Posts Made By: Roland Christen

That would only be the maker of the lens.

Rolando

Well, thank you all for your kind words. It was actally fun to take this image. I put it on Sequence in MaximDL and let it shoot away a series of filtered images. No clouds for once, and the seeing was quite good. Meanwhile I was inside the factory doing some final figuring on some 130 lenses.

Still , the image is not finished. Needs far more exposure in order to fill in the background, which is too noisy at this point. We don't get too many good days here for this kind of thing.

Rolando

I think this is a great image. Keep doing what you are doing. I can't see how it can be improved except maybe to do it in color with the other two narrow band filters.

Rolando

Using the words "Apo Barlow" is strictly a marketing game. At normal powers all Barlows are essentially apochromatic, regardless if they are 2 element or have 3 or more elements. It's not until you get to very high magnifications, around 8x when you might get a bit of color using a normal Barlow.

Rolando

The combination of BSL7 and FPL53 provides almost ideal color correction over a wide wavelength range. BSL7 is essentially the perfect mate for FPL53. It cannot be used in doublet form unless you go approximately F12, however in triplet form (2 BSL7 with one FPL53 in the middle) one can make it as fast as F7. This design is the same as the one I used in the AP 160F7.5 EDF refractors. The design has to be airspaced, it cannot be an oiled triplet.

Rolando

You won't break out of the pack until you get something larger than 4". However, if you want to stay with 4", investigate the NP101 or the Tak FSQ. Here's an example of what the NP101 can do with a big chip: http://www.astrophoto.com/M45WF.htm
You can hardly recognize the Pleiades any more in this image.

If you're looking for max resolution and you don't have the best of skies, then a 6" Apo will do a superb job. A 4" will never approach it in terms of resolution.

If you have superior skies (say down at sea level in Florida), then you can go for a 12" aperture to ring out the highest detail in tiny structures (like planetary nebulae and galaxies).

For each situation there is an ideal instrument, 3" - 4" being just a bit on the small side. Yes, you can do a nice job with these small apertures, but you will always be behind the curve.

What can you do with a 6", 7" or even 8" refractor under ideal conditions? Well, I've seen several examples of M33 on this group lately, and they look nice and represent that galaxy well. However, Tony Hallas just sent me a preliminary shot taken with his 8" refractor that is totally mindblowing. He has the proper conditions to take advantage of both the resolution and the purity of the image (lack of scattered light and very high contrast) that a refractive optical system can deliver. In his shot, the spiral arms are resolved into tens of thousands of individual stars. They extend outward far beyond what I have ever seen, and in fact if the image is stretched a bit, the galaxy begins to take on the shape of a giant oval instead of the spider leg pinwheel that we all know so well. The background is peppered full of tiny faint galaxies, and he actually had to crop the image to highlight M33 better. Otherwise it looks lost amid a sandstorm of miniature galaxies. I will post his finished product as soon as he sends me the final version (he is extremely picky about what he wants to show).

As far as what is the ultimate, there is no ultimate. The best that you can do is to match your local conditions, your pocket book and what you want to image, put it all in a blender and hit puree.

Rolando

dew won't really be a problem inside a dome. The only time I had any dew formed on my scopes in over 5 years in my observatory building was one day in spring. The temperature inside the building was colder than outside and the humidity was 100% after 3 days of steady rain. Everything inside was damp, but again the lenses were free of condensation because I keep them covered.

Rolando

And here is the color version

>>Then there is the Astro-Tech 8" RC, f/9 $3000, Feathertouch, narrow field, sub arc sec imaging.>>

I can't even do sub-arc second imagign with my 12" Mak. Sub-arc sec imaging is unrealistic for deep sky astrophotography. Even people with 20"+ scopes do not achieve better than 1.5 arc sec except in rare instances.

Besides, the mount is the most important thing for long exposure deep sky, and it isn't just the tracking accuracy. When imaging with focal lengths above 1500mm, the dynamics of the mount become very important - how well it follows tiny commands on both axes at the arc second level will determine the overall resolution that you get in a 10 - 20 minute subexposure.

Rolando

It's not a Jaegers.

Rolando