Help with Astrophotography through a Telescope

[SLPhotography]

Hello all,

I have been try basic Astrophotography for a while and recently I decided to grab a T-Ring and T-Adapter for my beginner Telescope so I could try to get some really detailed shots of the moon and maybe even snap a planet.

I am on a budget and right now this is more of a hobby so I don't have anything crazy expensive. In fact, I think the T-Ring and Adapter costs more than my scope ($40 used on Craigslist). All of my lenses are >$200 to give you an idea of my budget for this.

Here's my problem, upon correctly hooking up my Nikon D3100 to my telescope, I can't seem to get the moon in focus. It's almost there, but its all the way focused into the telescope (I think this is infinity) at it's closest to being focused and it still wont produce an acceptable shot. I didn't mess around with it too much because it seemed that it wouldn't produce any kind of results. I haven't had a chance to try to get a planet but I am hoping to try for Jupiter in the coming days.

Am I doing something wrong? I can get my doorway focused from inside the house with this setup, but I can't get the moon on either end of the focus range.

My equipment:

Nikon D3100 - T-Ring - T-Adapter - Meade Electronic Digital Series Refractor Telescope (I think it's a 70mm but it could be anywhere in the 70mm-90mm range)

I should note that I was trying to get the moon shot through a window, but it was clean and I didn't think it would make a difference. The closest it gets to being in focus is a white orb, with very soft/distorted edges, but you can at least make out that it is a sphere. Just no where close to getting ridges and such.

Any suggestions would be greatly appreciated.

 

[pgriz]

Sounds like with all the adapters in place, the sensor is still some distance from the actual plane of focus. You may need a barlow lens in there to bring the focus further out.

 

[SLPhotography]

Sounds like with all the adapters in place, the sensor is still some distance from the actual plane of focus. You may need a barlow lens in there to bring the focus further out.

Wait a minute, I must be doing this very stupidly....am I supposed to have the eyepiece in the T-Adapter still? I was doing it without the eyepiece...

 

[FotosbyMike]

Watch this video series, he has a lot of useful information that you are trying to solve.
Part 1
Part 2
Part 3

 

[pgriz]

Sounds like with all the adapters in place, the sensor is still some distance from the actual plane of focus. You may need a barlow lens in there to bring the focus further out.

Wait a minute, I must be doing this very stupidly....am I supposed to have the eyepiece in the T-Adapter still? I was doing it without the eyepiece...

No, no eyepiece. But the place where the eyepiece would normally be (the prime focus point), is where you need to have the sensor. Lets arbitrarily say that place is 2 inches outside the tube. However, by the time you've put all the various adapters on the camera, the sensor is (say) 3 inches outside the tube, and racking in the focuser just doesn't get you closer. So you need a barlow lens that will effectively "elongate" the focal length, and allow the focus point to reach the camera sensor. However, it's been a while since I've done astrophotography using a camera at the focuser, so I'll let several other members who do it routinely (like @astroNikon or @480sparky or @TCampbell ) chime in.

 

[480sparky]

The camera attaches to the T-adapter sans the eyepiece. You should be able to focus.

Are you able to focus the scope with your eye to an eyepiece? If not, there may be an issue with the scope.

 

[Joves]

Yeah I am with Sparky. How is the focus when you are merely observing through an eyepiece? Astrophotography has many things that can just throw a wrench into the attempts.
For example the seeing conditions. This is how stable the atmosphere is. If the stars are twinkling. Forget it. If they are nice and steady then you are good to go.
If you are not getting really good visuals when just looking then the optics are most likely out of collimation, this means that the objective, or the focuser are not in alignment. This can be fixed, but takes some time and patience.

 

[pgriz]

Watch this video series, he has a lot of useful information that you are trying to solve.
Part 1
Part 2
Part 3

Good series. Thanks for posting.

 

[astroNikon]

Your T-Adapter actually can unscrew into 2 pieces. You may want to try that.
I'll try to make some quick pics of it.

 

[astroNikon]

1 - Your main adapter probably looks like the one in the middle - the Meade tube

2 - 2 you can unscrew the tube to get 2 different length tubes

3 - such as the tube 2 different length tubes. You'll have to figure out which one works for your camera and scope.

 

[480sparky]

 

[astroNikon]

Then you add your T-Ring and then the ring to screw on the scope, such as this which has the T-Ring on the left and the scopes thread on adapter on the right:

 

[astroNikon]

Your T-Ring, if it's tight it may be adjustable. If there are little screws around it you can loosen them a bit and it will increase (or tighten decrease) the overall depth of the lock on the camera - at least mine is.

I would check the T-Ring on the camera first to make sure you understand how it work - yeah, just like a lens. Then check the Optical Tube threads as those can be tight. Make sure you can put it all together in the daytime before it's dark out and you need a flashlight.

 

[TCampbell]

Wrench #1... don't shoot through a window (well.. you can... but you won't like the results.) The scope needs to be outside in ambient temperatures (no matter how cold) and allowed to acclimate. Thermal temperature differences will really mess up the image more than you might guess. Remember that you're really magnifying a small area so it doesn't take much distortion to really mess up the image. The more you magnifying... the more every little focus flaw is amplified.

