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Old Mar 8, 2007, 4:12 AM   #1
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Hi,

I'm looking to pick up an old lens for my K100D, for taking some nicer indoors shots, portraits and the like, and also just to experiment and see how it works without spending a huge chunk of cash. I've had a bit of a look around ebay, and found some lens such as http://cgi.ebay.com.au/Pentacon-Auto...QQcmdZViewItem

A little confused as to how manual these are. My understanding is that I'll need an adaptor to mount it on the K100D, and from a few other posts here, I believe I'll need to manual focus, and use the AE/L button to set the aperature before taking the photo, or something? Is this right for the lens linked? Also, if that's not a good option, what sort of mount/focal length/F-stop should I be looking for?

cheers.
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Old Mar 8, 2007, 5:23 AM   #2
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If the seller's pic is good enough look to see the "A" setting on the aprerture ring of the lens.

That means it is at least an AE lens.... other than that likely full manual.... and pretty much for sure if a M42 screw mount.
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Old Mar 8, 2007, 6:26 AM   #3
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the item in question is a Pentacon Auto 1:1.8 50mm Lens. Not sure what the auto part refers to there at all.

Also, another lens i was looking at, a Pentax SMC Takumar m42 1:1.4 f/1.4 50mm
has the following in it's description, wondering if that's an issue for use with K100D.
"Aperture Pin has been snipped off to allow use with m42 adapter on a Sigma SD9."

cheers.
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Old Mar 8, 2007, 1:17 PM   #4
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The Pentacon lens is a screw-mount lens. You would need an adaptor to use it on the digital cameras, and there would be no way that the lens can "talk" to the camera. This means that you either focus with the lens wide open, then stop it down to whatever aperture you want, or you stop down the lens and try to focus through the darkened viewfinder. The manual K-Mount lenses have a lever that the camera uses to stop down the lens, allowing you to focus with the lens wide open, then stop it down when you push the shutter (when used in M mode, that's what you do when you push the AEL button - it temporarily stops down the lens so the camera can meter). You won't have that capability with screw mount lenses. On the other hand, your metering is easier because your lens is stopped down all the time, you won't have to remember to push the button.
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Old Mar 8, 2007, 2:17 PM   #5
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I believe the aperture pin is something that appears on the auto lenses which acted like the lever on K mount lenses (as mtngal described). The pin needs to be pushed in in order for the lens to be able to switch from manual to auto. I don't know if it's a problem (I'm guessing not if it worked OK on the Sigma), but you will need to have the lens switched to manual for it to work properly.

Personally, I like using m42 lenses, as long as they're bright like these 50mm lenses. You can use aperture priority mode with them which you can't do with a manual K mount lens, which means you can use exposure compensation, one of my favorite features. Since the camera will automatically adjust to your aperture in real time, it's a bit faster than a K mount M lens.

I find that in ok light, it's not too hard to look through the lens to compose the shot, even at f4 and higher, and it's nice to get a DOF preview without pushing a button. Of course shooting a very small apertures can be difficult, and that's where a K mount lens would have an advantage.

For an adapter, I suggest you search Ebay for the Roxsen adapter. I got one of these myself for $16 including shipping, which is the starting bid price. I had to try a couple times to avoid bidding against anyone, but last I checked they were posting these things regularly.

It's a very nice adapter. It's all metal and pretty durable, it comes with a leather pouch and a tool for getting the adapter in place and removing it. Most importantly, it supports focusing to infinity, which most cheap adapter do not. This is important because with one of these lenses, anything beyond 15 or 20 feet or so would be out of focus.

The adapter attaches to the body itself and not the lens. This is good if you want to use multiple m42 lenses as you only need one adapter, but makes it very tedious to switch between different mount types.

Good luck!
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Old Mar 9, 2007, 12:33 AM   #6
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The "Auto" here refers to Auto Diaphragm. The lens ignores the aperture ring setting while you are composing the picture. When mounted on a camera with the correct mechanical linkage, the camera automatically steps the lens down to the setting on the aperture ring, meters and takes the picture when you press the shutter release.

Since none of the Pentax digitals (or anything else since the screw mount) have the necessary linkage for an auto diaphragm lens, the feature must be turned off. Otherwise, you would always be shooting with the lens fully open. The is not a problem with Pentax auto diaphragm lenses as they have an Auto/Manual switch that turns off auto diaphragm and allows the aperture ring function as it would in a normal manual focus lens.Some third party lenses lack this switch.

Some M42 adapters are made to automatically turn off auto diaphragm, but to the best of my knowledge no such adapter is available for Pentax.

The bottom line is that at best this lens would be fully manual. Lacking a way to turn off auto diaphragm, it would only be usable at aperture 1.8.

I would buy a Pentax 50mm 1.4 or 1.7. You can get the SMC-M 50mm 1.7 for around $50. The SMC-A 1.7 for around $80. The equivalent 1.4 versions go around 50% higher. Personally, I prefer the 1.7.

