APO vs. Achro and comments on this scope

The feedback on solar scopes was great and maybe I'll look into the PST, but I'm leaning toward a larger refractor and since detailed views of objects are limited to the moon, sun and a few planets (namely Saturn, Jupiter, and Mars I don't really count seeing a moon of Saturn or Jupiter detailed as it is really a non-descript speck.) I would like a fast large aperture scope which brings me to this: http://www.astromart.com/classifieds/details.asp?classified_id=364980

I really enjoy the wide field of view that a good pair of 7x50 give of the Milky Way so this scope intrigues me as it would have a good FOV, so how noticeable is color in an achro? If I chose to do some imaging at some point would it really 'pollute' the image with false color and thus be unsuitable for imaging? Markus Ludes always privides the "strehl ratio" and "wavelength" metrics and I notice they aren't provided on this scope is this a reason for concern? With the cost of an 8" APO @ F6 probably at 3 to 4 times the cost it may represent a good value. Also what do you think is a fair price for the scope that I've provided a link to? I would just like to know the drawbacks to a scope of this design vs. an APO of like size and speed. If the main drawback is false color how troubling is this or is it usually very subtle? Thank you for your replies.

Hi Gary.

This is a specialized large-aperture achromat and will show vivid of chroma on brighter stars, planets, & the moon. However, it should really excel at its intended purpose -- dropping the viewer's jaw with deep, wide, sweeping views of star fields, clusters, & nebulae. This is certainly not a planetary scope, and Markus would be the first to say so. If the optic is fine (I'm guessing it's very good), then deep-sky imaging would certainly be an option, given a suitable mount (i.e. large, strong, & expensive), drive, imaging equipment, software, etc.

As for planetary views, I suppose one could craft a removable stop-down mask and have an excellent 4-inch (effective) f/12 achromat. But it's my opinion that this bird should always be allowed to fly at full aperture. Feeding this 8-inch f/6 achromat an excellent binocular viewer would also be a treat.

Several years ago, I had the opportunity to spend a few minutes "behind the wheel" of a 10-inch f/5 APM achromat (with a Pentax 40mm XL). Sweeping through Cygnus, Lyra, & Hercules was an eye-boggling experience. In that context -- visual observation of dimmer stars & star fields -- the inherent chroma wasn't at all obtrusive.

I won't dare guess a "fair price" for this rare bird, but if it were mine, I'd be looking for at least $4K -- likely more (again, that's just me). Component, design, & construction particulars would certainly be factors.

A comparable apochromat would (or should, if well designed & implemented) prove a much more versatile (& serious, & expensive) imaging platform.

Cheers & best wishes.
-Dan

Just a thought here:

Have you considered an 8 inch F4-F5 or even F6 Newtonian? This would provide the same field of view that the 8 inch F6 Refractor would but without the false color issues. It could be optimized for Widefield or just a standard sort of a design.

Last night I was enjoying the views in my 10 inch F5 fitted with a Paracorr. I did make an effort to get it cooled down but the views were just amazing with an old 32mm TV Widefield. A 31 Nagler or 41 Panoptic would seem to be the way to go with a scope like any of these. The 10 inch F5 scope has a 75% illuminated field of view of 1.9 degrees which is just about the maximum possible.

I don't know about cool down with an 8 inch F6 refractor, I have heard that it can take some time, I am sure Markus knows about this.

Just some thoughts....

Jon

I would stay away from this scope. For that kind of money you can get a TEC 140 if you like refractors with wide fields, whidch will give you far superior images -visit their Yahoo group -- or a Mag1 10inch F/5 or 8 inch F/5 Portaball, or an 11 inch Staarmster ELT, all of which will give widefield views far superior to an 8 inch F6 achromat. the TEC has a much wider maximum field but less bright images; all the others have the same focal length as the achromat you mention and therefore have the same maximum true field, but they are all much brighter (except for the 8Mag1 which has the same brightness as the 8 inch achromat.The image quality of these scopes will be vastly better.
If you just love 8 inch achromats, go ahead and get it, but if you are at all unsure, consider these other scopes and call their manufactureers (usually one person) and talk over the pros and cons.
Of for much less montey you can get a Guan Sheng or Synta 10 inch F5 *same maximum true field, brighter and better image) and take your family on a European vacation with the money you save.
Bill Meyers