Samyang 800mm + T2 -> Pentax infinity focus problem

k7bb · 06-20-2010, 02:46 AM

just bought a Samyang 800mm f8 mirror lens, it needed a T2 to Pentax mount for my K7.

tried 2 mounts but all cannot infinity focus, but T2 mount to Nikon ok.

please advice... do I have to do any adjustment with the T2 mount?

thanks in advance.

bigdog104 · 06-20-2010, 07:16 AM

Is the Nikon a "full frame" dSLR? That might be the difference.

According to Wikipedia:

"Because the T-mount has a long flange distance of 55mm and most 35mm cameras have shorter flange distances, a simple mechanical adapter called T/T2-Ring is needed to adapt a T-mount lens to any camera body without optical correction to achieve infinity focus."

I am thinking that the APS-C sensor in the K-7 would need a different adapter than one used on the FF sensor.

k7bb · 06-20-2010, 08:39 AM

Originally posted by bigdog104

Is the Nikon a "full frame" dSLR? That might be the difference.

According to Wikipedia:

"Because the T-mount has a long flange distance of 55mm and most 35mm cameras have shorter flange distances, a simple mechanical adapter called T/T2-Ring is needed to adapt a T-mount lens to any camera body without optical correction to achieve infinity focus."

I am thinking that the APS-C sensor in the K-7 would need a different adapter than one used on the FF sensor.

thanks bigdog

my Nikon is FF because it is a film camera

understand what you mean; my T2 mount is for FF PK mount instead of APS-C.

but it named can be used for k20d, kx, etc.

marcinski · 06-20-2010, 12:05 PM

No, it has nothing to do with FF and APS. The mount is the same. You simply have to adjust the infinity on focusing ring. Can't give you specific instructions for this lens but look for set of screws that will let you adjust focusing ring.

Marcin

Ben_Edict · 06-20-2010, 03:35 PM

Originally posted by bigdog104

Is the Nikon a "full frame" dSLR? That might be the difference.

According to Wikipedia:

"Because the T-mount has a long flange distance of 55mm and most 35mm cameras have shorter flange distances, a simple mechanical adapter called T/T2-Ring is needed to adapt a T-mount lens to any camera body without optical correction to achieve infinity focus."

I am thinking that the APS-C sensor in the K-7 would need a different adapter than one used on the FF sensor.

NO - that is not correct.

A T2 adapter is a T2 adapter and Pentax kept the flange distance between the 35mm film cameras and the current line of APS-C and all future cameras, that will be able to use K-mount lenses.

This is one of Pentax' main selling points!

Ben

Ben_Edict · 06-20-2010, 03:42 PM

Originally posted by k7bb

just bought a Samyang 800mm f8 mirror lens, it needed a T2 to Pentax mount for my K7.

tried 2 mounts but all cannot infinity focus, but T2 mount to Nikon ok.

please advice... do I have to do any adjustment with the T2 mount?

thanks in advance.

Though there is the possibility, that the lens does indeed not reach infinity focus, because the focusing ring might be misaligned, I would be hesitant with such an explanation.

First of all, you should be very(!) aware, that focusing a slow 800mm lens is anything but easy. If this is a new lens for you, I would not be surprised, if you need several days, before you even start getting the focus right!

Than you should be aware, that a mirror lens has usually not a mechanical stop at infinity - you can focus beyond infinity for several reasons - and the infinity mark on the focusing ring might also be just a rough indication and the real infinity focus may be offset from the indicator.

Also, you should consider, that if focusing a 800mm lens to infinity means, that you will have a lot of air between your camera and your target. This long distance will reduce sharpness under most circumstances significantly, due to haze, atmospheric turbulences etc.

–– I had a similar experience with a Pentax 500/4.5 lens, which - I thought - could not be focused to infinity. I even disassembled the focusing unit and readjusted it in a way, that I could focus beyond infinity, just to be on the safe side. But after a lot of trials, I finally could prove, that all the lack of sharpness was only due to atmospheric conditions during my initial tests.

