CS mount lens to PQ

[caerwall]

I imagine that I am not the first person to be caught by buying a "C-mount" lens and finding that it is really a "CS-mount" lens. This lens might physically screw into a C-mount will not work as the flange focal length is different. C=17.526 and CS=12.5.

You can fit a C mount lens to a CS mount camera by using one of the commonly available extenders but the other way around needs to decrease the flange back distance of the adapters.

I saw various remedies on the web - usually involving boring out and gluing in. I did find one enterprising suggestion on a Flickr forum which involved taking out the centre of one of those rotating internal mount adapters and fitting the CS mount lens in there. The adapter I had was an RJ brand C to Pentax Q adapter and it does have a removable centre. The difference between the C-mount ffd and the CS-mount ffd is 5.026 mm. The thickness of the insert is approximately 5.9mm. Therefore my contribution was to include a small display-card material made shim inside the mount which was about 0.8mm given or take a vernier notch or two. Thus assembled and the grub screws as recommended by my source now holding the lens stub in place - it works!

The lens is labelled "Polaroid 5.7-43.2mm f1.0" (zoom) and seems identical to the Computar T6Z5710-CS of the same specifications.

Conveniently the lens stub of this lens fits easily and with just enough clearance into the stub where the insert came out of to take the grub screws nicely - also the various control rings are well clear of any interference from the adapter. The parts just seem made for this job. Other CS-mount lenses may need a slightly different fit - or it may not even work - but it sure beats machining out and gluing and you have the ability to experiment with the shim.

Now I seem to have a useful 32-240mm equivalent f1.0 zoom on my Pentax Q.

TomC

[Lightshow]

Pictures or it didn't happen.

[caerwall]

Job is done, no step by step images but it is pretty simple. I am not about to pull out my carefully placed grub screws lest I stuff it up (grin).

But this lens whilst technically a wonder on paper has it's limitations. Three adjustments as you might except for a zoom and they are all capable of being locked down. But the focus changes during zoom and f1.0 is not usable at all settings. Consequently it is obviously designed for fixed camera surveillance. Whereby the lens is adjusted to the site and then locked down. Such cameras need not be restricted to settings that might work harmoniously under constant manipulation nor are patently not usable setting variations edited out by the mechanism. With some patient manipulation a video-cam image experience can be had on a Pentax Q.

Luckily the barrel end just fits nicely inside the remaining adapter piece and the grub screws seem to have enough barrel end to get purchase on. Obviously each and every CS lens that is a candidate to be adapted to C-mount in this manner is a completely new ball game, some might work, some will take a little modification and others might never work.

Tom

[caerwall]

Checking about the web there is a fair bit of information about Kern Paillard Macro Switar lenses ostensibly in C-mount. In fact most vendors seem to be selling H8 RX lenses as "C-mount lenses". Again like CS mount lenses there are traps for the unwary (me).

The facts are that the H8 RX lenses were made for Bolex reflex cameras and are C-mount lenses made to D-mount flange back distance with an adjustment for the reflex glass. Consequently they do not focus properly on a native C-mount. Something that is alluded to but not specifically pointed out. One might have thought that there would be more talk about this specific problem.

Facts:
C-screw mount fitting 25mm thread

"H8 RX mount" 15.305mm
"CS mount" 12.5
"C mount" 17.526mm

D-screw mount fitting 15mm thread

"D mount" 15.875mm

The H8 RX mount is 2.221mm shorter flange back distance than a regular C-mount.

Therefore a similar modification to an existing C-mount adapter could be made after the fashion of the original post. However this is more fraught by the then necessity of a much larger spacer and also less lens but to screw the grub screws into. In fact on my particular lens it may not have been possible or the grub screws would enter the lens thread itself (ouch).

Luckily I found what seem to be the only regular maker of a suitable adapter on the planet:

http://www.ebay.com.au/itm/H8-RX-to-PENTAX-Q-/320907649763?pt=US_Lens_Adapters_Mounts_Tubes&hash=item4ab79622e3&_uhb=1#ht_1284wt_1033

Hope it helped. Easier than getting an existing D-mount drilled out countersunk and tapped.

Tom

[Phenix jc]

Like you I was trapped by CS Mount and unscrupulous sellers.
Notably a Kern Switar which was probably an H8 RX lens in fact.
Recently, I was also trapped by a lovely D mount, but it was entirely my fault (I don't have a PQ).
Anyway, I've learned something, thanks for sharing.