Fotoman helical focus

[PBrooks]

I hope ya'll don't mind but I have a few questions regarding calibration of lenses for Fotoman.

Calibrate the lens for infinity focus in center of image? or Calibrate lens for correction of lens curvature?

What method have you used and why?

Thanks
PBrooks

[Kirk Keyes]

I use the ground glass.

I like the focuser, it's a little coarse in the motion, and someone packed a ton of grease into the bearing (probably to make up for the coarse machining), but for the price, it's worth it.

[PBrooks]

and you have a Fotoman not a Gaoersi?

[Dominique Cesari]

Though Fotoman, in the instructions, insists upon calibrating for correction of the curvature of field (COF), I choose to calibrate for infinity focus in the center of image. The reasons that I had in mind :
(i) it would be clearer to take care of COF at the different stages of the focusing range.
(ii) one can allways tune the focusing point at infinity to prevent the effects the COF.

But a part of the the photographs taken with the 72XL that I calibrated to my taste show clearly COF in the corners. I haven't been able to correct it by a focusing shift on the go. So, I procrastinate to calibrate in the future as Fotoman suggests it and check the difference.

[Kirk Keyes]

and you have a Fotoman not a Gaoersi?

Here is what I have:
http://cgi.ebay.com/WIDE-ANGLE-DEVIC...d=p3286.c0.m14
(ebay item #350128926772)

I'm not sure which one it is - a Fotoman or a Gaoersi?

[Bob Salomon]

Here is what I have:
http://cgi.ebay.com/WIDE-ANGLE-DEVIC...d=p3286.c0.m14
(ebay item #350128926772)

I'm not sure which one it is - a Fotoman or a Gaoersi?

Since it was made for a 65mm how do you lengthen it for the proper flange focal length for 72 to 90mm lenses? And how do you shorten it for 45 to 58mm lenses? Those are far bigger problems then the distance markings.

And, so that there is absolutely no confusion, this is not a Linhof made item!

[Ben Syverson]

The helical itself is 100% the same for different focal lengths, with the exception of the markings on the barrel. You set the focus to infinity, and rack the whole assembly (helical and lens) until infinity is in focus on the GG. At that point you can use the helical to set distances without looking at the GG, which is its purpose.

I think it's important to get the helical with the right markings. I wouldn't use, for example, a 65mm helical with a 90mm lens, because the markings would be all wrong, and would defeat the purpose of the thing.

[Paul Droluk]

Here is what I have:
http://cgi.ebay.com/WIDE-ANGLE-DEVIC...d=p3286.c0.m14
(ebay item #350128926772)

I'm not sure which one it is - a Fotoman or a Gaoersi?

You have a Gaeioursi... which requires lots of grease to cover up the crude machine work... unlike the Fotoman HFM, which is as smooth as a Schneider or Rodenstock HFM.

[Kirk Keyes]

I think it's important to get the helical with the right markings. I wouldn't use, for example, a 65mm helical with a 90mm lens, because the markings would be all wrong, and would defeat the purpose of the thing.

I guess it depends on your purpose.

As I focus on the ground glass, I don't pay any attention to the markings, and I really don't care what the markings say. They could be in inches or furlongs, for a 2000 mm lens or a 12mm lens, and the helical still works for ground glass foucing.

[Kirk Keyes]

You have a Gaeioursi... which requires lots of grease to cover up the crude machine work... unlike the Fotoman HFM, which is as smooth as a Schneider or Rodenstock HFM.

thanks