New Explore Scientific large Achromats.

I recently saw an ad for Explore Scientific's 127mm and 152mm f/6 achromatic refractors and at $600 and $700 for the OTA plus case and accessories these really fit well into my budget. Apo's at these apertures are out of the question.

However my question is if anyone knows the weights of these OTA's and what are the accessories that come with them?

I realize that these are medium focal length and may exhibit CA but if they're at least close to Orion's 120 f/8.3 achro. I can live with that. The tubes should be about 3 feet long, no problems there.

Thanks for any info.

Wayne Wlocka said:

I recently saw an ad for Explore Scientific's 127mm and 152mm f/6 achromatic refractors and at $600 and $700 for the OTA plus case and accessories these really fit well into my budget. Apo's at these apertures are out of the question.

However my question is if anyone knows the weights of these OTA's and what are the accessories that come with them?

I realize that these are medium focal length and may exhibit CA but if they're at least close to Orion's 120 f/8.3 achro. I can live with that. The tubes should be about 3 feet long, no problems there.

Thanks for any info.

If one does a bit of scaling based on the Chromatic ratio (focal ratio/aperture (in)), a 150mm F/6 would scale to a 120mm F/4.8 while the 127mm would scale to an F/5.7. Or looking from the other side, the 120mm F/8.3 would scale to a 127mm F/8.8 and to 150mm F/10.4.

With either scope, I would expect substantially more false color than the 120mm F/8.3, more in the realm of the the 120mm F/5.

Jon

I found the CA of an f/8 6" too much to bear. Also they cannot be profitably used with a radical violet blocker like the Baader SemiAPO because the best focus on stars results in a rosy colored fringe on them, even at low power, which is worse than the unfiltered CA! So much blue is defocused that planets take on a sickly yellowish color. The minimum acceptable range for a standard crown/flint achromat is 5" f/9 and 6" f/12. Now if they are using lower dispersion glass, they may be able to get away with faster scopes. Still, in that case, one is better off with a premium 6" f/4 or f/5 mirror.

For a 6" f/8 doublet one is more or less forced to go with an ED achromat at a minimum, I think, and then one has the issue of super-critical collimation. No free lunch!

I have a 5" f/9.3 Fraunhofer and it gives outstanding performance. In direct comparison with the 6" f/8 from the same optical shop, the 5" won in every way other than light gathering power, and weighs 10 lbs less.

-drl