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10-02-2010, 08:38 PM   #1
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Question regarding Av setting and manual lenses- newer gen bodies

Hey all-

100DS owner here for 3+ years, and I use quite a few manual lenses. Normally I use the stop-down button press method, but recently acquired a screw mount lens that I'm using in manual mode in conjunction with Av mode on my camera, and very much happy with this combo.

When I use other non-auto aperture K-mount lenses (not screw mount), I was thinking that I could use the lens in Av mode, set the aperture on the lens a few stops down (knowing the camera will meter at wide open aperture) then use exposure compensation (with the K100DS I only have two stops, but that's fine for now!) to handle the stopped down aperture when I shoot.

Fine in theory, but it seems that when using Av mode in this manner that the body doesn't release the stop-down lever on the lens at all and of course the shot is just over-exposed.

My question is- do the newer series bodies actually release the stop-down lever when using Av mode, so this manner of shooting would work? I'm seriously going to start looking into the used K-7 market once the K-5 hits shelves, and with +- stops, this would work out great with my manual glass! To me, the only miss on the K5 was to continue on with the crippled K mount, which Nikon got right on the D7000.

10-02-2010, 08:56 PM   #2
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Yes- the above should work, in theory. I just tested it with my 85mm FA and exposure was fine. Keep in mind, however, that you're limited to shooting at 5 (or 3, depending on camera model) stops above the minimum aperture.

For reference, here's the right way to meter with manual lenses (this is much easier that the above if you're used to it):

All Pentax DSLRs can properly meter with manual lenses, or when the aperture ring is used to set the aperture on an otherwise-automatic lens.

Instructions on how this is done are found here: https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-manua...7-k-x-etc.html

In a nutshell, simply set the aperture, meter, and shoot. The only catch is that you need to have your camera in M mode (once you meter, the camera will set the shutter speed automatically, thus effectively putting you in Av mode). Metering is accomplished by stopping the lens down using the DOF preview button, or the green button. More details found at the link above- hope this helps!

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10-02-2010, 08:58 PM   #3
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Well, no, in Av mode the lens is not stopped down... At least not on my K7 and Kx...

But if the m42 handling satisfies you, then maybe you can consider modifying your PK lenses so they behave likewise.
All it takes is drilling another locking groove into the lens, so it will lock halfway into the mount (its aperture lever won't be engaged), and it will become a preset lens... Quite easy, and non-destructive, as you can always lock it fully into the mount.
10-03-2010, 06:25 AM   #4
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QuoteOriginally posted by dlacouture Quote
Well, no, in Av mode the lens is not stopped down... At least not on my K7 and Kx...

But if the m42 handling satisfies you, then maybe you can consider modifying your PK lenses so they behave likewise.
All it takes is drilling another locking groove into the lens, so it will lock halfway into the mount (its aperture lever won't be engaged), and it will become a preset lens... Quite easy, and non-destructive, as you can always lock it fully into the mount.
Thank you so much, dlacouture- it's as I thought, but I wanted to verify. Good tip- I'll look into a mod, not afraid of a bit of home tooling! Getting the location down for the lock groove is the only thing I would have to look into.

Adam: the stop-down method is my standard method when using non auto-aperture K mount lenses. After using the screwmount lens, esp. indoors where it's rare to stop down to more than f/4 (depending on lighting, of course) I dig being able to have metering being adjusted constantly for me depending on the shot. I do have to say, though, with any lens (modern or vintage) I'm usually locking aperture 1/2 the time..

Wouldn't it be nice, if, when you mount a lens without aperture contacts (which the body can sense) the bloody body would just stop down the lens in aperture priority? At least this would be a firmware addition giving us 1/4 broken K mount, not having to add the mechanical assembly/electronics to couple with the manual aperture ring position...

10-03-2010, 09:23 AM   #5
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I have long sought a software mod for pentax to enter max and min aperture to allow the camera to work in av mode with k lenses It would be easy to do
10-03-2010, 11:04 AM   #6
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QuoteOriginally posted by virgilr Quote
Wouldn't it be nice, if, when you mount a lens without aperture contacts (which the body can sense) the bloody body would just stop down the lens in aperture priority? At least this would be a firmware addition giving us 1/4 broken K mount, not having to add the mechanical assembly/electronics to couple with the manual aperture ring position...
That would be awesome! (and a great custom function, possibly just a bit power-consuming, but certainly would be worth it)

QuoteOriginally posted by Lowell Goudge Quote
I have long sought a software mod for pentax to enter max and min aperture to allow the camera to work in av mode with k lenses It would be easy to do
That also sounds like a feasible solution, but I have a hunch that the camera might need more info than that, since A lenses go by a logarithmic scale.

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10-03-2010, 12:11 PM   #7
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QuoteOriginally posted by virgilr Quote
Thank you so much, dlacouture- it's as I thought, but I wanted to verify. Good tip- I'll look into a mod, not afraid of a bit of home tooling! Getting the location down for the lock groove is the only thing I would have to look into.
Well, it's quite easy : if you take a look of your lens, you'll notice the aperture actuator right next to the locking notch (see BDimitrov's site for a diagram, where you can see the aperture actuator in its open position, the contrary of its natural position).

I drilled the second locking notch facing the other end of the aperture actuator course (where the aperture actuator actually is when the lens is not mounted on a body).

That's about 1cm counterclockwise from the original locking notch.
10-03-2010, 04:05 PM   #8
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As I thought, dlacouture- I'll take a look. Not that crucial at the moment- one thing I run into with the particular m42 lens I'm using is that at the wide end of the aperture, I need to dial in 2 stops over exposure, and that isn't quite enough- although I prefer under to over exposure, that's for sure! I always shoot raw, so don't mind pushing exposure a bit. That being said, I'll probably wait until the acquisition of a newer generation body that allows +-5 stops before I start modding lenses in this fashion. As well, I won't TOUCH the K 30mm I have- want to keep it original as possible in case I ever decide to sell it.

I always begrudged the K10 for the ISO 1000 setting, but now I realize, I just shoot at ISO 800 and under-expose by 1/2 stop, giving me ISO 1200! I adore ISO 800 on this body- I use it without any reservation- and 1600 is actually quite usable- esp. with Lightroom 3 NR algorithms.

10-03-2010, 04:09 PM   #9
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QuoteOriginally posted by Adam Quote
That would be awesome! (and a great custom function, possibly just a bit power-consuming, but certainly would be worth it)
Adam- I thought the natural position of the stop down lever on the lens is to rest at the actual aperture ring setting- so in reality, wouldn't it take less power on the body to not have to tension this lever constantly? Just an option to the effect to allow the aperture setting to be reflected in the viewfinder" something, like that..
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