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| Infrared photography with Busch Pressman Model C | |
| Author | Message |
|---|---|
| Capitain Boar Joined: 20 Mar 2011 Posts: 18 |  Posted: Sat Jun 04, 2011 6:17 pm Post subject: Infrared photography with Busch Pressman Model CI would like to shoot some Ilford SFX 200 with my Pressman. I think I'll have to make some focus corrections to get sharp image. How can I calculate it? The lens is 100 mm Tessar with a 720 nm filter. |
| 1banjo Joined: 16 Nov 2008 Posts: 492 | Posted: Sun Jun 05, 2011 3:51 am take a look at http://www.ilfordphoto.com/Webfiles/2007651134552223.pdf |
| 1banjo Joined: 16 Nov 2008 Posts: 492 | Posted: Sun Jun 05, 2011 3:55 am this is all they say FOCUSING With some lenses, red light focuses at a slightly different point to other visible light. With these lenses there may be a focus shift when focusing in white light compared with red light. However, it is almost impossible to focus a camera with a deep red filter in place. With short to moderate focal length lenses, this difference can easily be accommodated by stopping down to the smallest workable aperture. Some lenses, particularly apochromatic (APO) designs, may need no correction. |
| 45PSS Joined: 28 Sep 2001 Posts: 4081 | Posted: Sun Jun 05, 2011 6:21 am http://photo.net/large-format-photography-forum/00FQq9 the posted links are dead but the most relevant, and another discussion http://photo.net/bboard/q-and-a-fetch-msg?msg_id=004J7h as banjo said, depends on the lens. |
| Capitain Boar Joined: 20 Mar 2011 Posts: 18 | Posted: Sun Jun 05, 2011 7:47 am Thank you for the information. Ok, I think I will take a glow-lamp and focus the lens with the filter on some distances to mark a scale on my camera. I'll focus on the sun to get infinity focus. |
| Henry Joined: 09 May 2001 Posts: 1662 | Posted: Sun Jun 05, 2011 12:51 pm Uh, make that the moon, not the sun, or you'll risk damaging your lens and your eyes! |
| Capitain Boar Joined: 20 Mar 2011 Posts: 18 | Posted: Sun Jun 05, 2011 2:06 pm Hmm, The filter is pretty deep (more than 512x), so the sun isn't so bright when I look through the filter. |
| C. Henry Joined: 13 Dec 2005 Posts: 360 | Posted: Sun Jun 05, 2011 6:14 pm Don't look directly at the sun, only at the image of it on the ground glass and then only from an off center position. The filter you are using seems to approximate the "sun screen" used on mariner's sextants used for celestial navigation which required viewing an image of the sun in order to determine the exact angle between the sun and the sea horizon. BTW I'm the "other Henry" not the same one as posted an earlier reply! C. Henry |
| 45PSS Joined: 28 Sep 2001 Posts: 4081 | Posted: Sun Jun 05, 2011 7:42 pm http://www.msnbc.msn.com/id/3541480/ns/technology_and_science-space/t/how-view-sun-safely/ I use a piece of aluminized mylar, works well. |
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