Autoguiding with EQ5 mount

[Jm1973]

Hi. At the moment I am using an EQ5 Pro Goto Synscan mount with a Skywatcher 200P and DSLR. I am getting 120 second unguided subs when I get decent polar alignment.

I've just bought a GPCAM2 and an adaptor, and I have fitted it to my 9x50 finderscope (to save weight). I control the mount and camera via a laptop already, and I will be using PHD2 to do the guiding.

My question is, what sort of exposure times can i realistically expect to get with the addition of autoguiding, with my current setup?

Thanks in advance for any insights. 

[geordie85]

It really all depends on balance, polar alignment and most importantly the wind. 

I used to use the same set up and have achieved 30 minute subs but the slightest blow would ruin my subs due to the lightweight mount and the 200p acting like a sail.

[Jm1973]

1 hour ago, geordie85 said:

It really all depends on balance, polar alignment and most importantly the wind. 

I used to use the same set up and have achieved 30 minute subs but the slightest blow would ruin my subs due to the lightweight mount and the 200p acting like a sail.

Ah, I see. I guess then it is striking a compromise between getting the longest exposures you can, and keeping them short enough so they don't all get ruined by wind.

If I could get 5 or 10 mins I'd be happy to be honest. I might invest in a couple of windbreakers. I've got one in the shed that I never use...

[Phillyo]

What DSLR are you using and why do you think going for the 'longest exposures you can' is a good thing? Not a dig, but a genuine question. The reason I ask is because your camera uses a CMOS sensor, not a CCD sensor. Once you have exposed long enough to get above the noise floor, the limiting factor for sub length is likely to be your light pollution levels. I would assume that Bristol LP isn't amazing so exposing for longer won't get you any more detail, just more light pollution. I would much rather shoot 100 x 2min subs than 2 x 100min subs. The longer subs also means more data lost due to aeroplanes, satellites, wind movement, bad guiding etc. If you take 2 subs at 100min and one of them is rubbish, you've lost 100min of data. If you take 100 subs at 2min and even 10 of them are rubbish, you've only lost 20min of data. Plus, with a lot of subs stacked together you can use an average combination method to remove satellite trails anyway.

Try not to get into the mind set that longer is always better. More data is always better sure but not always longer, not unless you're imaging from a bortle 1 zone of course  

[Jm1973]

12 minutes ago, Phillyo said:

What DSLR are you using and why do you think going for the 'longest exposures you can' is a good thing? Not a dig, but a genuine question. The reason I ask is because your camera uses a CMOS sensor, not a CCD sensor. Once you have exposed long enough to get above the noise floor, the limiting factor for sub length is likely to be your light pollution levels. I would assume that Bristol LP isn't amazing so exposing for longer won't get you any more detail, just more light pollution. I would much rather shoot 100 x 2min subs than 2 x 100min subs. The longer subs also means more data lost due to aeroplanes, satellites, wind movement, bad guiding etc. If you take 2 subs at 100min and one of them is rubbish, you've lost 100min of data. If you take 100 subs at 2min and even 10 of them are rubbish, you've only lost 20min of data. Plus, with a lot of subs stacked together you can use an average combination method to remove satellite trails anyway.

Try not to get into the mind set that longer is always better. More data is always better sure but not always longer, not unless you're imaging from a bortle 1 zone of course  

Well at the moment my exposures are getting swamped by light pollution. For a 2 minute exposure I have to keep my ISO down to 400, otherwise the histogram is too far to the right, and that is with no moon. If the moon is prominent then I have to keep them shorter than that. I'm in a Bortle 6 with LED streetlights, and I am fairly close to shopping centres etc, so a fair amount of LP. By the time I have got rid of the LP my images are pretty noisy.

My attempted solution to this is to buy an l-extreme filter. From what I've read, this will cut down on the LP pretty well, but will require much longer subs. Hence the need to start auto-guiding.

 

Edited December 15, 2020 by Jm1973

[Ouroboros]

I find 300s (5 mins) guided in Bortle class 3 at 400ISO for my 460D is about optimum. I could run for longer but tend not to as the chance of wind shake  or satellites ruining the shot increase. I hardly ever image now under the Bortle class 5 skies of Oxfordshire but I seem to recall that 2 to 3 minutes was about the limit. That’s not much more than you’re getting unguided, which incidentally is pretty good I reckon. But guiding is still worthwhile because you can dither and thus avoid taking darks if you want to. 

