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01-27-2009, 01:19 PM   #1
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Dumb noobie question on M42 vs. k mount lenses...

I have a k100d (with the zoom kit lens) and the only other lenses I've purchased are M42's. Awaiting my adaptor ring, so I have not shot anything with the M42's yet.

Locally I see some pretty attractive prices on some k mount lenses as well as more M42 lenses so I'm tempted to buy more lenses even though I know this is that addiction you all talk about and I should curb it.

Anyway, I'm trying to determine which inexpensive k mount lenses offer better combination with the k100d than the M42's. I think I am more interested in things like seeing the M42 aperture setting in my viewfinder and having the camera set my shutter speed for the correct exposure, than in autofocus.

My k100d manual is tough to decipher in this regard, and I realize I can get the answer by searching this forum, but that would take hours, if not days, and the deals I see may not be available for that long.

I hope I've expressed my need clearly enough for someone to respond. This is a wonderful forum, so thanks in advance...

PS... I've also picked up a Spotmatic and want to get back into film, so the M42's will serve a dual purpose.

01-27-2009, 01:42 PM   #2
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welcome to the LBA clinic!

as far as M42 vs K mount, neither (unless you go for KA mount with electrical contacts) show apature in the view finder.

the real difference is the following

M42
Pros
- can use in Av mode and the camera will automatically set exposeure as you stop the lens down

Cons
-switching between M42 and K mount can be a bit of a pain because you need to remove the adaptor from the body
- lens coatings are not as good as K mounts unless you have SMC Takumars

K mount
Pros
- focusing is done at full apature and camera stops down to shoot
- easier to switch between lenses (no adaptor)
- SMC coatings, and generally better lens designs (although I am sure this will bring rebuttals)

Cons
- must use manual mode and meter using green button (K10/K20) or AE-L (on other bodies) or use DOF preview to meter
- Av mode works but only gives full apature , will not stop down lenses
01-27-2009, 02:16 PM   #3
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There are no dumb noobie questions, just dump wannabe-pro answers

EDIT: Just to avoid anybody feeling offended: Of course, nobody on this forum behaves like 'wannabe-pro', but some people at other places do ...

All you said, Lowell, is certainly correct. Allow me to add some things, though

QuoteOriginally posted by Lowell Goudge Quote
M42
Pros
- can use in Av mode and the camera will automatically set exposeure as you stop the lens down
This applies only to M42 lenses with an Auto to Manual Aperture switch, or to those with manual aperture only. Genuine Pentax lenses should be fine mostly, but some third party lenses only stop down when the aperture pin on the back is pressed (auto mode only), which only an M42 camera can do. In that case they can be used wide open only.

QuoteQuote:
-switching between M42 and K mount can be a bit of a pain because you need to remove the adaptor from the body
If you own multiple M42 to K-mount adaptors, you can leave them on the M42 lenses instead of leaving one on the camera, and mount the lenses like a K lens. You have to remove the spring on the adapter, there is a tiny screw. Be sure that your lens sits properly and won't fall off the camera without the spring keeping the adaptor in place!

I for one decided to rather go for manual K-mount lenses if possible, just because they are similarily priced and all have SMC coating, while SMC Takumars are sometimes hard to find...
01-27-2009, 02:36 PM   #4
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QuoteOriginally posted by Noisychip Quote
There are no dumb noobie questions, just dump wannabe-pro answers
actually there are, they are the ones that people feel are so dumb they don't ask, but should have
QuoteQuote:
EDIT: Just to avoid anybody feeling offended: Of course, nobody on this forum behaves like 'wannabe-pro', but some people at other places do ...

All you said, Lowell, is certainly correct. Allow me to add some things, though


This applies only to M42 lenses with an Auto to Manual Aperture switch, or to those with manual aperture only. Genuine Pentax lenses should be fine mostly, but some third party lenses only stop down when the aperture pin on the back is pressed (auto mode only), which only an M42 camera can do. In that case they can be used wide open only.
never seen one of those, but i'll believe you.
QuoteQuote:
If you own multiple M42 to K-mount adaptors, you can leave them on the M42 lenses instead of leaving one on the camera, and mount the lenses like a K lens. You have to remove the spring on the adapter, there is a tiny screw. Be sure that your lens sits properly and won't fall off the camera without the spring keeping the adaptor in place!
there is a great posting here, maybe it was you, about what happens when you do this and foregt there is no locking pin
QuoteQuote:

I for one decided to rather go for manual K-mount lenses if possible, just because they are similarily priced and all have SMC coating, while SMC Takumars are sometimes hard to find...
I started that way but I have had trouble finding some lenses, fast wide angles specifically, and have ventured into the M42 universe, because I came across a 35mm F2 and 28mm F2.5 at good prices.

