TheSkySearchers-Welcome!

Basic Astrophotography


There are basically four ways to connect your camera to a telescope. The most obvious is to remove your camera lens and use the telescope as a telephoto lens, usually called Prime Focus or Direct Objective photography. The other three are a form of Projection lens photography. Diagram from Sam Brown...
Read more...

Nice post!
I did a whole semester of optics and ray diagrams still make me shudder.

Cheers

jrm_astro wrote: ↑Tue Jan 21, 2020 12:08 pm Nice post!
I did a whole semester of optics and ray diagrams still make me shudder.

Cheers

Thanks,
I think that everyone who is serious about this hobby needs to know some simple 'thin lens' ray tracing techniques. The quoted reference by Sam Brown introduces these and is quite useful to understanding that simply placing a lens here or there in the optical train will not produce the desired results. Barlows and focal reducers come to mind as do cameras.

I posted this Article to just introduce the beginner to the simple ways to put a camera on a telescope and actually get an image. All those pesky details of field curvature, coma, astigmatism, vignetting, and such are left for more advanced discussions.

Clear skies,
Steve

The article says this "Type 4: Best for planetary photos, need great magnification to enlarge those tiny spheres. Varying the negative lens, Barlow, position by only an inch or two will change the enlargement from 1x to infinity."

I have (yet) to try and use this method for planets. Do I understand that you put a barlow (say a 2x) in the focuser and then all you need do is to vary the distance from the resultant focal point to enlarge the image on the camera sensor? Or do you vary the barlow distance in the focuser keeping the distance the same between barlow and camera?

This sounds very intriguing and I had never considered doing that. I had always thought that #2 was the way to go. I have an adjustable mounting frame to which I can attach a camera - sans lens.

Star Dad wrote: ↑Tue Jan 21, 2020 5:52 pm The article says this "Type 4: Best for planetary photos, need great magnification to enlarge those tiny spheres. Varying the negative lens, Barlow, position by only an inch or two will change the enlargement from 1x to infinity."

I have (yet) to try and use this method for planets. Do I understand that you put a barlow (say a 2x) in the focuser and then all you need do is to vary the distance from the resultant focal point to enlarge the image on the camera sensor? Or do you vary the barlow distance in the focuser keeping the distance the same between barlow and camera?

This sounds very intriguing and I had never considered doing that. I had always thought that #2 was the way to go. I have an adjustable mounting frame to which I can attach a camera - sans lens.

The barlow to camera distance is varied, with extension tubes, to get a different magnification factor. Just like using a 2x barlow and then adding a star diagonal you get about 3x in an eyepiece view. Basic lens formula shows that the 1x is when the barlow is placed on the sensor, totally useless, and for infinity it is placed back at the barlow's focal length, usually a couple inches, also totally useless. So use a distance in between for an acceptable enlargement. But barlows are not spec'd with their focal length, so spacing is sort of a guessing game.

Using a #2 setup with a camera without its prime lens is just a #3, eyepiece projection, and I have a lot of reservation about this method as eyepieces are not designed to project images, barlow are so designed.

Clear skies,
Steve

sdbodin wrote: ↑Tue Jan 21, 2020 4:18 pm

jrm_astro wrote: ↑Tue Jan 21, 2020 12:08 pm Nice post!
I did a whole semester of optics and ray diagrams still make me shudder.

Cheers

Thanks,
I think that everyone who is serious about this hobby needs to know some simple 'thin lens' ray tracing techniques. The quoted reference by Sam Brown introduces these and is quite useful to understanding that simply placing a lens here or there in the optical train will not produce the desired results. Barlows and focal reducers come to mind as do cameras.

I posted this Article to just introduce the beginner to the simple ways to put a camera on a telescope and actually get an image. All those pesky details of field curvature, coma, astigmatism, vignetting, and such are left for more advanced discussions.

Clear skies,
Steve

Definitely agree. It's obviously not essential, but the knowledge sure helps when things start to go wrong.

Thanks again for the post Steve.

Cheers

Thanks very much. I am planning on getting into AP this year. (I am long in the tooth as a visual observer and need some new challenges!)

helicon wrote: ↑Fri Jan 24, 2020 12:57 am Thanks very much. I am planning on getting into AP this year. (I am long in the tooth as a visual observer and need some new challenges!)

Thanks Michael,
Imaging is a life long endeavor, I remember back 50+ years waiting for that film to come back from the store and see if the moon was actually there. Yes it was, I was hooked, a big crescent with craters on the terminator. Boy, how easy today, just hold up your cell phone to the eyepiece and duplicate that in seconds.

But, be prepared for a wallet emptying endeavor.
Steve

As an aside to this topic....

I'm in the market for a replacement to my 120MM which has given up. There's a plethora of choice if one really digs in.

If one doesn't exist, would a table of cameras and their properties be useful. I've started a spreadsheet and could download it as a starter if anyone's likely to find it useful as a beginning process of choosing a suitable unit for their imaging 'scopes.

Altocumulus wrote: ↑Mon Feb 10, 2020 9:37 am As an aside to this topic....

I'm in the market for a replacement to my 120MM which has given up. There's a plethora of choice if one really digs in.

If one doesn't exist, would a table of cameras and their properties be useful. I've started a spreadsheet and could download it as a starter if anyone's likely to find it useful as a beginning process of choosing a suitable unit for their imaging 'scopes.

But then I find "Agena Buyer's Guide to ZWO Astronomy Cameras" which shows way more information than I could provide, and in various tables.

Given many of the common chips are used across different manufacturers - makes my puny attempts somewhat superfluous.

Thanks sdbodin,

Thanks for your article. It's good to have a refresher on Astrophotography.
Yet, for me their is so much more to learn and experiments to do.
Thanks again.

Clear Skies,
kip