Poll: Two choices

[Jules Tohpipi]

On 25/07/2023 at 12:31, Mark2022 said:

I read of people a lot who use the 200P, as is, for imaging. What keeps me questioning is how an 8 inch F5 doesn't allow for faster exposures than a 5 inch F5. I guess it's just the same amount of light but from a wider  FOV?

It’s a lot more light in the 8 inch but at much higher magnification (because the focal length of the 8 inch is longer). 
 

In simple loose terms, the extra magnification of the 8 inch (due to its longer focal length) reduces the intensity of the light. But it has a bigger mirror to compensate.
 

End result is Jupiter (say) will look bigger in the 8 inch and have better resolution, but still maintain the same brightness as the much smaller (less magnified) image of Jupiter in the 5 inch. 
 

The above is the case if both scopes are F5 as you say. 

Edited July 26, 2023 by Jules Tohpipi

[Neil H]

Hi I was lucky enough to get the HEQ5PRO and a UK Orion optics 200/1200 for £600 I have never looked back does everything I ask it to do 

[Mandy D]

On 25/07/2023 at 12:31, Mark2022 said:

I read of people a lot who use the 200P, as is, for imaging. What keeps me questioning is how an 8 inch F5 doesn't allow for faster exposures than a 5 inch F5. I guess it's just the same amount of light but from a wider  FOV?

This is something all photographers are familiar with. f/5 is the ratio of the lens (telescope) focal length to the aperture of the lens. Doubling the focal length will cause the image produced to be twice the diameter or four times the area, hence dimmer by a factor of four. Given the greater focal length of an 8 inch telescope at f/5 compared with a 5 inch, you can see it will produce a larger image with light that has been gathered by a larger mirror, but will retain the same brightness level. The field of view of the 8 inch will be narrower than the 5 inch at the same focal ratio.

A 200P at f/5 will be 1000 mm FL, compared with just 635 mm FL for the 5 inch.

[Mark2022]

10 hours ago, Mandy D said:

This is something all photographers are familiar with. f/5 is the ratio of the lens (telescope) focal length to the aperture of the lens. Doubling the focal length will cause the image produced to be twice the diameter or four times the area, hence dimmer by a factor of four. Given the greater focal length of an 8 inch telescope at f/5 compared with a 5 inch, you can see it will produce a larger image with light that has been gathered by a larger mirror, but will retain the same brightness level. The field of view of the 8 inch will be narrower than the 5 inch at the same focal ratio.

A 200P at f/5 will be 1000 mm FL, compared with just 635 mm FL for the 5 inch.

I know. I know this stuff but sometimes I just forget it and I'm being slow. When your mind gets filled up with stuff  it's like a computer's memory getting full.  The computer slows down. 🙂

[ollypenrice]

On 25/07/2023 at 13:17, Space Hopper said:

Aperture rules, but understand a 200P is a fair old size and may be pushing an EQ5 class mount a bit.

Not in imaging.

I wouldn't want to image with an 8 inch Newt on an HEQ5. Too big.

Olly

[Space Hopper]

On 28/07/2023 at 08:27, ollypenrice said:

Not in imaging.

I wouldn't want to image with an 8 inch Newt on an HEQ5. Too big.

Olly

Not on an HEQ5 no.......