[Visker]

Bonjour,

I've been led here trying to revive an old enthusiasm for photography starting with the MX, back in 1980. I accumulated just 5 objectives to use with this and all stashed in the attic during several decades.

Until ... I discovered that older vintage K-mounts should be compatible with modern DSLR models. The only lens of my collection which drives this is a Sigma 600mm mirror lens.

So, I have just acquired a K5 DSLR, lo and behold the Sigma 600mm lens does NOT fit. Am I vexed ! I note specific reassurance on this forum that older lenses are upward compatible, so, even if I can't resolve this issue for myself - then I can help other enthusiasts with the knowledge of this issue.

The 3 K-mount flanges (of the 600mm) appear to match the K5 ok. The problem appears to be the black (orientation ?) 'tooth' (of the 600mm) which is offset 10degrees CCW / ACW w r t the 'tooth' of a modern Sigma objective. This tooth clashes in depth with a small plinth in the K5 body - a plinth which presents 2 (electrical) pins (for autofocus ?).

In what year and for which models did Pentax begin to install the 2-pin plinth ? This isue appears to conflictual with compatability of all older lenses.

Cordialamente

[PePe]

The two power contacts were introduced way back in the 1980´s or 1990´s to provide power for the Power Zoom lenses. Thereafter many - but not all - Pentax DSLR´s have the contacts as more functions have been added to the lenses. I am not aware of any compatibility issues with the power contacts.
Is your lens this one ? Sigma Mirror 600mm F8 Lens Reviews - Sigma Lenses - Pentax Lens Review Database If so, it should work fine. Do you know whether the lens mount has been assembled correctly?

[OrchidJulie]

Welcome to PentaxForums! I'll leave the lens mount question to the experts, I'm sure you'll get excellent guidance!

[pschlute]

Basically any PENTAX K mount lens that would have worked with your MX will fit on a modern DSLR

There may be compatibility issues with some third party lens but the vast majority should fit fine

[bdery]

Hi!

If you can share a picture that would be great. You can also write in French if it's easier, I'm from Quebec city so English is my second language just like you.

I'm assuming you refer to the curved flange which protects the aperture lever. On some third-party lenses, this flange is longer than it should be (compare with a native Pentax lens to make sure). If that's indeed the case, you can just buff it out. I did that on a Vivitar Series 1 several years ago. You remove it from the lens (normally 3-4 tiny screws), then use a tool like a dremel or fine grinder to remove the excess metal, use a file (une lime) to make things smooth, maybe use a sharpie to make the metal black, and re-assemble. Looks scary but is really easy.

[Visker]

Hi!

If you can share a picture that would be great. You can also write in French if it's easier, I'm from Quebec city so English is my second language just like you.

I'm assuming you refer to the curved flange which protects the aperture lever. On some third-party lenses, this flange is longer than it should be (compare with a native Pentax lens to make sure). If that's indeed the case, you can just buff it out. I did that on a Vivitar Series 1 several years ago. You remove it from the lens (normally 3-4 tiny screws), then use a tool like a dremel or fine grinder to remove the excess metal, use a file (une lime) to make things smooth, maybe use a sharpie to make the metal black, and re-assemble. Looks scary but is really easy.

Grand merci for your response I was getting towards these same conclusions - what an irony that they have this protective tooth (fin) in place when there is no aperture control fin - the aperture is fixed at f8

In response to others - it seems that the generalisation is false. I have 2 Sigma K mounts and they have the same problem. The 75-250 zoom does however have an aperture fin - so the fixed fin is functional.

I also have an old Tokina objective (24mm) which has no protective fin - so there you have the 2 categories. But the problem is not 'fin / not fin' but rather - to have a fin which in older lenses was offset CCW

PS. bdery - I am an expat englishman in France, mais bien sûr apres 20 ans je parle le franglais tres bien

[pschlute]

n response to others - it seems that the generalisation is false

Sir, you have two lenses that have issues. There are hundreds of third party lenses that do not

[OrchidJulie]

PS. bdery - I am an expat englishman in France, mais bien sûr apres 20 ans je parle le franglais tres bien

Gentlemen, just a friendly reminder that we require English here in PentaxForums. If you're more comfortable with French (or whatever), by all means express yourself, but you'll have to provide a translation to English.

[Kerrowdown]

Welcome to the forum from the Highlands of Scotland

[hcc]

Welcome to the Forum.

To the OP, your described problem might suggest that you purchased a Sigma 600mm without a Pentax K-mount. Sigma sells lenses with many different mounts. Only the K-mount will be compatible to your Pentax K-5.

Hope that the comment may help...

[sota]

pictures, as they say, are worth a thousand words. perhaps one of the mount on the lens would be beneficial?

[Visker]

Welcome to the Forum.

To the OP, your described problem might suggest that you purchased a Sigma 600mm without a Pentax K-mount. Sigma sells lenses with many different mounts. Only the K-mount will be compatible to your Pentax K-5.

Hope that the comment may help...

I have 4 older objective lenses here as used with my Pentax MX. Two of them are Sigma. All have K mount bayonet.


The Pentax 40mm fits the K5 DSLR. The aperture lever does have a protective fin.
The Tokina 24mm fits the K5. Aperture lever without protective fin.

The Sigmas do not fit the K5. Protective fins are offset.


