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04-15-2009, 11:20 AM   #1
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Av mode with lens not on A position

Recently with my Pentax-A 50mm 1.4 I accidentally used Av instead of M as I wanted to. I set the aperture (on the lens aperture ring) to F4, but on the body it was 1.4. When I realized this I quickly switched to Mmode. But the pics turned out okay, the camera also meter okay in my opinion, no obvious underexposure nor overexposure compare to those taken after with the correct M mode. But, which aperture was actually used, my guess is F4 and not F1.4 (EXIF says 1.4 though). Am I correct?

But if that's the case, then what would stop me from using for example, a fully stop down lens, like a Jupiter-9 85mm preset or my nikon mount Tokina lens, in a similar manner? I.e. Av mode, set any aperture on the lens and let the camera meter automatically without me pushing green/AE-L button? From what I read (mostly from this forum), I was under contention that this is not possible for all aperture setting except the maximum aperture setting / wide open.

I did a simple test, pointing my camera at a fixed object, with M mode f2.0 my AE-L button metering gave me shutter 1/50, turned aperture ring to f4.0 and click AE-L button again and it gave me 1/5. Switched to Av mode, and the camera auto meter gave me 1/5, I turned the aperture ring back to f2.0 and it changed to 1/50.

It's 3AM in the morning and I must have missed something.. Please enlighten me so I can get some sleep lol. As always, thanks in advance.

04-15-2009, 11:39 AM   #2
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QuoteOriginally posted by sajah Quote
Recently with my Pentax-A 50mm 1.4 I accidentally used Av instead of M as I wanted to. I set the aperture (on the lens aperture ring) to F4, but on the body it was 1.4. When I realized this I quickly switched to Mmode. But the pics turned out okay, the camera also meter okay in my opinion, no obvious underexposure nor overexposure compare to those taken after with the correct M mode. But, which aperture was actually used, my guess is F4 and not F1.4 (EXIF says 1.4 though). Am I correct?
The aperture when the photo is taken is actually F/1.4, regardless of the setting of the lens's aperture ring.

QuoteOriginally posted by sajah Quote
But if that's the case, then what would stop me from using for example, a fully stop down lens, like a Jupiter-9 85mm preset or my nikon mount Tokina lens, in a similar manner? I.e. Av mode, set any aperture on the lens and let the camera meter automatically without me pushing green/AE-L button? From what I read (mostly from this forum), I was under contention that this is not possible for all aperture setting except the maximum aperture setting / wide open.
The Jupiter lens is already in stop down mode when the photo is taken. So Av works. This also applies to Nikon-mount lens.

This is different with a PK-mount lens (or PKA-mount lens at non-A aperture setting). The lens is in full aperture mode, and relies on the camera to stop down when the photo is taken. The camera does NOT stop down the lens in Av mode. Thus the photo is taken at full aperture.
04-15-2009, 12:30 PM   #3
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QuoteOriginally posted by SOldBear Quote
The aperture when the photo is taken is actually F/1.4, regardless of the setting of the lens's aperture ring.

The lens is in full aperture mode, and relies on the camera to stop down when the photo is taken. The camera does NOT stop down the lens in Av mode. Thus the photo is taken at full aperture.
Oh i see. Now everything's making sense again. Thank you!
But that means this pic is taken with F1.4 instead of F4! It explains the OOF highlights but I thought the DOF in this pic is more of F4 than F1.4, but what do I know I only have a DSLR for about one and a half month :ugh:



QuoteOriginally posted by SOldBear Quote
The Jupiter lens is already in stop down mode when the photo is taken. So Av works. This also applies to Nikon-mount lens.
So for M42 and all stop down lenses Av works huh, dang how come I never heard about it

Thanks again, now I can go to sleep.
04-15-2009, 12:54 PM   #4
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QuoteOriginally posted by sajah Quote

So for M42 and all stop down lenses Av works huh, dang how come I never heard about it
It is a deep truth kept by the Guardians of the Ancient Glass...

Steve

04-15-2009, 07:31 PM   #5
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I shoot my Takumar 135 M series lens wide open in Av mode so that I have simple access to exposure compensation and don't have to fuss with stop down metering.
04-15-2009, 10:24 PM   #6
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QuoteOriginally posted by stevebrot Quote
It is a deep truth kept by the Guardians of the Ancient Glass...

