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02-10-2019, 03:42 PM   #1
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rokinon 16 mm f2.0 on K30 with failed aperture block

Hello I'm interested in trying out some landscape and night photography, and the rokinon 16 mm/f2.0 seems like a fairly cheap way to start.

However, my K30 has a failed aperture block. The Rokinon seems like a totally manual lens. Will it work just fine on a K30 with a failed aperture block? I imagine I can set the aperture with the aperture ring and select a shutter speed using the dial?

Thanks, Wayne

02-10-2019, 03:59 PM   #2
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yes of course, and in manual mode you can even stop down your shutter with the green button. think of it as a manual Av mode

Last edited by photolady95; 02-11-2019 at 03:00 AM.
02-10-2019, 04:34 PM   #3
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I'm not so sure, as it may fail to stop down to the selected aperture. However, it will definitely work wide-open.

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02-10-2019, 05:19 PM   #4
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Thanks for the helpful feedback. I didn't think I had any way to test it since I don't have any old Pentax K lenses laying around.

I did find an old Tamron Adaptall lens with a KA adapter. I set the aperture ring to a value other than "A", set the shutter speed to 1 sec, and looked thru the front of the lens and it does look like it stops down correctly at any aperture setting. So that's a good sign.

Thanks again.

02-10-2019, 07:45 PM   #5
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QuoteOriginally posted by pentax_wayne Quote
Will it work just fine on a K30 with a failed aperture block? I imagine I can set the aperture with the aperture ring and select a shutter speed using the dial?
Another "Yes" vote.

I have a K-70 with a failed aperture block, and all of my lenses with an aperture ring including a Rokinon 85mm f/1.4 work fine by turning the ring off of the "A" setting and selecting aperture & shutter speed manually. And green button stop down metering also works.
02-10-2019, 08:24 PM   #6
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It should work fine using the aperture ring. The failure manifests itself by always stopping down completely. The aperture ring setting will hold the iris open at the set aperture rather than always closing to the minimum.
02-11-2019, 06:24 AM   #7
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With lenses that do not have a camera-controlled aperture (=fully manual aperture, no "A" setting), or if the lens has an "A" position and you don't use it, be sure to selected "fire with no lens attached" option in the menu. You can either use manual exposure with the green button, but if you use "AV" the camera should automatically set the shutter speed for whatever aperture you've set on the lens' aperture ring (experiment: set camera to "AV" and select "fire with no lens," look through the viewfinder or watch the LCD and rotate the aperture ring - the shutter speed should change appropriately). What may be troublesome is focusing with the lens stopped down. You may want to focus with the lens wide open then manually turn the aperture ring to the desired f-stop just before tripping the shutter or pressing the green button.
Interesting how with all the automation built into a modern DSLR, we are willing to go deeply retro to techniques that date from the earliest days of SLR's. What next? Maybe the return of Weston selenium-cell hand-held meters, or even better, those sheets of paper with exposure guidelines for "sun," "open shade," "cloudy bright," etc.
02-11-2019, 06:36 AM   #8
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The thing that confuses me is that I didn't think A type lenses worked like that ....I thought they remained wide open, even when not in the A position, until the camera stops them down at point of exposure. So for this reason I cannot understand how the Rokinon lenses can work completely (ie taking photos at all possible apertures) with a camera where the aperture motor/block thing has failed...?

02-11-2019, 07:07 AM   #9
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QuoteOriginally posted by mcgregni Quote
The thing that confuses me is that I didn't think A type lenses worked like that ....I thought they remained wide open, even when not in the A position, until the camera stops them down at point of exposure. So for this reason I cannot understand how the Rokinon lenses can work completely (ie taking photos at all possible apertures) with a camera where the aperture motor/block thing has failed...?

It depends on how the mechanism has failed. The original pin-press M42 Takumar lenses remain wide-open until the pin at the back of the lens was forced in by an actuator in the camera. But when the K-mount was introduced, a diaphragm-closing spring was placed inside the lens. The actuator in the camera presses the lever on the lens to the wide-open position, then drops down to release the lever allowing the lens to stop down when the shutter is pressed. So it depends on where the mechanical actuator in K-mount camera body is stuck = up (only maximum aperture is possible) or down (any aperture can be used). The Rokinon 16mm f2 does have an aperture lever at the back, so it is not 100% manual. Some Rokinon/Samyang lenses have no connection mechanical or electronic with the camera body.
02-11-2019, 08:08 AM   #10
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Thanks for that extra info ...I have long been concerned that there has been a tendency to look towards A type lenses as somehow being an easy all-in solution to " aperture block failure", but it seems not to be that certain
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