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10-07-2012, 07:49 PM   #1
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Manual lens for K-7?

Hello, I'm requesting your help selecting a special lens for my K-7. I shoot time lapse jpg's (hundreds or thousands sequentially) and stitch them together to form a video. All my shooting is fully manual - aperture, shutter speed, focus, white balance, etc. A common problem with time lapse videos (including mine) is flicker resulting from minute differences in the aperture size from frame to frame, because the mechanical iris does not return to the EXACT f-stop from shot to shot, even though the camera's settings have stayed the same. While these small differences might not be noticeable in a side-by-side comparison of two images, they are annoying when displayed in a video. A common way to solve this problem is to force the aperture to stay physically locked in position from shot to shot - in other words, the iris does not open and close between shots. I haven't found a way to do this with my current lenses (Sigma 10-20mm, Sigma 18-200). With both of these lenses, the iris goes wide open between shots. Time lapse photographers often attach older non-automatic lenses to modern camera bodies to manually force the aperture to stay locked in position throughout the shooting sequence, thereby removing this source of flicker.

I would appreciate any recommendations for a wide angle lens (15 - 24mm in 35mm equivalent, fixed or zoom, Pentax or 3rd party), manual focus, that would allow me to lock the aperture in position between shots. I would like to set the shutter speed according to the manual metering through the stopped-down lens. Thanks in advance!

10-07-2012, 08:02 PM   #2
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QuoteOriginally posted by stuskier Quote
Hello, I'm requesting your help selecting a special lens for my K-7. I shoot time lapse jpg's (hundreds or thousands sequentially) and stitch them together to form a video. All my shooting is fully manual - aperture, shutter speed, focus, white balance, etc. A common problem with time lapse videos (including mine) is flicker resulting from minute differences in the aperture size from frame to frame, because the mechanical iris does not return to the EXACT f-stop from shot to shot, even though the camera's settings have stayed the same. While these small differences might not be noticeable in a side-by-side comparison of two images, they are annoying when displayed in a video. A common way to solve this problem is to force the aperture to stay physically locked in position from shot to shot - in other words, the iris does not open and close between shots. I haven't found a way to do this with my current lenses (Sigma 10-20mm, Sigma 18-200). With both of these lenses, the iris goes wide open between shots. Time lapse photographers often attach older non-automatic lenses to modern camera bodies to manually force the aperture to stay locked in position throughout the shooting sequence, thereby removing this source of flicker.

I would appreciate any recommendations for a wide angle lens (15 - 24mm in 35mm equivalent, fixed or zoom, Pentax or 3rd party), manual focus, that would allow me to lock the aperture in position between shots. I would like to set the shutter speed according to the manual metering through the stopped-down lens. Thanks in advance!
Any K-mount (bayonet) would have the same problem unless you removed the aperture lever (which is possible), so'd probably want to stick with an m42 screw-mount using an adapter which will allow the aperture to be set and not move. Wide-angles in m42 can be hard to find and aren't the greatest IQ compared to modern ones, although if 24mm is ok there are some Vivitars are there not too hard to find...
10-07-2012, 08:02 PM   #3
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You're going to be looking at screw mount lenses to be able to avoid the aperture opening back up, all Pentax K mount lenses have aperture couplings. The problem is, there isn't very many ultra wide angle screw mounts.

The closest thing I can think of is the 16mm Zenitar fisheye, it isn't very fishy on APS-C if you're careful with it and it is available in M42 screw mount.
10-07-2012, 08:07 PM   #4
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Cheapest high quality solution would be a 17mm or 24mm Tamron SP adaptall 2 . Buy a cheap after market Adaptall for pk mount for $20 that are just machined metal mounts with no interface.




Last edited by Sliver-Surfer; 10-07-2012 at 08:35 PM.
10-07-2012, 08:24 PM   #5
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If you could find a wide lens with an aperture ring, you could mount it partially, but not turn it until it locked. That would keep the camera's aperture control arm from touching the lever on the lens. You'd need the aperture ring to set the lens. I don't know what wide lenses to suggest that have a ring. Even partly mounted, the lens should be stable enough for tripod use.
10-08-2012, 04:40 AM   #6
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I suspect that it may be somewhat more reliable with a K than A lens because the apertures always returning to the hard stop set by the lens, not the aperture activation lever. However, as others have pointed out, an M42 lens would solve that problem.
10-08-2012, 05:02 AM   #7
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QuoteOriginally posted by stuskier Quote
I would appreciate any recommendations for a wide angle lens (15 - 24mm in 35mm equivalent, fixed or zoom, Pentax or 3rd party), manual focus, that would allow me to lock the aperture in position between shots.
As previous posters have suggested, M42 would be the best way to go.
However, there are very few rectilinear options in the 10-16mm range
(your 15-24mm in 35mm equivalent).
About the only Pentax lens like that is
SMC Takumar 15mm F3.5 Reviews - M42 Screwmount Extreme Wide-Angle Primes - Pentax Lens Reviews & Lens Database

So part-mounting a K-mount lens may be more practical.
10-08-2012, 05:05 AM   #8
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QuoteOriginally posted by Sliver-Surfer Quote
Cheapest high quality solution would be a 17mm or 24mm Tamron SP adaptall 2 .
Only the 17mm is close to a 24mm equivalent, but no cigar.

10-08-2012, 05:35 AM   #9
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You could easily take any other maker's lens and convert it to M42 by swapping mounts. I did this with a Nikon 300/4.5 recently
10-08-2012, 05:51 AM   #10
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QuoteOriginally posted by stuskier Quote
Hello, I'm requesting your help selecting a special lens for my K-7. I shoot time lapse jpg's (hundreds or thousands sequentially) and stitch them together to form a video. All my shooting is fully manual - aperture, shutter speed, focus, white balance, etc. A common problem with time lapse videos (including mine) is flicker resulting from minute differences in the aperture size from frame to frame, because the mechanical iris does not return to the EXACT f-stop from shot to shot, even though the camera's settings have stayed the same.

Even if the aperture remains strictly constant,
and you don't change the nominal camera settings,
is the K-7's shutter sufficiently consistent to avoid flicker?
10-08-2012, 07:15 PM   #11
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If you want a simple not elegant solution. Tape every opening of a lens with a pentax bayonet mount and an aperture ring and cut the auto aperture lever off with a dremel. Test first with a cheap lens to see if the aperture return is what is causing your problems. I haven't seen m42 any smaller than 15mm.
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