answer to query please

[bruno]

Can anyone please tell me when i put my camera (1100D) on my mount(ioptron zeq 25), i can take images for as long as want (20 mins so far) without any help from PHD2 but when i put my telescope (80mm) on i can't get more than 3 mins best using polemaster, when i use PHD everything connects but i can't seem to get it to run smoothly.

Also due to the light pollution where i am i struggle to find a guide star is there any way i can enhance this.

Any help would be greatly appreciated. 

 

  

[alacant]

1 hour ago, bruno said:

i struggle to find a guide star is there any way i can enhance this

Hi. Put another cls -or a cheap moon and skyglow- before the guide camera. Unless the star is well defined, PHD2 will struggle.

HTH

[bruno]

i will try that thanks Alacant

[newbie alert]

The difference is focal length...you don't say what sized lens but say 50mm in comparison to 600mm on the ed80..

For guide stars in phd2  you could up the gain slightly and a slight de-focus on the stars as recommended by others ..

I'd first check that they'e indeed stars as hot pixels can look like stars..fooled me completely , great tip is to use the onsite handset to move the mount..if the stars don't move they'e not stars..

[cjdawson]

Hey wait,    I'm confused am I missing something as there's loads of gaps in the information provided.

So you put the camera on the mount... what what lens are you using when you can do your 20 min exposures?

What are you using for guiding?   PHD2 is the software, I get thats the software, but what camera is it using?

Have you made a dark library and bad pixel map?

[bruno]

Thats the point, I put my 50mm on and i don't need any software to guide only stellarium to find 

[Cornelius Varley]

18 minutes ago, bruno said:

Thats the point, I put my 50mm on and i don't need any software to guide only stellarium to find 

At 50mm focal length you can get longer unguided exposures compared to using the telescope.

[cjdawson]

Ah, I think I figured out why you are struggling.

You put a 50mm lens on your camera, and can take wide field shots great.   There is a rule calls the 500 rule.  Take the focal length of the lens (50mm) in your case and divide 500 by that, so 500/50 = 1 second of exposure before you get star trailing....... but that's for a static camera.  Add that your camera is tracking using the mount and yes, you can go for a huge amount of time and stay within the amount of drift that you'd get for that 1 second exposure.   hence, 20 mins, without needing to guide.

 

Then you say that you put it on your 80mm telescope and everything changes.   However, the 80mm that we're talking about here is the diameter of the objective lens.   Not the focal length.  The focal length of my telescope the Skywatcher ST-80, is 400mm.  That's the figure that's the equivalent of the 50mm of your camera length.

When you look at those two figures, 50mm v 400mm that's a huge difference.   I know it won't help solve the problem, but I'm hoping that it will help you to understand why there's a huge difference.

The example that I did is for my telescope, you should check your telescope and see what it's focal length is.

[Skipper Billy]

45 minutes ago, cjdawson said:

 

45 minutes ago, cjdawson said:

, so 500/50 = 1 second of exposure

Surely 10 seconds.

 

[Stub Mandrel]

Simpler calculation:

50mm lens does 20 minutes.

500mm lens is ten times longer, so the stars drift across the sensor 10 times faster. So you can image for only  1/10 as long without trailing,- 2 minutes.