I've got a beautiful Asahi Prime, but it can't change aperture?

DSLR noob · Feb 7, 2008

Yeah, I figured, I'm glad to have helped, and the aperture blades in an object are a fairly simple system. I took one apart once because I was bored, they don't seem like something that'd break over time with usage, maybe dropping the lens, but not from usage.

Helen B · Feb 8, 2008

Here's what the manual says about exposure etc in Av camera mode with an M lens:

"The aperture remains open regardless of the aperture ring position. The shutter speed changes in relation to the open aperture but an exposure error may occur."

Note that it says that the shutter speed changes with the open aperture, not the set aperture. If the shutter speed does not change as you turn the aperture ring, the camera is not getting data about which aperture has been set, so it can't meter correctly at any other aperture than the one the aperture blades themselves are at.

This is what the manual says for 'All lenses' in M camera mode: "Pictures can be taken with the set aperture value and shutter speed. ... When depth of field is checked (Optical Preview), AE Metering is switched on. Exposure check is possible."

When the Optical Preview is in use, the lens is stopped down to the aperture set on the lens, and the meter can now read properly because it no longer needs to know if there is a difference between the actual aperture and the one that will be used when the picture is taken.

Best,
Helen

Iron Flatline · Feb 8, 2008

I'm always happy when someone discovers old gear. With lenses, they're often better than their contemporaries.

And the Pentax especially has an embarrassment of riches when it comes to legacy lenses.

Dubious Drewski · Feb 13, 2008

This lens is something to get used to. I'm noticing a few things.

First, it's fast! I was out shooting in the snow today at f/22 1/4000 iso100 and my shots were STILL overexposing. I finally slapped an ND8 and and ND4 on there so I could shoot with a wider aperture.

This is also my first prime lens. ...So it turns out it's much more challenging to focus with a prime lens! I didn't anticipate that at all. With a zoom lens, I just compose the shot, extend to maximum zoom, focus, zoom back out, shoot. Perfect focus every time. With a prime, I have to really concentrate to get a good focus. And then I still focus wrong now and then.

I love this lens, but I can see it will take some skill to get the most out of it.

usayit · Feb 13, 2008

f/22 /4000 at ISO 100. Wow it must be bright out there today. Shooting at f/22 you shouldn't have issues with focusing...

Focusing is/was a lot easier back in the day when SLRs were designed with a viewfinder intended to be used with manual focus lenses. It should be a lot easier if you can find a focusing screen that fits your K10D.

Seefutlung · Feb 13, 2008

DSLR noob said:
Yeah, I figured, I'm glad to have helped, and the aperture blades in an object are a fairly simple system. I took one apart once because I was bored, they don't seem like something that'd break over time with usage, maybe dropping the lens, but not from usage.

My first 35mm was a Yashica Rangefinder w/o meter. I used that camera until the wire which connected all the blades wore out and left hanging/dangling blades which moved with the camera.

Gary

DSLR noob · Feb 13, 2008

Seefutlung said:
My first 35mm was a Yashica Rangefinder w/o meter. I used that camera until the wire which connected all the blades wore out and left hanging/dangling blades which moved with the camera.

Gary

the component I took apart (the canon 50mm 1.8 II haha) had all the blades wedged between 2 rings with a pivot point in one ring, and an anchor point in the other. The ring with anchor points would rotate, causing the blades to pivot over the selected pivot point bringing the tips of the blades inward in an overlapping manner. I don't know what Ashi/Pentax did but this system looks fairly fool proof.

Dubious Drewski · Feb 13, 2008

Hmmm, a focusing screen, eh? So I fired up google and went and learned what the heck those are, and I think this thread has convinced me to buy one for my k10. It sounds like a wonderful modification that would make focusing primes easy as pie. (Not to mention the "oohs" and "ahhs" I'd get everytime I'd mention I was shooting with a "modified K10D")

Now... about that warranty of mine. I'm guessing I'd revert back to the regular screen if I ever had the need to send my K10 in for repair. Heh. I wouldn't want them thinking I was taking apart my camera and playing with its insides! No way!

DSLR noob · Feb 14, 2008

I thought Pentax was one of the few to offer interchangable focusing screens for their DSLRs before anyone else started. (as in, they pop in and out, where as most are built in, and removing one is permanent.

Dubious Drewski · Feb 14, 2008

Yay! I bought one for $29.90 including shipping. 10-14 days to ship

. I can't wait.

And yeah, I'm looking at the screen in my K10 now and it has a little spring-latch that allows me to pop it out if I want to. How considerate of them!

Dubious Drewski · Feb 14, 2008

Hmm, I thought I read up on everything I needed to know about these things, but just now I came across this in some other forum:

There's one other thing I should probably caution you on, however. Most focusing aides, including the split image and the microprism, will "black out" when used with small aperture lenses. The kit lens included with most cameras typically has a maximum aperture of 3.5 on the wide end, and 5.6 on the long end. There are very few focusing aides which will work at 5.6, and many won't work very well even at 3.5. With that in mind, there's a good chance that a split image focusing screen may be all but useless with the kit lens included with your camera.

Is there any truth to this? Anyone here use a split-image focusing screen?

Stratman · Feb 18, 2008

I have that same lens, you need to shoot only in "M" mode with it, otherwise it will ALWAYS be wide open, regardless of what aperture you choose on the ring. To meter, set your aperture, then press the" green button" next to the shutter button, it will stop down the lens, and determine the best shutter speed for ya. one thing to note though, seems the K10D doesn't meter very well with the older lenses with the green button, except from about F4-F5.6, higher F stops it seems to over expose, and lower than F4 it seems to underexpose.. so what you need to do, is to pull the power switch, to the DOF preview spot, and then you'll see the meter in your viewfinder, adjust the shutter speed or aperture to where it is dead center, then shoot, will be correctly exposed. or even more fun, buy a hand held light meter, and use it, my pop had an old Kalimar in a bag he bought at an estate sale, and I used it a few weeks ago, and it is pretty much spot on for exposure.

Dubious Drewski · Feb 19, 2008

Actually, you can still meter with it, you just need to do a certain trick - And you're wrong about the aperture, it does work just fine on these old lenses.

First of all, the aperture snaps to position at the instant you take a photo, no matter the lens, so that's fine. You just need to be in aperture priority or manual, etc.

Secondly, for metering, the K10 has that really cool "preview" button at the shutter release that works almost exactly like a shutter release. In manual, it moves the aperture to position so you (and the built-in lightmeter) can see exactly how bright your shot will be.

Pentax has really stopped to consider users who want to use the older equipment, that's for sure! (Removable focusing screen, old-lens compatibility, etc)

selmerdave · Feb 19, 2008

Dubious Drewski said:
Hmm, I thought I read up on everything I needed to know about these things, but just now I came across this in some other forum:

Is there any truth to this? Anyone here use a split-image focusing screen?

This is an issue for lenses with a maximum aperature of f4 or smaller. Certainly for your 1.4 it won't be an issue. Even with the smaller maximum aperatures it's usable but tricky, the exact position of your eye will make the difference between it blacking out and not. FWIW it's only the small split-image circle in the middle of the screen that blacks out.

Dave

Dubious Drewski · Feb 19, 2008

selmerdave said:
This is an issue for lenses with a maximum aperature of f4 or smaller. Certainly for your 1.4 it won't be an issue.

Ah, but my mediocre 70-300 f/4-5.6 and my 18-55 f/3.5-5.6 will be a problem. So I've gotta shell out the big bucks for some f/2.8 variations of these lenses someday!

But...