With respect to the OP and LBA, I will offer one bit of advise.

I have passed up tons of lenses even when the price is good, only because I set a policy that so far, I have not broken.

I only get lenses that either extend my range, or offer larger maximum apature than anything I already own.considering I have F2.8 covered from 28mm to 200mm with 2 really good zooms, I pass up a lot. My interest in MF lenses is therefore a little restrictive, but it is a good sanity check on my LBA, otherwise I would run out to a locak store I know and get the M42 SMC Takumar 200 F3.5, 135mm F2.5 (I already have the SMC K mount in this) a 105mm F2.8 (again I have the SMC K version), a 100mm Macro (I have SMC-M of this) etc. They are all there just waiting for someone with serious LBA

01-27-2009, 02:58 PM   #5
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QuoteOriginally posted by Lowell Goudge Quote
actually there are, they are the ones that people feel are so dumb they don't ask, but should have
Right!

QuoteQuote:
there is a great posting here, maybe it was you, about what happens when you do this and foregt there is no locking pin
It wasn't me But you are right, one could easily forget that.

I remember some guy, who blogged about how he drilled a little hole in the base of his M42 lenses for the locking pin to fit in ... Good idea IMHO, but I'm not brave enough for that kind of lens surgery

QuoteQuote:
I started that way but I have had trouble finding some lenses, fast wide angles specifically, and have ventured into the M42 universe, because I came across a 35mm F2 and 28mm F2.5 at good prices.
How is the M 35/2? Is it the same optically like the FA 35?

QuoteQuote:
I only get lenses that either extend my range, or offer larger maximum apature than anything I already own.considering I have F2.8 covered from 28mm to 200mm with 2 really good zooms, I pass up a lot. My interest in MF lenses is therefore a little restrictive, but it is a good sanity check on my LBA, otherwise I would run out to a locak store I know and get the M42 SMC Takumar 200 F3.5, 135mm F2.5 (I already have the SMC K mount in this) a 105mm F2.8 (again I have the SMC K version), a 100mm Macro (I have SMC-M of this) etc. They are all there just waiting for someone with serious LBA
That sure is a good policy. Buying lenses just because they are cheap doesn't pay in the end. I noticed that for used lenses, the same applies as for new ones: You get what you pay for. There may be some local dealers who have no idea about realistic price levels, but most do ...

There are some very helpful price guides for used K-mount stuff around the net, e.g. the lens review section of this forum.
01-27-2009, 05:24 PM   #6
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QuoteOriginally posted by speedoo Quote
Anyway, I'm trying to determine which inexpensive k mount lenses offer better combination with the k100d than the M42's. I think I am more interested in things like seeing the M42 aperture setting in my viewfinder and having the camera set my shutter speed for the correct exposure, than in autofocus.
I don't think the previous responses addressed this directly, so here's my attempt:

Any lens with an "A" position on the aperture ring will let you view aperture in the viewfinder and allow the camera to use the full range of autoexposure modes, include Av as well as Tv, P, etc. This includes the manual focus lenses marked "Pentax-A" as well as probably some other lines by other manufacturers. It's the "Pentax-M" and "SMC Pentax" (often referred to as the "K" series even though that letter doesn't appear in the name of the lens) lenses that are limited in functionality. That doens't make them useless, though. Green button (AE-L on the K100D) metering is *that* complicated, and the "Pentax-A" lenses are often a lot harder to find and a lot more expensive than the "M" lenses. Exception: the A50/1.7 and A28/2.8 lenses are not really much harder to find or much more expensive than the M50/1.7 and M28/2.8.

The other advantage of the "A" series is that the onboard flash works correctly - which is to say, it automatically sets what it thinks is the correct light level. With older K-mount lenses 9and M42, I assume), the flash always fires full power, meaning your shot will be overexposed unless you figure out what aperture you need to stop down to.
01-27-2009, 05:53 PM   #7
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Wow, thanks all for all that great info. I have some follow up questions, but I will wait until tomorrow or tomorrow night because I expect to have my adaptor ring tomorrow, which means I will finally be able to mount some M42's on my K100d and see what's going on. I should be able to apply some of what's been said in the responses and be a "less dumb noobie"!

