Skyler Carrico Posted July 19, 2023 Share Posted July 19, 2023 What's the difference between RX C mount lenses (for Bolex) and regular/non-RX lenses? I see this 10mm for sale on eBay with no mention of RX and this one that says RX, but I can't really see what's different about them. Which C Mount Switar lenses will work on an ACL? Link to comment Share on other sites More sharing options...
Skyler Carrico Posted July 19, 2023 Author Share Posted July 19, 2023 Sorry for the double-post, not sure how that happened. Can't delete the first one Link to comment Share on other sites More sharing options...
Skyler Carrico Posted July 19, 2023 Author Share Posted July 19, 2023 Another question... Is Les Bosher's $500 PL adapter really 400% better than this: https://www.ebay.com/itm/252925685539 Having a hard time justifying that extraordinary cost for an adapter. Can someone help me understand how and why it's so much better? Link to comment Share on other sites More sharing options...
Skyler Carrico Posted July 19, 2023 Author Share Posted July 19, 2023 And finally... If I have a TS to Arri-S adapter, can I use this lens on an ACL? Link to comment Share on other sites More sharing options...
Premium Member Duncan Brown Posted July 19, 2023 Premium Member Share Posted July 19, 2023 9 hours ago, Skyler Carrico said: What's the difference between RX C mount lenses (for Bolex) and regular/non-RX lenses? I see this 10mm for sale on eBay with no mention of RX and this one that says RX, but I can't really see what's different about them. Which C Mount Switar lenses will work on an ACL? The Bolex split prism reflex viewing system (unlike, say, the ACL with its mirror/shutter arrangement) can do weird things to light that comes in at shallow angles, like with wide lenses at large apertures. So the RX variations of lenses are designed to compensate for that. There is no need for an RX lens on an ACL, leave those for the Bolex users. Duncan Link to comment Share on other sites More sharing options...
Premium Member Duncan Brown Posted July 19, 2023 Premium Member Share Posted July 19, 2023 9 hours ago, Skyler Carrico said: And finally... If I have a TS to Arri-S adapter, can I use this lens on an ACL? In theory yes. (I don't have a TS-Arri adapter, though I wish I did! I have a lot of Arri-S lenses and an ACL.) Duncan Link to comment Share on other sites More sharing options...
Premium Member Dom Jaeger Posted July 20, 2023 Premium Member Share Posted July 20, 2023 Lenses marked "RX" or sometimes "DV" have a slightly modified optical design to compensate for the Bolex beamsplitting prism found in reflex Bolex models. The prism can introduce aberrations on normal lenses that are 50mm and under, though the aberrations are generally reduced the more you stop down. For an ACL or any C mount camera that's not a reflex Bolex you'd want to use normal lenses. If you did use an RX one it would probably be OK stopped down past around f/4. Be very careful with certain C mount lenses that have a mounting thread that extends more than about 4mm, like older AR (normal) Switar 25mm lenses, as they will screw in too far and can damage the baffle and potentially break the mirror on an ACL. I've seen a few broken ACL mirrors because of this. With adapters, you pay for things like material quality and machining accuracy, and whether the adapter spaces out to the correct flange depth. A Les Bosher adapter will be made from stainless steel, and should be very accurate in terms of flange depth and flatness, the PL lock ring will lock smoothly and at the right depth and the finish will be nicer etc. Cheaper adapters will be made from aluminium or brass alloys, which are more susceptible to wear, they may have burrs or machining defects, and they may not seat a lens accurately. If the flange depth is off even by a few hundredths of a mm it can cause a zoom to lose focus as you zoom out or a prime to not reach infinity. That said, the Raf Camera adapters are usually pretty decent. Be aware that PL to C mount adapters may not accept all PL lenses, or work on all C mount cameras. Check the drawing dimensions to work out compatibility. Again, expensive adapters tend to have been better designed to be more compatible. The Eclair TS adapters are exceptionally good quality, if you have one for Arri Standard you can use any Standard mount lens with it. Link to comment Share on other sites More sharing options...
Gregg MacPherson Posted July 20, 2023 Share Posted July 20, 2023 (edited) On 7/19/2023 at 2:40 PM, Skyler Carrico said: And finally... If I have a TS to Arri-S adapter, can I use this lens on an ACL? There's a good history of Q&A on useful older primes that used to come up on eBay with Arri-B or S mount. Actually they still do. There are a few good Schneiders showing on that page you link to. Also look for Cooke Kinetals. Some early lenses, like the Zeiss distagon 8mm in your link, focus by having the mount rotate in the port. A little vaseline on there and the old timers were fine with it. If you do get an ACL and are thinking about mounting early lenses, there is a very common ver of the factory TS/Arri-B mount that also takes Arri-S. Gregg Edited July 20, 2023 by Gregg MacPherson more words Link to comment Share on other sites More sharing options...
Premium Member Duncan Brown Posted July 20, 2023 Premium Member Share Posted July 20, 2023 8 hours ago, Gregg MacPherson said: If you do get an ACL and are thinking about mounting early lenses, there is a very common ver of the factory TS/Arri-B mount that also takes Arri-S. I have not found those to be common. In fact I haven't found one at all! Someone sell me one. Duncan Link to comment Share on other sites More sharing options...
Skyler Carrico Posted July 20, 2023 Author Share Posted July 20, 2023 15 hours ago, Dom Jaeger said: Lenses marked "RX" or sometimes "DV" have a slightly modified optical design to compensate for the Bolex beamsplitting prism found in reflex Bolex models. The prism can introduce aberrations on normal lenses that are 50mm and under, though the aberrations are generally reduced the more you stop down. For an ACL or any C mount camera that's not a reflex Bolex you'd want to use normal lenses. If you did use an RX one it would probably be OK stopped down past around f/4. Be very careful with certain C mount lenses that have a mounting thread that extends more than about 4mm, like older AR (normal) Switar 25mm lenses, as they will screw in too far and can damage the baffle and potentially break the mirror on an ACL. I've seen a few broken ACL mirrors because of this. With adapters, you pay for things like material quality and machining accuracy, and whether the adapter spaces out to the correct flange depth. A Les Bosher adapter will be made from stainless steel, and should be very accurate in terms of flange depth and flatness, the PL lock ring will lock smoothly and at the right depth and the finish will be nicer etc. Cheaper adapters will be made from aluminium or brass alloys, which are more susceptible to wear, they may have burrs or machining defects, and they may not seat a lens accurately. If the flange depth is off even by a few hundredths of a mm it can cause a zoom to lose focus as you zoom out or a prime to not reach infinity. That said, the Raf Camera adapters are usually pretty decent. Be aware that PL to C mount adapters may not accept all PL lenses, or work on all C mount cameras. Check the drawing dimensions to work out compatibility. Again, expensive adapters tend to have been better designed to be more compatible. The Eclair TS adapters are exceptionally good quality, if you have one for Arri Standard you can use any Standard mount lens with it. Appreciate this info, thanks Dom! Link to comment Share on other sites More sharing options...
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