A superfast normal on the G1

[monza]

There is a Pen F adapter for sale from Hawk, it's actually the same as his c-mount adapter. It works with Pen F lenses via a Pen F extension tube flange which screws into the front of the adapter. He's supposed to be designing his own flange, but it's not ready yet.

If anyone wants to use Pen lenses, drop me a PM, I have some spare extension tube sets.

 

[Godfrey]

Godfrey - did you adapt the lens yourself or does someone now have a Pen F lens adapter for sale?

I am using an adapter made by screwing the lens mount portion of a Pen F extension ring set into a micro-FourThirds telescope mount flange adapter (available for $43 from Hutech). This is essentially identical to what Hawk is producing at present and works well, but the Pen F extension ring sets are a little hard to find.

jinfinance is working on a direct Pen F to micro-FourThirds adapter. I thought it would be available by now but last I talked to him he was delayed a couple of weeks. I'll send him another note ... I'd like a second one so that each of my Pen F lenses (40/1.4 and 70/2) will be easy to handle.

 

[monza]

The difference between the Hawk and the Hutech is that the focus scale is oriented properly with the Hawk adapter, and it's a correct 50mm thread instead of 49.8mm on the Hutech which is close, but not quite a match to the Olympus extension rings.

Not sure what is up with Jinfinance, he first said March for the Pen adapter...

 

[Godfrey]

The difference between the Hawk and the Hutech is that the focus scale is oriented properly with the Hawk adapter, and it's a correct 50mm thread instead of 49.8mm on the Hutech which is close, but not quite a match to the Olympus extension rings.

Not sure what is up with Jinfinance, he first said March for the Pen adapter...

Thanks! The Hutech thread is close enough, in practical use. Actually, the odd position of the focus scale lets me see the aperture markings on my FT series 40/1.4 lens more easily. I only rarely look at the distance scale for this long a focal length as I focus it through the viewfinder. Since I put the 40 on the adapter, I've only rarely taken it off: the position doesn't bug me.

Yeah, jinfinance told me ten days about three weeks ago. Must be busy.

 

[Jonas]

(...) the odd position of the focus scale lets me see the aperture markings on my FT series 40/1.4 lens more easily.

It owuld be great with a direct and proper adapter.
The aperture ring and the markings... On my 40/1.4, and I guess they are all made the same way, you can pull the aperture ring towards the front of the lens and then turn it 180 degrees. That way you can chose between the Pen index numbers or the normal f-stop values.

I hope Hawk or jinfinance or anyone make agood adapter, and ship it some time soon.

 

[monza]

Hawk is shipping. Here is a photo of the extension flange on a Hutech adapter (49.8mm thread to micro 4/3.) The red dot needs to be at about 2 oclock for proper lens orientation. Sometimes removing the lens is tricky as it's a bit too easy to unscrew the flange, but it works.

 

[Jonas]

(...) I'd like a second one so that each of my Pen F lenses (40/1.4 and 70/2) will be easy to handle.

You have the 70/2. Great! I'm interested in that lens. Do you have any words on how it performs?

thank you, /Jonas

 

[Godfrey]

It owuld be great with a direct and proper adapter.
The aperture ring and the markings... On my 40/1.4, and I guess they are all made the same way, you can pull the aperture ring towards the front of the lens and then turn it 180 degrees. That way you can chose between the Pen index numbers or the normal f-stop values.

Didn't know that, cool. ;-)

But the external aperture ring mechanism is a bit gummed up on this one and I won't force it ... should get a CLA but eh? The lens works beautifully as is, so I'm leaving it alone.

 

[Godfrey]

You have the 70/2. Great! I'm interested in that lens. Do you have any words on how it performs?

It's a slender, pretty piece ... much like the 40/1.4 but about an inch or so longer. I have it fitted with a B+W Telephoto metal lens hood (49mm on a 43->49mm step up ring). Imaging qualities are much like the 40/1.4 too. Four quick examples ...

All taken between f/2 and f/2.8.

I haven't used it much as yet, it's a bit longer than I normally shoot with, but I'm pleased with it. It was a bit on the pricey side of things.

