Metering without aperture simulation

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I4ve made a macro lens from a Vivitar VHE F5,6/135mm enlarger lens (6 elements, seems to be identical to Componon, very fine enlarging lens, max. aperture F45!!), an old enlarger bellows, the male half of a disected macro ring nr. 1, the focusing rail of an old enlarger and some home-made wood bits. It is able to swing vertically and horizontally, no shift. When the first prints are ready I will scan them and trie to put them on the net. My question is: I cannot measure correctly with the TTL, because there is no aperture coupling. How do I solve this? The meter reacts to changing the aperture, but the times are about 3 stops low (unfortunately not constant). Ofcourse I can use a handheld meter and a macro scale to correct the measured time, but the pleasure of making this for about $15 will be sublimized when I can use through the lens metering. By the way, I have read almost all threads, being in love with this unhandy camera, but where are the pictures?

Peter

-- Gooijer Peter (rockrose@freeler.nl), September 13, 2000

Answers

Yes, that little pin in the back of the lens tells the body what f-stop the auto lens is at in the manual mode. But, the outer bay manual lenses don't have the pin and so the TTL meter reads in the manual mode without any connections. My point is that you should not have to modify your lens to get a correct reading. Just so long as the diaphragm is working and the meter activating pin in the body's lens mount face are working, you should be OK. SR

-- Steve Rasmussen (srasmuss@flash.net), September 16, 2000.

Needless to add that I can focus to infinity with this lens mounted. I tried to do the same with another enlarger lens, the Vivitar VHE 5,6/100mm (bought in the same deal, $10 each, brandnew) but I could not make the bellows thingy thin enough to focus at infinity. It can be used for macro, though, and with the 100mm over 1:1. These lenses have a screw mount diameter of 50 mm.

-- Peter Gooijer (rockrose@freeler.nl), September 14, 2000.

First of all how do you know the reading is off? If you are using an external meter are you compensating for bellows? You say the reading is not constant which is consistent with varying bellows draw. The TTL reading should be accurate. The way the meter works is: in AUTO mode the lens is always at max aperture so the meter needs to use the aperture setting that you dial on the aperture ring to calculate exposure because the aperture will be changed to the "taking" aperture when the picture is taken (this is done so that the lens is always wide open to aid focusing and only closes down when the picture is taken). So in AUTO mode the meter needs to know aperture setting. In MANUAL mode the meter does not need aperture info because it just measures the current light level (in MANUAL mode the "viewing" aperture is the same as the "taking aperture". Indeed your setup is like MANUAL mode and is the same situation as when using extension tubes. The TTL meter still works when using extension tubes even though there is no aperture coupling provided you set the lens to MAN when you take the TTL reading. If you really want to make sure here is what you need to do: your bellows thing can be used like a regular pentax lens that is set to MAN mode. When you put the lens in MAN mode the TTL meter ignores aperture coupling and just uses the light reading it gets because it assumes that the current "viewing" aperture is the "taking" aperture which is true for the enlarger lens (i'm assuming your enlarger lens sets actual aperture as it is dialed like most other enlarger lenses). So how do you tell the camera the lens you are using is in MAN mode? If you take a pentax lens looking at the mount and press the MAN lever you will see a little pin on the lens mount moving (this is what tells the camera that the lens is in MAN mode. What you need to do is to modify your mount to simulate this operation, i'll leave the details to you...much luck

-- m.b. (mbarroca@americasm01.nt.com), September 14, 2000.

Thank you for your answer. I will try what you suggest. I4ll be back. Peter

-- Peter Gooijer (rockrose@freeler.nl), September 16, 2000.

Thank you for your respons, nice to know someone else is trying similar things with his equipment. I sent some pictures by mail, I don4t know how to put them on the net without a homepage. If someone is interested, I will mail them. They are scanned with an Acer flatbed scanner, capable of scanning transparancies. The results are reasonable for this purpose. Not comparable with a negative scanner, but these are expensive and only for 35mm, as far as I know. The pictures are made with a simple flash, some in automatic, some in manual setting. Therefore the colours differ somewhat, and in picture Lego4 (I made it a bit brighter with Photoimpact) the flash wasn4t sufficient for F45, even at 30 cm. The results (as the other subscriber can see) are precisely what I had in mind, the possibility to use my P67 with dof manipulation. I was astonished about the results on the transparancies (Fuji Provia F): very sharp, beautiful contrast, and warm colors. I4m very happy with this lens, I will wait a little while before buying the 4/135mm macro. I4m waiting for the first result of using it outside as a moderate telelens. I own a Kenko AP6 2x converter, so I can experiment still further. I now know what is wrong, concerning my original question: if I set my lens to manual, the needle immediately jumps up, and stops measuring. I had my TTL fixed when I bought it, because it was off (see my other thread). Maybe this is the reason why it doesn4t work, my meter stops measuring when the little pin is pushed. I tried it without a lens (there is this little pin inside another litlle pin, the smallest is for the meter). Mine seems not to work correct. I don4t know. But the first results are very good. Peter

-- Peter Gooijer (rockrose@freeler.nl), September 21, 2000.


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