Honesty?

I only ever planned to do solar system... :roll: And look what happened to me

Once you get the hang of it though, you'll soon be trying deep sky stuff. And the leap from planets to deep sky isn't really as large as you might think. A 30 second exposure of a bright-ish galaxy will give an image you could be proud of.

I think the best plan is to keep your options open - and you can do that with a careful choice of kit. You can take solar, lunar and planetary images and still go for the deep sky stuff.

A good setup would start with the mount - this is your key piece of equipment. The best OTA and CCD in the world will be worth nothing on a poor mount. So, spend your time looking at mounts.

Even for lunar photography, if you want to take detailed images at high magnification (like Anthony from Greece) you'll need good tracking and a mount that will track at the lunar rate (not just sidereal). Same goes for Solar imaging.

As for the CCD, if you get an SBIG or Starlight Express CCD, you can autoguide. If your budget limits you to a webcam, you can use software guiding.

For the OTA, the refractor is a good choice for planetaries though as mentioned by Michael O'C, if you want aberration-free images, you'll need an apochromat. And that's serious money. The AP Starfire is about $8K and you'll wait at least 7 years to get one. TMB do good large APO's, but they're pricey too. Perhaps consider a good quality reflector.

By the way, you kight be thinking that there's some hard choices to make - you'd be dead right! I've spent over a year deciding on my next OTA and CCD combo! But I got the mount right

Cheers

Dave

One option you have is choice of focal length. The shorter the focal length, the less that tracking matters.

Dave,
without wanting to stray off lunartic's original thread, can you explain the 'physics' behind this? I always assumed a better image would be seen with a longer focal length mirror/lens, as there is less grinding, therefore less error.

Seanie.

No My physics knowledge is as advanced as my knowledge of the lesser known spotted warbler mating habits in northern siberia!

The focal length (and focal ratio) determines the length of exposure to capture a particular light-source. Longer exposures require better tracking. But even for bright sources, planets for example, if you have a small field of view (large aperture, long focal length) then you will still need good tracking. Of course, if you are webcamming and stacking hundreds/thousands of images then you can filter out poor quality images but if tracking is really bad or seeing is very poor, expect to throw out most if not all of them or end up witha mediocre image.

Here's a good summary of the focal length ranges.

Hope this helps

Dave



400-800mm - This is a great range for beginning CCD imagers. The demands on your mount range from very light at 400mm, to moderate at 800mm. Many small refractors (mostly 3” to 4”) fit in the 500mm to 800mm range. Smaller Newtonian reflectors also fit into this range of focal
lengths. The fields of view are wide, perfectly suited to many nebulae. You can get nice detail in many of the larger, brighter galaxies. The larger open clusters are also often well suited to this focal length. The fields of view at the short end are wide enough to make seeing a rare issue. At 800mm, seeing will sometimes make imaging impossible, but most of the time you are fine as long as seeing is average or better. Unguided exposures are reasonable, but that approach gets more demanding as you approach 800mm.

Beyond 800mm in focal length, imaging becomes a little more technical. The demands on the mount are high enough that any old mount will not do; you need to have a mount that is specifically suitable for imaging purposes. You will find a lot of 5” and 6” refractors fitting into this range at the high quality end, but an 8” Schmidt-Cassegrain with an f/5 or f/6.3 focal reducer also fits in this range. There are always some larger Newtonians to pick from in this range as well. Scopes in this focal length are excellent at galaxies that go beyond the Messier catalog, globular clusters, and tight shots of interesting detail in larger nebulae. Unguided exposures are challenging.

1500-2000mm - This zone is a gray area. An f/10 SCT fits in at the high end, and many large, fast Newtonians fit in at the low end. But the technical requirements, while higher than for telescopes under 1500mm, are still reasonable and if you are serious about CCD imaging, you can start out in this zone successfully, but expect a steeper learning curve. A good mount is fundamental to success. This range of focal lengths really
opens up the galaxy imaging options. You can also image details in nebulae, and faint globulars really come to life. In this range of focal lengths seeing is almost always a factor. Average seeing will affect the
appearance of your image unless you use a large-pixel camera to reduce resolution. Unguided exposures require the utmost in precision mounts.

>2000mm - This is the zone of “serious imaging.” You probably want to cut your teeth on shorter focal lengths before diving in here, but experienced film imagers and patient newcomers can succeed. Above all else, you must have a superb mount to image in this range, with nearly perfect tracking, very low backlash, and the ability to carry the weight of larger scopes. If
your mount is marginal, you may be able to compensate using extremely short guide exposures. The list of potential targets is endless. Galaxy imaging is wide open, and you can really zoom in on details of larger
objects. Seeing is a dominant factor. If the seeing isn’t above average, you wont’ be able to image at these focal lengths without large pixels or binning. If you want to buy a telescope with a focal length longer than 2000mm, take the time to get to know your local seeing conditions first.
You can use reducers, reducer-flatteners, Barlows, eyepiece projection, and other techniques to alter your native focal ratio. There are always some trade-offs involved in changing your focal ratio, however, so having
a scope that works natively at the focal length you prefer is often the best choice.

Lunartic, I have nothing but praise for telescope-sevice, I bought some gear from them earlier this year, and could have not dealt with a more honest seller
As for the 6-inch, it is probably an achromat, so do get that filiter if the pocket is deep enough

Keith..

I was scrolling through the telescope-service website, drooling over the 152mm refractors, as you do, going through their information they mention residual false colour and recommend a Baader Contrast Booster for both their f8 and f6.5 models.
My question is this, are they being brutally honest, or is this a sales pitch to get you to purchase the filter?
I am considering a purchase of one of these scopes, as soon as I scrape the money together :roll:

Might be better to buy the Baader Fringe Killer filter instead.

Hi Lunartic,

I was also going to get this scope and Patrick in Telescope-Service was extremely helpful with any questions I had. I ended up with the GSO Newt instead for wider views, but the refractor is supposed to be excellent. Without a doubt you would need a fringe killer or similar for this scope as it is supposed to exhibit noticeable false colour at mags over 120 if I remember correctly, especially on the shorter scope.

If you drop a mail to Sales@telescope-service.com they usually get back within a couple of hours. IMHO they are the most honest and professional vendor I have come across.

Cheers,

Trev

Might be better to buy the Baader Fringe Killer filter instead.

Definitely, if you are used to looking through reflectors or SCTs, then the false colour will definitely stand out, photography only makes it worse.
Achromats are inherently "non perfect" when it come to colour correction.

A good test is to look at the moon through the scope and see what colour the edge is, blue is best, yellow is bad but workable, while red indicates terrible optics. (I'm going from memory so I'm open to correction).