 

[Vivek]

It owuld be great with a direct and proper adapter.
The aperture ring and the markings... On my 40/1.4, and I guess they are all made the same way, you can pull the aperture ring towards the front of the lens and then turn it 180 degrees. That way you can chose between the Pen index numbers or the normal f-stop values.

That is a preset mechanism and is only available in Pen FT lenses. The Pen F lenses do not have the pen numbering (that was for metering) and do not have that. So, if you do not see the pen FT (whole) numbers or see a sticker (instead of engraved numbers), pulling and trying to twist that ring could damage the aperture!

 

[Jonas]

(...) So, if you do not see the pen FT (whole) numbers or see a sticker (instead of engraved numbers), pulling and trying to twist that ring could damage the aperture!

Ah. Oh. Thank you Vivek. I'll remember that in the future! Regards, /Jonas

 

[Jonas]

Didn't know that, cool. ;-)

But the external aperture ring mechanism is a bit gummed up on this one and I won't force it ... should get a CLA but eh? The lens works beautifully as is, so I'm leaving it alone.

Yes, it is cool. But I didn't know about the difference between the F and FT lenses (Vivek's post). Anyway, it doesn't matter a lot what numbers there are. As I'm used to f-stop values it felt natural to set them to show, that's all.

 

[monza]

On the Pen F lenses (with just f/stops and no meter numbers) it's not really possible to pull up the aperture and turn, as on the Pen FT lenses...if one were able to accomplish that, yes, the lens would be seriously damaged.

 

[lcubed]

i've got a macro switar 26mm f1.1 and a jinfinance c-mount to mFT adapter on its way.

is a shim needed since this is a bolex rx lens??

i came across this:

From lensseat to filmplane is 20.76mm in the Bolex H16 RX, while it is 17.52mm in a C-mount camera.

 

[Y.B.Hudson III]

"is a shim needed since this is a bolex rx lens??"...

no... the 26mm switar will focus a little past infinity with close focus distance at 18cm±... with the focus throw at 590° ±...

A 3mm shim would not leave enough exposed threads to mount the lens...



regards Hudson

 

[lcubed]

great news. i was afraid that i wouldn't be able to focus to infinity.

now the long wait for the adapter...

 

[apicius9]

"is a shim needed since this is a bolex rx lens??"...

no... the 26mm switar will focus a little past infinity with close focus distance at 18cm±... with the focus throw at 590° ±...

A 3mm shim would not leave enough exposed threads to mount the lens...



regards Hudson

Thanks for the info - I hope that also works for the 50/1.4RX that should be over one of the oceans between England and Hawaii right now

Stefan

 

[Ranger 9]

i've got a macro switar 26mm f1.1 and a jinfinance c-mount to mFT adapter on its way.

is a shim needed since this is a bolex rx lens??

i came across this:

From lensseat to filmplane is 20.76mm in the Bolex H16 RX, while it is 17.52mm in a C-mount camera.

That "information" about Bolex flange distances is all over the Internet, but when we discussed this before I think the consensus we reached is that it's incorrect.

According to this 1974 technical bulletin from Bolex, which I found on the Bolex Collector website: All Bolex C-mount lenses, whether RX or not, have the same back focus distance (in air) of 17.52mm. This suggests there should be no reason to shim the lens to use it on your G1, since there's nothing but air between the back of the lens and the imager.

The 20.76mm distance you sometimes hear about is based on a misunderstanding about how Bolex dimensioned their reflex and non-reflex cameras. The reflex prism in the RX models displaced the image rearward slightly. (Actually, ANY parallel-faced block of glass you put behind a lens will displace the image rearward by about 1/3 the thickness of the block.)

Specifically, the Bolex prism is 9.5mm thick and displaces the image by 3.24mm. This meant that a lens set up for the standard 17.52mm back focus distance would actually form its image through the prism at 20.76mm, and the RX bodies were dimensioned to allow this extra distance. Without the prism, though, the same lens would form its image at the standard 17.52mm.

