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Old 24-11-2020, 06:49 AM
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OneCosmos (Chris)
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Fsq-85 + flattener 1.01x

Hi

I have an fsq-85 and want to use it with a full frame camera so purchased the 1.01x flattener. Unfortunately the camera I am using it with is the Canon EOS Ra, which therefore requires a wider than normal T-Mount to avoid vignetting but Takahashi don’t make one for the new Canon RF fit bodies (yet).

It will of attach happily to the RF-EF adapter but that means the flattener is now slightly further from the sensor than it would otherwise have been. I always understood that you don’t have much latitude with distance between the flattener and sensor so perhaps it will no longer produce a 44mm image circle?

If that’s true I’d have to image without the flattener which would no doubt be disappointing. Does anyone know if I would run into problems or not?

Alternatively does anyone know if I can buy a wide T Mount for the RF fit or is it possible for someone to make one?
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Old 24-11-2020, 10:29 AM
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Peter Ward
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The EosR mount to sensor distance is 20mm( Source: Canon) , however the FSQ flattener requires 56.2mm (Source: Takahashi America)
which.....oddly enough... is what you will get when you attach the EOS to EOSr lens adapter.

In short, use a wide-mouth EOS T-adapter (there are many available) with the Canon EOS to EOSr adapter and it should all work out nicely.
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Old 24-11-2020, 07:49 PM
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OneCosmos (Chris)
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Quote:
Originally Posted by Peter Ward View Post
The EosR mount to sensor distance is 20mm( Source: Canon) , however the FSQ flattener requires 56.2mm (Source: Takahashi America)
which.....oddly enough... is what you will get when you attach the EOS to EOSr lens adapter.

In short, use a wide-mouth EOS T-adapter (there are many available) with the Canon EOS to EOSr adapter and it should all work out nicely.
Thanks Peter, that is most helpful. It does, however raise the interesting question of why the Takahashi connection chart shows that for a DSLR the flattener should connect directly to the T Mount (no lens adapter needed) but wouldn’t that turn mean the regular DSLR wouldn’t end up with a flat field?

Anyhow, I won’t know until the Aux Ring arrives which is necessary to allow the camera to come to focus.
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Old 24-11-2020, 11:14 PM
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Peter Ward
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The T-mount standard expects the focal plane to be at 55mm from the
front of the t-mount. Hence an EOSr T-mount would need to be quite thick to comply...but for a normal DSLR the native spacing is quote close.

You'll be off by 1.2mm ......I wouldn't lose sleep over it
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Old 25-11-2020, 06:35 AM
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OneCosmos (Chris)
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Quote:
Originally Posted by Peter Ward View Post
The T-mount standard expects the focal plane to be at 55mm from the
front of the t-mount. Hence an EOSr T-mount would need to be quite thick to comply...but for a normal DSLR the native spacing is quote close.

You'll be off by 1.2mm ......I wouldn't lose sleep over it
Thanks Peter, I’ll have to check the depth of the Takahashi wide T-Mount for Canon because it is indeed quite thick compared my older non-wide T-mount (which is barely thicker than plate metal and needs a special tool to extract it as there’s nothing to grip on to!). Perhaps I’ll manage to find the dimensions of the Tak wide T-Mount online.

*Update. Takahashi America seems to suggest the wide T-Mount is 15mm and the canon adapter is 24mm for a total therefore of 39mm so I remain at least 17mm shy of the required distance between flattener and sensor. Or, have I misunderstood something?

*update 2: I forgot to add the 20mm mount to sensor didn’t I? So now the distance will be 59mm so I will actually be 2.8mm over. Is that kind of tolerance acceptable?

Last edited by OneCosmos; 25-11-2020 at 07:30 AM.
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