Samyang 800mm + T2 -> Pentax infinity focus problem

rhodopsin · 06-21-2010, 04:35 PM

The humor here is the lens works fine on Canon & Nikon but not Pentax.

Given that, and if the lens on Pentax can focus close but not to or past infinity, then the T2-Pentax adapter is too (edit)THICK, try another adapter.

Last edited by rhodopsin; 06-22-2010 at 11:05 AM.

k7bb · 06-22-2010, 02:12 AM

Originally posted by Ben_Edict

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

thanks Ben,
as a newbie, I like step by step
will shot later, on hand images just blur...

k7bb · 06-22-2010, 02:23 AM

Originally posted by rhodopsin

The humor here is the lens works fine on Canon & Nikon but not Pentax.

Given that, and if the lens on Pentax can focus close but not to or past infinity, then the T2-Pentax adapter is too thin, try another adapter.

right

, not Pentax

too thin or too thick? I bought 2 adapters for Pentax, both claim support infinity focus, one of them (same model but not mine) used with Kenko 800mm mirror lens (suppose same as Samyang) work ok

advised by Ben, I will take photos let brothers see what problem, at the same time arranging the shop for checking with another lens+adapter

thanks for your help

Ben_Edict · 06-22-2010, 03:57 AM

Originally posted by rhodopsin

The humor here is the lens works fine on Canon & Nikon but not Pentax.

Given that, and if the lens on Pentax can focus close but not to or past infinity, then the T2-Pentax adapter is too thin, try another adapter.

If you cannot focus to infinity, but only at near distances, the adapter would be too thick, not too thin. Too thin would allow to focus beyond infinity.

T2-adapters are not exactly high tech products and I still wonder, whether the adapter could really be the culprit - except if it doesn't screw fully onto the lens threads.

But I guess, it would be best to await some example shots to get an idea about the degree of misfocus.

Ben

wildman · 06-22-2010, 06:35 AM

Just a speculation:

Perhaps the threads on the lens are not T mount threads but M42 threads and intended for direct mount to a M42 body?

M42 mount= M42x1.00mm (FFD 45.46mm on Pentax)
T mount = M42x0.75mm (FFD 55.00mm)

rhodopsin · 06-22-2010, 11:27 AM

Right, thanks everybody, if focus doesn't reach to infinity, adapter is too THICK, acting as extension tube for closer focus. (I don't know why I wrote 'too thin'

)

I wonder if that adapter for Pentax camera is really a CS adapter, which looks like a T2-adapter but is a little thicker? (ref: Spiratone CS-mounts and T-Mounts - Photo.net Classic Manual Cameras Forum )

Elva · 06-25-2010, 12:11 AM

I seem to have this same problem with a 300mm mirror lens, the t adaptor works fine in a 125 mm preset apature lens that it came on. Thanks for this as it helps me to sort out this problem. As the 135 is in my small museum of cameras and the 300mm is a lens that I use I can work on the t mount and sort out this problem.

rhodopsin · 06-25-2010, 06:21 AM

For anybody with lens that will not reach infinity focus (it focuses closer), check the T adapter thickness -- there is a 'CS' mount by Spiratone, perhaps others, with T-mount size threads, however it is slightly thicker. On a T-mount lens, a CS adapter is too thick; infinity focus cannot be reached.

There is a pictorial reference in this thread Spiratone CS-mounts and T-Mounts - Photo.net Classic Manual Cameras Forum:

reeftool · 06-27-2010, 08:11 AM

Originally posted by Ben_Edict

If you cannot focus to infinity, but only at near distances, the adapter would be too thick, not too thin. Too thin would allow to focus beyond infinity.

T2-adapters are not exactly high tech products and I still wonder, whether the adapter could really be the culprit - except if it doesn't screw fully onto the lens threads.

But I guess, it would be best to await some example shots to get an idea about the degree of misfocus.

Ben

I will chime in and make a guess that the adapter is off a little somehow. The lens works on a different camera with a different adapter so that would seem to rule out the lens. I have a Samyang 500/8 and the adapter is a rather sloppy fit but works. I worried that it might leak light as the bayonet isn't a tight fit but it seems ok. The quality control on their adapters isn't good.

k7bb · 06-29-2010, 10:37 AM

sorry for late (due to poor weather in Hong Kong)

Thanks for all brothers' help

I got confuse of "infinity focus", I need to focus for 300m, even few kilos... but the lens marked after 100ft is infinity, anyway, my objective is focus moon, now seems ok.

my K7 shown correct focus sign, but still blur (maybe my issue)

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06-21-2010, 04:35 PM	#16
rhodopsin Veteran Member Join Date: Dec 2009 Location: Deep Forest Posts: 643	The humor here is the lens works fine on Canon & Nikon but not Pentax. Given that, and if the lens on Pentax can focus close but not to or past infinity, then the T2-Pentax adapter is too (edit)THICK, try another adapter. Last edited by rhodopsin; 06-22-2010 at 11:05 AM.

