Support our Sponsors, they keep FADU free: AG Photographic The Imaging Warehouse Process Supplies RH Designs Second-hand Darkroom Supplies |
> What is a 6 stop increase |
*** Click here for the FADU 2015/2014 Yearbooks *** |
|
Thread Tools | Search this Thread | Display Modes |
#1
|
|||
|
|||
What is a 6 stop increase
Do you have a moment when you know you know the answer but do you.............
HELP I am out soon IR film in hand with IR 760 Nm filter Someone said " I believe you will find 760 nm cutoff is awfully high for SFX200, you might do better with a 720. A 760 could require another five or six stops of exposure over a 720 on today's "IR" films which do not extend very far into the IR range." Am I right that this is. eg. Normal exposure 1/125th so 5 stop increase is 1/4 second ??? or 1/2 Thanks |
#2
|
||||
|
||||
From 1/125 to 1/4 is 5 stops. Or, to put it another way, meter ISO 200 SFX at ISO 6 using a 720nm IR filter. In practice, that is probably a little high and ISO 3 will probably get you a better neg. By all means, feel free to bracket a couple of stops either side of ISO3 - you never really know how much IR is about.
As I mentioned before, I have serious doubts about using a 760nm filter with SFX. A quick look at the graph on the Ilford datasheet (such as it is) suggests there is no response much above 730-750nm. Hopefully, the filter's response is less than sharp and it lets through anough light away from its centre band of 760nm to provide an image, but I would error on the side of safety and use something like ISO 1 as my base and bracket 2 or 3 stops either side. |
#3
|
||||
|
||||
720nm is typically the value I would expect - the usual filter IIRC is an R72 for example
|
#4
|
||||
|
||||
The Ilford chart shows a good response at 720nm, but it then falls off a cliff. There is some response up to 760, but it is very weak.
A 760 could require another five or six stops of exposure over a 720 on today's "IR" films That quote is suggesting you need 5 more stops even after rating the film at ISO 6. To put some numbers to that: Full sunlight, SFX200 in camera, 720nm filter in place, exposure would be something like 1/4 seond at F16 Same situation, 760nm filter in place, you'd add 5 more stops, That is, full sunlight becomes 1/4 second at F4. If you need more depth of field that could be 4 seconds at F16. Unfortunately you then hit a thing called reciprocity failure. Basically, the film becomes more sluggish and needs a whack more exposure. Realistically you could need 10 seconds or more in full sunlight. I'd go with the 720 filter Last edited by skellum; 10th October 2019 at 06:52 PM. Reason: Sticky keys on my keyboard! |
Support our Sponsors, they keep FADU free: AG Photographic The Imaging Warehouse Process Supplies RH Designs Second-hand Darkroom Supplies |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Using filters to increase ND | longhouselife | Darkroom | 27 | 8th March 2019 12:25 PM |
Price Increase. | John King | Darkroom | 12 | 5th October 2015 10:01 AM |
Increase in film sales. | Dave miller | Monochrome Film | 31 | 5th August 2011 04:23 AM |
How do I increase my post ratings? | Annie | Help! | 9 | 9th December 2010 11:55 AM |
VAT increase | RH Designs | New products and offers | 1 | 21st November 2009 08:36 AM |