I tried taking a picture of a building using a substantial amount of front-rise and I got very serious light-fall off (not beyond the image circle because I can still see very dark features in the ground glass all the way to edge). Which Heliopan CF (3x or 8x) should I use with the Grandagon 90/6.8. I know Ellis uses and recommends a 3x for the 90/4.5 which if I recall correctly from I read in the Rodenstock brochure has some tricks in it to minimize light fall-off. By eye, the difference between the center and outer regions is definitely more than 1.5 stops at f6.8, but I'm worried that 3 stops from the 8x CF might be excessive. Does the light fall-off or difference between center and edges increase or decrease as the aperture is closed down to f22? Does anyone have experience on putting a Heliopan 8x CF on the Grandagon 90/6.8? I won't consider getting a "proper" 2x more expensive Rodenstock CF unless someone convinces me that both 3x and 8x Heliopan CF definitely won't work.

-- Carlos Co (co@che.udel.edu), March 01, 1999

Answers

To clarify: I am using the Heliopan 3x on the 90mm f/4.5 Grandagon. One the reasons I have this larger lens is because of the much larger image circle which I need for my 6x17cm work. A side result is less falloff when shooting 4x5. Might this (image circle diameter) be a factor in your use of the f/6.8 version?

The only "slow" 90mm I found in my research that produced a large image circle was the 90mm f/8 Nikkor SW: 235mm. Same as the Grandagon 90mm f/4.5 and the 90mm f/4.5 Nikkor. I haven't tested this lens however.

Lightfall off improves as you stop down to f/22. Are you judging amount of fall off by what you see on film or on the groundglass?

I think you should try the Heliopan 3x and judge for yourself. Spend the extra US$30+ and get the filter from a shop like Lens & Repro in New York or Photomark in Phoenix who will let you return it if it does not work for you, also ask for their advice.

-- Ellis (evphoto@insync.net), March 01, 1999.

We stock some of the dneser Heliopan CF and have sold virtually none. You would lose so much light (3 stops) + you must stop a lens down at least 2 stops for the filter to work that the denser version is not too useable for most people.

Virtually every CF sold is either .40 (Rodenstock) or .45 (Heliopan and others) so the more popular one should also work well for you.

if you would like to receive a 2 page detailed explanation of center filters and how and why they are used we can mail you the latest one from Rodenstock.

Of course we would need a mailing ad

-- bob salomon (bob@hpmarketingcorp.com), March 01, 1999.