Flange questions

[Jim Lafferty]

Hiya...

OK, the two mounts in question are the Nikon F and Canon FD, flanges listed as 1.831 and 1.654 inches, respectively. Questions:

1) Fill in the blank, please. Flange distance measures the distance between ________ and the focal plane. Is it the rear-most optical element, or is it the face of the mount? I thought I knew this one but I've had my doubts these past few days...

2) If you're looking to engineer an adapter that accepts both mounts, you would place the GG at a fixed position, and then make the mounts deeper or shallower depending on flange distance. Would this be a reflection simply of the numbers above (i.e. a Nikon mount that is .177 inches deeper than an FD mount), or are there other factors that come into play? For instance -- are the lenses the same depth (i.e. do they sit in their respective mounts the same way, or does one lenses rear element sit deeper?)

I'm looking to dev an adapter with both mounts and if I can get some constructive help, I'd offer a respectable discount on the final product form those involved who contribute conclusive info. I don't have a Canon FD mount/lens system here to test the numbers, nor does my machinist -- so I'm reaching out to the community here looking for some help.

Thanks!

- jim

[Toenis Liivamaegi]

1) Flange distance measures the distance between lens (mount) flange and the focal plane.
http://www.rainbowcctv.com/images/tech/flange.gif

2) I personally would make a adapter with native FD mount and use FD to Nikon mount adapter when I want to use F lenses because FD flange distance is smaller than Nikon`s thus you should be able to make it work that way.
Unfortunately I couldn`t find any FD to Nikon lens adapters for sale.

3) Be sure that you have lens mount(s) that will not screw off (like plastic lens cap style mounts) when used with FF for example.

[Francois Poitras]

I think Quyen sells a version of the Letus with both mounts in one ring, a "swapable mount", i.e. an FD mount at one end and a Nikon AI mount at the other.

[Dennis Wood]

1. Jim, the flange to optical plane distances for the different manufacturers are measured from the top surface of the lens mount flange to the GG. If you take a vernier caliper with a depth probe, sit this on your flange and drop the depth probe, you should contact the diffuser surface at the published Flange to GG distance. I'm sure you're aware that you need to adjust for GG thickness if the diffuser surface is at the rear. For these purposes, ignore the rear optical element...use the flange. Unless you're opposed, I'd stick with millimeters as all the optical measurements are done that way.

2. If you fix your GG, then yes, your Nikon flange will sit .177 inches higher than your Canon flange.

[Bob Hart]

Flange face = the rear matching face of the mount on the lens where it contacts the front face of the camera mount.

I also think Quyen's method is the most viable.

I wonder if he began to scrap one of his Nikon mounts to make up the prototype Canon mount or vice versa, then saw the light and said this can be done both ways.

He might be able to do something similar with the more common medium format mounts which likely have a deeper flange to focal plane, maybe even the PL mount.

In my PL mount searches there was reference to microscopic differences in the flange to focal plane distances between motion picture film camera types due apparently to different gate designs allowing the film to "float" at different distances off the surface of the gate.

There was also a reference to the backfocus of any lens having to be meticulously set as it apparently takes very little (in the order of thousanths of an inch) of misadjustment for the overall performance of the lens to fall away. Twas something I suspected but did not realise was as critical - I am no engineer after all.

On my device and not by deliberate intent but by lucky co-incidence, I have a second fine adjustment for backfocus in the form of the disk motor mount plate which is fitted to the case on three studs with springs beneath the plate and nuts on top.

That last little bit of really fine adjustment does make a difference so I would recommend this ability be incorporated in your design.

[Dennis Wood]

For what it's worth Bob, I don't think that the backfocus adjustment is super critical. By that, I mean that if you're in the ballpark by .2mm I suspect you're fine. I certainly have not seen the effects of this on EIA1956 charts.

The reason I suggest this is that extension tubes for macro photography are a popular method for SLR photogs. These space the lens farther from the film plane to allow closer focus without introducing additional optics. These do at some point introduce aberrations as the lens is pushed beyond design limits..but these extension tubes typically allow 10 to 70mm of extension.

I'm pretty convinced that .2mm would not be perceived by an SD or HD cam.

[Bob Hart]

The backfocus did not seem to matter at all with the longer lenses but the Sigma for Nikon f1.8 28mm which I thought was a dud came good when backfocus was set carefully for infinity at infinity not over.

The same goes for a Nikon 12mm - 24mm which was sold to me as an f1.8 but turned out to be an f4 and digital. It was a dog until I took special care to set it correctly for infinity. (This one also vignettes at the 12mm end but by about 15mm is clear.)

