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pshute
Joined: 16 Oct 2009 Posts: 15
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Posted: Wed Oct 21, 2009 8:06 pm Post subject: Modifying minimum focus distance |
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pshute wrote:
Many old long lenses, e.g. 400mm f6.3 Spiratone, can only focus as close as 20 feet or more. I know I can add macro rings, etc, to decrease this, but it would be good to still be able to focus to infinity.
I thought this was impossible till I read an old posting at:
http://photography-on-the.net/forum/archive/index.php/t-43941.html
"If you are mechanically inclined it is quite easy on some of these to modify the focus limiter to get closer focus."
(second last posting on that thread)
This makes it sound like you could open the lens up, remove some obstruction, and the barrel will then be able to turn a little further and focus a little closer. I can't find any other discussions anywhere about this. The term "focus limiter" seems to mostly refer to a switch on AF lenses to restrict the AF range to reduce focus hunting.
I'm not trying to turn a lens into a macro lens, just get the distance down from, say, 23' to 20'.
Does this sound like a practical idea? Has anyone tried it? I can't imagine the manufacturers limited the distance without a reason, so is the image quality likely to suffer from this? |
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cooltouch
Joined: 15 Jan 2009 Posts: 9096 Location: Houston, Texas
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Posted: Wed Oct 21, 2009 8:17 pm Post subject: |
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cooltouch wrote:
Based on my not terribly comprehensive experience in dismantling (and even re-mantling) lenses, I'd have to say that the stop is placed there for a good reason. More often than not, if it is removed, there is a strong chance that if the focusing ring is turned too far, the helical will become decoupled to its threads, and the lens might even come apart. Can't say specifically if this is a possibility with this type of optic, but I would be inclined to think it would. _________________ Michael
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Arkku
Joined: 28 Feb 2007 Posts: 1416 Location: Helsinki, Finland
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Posted: Wed Oct 21, 2009 8:58 pm Post subject: |
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Arkku wrote:
Sometimes there is a little extra room available in the focus range, whereas the original stop plays it safe and keeps the focusing helicoid from coming off its threads. But if your particular lens happens to be closer to one end of range for register distance adjustment, it may be that you can get away with modifying the stop for better close focusing.
However, usually the changes in focusing range are very small and not worth the effort, unless some other modifications accompany them. The best I've been able to gain in a regular lens is when I re-adjusted infinity focus position on a Canon FL lens to focus to infinity with Minolta AF mount, which required a rather extreme infinity focus position (does not hit the stop but rather the end of the helicoid). Even this extreme case gave only 10 cm more close focus distance (from 60cm down to 50cm)… With a longer lens you need more extension to get a given amount of close focusing, so I doubt it's worth trying. |
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pshute
Joined: 16 Oct 2009 Posts: 15
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Posted: Wed Oct 21, 2009 10:47 pm Post subject: |
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pshute wrote:
OK, thanks, I won't expect it to help much, but I feel I ought to give it a try.
Can anyone give me some tips on how to get at the stop? I've never pulled a lens apart. |
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kds315*
Joined: 12 Mar 2008 Posts: 16634 Location: Weinheim, Germany
Expire: 2021-03-09
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Posted: Wed Oct 21, 2009 11:11 pm Post subject: |
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kds315* wrote:
Close up lenses, easy.
