Posts Made By: Alex McConahay

Interesting name you have there, Dan,

As for your initial question, I have heard that the focal ratio shifts ever so slightly, but I do not believe it could change from F/10 to F/12. The only way it could do that would be if the focal length of the system changed, or if the aperture changed. And the change would have to be some 20%.

Maybe there is a way this could happen. But I could not see how.

Alex

I'm a retired teacher and high school principal.

Alex

Figure out medical benefits.

Watch out for the "I can do it later" syndrome. It is absolutely easy to put anything off, because nothing again ever has to get done.

Depending on your age, be aware that everybody else has to work. So, you hang around with the wife and such on the weekdays and goof off with your working buddies on the weekend.

There are probably other little things to think about, but there will be time to think about them. (I can do it later.)

Alex

I think it would be worth a try--but I gotta ask--aren't star trails mostly white light, full spectrum. What advantage is there in filtering out part of the spectrum?

Alex

Ansuman,

You are welcome to ask here, but you might get more responses among the Solar System or Deep Sky imaging forums. I'm not sure the Beginner's Forum will be able to help much.

Alex

I don't know the answer to your question, but I wanted to get your post above that ugly monster thread about whether GOTO is worth it. I hate it when somebody resurrects those long old threads.

Alex

Keith,

They are a lot more expensive than you need to pay.

I have (for my Olympus) a machined metal adapter that accepts OM-1 lenses on one end, and has a 1.25 adapter on the other,which allows one to put an eyepiece to a camera lens.

If you want to make one up yourself, and have a spare 2 inch to 1.25 adapter, go to my website and see how you can make what you are looking for pretty cheap.

http://users.adelphia.net/~alexmcconahay/Equipment/Finder-Parfocuser/parfocuserindex.html


I use it in astropotography as a parfocal lens adapter.
Alex

Actually, it will be less than a few seconds. It will probably be on the order of 1/500 of a second, or whatever.

The moon is a daylight object. And it is about noon up there right now. So you will need about the same exposure you would need on a regular bright day on earth.

If you know how to use spot metering on your D70, do so. Point the spot on the center of the moon, and use aperture preferred autoexposure (The one where you have a fixed aperture and it sets the exposure.)It should come out pretty good.

Then go to the info window and look at the histogram. I don't know how to do that on a D70. See if you get a big hill in the histogram about a third of the way across the histogram, and that you have nothing at the very right end, or next to nothing. If so, you have a good exposure, If not, go to full manual and try some shorter or longer exposures.

Hey, it's digital, and you can expose all you want. Throw out what does not work.

Focusing will be the big problem. After you take a picture, blow it up as large as possible on your viewscreen and see how it looks. Focus just a touch. (Remembering which way you moved it.) Then take another, blow it up, etc. And by just a touch, I generally mean less than one tenth of a knob turn is way too much (once you are close to focus).

And forget the moon filter. It will do nothing but increase your exposure time. (Of course, there are those who say you want longer exposures to average out seeing. I don't buy that.)

Alex

Okay, Casey, So, How did it go last night on your first moon shot?

Alex

Astrophotography is not easy, and Dobs are not suited to the task. For anything but snapshots of the moon, you need a tracking mount.

A good place to learn is a small refractor. Their short focal length makes wide field imaging relatively easy. When you have focusing and exposure down pretty well, you may want to move on to a larger scope like a newt, or the ever popular SCT. SCT's are a little difficult to learn on because of their higher magnification and smaller field of view.

But the most critical elelmlent is a proper mount. THat is where the money has to go.

Alex