Placing of barlow

[Chrb1985]

Hi guys.

It's one thing I need to know. Is the placement of the barlow according to the filterwheel important? I have placed the spacer in my baader vip behinded the filter wheel now. And the lens is in thw nosepice on the other side of the filterwheel.

Most pictures I see of setups, the barlow or spacers are infront of the filterwheel.

[vlaiv]

As long as you've calculated in optical path of filter wheel and you are happy with magnification that you are getting - it should not matter.

[Chrb1985]

Jupp it's the right distance. I at least think it is. It should be 64mm to get 2x. And as we talked about I should be at little more than that since I'm using the 174mm camera, so I added one more spacer. And the total got to 74mm I'm no math genius but it's at least a little more than 2x

If you can weigh in on this it will be much appreciated:)

[vlaiv]

Don't forget that sensor is not right at the beginning of the camera - but a little bit inside - depending on model, it can be something like 6.5mm inside.

Otherwise, yes, you seems to have it covered.

[Chrb1985]

 

7 minutes ago, vlaiv said:

Don't forget that sensor is not right at the beginning of the camera - but a little bit inside - depending on model, it can be something like 6.5mm inside.

Otherwise, yes, you seems to have it covered.

Thank you buddy

[CraigT82]

You can calculate you FL pretty accurately from your images. Just need to see how mamy pixels across the target (mars?) Is on your image, then you just need the pixel size and the apparent diameter of the target and you can get focal length. 

Sixth formula down on this page...

http://www.wilmslowastro.com/software/formulae.htm

[Chrb1985]

30 minutes ago, CraigT82 said:

You can calculate you FL pretty accurately from your images. Just need to see how mamy pixels across the target (mars?) Is on your image, then you just need the pixel size and the apparent diameter of the target and you can get focal length. 

Sixth formula down on this page...

http://www.wilmslowastro.com/software/formulae.htm

So "count" the pixels over my mars globe? Or the whole image? If the whole image than I should not be using roi right? Hmm I will check the link:)

[vlaiv]

2 minutes ago, Chrb1985 said:

So "count" the pixels over my mars globe? Or the whole image? If the whole image than I should not be using roi right? Hmm I will check the link:)

Same as plate solving - which uses stars and distance between them, this method is simpler - you record a planet and measure its diameter in pixels, then turn on Stellarium and adjust the time to that of your recording and note this number:

Divide the two to get arc seconds per pixel value for your scope and camera.

[CraigT82]

5 minutes ago, Chrb1985 said:

So "count" the pixels over my mars globe? Or the whole image? If the whole image than I should not be using roi right? Hmm I will check the link:)

• Just open your best sharpest image in gimp or PS or whatever you use, and set it to 100% zoom (make sure the image hasn't been resized)
• Hover the mouse pointer over the right edge of the planet at the equator and you should get a readout number somewhere on screen of what pixel in the row that is (lets say 500), in gimp there is a kind of ruler at the top of the display.
• Next hover over the edge of the planet at the left hand side at the equator too, lets say this is pixel number 300, so your image of the planet if 200 pixels across (500-300)
• Plug that number in along with the camera pixel size and the planet apparent size in arc seconds (from stellarium or skysafari or whatever) and oyu'll get your FL.

Note, the planet has to be 100% illuminated ideally, but you're near enough there with Mars currently.

[Chrb1985]

11 hours ago, CraigT82 said:

• Just open your best sharpest image in gimp or PS or whatever you use, and set it to 100% zoom (make sure the image hasn't been resized)
• Hover the mouse pointer over the right edge of the planet at the equator and you should get a readout number somewhere on screen of what pixel in the row that is (lets say 500), in gimp there is a kind of ruler at the top of the display.
• Next hover over the edge of the planet at the left hand side at the equator too, lets say this is pixel number 300, so your image of the planet if 200 pixels across (500-300)
• Plug that number in along with the camera pixel size and the planet apparent size in arc seconds (from stellarium or skysafari or whatever) and oyu'll get your FL.

Note, the planet has to be 100% illuminated ideally, but you're near enough there with Mars currently.

Ok I will try this tomorrow! Thanks alot guys!