http://fuzzcraft.com/achromats.html _________________ Klaus - Admin
"S'il vient a point, me souviendra" [Thomas Bohier (1460-1523)]
http://www.macrolenses.de for macro and special lens info
http://www.pbase.com/kds315/uv_photos for UV Images and lens/filter info
https://www.flickr.com/photos/kds315/albums my albums using various lenses
http://photographyoftheinvisibleworld.blogspot.com/ my UV BLOG
http://www.travelmeetsfood.com/blog Food + Travel BLOG
https://galeriafotografia.com Architecture + Drone photography
Currently most FAV lens(es):
X80QF f3.2/80mm
Hypergon f11/26mm
ELCAN UV f5.6/52mm
Zeiss UV-Planar f4/60mm
Zeiss UV-Planar f2/62mm
Lomo Уфар-12 f2.5/41mm
Lomo Зуфар-2 f4.0/350mm
Lomo ZIKAR-1A f1.2/100mm
Nikon UV Nikkor f4.5/105mm
Zeiss UV-Sonnar f4.3/105mm
CERCO UV-VIS-NIR f1.8/45mm
CERCO UV-VIS-NIR f4.1/94mm
CERCO UV-VIS-NIR f2.8/100mm
Steinheil Quarzobjektiv f1.8/50mm
Pentax Quartz Takumar f3.5/85mm
Carl Zeiss Jena UV-Objektiv f4/60mm
NYE OPTICAL Lyman-Alpha II f1.1/90mm
NYE OPTICAL Lyman-Alpha I f2.8/200mm
COASTAL OPTICS f4/60mm UV-VIS-IR Apo
COASTAL OPTICS f4.5/105mm UV-Micro-Apo
Pentax Ultra-Achromatic Takumar f4.5/85mm
Pentax Ultra-Achromatic Takumar f5.6/300mm
Rodenstock UV-Rodagon f5.6/60mm + 105mm + 150mm
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rick_oleson
Joined: 26 Feb 2007 Posts: 386 Location: Lexington Kentucky USA
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Posted: Wed Oct 21, 2009 11:23 pm Post subject: |
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rick_oleson wrote:
You can do it, but to gain much on the Spiratone 400 you'd need to add a lot of travel - I think if you add 40mm it will get you down to 13 or 14 feet - and the chances of you having that much extra thread on the focus helical beyond the stop is not very great. I removed the close focus stop on a cheap mirror lens once and got it down to a few feet before the front end fell off. But, of course, that's the other issue ... the front end WILL fall off.
I have not tinkered with the stops on my Spiratone. My guess is to look under the rubber grip on the focus ring, but I'm not sure. _________________ I don't know what I want to be when I grow up |
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estudleon
Joined: 15 May 2008 Posts: 3754 Location: Argentina
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Posted: Wed Oct 21, 2009 11:49 pm Post subject: |
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estudleon wrote:
You can see:
http://www.pentaxforums.com/userreviews/showproduct.php?product=411&cat=88
5th post.
Refer to J-9 (it's a job that may be done over my lens too, 'cos it focus from 0,65 m and I pirchased as it).
Rino. _________________ Konica 2,8/100
CZJ: 4/20, 2,4/35, 1,8/50 aus jena, 3,5/135MC, Pentacon 1,8/50
Pentax S-M-C-1,4/50
Helios 44-3
Mamiya 2,8/135
Misc. : jupiter 9
Stuff used:
A) SRL
Alpa 10 D - kern macro Switar 1,9/50 -black, Kilffit apochromat 2/100.
Asahi pentax spotmatic super takumar 1,4/50
Contaflex super B tessar 2,8/50 Pro-tessar 115
Leica R3 electronic summicron 2/50 elmarit 2,8/35
Konica Autoreflex 3 (2 black and chrome one), TC, T4. 2,8/24, 3,5/28 not MC and MC, 1,8/40, 1,4/50, 1,7/50 MC and not MC, 1,8/85, 3,2/135, 3,5/135, 4/200
Minolta XG9 2,8/35, 2/45, 3,5/135
Nikkormat FTn 1,4/50, 2,8/135
Fujica ST 801, 605, 705n. 3,5/19, 1,4/50, 1,8/55, 4/85, 3,5/135.
Praktica MTL 5 and a lot of M42 lenses.
Voigtlander. Bessamatic m, bessamatix de luxe, bessamatic cs, ultramatic and ultramatic cs.