Ben

bigdog104 · 06-20-2010, 03:51 PM

Originally posted by Ben_Edict

NO - that is not correct.

A T2 adapter is a T2 adapter and Pentax kept the flange distance between the 35mm film cameras and the current line of APS-C and all future cameras, that will be able to use K-mount lenses.

This is one of Pentax' main selling points!

Ben

Well I guess I will lose some reputation points for that suggesting it might be the APS-C vs FF.

k7bb · 06-20-2010, 05:25 PM

thanks Marcin & Ben, also bigdog

another thing is, afterwards attached the lens to a Canon DSLR (as you know crop factor is 1.6x instead of 1.5x), I got wider view angle and can be infinity focus...

so, Ben, I'll try again with your advice. if still not work, I think I have to search 3rd mount

thanks all

noblepa · 06-20-2010, 08:03 PM

Are you sure that the T2 adapter you're using is for a k-mount? I have a T2 adapter that I use on a cheap 500mm mirror lens I picked up on eBay. It works perfectly on my K10D, as well as on my Pentax 35mm film cameras.

You say that the lens can focus to infinity on other cameras, so it is probably not the lens. The only way I can think of that it would not focus to infinity on a Pentax camera is if you were using a T2/M42 screwmount adapter, along with a M42/K-mount adapter that has the large flange outside the lens mount.

k7bb · 06-20-2010, 11:34 PM

thanks noblepa,

since I have never seen M42 mount, can only trust the packing, it is T2...

Ben_Edict · 06-21-2010, 01:14 AM

Originally posted by k7bb

thanks noblepa,

since I have never seen M42 mount, can only trust the packing, it is T2...

Could you provide some detailed images of the lens' rear? The images, you linked to, are mostly of the front element and do not give a clue about the mount.

Thanks,
Ben

k7bb · 06-21-2010, 09:46 AM

photos of the adapter and lens mount

Ben_Edict · 06-21-2010, 01:48 PM

Originally posted by k7bb

photos of the adapter and lens mount

O.k. - thanks for the images. Looks fine to me, with the T2 thread on the lens and the T2-K adapter. Can you screw the T2 adapter fully onto the lens threads? The lens flange and the flange of the adapter should be flush, with no space between.

If that is also thew case, the only other thing, I would like you to do,: please provide two or three images, where you tried to achieve infinity focus and couldn't. Perhaps we can draw a conclusion from those.

Ben

marcinski · 06-21-2010, 02:22 PM

I'm pretty sure that it's adjustment problem. I had the same with my russian lens. The fact that it works with other mounts supports it. Look for a way to adjust infinity range on focusing ring. If you are not confident enough to do it, give to professional but it should be relatively straightforward. I did it myself on my lens.
Marcin

Ben_Edict · 06-21-2010, 03:44 PM

Originally posted by marcinski

I'm pretty sure that it's adjustment problem. I had the same with my russian lens. The fact that it works with other mounts supports it. Look for a way to adjust infinity range on focusing ring. If you are not confident enough to do it, give to professional but it should be relatively straightforward. I did it myself on my lens.
Marcin

What kind of adjustment problem would that be, if the same lens reaches infinity on one brand camera and not on the next, if both are connected by a T2-adapter? The T2 system should make the lens itself fully independent of the camera system, as the adapters compensate the different register distances of the different bodies.

Ben

06-20-2010, 02:46 AM	#1
k7bb Inactive Account Join Date: Jun 2010 Location: HK Posts: 16	Samyang 800mm + T2 -> Pentax infinity focus problem just bought a Samyang 800mm f8 mirror lens, it needed a T2 to Pentax mount for my K7. tried 2 mounts but all cannot infinity focus, but T2 mount to Nikon ok. please advice... do I have to do any adjustment with the T2 mount? thanks in advance.

