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Most often, the problem is too little exposure: a red filter blocks some of the light reaching Ilford SFX 200, and deep red filters can also mislead some through-the-lens (TTL) meters. Check the exact filter’s factor, compensate for it or meter through it cautiously, then bracket exposures. Ilford’s guidance gives different corrections for different red filters, so “add a stop” is not a reliable rule for every filter.
First, check whether the negative is actually underexposed
A thin negative is consistent with insufficient exposure, which is the problem addressed here. But “dark” can also describe a scan or print: a dark positive image alone does not establish that the negative is thin. Inspect the negative itself before changing camera exposure; this exposure guidance cannot diagnose a particular scanning, printing, or processing problem.
SFX 200 is ISO 200 film with extended red sensitivity, intended to create infrared-style effects with colored filters. Ilford says a deep red filter can make blue skies almost black and green vegetation almost white. That dramatic tonal rendering is intentional, but the filter also reduces the light reaching the film. ILFORD PHOTO’s product information lists SFX 200 in 35mm and 120 formats.
Identify the filter and apply its own factor
Use the designation and exposure factor printed on the filter or in its maker’s documentation. A filter factor expresses how much exposure to add when metering without the filter. Ilford’s SFX 200 technical information, labeled November 2018, gives these examples:
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| Ilford filter designation | Factor | Exposure increase |
|---|---|---|
| Kodak Wratten 25 red | 2.8 | 1½ stops |
| Kodak Wratten 29 deep red | 3 | 1⅔ stops |
| Kodak Wratten 89B very deep red | 16 | 4 stops |
These are Ilford guide values, not universal corrections for every filter sold as red. The difference matters: an 89B’s four-stop increase is much greater than the 1½ stops Ilford lists for a Wratten 25. For the full guidance, see Ilford’s SFX 200 Technical Information.
Meter and bracket the exposure
Ilford warns that some common TTL meters can underexpose by up to 1½ stops with deep red or orange filters. Treat the camera’s reading as a starting point, not a guarantee. Ilford recommends trying a bracket of ±2 stops around the TTL reading with the filter in place, or around the reading after applying the factor if you meter without the filter.
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- 2 rolls of film
- ISO 400
- 35 mm
- 36 poses
- Black and white film
- Read the filter label or documentation. Confirm its exact designation and stated factor; do not assume that all red filters transmit the same amount of light.
- Choose a metering method. If metering without the filter, increase exposure by the factor for that specific filter. If metering through it, remember Ilford’s warning about possible TTL underexposure with deep red or orange filters.
- Make a bracket. Start with Ilford’s suggested range of two stops below to two stops above the chosen base exposure. Keep other capture choices consistent so the negatives can be compared.
- Compare the negatives under consistent conditions. Use the results to judge how your camera meters that filter and film combination before settling on a personal adjustment. This is a practical way to learn the setup, not a guarantee of a particular result.
Ilford’s example for bright sunlight with a deep red filter is about 1/30 second at f/5.6. It is an example, not a universal setting: actual exposure depends on the light, filter, and metering method.
Expect longer exposures and take care with focus
Very dark filters can require very long exposures; Ilford recommends a tripod in those circumstances. It is not necessary for every red-filter exposure. A deeper red filter also makes viewing and focusing through the filter difficult. Ilford notes that red light can focus at a slightly different point on some lenses; for short to moderate focal lengths, it says stopping down to the smallest working aperture can accommodate the difference. Some apochromatic (APO) lenses may need no correction.
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Load SFX 200 in subdued light. Ilford says total darkness is not required, unlike with true infrared film.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why a deeper red filter changes the look
Ilford says the redder the filter, the more dramatic the effect. The tonal shift—dark skies and pale vegetation—is part of the intended infrared-style rendering, not by itself evidence of an exposure fault. Exposure and tonal appearance are separate questions: use the negative’s density to assess exposure, and the scene’s rendering to assess the filter effect.
Quick Recap
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- Low Speed Color Negative: for kodak gold 200 35mm gold film is a low speed color negative.
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