Skoparex 3,5/35, skopagon 2/40, skopar 2,8/50, skopar X 2,8/50, super lanthar (out of catalogue) 2,8/50, dinarex 3,4/90, dinarex 4,8/100, super dinarex 4/135, super dinarex 4/200, zoomar 2,8/36-83, portrait lens 0, 1 and 2. Curtagon 4/28 and 2,8/35
Canon AV1, 1,8/50
Rolleiflex SL35 and SL35 E. 2,8/35 angulon, 2,8/35 distagon, 1,4/55 rolleinar, 1,8/50 planar, 4/135 tessar, 2,8/135 rolleinar, x2 rollei, M42 to rollei adap.
Etc.
RF
Yashica Minister III
Voightlander Vito, vitomatic I, Vito C, etc.
Leica M. M2, M3 (d.s.) and M4. Schenider 3,4/21, 2/35 summaron 2,8/35 (with eyes). Summicron 2/35 (8 elements with eyes), 2/35 chrome, 2/35 black, 1,4/35 pre asph and aspheric - old -, 2/40 summicron, 2,8/50 elmar, 2/50 7 elements, 2/50 DR, 2/50 - minolta version, 1,4/50 summilux 1966 version, 1,4/75 summilux, 2/90 large version, 2/90 reduced version of 1987, 2,8/90 elmarit large version, 4/135 elmar. |
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egidio
Joined: 02 Sep 2009 Posts: 222 Location: slovenia
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Posted: Thu Oct 22, 2009 12:19 am Post subject: |
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egidio wrote:
why not use shallow macro extension ring _________________ I use: Flektogon 2.8/20, Flektogon 2.8/35, planar 50mm/1.4, Takumar 1.4/50mm, Takumar 1.9/85, MIR 24H, Mir1v, Industar-50-2, Helios-44-2, Pentacon 2.8/135, cyclop 85 1.5 |
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pshute
Joined: 16 Oct 2009 Posts: 15
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Posted: Thu Oct 22, 2009 12:53 am Post subject: |
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pshute wrote:
egidio wrote: |
why not use shallow macro extension ring |
This is for bird photography, I don't want to lose infinity focus, that would be worse than not being able to get close.
I wonder why these lenses have such long minimum distances. Is it a difficult design constraint, or did they simply assume no one would want to get that close?
I find that for bird photography, about 5m would be about right for my 300mm lens (which only focuses to 6m). Closer would be nicer, but I wouldn't often need it, and without being able to zoom out, it can get hard to frame something that close with a long lens when you're too close. |
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cooltouch
Joined: 15 Jan 2009 Posts: 9096 Location: Houston, Texas
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Posted: Thu Oct 22, 2009 1:20 am Post subject: |
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cooltouch wrote:
The optical formula typically used by these lenses, which is usually an achromatic doublet, requires a lot of extension to achieve close focus. Probably more than 360 degrees of rotation of the focusing ring, so . . . _________________ Michael
My Gear List: http://michaelmcbroom.com/photo/gear.html
My Gallery: http://michaelmcbroom.com/gallery3/index.php/
My Flickr Page: https://www.flickr.com/photos/11308754@N08/albums
My Music: https://soundcloud.com/michaelmcbroom/albums
My Blog: http://michaelmcbroom.com/blogistan/ |
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rick_oleson
Joined: 26 Feb 2007 Posts: 386 Location: Lexington Kentucky USA
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Posted: Thu Oct 22, 2009 2:34 am Post subject: |
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rick_oleson wrote:
The amount of extension required to achieve close focus is proportional to the focal length of the lens. A 400mm lens like the Spiratone needs about 40mm of extension to get to its minimum focus of about 27 feet, and another 40mm will cut that in half. To cut it in half again (to get to about 6 1/2 feet) would require doubling the extension again, so you'd now be 160mm out from the infinity position.
There are ways of shortening the extension required - the simplest is front-element focusing, which actually shortens the effective focal length of the lens rather than increasing its distance from the film (the close-focus capability being the difference between the focal length and the distance from the film). Generally speaking, unit focusing gives better optical performance, so that's the basic trade-off. _________________ I don't know what I want to be when I grow up |
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