Schierer Space

Apologies in advance for the length of this post. This has been developing over the last two weeks, but I never got around to posting it. So consider this all of last week’s posts in one installment.

So the other day I broke down and walked into my local camera store, Johnson Camera (aside: they have a really crappy website). I had decided it was time to attempt to use my telescope, a Meade 127NT as a really long lens for my camera, a Canon 20D. My telescope, in camera lingo, would be a 1020mm f/8 “lens”. Technically, it’s not a lens at all, because it is a Newtonian reflector and has only mirrors.
To attach a camera body to a telescope, one needs a T-ring and a T-adapter. The T-ring has the correct flanges and features to connect to the camera body and is specific to the lens mount style (Canon EOS in my case). On the other side of the T-ring is a thread which allows it to attach to the T-adapter. The T-adapter is essentially a tube which mounts in the eyepiece holder of the telescope with threads on the other end to accept the T-ring. Sounds simple, right? And it should be… people have been attaching their cameras to telescopes pretty much since camera were invented. But it wasn’t.

So I walk into the camera store to ask about the setup, and somehow the lady at the store talks me into buying a T-ring. I hadn’t really intended to buy anything because a) camera stores are a rip off unless you need technical help… b) I was still working part time due to Nate’s arrival and I really shouldn’t have been spending extra cash. Anyhow, I am somehow convinced that buying JUST the T-ring is a good idea (she seemed to think the T-adapter would not be needed on some ’scopes). And ~$30 poorer, home I go. After some manipulation (the T-ring seemed to be a bit too closely toleranced to the EOS mount) snick-click the ring is attached. Great. Not surprisingly, there is nowhere to magically attach the T-ring to my scope, focuser, etc.
Back to the camera shop (trip 2) where now essentially I’m forced to buy more stuff to make the other (overpriced) widget I bought useful. Another $30 poorer and I have a T-adapter. Mr. Storekeeper (the owner I think, and nice lady’s father) recommends I give it a spin in the daylight to get things squared away before attempting anything tricky. He recommends the moon for a first light night shot. Cool. I’m psyched. I thread the T-adapter onto the T-ring, click it into the camera, slide the camera into the eyepiece holder…. and vwalla I have a REALLY zoomed in look at the lamp on the other side of the house. A bit washed out, and lacking contrast, but REALLY zoomed in. So I turn the scope and aim it at the top of a power pole about 200 yards away. Hmmm… blurry. I turn the focuser as short as it will go… still blurry. Hmmm… I turn the camera downward until something comes into focus. Yay. Grass. Grass about 50 feet past my deck. The moon is, unfortunately, a wee bit farther. After some messing around I punt…
Camera store visit 3: I explain the problem. “That’s strange” they say. We talk about optics, we talk about prime focus, we talk about machining down the T-adapter (”We have a machine shop” they say) all in the intent of shortening the distance between the camera and the mirror. A Newtonian is pretty simple: a curved mirror focuses light, a flat secondary redirects it out the side (it would work without the secondary, but your head would have to be in front of the scope… works great to look at your eye… but not much else). Nothing else matters but the distance of the camera’s CCD to the mirror. “How much are you off by?” they ask. I’m pretty sure its a lot, but store owner says “It doesn’t take much! An inch goes a long way at that [lens] length.” I mention that I’ve collimated the scope. Hands fly into the air, gnashing of teeth, rending of clothes “Well there’s your problem!” Now I’m no camera store owner, or PhD in optics, but I know what collimating is… and what it is not. Collimating is all about getting the mirrors lined up with each other, and the eyepiece holder. Although a gross adjustment of either mirror can move the focal point relative to the optical tube assembly, the maximum range of motion of either mirror is maybe 1/2″. I explain this. More hands fly into the air. He recommends I take a look at it… after all “It doesn’t take much!” He also recommends I call Meade to see if they have any ideas.
I re-collimate. I remove and replace the secondary mirror (and have to disassemble it to reattach it, but that’s another story). I adjust the primary. I remove the eyepiece holder. I remove the T-ring from the camera. I set (precariously) the camera body directly on the focusing tube (a full 2″ closer than any tube attachment could possibly allow). And I’m still not close enough (I’m out to about 100 yards now). Not by far.
Phone call to Meade. I talk with the “helpful” young man on the other end. His first comment is “that’s an old scope”. Thanks. I explain the problem. He says, “hmmm, are you using a [insert brand name of Meade expensive CCDs here]?”
“No I’m using my camera.”
“Oh, it must be a problem with your camera.”
“What’s my camera got to do with it?”
“The CCD is in a different place.”
Ok, that’s fair enough, but the telescope manual has a T-adapter accessory listed.
“So what’s the T-adapter accessory for?”
“To connect a camera.” Just not my camera apparently. My camera is 2.8″ thick… but the camera is thinner where the lens mounts. SO at worst the CCD is 2.7″ from the lens mount. The Meade T-adapter (shown in the manual) is a full 1″ longer than the T-adapter I bought (above). If I can’t get the focus short enough with my shorter adapter, how in heck is the Meade adapter supposed to work? I can’t get close enough when the T-adapter isn’t even on the camera. Apparently I need a camera with negative thickness. He’s not sure… but now he’s defensive. Defensive in that way that says “I’m not going to help you anymore because you made me feel dumb, and I’m on the phone far away from you and there’s nothing you can do about it.”
Camera store visit 4: Return parts for store credit. They don’t give refunds. Store policy.

Apparently, the design of my scope is such, that the prime focus point is somewhere inside the focusing tube. Probably right at the surface of the draw tube. My camera won’t fit there. Nobody’s will. With the eyepiece installed, the ‘theoretical’ light beams actually cross, and then enter the back of the eyepiece lens.

Hmmm… maybe I need a new telescope…

This entry was posted on Saturday, July 14th, 2007 at 12:19 am and is filed under Astronomy, Computer / Tech, Life, Photography. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.