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09-07-2009, 01:35 AM   #1
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M42 lenses & adapter

Hello,

Before I take the plunge and purchase some M42 primes for use with a K-7, can I just check that I have all the facts?
  • A major thing to be aware of is that you have to make sure that the adapter is the correctly flanged type. Some are too thin and so can't achieve infinity forcus.
  • The 'downside' is manual focus, which I prefer anyway.
  • You can still use the inbuilt lightmeter and you'll adjust aperture manually, which I'm used to anyway

Is that about it - are there any other gotchas I need to be looking out for? Can anyone point me to a discussion of these? Ie does a 1.4 Jena really behave like a 1.4 Jena aperture-wise doing this?

Many thanks in advance

09-07-2009, 01:41 AM   #2
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QuoteOriginally posted by Nass Quote
Hello,

Before I take the plunge and purchase some M42 primes for use with a K-7, can I just check that I have all the facts?
  • A major thing to be aware of is that you have to make sure that the adapter is the correctly flanged type. Some are too thin and so can't achieve infinity
Wrong, wrong, wrong! You don't want a flange type at all. The thickness of the flange, no matter how thin is what causes loss of infinity focus. The original Pentax adapter is the best and it sits down inside of the k-mount, with NO external flange at all.

Regards,
Mike
09-07-2009, 02:02 AM   #3
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QuoteOriginally posted by X Man Quote
Wrong, wrong, wrong! You don't want a flange type at all. The thickness of the flange, no matter how thin is what causes loss of infinity focus. The original Pentax adapter is the best and it sits down inside of the k-mount, with NO external flange at all.

Regards,
Mike
Lorrdylordylord what a plum I am . I just got too excited at the prospect of finding a way to use some lenses of the quality I craved!

But - that error aside, in terms of the mechanics though, I'm not going to have to start shaving metal pins or putting bits of filler metal into weird places or leaving the thing only half screwed on to use them (clearly though do your homework first, ie some m42 lenses seem to clash with the mirror)?

Many thanks Mike
09-07-2009, 02:28 AM   #4
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Just some useful links for anyone doing research on M42 & Pentax digital compatibility like I am. If I find others I'll add them.

Pentax Digital Pentax Lens Types + K Mount info - summary

09-07-2009, 11:16 AM   #5
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QuoteOriginally posted by Nass Quote
Lorrdylordylord what a plum I am . I just got too excited at the prospect of finding a way to use some lenses of the quality I craved!

But - that error aside, in terms of the mechanics though, I'm not going to have to start shaving metal pins or putting bits of filler metal into weird places or leaving the thing only half screwed on to use them (clearly though do your homework first, ie some m42 lenses seem to clash with the mirror)?

Many thanks Mike
With the Pentax adapter, you should be 100% safe in regards to mount compatibility. As for the lens mirror issue reported on another recent thread...that kind of thing is extremely rare and is the result of Yashica having developed a line of lenses (DX) for a particular body series that were not even compatible with other Yashica bodies. Go figure...

The only general issues regarding M42 lenses are:
  • Proper adapter
  • Ability to have fully manual aperture
The first point, you are aware of. The last is not well appreciated until you get a lens that will not stop down for metering or exposure. The key to the second point is to only buy lenses that lack the auto-aperture pin or have the "auto/manual" switch. Almost all M42 lenses will pass this rule. The most obvious exceptions are certain Russian lenses of recent manufacture that have the auto-aperture pin, but lack any way to use the lens in manual aperture mode (e.g. MC Zenitar 16/2.8, Helios 44M-4, and others in M42/Zenit mount).

Steve
09-07-2009, 01:20 PM   #6
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If you are using the genuine Pentax adapter with Pentax lenses there should not be any mounting issues. Mirror clearance with protruding rear elements and non pentax M42 mechanism is what you need to check in case of non-Pentax M42 lenses. Some manufactureres of lenses across different mounts might have aperture level/pin shields which interfere with lens mounting and mirror up/down operations
09-07-2009, 01:55 PM   #7
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You see, Pentax made the K mount so that it fullfilled two criteria:

1) It has the same registration distance as the m42 mount, that is the distance between the lens and the sensor (film in those days) are the same.
2) The diameter of the K mount is larger than that of the m42 mount and leaves room for an adapter in between.

If you use an adapter with a flange, even if it is just a mm or so, it will be like adding a thin extension tube in between lens and camera. This will enable you to focus a little bit closer, but you will also lose the ability to focus at infinity. And in that end 1 mm has a large effect.

So why are their adapters with a flange?
They are easier to build (and will cost less and sound like a good buy).
I suspect some cheap m42-to-K mount adapters are simply K mount versions of adapters for other brands, brands with a shorter registration distance, where a flange is needed, such as Sony (Minolta), Canon EF, Olympus 4/3, Konica etc. If you have a machine that makes simple flanged m42 adapters, it must be tempting to make some also for brands that should not have a flange (Pentax, Nikon etc), and to sell them without being to clear about the effect.
09-07-2009, 04:08 PM   #8
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I've got a genuine adaptor and one of these -

M42 lenses on Pentax K

from the UK company SRB-Griturn, and the copy fits better, although both work perfectly well.

On their website it mentions using a 'pen top' to release the spring clip but mine came with the proper tool, exactly like the Pentax one.

They show a Euro and American flag on their website so I assume they ship internationally.

I have no connection with SRB-Griturn, but they have always proved good to deal with in my experience.

09-08-2009, 01:36 AM   #9
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Thanks fellas, your clarifications have been useful and are appreciated. The M42 world is a dangerous one for marital harmony - there seem to be fabulous old lenses around with prestigious names and sexy f stops...
09-08-2009, 02:38 AM   #10
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You got that right Nass, although nowhere near as dangerous grabbing the modern equivalents. You'd be surprised at the number of decent lenses you can get for a decent price with a bit of discipline. And keep your eyes on the old SLR auctions, especially when the seller forgets to mention the attached lenses.
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