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01-04-2010, 01:54 PM   #1
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Digital lens on Full-manual SLR

Hey everybody

Like many other full-manual SLR owners, i was pretty bummed when i found out i couldn't use my digital K-mount lens on my MX without shooting at F22-F40 [Sigma 17-70].

So i made a little demonstration for the n00bies, and here's what i did to (somewhat) solve the problem!

My two babies.


Because the lens doesn't have an aperture ring, and the MX also has no control over the aperture, the two don't play very nice.


Sigma 17-70, mounted on Pentax MX, without DOF lever depressed, the aperture remains wide open for composing the shot.


DOF lever is depressed, aperture blades close down to F22 [at 17mm], almost unusable unless using fast film and in bright sunlight.


The aperture control switch needs to be held open. This will prevent camera body from letting it slide all the way to the min-aperture position when taking a shot.


Now we're talking


Cut a thin slice of tape.


Firmly apply is to the protruding part of the lens near the aperture control switch. CAUTION: DONT LET THE TAPE TOUCH YOUR REAR ELEMENT.


Push the lever all the way open [or to desired aperture], and firmly stick the tape to the lever.


Press the tape down as much as possible and form it to the rear parts of the lens, to minimize the chance of the tape touching anything inside your camera. Note the aperture is "stuck" open now.


Mount your digital lens on your full-manual film body, take caution that you don't peel the tape off in the process.


DOF preview is depressed and the lens stays open at F4.5 [at 70mm].


View through the view-finder:


There you have it! Sorry if this tutorial was a bit lengthy for such a simple operation.

Now you can take those weird-looking, rock-concert, skateboarding, looking photos, where the image circle doesn't cover the full frame area!

note: you can tape the aperture to whatever position you like. if you're going to be outside on a relatively sunny day, shooting with some 100 speed film for example, you can tape the lens at ~F5.6, to effectively stop down the aperture, it doesn't have to always be wide open.

also note: don't use really sticky tape in this procedure, or any kinda of tape that's going to leave a residue behind!

Hope you enjoyed reading!

01-04-2010, 04:13 PM   #2
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Nice work, I love "MacGyver" fixes!

Phil.
01-04-2010, 04:38 PM   #3
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The digital lens would be a lot more usable on a P30t or a Super Program. You could change the shutter speed and the camera would compensate by changing the aperture. At about >24 mm, you would propbably not get any vignetting. That has been my experience with the 18-55mm kit lens for my K200D.
01-05-2010, 12:44 AM   #4
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So you've wedged the aperture wide open but the camera will meter incorrectly, right?

01-05-2010, 08:40 AM   #5
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QuoteOriginally posted by Tom in Delaware Quote
The digital lens would be a lot more usable on a P30t or a Super Program. You could change the shutter speed and the camera would compensate by changing the aperture. At about >24 mm, you would propbably not get any vignetting. That has been my experience with the 18-55mm kit lens for my K200D.
Hi! sorry for my english.. i've just bought a program A (program plus) with a smc-m 50 f/2. I'm very satisfied about that, i've tried the lens with my k200d and.. what a bokeh!

then i tried to do the opposite, fit the program a with the DA 18-55 lens. When i switch auto the aperture is always f4 and it change shutter speed in automatic mode.. if i switch to manual mode or bulb the viewfinder shows me an "E" (the manual says: error). Is it possible to change the aperture or the lens stays always wide open?
01-05-2010, 10:09 AM   #6
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If the camera is not getting enough light it'll always keep the aperture open to get as much as possible. Try it in daylight, I'm sure it'll choose smaller apertures if there's plenty of light. That said, you'll get very heavy vignetting below 24mm.

01-05-2010, 02:58 PM   #7
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here's one of the shots i did:


that's with Portra 400VC

and another on the same role:

gosh i love my film camera :]

Last edited by PNTXFTW12; 01-05-2010 at 05:07 PM.
01-05-2010, 03:14 PM   #8
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QuoteOriginally posted by brkl Quote
If the camera is not getting enough light it'll always keep the aperture open to get as much as possible. Try it in daylight, I'm sure it'll choose smaller apertures if there's plenty of light. That said, you'll get very heavy vignetting below 24mm.
Tanks a lot! i've tried shooting half meter from a lightbulb f8.5 and more.. the 18-55 kit lens is slow but it could be a superwide angle in daylight.. i've always believed that digital lens couldn't work with 35 mm film, that's 80% wrong


Last edited by Marco_pentax; 01-05-2010 at 03:20 PM.
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