WO Reducer/Flattener 4

[pmrid (Peter)]

Does anyone know how to measure the backfocus distance for the WO Reducer 4? The schematic WO provide shows the distances to the top of the T-thread to the lens surface and also, to the lens frame. And it shows both these measurements for the 3 different positions the device is capable of providing - i.e 66,76 and 86 mm.

And the external thread on the CCD end is also given at 4.5 mm. So calculating the correct distance from the face of the device seems to be a matter of deciding on the reduction factor you want first and then some subtraction of the thread length from the provided internal measurements and from the backfocus setting chosen.

But which one? The last glass has a deep meniscus of 7.5mm - an appreciably large meniscus. So, do you start with the distance to the bottom of the meniscus or to the edge of the lens frame?

The difference would seem to be, on my simple maths, and working on the 76mm setting as an example:
Either 76 - 24.1 - 4.5 = 56.4 or
76 - 16.6 - 4.5 = 63.9 mm.

Appreciate any enlightenment.

Peter

[cfranks (Charles)]

I just used a nylon 'stick', very carefully. My WO FLattener 4 is fixed focus and the diagram gives all measurements from the meniscus. I make my own adapters and thus had to find the meniscus-to-flange distance.

Charles

[pmrid (Peter)]

Originally Posted by cfranks

I just used a nylon 'stick', very carefully. My WO FLattener 4 is fixed focus and the diagram gives all measurements from the meniscus. I make my own adapters and thus had to find the meniscus-to-flange distance.

Charles

Thanks Charles. I'm working on the "bottom-of-the-meniscus "theory as well. It makes a kind of sense.
Peter

[Andy01 (Andy)]

Are you a member if the William optics Yahoo Group? If you can search it there was an informative thread about this earlier this year. If you get stuck I'll try and locate it for you.
Cheers
Andy

[pmrid (Peter)]

Originally Posted by Andy01

Are you a member if the William optics Yahoo Group? If you can search it there was an informative thread about this earlier this year. If you get stuck I'll try and locate it for you.
Cheers
Andy

Thanks Andy.
I'm not in that discussion group so any links you can find will be helpful
Peter

[Andy01 (Andy)]

Does this reply & diagram from the W/O yahoo group help?

http://farm6.staticflickr.com/5480/1...3d16563d_c.jpg

If it is what you have to remember is the FF4 is design for a DSLR with the CCD 55mm away from the collar of the FF4, you need get the ST8300C sensor to be as close as possible to 55mm away from the collar as possible; I have the FLT110, FF4, ST8300M and FW8 and had the same problem. The back focus of the ST8300C is 17.5mm so you will need a spacer as close as possible to 37.5mm (55mm - 17.5mm) you will then need to dial in the delta from 73.5mm (the standard setting for the FLT110 and FF4).

I my case the combined distance of the FW8 and ST8300m was 37.5mm, I added a 20mm extension which makes the CCD 58mm from the FF collar (yes I know this doesn't add up call it a manufacturing error) I then adjusted the FF to 70.5 to compensate. I adjust the WO document and produced this diagram to explain the difference.

Cheers
Andy