06-20-2010, 03:35 PM	#5
Ben_Edict Veteran Member Join Date: Jul 2007 Location: SouthWest "Regio" Photos: Albums Posts: 3,309	Originally posted by bigdog104 Is the Nikon a "full frame" dSLR? That might be the difference. According to Wikipedia: "Because the T-mount has a long flange distance of 55mm and most 35mm cameras have shorter flange distances, a simple mechanical adapter called T/T2-Ring is needed to adapt a T-mount lens to any camera body without optical correction to achieve infinity focus." I am thinking that the APS-C sensor in the K-7 would need a different adapter than one used on the FF sensor. NO - that is not correct. A T2 adapter is a T2 adapter and Pentax kept the flange distance between the 35mm film cameras and the current line of APS-C and all future cameras, that will be able to use K-mount lenses. This is one of Pentax' main selling points! Ben Last edited by Ben_Edict; 06-20-2010 at 03:43 PM.

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06-20-2010, 07:16 AM	#2
bigdog104 Senior Member Join Date: Apr 2010 Location: South Carolina Photos: Gallery Posts: 289	Is the Nikon a "full frame" dSLR? That might be the difference. According to Wikipedia: "Because the T-mount has a long flange distance of 55mm and most 35mm cameras have shorter flange distances, a simple mechanical adapter called T/T2-Ring is needed to adapt a T-mount lens to any camera body without optical correction to achieve infinity focus." I am thinking that the APS-C sensor in the K-7 would need a different adapter than one used on the FF sensor.

06-20-2010, 08:39 AM	#3
k7bb Inactive Account Join Date: Jun 2010 Location: HK Posts: 16 Original Poster	Originally posted by bigdog104 Is the Nikon a "full frame" dSLR? That might be the difference. According to Wikipedia: "Because the T-mount has a long flange distance of 55mm and most 35mm cameras have shorter flange distances, a simple mechanical adapter called T/T2-Ring is needed to adapt a T-mount lens to any camera body without optical correction to achieve infinity focus." I am thinking that the APS-C sensor in the K-7 would need a different adapter than one used on the FF sensor. thanks bigdog my Nikon is FF because it is a film camera understand what you mean; my T2 mount is for FF PK mount instead of APS-C. but it named can be used for k20d, kx, etc.

06-20-2010, 12:05 PM	#4
marcinski Forum Member Join Date: Jan 2009 Location: Dundee, Scotland Posts: 95	No, it has nothing to do with FF and APS. The mount is the same. You simply have to adjust the infinity on focusing ring. Can't give you specific instructions for this lens but look for set of screws that will let you adjust focusing ring. Marcin

06-20-2010, 03:42 PM	#6
Ben_Edict Veteran Member Join Date: Jul 2007 Location: SouthWest "Regio" Photos: Albums Posts: 3,309	Originally posted by k7bb just bought a Samyang 800mm f8 mirror lens, it needed a T2 to Pentax mount for my K7. tried 2 mounts but all cannot infinity focus, but T2 mount to Nikon ok. please advice... do I have to do any adjustment with the T2 mount? thanks in advance. Though there is the possibility, that the lens does indeed not reach infinity focus, because the focusing ring might be misaligned, I would be hesitant with such an explanation. First of all, you should be very(!) aware, that focusing a slow 800mm lens is anything but easy. If this is a new lens for you, I would not be surprised, if you need several days, before you even start getting the focus right! Than you should be aware, that a mirror lens has usually not a mechanical stop at infinity - you can focus beyond infinity for several reasons - and the infinity mark on the focusing ring might also be just a rough indication and the real infinity focus may be offset from the indicator. Also, you should consider, that if focusing a 800mm lens to infinity means, that you will have a lot of air between your camera and your target. This long distance will reduce sharpness under most circumstances significantly, due to haze, atmospheric turbulences etc. –– I had a similar experience with a Pentax 500/4.5 lens, which - I thought - could not be focused to infinity. I even disassembled the focusing unit and readjusted it in a way, that I could focus beyond infinity, just to be on the safe side. But after a lot of trials, I finally could prove, that all the lack of sharpness was only due to atmospheric conditions during my initial tests. Ben

06-20-2010, 03:51 PM	#7
bigdog104 Senior Member Join Date: Apr 2010 Location: South Carolina Photos: Gallery Posts: 289	Originally posted by Ben_Edict NO - that is not correct. A T2 adapter is a T2 adapter and Pentax kept the flange distance between the 35mm film cameras and the current line of APS-C and all future cameras, that will be able to use K-mount lenses. This is one of Pentax' main selling points! Ben Well I guess I will lose some reputation points for that suggesting it might be the APS-C vs FF.

