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#1
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T-Mount adjustment
T-mount is a universal adapter for old 3rd party lenses with an approx.
42mm female thread to recieve the lens. There are 3 set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? I don't want to mess it up experimenting. I also don't want to strip the flat-head screwdriver slot if it's going to require a real tight twist. It already rotates a little if given a firm twist. What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other lenses with teleconverters which revealed that it is not very sharp at all at infinity (2 miles away) but pretty darn sharp at 100 feet away. I noticed some other shots where 2 miles away was decent stopped down but lights at night 10 miles away appeared to be out of focus: that might just be the lights at night. Some long lenses allow focus beyond infinity and now I'm starting to understand why! I do have a split focusing screen but it's still hard to tell, particularly because the focus on this lens is soooo gradual: there is a half inch of turn between 500 feet and infinity. |
#2
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T-Mount adjustment
"Paul Furman" a écrit dans le message de news: ... T-mount is a universal adapter for old 3rd party lenses with an approx. 42mm female thread to recieve the lens. There are 3 set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? I don't want to mess it up experimenting. I also don't want to strip the flat-head screwdriver slot if it's going to require a real tight twist. It already rotates a little if given a firm twist. Yes, the screws are to line up the lens with the camera, do it once and forget it. What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other lenses with teleconverters which revealed that it is not very sharp at all at infinity (2 miles away) but pretty darn sharp at 100 feet away. I noticed some other shots where 2 miles away was decent stopped down but lights at night 10 miles away appeared to be out of focus: that might just be the lights at night. Some long lenses allow focus beyond infinity and now I'm starting to understand why! At that distance, air currents may blurr and distort the image, no fault with the lens (prolly) I do have a split focusing screen but it's still hard to tell, particularly because the focus on this lens is soooo gradual: there is a half inch of turn between 500 feet and infinity. Jean |
#3
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T-Mount adjustment
Paul Furman writes:
There are 3 set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? Just the rotation. Run the screws well out and remove the insert they're holding in, and you'll see it's just a dovetail. |
#4
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T-Mount adjustment
Paul Furman wrote:
T-mount is a universal adapter for old 3rd party lenses with an approx. 42mm female thread to recieve the lens. There are 3 set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? What they said - just the angle, normally, but it might be worth just checking, given your problem... However, if it's old, the screws may have corroded/self-welded themselves.... What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other lenses with teleconverters which revealed that it is not very sharp at all at infinity (2 miles away) but pretty darn sharp at 100 feet away. I noticed some other shots where 2 miles away was decent stopped down but lights at night 10 miles away appeared to be out of focus: that might just be the lights at night. Some long lenses allow focus beyond infinity and now I'm starting to understand why! You should be able to tell if it's short, simply by watching as you focus - pick your scene carefully, so as to include lost of far detail at varying distances - you'll see it if it goes beyond infinity, and should be able to tell if it's coming up slightly short. If it is short and you are brave and mechanically gifted, it's worth investigating - some lenses are as easy to adjust as peeling back the rubber sleeve over the focusing ring, and loosening set screws so you can rotate the focus sleeve slightly relative to the barrel so that you can rotate it further than it did. Other lenses are nowhere near that easy... If disassembly required, work on a large white sheet, mark the alignment of any parts before moving/removing them (especially sleeves, barrels, helicoids), and be very afraid of small springs and tiny ball bearings... Work slowly and carefully, carefully keep any grease you may want to wipe away (you may need to reapply it), and .. er.. don't get any on the glass (sorry for stating the obvious!)... Good luck. (O: |
#5
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T-Mount adjustment
On Feb 27, 11:05 pm, Paul Furman wrote:
T-mount is a universal adapter for old 3rd party lenses with an approx. 42mm female thread to recieve the lens. There are 3 set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? I don't want to mess it up experimenting. I also don't want to strip the flat-head screwdriver slot if it's going to require a real tight twist. It already rotates a little if given a firm twist. What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other lenses with teleconverters which revealed that it is not very sharp at all at infinity (2 miles away) but pretty darn sharp at 100 feet away. I noticed some other shots where 2 miles away was decent stopped down but lights at night 10 miles away appeared to be out of focus: that might just be the lights at night. Some long lenses allow focus beyond infinity and now I'm starting to understand why! I do have a split focusing screen but it's still hard to tell, particularly because the focus on this lens is soooo gradual: there is a half inch of turn between 500 feet and infinity. I have a 400mm f5.6 Kilar in Leica Visoflex screw mount, founs a Visoflex to Nikon mount but the lens is so off on the mount it is difficult to use, doesn't help that the tripod socket on the lens is fixed. With the Canon mount I bought it with (FD) infinity was a little off, it is way off with the Nikon mount, luckily infinity is within the focus range on outside it. I guess it means the mount is too short. Great old lens but tought to use. Century optics were made for the movie industry and should be first rate. No surprise your images at 2miles are worse than the ones closer in atmospheric haze will degrade almost any image. Can be a bright sunny day there is still a lot of air and particles between you and the subject 2 miles away. Tom |
