Focus shift is focus shift. If you place a filter behind the lens, and that lens was not designed for a rear filter, then you have created a focus shift.Originally Posted by Oslolens
Focus shift is focus shift. If you place a filter behind the lens, and that lens was not designed for a rear filter, then you have created a focus shift.
Bob, of course you're right. But sometimes, "the perfect is the enemy of the good".
Sinar shutter has a 103mm glass or gel filter holder built in. Some LF lenses have a threaded rear element specifically designed for a threaded on filter. Some small imager/roll film lenses like the Canon 14mm f2.8 has a gel filter holder on the rear lens mount.
Rear of the lens filter works. The focus shift incurred MUST be compensated for by checking focus with the filter in place on the lens rear.
Bernice
Gel filters are just so damn susceptible to hazing, embedded grit, and fingerprints, that I only use them in the lab (never in the field), and only when I need a particular flavor which simply isn't available in high quality glass.
Mark - here we go again with the old mythology - "as per Ansel Adams", as if his opinion was definitive. Put that in context, way back when he said it. Ever seen some of his prints from sheet film negs enlarged more than 3X ? - they're anything but sharp, often a mess, really. I'm personally more interested in how to do things today, with far more optimal films, lenses, cameras, and yes, way better multicoated filters too. Not everyone is after a "retro" look.
Gel filters do not like getting wet... They are very fragile and easy to damage. Good high quality dye in mass glass filters hold up good for all the correct reasons.
Bernice
Gels also widely differ in how the fade and age. The official Wratten handbook gives the relevant specifications for every one of them. And there is always a risk when buying old bargain ones, even in unopened sleeves, that they might be be partially faded. On a positive note, having all those specifications available, including the actual spectral transmission charts, makes Wratten gels very valuable for those kinds of technical applications many of them were designed for to begin with. But it's a big mistake thinking one is going to save money going gels over coated glass; many of them are quite expensive. I have quite a set of specialized gels, but pamper them; some of these are no longer available.
In 1986 we became the USA distributor for B+W filters. First thing that happened is that Helix asked us to take back drawers full of special order B+W custom made Wratten filters that they had ordered years earlier from Bogen. While they originally thought that this was a great idea they found that Wratten gels, sandwiched between glass, also faded over time and with exposure to light and temp.
Helix eventually threw out whatever they had.
Think Tiffen also did this with similar results.
Gel filters simply do not last, they are essentially disposable filters. IMO, if one wants to have durable, reliable-predictable filters, get high quality glass filters. They are worth the $ in the long run. Have a good number of B+W filters that are decades old, they have held up good. Their brass rings are a plus even if the weight is more.
Gel filter sandwiched in glass Bad idea,
Bernice
When we dropped B+W to become the Heliopan distributor they also refused to do sandwiches.
Tiffen has a special thermal film sandwich process involving their own materials, not Wratten gels. I'm glad they've been around for a long time because in terms of glass filters per se, they have the biggest selection available. Only quite recently, and with just a few items, has coating become an available option. It helps, but don't expect it to be in the same league as Heliopan or B&W or Hoya.
The ordinary uncoated Tiffen filters attract smudge and condensation quite easily, and have to be constantly cleaned. And the sandwich-style construction does affect sharpness a tiny bit, relatively negligible in large format applications, but potentially a practical factor in enlargements from smaller formats. There's also obviously a greater risk of flare with uncoated filters; but that's what shades are for.
Consistency? - I dunno; I don't buy replacement Tiffens often enough. But I do know a 47 blue I bought recently certainly isn't as dense and deep a blue as a 47 I bought from them several decades back (and I'm not confusing these with 47B, which I also have). Reverse fading??? The Fountain of Youth??? I'd like to get ahold of that patent.
Last edited by Drew Wiley; 19-Nov-2021 at 15:55.
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