06-20-2010, 05:25 PM	#8
k7bb Inactive Account Join Date: Jun 2010 Location: HK Posts: 16 Original Poster	thanks Marcin & Ben, also bigdog another thing is, afterwards attached the lens to a Canon DSLR (as you know crop factor is 1.6x instead of 1.5x), I got wider view angle and can be infinity focus... so, Ben, I'll try again with your advice. if still not work, I think I have to search 3rd mount thanks all

06-20-2010, 08:03 PM	#9
noblepa Veteran Member Join Date: Sep 2007 Location: Bay Village, Ohio USA Posts: 1,142	Are you sure that the T2 adapter you're using is for a k-mount? I have a T2 adapter that I use on a cheap 500mm mirror lens I picked up on eBay. It works perfectly on my K10D, as well as on my Pentax 35mm film cameras. You say that the lens can focus to infinity on other cameras, so it is probably not the lens. The only way I can think of that it would not focus to infinity on a Pentax camera is if you were using a T2/M42 screwmount adapter, along with a M42/K-mount adapter that has the large flange outside the lens mount.

06-20-2010, 11:34 PM	#10
k7bb Inactive Account Join Date: Jun 2010 Location: HK Posts: 16 Original Poster	thanks noblepa, since I have never seen M42 mount, can only trust the packing, it is T2...

06-21-2010, 01:14 AM	#11
Ben_Edict Veteran Member Join Date: Jul 2007 Location: SouthWest "Regio" Photos: Albums Posts: 3,309	Originally posted by k7bb thanks noblepa, since I have never seen M42 mount, can only trust the packing, it is T2... Could you provide some detailed images of the lens' rear? The images, you linked to, are mostly of the front element and do not give a clue about the mount. Thanks, Ben

06-21-2010, 01:48 PM	#13
Ben_Edict Veteran Member Join Date: Jul 2007 Location: SouthWest "Regio" Photos: Albums Posts: 3,309	Originally posted by k7bb photos of the adapter and lens mount O.k. - thanks for the images. Looks fine to me, with the T2 thread on the lens and the T2-K adapter. Can you screw the T2 adapter fully onto the lens threads? The lens flange and the flange of the adapter should be flush, with no space between. If that is also thew case, the only other thing, I would like you to do,: please provide two or three images, where you tried to achieve infinity focus and couldn't. Perhaps we can draw a conclusion from those. Ben

06-21-2010, 02:22 PM	#14
marcinski Forum Member Join Date: Jan 2009 Location: Dundee, Scotland Posts: 95	I'm pretty sure that it's adjustment problem. I had the same with my russian lens. The fact that it works with other mounts supports it. Look for a way to adjust infinity range on focusing ring. If you are not confident enough to do it, give to professional but it should be relatively straightforward. I did it myself on my lens. Marcin

06-21-2010, 03:44 PM	#15
Ben_Edict Veteran Member Join Date: Jul 2007 Location: SouthWest "Regio" Photos: Albums Posts: 3,309	Originally posted by marcinski I'm pretty sure that it's adjustment problem. I had the same with my russian lens. The fact that it works with other mounts supports it. Look for a way to adjust infinity range on focusing ring. If you are not confident enough to do it, give to professional but it should be relatively straightforward. I did it myself on my lens. Marcin What kind of adjustment problem would that be, if the same lens reaches infinity on one brand camera and not on the next, if both are connected by a T2-adapter? The T2 system should make the lens itself fully independent of the camera system, as the adapters compensate the different register distances of the different bodies. Ben