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08-23-2011, 11:19 PM   #1
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Use of Manual Lens Exposure

Hi this is the first time on this forum. I have a 500mm pentax mount mirror lens which I used with difficulty on my *istd Pentax DSLR. I upgraded to a Pentax Kx-r and found it was not usable
at all. I was thinking of buying an ODS Mirror Lens and asked the dealer for assurance that the adaptor for the 500mm Mirror lens would solve the exposure problem. That is the Kx-r will know it is a F/8 aperture and set the exposure properly. The dealer came back and said it is entirely manual so everything must be set manually. Is there anyone here that is using such a lens as the ODS or Samyang telephoto lens? If so how do you get a correct exposure? In the past I have found using an external exposure meter unsatisfactory because the different angle of view.

08-24-2011, 12:25 AM   #2
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You have to use stop-down metering, which is detailed in an guide I've posted in the articles section.

A forum search for "m42 lens on k-x" should take you straight to it
08-24-2011, 03:32 PM   #3
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Thanks I found the article on manual focusing and have things working. The critical point was allowing the camera to ignore the aperture setting!
08-24-2011, 11:18 PM   #4
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Correct me if I am wrong but...

QuoteOriginally posted by Horus28 Quote
Thanks I found the article on manual focusing and have things working. The critical point was allowing the camera to ignore the aperture setting!
Correct me if I am wrong but the camera doesn't ignore the aperture setting. It sets the iso and shutter speed from the f-stop that you set on the lens aperture ring based on light metering. Manually change any one of the three and the camera will change the other two. The camera won't indicate the f-stop that you have the aperture ring set to with a manual lens, if that is what you mean.

08-25-2011, 12:28 AM   #5
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Perhaps I was not clear enough. On my kx-r in custom settings 22 use of apperture ring is set by default to prohibited. I had to change that to permited. Previous to that the shutter would not release with my manual lens. That is also in the instruction in the article I found on the forum.
08-25-2011, 09:33 AM   #6
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QuoteOriginally posted by lammie200 Quote
Correct me if I am wrong but the camera doesn't ignore the aperture setting. It sets the iso and shutter speed from the f-stop that you set on the lens aperture ring based on light metering. Manually change any one of the three and the camera will change the other two. The camera won't indicate the f-stop that you have the aperture ring set to with a manual lens, if that is what you mean.
The camera does not Ignore the aperture setting, it doesn't know what the aperture is. It doesn't with ANY manual lens. However, the mirror lens being a single aperture lens (there IS no aperture on them), Av should work in this case. That is, once you set Use Aperture Ring to Permitted. M42 lenses such as Super Taks that have no coupling to the camera aperture mechanism will Also work in AV mode just taking a light reading once you put them on Manual (so the blades move with the ring). In fact, they All will 'work' but with an M or K lens (no A Setting), in any mode but Manual, the lens will remain wide open regardless of the aperture ring. In That mode, you set your aperture ring and hit the Green button (or what ever button stops down the aperture for a meter reading, on some I understand it's the +/- button) and that will center the meter. You can then take your shot or adjust exposure to taste by changing one of the 3 exposure legs (Aperture, Shutter Speed, ISO) and then shoot. In M mode, there is no Auto ISO so if you want to change it, you must do so manually. That's the way it works on the weather sealed cameras anyway.

With other lenses (A and later), the camera knows Where to stop the blades down and based on the meter reading can give a shutter speed at a given ISO. That is, if you've called for f8 on an f2.8 lens, the camera knows that you want to go 3 stops so it's quite simple to adjust the shutter speed by that amount. That, I'm sure is a very simplistic way of stating the way it works but in my mind, it's the only way it Can work. In Tv, again, in my mind, you would set a shutter speed, the meter takes the reading and determines how far to stop down the aperture for a centered meter exposure. If Auto ISO is enabled, and if a limit is reached (calls for f2.0 on that f2.8 lens), then it will adjust the ISO for the exposure.


Last edited by JeffJS; 08-25-2011 at 09:45 AM.
08-25-2011, 11:49 AM   #7
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Good explanation...

QuoteOriginally posted by JeffJS Quote
The camera does not Ignore the aperture setting, it doesn't know what the aperture is. It doesn't with ANY manual lens. However, the mirror lens being a single aperture lens (there IS no aperture on them), Av should work in this case. That is, once you set Use Aperture Ring to Permitted. M42 lenses such as Super Taks that have no coupling to the camera aperture mechanism will Also work in AV mode just taking a light reading once you put them on Manual (so the blades move with the ring). In fact, they All will 'work' but with an M or K lens (no A Setting), in any mode but Manual, the lens will remain wide open regardless of the aperture ring. In That mode, you set your aperture ring and hit the Green button (or what ever button stops down the aperture for a meter reading, on some I understand it's the +/- button) and that will center the meter. You can then take your shot or adjust exposure to taste by changing one of the 3 exposure legs (Aperture, Shutter Speed, ISO) and then shoot. In M mode, there is no Auto ISO so if you want to change it, you must do so manually. That's the way it works on the weather sealed cameras anyway.

With other lenses (A and later), the camera knows Where to stop the blades down and based on the meter reading can give a shutter speed at a given ISO. That is, if you've called for f8 on an f2.8 lens, the camera knows that you want to go 3 stops so it's quite simple to adjust the shutter speed by that amount. That, I'm sure is a very simplistic way of stating the way it works but in my mind, it's the only way it Can work. In Tv, again, in my mind, you would set a shutter speed, the meter takes the reading and determines how far to stop down the aperture for a centered meter exposure. If Auto ISO is enabled, and if a limit is reached (calls for f2.0 on that f2.8 lens), then it will adjust the ISO for the exposure.

You are totally correct. Perhaps, I was being unclear. I know that the camera will not change the aperture on an "M" lens. However, the shooter can change it manually and stop down to also change the shutter speed and/or iso. That is basic shooting 101. The camera's light metering doesn't ignore the aperture setting. It uses the actual light coming in from the setting that the shooter chooses to determine the shutter speed and iso. But you are right that the camera doesn't actually know what f-stop a "M" lense is set at.

It is a balancing act between the three depending on what you are shooting and what kind of result you want in terms of focus, DOF, exposure, etc. I usually set the aperture to get the relative DOF that I want then play with the iso to get the shutter speed that I want. Of course it all depends on available light. Trial and error for me. Hopefully fewer errors along the road.
08-25-2011, 12:14 PM   #8
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We're talking general knowledge type stuff here in the last few posts, information every photographer, amateur hobbiest and pro alike should have. My post started out simply to explain that the Mirror lenses in question by the OP, do not have apertures and thus, aperture rings. To actually Change the amount of light passing through the lens to the sensor/film, one must install a ND filter on the rear of the lens. I guess a front one would work too but may be cost prohibitive for most people (depending on the actual filter). I've also seen people talk about using stacked linear polarizers as variable ND filters as well.



08-25-2011, 01:54 PM   #9
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[langtitle=nl]Yep...[/langtitle]

QuoteOriginally posted by JeffJS Quote
We're talking general knowledge type stuff here in the last few posts, information every photographer, amateur hobbiest and pro alike should have. My post started out simply to explain that the Mirror lenses in question by the OP, do not have apertures and thus, aperture rings. To actually Change the amount of light passing through the lens to the sensor/film, one must install a ND filter on the rear of the lens. I guess a front one would work too but may be cost prohibitive for most people (depending on the actual filter). I've also seen people talk about using stacked linear polarizers as variable ND filters as well.

I lost sight of the OP and the mirror lens.
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