#6
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T-Mount adjustment
tomm42 wrote:
Paul Furman wrote: What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other lenses... I have a 400mm f5.6 Kilar in Leica Visoflex screw mount, Fun. One of very few mounts that can be adapted to Nikon. found a Visoflex to Nikon mount but the lens is so off on the mount it is difficult to use, doesn't help that the tripod socket on the lens is fixed. With the Canon mount I bought it with (FD) infinity was a little off, it is way off with the Nikon mount, luckily infinity is within the focus range on outside it. I guess it means the mount is too short. Great old lens but tough to use. Yes this one is also not easy ack. Century optics were made for the movie industry and should be first rate. |
#7
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T-Mount adjustment
Thanks everyone for comments, I'm just replying once here to similar
questions. David Ruether wrote: "Paul Furman" wrote in message news T-mount is a universal adapter for old 3rd party lenses with an approx. 42mm female thread to recieve the lens. There are 3 set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? I don't want to mess it up experimenting. I also don't want to strip the flat-head screwdriver slot if it's going to require a real tight twist. It already rotates a little if given a firm twist. As others have said, the set screws are just for changing rotation of the lens relative to the camera body... Yep. Hmm, one possibility might be to grind off a bit of the T-mount adapter so it gets closer. What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other lenses with teleconverters which revealed that it is not very sharp at all at infinity (2 miles away) Few long lenses are except under unusual conditions (VERY clear air, NO heat rising through the air you are shooting through [or any other air disturbance caused by traffic, water, etc.], I compared 1.4x & 2.x teleconverters (with without & stacked) on a 300mm f/2.8 Tokina MF and 70-200/2.8 and the 500 was even beat by the 200 with stacked converters in some cases so it's not just turbulent air. So then tried various apertures and that makes a big difference. But I think that was just because of the increased DOF because then I did close up tests (100 feet) and it performed very well wide open at that distance. and absolute freedom from movement of the camera./lens, including tripod resonances [and the sturdiest tripods are sometimes not good for minimizing these...]). The lens came with a monstrous heavy tripod: http://edgehill.net/Misc/photography...thenar/pg3pc17 but yeah it's annoying to see how much bounce there still is in the viewfinder so I did these tests with the big metal bracket resting on a table, mirror lockup, etc. I have done some successful long distance shooting with 700mm on FF (see numbers 8, 9, and 10 under "Cornell" at http://www.donferrario.com/ruether/commercial.html, taken with a 500mm older Nikkor mirror Wow, that really flattens out the architecture! + TC 14 - the one made for long lenses). Yep, got those. Notice the times of day when these were taken (when the air is usually "quietest" - at sunrise and after sunset...;-). I woke unreasonably early this morning & caught the moon :-) and did a bunch of bracketed shots (lots of variability depending on bounce, wind gusts, etc but at least I knew this is close enough to infinity not to matter :-) http://edgehill.net/Misc/moon/2-27-08 I forgot tho crank the ISO though for the darker stacked TC stopped down ones. but pretty darn sharp at 100 feet away. I noticed some other shots where 2 miles away was decent stopped down but lights at night 10 miles away appeared to be out of focus: that might just be the lights at night. Did you see them "twinkle"? If so, the air was not still (the air was likely over surfaces that were warmer than the air, as with over buildings on cool evenings...). I didn't notice but good thing to check. Some long lenses allow focus beyond infinity and now I'm starting to understand why! No. This is due to the inclusion of glass that changes FL a bit with temperature change - and your lens is unlikely to have it. If it needs recalibration for infinity focus (unlikely, if nothing is loose), it should be easy to do. It's got what looks like recessed hex nuts all over but I'd hate to mess it up. I could send it to the manufacturer but heard they charge a lot for CLA. I do have a split focusing screen but it's still hard to tell, particularly because the focus on this lens is soooo gradual: there is a half inch of turn between 500 feet and infinity. |
#8
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T-Mount adjustment
Paul Furman wrote:
Thanks everyone ... David Ruether wrote: Paul Furman wrote T-mount is a universal adapter for old 3rd party lenses with an approx. 42mm female thread to recieve the lens. There are 3 set-screws on the side. Is that for the purpose of adjusting the flange distance or just the rotation? I don't want to mess it up experimenting. I also don't want to strip the flat-head screwdriver slot if it's going to require a real tight twist. It already rotates a little if given a firm twist. As others have said, the set screws are just for changing rotation of the lens relative to the camera body... Yep. Hmm, one possibility might be to grind off a bit of the T-mount adapter so it gets closer. Alright, I was able to file the adapter down and I now have infinity focus, plus a little beyond. I only moved it less than half a millimeter. With the set screws loosened it was pretty easy to file the soft aluminum of the inside part so you don't see it when reassembled. I suppose I could put a thin washer in there to bring back to infinity but I'm happy with it like this for now. It's pretty amazing with stacked teleconverters 2x & 1.4x. Chromatic aberration is kind of bad but sharpness is good even wide open, stopping down hardly changes sharpness but does improve the CA considerably. It looks like this is a 1978 design. It came with a 1991 lens catalog showing a list price of $2750 and I paid $500 including a heavy duty Bogen tripod. I'm happy. It's not a $7,000 Nikkor but it's pretty good. What I've got is an old 500mm f/4 Century Tele-Athenar II lens (not a mirror lens) and I was doing some tests today against other lenses with teleconverters which revealed that it is not very sharp at all at infinity (2 miles away) |
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