Minimum size refractor for photometry

[John Coffin]

Hi, I’d like some advice on the minimum size of telescope I can use for photometry. I am thinking of piggy backing my 60 mm guide scope (225mm focal length) onto my C11 so I can measure the magnitude of a target star when performing spectroscopy. I would be using an ATIK 460 which has 4.56 micron pixels, so I imagine I would have to add a x 2 Barlow to the image chain in order to get a reasonable pixel scale.
The targets are generally down to around mag 12.
Is this a viable proposition? I also have a 80 mm Skywatcher Equinox ED scope with a focal length of 500mm but this is rather heavy for my setup. Thanks. John

[Jeremy Shears]

Hello John,

I don’t see why this should not be possible. Might need to increase exposure to get suitable SNR for fainter targets.
VSS observer David Conner has routinely used a 50mm finder for photometry. Lots of details and links to his articles in the VSS Circular on his website: https://davidsconner.weebly.com/. I can see he doing pre use photometry on EBs below mag 11. Also examples of using a Seestar S30.

Jeremy

[Dr Paul Leyland]

To amplify what Jeremy says: I have over sixty thousand images of T CrB taken with a Seestar S50. The size of the data processing task is daunting and automation will be essential. Your proposed system has a bigger aperture and, presumably, a better quality and equatorial mount.

The SS50 has a OSC camera, with its inevitable loss of sensitivity for precision photometry. If you can fit a mono camera and a photometric filter — almost certainly Johnson V — you should be able to do markedly better than a stock SS50.

Paul

[John Coffin]

Thanks, that’s very useful. I will go ahead with my 60mm guide scope.
John

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