Wrench #2... many refractor telescopes are designed so that the focal length of the scope relies on that 90º diagonal being in the image path. A camera is usually setup to shoot "straight through" the scope -- no diagonal. The problem with this is that it shortens the focal length of the scope by about 2". That loss of 2" can mean that as you focus the scope, you end up racking the focus all the way "out" and then run out of focus travel just as the focus was only just starting to come to focus. The solution to this problem is to buy a 2" extension (it's just an empty tube that attaches to the end of the scope and lets you extend so that the camera is pushed back an extra 2" putting the thing back in range of focus again.

If I knew specifically which scope you have (the exact model... is it a Meade DS-2070, DS-2080, etc.?) I'd be able to determine what you need to connect the camera to the scope. My camera attaches with a T-ring and a "nosepiece" that drops into the 2" diameter eyepiece receiver (common sizes for telescopes are 1.25" and 2"... my scopes happen to use 2". Some scopes might use .965" but that's less common. Your scope probably uses a 1.25" eyepiece receiver.

There is something called "afocal" astrophotography and "prime focus" astrophotography.

In "afocal" astrophotography the scope has an eyepiece in it... and the camera actually has a lens attached. This is the typical method when shooting with a camera phone or point & shoot camera (something where the lens cannot be removed from the camera).

In "prime focus" astrophotography, the telescope IS the lens. The telescope does not have an eyepiece and the camera does not have a lens. When using a DSLR camera, you'd almost always want to do "prime focus" (no eyepiece & no camera lens.)

Without knowing exactly what telescope model you own, it's hard to guess... but probably you need:

A 1.25" diameter 2" (length) extension: Amazon.com Orion 5123 1.25-Inch Telescope Eyepiece Extension Tube Camera Lens Extension Tubes Camera Photo

A 1.25" nosepiece (ends in a t-thread): Amazon.com Celestron 93625 Universal 1.25-inch Camera T-Adapter Telescope Photo Adapters Camera Photo

A T-thread to Nikon mount T-ring: Amazon.com Celestron 93402 T-Ring for Nikon Camera Attachment Celestron Adapter Camera Photo

That's a guess... if you can tell us specifically which telescope model you own I might be able to provide better info (no promises.)

You might get a bit of vignetting around the edges when using a 1.25" nosepiece but if your telescope cannot accommodate 2" eyepieces then you really don't have a choice (other than buy a different telescope.) Usually this is minimal when using a camera with an APS-C sensor. With a full-frame sensor camera you really need a 2" diameter nosepiece.

I'm a Canon shooter but I helped out a local camera club that wanted to shoot images of the moon last year -- and they all had Nikons. There was an issue we discovered with Nikons in that they don't support "exposure simulation" on the live-view screen... and this made focus especially difficult because the image on the liveview screen was an over-exposed white blob with no detail available to help us focus. The camera wasn't trying to compensate for the completely black background by rendering the moon so over-exposed that we couldn't tell if it was focused or not. Nikon has now announced (not sure if shipping yet) the D810a. The "a" is for astrophotography and among other feature changes, the camera is the first Nikon to have "exposure simulation" for live-view (making it vastly easier to focus when doing astro-imaging.) The camera has a few other very significant advantages when imaging deep space nebulae. This means if you are trying to use "live view" to help focus the camera on the moon... it's going to be quite a struggle. Use the viewfinder instead (I use something called a Bahtinov focusing mask which caps onto the front end of the telescope and causes all bright stars to throw diffraction spikes which converge to a center point once the camera is perfectly focused.)

You'll like the detail in the moon image more when you don't shoot during a full moon. E.g. a 1st quarter moon (or close to 1st quarter) looks nice because the sun lights the moon from the side and that means all mountains and craters cast nice long shadows and those REALLY help give the lunar surface a very "3D" look. If you shoot at or near the full-moon you just see a flat "2D" disk of the moon with no shadow detail at all.

Exposure for the moon follows something called the "Loony 11" rule (no, I did not make that up.) This rule suggests that if you shoot at f/11 (more on that in a moment) then the shutter speed should be set to the inverse of the ISO setting. E.g. at ISO 100 use 1/100th sec. At ISO 400 use 1/400th sec. etc.

But about that "f/11"... your scope is whatever it is. There are no aperture blades. You can't change it. Part of the reason it's important to know "which" scope you have is so we can look up the focal ratio of the scope. A DS-2070 is an f/10 scope. The DS-2080 is an f/11.3 scope. So let's suppose it's one of these two... f/10 is within a third of a stop of f/11 that it won't affect the exposure much. This means you'd connect the camera, set the camera to "manual" exposure mode on the mode dial... dial in ISO 200, dial in a shutter speed of 1/200th sec, and you can't set the f-stop (that's controlled by the scope.) Focus the scope and take the shot and you'll get a good exposure.

Here's a link to an example:

Gibbous Moon by Tim Campbell1, on Flickr

The moon is one of the easiest things to image. Wide angle sky images are a little more difficult. Planets are a yet another level of increased difficulty. Deep space objects are significantly more difficult.

 

[cclhuzhou]

You may need a barlow lens in there to bring the focus further out.