120mm v 132mm Refractor

[Hoges]

Hi guys, what differences would you expect to notice between 120mm v 132mm for visual on comparable triplet refractors? When I had the opportunity to look through a 120 ed doublet several years ago at Vicsouth, the improvement in resolution on globulars was a noticeable jump from my 100mm ed. Cheers - John.

[astro744]

The relative difference in light gathering power purely by the numbers for 120 over 100 is 1.44 and 132 over 120 is 1.21. (Squared ratio). There will be a difference but the jump is not as large.

Resolution difference will be perhaps less pronounced than light gathering to the eye but noticeable under ideal conditions. Contrast can affect the perception if there is a considerable difference in f ratio between the two.

I base my comments on many observing sessions with both Astrophysics 6” f12 Super Planetary vs 7” f9. The 7” f9 gave a clearly brighter view of Mars but the contrast between light and dark features through the 6” f12 was clearly more remarkable. Syrtis Major was quite dark in the Super Planetary! I only ever used these telescopes for the planets when I was fortunate to have time alone with them. I did use both at the same time on occasion just to compare. The relative difference light gathering between these two is 1.36.

As much as I liked the 6”/f12 for contrast I welcomed the brighter view at similar magnification (difference eyepiece to get this) in the 7”/f9. Eyepieces used were Nagler Type 1, 2, and Clave Plossl/Clave Barlow. It was all a long time ago now.

Personally I think it would be worth the jump but other factors such as cost, weight and size and mount requirements come into play. A jump to 140mm would be nicer at more cost, weight and size.

[Hoges]

Many thanks, Astro. I'm looking at the two WO Fluorostars, so there's around 2kg and 130mm focal length between them. Trying to weigh up the trade offs between slightly more aperture v weight/bulk. Mount will be an AZeq6 which I believe will handle either. There's also the Espirit 120 and Skyrover 130 with similar differences.

[charmec]

My friend has the WO 130 and it’s a very nice scope but I guess you say visual are you going to do photography in the future? . With the WO you have to purchase the flatter ,reducer but with the Sprit 120 it comes with the scope so you save some bucks. Hard choice and good luck with the purchase

[Hoges]

Cheers Manuel. The photography with the 132/120 could be a while away. I've got the little 72ed and flattener which from everything I've seen should be a good little astro scope. I'll use that for a while, then consider the whole 'auto guiding' thing (which I haven't done at this point). Should keep me busy for a while.

[Bart]

The FLT is quite a large scope, both in length and diameter. It rides reasonably well on an EQ6 type mount as long as it is balanced well due to its length. My thoughts are that if the F ratios are similar or the same, for what it is worth, go for the aperture. Both scopes have comparable glass quality a far as it seems.

[AdamJL]

For visual I’d go with the WO. For AP, the Esprit because of the included flattener. AP is expensive enough so every little bit helps.
I went through the same decision a while back and chose the Esprit because of that. Next big scope will be either a 140 or 150mm frac but that’s a long time away and the jump from 120 will be bigger