[Rodstar (Rod)]

What's the closest double star you can split in your scope?

I am interested in your experiences, and any tips you may have.

I have been getting into doubles in the last 6+ months, especially at times of the month when Lunar drowns out the deeper objects. Over time I have slowly been whitling down the separation I can comfortably split, as seeing conditions allow.

I have decided that close doubles where both stars are around the mag 8-9 mark are the easiest to split in my scope. If the secondary is more than about 2 mag fainter than the primary, I find the closer doubles very difficult. Separation often needs to be at least 2.5 arc" in those circumstances.

I made a hexagonal aperture mask a few months ago to help (enables close secondaries hiding in the glare of the primary to be identified between the diffraction spikes thus created), but my experience so far is that this method is only helpful with getting around very bright primaries.

A critical aspect to double splitting is making sure your scope has properly cooled. It is quite incredible how even 3 or 4 arc" splits can be difficult if the scope is not at ambient temperature. I have my scope out for 2 or 3 hours before observing now to make the most of my 10 inches of aperture.

Last night I spent some time looking at doubles in Triangulum Australe. The seeing was superb, so I decided to push the limits with my scope, and cranked up the magnification to achieve clean splits of the following:

1. HJ 4809 (SAO 253344), sep 1.2", constituents 6.5 & 8.5 mag, at 495x clean split.

2. I 333 (SAO 253588), sep 1.2", constituents 8.0 & 8.5 mag, clean split at 195x

This separation of 1.2 arc" is the closest I have achieved so far. I am bucking to try to break the 1 arc" mark. Last night I tried I 332 (SAO 253115), separation 1.1 arc", constituents 6.5 & 9 mag, but I could only achieve elongation, not a clean split.

What's the closest pair you have split? Do you have any tips for squeezing the most out of your scope?