[Jm1973]

1 minute ago, Ouroboros said:

I find 300s (5 mins) guided in Bortle class 3 at 400ISO for my 460D is about optimum. I could run for longer but tend not to as the chance of wind shake  or satellites ruining the shot increase. I hardly ever image now under the Bortle class 5 skies of Oxfordshire but I seem to recall that 2 to 3 minutes was about the limit. That’s not much more than you’re getting unguided, which incidentally is pretty good I reckon. But guiding is still worthwhile because you can dither and thus avoid taking darks if you want to. 

I should have added I am intending to use the Optolong l-extreme filter to cut down on the LP and skyglow, so should be able to get longer exposures without blowing out the histogram.

[Phillyo]

Guiding is absolutely worth doing, as pointed out above you can dither which is always great. The l-extreme is a dual narrowband filter for Ha and Oiii which will work well with your DSLR (although your Ha will be limited due to the IR block inside a DSLR) but only on emission type objects, not galaxies or reflection type objects. 5min should be plenty and you can always up the ISO a little bit if needs be. 

[Jm1973]

2 minutes ago, Phillyo said:

Guiding is absolutely worth doing, as pointed out above you can dither which is always great. The l-extreme is a dual narrowband filter for Ha and Oiii which will work well with your DSLR (although your Ha will be limited due to the IR block inside a DSLR) but only on emission type objects, not galaxies or reflection type objects. 5min should be plenty and you can always up the ISO a little bit if needs be. 

The DSLR has had the rear filter removal mod (not the full spectrum) so should be ok for picking up Ha. 

Do you think 5 mins will be long enough to pick up enough signal when using the l-extreme? If so that would be good.

[Phillyo]

I would think so yes. The only way to find out is to run some tests for your sky. You could always try using the sensor analysis inside Sharpcap software? It'll cost you £10 for the year but it's fantastic and will tell you what exposure lengths to use for optimal results.

[Jm1973]

2 minutes ago, Phillyo said:

I would think so yes. The only way to find out is to run some tests for your sky. You could always try using the sensor analysis inside Sharpcap software? It'll cost you £10 for the year but it's fantastic and will tell you what exposure lengths to use for optimal results.

I've actually got SharpCap pro, as I use their PA tool. I'll take a look at the sensor analysis. Thanks.

[Gaurav Mk]

On 15/12/2020 at 18:55, Jm1973 said:

Hi. At the moment I am using an EQ5 Pro Goto Synscan mount with a Skywatcher 200P and DSLR. I am getting 120 second unguided subs when I get decent polar alignment.

I've just bought a GPCAM2 and an adaptor, and I have fitted it to my 9x50 finderscope (to save weight). I control the mount and camera via a laptop already, and I will be using PHD2 to do the guiding.

My question is, what sort of exposure times can i realistically expect to get with the addition of autoguiding, with my current setup?

Thanks in advance for any insights. 

Hi, I was looking for support about attaching the camera to the finderscope? I have a similar setup, but my finderscope is 8*50. 

I kindly request you to help me what adapter you used or an image with details. Thanks in advance.

[smashing]

On 15/12/2020 at 16:06, Jm1973 said:

The DSLR has had the rear filter removal mod (not the full spectrum) so should be ok for picking up Ha. 

Do you think 5 mins will be long enough to pick up enough signal when using the l-extreme? If so that would be good.

Yes it is, I tried it out the other day although I'll see how far I can push it...when we get some clear skies

[Altair8389]

Hi, what target are you looking to image ? I think your exposure length depends on this. Also what type of sky darkness are you in, and what about neighbours security lights, house lights (bedrooms) and what about street lights ? Sharpcap has an exposure calculator to tell you the optimal exposure depending on your location.

You can always start using lower exposure values to get an idea if your camera setup is ok, and do guiding at another time. Autoguiding is for longer exposures really, so may not be really necessary unless you are in a dark sky site and can do 20 + minute exposures of 22+magnitude galaxies !