7 replies to this topic

[Jack Frost]

Another question!!!

While looking at a site selling Televue eyepieces, they also sold a 'paracorr' which, it said, was a necessity in large apeture fast scopes such as 12" f5.3.

Now, my scope is also 12" f5.3. Would it really benefit from a paracorr, or is it just sales blurb? I ask because it's bloody expensive, and I could get a few decent eyepieces for that price!

[jrcrilly]

Now, my scope is also 12" f5.3. Would it really benefit from a paracorr, or is it just sales blurb? I ask because it's bloody expensive, and I could get a few decent eyepieces for that price!

It's subjective; some folks are more offended by coma than others (just as some are more offended by chromatic aberration in fast refractors than others). With Naglers, I see no benefit at all in my F/5 but some in my F/4. I usually do without the Paracorr in both.

[Jack Frost]

I think I'll just keep the money for now. Would it be more noticable if doing ccd work?

[jrcrilly]

With the typical dedicated astro CCD's the field is small enough that I wouldn't expect coma to be very obvious. With film or a large chip it'd be more likely to be there. It's more critical, of course, because such aberrations are easier to see after staring at an image for a while!

[Jarad]

The paracorr helps with fast scopes. I have an f4.3 scope, and consider the paracorr a permanent part of the scope. I also have an f5.6 scope, and don't bother with it in that scope. Most people use them at f4.5 or below. Relatively few use them over f5. Where the cutoff is for you depends on how much coma bothers you. I would say start off without it in an f5.3. If you are at a star party and someone else has one, borrow it and try it out in you scope with your lowest power eyepiece. If you think the difference is worth ~$300, then buy one.

Jarad

[Jack Frost]

You forget - I'm from the UK! The price is equivelant to $520.

[Jarad]

Same advice, difference cutoff point. Like I said, at f5.3 I don't think it's critical. You can certainly use the scope without one, but if you get the chance to try one, try it and then decide if it's worth it. IF you do decide to get one, check Astromart. They go for around $250 there, plus shipping, and the shipping isn't going to add THAT much, even to the U.K. And at least that way the exchange rate will work in your favor...

Jarad


Jarad

[Simon Chung]

Jack,

My take on this is that it is worth it for planetary viewing, because it allows for a larger diffraction-limited FOV. You have a large, relatively fast scope so coma is noticeable. Without it, even at F5.3, the "sweet spot" is still very small. It is rather subjective and you may find the differences very small. In my F4.8 dob, I find the views very good almost right out to the edge. Planetary performance is excellent, with only a slight dimming caused by the extra magnification.

The downside is the extra infocus travel, the slight increase in magnification, weight, and cost.

Simon