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Get a quality 2x Barlow and use with your 5mm DeLite. A Powermate would be better to maintain eye relief but there is none at 2x in 1.25” size so you need a different focal length eyepiece to start with if using a 2.5x or 5x Powermate.
2.5mm at f6 gives 0.42mm exit pupil which for me personally is the smallest I prefer before the image starts looking dim. 252x is a nice power for Mars.
Note 0.5mm increments in focal length of the eyepiece are noticeable even at 630mm focal length.
Between 3.5, 3 and 2.5 you go from 180x, 210x and 252x and seeing will determine which yields the best image. On my TV-101, I use the 6-3mm and 4-2mm Nagler zooms for variable magnification. If seeing is superb, I use the 4-2 zoom for 135 to 270 magnification. Then again when seeing is superb I often switch to a larger aperture (Newt) for a lot more light at the same magnification, (achieved with differing focal length eyepieces).
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