#1  
Old 24-11-2020, 06:49 AM
OneCosmos's Avatar
OneCosmos (Chris)
Registered User

OneCosmos is online now
 
Join Date: Apr 2010
Location: Brisbane
Posts: 419
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 donít 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 donít have much latitude with distance between the flattener and sensor so perhaps it will no longer produce a 44mm image circle?

If thatís true Iíd 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?
Reply With Quote
  #2  
Old 24-11-2020, 10:29 AM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 7,200
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.
Reply With Quote
  #3  
Old 24-11-2020, 07:49 PM
OneCosmos's Avatar
OneCosmos (Chris)
Registered User

OneCosmos is online now
 
Join Date: Apr 2010
Location: Brisbane
Posts: 419
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 wouldnít that turn mean the regular DSLR wouldnít end up with a flat field?

Anyhow, I wonít know until the Aux Ring arrives which is necessary to allow the camera to come to focus.
Reply With Quote
  #4  
Old 24-11-2020, 11:14 PM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 7,200
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
Reply With Quote
  #5  
Old 25-11-2020, 06:35 AM
OneCosmos's Avatar
OneCosmos (Chris)
Registered User

OneCosmos is online now
 
Join Date: Apr 2010
Location: Brisbane
Posts: 419
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, Iíll 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 thereís nothing to grip on to!). Perhaps Iíll 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 didnít 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.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 09:32 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.
Advertisement
NexDome Observatories
Advertisement
Testar
Advertisement
Bintel
Advertisement
Limpet Controller
Advertisement
Astronomy and Electronics Centre
Advertisement