How to Adapt / IF the Sigma XQ 500mm

**jawats** · 08-04-2018, 12:25 PM

All,

I purchased a Sigma XQ 500mm, which focused fine on the manual camera of the user I purchased it from, but doesn't make it to IF on my K-3. I suspect it may be the adapter - the camera focuses...almost to infinity (and indicates infinity on the outside of the camera), but doesn't reach it visually. If anyone has any experience, I could use the input.

Here's how it works:

The lens itself has an open back (T?) mount, as seen here: https://imgur.com/GPVsVzW.jpg

There is a spacer / adapter which fits into the mount which is graduated on one side (seems to be locked in by the large hand-screw on the lens): https://imgur.com/0DUkWQ2.jpg

The adapter fits either this K-mount (https://imgur.com/5pjmSSq.jpg), or this M42 mount (https://imgur.com/78vpDfm.jpg) which says "T-PS" on the obverse (I am not sure what it means).

There was a random ring here, which fits inside the obverse of the K-mount adapter (https://imgur.com/Si3ACFh), but I am not sure of its purpose: https://imgur.com/K5ipMeB.jpg

Now, I have tried the M42 (with an adapter which permits my Taks to infinity focus) and the K-adapter, and both do not make infinity. Perhaps I have to adjust the mirror, but I am hesitant to open any lens until I have exhausted all other options. Thanks for any advice!

**BigMackCam** · 08-04-2018, 12:45 PM

It sounds like this lens has a T-mount, to which you then fit a T-to-K, T-M42 (or T-PS... "Pentax Screw") or other suitable adapter depending on your mount.

The first thing I'd say is, make sure that the T-to-K and T-PS adapters are fully screwed onto the lens. This sounds obvious, but I've had several T-mount lenses that weren't fully screwed into the relevant adapter due to tight threads, and it only takes a tiny amount to cause the lens to sit too far forward, resulting in no infinity focus.

If the adapters are mounting fully and you still get no joy, then the lens will probably require infinity adjustment.

**jawats** · 08-04-2018, 01:13 PM

Originally posted by BigMackCam

It sounds like this lens has a T-mount, to which you then fit a T-to-K, T-M42 (or T-PS... "Pentax Screw") or other suitable adapter depending on your mount.

The first thing I'd say is, make sure that the T-to-K and T-PS adapters are fully screwed onto the lens. This sounds obvious, but I've had several T-mount lenses that weren't fully screwed into the relevant adapter due to tight threads, and it only takes a tiny amount to cause the lens to sit too far forward, resulting in no infinity focus.

If the adapters are mounting fully and you still get no joy, then the lens will probably require infinity adjustment.

I suspect it may need infinity adjustment.

Now, how...

**BigMackCam** · 08-04-2018, 01:22 PM

Originally posted by jawats

I suspect it may need infinity adjustment.

Now, how...

I don't know your particular lens model. With some mirror lenses, the infinity stop is simply part of the focusing barrel, so you can loosen one or more screws on that and move it slightly to accomodate further rotation. But I honestly don't know if that's going to be the case with your Sigma...

Last edited by BigMackCam; 08-04-2018 at 01:47 PM.

**jawats** · 08-04-2018, 01:25 PM

Originally posted by BigMackCam

I don't know your particular lens model. With some mirror lenses, the infinity stop is simply part of the focusing barrel, so you can loosing one or more screws on that and move it slightly to accomodate further rotation. But I honestly don't know if that's going to be the case with your Sigma...

I cannot find any exterior screws on this thing, so I suspect it's full disassembly. Sigh.

**BigMackCam** · 08-04-2018, 01:30 PM

Originally posted by jawats

I cannot find any exterior screws on this thing, so I suspect it's full disassembly. Sigh.

Have you checked under the rubber focusing grip (assuming it has one)? Often, if you peel that back you'll find one or more screws underneath.

Proceed with caution, though. As I say, I don't know this lens. It would be worth doing some research before you start dismantling...

**jawats** · 08-04-2018, 01:34 PM

Originally posted by BigMackCam

Have you checked under the rubber focusing grip (assuming it has one)? Often, if you peel that back you'll find one or more screws underneath.

Proceed with caution, though. As I say, I don't know this lens. It would be worth doing some research before you start dismantling...

I am doing some research now, before I unscrew anything. Thanks for the advice!

