' lenses were neat, but full of fuzzy, wierd, dreamy qualities. Definitely not for product/catalog photography!!!