The M version requires you to set the aperture ring and focus manually. You can meter with the AEL button. The A version will support autoexposure and allows aperture to be set from the camera, so you only have to worry about focusing.
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Old Mar 9, 2007, 5:22 AM   #7
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dave_g wrote:
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I would buy a Pentax 50mm 1.4 or 1.7. You can get the SMC-M 50mm 1.7 for around $50. The SMC-A 1.7 for around $80. The equivalent 1.4 versions go around 50% higher. Personally, I prefer the 1.7.

The M version requires you to set the aperture ring and focus manually. You can meter with the AEL button. The A version will support autoexposure and allows aperture to be set from the camera, so you only have to worry about focusing.
Not sure I fully understand this, I thought you said that new DSLRs would not have the required interface to support auto exposure, or did that only apply to the prev. lens I had listed?
Am I to understand that the Pentax SMC-M lens would function the same as an M42 lens? set aperture ring manually, put camera in aperture priority mode and set value to match lens and it will then calculate shutter speed? When you say AEL button is used to meter, does that mean pressing the AEL button will measure light and adjust settings appropriately for the moment at which the AEL button is pressed?

Also, with the lens you are suggesting, the Pentax SMC-M 50mm 1.7, are these called K-mount? My understanding is that the M42 adaptors convert the M42 to a K mount?

Sorry for the barrage of questions, really trying to get a handle on this stuff.
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Old Mar 9, 2007, 6:02 AM   #8
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An M42 lens with adapter for K-mount (thats the mount of your K100D) is as manual as you can get with Pentax.

You will be able to use M42 lenses in Av mode as well as in M mode, but you'll have to change the aperture yourself on the lens, not with the dial on the camera. In Av mode the camera will choose the correct shutter speed to go with the aperture you've selected on the lens. Also the viewfinder will get dimmer as you make the aperture smaller.

With M42 lenses you will not have the focus confirmation beep as with K-mount lenses. (at least I don't have it on my cosinor 35mm f2.8 )

That being said, there are true gems among those M42 lenses.

K-mount lenses are a whole different thing considering usage.

You will have manual focus only with older lenses, but the camera will give you a green light and/or a beep when it thinks you've focused correctly. very handy.

Exposure can be automatic with all K-mount lenses.

With M-lenses, you can only use M mode, but if you press the AE-L button, the camera will expose automatically with the aperture you've selected on the lens.
However, unlike with M42 lenses, the viewfinder will not get dimmer as you select a smaller aperture. This is because the camera is able to interact with the lens, and keeps the diaphragm blades open until you press the AE-L button. Then it will briefly stop down the aperture, select a correct shutter speed, and tell you you're ready to shoot.

A-lenses are a lot easier. They simply have everything a more recent lens would have, except the autofocus. You cna use them in P,Tv,Av,M mode and all other programs.

Most Pentax brand M and A lenses are outstanding in optical quality. Some third party manufacturers have very good ones too. (Kiron, Vivitar,...)

And then you have the more recent AF lenses that will do anything you want.
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Old Mar 12, 2007, 12:40 AM   #9
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Yes, SMC-M would normally indicate a K mount. K mount lenses are normally referrred to as SMC-something (A, K, M,F, FA, FAJ, DA ). There's a good write-up here that covers both nomenclature and labeling of both K mount and screw mount (M42) Pentax lenses.

http://www.jcolwell.ca/_SPLOSdb/

Click on the SPlosDB.PDF link. You have to be careful with e-Bay listings though. There is not much consistency in the descriptions people use. For instance,an SMC Takumarlens (which is screw mount) may say SMC M in the description. Whenver possible, check the picture, or ask the seller specifically if the lens is K mount (sometimes referred to as bayont mount) or screw mount.

It's not quite correct to say that an M42 adapter "converts" an M42 to K mount, since as TDN pointed out above not all of the capabilities of a K mount lens are provided,. An adapterdoes allow an M42 mount lens to be used on a K mount camera.
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Old Mar 12, 2007, 2:53 AM   #10
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dave_g wrote:
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K mount lenses are normally referrred to as SMC-something (A, K, M,F, FA, FAJ, DA ).
SMC stands for Super Multi Coated and doesn't have anything to do with the mount, though I'm not sure I've ever seen a screw mount lens that had SMC on it. Rather, it would spell it out "Super-Multi-Coated".

From my own limited experience shopping for used lenses, every lens that said Pentax on it was a K mount, and were usually labeled M, A, F, or FA.

Most screw mount lenses are labeled Asahi or Takumar, though I know some K mount lenses are as well. I have a K mount Takumar which says "(BAYONET)" on it.

These are generalizations though, and there may be exceptions that I haven't seen.

As stated, be careful on the ebay listings. If you're going by the pictures, make sure that the picture is supposed to be of the actual item. Some listings might say that it will work on a K mount camera even though it's a screw mount only because the seller heard all Pentax lenses will work, so be doubly sure it's the right mount.

Never hesitate to send the seller a question, it's very quick and easy. I ask questions even when I doubt I'll bid on something, and occasionally I find out the item is way better than what the listing makes it out to be, which often means I'll get a great price.
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