The thread is digressing a bit but my main reason for 18" f 3.7 was no ladder at zenith and I love that advantage to this day. I zip around with fewer obstacles. When I go high mag which is how I tend to use the 6mm or 8mm eyepieces I am mostly only caring about the middle of the field as this is typically for tiny objects. I often take out the Paracorr for going real deep as it turns out the need for it is mostly for when you are using more of the light cone like 16mm or more. So I take it out and as such light loss (whatever it may be) is out of the picture (literally). I'm no expert on this but that is what I have heard and it seems reasonable. Everything is a tradeoff. If I only used it in a fixed location your argument seems reasonable and sure, 4.8 would offer a better view. For me, a ladder in the van is one more piece of stuff in there and one more thing to forget and be real sorry I forgot.
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