# New Refractor and Planetary Imaging

### #1

Posted 24 July 2021 - 08:17 PM

GM

### #2

Posted 24 July 2021 - 10:36 PM

Since your camera pixel size is 2.9um, the general thought is that your imaging F-ratio should be no more than 5-7 times your pixel micron size. so 2.9x5=14.5. 2.9x7=20.3.

Your scope appears to have a 714mm focal length and a 101.5mm diameter.

If you place a x TV barlow in your imaging train with no diagonal (checking the Televue website a 1.25" barlow equals 3.5x rather than 2x) we get the following:

714 X 3.5 (2x barlow) = 2499mm focal length. Now divide that by your diameter and you get f-24.6, a little more than the 14.5 to 20.3 recommended. The ADC in that path would also increase the F-number further.

That said, I have stacked 2x and 3x barlows in my 100mm F8 refractor and got what I thought were decent images.

If i get clear skies, I'll try to take a Saturn or Jupiter image with my refractor and use both the 2x and 3x 1.25" TV barlows along with my ASI462mc. This might give you an idea of whats possible. If I dont follow up in a few days remind me via messaging but I'll try to send some examples soon.

### #3

Posted 24 July 2021 - 10:49 PM

Since your camera pixel size is 2.9um, the general thought is that your imaging F-ratio should be no more than 5-7 times your pixel micron size. so 2.9x5=14.5. 2.9x7=20.3.

Your scope appears to have a 714mm focal length and a 101.5mm diameter.

If you place a x TV barlow in your imaging train with no diagonal (checking the Televue website a 1.25" barlow equals 3.5x rather than 2x) we get the following:

714 X 3.5 (2x barlow) = 2499mm focal length. Now divide that by your diameter and you get f-24.6, a little more than the 14.5 to 20.3 recommended. The ADC in that path would also increase the F-number further.

That said, I have stacked 2x and 3x barlows in my 100mm F8 refractor and got what I thought were decent images.

If i get clear skies, I'll try to take a Saturn or Jupiter image with my refractor and use both the 2x and 3x 1.25" TV barlows along with my ASI462mc. This might give you an idea of whats possible. If I dont follow up in a few days remind me via messaging but I'll try to send some examples soon.

Thanks so much. This will help me have an idea.

GM

### #4

Posted 25 July 2021 - 11:44 PM

So clouds were out and I did this quick but I managed to get about 500 frames for a quick process to give you an idea.

This was a 100mm refractor at F/8 using a 3x TV barlow and an ADC on top of that.

Camera was an ASI 224mc.

This is likely the max you would want to go. Seeing was not great but it was not poor.

With better seeing I think you'd get some nice images.

- Kenny V. and Jaimo! like this

### #5

Posted 26 July 2021 - 03:39 AM

So clouds were out and I did this quick but I managed to get about 500 frames for a quick process to give you an idea.

This was a 100mm refractor at F/8 using a 3x TV barlow and an ADC on top of that.

Camera was an ASI 224mc.

This is likely the max you would want to go. Seeing was not great but it was not poor.

With better seeing I think you'd get some nice images.

Very nice and that image scale is pretty much what I am after. Thanks for posting this as now I know where I am headed. Pretty exciting.

GM

### #6

Posted 26 July 2021 - 06:57 AM

Since your camera pixel size is 2.9um, the general thought is that your imaging F-ratio should be no more than 5-7 times your pixel micron size. so 2.9x5=14.5. 2.9x7=20.3.

Your scope appears to have a 714mm focal length and a 101.5mm diameter.

If you place a x TV barlow in your imaging train with no diagonal (checking the Televue website a 1.25" barlow equals 3.5x rather than 2x) we get the following:

714 X 3.5 (2x barlow) = 2499mm focal length. Now divide that by your diameter and you get f-24.6, a little more than the 14.5 to 20.3 recommended. The ADC in that path would also increase the F-number further.

That said, I have stacked 2x and 3x barlows in my 100mm F8 refractor and got what I thought were decent images.

If i get clear skies, I'll try to take a Saturn or Jupiter image with my refractor and use both the 2x and 3x 1.25" TV barlows along with my ASI462mc. This might give you an idea of whats possible. If I dont follow up in a few days remind me via messaging but I'll try to send some examples soon.

Hmmm.....I’ve been researching and following threads here on actual magnification factors of Barlows and power mates vs distance to camera sensor and have referenced the Televue chart below

https://www.televue....b=_app#MagChart

So above, you stated the 2x TV is actually 3.5x?.........can you help me understand this number and how that’s arrived at from the TV chart?.......please excuse my newbie confusion? Thx for being patient!

### #7

Posted 26 July 2021 - 07:28 AM

Sure but that link you posted is for Powermates. Here is the chart for barlows

https://www.televue....d=52&Tab=_photo

"For astro-imagers, the above chart indicates the magnification for each Barlow (2x, 2x Big & 3x) as a function of distance from the Barlow top surface to the imaging surface (CCD or film)."

Let me know if you still have questions

Todd

### #8

Posted 26 July 2021 - 07:29 AM

Very nice and that image scale is pretty much what I am after. Thanks for posting this as now I know where I am headed. Pretty exciting.

GM

I'll be curious to see what you come up with. Keep us posted.