Focal reducers ( speedboosters ) at DVinfo.net

Bob Hart · October 14th, 2020, 10:55 AM

Just a little hint for folk to do their own fixit if you happen to have an URSA with a focal reducer fitted in the throat. My arrangement has a Caldwell (speedbooster) in the throat of a "big" URSA.

A few Lucadapters may have been ordered with the optional Caldwell optical cell for URSA and URSA Mini.

If you dismantle for a clean, be aware that the Caldwell optical cell can be refitted back to front and it will still work.

Rather it will seem to work but you will soon find the collimation (what some call backfocus) of the lenses is way out.

The long lenses will work. The zooms will go nuts, The ultrawides in the ballpark 12mm to 25mm will be way off infinity focus and be very furry in the corners as well.

I have just sent myself a little insane thinking I had messed my shimming up. I pulled things to bits and totally missed the Calwell optical cell having been reversed.

While I was in the guts of the turret stomping about, I cleaned out and replaced the thermal compound where needed.

I had swapped out a sensor from an EF-Mount turret into a PL-Mount turret and found the shimming brought across from the EF-Mount turret was off for the PL-Mount turret, so used the original shim set for the PL-Mount turret and all was well or so it seemed.

It is probably good practice to take notes, even phone photos as well as systematically laying out parts.

October 14th, 2020, 10:55 AM	#1
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,476	Focal reducers ( speedboosters ) Just a little hint for folk to do their own fixit if you happen to have an URSA with a focal reducer fitted in the throat. My arrangement has a Caldwell (speedbooster) in the throat of a "big" URSA. A few Lucadapters may have been ordered with the optional Caldwell optical cell for URSA and URSA Mini. If you dismantle for a clean, be aware that the Caldwell optical cell can be refitted back to front and it will still work. Rather it will seem to work but you will soon find the collimation (what some call backfocus) of the lenses is way out. The long lenses will work. The zooms will go nuts, The ultrawides in the ballpark 12mm to 25mm will be way off infinity focus and be very furry in the corners as well. I have just sent myself a little insane thinking I had messed my shimming up. I pulled things to bits and totally missed the Calwell optical cell having been reversed. While I was in the guts of the turret stomping about, I cleaned out and replaced the thermal compound where needed. I had swapped out a sensor from an EF-Mount turret into a PL-Mount turret and found the shimming brought across from the EF-Mount turret was off for the PL-Mount turret, so used the original shim set for the PL-Mount turret and all was well or so it seemed. It is probably good practice to take notes, even phone photos as well as systematically laying out parts.