So if reflex and non-reflex lenses focused at the same distance, why did Bolex offer a special RX version of some lenses? According to the same paper, it was because the prism block introduced spherical aberration in some lenses (mostly shorter ones) and the RX-series lenses were designed to take this into account and neutralize it. That means that an RX lens used on a non-RX camera (such as your G1) probably won't perform as well as a non-RX lens when used at its widest apertures. The remedy is simply to stop the lens down a bit when sharp results are critical.

If you really want to dig into this further, a cinematographer named Dennis Couzin wrote a very detailed analysis in 1976, along with several follow-up articles. Couzin's "Revised RX Rule" of 1978 posits:

RX-mount lenses work well on C-mount cameras provided they are used (for focusing and taking) stopped down past about f/2.8 and provided they meet the exit pupil test.

Exit pupil test: Stop down a lens and view it from the rear. If the pupil appears deep set in the lens, an inch or more back from the mount, then the lens passes. If it appears shallow in the lens then the lens fails, and even with much stopping down will not give good corner images used o the opposite kind of camera [RX vs. non-RX.]​

I suspect that the different spherical aberration correction given to RX vs. non-RX lenses may be the cause of the semicircular "swirlies" we see in the corners of some G1 pictures made with Bolex lenses, when other examples of apparently the same lens don't produce the same effect. But I don't have any way to investigate that. Maybe if you post some pictures made with your RX Switar we can all compare them to pictures made with similar non-RX Switars, and we'll be able to see whether my guess is true or not.

 

[dcouzin]

Thanking Ranger9 for getting the matter of the Bolex RX-mount lenses mostly correct.
Actually it's an oversimplification to say that the RX-mount lenses and C-mount lenses have identical 17.52mm backfocus (in air). The backfocus is identical for the paraxial rays -- the rays left after the lens is greatly stopped down. But the backfocus is significantly different for marginal rays -- the first rays removed as the lens is stopped down from full open. In Figure 3 of my 1976 "The Truth about the Bolex Prism" this difference is the distance from point P to point Q. [Thankfully that one figure wasn't distorted by whoever copied the original 1976 article for Ranger9's first link, but thE copiest omitted the distance scale from the figure. Readers of the 1976 article should better look at the original posted at Ranger9's second link.] For an f/1.1 RX-mount lens the distance from P to Q is about 0.28mm. Properly speaking, there is no backfocus measurement for such a lens.

The following improved version of the RX/C Rule appeared in the 1987 article (also available at Ranger9's second link):

A C-mount lens works well on a RX camera or a RX-mount lens works well on a C camera, if and only if:

(1) the lens is slower than about f/2 or f/2.8, or stopped down this far;​

AND (2) the lens has deep set exit pupil, about 1½ inches or farther into its screw mount.​

Thus the 26mm f/1.1 Macro-Switar, being an RX-mount lens, is a very poor choice of "superfast normal" for the G1 camera (unless you plan to mount a 9.5mm thick pane of glass behind the lens to compensate its RX-mount aberrations).

In general, this strand's fascination with using C-mount lenses on the G1 is optically perverse. The C-mount lenses were mostly designed to cover the 16mm cine frame having image diagonal about 12.6mm. The G1 camera sensor has diagonal about 21.6mm. "Covering" in photographic optics doesn't mean simply "putting light onto". That some C-mount lenses don't vignette much of the G1 frame should not suggest that these lenses are optically corrected for that oversize area. Actually, well-designed 25mm lenses for 16mm cine (like the Zeiss Distagon 25mm f/1.2) are already losing correction at the extreme 12.6mm diameter. They pack their sharpness into the intended frame area. By 16mm diameter they are perhaps 1/10 as sharp as at 10mm diameter.

 

[Vivek]

In general, this strand's fascination with using C-mount lenses on the G1 is optically perverse.
..
..


They pack their sharpness into the intended frame area. By 16mm diameter they are perhaps 1/10 as sharp as at 10mm diameter.

Optically perverse. Love that.:ROTFL::ROTFL:

Do you know of any lens that does not drop sharpness (and other corrections) from the center, that is made for still cameras?