Thanks again!
01-28-2009, 01:52 AM   #8
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I will just add that it is entirely possible to avoid the hassle of mounting/removing the adapter when switching back and forth between K-mount and M42 lenses by the simple expedient of.....not switching back and forth. When you carry K-mounts, leave the M42s at home. When you carry M42s, leave the K-mounts at home.

01-28-2009, 03:05 AM   #9
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QuoteOriginally posted by Mike Cash Quote
I will just add that it is entirely possible to avoid the hassle of mounting/removing the adapter when switching back and forth between K-mount and M42 lenses by the simple expedient of.....not switching back and forth. When you carry K-mounts, leave the M42s at home. When you carry M42s, leave the K-mounts at home.
Or bring two bodies? (Which, by the way, I don't have...)
01-28-2009, 03:23 AM   #10
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QuoteOriginally posted by Rense Quote
Or bring two bodies? (Which, by the way, I don't have...)
Another excellent idea.

You could always get a nice film body inexpensively, you know.
01-28-2009, 03:45 AM   #11
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QuoteOriginally posted by Marc Sabatella Quote
Any lens with an "A" position on the aperture ring will let you view aperture in the viewfinder and allow the camera to use the full range of autoexposure modes, include Av as well as Tv, P, etc. This includes the manual focus lenses marked "Pentax-A" as well as probably some other lines by other manufacturers.

Just to reinforce what Marc is saying here: the most K100D (and other dSLR/program camera) compatible lenses are the K-A mount ones.

You know them by both the aperture ring having an "A" setting and the mount itself having electrical contacts (look at your kit lens to see). Apart from Pentax, the third party manufacturers made lenses in K-A mount, and there was a Tamron Adaptall-2 in K-A mount as well.

Due to this forward compatibility and a smaller supply of lenses (Pentax by that time was riding the p&s market hard: they were innovating ahead of the competition in that area).... the K-A lenses tend to go at a premium used. And the K-A adaptall prices are ridiculous!

Like Marc says, the plain K mount lenses are not that much of a pain, but there's no exposure automation. Sometimes I do like that.

The M42's once you get the hang of them - as Mike says - are actually more dSLR compatible than the plain K mounts are. Well, in most ways.

And, yeah, like Mike I go out with just a couple of M42's, no hassle!


(to further entice you to a film body: often even SMC-A lenses come much cheaper on the bay when sold with a camera. That's true of all lenses actually, most of the time.)
01-28-2009, 07:05 AM   #12
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QuoteOriginally posted by Noisychip Quote
How is the M 35/2? Is it the same optically like the FA 35?
Note I am not talking about an SMC-M 35mm F2 which uses a K mount, I am talking about an SMC-Takumar 35mm F2 with M42 screw mount. Just wanted to make that point clear

I am quite sure it is a completely different design than the FA 35 F2.

I have posted a few shots with the 35 F2 and will provide links here

https://www.pentaxforums.com/forums/attachments/post-your-photos/22358d122679...p-ho-ho-ho.jpg
https://www.pentaxforums.com/forums/attachments/pentax-slr-lens-discussion/21...-club-eyes.jpg
01-28-2009, 04:12 PM   #13
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QuoteOriginally posted by Lowell Goudge Quote
Note I am not talking about an SMC-M 35mm F2 which uses a K mount, I am talking about an SMC-Takumar 35mm F2 with M42 screw mount. Just wanted to make that point clear

I am quite sure it is a completely different design than the FA 35 F2.

I have posted a few shots with the 35 F2 and will provide links here

https://www.pentaxforums.com/forums/attachments/post-your-photos/22358d122679...p-ho-ho-ho.jpg
https://www.pentaxforums.com/forums/attachments/pentax-slr-lens-discussion/21...-club-eyes.jpg
Thanks for posting these images! Don't know why, but I thought the Tak 35 was the same design. Never mind ...

Funny cat you got there, hope it isn't stuck in the cup
01-28-2009, 04:19 PM   #14
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Thanks Marc for bringing us back on track ... seems like I forgot to reply to the actual question ...

Must be LBA driving me mad

As you stated, there is no other way than going for A lenses (or F, FAJ, FA, DFA and DA, of course) to see the aperture in the viewfinder. The bad thing is, these are usually not inexpensive, even used ...
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