powermate question

[ninjageezer]

Is it possible to use a televue powermate 5x to increase the small 430mm focal length of my william optics zenithstar 73 to image M51 and other smaller objects or will this ruin things ,also have the WO field flattener fitted .the 2 images are from NINA framing tool a big difference. you will have to excuse me if this a daft question as i am very new to this.

camera is a astro 60D.

[vlaiv]

You can but you will gain nothing and even make life very hard for yourself.

At the moment, you have 73mm aperture telescope and 4.3um pixel size camera. With 430mm focal length of telescope you are at 2"/px sampling rate.

That is about perfect for that aperture size. You can't get any more detail than that in your image. Any attempt to "zoom" in more than that - and you will get blurry image.

What you see above is size of FOV compared to size of target. Your sensor has very big resolution in terms of pixels - 5184 x 3456.

To put things in perspective - "width" of M51 is only about 15 arc minutes. That is 15 * 60 = 900 arc seconds across. Even with large telescope and very good mount and excellent seeing - best you can hope to do is around 1"/px - which would make that target 900px across. That is again going to be small compared to full FOV of your sensor - which is x6 larger in width than galaxy at this sampling rate.

What you can do is image with setup you have, try to maximize sharpness on what you already have (very good focus, very good seeing and guiding) and simply crop your image to frame the target the way you want.

You can still get very detailed image of the galaxy that way - for example, here is M51 at ~2"/px. Image is only 860x670px, but there is no point in making it larger as target is not large enough and effective detail is just not enough to justify higher sampling resolution.

[ninjageezer]

On 13/03/2022 at 22:11, vlaiv said:

You can but you will gain nothing and even make life very hard for yourself.

At the moment, you have 73mm aperture telescope and 4.3um pixel size camera. With 430mm focal length of telescope you are at 2"/px sampling rate.

That is about perfect for that aperture size. You can't get any more detail than that in your image. Any attempt to "zoom" in more than that - and you will get blurry image.

What you see above is size of FOV compared to size of target. Your sensor has very big resolution in terms of pixels - 5184 x 3456.

To put things in perspective - "width" of M51 is only about 15 arc minutes. That is 15 * 60 = 900 arc seconds across. Even with large telescope and very good mount and excellent seeing - best you can hope to do is around 1"/px - which would make that target 900px across. That is again going to be small compared to full FOV of your sensor - which is x6 larger in width than galaxy at this sampling rate.

What you can do is image with setup you have, try to maximize sharpness on what you already have (very good focus, very good seeing and guiding) and simply crop your image to frame the target the way you want.

You can still get very detailed image of the galaxy that way - for example, here is M51 at ~2"/px. Image is only 860x670px, but there is no point in making it larger as target is not large enough and effective detail is just not enough to justify higher sampling resolution.

Ok many thanks for the explanation ,its just some of the targets will look very small with a 430mm focal length....

 

[vlaiv]

23 minutes ago, ninjageezer said:

Ok many thanks for the explanation ,its just some of the targets will look very small with a 430mm focal length....

 

They look small in context of full FOV - but do crop and keep them at 2"/px and they won't look small any more.

 

[ninjageezer]

14 minutes ago, vlaiv said:

They look small in context of full FOV - but do crop and keep them at 2"/px and they won't look small any more.

 

brilliant