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12-21-2010, 11:07 PM   #1
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500/4.5 SMC Takumar infinity focus issues?

Hi all,

Anyone have experience with the 500/4.5 SMC Tak lens and have infinity focus issues? Admittedly I was shooting at the eclipse last night and it wasn't ideal conditions for testing, but I just couldn't lock on, and had to stop down a lot to extend the DOF. I don't think I was PAST the infinity mark either.

Any suggestions on methods for testing infinity focus on a lens like this? Tripod and live-view would be a good start I guess, but how far away is considered "infinity"

Thanks!
Damian

12-22-2010, 02:40 AM   #2
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They usually say the moon is a good infinity target for long lenses. I am not surprised, seeing as the moon is as far away as you'd need to focus on anyway.

With that being said, I've only had problem with focusing beyond or less than infinity when I was messing around with my lenses. Has your lens been disassembled?
12-22-2010, 06:36 AM   #3
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I had that lens but not that problem.

Note that the moon really is somewhat closer than infinity (which is very far away ;~) Also keep in mind that the moon is a sphere not a disk so DOF is a real issue: I don't know what aperture would be required to get it all in focus but it's probably in the diffraction zone. And then, there's atmospheric disturbance to consider. Beyond that, my advice is to use a super steady tripod and MLU.
12-22-2010, 10:17 AM   #4
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I have found a good way to test very long zooms is to focus on a tree or something with sharp edges at a 1 to 2 mile range if you can find a sight line like that. I happen to have a mountain at about that distance off my back deck so it works well for me.

I do not think the moon is a good test. Not sure where you are located but we had high moving, hazy overcast during the eclipse so I got shots but nothing very sharp.

And a really solid tripod with a shutter release or timer is necessary with anything that long. It is a whole other world at that focal length and the slightest vibration is magnified tremendously.

12-22-2010, 10:24 AM   #5
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The lens is probably adjustable for infinity focus, but because of its size, it may require long screwdrivers.

I can see a mountain 55 miles away and use that as an infinity focus target. I think even that is overkill. With a K300/4, focusing on the mountain is the same as focusing on a highway bridge 3 miles away. I use an MX film camera on a tripod because it has a split prism and a huge bright viewfinder. Live view should work fine too.
12-22-2010, 11:06 AM   #6
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I bought one of these a few months ago, and when I tested it prior to purchase, it also could not focus on infinite. The guy I bought it from was clueless (a second-hand dealer), but the lens was mounted with a 13mm extension tube when I opened the case. Naturally I removed the extension tube when I mounted it. After some frustration not being able to get focus at infinity, I remounted the 13mm extension tube and presto, it focused at infinity. The extension tubes set and several other bits including PK/A-1.4XL rear adapter came thrown in, so I was not concerned about the focus issue.

I have not attempted to resolve the infinity focus issue, but just use it with the extension tube. When using the 1.4X rear adapter, I have to use a longer extension tube. But it all works fine as shown by this moon shot at 700mm.

But you've got me thinking now about whether it can be adjusted..

12-22-2010, 11:53 AM   #7
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I have this lens and wonder how accurate is infinity, which is bang up against the stop. The Moon is NOT at infinity. Mountains, not either. I tested on Spotmatic, and center prism indicates focus is attained on moon, but I still think adjustment is needed, I just haven't had the time. For other lenses I have used Sirius, the brightest night sky star, with excellent results. It may take 1/2 hour for eyes to produce enough, ahem, rhodopsin, to see it in viewfinder -- best to cover camera display, rhodopsin gets destroyed easily! With lens this long, adjusting infinity using a star is a pita it moves so fast across fov, and my experience is on FF, so with crop sensor smaller field makes problem worse, but it can be done -- use a dim red torch (flashlight) to see where to put screwdriver.
12-22-2010, 12:32 PM   #8
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The moon IS at infinity for anything that matters photographically. Also, the fact that it is a sphere is also irrelevant. The whole thing is at infinity.

12-22-2010, 01:01 PM   #9
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Where do I look for the adjustment screw? (no I don't have the lens in front of me)
12-22-2010, 02:47 PM   #10
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Are you using a flanged adaptor?
12-22-2010, 03:08 PM   #11
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QuoteOriginally posted by Lowell Goudge Quote
Are you using a flanged adaptor?
Nope, native pentax K adapter from the m42 mount on the lens.
12-22-2010, 03:21 PM   #12
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QuoteOriginally posted by sewebster Quote
The moon IS at infinity for anything that matters photographically. Also, the fact that it is a sphere is also irrelevant. The whole thing is at infinity.
Then I must be misinterpreting my experience. I achieved sharpest focus somewhat short of the max focus distance and also found I couldn't get everything in focus at the same time.
12-22-2010, 04:14 PM   #13
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QuoteOriginally posted by d.bradley Quote
Where do I look for the adjustment screw? (no I don't have the lens in front of me)
Here are the threads I've saved for when I get around to it:

should be very similar Soligor 400 f/6.3 : Infinity adjustment?::Manual Focus Lenses

also How to adjust infinity focus on a Pentax 500/4.5 (Page 1) - Maintenance & Repairs - Manual Focus Forum



QuoteOriginally posted by KevinR Quote
I bought one of these a few months ago, and when I tested it prior to purchase, it also could not focus on infinite. The guy I bought it from was clueless (a second-hand dealer), but the lens was mounted with a 13mm extension tube when I opened the case. Naturally I removed the extension tube when I mounted it. After some frustration not being able to get focus at infinity, I remounted the 13mm extension tube and presto, it focused at infinity. The extension tubes set and several other bits including PK/A-1.4XL rear adapter came thrown in, so I was not concerned about the focus issue.

I have not attempted to resolve the infinity focus issue, but just use it with the extension tube. When using the 1.4X rear adapter, I have to use a longer extension tube. But it all works fine as shown by this moon shot at 700mm.

But you've got me thinking now about whether it can be adjusted..
Kevin it sounds like your lens has been disassembled and the helical started onto the wrong threads (there are multiple starting points on helical threads). Maybe not, 13mm is a LOT.
12-22-2010, 06:29 PM   #14
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Just to be clear. You say the sharpest image is before infinity? Note many long lenses can focus past infinity to take into account thermal expansion. It may be normal
12-22-2010, 06:57 PM   #15
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QuoteOriginally posted by Lowell Goudge Quote
Just to be clear. You say the sharpest image is before infinity? Note many long lenses can focus past infinity to take into account thermal expansion. It may be normal
The sharpest focus was achieved a bit short of the long extreme of the focus range. How that extreme relates to infinity is the question, I guess--but only a theoretical one: the important thing was that I was able to focus.)
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