Another Lunar try

[Grandpa Ron]

I think I have reached the limits of my department store telescope lens and my camera adapter. This is "as shot" and the chromatic aberration only increases with magnification.

I have a Newtonian scope to try next but I am told they are not camera friendly because of the geometry.

Still these are fun projects when you are "sheltering in place".

 

[zombiesniper]

Not bad at all for an inexpensive scope.
Converting to black and white can lessen the obviousness of the chromatic aberration. Also taking multiple images and stacking them may assist in the clarity but I agree it looks like you have reached the limit of this scope.

 

[photoflyer]

What is your longest telephoto? I have a Celestron 6 Evolution but my best moon shot was last week using the 100-400 with a 2x teleconverter on a crop sensor. That comes to 1280mm f 11. I focused manually using live view and 5x magnification. The telescope is 1500 mm F 10 but for the moon I've found telephotos to be better.

It won't make it go away but it will make it less noticable: bring the saturation way down, almost making it black and white, to reduce chromatic aberration. Oops, I see someone else suggested this.

 

[Original katomi]

Just some advice learnt the hard way
When you decide to up grade if you can ask
1. Will the eye piece mount support the weight of my.... insert camera
2 do I need any adapters to mount my , camera, to this scope. If so what how much and brand compatibility canon, Nikon, Pentax, other
3 is there a lens between my camera and the open space of the scope, ( entery of dust and so on)
Reasons
Ripped eye piece mount off scope, only saved canon because did not trust mount and added safety strap
Needed adapter not one for canon EF/EFS had to convert to T 2 then adaptor
No lens in adapter so camera body wide open to dust etc in scope tube,air

hope this helps you not make th3 same mistakes I did

 

[TCampbell]

Hi Ron

The trick with the reflectors (newtonian reflectors) is that every scope has a "focal length" ... the distance from where they start focusing light... to the point where the light comes to sharp focus.

Suppose you have a generic telescope and suppose it's a refractor (not a reflector). Suppose the focal length is 500mm. What you'd find when you measured the scope is that the distance from the objective lens to the back of the scope is less than 500mm... e.g. maybe it's 450mm (or possibly even a bit shorter). This is because when using a refractor, commonly a 90° diagonal is added to the scope so that you can comfortably look "down" into the eyepiece instead of having to kneel down on the ground and try to look up. This avoids the need to visit the chiropractor to sort out your back and neck the following day.

But this 90° diagonal adds a bit of distance to the focal length and the refractor design *counts* on that extra distance.

When you attach a DSLR camera, the sensor is near the back of the camera body to allow room for the reflex mirror. That adds just about 2" (or around 50mm). The camera sensor is now farther from the focus plane than the telescope was designed to handle. So you try to rack in the focuser to bring the sensor nearer to the scope... but usually run out of travel on the focuser before the image comes to sharp focus.

But with a refractor you can remove that 90° diagonal (which added a couple of inches to the focus distance) and add the camera directly to the back of the scope to shoot "straight through" without the diagonal. Now you lose a couple of inches from the diagonal... but gain those inches back on the camera and it works out that you can bring the camera to sharp focus.

When you use a newtonian reflector design, there is no 90° diagonal. The eyepiece is near the front of the optical tube and is already at a 90° angle (due to the 'secondary mirror' inside the scope). This built-in diagonal cannot be removed. This means when you add the camera, the sensor is now a couple of inches farther away than it needs to be to achieve focus... you wont have enough travel on the focuser ... and there's nothing you can remove to compensate. So the scope wont come to focus.

There is an alternative newtonian reflector called a "newtonian astrograph". This scope is identical *except* it shims the primary mirror forward a couple of inches to shorten the focus path and now the camera focuses correctly.

Newtonian reflectors have "coma" near the edges of the field ... and a moderately expensive (a few hundred $$) device called a "coma corrector" is usually needed to fix this.

There *is* one other trick...

IF you use a 2x barlow lens ... the focus is delivered to the barlow which, in turn, pushes the image to the camera. You can an enlarged image (the barlow effectively doubles the focal length and focal ratio) *but*... the scope will likely be able to provide a focused image for your camera.

Clear skies!
Tim

 

[Grandpa Ron]

I brought out my 6" Newtonian scope. With the camera adapter and the viewing lens giving the least magnification, I was able to focus but the image exceeds the view limits of my camera and the image is cropped.

When I tried to couple the camera directly, using just the mirror as a prime focus lens with a scope mount that was flush with the cameras, the lens adjustment holder lacked about 3/4 inch of travel when racked completely in. I built the scope back in 1999. I may opt to remove the viewing lens holder to try to gain that extra distance I need. However the planets are out so I may chase them first.

As you can see in the photo, I am just a bit over full frame, and with a 6 inch mirror an a viewing lens, the chromatic aberration was reduces. So having plenty of light to work with, I added a red filter to block the blue aberration ring then converted to B&W.