C8 and StellaMira 125 - on the moon and a double

[Paz]

I was observing this evening with the C8 and started wondering how the SM125 would compare when I was getting softer views at higher magnifications and when I tried a double with the C8 it highlighted quite poor seeing, I think a combination of local rooftop heat and tube currents although the C8 had been out for a couple of hours. So I swapped scopes and went back over the same targets again with the SM125 at similar magnifications to compare. Here's what I thought...

The C8 was at about 230x and 345x with binoviewers.

The SM125 was at about 254x and 317x with binoviewers.

• Porrima - when the moon in the C8 was looking a bit murky I moved over to Porrima to check out the seeing more objectively, and defocused it was showing poor seeing and constantly moving/breaking diffraction rings. In the SM125 the view was a lot more clean and still and with fewer diffraction rings. A straight win for the SM125.
• Hortensius Domes (Lunar 100, number 65), the dark/light contrast and resolving the domes was slightly clearer in the SM125.
• Copernicus H (Lunar 100 number 74), the crater was resolved about the same, but the dark halo was slightly clearer in the SM125.
• Pico mountains (Lunar 100 number 23) I thought I got slightly more detail in the C8 but a more contrasty view in the SM125.
• Plato craterlets (Lunar 100 number 83) it wasn't a good time to try but I was ticking off Lunar 100 objects so had a go. I thought I could (barely) make out 3 with the C8 (and they didn't look like craterlets, they looked like slight imperfections in the floor), I don't think I could see any in the SM125, but I wondered how much difference an hour might make as the lighting would have been slightly worse for the SM125.
• Lambert R (Lunar 100 number 78) - a ghost crater, I thought this was slightly clearer in the C8 but again I wondered if the lighting was slightly worse by the time the SM125 had a go.

In other respects the C8 is higher workload to operate, I have to put a separate dew shield on the C8 and it needs 2 counterweights rather than 1 on an EQ5 as the C8 is a similar weight to the SM125 but it is fatter so its centre of gravity is further away from the counterweights , the SM125 focuser is better, the C8 takes longer to acclimatise, and I don't have to think or worry about collimation with the SM125.

Overall I thought the SM125 did slightly better on the views today, and if ease of use is added into the equation it was clearly better, but the C8 is no slouch.

It would have been good to have them side by side in the field to eliminate some of the variables in comparing them but I don't have the facilities to do that.

[John]

Very interesting report 👍

The more I read about the SM 125, the more I would like to try one 🙂

 

[Paz]

I've been mulling over the fairness of this comparison, and I think the SM125 had the benefit of going second as the seeing was getting slightly better as the night went on and the lighting of most of the lunar targets was only going to get slightly worse not better.

I also think the second scope gets the benefits of my eye/brain dialling in while I'm using the first one.

I thought the conditions meant that  the SM125 was giving a view closer to its best but the C8 had significantly more headroom to show better views if conditions were optimal.

I also realise I was using very high magnifications that I don't normally use, it would have been more sensible to compare at 150x-200x or so as that's much more commonly what I use.