Getting focus with redcat51 and dslr

[amateur-astro]

Hi I can't seem to get focus with my redcat 51 and my canon 2000D dlsr.

 

Could someone please advise 

 

Many thanks 

[pie_in_the_sky]

Hi,

What are you trying to capture - star, planet, nebula?

For deep sky (stars and nebula - which I'm assuming you're doing with the redcat), the process I started with was to turn the ISO on the camera up as high as possible (this is temporary, just for focusing) and then try and use the preview screen. For this you'll need to turn on the live preview mode. The 2000D definitely has this feature - a quick workflow recommendation, turn off the live preview mode timer otherwise you'll forever be turning it back on when it times out.

The focusing process is then to turn the focus wheel on the redcat and try and make the stars as small as possible.

A better option though is to use the bahtinov mask that is inside the lens cap of the redcat. The idea here is similar to the process above but you want to make as clear an X as possible across the bright stars in the preview screen.

If you can't see anything, take a couple of test shots with the mask on and you should see the clear X pattern on the stars - if you don't see this pattern you don't have focus and need to adjust. Like this

Then when you're done, reset the camera settings and remove the mask if used (which I've forgotten to do in the past).

For both options, it may help to zoom in on the preview screen.

If it's something closer, i.e. the moon, then capture the moon in the view finder, zoom in on the camera, and then focus.

That's a very quick summary - happy to dive into the particulars...

 

 

Edited January 31 by pie_in_the_sky

[pie_in_the_sky]

btw, that pic is from http://www.stubmandrel.co.uk/astronomy/18-focusing-with-a-bahtinov-mask (not a secure site)

[Richard_]

You don't mention which version of the Redcat51 you have, so let me explain how I did it with mine (v1.5).

First,attach your camera to the Redcat51 using a T-ring mount. This should get your back focus distance (the distance between the rear lens element and your camera sensor) to 55mm. If you have any other accessories or spacers in between the telescope and camera, this will affect your focus position.

In the day time, try and focus on something in the distance (like an electric pylon, tree etc). The further the better. Now focus your camera as you would using a traditional lens. Rotate the helical focuser until you reach focus. Your focuser should be somewhere withing the graduated markings as per the picture below.

Fast forward to the evening where you are ready to image... Find a bright star in the sky, and try to get it in view of your camera. Unscrew the lid on the Redcat's dust cap to reveal the transparent bahtinov mask. With the bahtinov mask mounted to your Redcat, take an image of this bright star at sufficient exposure time to reveal the X diffraction pattern. I find it easier to have the lines show as vertical than horizontal, so rotate the dust cap bahtinov mask until you are happy.

You want the virtical line to run right through the middle of the X pattern, per the second image below. If it's not, make very slight adjustments to focus (something like one graduation mark on the Redcat scale per first picture) and take another picture. Make note of which direction the line moves in compared to which way you rotated the focuser. Repeat until the line is as close to the middle as possible. Once complete, lock the ring just in front of the focuser to ensure you keep focus locked in place.

The focus position will slightly change with temperature, so if the weather is colder the next night, double check your focus again. Also, if you happen to use filters (like a light pollution filter, or narrowband filter like the l-extreme), then the focus position will be different again, so repeat the process each time you swap filters.

Once you've done it a couple of times, it becomes pretty straight forward to do