Pentax A 50mm F1.7 and K100D

Hi,

I've managed to get hold of a Pentax A 50mm F1.7 lens and if my understanding is correct this will work with full auto focus on my K100D?

Do I need to still set the use aperture ring option to enabled to use it properly?

Any comments on this lens on a digital camera, I guess with the K100D it equates to a 75mm equivalent?

Many thanks,

Craig, you need to sit down quietly in a dark room and ask yourself how a manual-focus lens can magically transform itself into an auto-focus lens.

To save you time, let me tell you that it can't.

What it can do, is to use most of the automated exposure modes provided by modern cameras. But it won't give you auto-focus, and whoever told you that it would needs a kick in the derriere.

Always use it with the aperture ring set to A, and yes, it does give you an angle of view equivalent to that of a 75mm lens.

Don't bother with the "Use aperture ring" option, because you won't be.

G

First off, George is right. Well very, very nearly
On its own, an "A" series 50mm lens (manual focus) cannot magically focus itself - it's missing all the cogs and linkages to do that But the camera can give you focus confirmation (so you turn the focus ring and the camera tells you if it's in focus).
You need to switch the body focus mode to "M" (rather than AF). When you half press the shutter the camera will indicate if it's in focus - look at the green octagon at the bottom (not the red dot overlay).

If you get the (rare) Pentax 1.7x AF converter, then a manual lens becomes auto-focus, but a touch longer focal length too

Matt

Thanks for the info guys... in fairness i think it was me that misunderstood what i was being told about the lens rather than being told that it would auto focus... i did wonder how it would auto focus without the mechanics.. but brain didn't kick in.. apologies

Will try harder to engage brain next time

Hi Craig... I have a K100D and use all Pentax M lenses... the trick, as I was so helpfully told on here, is to set the little lever under the shutter button to open and close the aperture (in custom settings). Put the camera on manual and when you pull the lever round you can set the exposure with the wheel at the back and the aperture with the aperture ring on the lens.... just like in the old days
If I've just repeated what someone else has said... sorry I didn't read the whole thread..
Lee

Even easier is to use the AE-L button.

But this is not relevant to Craig as he has an A lens

How do you do that then?? I didn't know about that??
Lee

In Manual mode with an 'M' lens.........

The Depth of Field Preview lever you mention, Lee, stops down the lens to get a light reading and displays a "+/-" EV.

The AE-L button* does the same thing except instead of displaying the reading, uses it to set the shutter speed for you. You're still free to vary it manually with the wheel before taking the picture if you wish -- so adding a bit of compensation is easy.

AV mode also works with 'M' lenses when you're happy to use the largest aperture only.

* Normally Auto Exposure Lock - but does other things in Manual mode!

Blimey thats fantastic... I can't imagine why I didn't realise that! I thought I'd read that manual cover to cover. This is the first DSLR I've had and I just think its such a good camera... I've got nothing to compare it to obviously but after using Film SLR's its just the perfect progression for me... especially with the M lenses which I really like using.
Thanks for that...Lee

I have M and A lenses so all advise is relevant and gratefully received

I have been playing about with those techniques but the weather hasn't been that great so no decent photgraphic opportunities

Several people have asked about books that do a better job of explaining the cameras features than the manual so t might be appropriate to mention this book here :- http://astore.amazon.com/penta-20/detail/160059185X/002-8377604-0248830

Can anyone confirm whether it's possible or not to use stop-down metering with the K10D like you can with the *ist DS using the methods I describe above, or anything equivalent?

I've read vague comments here about the K10D not working as well as other models with non 'A' lenses - but I don't know the details.

For instance, with Manual mode and a non 'A' lens on a medium aperture, what happens when you press AE-L?

Cheers,

functionally it works exactly the same, except the K10 uses the green button instead of AE-L in this mode. Unfortunately somewhere along the line there is a problem with the K10's metering in stop down mode so the reading you get isn't accurate. It is consistent for a given aperture though so it is possible to get used to it and work around it. I use my Tamron macro lens on my K10D with no problems, despite being unwilling to pay the current going rate of £60 on ebay for a KA adaptall mount.