Here's a better way to explain: On the Pentax 40mm, the protective fin is 'in sector' with the smaller of the 3 K-bayonet flanges. On the Sigmas, the protective fin crosses out of the sector defined by the smaller K-bayonet flange.

I'll try to take some photos.

[Sandy Hancock]

There is a long history of Sigma making K-mount lenses. I have owned several over the years, and still have the 35/1.4 Art, with no compatibility issues at all.

Photos are definitely required to solve this mystery.

[Lord Lucan]

I was getting towards these same conclusions - what an irony that they have this protective tooth (fin) in place when there is no aperture control fin - the aperture is fixed at f8In response to others - it seems that the generalisation is false. I have 2 Sigma K mounts and they have the same problem.

What generalisation is it that's false? As far as I know, any K-mount lens made by Pentax (which is from 1975 onwards) will fit any Pentax K-mount camera with a few oddball exceptions. With some combinations there will be limited functionality, but all will fit and allow a photo to be taken.

It is not true however that any nominally K-mount lens made by anybody will fit any K-mount camera made by Pentax or anybody else. Numerous 3rd party lenses, nominally K-mount, have been made by 3d parties, of various quality, and quite a few nominally K-mount cameras have been made by other makers because the basic K-mount "standard" is open-source. At the same time the K-mount itself has evolved over time into something significantly more complex than it was in 1975. A bit of inside knowledge is needed to know whether A will fit B, if A and B were made by different companies at separate times - this forum is the type of place to get that sort of knowledge.

For example Ricoh (long before it became Pentax's parent) were making their own nominally K-mount SLRs and corresponding lenses around 1980, but don't even think about putting one of those old Ricoh lenses on a modern Pentax camera.

That Pentax have managed to keep lens compatibility within their own brand since 1975 is quite a technical achievement. No other camera maker has managed to do this for such a long time right up to the present, although Nikon kept up a long period of back-compatibility until they introduced their mirrorless cameras. However don't expect the same level of compatibilty with third party equipment, because the third party lens makers are inclined to make economies by minimising the changes needed between the different mounts they are selling for, which might have been OK for a while at the time.

There is a long history of Sigma making K-mount lenses. I have owned several over the years, and still have the 35/1.4 Art, with no compatibility issues at all.

Sigma are one of the better independent lens makers, but I have a manual 75-250mm made around 1985 which fits my LX and my K-1, but does not fit a K10-D. It is the usual problem, same as the OP's, that the light baffle by the aperture lever is too long and prevents the bayonet from twisting up fully. I guess Sigma made it as long as it is in order to cover several bases so to speak. The simplest solution is to remove it if you can get the screws undone.

[Visker]

There is a long history of Sigma making K-mount lenses. I have owned several over the years, and still have the 35/1.4 Art, with no compatibility issues at all.

Photos are definitely required to solve this mystery.

Which year do your Sigma lenses date from ? What camera did you 1st use them with ?


Here we go ! img 63 is the Pentax, img 62 is the Sigma

---------- Post added 05-17-23 at 06:47 AM ----------

What generalisation is it that's false? As far as I know, any K-mount lens made by Pentax (which is from 1975 onwards) will fit any Pentax K-mount camera with a few oddball exceptions. With some combinations there will be limited functionality, but all will fit and allow a photo to be taken.

It is not true however that any nominally K-mount lens made by anybody will fit any K-mount camera made by Pentax or anybody else. Numerous 3rd party lenses, nominally K-mount, have been made by 3d parties, of various quality, and quite a few nominally K-mount cameras have been made by other makers because the basic K-mount "standard" is open-source. At the same time the K-mount itself has evolved over time into something significantly more complex than it was in 1975. A bit of inside knowledge is needed to know whether A will fit B, if A and B were made by different companies at separate times - this forum is the type of place to get that sort of knowledge.

For example Ricoh (long before it became Pentax's parent) were making their own nominally K-mount SLRs and corresponding lenses around 1980, but don't even think about putting one of those old Ricoh lenses on a modern Pentax camera.

That Pentax have managed to keep lens compatibility within their own brand since 1975 is quite a technical achievement. No other camera maker has managed to do this for such a long time right up to the present, although Nikon kept up a long period of back-compatibility until they introduced their mirrorless cameras. However don't expect the same level of compatibilty with third party equipment, because the third party lens makers are inclined to make economies by minimising the changes needed between the different mounts they are selling for, which might have been OK for a while at the time.

Sigma are one of the better independent lens makers, but I have a manual 75-250mm made around 1985 which fits my LX and my K-1, but does not fit a K10-D. It is the usual problem, same as the OP's, that the light baffle by the aperture lever is too long and prevents the bayonet from twisting up fully. I guess Sigma made it as long as it is in order to cover several bases so to speak. The simplest solution is to remove it if you can get the screws undone.

Thanks for this 2nd opinion - action needed ! I have already tested the screws with my humble range of 2 micro drivers. One (of 3) screws turned easily, the others resisted and I quit before head damage occurred. I now speculate about an in-situ hacksaw job - with great trepidation ! If I fasten some plastic sheet over the lens hole - with fin protruding (cut precisely) and back it up with masking tape - perhaps I can prevent the invasion of iron filings ?! The plastic can be prevented from abrasive rupture by holding a strip of sheet metal in front ie. so that the saw rubs against this instead.