AAA (All About Astrophotography)

[SilverStag]

I was hoping you could tell me about it.

Specific questions, since I’ve never tried it:

What does it take to connect a DSLR (Nikon in my case) to a telescope?

Is the a particular type of telescope that works better than another?

Thanks in advance.

[ravnostic]

There are adapters for DSLRs that replace the lens with a telescope eyepiece mount. I have a canon adapter but Nikons are available. This is prime focus photography; essentially the telescope is your lens (thus I say ‘I took that shot with a 2800mm lens’). Here’s a link to Celestron’s page; other telescope manufacturers have much the same:

http://www.celestron.com/c3/page.php?PageID=437

My telescope (Celestron CPC 1100) has a whole section on how to do astrophotography, but there’s also plenty of links on the interweb. Here’s one:

http://www.covingtoninnovations.com/dslr/EOS300Dastro.html

Happens to be for Canon, which I have, but the general rules are the same for any camera. There’s links on Covington’s stie to others, or just Google it.

You will, if possible, want an equatorial mount rather than alt-az, else field rotation limits exposure times (the stars will appear to spin about a central axis). With the equatorial, you won’t have that issue and can take pictures even up to hours long (but it’s better to take shorter exposures and stack them using registax or other software.)

As I still don’t have an eq. mount, I’m limited in what I can do, but I’ve had pretty good results even without the ability to stack (In the gallery you can find some of my shots.)

‘Seeing’, the term for turbulence in the atmosphere, will affect the clarity of your shots, and focusing can be a real challenge–though I’ve heard Nikons are easier than Canons in this respect. Stacking also reduces this problem, especially for planets, which require rather short exposures as they are relatively very bright in a scope compared to things like nebulae and galaxies.

If you have a local astronomy club, you can probably join them for a night and someone there with experience (and probably more than I) can show you how it’s done, and help you decide if you want to invest in it.

As for scopes, Newtonians are said to be rather good, but any will do, so long as you have a mount that can withstand the weight of the DSLR comfortably. Look for ones with wider field of views; I have a Schmidt-Cass scope and one of the problems with a 2800mm focal length telescope in prime is that I’m limited to less than the moon’s width of a view. I’ve helped this situation considerably with a reducer lens for my scope, reducing the focal length by 1/3 to about 1800mm, and widening the field of view to over 1/2 a degree, allowing full moon shots. It also decreases my f/ratio from 10 to 6.67, so I can take shots of less duration with results of much brighter images.

And it’s worth it to have a light pollution reduction filter (LPR), which really helps with the image colors yet doesn’t really lengthen the necessary exposure length much.

Alternately, there are adaptors to mount your lens to the telescope and view through regular telescope eyepieces, but I’ve heard it’s harder to find ones for DSLRs. However, it’s fairly easy with P+S’s, and with stacking software you can get really good results.

This link to Celestron’s FAQ on my particular telescope has some good Q/As on astro shooting:

http://www.celestron.com/c3/product.php?CatID=9&ProdID=37

You can also piggyback your camera on the scope to allow long exposures of fuller sky views without star trailing.

Stacking is pretty much required to get stuff like you see from Hubble out of a ground based scope, without it, though you can get some decent shots–but I’ve found these don’t impress a world that has become accustomed to Hubble images.

On the other hand, you might. Here’s a full size, totally unedited shot of the moon, jpg version, about 1.5 megs:

http://fossilspringsaz.com/pics/2011/jan/02/img_3210.jpg

Contrast adjustments, sharpening, and resizing etc gets better results:

http://fossilspringsaz.com/pics/2011/jan/02/moonlg.jpg[/list]

[ravnostic]

I should add that I’m only an egg when it comes to astroshooting, I don’t have nearly the toys I’d like, and much like camera lenses, filters and equipment is fairly costly to come by. I bought my scope after selling my condo, so I had a lot of cash at the time to spend on the scope, but didn’t get all the toys I’d like to have.

Since they cut the OT at work last year, and on my base pay, I’m lucky I can pay rent, all my hopes and dreams of fancier equipment are waiting on the lottery.

Oh, and you can get the Moon, Venus, Jupiter, and Saturn without anything more than the scope itself, even if it doesn’t track at all–the exposure times are short enough that they don’t move in the time it takes to expose them. You don’t even need an adapter–just hold the camera up to the telescope lens (but don’t touch it). Deep sky stuff, though, needs tracking.