**alfa75ts** · 08-04-2018, 01:51 PM

It is possible that the K-mount adapter (https://i.imgur.com/5pjmSSq.jpg) is two parts, an inner ring held in with grub screws an the outer bayonet adapter.
If so, the inner ring may be reversed as the groove the grub screws fit in is offset.

**jawats** · 08-04-2018, 02:14 PM

Originally posted by alfa75ts

It is possible that the K-mount adapter (https://i.imgur.com/5pjmSSq.jpg) is two parts, an inner ring held in with grub screws an the outer bayonet adapter.
If so, the inner ring may be reversed as the groove the grub screws fit in is offset.

I'll try it every which way. Thanks, Craig.

**i_trax** · 08-04-2018, 10:35 PM

I thought that had the same problem with old Upsilon Tele ( Sigma) 200mm 2.8.
Upsilon Tele 200mm 2.8 Sigma made | Flickr
it turned out that this lens needs to be stopped down significantly to get far objects in focus.

**jawats** · 08-05-2018, 10:55 AM

Originally posted by i_trax

I thought that had the same problem with old Upsilon Tele ( Sigma) 200mm 2.8.
Upsilon Tele 200mm 2.8 Sigma made | Flickr
it turned out that this lens needs to be stopped down significantly to get far objects in focus.

How would one stop down a fixed F8 lens?

**i_trax** · 08-05-2018, 09:36 PM

Originally posted by jawats

How would one stop down a fixed F8 lens?

I see, so that is a mirror lens.

**jawats** · 08-06-2018, 12:43 PM

Originally posted by i_trax

I see, so that is a mirror lens.

Yessir!

08-04-2018, 12:25 PM	#1
jawats Site Supporter Join Date: Nov 2017 Photos: Gallery \| Albums Posts: 756	How to Adapt / IF the Sigma XQ 500mm All, I purchased a Sigma XQ 500mm, which focused fine on the manual camera of the user I purchased it from, but doesn't make it to IF on my K-3. I suspect it may be the adapter - the camera focuses...almost to infinity (and indicates infinity on the outside of the camera), but doesn't reach it visually. If anyone has any experience, I could use the input. Here's how it works: The lens itself has an open back (T?) mount, as seen here: https://imgur.com/GPVsVzW.jpg There is a spacer / adapter which fits into the mount which is graduated on one side (seems to be locked in by the large hand-screw on the lens): https://imgur.com/0DUkWQ2.jpg The adapter fits either this K-mount (https://imgur.com/5pjmSSq.jpg), or this M42 mount (https://imgur.com/78vpDfm.jpg) which says "T-PS" on the obverse (I am not sure what it means). There was a random ring here, which fits inside the obverse of the K-mount adapter (https://imgur.com/Si3ACFh), but I am not sure of its purpose: https://imgur.com/K5ipMeB.jpg Now, I have tried the M42 (with an adapter which permits my Taks to infinity focus) and the K-adapter, and both do not make infinity. Perhaps I have to adjust the mirror, but I am hesitant to open any lens until I have exhausted all other options. Thanks for any advice!

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08-04-2018, 12:45 PM	#2
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,705	It sounds like this lens has a T-mount, to which you then fit a T-to-K, T-M42 (or T-PS... "Pentax Screw") or other suitable adapter depending on your mount. The first thing I'd say is, make sure that the T-to-K and T-PS adapters are fully screwed onto the lens. This sounds obvious, but I've had several T-mount lenses that weren't fully screwed into the relevant adapter due to tight threads, and it only takes a tiny amount to cause the lens to sit too far forward, resulting in no infinity focus. If the adapters are mounting fully and you still get no joy, then the lens will probably require infinity adjustment.

08-04-2018, 01:13 PM	#3
jawats Site Supporter Join Date: Nov 2017 Photos: Gallery \| Albums Posts: 756 Original Poster	Originally posted by BigMackCam It sounds like this lens has a T-mount, to which you then fit a T-to-K, T-M42 (or T-PS... "Pentax Screw") or other suitable adapter depending on your mount. The first thing I'd say is, make sure that the T-to-K and T-PS adapters are fully screwed onto the lens. This sounds obvious, but I've had several T-mount lenses that weren't fully screwed into the relevant adapter due to tight threads, and it only takes a tiny amount to cause the lens to sit too far forward, resulting in no infinity focus. If the adapters are mounting fully and you still get no joy, then the lens will probably require infinity adjustment. I suspect it may need infinity adjustment. Now, how...

