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aperture settings on camera lens + QHY

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7 replies to this topic

#1 altair05

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Posted 06 May 2021 - 07:36 AM

I'm trying my QHY268C with Canon lenses for the first time. Something I hadn't thought about before, but how do you control aperture settings? If you set the required aperture when it's attached to the Canon camera body, will it remain at this f/stop when transferred to the QHY?



#2 SilverLitz

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Posted 06 May 2021 - 07:43 AM

You can use thread on step-down rings.  They have the advantage of not causing spikes in stars.

 

Astromechanic's EOS adapter does allow you to control aperture and even AF with your computer.  You will need to check the backfocus to make sure you have ~44mm from the back of the lens flange to the camera sensor.



#3 kathyastro

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Posted 06 May 2021 - 09:07 AM

If you set the required aperture when it's attached to the Canon camera body, will it remain at this f/stop when transferred to the QHY?

The best answer is "it depends". 

 

On my Pentax lenses, both the old ones from my manual SLR and the newer one from my DSLR, the aperture is held open for metering by a lever in the camera.  When the lens is detached, a spring in the lens stops the aperture down to its preset value.  So you could use either type of lens on a non-cooperating camera in manual aperture mode.

 

Different manufacturers likely use different mechanisms to interface their cameras to their lenses.  The best way to check your lens is to detach it from the camera and look through it while adjusting the aperture ring.  If you see the diaphragm stopping down the aperture, then it will work on your QHY.  If you don't see it stopping down, then the lens requires cooperation from the camera, which it won't get from the QHY

 

If the lens doesn't have an aperture ring, then there is little hope of getting it to stop down on the QHY.


Edited by kathyastro, 06 May 2021 - 09:09 AM.


#4 altair05

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Posted 06 May 2021 - 09:35 AM

Yes, understood. I realise the QHY won't be able to adjust the aperture of the lens. Just would like to be able to know before an imaging session what aperture it's set to. There is no manual aperture ring. I will experiment though, setting a smaller aperture with it attached to the EOS camera and then detaching it and seeing if the iris remains decreased. The step-down rings aren't a bad answer. I do have a set for my 70 - 200 zoom. Just a bit of maths involved to work out what f/stop you're working at.



#5 altair05

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Posted 07 May 2021 - 09:58 AM

In case anyone else had this problem, I've just been given a simple solution. With the lens on your DSLR, you select the aperture you want and then hold down the depth of field preview button while detaching the lens. The set aperture remains the same when transferring the lens to the QHY.


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#6 jkcolli

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Posted 07 May 2021 - 02:55 PM

Buy this:

 

Astromechanics ASCOM Canon Lens Controller Mark II  M54x0.75mm adapter for APS-H/FF camera.

 

 

It works great and lets you adjust aperture and focus via USB.  You can use the Astromechanics executable(CanonEFDesktopControl.exe) or NINA or APT.

 

Below is a table showing the backfocus setup.  The QHY 02002 Adapter and 0.5mm spacer came with your camera(QHY268C)

EOS Lens                                                 0.0
Astromechanics Canon EF Controller   20.0
QHY 02002 Adapter                                6.0
Spacer 0.5mm                                         0.5
QHY268C Backfocus                            17.5


Total Backfocus                                    44.0

 

Jack



#7 altair05

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Posted 07 May 2021 - 09:34 PM

Thanks for the detailed breakdown, Jack. Expensive solution but looks good. 



#8 t-ara-fan

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Posted 08 May 2021 - 02:55 PM

  Expensive solution but looks good. 

I have an Astromechanics adapter enroute to me right now.  Expensive?  I paid more than double that for my Birger EOS adapter, which cannot autofocus due to the nature of the driver.

 

I am looking forward to using my ASI071MC with a Canon 200mm f/2.8 prime and having autofocus capability all night as I hunt for IFN.
 




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