I don’t know what you’re looking to spend, but if I could buy another scope specifically for astrophotography and money weren’t nearly the issue it is, I’d look at something like this, which has a 4.2 focal ratio and would get much brighter images:

http://www.celestron.com/c3/product.php?CatID=107&ProdID=663

[SilverStag]

Wow, thank you for your complete and thoroughgoing reply, ravnostic! You’ve given me a lot to think about!

[orionid]

I’ve also made some attempts. I have an adapter that goes from nikon F-mount to T mount, and then a t-mount tube that fits a 1.25″ telescope eyepiece. That part of my rig works great. It’s also fitted to hold eyepiece filters, of which I have Hydrogen-alpha, oxygen III, sulfur II, light pollution blocker, and nebula optimized. My scope is a Meade 5.1 inch /1000mm.

It’s roughly f/8. But I haven’t taken any photos with it yet. The drive mount, as it came out of the box, was clicking and popping like the gears were skipping. I sent it back to Meade for warranty service. Six months, and several angry phone calls later, they gave up and sent me a brand new replacement. It did the same thing. Sent that one back, was told my six month warranty period had expired. Talked to supervisor. Got another new one. That one doesn’t seem to know the difference between the moon, saturn, and my neighbors cat and tracks all three equally as poorly. I’m pretty sure my next small/portable will be a celestron.

In other areas, I have done solar photography with filters from Thousand Oaks Optical with my 70-300mm and a kenko doubler and tripler (1800mm total!).
http://www.flickr.com/photos/orionid/3422358841/
http://www.flickr.com/photos/orionid/3486626087/
http://www.flickr.com/photos/orionid/3472890773/
I want to get and/or rent some better glass while we’re on the sunspot upswing right now and do some more of these, but haven’t gotten back around to it yet.

And, also, in my dad’s garage is the ultimate astro $20-yard-sale-find. An 18-inch diameter (read $4500-ish) scope, 10-foot focal length (f/6.6). It weighs about 80 pounds. Someday, I’ll get one of these to drive it.

[ravnostic]

Orionid, I have filter envy.

[chupathingie]

I suppose I’ll toss in a few comments on telescope types.

Newts: Overall best bang for the buck. Simple construction, easy to collimate BUT suffers from coma (smears stars into a comet-like tail towards the edge of the image) especially at faster focal lengths. Add a focal reducer/coma corrector though and it gets very sharp.

Cassegrains: These are the typical Celestron telescopes. Folded optics, usually f10 or more. Won’t need any collimation unless it’s manhandled. Makes for a short tube that is relatively easy to transport. If it’s 10″ or more, you can add a Hyperstar unit in place of the secondary mirror and mount a DSLR to it. This effectively turns the scope into a Schmidt camera, at around f2. Wicked fast.

Refractors: Don’t even go here unless you have either a healthy budget or an affinity for chromatic aberration. Achromats are cheap, and the image quality reflects it. There are a number of good quality triplets and quad APOs out there, though; Borg and Takahashi come to mind. Some of these are even available with 4″ focusers for medium-format use. Typically refractors don’t come any faster than f6, but focal reducers are available for them as well.

Resolution is almost strictly a factor of main lens diameter (or mirror diameter). Well-made refractors excell at resolution and contrast based on size due to having no central obstruction (which adds diffraction and robs contrast), however when cost is figured in you can easily best a 4″ refractor with a 10″ newt and still pay less (but have a bulkier rig).

There is a difference in results depending on whether you are shooting diffuse or pinpoint light sources. Larger aperture=smaller stars (better resolution) and dimmer stars captured due to the added light gathering ability. Nebulae on the other hand are affected much more by f-ratio, and you can get some stunning results with a fast 4″ scope.

One odd design is a maksutov (either mak-newt or mak-cassegrain). All the mirrors are spherical, and a corrector plate that is easily figured make the optics cheap and relatively coma-free (much easier and faster to grind spherical elements than parabolic ones).

There are many more types out there (some of these home-build folks really have some arcane designs) but most folks are going to wind up with one of the first 3 above.

[ravnostic]

Cassegrains: These are the typical Celestron telescopes. Folded optics, usually f10 or more. Won’t need any collimation unless it’s manhandled. Makes for a short tube that is relatively easy to transport. If it’s 10″ or more, you can add a Hyperstar unit in place of the secondary mirror and mount a DSLR to it. This effectively turns the scope into a Schmidt camera, at around f2. Wicked fast.

This is on my wishlist to do. After I get the wedge mount, maybe in March when I get a stock payout.

[olavf]

It’d be as well to let it go. It’s too far out of range.

http://legault.perso.sfr.fr/eclipse110104_solar_transit_25.jpg

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