It might be something to do with their being retrofocus lenses. Those with their little side windows and motors inside are a dark art I do not comprehend. Something which I can see screws a piece of glass closer or furthur away from the film plane makes more sense to this feeble mind.

[Dennis Wood]

Interesting. My shortest prime lens is 50mm...although I have a fast 28 - 70 zoom. My new adapter is user adjustable for back focus, so I guess folks can fine tune all they like.

My spinner had the motor support plate mounted to supports with compressible bushings...like your motor mount. It's a nice idea as you can fine tune the relationship of the GG to the 35mm lens.

I kind of favour actually having the GG, lens mount and adapter/camera mount all adjustable. Rather than killing yourself trying to get everything perfect during construction, you can relax a bit, then align everything once completed.

[M. Krishna Babu]

jim,
this is how iam working on my version of the adapter.
its still under construction. here are a few photos that show how i am planning to address the adjustable mount to solve the varying flange distances.

http://show.imagehosting.us/show/120...-1_1207880.JPG

http://show.imagehosting.us/show/120...-1_1207882.JPG

hope this helps
krishna

[Bob Hart]

Dennis.

I agree and have that facility luckily because I am using pipe caps to carry the mounts. It is simply a matter of slots in the sides of the caps for screw holes and there is the coarse adjustment with the motor mount nuts taking up the last fine touches. Because the caps are tapered you can cheat in a little bit of axial alignment as well. It gets a bit complicated with having a prism block because that has also to track any axial adjustments made to the path.

The thing is as bad as trying to fly a helicopter with no fewer than four interacting adjustments.

Quyen's mirror emulation of the pentaprism ( I think ??? ) is probably a little bit more forgiving and bulletproof in that regard once the mirrors have been aligned and fixed down.

M. Krishna Babu.

Your backfocus adjustment method should work, but you may want to consider more than one locking screw, I would favour three in 120 degree sseparation around the nut, otherwise the plastic you are using may deform with the pressure from just one and make focus adjustment difficult.

You will also have to find a way to adjust the groundglass so that it is at a dead right angle to the lens centreline otherwise from one side to the other or top to bottom or combination of all, there will be a focal shift across the image which will be noticeable when panning or tilting.

You may find that you will have to trim a few millimetres off the plastic nut because the proper lens mount is going to add a few mm. If that nut is a hollow moulding, then you may have a bit of trouble but if it is a water reticulation fitting, then there should be no problem with trimming it down a little.

You may otherwise not be able to get the lens back close enough for backfocus.

Is that a Nikon or X-Fujinon lens. The Nikon is 46.5mm flange to film plane. The X-Fujinon seems to be closer to about 40mm gve or take one mm either waywhich might make your arrangement a bit longer than the flange to film plane of that lens..

It looks to me like a fixed groundglass design unless you are going to orbit or shake the groundglass. It seems you have the centre of the groundglass centred with the lens.

If that groundlgass is going to be a spinning disk rolling inside several small channelled wheels, it is not going to work because you will have a slow moving spot fair in the centre which the camcorder will see.

Depending on the shutter speed of the camera or the rotation speed of the disk, the size of the seeable area will vary but it will be visible.

[M. Krishna Babu]

bob,

I would favour three in 120 degree separation around the nut

yes. you are right.

It looks to me like a fixed groundglass design

yes , its a static design. i wanted to graduate from static to rotating once i get a satisfactory image free from distortions...

Is that a Nikon or X-Fujinon lens

had to sacrifice an old konica camera

its still under construction. i have collected all the parts but havent actually started to machine them for prescision. i have been reading posts from different people making adapters and my knowledge is constantly being updated. thank you very much for your suggestions bob, and i shall defnitely put them to practice.

krishna.

[Jim Lafferty]

Innexpensive digital caliper review... click the SKU link at the top to be taken to the order page.

[Rich Hibner]

Hey, while on the questoin of Flange I guess. Is there a certain length that the macro has to be from the GG?

[Bob Hart]

Rich

One specification for you :-

24mm wide image target in 16:9 frame shape >> Nikon lens + 46.5mm to groundglass surface + 121mm to front rim edge of 7+ Century Optics Achromatic dioptre to HDRFX1P.

Camera lens settings - Zoom full. Focus setting 1.4M as displayed in the LCD screen.

The PD150 and DVX100 yield full coverage of the 24mm x 18mm high 4:3 frame with this setup with the zoom backed off a little from full.

[Bill Porter]

Be careful. Calipers are good for getting in the ballpark but different people use different amounts of thumb pressure on the caliper, often inducing inaccuracy. It's easy to be off by enough to set up your GG incorrectly.

The best way to set registration distance is to dial it in visually with a loupe, looking at the GG, while focused on an extremely distant object. I do it at night, focusing on a distant pinprick of light.