08-04-2018, 01:22 PM	#4
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,705	Originally posted by jawats I suspect it may need infinity adjustment. Now, how... I don't know your particular lens model. With some mirror lenses, the infinity stop is simply part of the focusing barrel, so you can loosen one or more screws on that and move it slightly to accomodate further rotation. But I honestly don't know if that's going to be the case with your Sigma... Last edited by BigMackCam; 08-04-2018 at 01:47 PM.

08-04-2018, 01:25 PM	#5
jawats Site Supporter Join Date: Nov 2017 Photos: Gallery \| Albums Posts: 756 Original Poster	Originally posted by BigMackCam I don't know your particular lens model. With some mirror lenses, the infinity stop is simply part of the focusing barrel, so you can loosing one or more screws on that and move it slightly to accomodate further rotation. But I honestly don't know if that's going to be the case with your Sigma... I cannot find any exterior screws on this thing, so I suspect it's full disassembly. Sigh.

08-04-2018, 01:30 PM	#6
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,705	Originally posted by jawats I cannot find any exterior screws on this thing, so I suspect it's full disassembly. Sigh. Have you checked under the rubber focusing grip (assuming it has one)? Often, if you peel that back you'll find one or more screws underneath. Proceed with caution, though. As I say, I don't know this lens. It would be worth doing some research before you start dismantling...

08-04-2018, 01:34 PM	#7
jawats Site Supporter Join Date: Nov 2017 Photos: Gallery \| Albums Posts: 756 Original Poster	Originally posted by BigMackCam Have you checked under the rubber focusing grip (assuming it has one)? Often, if you peel that back you'll find one or more screws underneath. Proceed with caution, though. As I say, I don't know this lens. It would be worth doing some research before you start dismantling... I am doing some research now, before I unscrew anything. Thanks for the advice!

08-04-2018, 01:51 PM	#8
alfa75ts Loyal Site Supporter Join Date: Jun 2009 Location: Melbourne Australia Photos: Albums Posts: 1,356	It is possible that the K-mount adapter (https://i.imgur.com/5pjmSSq.jpg) is two parts, an inner ring held in with grub screws an the outer bayonet adapter. If so, the inner ring may be reversed as the groove the grub screws fit in is offset.

08-04-2018, 02:14 PM	#9
jawats Site Supporter Join Date: Nov 2017 Photos: Gallery \| Albums Posts: 756 Original Poster	Originally posted by alfa75ts It is possible that the K-mount adapter (https://i.imgur.com/5pjmSSq.jpg) is two parts, an inner ring held in with grub screws an the outer bayonet adapter. If so, the inner ring may be reversed as the groove the grub screws fit in is offset. I'll try it every which way. Thanks, Craig.

08-04-2018, 10:35 PM	#10
i_trax Loyal Site Supporter Join Date: Jan 2011 Location: Perth Western Australia Photos: Gallery \| Albums Posts: 2,621	I thought that had the same problem with old Upsilon Tele ( Sigma) 200mm 2.8. Upsilon Tele 200mm 2.8 Sigma made \| Flickr it turned out that this lens needs to be stopped down significantly to get far objects in focus.

08-05-2018, 10:55 AM	#11
jawats Site Supporter Join Date: Nov 2017 Photos: Gallery \| Albums Posts: 756 Original Poster	Originally posted by i_trax I thought that had the same problem with old Upsilon Tele ( Sigma) 200mm 2.8. Upsilon Tele 200mm 2.8 Sigma made \| Flickr it turned out that this lens needs to be stopped down significantly to get far objects in focus. How would one stop down a fixed F8 lens?

08-05-2018, 09:36 PM	#12
i_trax Loyal Site Supporter Join Date: Jan 2011 Location: Perth Western Australia Photos: Gallery \| Albums Posts: 2,621	Originally posted by jawats How would one stop down a fixed F8 lens? I see, so that is a mirror lens.

08-06-2018, 12:43 PM	#13
jawats Site Supporter Join Date: Nov 2017 Photos: Gallery \| Albums Posts: 756 Original Poster	Originally posted by i_trax I see, so that is a mirror lens. Yessir!