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JohnBar
Joined: 21 Jun 2012 Posts: 581 Location: Liverpool
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Posted: Thu Jan 16, 2014 9:41 pm Post subject: Knowledge of Taylor Hobson Projection Lenses? |
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JohnBar wrote:
I have acquired some TH lenses at good price.
I have heard about the silver ones having short BFL, but what about the painted brass ones?
Anyway if I am unlucky I was thinking about a relay lens to increase BFL. A 10mm achromat should increase BFL by 40mm without image deterioration but with Tstop penalty and upside down image.
Has anyone tried a relay lens solution? _________________ Rectilux 3FF Series single focus anamorphic attachments
http://www.transferconvert.co.uk/cinemania/rectilux-3ff.html
Regular News on https://www.facebook.com/pages/Rectilux/704770636267200 |
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ZoneV
Joined: 09 Nov 2009 Posts: 1632 Location: Germany
Expire: 2011-12-02
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Posted: Fri Jan 17, 2014 7:57 am Post subject: Re: Knowledge of Taylor Hobson Projection Lenses? |
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ZoneV wrote:
JohnBar wrote: |
....
I have heard about the silver ones having short BFL, but what about the painted brass ones?
Anyway if I am unlucky I was thinking about a relay lens to increase BFL. A 10mm achromat should increase BFL by 40mm without image deterioration but with Tstop penalty and upside down image.
Has anyone tried a relay lens solution? |
I have not tried relay lenses with projection lenses up to now. I experiment with relay lenses with CCTV / Cine taking lenses or to use the Zenitar 16mm fisheye as fisheye on a crop camera.
I work at the moment a lot with Shapley lenses / focal reducters with positive focal lengths - but those shorthen BFL. The other way round would be with teleconverters to get more BFL works with negative focal lengths, a diverging lens.
Cine projection lenses for 35mm film have sometimes long BFL - but not all. _________________ Camera modification, repair and DIY - some links to look through: http://www.4photos.de/camera-diy/index-en.html
I AM A LENS NERD!
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dan_
Joined: 05 Dec 2012 Posts: 1055 Location: Romania
Expire: 2016-12-19
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Posted: Fri Jan 17, 2014 8:33 am Post subject: |
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dan_ wrote:
I've tried to increase the focal length and register distance of a projector lens (Angénieux 50mm f/1.2) using diopters (-2 glasses lens) mounted in front of the lens and it works but the resolution decreases a little and the CA is more pronounced.
I was not satisfied with the result and I gave up.
Probably with negative achromats it works a little better but they are hard to find and expensive. Surplus Shed probably still has some cheaper ones.
ZoneV wrote: |
I work at the moment a lot with Shapley lenses / focal reducters with positive focal lengths - but those shorthen BFL. |
On the other hand, using positive achromats as focal reducers works quite well in some circumstances. |
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ZoneV
Joined: 09 Nov 2009 Posts: 1632 Location: Germany
Expire: 2011-12-02
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Posted: Fri Jan 17, 2014 1:00 pm Post subject: |
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ZoneV wrote:
dan_ wrote: |
On the other hand, using positive achromats as focal reducers works quite well in some circumstances. |
I suppose for not to extreme reduction factor or low speed systems achromats work well. At the moment I try to get a reasonable good high speed medium tele ~ 135/1.4. There I need better optical elements. Have a way, but this would work much better with short register samera like the Sony 7. _________________ Camera modification, repair and DIY - some links to look through: http://www.4photos.de/camera-diy/index-en.html
I AM A LENS NERD!
Epis, Elmaron, Emerald, Ernostar, Helioplan and Heidosmat.
Epiotar, Kameraobjektiv, Anastigmat, Epis, Meganast, Magnagon, Quinar, Culmigon, Novotrinast, Novflexar, Colorplan, Sekor, Kinon, Talon, Telemegor, Xenon, Xenar, Ultra, Ultra Star. Tessar, Janar, Visionar, Kiptar, Kipronar and Rotelar.
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JohnBar
Joined: 21 Jun 2012 Posts: 581 Location: Liverpool
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Posted: Fri Jan 17, 2014 1:32 pm Post subject: |
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JohnBar wrote:
These lenses are old, so may have a decent BFL. When they arrive I will know.
http://en.wikipedia.org/wiki/Relay_lens
Placing an achromat at 2 x focal length just relays the image without much effect on quality, but light loss.
Bad news is a new relay lens 4/15mm costs about $250 _________________ Rectilux 3FF Series single focus anamorphic attachments
http://www.transferconvert.co.uk/cinemania/rectilux-3ff.html
Regular News on https://www.facebook.com/pages/Rectilux/704770636267200 |
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JohnBar
Joined: 21 Jun 2012 Posts: 581 Location: Liverpool
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Posted: Mon Jan 20, 2014 2:20 pm Post subject: |
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JohnBar wrote:
The lenses arrived today and the gods have smiled on me. It seems both can be adapted to NEX etc.
On the 3 inch F1.6 the BFL is 30+mm
It seems they are of Petzval type design see Patent GB376025 _________________ Rectilux 3FF Series single focus anamorphic attachments
http://www.transferconvert.co.uk/cinemania/rectilux-3ff.html
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