Reflex Lens on Filmo 70DR

[John Crowe]

I have a Som Berthiot Pan-Cinor 17-70 reflex dogleg lens and a Filmo 70 DR. I just put them together, and because of the weight of the lens the Filmo lens turrent just falls down instead of locking.

Wondering if anyone has ever tried this, or a solution for this. It would be very nice to have a reflex and be able to focus. The other mystery to me is some folks online say the labeled f-stops are actually T-stops, but other places say just f-stops, and to adjust for light loss.

Any input would be nice. Thought since I had them both would be great to get them working, I could swap some c mount primes from a bolex to use with the Filmo(it has the viewfinder lenses)...but a double reflex on the bolex seems silly. I'm unlikely to spend money on more lenses at this time.

thanks

[Simon Wyss]

As silly as it may appear, you can try out the Elgeet Cine-Flex. That’s a very lightweight accessory you occasionally find on ebay, basically a rectangular plastic box with a partially reflecting glass pane in it. Above the glass you have an ocular and scribes for various focal lengths. It doesn’t help with focusing but it gives parallax-free framing. The Cine-Flex was made for 16-mm. and for 8-mm. cameras.

Pan-Cinor are heavyweights. You may want to find a Compact Vario-Switar or a modern zoom lens (why does it have to be an ancient varifocal conundrum?). In any case the Filmo 70-DR was not made for zoom optics. What speaks against nice compact primes?

[Dom Jaeger]

6 hours ago, John Crowe said:

It would be very nice to have a reflex and be able to focus.

The Pan Cinor 70 (17.5-70) is not a focussing dogleg zoom, the reflex finder is only good for framing. 

6 hours ago, John Crowe said:

The other mystery to me is some folks online say the labeled f-stops are actually T-stops, but other places say just f-stops, and to adjust for light loss.

The zoom is marked in f stops. The front barrel describes the geometric aperture as 1:2.4 so f/2.4 is the maximum aperture, which is what's marked on the aperture ring. Most C mounts and early zooms were only marked in f/stops. Later zooms sometimes had 2 marks on the aperture ring for f and T stops. 

It's hard to say exactly how much light is lost due to both the internal light loss and the reflex finder, but you can look at literature for a near-contemporary (slightly later) zoom like the Angenieux 12-120 which had both dogleg and normal versions and it describes the light transmission:

https://www.pacificrimcamera.com/rl/01068/01068.pdf

Light transmision for the normal zoom is 78%, while transmission for the dogleg version is 63%. 

If the Pan Cinor zoom has similar light loss, the dogleg version would be around T3. The normal versions that you sometimes see with Arriflex mounts for instance would be around T2.7.

[John Crowe]

Thank you both, very helpful. I will wait to get some primes when $ allows.

[Simon Wyss]

You don’t need to spend much money. Some four-glass lenses deliver first class imagery such as the original Perlynx of Hermagis (yes, exists as C-mount lens), continued as Cinor B after the merge Hermagis-Berthiot in 1934, or the Zeiss Tessar or the Ernostar variants. One of them is the Kern-Paillard Yvar 25 mm (one inch), f/1.8, often cheap because many people don’t bother about the construction. Another one is the one-inch Ivotal by TTH, and then you have a modern Petzval-type lens, the Animar 26 mm, f/1.9 by Bausch & Lomb, tack sharp in the centre, becoming sharp all over when stopped down progressively.

Triplets deliver well when used smartly on black-and-white film with filters. Cut out excess blue with a yellow filter and you’ll open your eyes upon projection. C-mount triplets are legion, almost every lens manufacturer made such.