06-22-2010, 02:12 AM	#17
k7bb Inactive Account Join Date: Jun 2010 Location: HK Posts: 16 Original Poster	Originally posted by Ben_Edict 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 thanks Ben, as a newbie, I like step by step will shot later, on hand images just blur...

06-22-2010, 02:23 AM	#18
k7bb Inactive Account Join Date: Jun 2010 Location: HK Posts: 16 Original Poster	Originally posted by rhodopsin The humor here is the lens works fine on Canon & Nikon but not Pentax. Given that, and if the lens on Pentax can focus close but not to or past infinity, then the T2-Pentax adapter is too thin, try another adapter. right , not Pentax too thin or too thick? I bought 2 adapters for Pentax, both claim support infinity focus, one of them (same model but not mine) used with Kenko 800mm mirror lens (suppose same as Samyang) work ok advised by Ben, I will take photos let brothers see what problem, at the same time arranging the shop for checking with another lens+adapter thanks for your help

06-22-2010, 03:57 AM	#19
Ben_Edict Veteran Member Join Date: Jul 2007 Location: SouthWest "Regio" Photos: Albums Posts: 3,309	Originally posted by rhodopsin The humor here is the lens works fine on Canon & Nikon but not Pentax. Given that, and if the lens on Pentax can focus close but not to or past infinity, then the T2-Pentax adapter is too thin, try another adapter. If you cannot focus to infinity, but only at near distances, the adapter would be too thick, not too thin. Too thin would allow to focus beyond infinity. T2-adapters are not exactly high tech products and I still wonder, whether the adapter could really be the culprit - except if it doesn't screw fully onto the lens threads. But I guess, it would be best to await some example shots to get an idea about the degree of misfocus. Ben

06-22-2010, 06:35 AM	#20
wildman Veteran Member Join Date: Jun 2008 Location: Flyover America Posts: 4,469	Just a speculation: Perhaps the threads on the lens are not T mount threads but M42 threads and intended for direct mount to a M42 body? M42 mount= M42x1.00mm (FFD 45.46mm on Pentax) T mount = M42x0.75mm (FFD 55.00mm)

06-22-2010, 11:27 AM	#21
rhodopsin Veteran Member Join Date: Dec 2009 Location: Deep Forest Posts: 643	Right, thanks everybody, if focus doesn't reach to infinity, adapter is too THICK, acting as extension tube for closer focus. (I don't know why I wrote 'too thin' ) I wonder if that adapter for Pentax camera is really a CS adapter, which looks like a T2-adapter but is a little thicker? (ref: Spiratone CS-mounts and T-Mounts - Photo.net Classic Manual Cameras Forum )

06-25-2010, 12:11 AM	#22
Elva Senior Member Join Date: Sep 2009 Location: Grahamstown in the Eastern Cape province of South Africa Photos: Gallery Posts: 125	I seem to have this same problem with a 300mm mirror lens, the t adaptor works fine in a 125 mm preset apature lens that it came on. Thanks for this as it helps me to sort out this problem. As the 135 is in my small museum of cameras and the 300mm is a lens that I use I can work on the t mount and sort out this problem.

06-25-2010, 06:21 AM	#23
rhodopsin Veteran Member Join Date: Dec 2009 Location: Deep Forest Posts: 643	For anybody with lens that will not reach infinity focus (it focuses closer), check the T adapter thickness -- there is a 'CS' mount by Spiratone, perhaps others, with T-mount size threads, however it is slightly thicker. On a T-mount lens, a CS adapter is too thick; infinity focus cannot be reached. There is a pictorial reference in this thread Spiratone CS-mounts and T-Mounts - Photo.net Classic Manual Cameras Forum:

06-27-2010, 08:11 AM	#24
reeftool Pentaxian Join Date: Dec 2007 Location: Upstate New York Photos: Gallery \| Albums Posts: 9,555	Originally posted by Ben_Edict If you cannot focus to infinity, but only at near distances, the adapter would be too thick, not too thin. Too thin would allow to focus beyond infinity. T2-adapters are not exactly high tech products and I still wonder, whether the adapter could really be the culprit - except if it doesn't screw fully onto the lens threads. But I guess, it would be best to await some example shots to get an idea about the degree of misfocus. Ben I will chime in and make a guess that the adapter is off a little somehow. The lens works on a different camera with a different adapter so that would seem to rule out the lens. I have a Samyang 500/8 and the adapter is a rather sloppy fit but works. I worried that it might leak light as the bayonet isn't a tight fit but it seems ok. The quality control on their adapters isn't good.