Steve


QuoteOriginally posted by Robert S Donovan Quote
I shoot my Takumar 135 M series lens wide open in Av mode so that I have simple access to exposure compensation and don't have to fuss with stop down metering.
I see, it's good to know that I have the option to use Av mode with my manuals lenses.
04-15-2009, 10:59 PM   #7
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QuoteOriginally posted by Robert S Donovan Quote
I shoot my Takumar 135 M series lens wide open in Av mode so that I have simple access to exposure compensation and don't have to fuss with stop down metering.

I found that out yesterday with my Super Tak 55 f1.8 while playing with it after my adapter arrived!
04-16-2009, 01:17 AM   #8
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This is somewhat related: I dont have a K lens, I'm wondering if K lenses are stop down lenses like M42 or rely on camera to open/close the aperture like M and A lenses? Again only from what I gathered off internet, I cant seem to find any differences between the K and M lenses

04-16-2009, 10:14 AM   #9
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QuoteOriginally posted by sajah Quote
This is somewhat related: I dont have a K lens, I'm wondering if K lenses are stop down lenses like M42 or rely on camera to open/close the aperture like M and A lenses? Again only from what I gathered off internet, I cant seem to find any differences between the K and M lenses
There may be a size and cosmetic differences between the K and M lenses, but the camera/lens mechanicals are the same. You cannot use stop down on the K lens. The aperture is wide open when the lens is mounted. Someone on this forum figured out that if you release the lens and gently turn it towards removal, the lever no longer contacts the aperture control on the lens, and it works just like an M42. I have used this trick on cameras that don't have depth of field preview, but I cannot recommend it. I have high enough blood pressure without the stress of having a lens that is not completely mounted on the camera.
04-16-2009, 01:14 PM   #10
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QuoteOriginally posted by sajah Quote
Again only from what I gathered off internet, I cant seem to find any differences between the K and M lenses
There is no functionality difference at all - the M series lenses are K series lenses that were re-designed to be a bit smaller. BTW, as you may know, the letter "K" doesn't actually appear on the "K" series lenses. Officially, they are simply "SMC Pentax", as opposed to "SMC Pentax-M".

Last edited by Marc Sabatella; 04-17-2009 at 10:55 AM.
04-16-2009, 05:33 PM   #11
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QuoteOriginally posted by Canada_Rockies Quote
There may be a size and cosmetic differences between the K and M lenses, but the camera/lens mechanicals are the same. You cannot use stop down on the K lens.
QuoteOriginally posted by Marc Sabatella Quote
There is no functionally difference at all - the M series lenses are K series lenses that were re-designed to be a bit smaller. BTW, as you may know, the letter "K" doesn't actually appear on the "K" series lenses. Officially, they are simply "SMC Pentax", as opposed to "SMC Pentax-M".
I see. No wonder I didnt find anything on the web. Yeah I know about the imaginary "K"

QuoteOriginally posted by Canada_Rockies Quote
The aperture is wide open when the lens is mounted. Someone on this forum figured out that if you release the lens and gently turn it towards removal, the lever no longer contacts the aperture control on the lens, and it works just like an M42. I have used this trick on cameras that don't have depth of field preview, but I cannot recommend it. I have high enough blood pressure without the stress of having a lens that is not completely mounted on the camera.
Thanks for the tip! I wouldn't probably need it but still it's good to know
04-17-2009, 08:59 AM   #12
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QuoteOriginally posted by sajah Quote
So for M42 and all stop down lenses Av works huh, dang how come I never heard about it

Not exactly. For K/M k-mount glass Av will always shoot wide-open regardless of the aperture ring position.

For M42 or other non-K-mount glass you can make use of Av but you are manually stopping down the lens; depending on the lens design this may involve presetting via ring then activating a switch between wide open and stopped-down.
04-17-2009, 09:31 AM   #13
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Yeah, when I said stop down lenses I meant for non-K-mount lenses. Anyway, not knowing this actually gave me some benefits, since I 'was forced' to use M mode and learned a thing or two about it :ugh:
04-17-2009, 02:55 PM   #14
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QuoteOriginally posted by AndrewG NY Quote
Not exactly. For K/M k-mount glass Av will always shoot wide-open regardless of the aperture ring position.
For the sake of clarity "shoot" should be "meter".
04-17-2009, 03:12 PM   #15
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QuoteOriginally posted by Mike Cash Quote
QuoteOriginally posted by AndrewG NY  Quote
Not exactly. For K/M k-mount glass Av will always shoot wide-open regardless of the aperture ring position.
For the sake of clarity "shoot" should be "meter".
No, no. It is "shoot" alright, not just "meter."

Unless you do the "not rotating the lens all the way" stop-down trick.
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