Advantages of short focal length refractors

[Leo.G (Leo)]

I'm always seeing APO refractors for sale in the classifieds, these are mostly shorter focal lengths. I understand faster units (f ratio) for photography and wider field of view compared to comparative sized longer focal lengths but do longer focal length tubes have any strengths?


I don't have the luxury of owning an APO, champagne tastes on tap water income but I always keep an eye out just in case, one day.....
Do they make longer focal length APO's?


My original model Megrez 80mm is a semi APO, I've never figured that "semi" bit out and it has more much CA than my old 152mm x 1200mm Skywatcher which is an Achromat. Actually, the Skywatcher is stunning visually for my old eyes.
CA does show up in images though but not significant, nothing that can't be removed (or significantly reduced) in PhotoShop with the eye dropper used on RAW images.

[The Mekon (John Briggs)]

Well astrophotography is the popular theme of astronomy today, so that is why fast APO's are popular. The Megrez was never a good choice for AP or visual, and I am pleased I avoided buying one years ago and bought a Sharpstar 106 instead.
Your 152/1200 will only beat my 132 CFF on deep sky, double stars and planets will show much better in the CFF.
The only advantage I see in long focal length refractors is their depth of focus.
Modern focusers make this unimportant.

[Leo.G (Leo)]

Thanks John!



The Megrez I picked up near new for next to nothing, some yuppie in Sydney had it as a conversation piece in his apartment mainly for work parties and absolutely no idea how to use it.. The only problem is his meat head guests (I'm guessing this) all had p!ssing competitions to see who could tighten the mount head the most with the lock arm and it was damaged. It's still a nice little grab and go scope for visuals. The guy had no idea when I sent some simple images of the moon taken through it.
My 152, I long ago changed the standard clunky Skywatcher focuser for a nice Williams Optics DDG Synta unit. I've seen good and bad reviews of the same focuser but it's sturdy and well made, I love it. I also have adaptors on other Achromat reftractors I can slip the focuser onto.