Testing KIPON Baveyes LPL to Mamiya 645 focal reducer - NOT achieving the advertised 0.7x boost

[Tim Sessler]

Hi everybody -

I recently bought a Kipon Baveyes 0.7x focal reducer for my Mamiya Sekor C 645 lenses. The 80mm was the lens I was most excited about as with the speedbooster it should match one of my all time favorite lenses: a Canon FD 55mm.  Funny enough all the Mamiyas felt much longer than what I would have expected. The 35mm should match a 24, the 45 a 32 and the 80 a 55.

To verify my suspicion I used a PL to LPL adapter, which would allow me to quickly swap from the LPL Kipon focal reducer to my rehoused Canon FDs. 

Here is what I found: 

 

 

As you can see the Mamiyas are significantly tighter. In fact the actual crop factor/focal reduction seems to be closer to 0.8x. 

Which means the 80 isn't matching a 55 but rather 64mm and the 35mm isn't as wide as 24mm but much rather matching a 28mm.

Here is a full write up with more samples (both from me and also shots from other lens tests): 

http://brooklynaerials.com/blog/2022/8/7/calculating-kipon-baveyes-true-crop-factor

 

 

This seems to be a pretty big deal and very misleading advertising on Kipon's end.  I am surprised nobody else has pointed this out (at least I could not find anything along those lines). 

I'd be curious if this is the same for the other KIPON Baveyes adapters like the LPL to Hasselblad V Mount or the Baveyes focal reducer made for RED DSMC2. 

 

Let me know what you think and if you've seen similar discrepancies with focal reducers. 

 

Cheers!

 

[Dom Jaeger]

There is often some approximation to focal length calculation. 

It’s also worth noting that many lenses breath, causing significant shifts in the apparent focal length at different distances. If two lenses of the same focal length breath differently, one may have quite a different field of view at close focus than another. Try testing at infinity, where the focal length is calculated.

That said, you may be right that this focal reducer is not actually what it advertises itself to be. I haven’t tested one personally.

[Tim Sessler]

4 minutes ago, Dom Jaeger said:

There is often some approximation to focal length calculation. 

It’s also worth noting that many lenses breath, causing significant shifts in the apparent focal length at different distances. If two lenses of the same focal length breath differently, one may have quite a different field of view at close focus than another. Try testing at infinity, where the focal length is calculated.

That said, you may be right that this focal reducer is not actually what it advertises itself to be. I haven’t tested one personally.

Both very valid points, Dom!   That being said - from what I understand - lenses are typically rounded up or down to get to even numbers but should not have a significant difference. E.g. a 80 might actually be a 79.xx or 80.xx  but wouldn't be a 90mm. 

As far as the breathing that is also spot on - and especially accurate for the Mamiyas as they breath A LOT!  That being said I tested both the 55 FD and 80mm Mamiya at infinity today and they are still FAR from a match. 

Hope this makes sense.

[Dom Jaeger]

Yes, you seem to be finding more of a discrepancy than the points I brought up explain. 

It might be worth contacting the manufacturer to get their response.

I think TLS use these reducers for their Mamiya rehousings. A local rental house has a set, so next time we sub-hire them I’ll put them on the projector and do a focal length check. You could send TLS an email as well.

[Michael Lindsay]

to re-iterate Dom's point re breathing... Mamiya FOV really change massively with focus

I quickly tested the 

TLS Mamiya 25mm (as you know made from a 35mm 645 lens and the Kipon reducer) against a Arri Signature 25mm

TLS Mamiya 57mm (as you know made from a 80mm 645 lens and the Kipon reducer) against a Arri Signature 58mm

TLS Mamiya 78mm (as you know made from a 110mm 645 lens and the Kipon reducer) against a Arri Signature 75mm

I tested at 5-6ft (so the mamiyas will have contracted quite a bit due to breathing) and did my best to line up the entrance pupils!

In every instance the signatures are wider! ... and if you consider just a 16mm portion from the centre then even more so.. 

But due to breathing I would assume I'd see the results I got.. 

I can measure the focal length of lenses but I am not quick or clever in doing so... others would laugh at my process and I have to assume non variable magnification across frame.

If I get time I will try at infinity ALSO but on refection I think I need to look at the the whole image as the Mamiyas are far from rectilinear in projection so it gets a bit complicated re focal length.. 

Edited August 27, 2022 by Michael Lindsay

[Michael Lindsay]

Ok I just quickly looked again at the 25mm and the 57/58mm 

very rough test indoors but set to infinity and stopped down.. 

the Signature 58mm was now a tad longer but very close.. (as it should be) 

the Signature 25mm was still a little wider but much closer than before... 

So breathing is a big deal..

I do think the optical design of the reducer prob needs tweaked per lens so maybe .71x is just an average or ideal use abstraction... As I mentioned on another forum the Mamiya 45mm N is narrower via the Kipon than the Mamiya C older design used in the same way.. 

 

[Tim Sessler]

Hi Michael -

Interesting one. I did also test at infinity against my FD and found very similar results to the closer focus (though just a tad less extreme). 

 

I finally heard back from Kipon but they have not been super helpful trying to resolve this.  

See text exchange attached. According to them its Mamiya focal length x diagonal ratio x 0.7. 

That being said all the calculations that I could come up with did not make any sense at all.  They unfortunately could not answer what exactly they meant with 'diagonal ratio'.  Though according to them the TLS rehoused ones are actually correct focal lengths, while the standard non-rehoused ones are not. Adding more confusion and unfortunately not properly clearing things up.

 

Let me know if any of this makes any sense. 

 

Cheers!

Tim

 

 

 

[Michael Lindsay]

I have tried reading the above sober and drunk and it made no sense sober and some sense drunk but I am sober now so I can't remember what I thought it meant when I read it drunk ? 

Sorry to be no help!