Frame per second question…

[JonHigh]

I have been capturing 2 minute solar images with my ASI585 camera with fairly good results but is a 2 min capture long enough at 20fps at full frame?

If I choose a ROI of 1920x1080 the fps jumps to 33fps. Is that fast enough? If not, I was thinking of using the reducer for the EdgeHD 8” and then using ROI to get me back to a rough native FL or smaller to increase frame rate. Plus I’ll be upping the f stop, so maybe faster fps as it gathering more light? Any thoughts on that? Would the same apply to any future lunar captures I do? 
 

Edited June 28 by JonHigh

[Elp]

What are you trying to achieve? (Your goals).

[JonHigh]

1 hour ago, Elp said:

What are you trying to achieve? (Your goals).

Increasing my chances of good frames there by better end results. Is a longer capture time better than trying to increase frame rate? Or is it a mix of both? My thinking was if I increase capture time I might start getting slight blur from rotation so kept it short but wanted to increase the fps for better lucky imaging. As you may know I put the question about going mono but for the marginally better results I’m sticking with the 585. So just want to work out how to maximise what I have. 

Edited June 28 by JonHigh

[Elp]

Either or. As you know lowering the resolution of the camera increases FPS, note you also need a usb 3 port on the connected computer and an SSD drive in the computer may also help with FPS to overcome any potential data transfer bandwidth issues.

I think with the sun in white light the features may not change as quick as hydrogen alpha so you could get away with longer. Your stacking program will follow any alignment points and stack good frames accordingly, I normally do 2 minutes or so of raw video, then stack around 10 percent. Seeing on the day will largely affect any time you spend imaging and how much longer you need to image for. I find with white light more time doesn't really necessitate more detail, you can usually capture detail quite quick because the signal is so strong, same with HA but with the latter the features change much quicker.

 

Edited June 28 by Elp

[Hughsie]

Unlike deep sky and lunar imaging, the solar surface whether photosphere or chromosphere is continuously moving. It is therefore important to capture as much data as possible within the shortest time possible. In effect you need to ‘fix’ the seeing. This is achieved through taking very short exposures typically around 2-3 ms for around 10 seconds, typically 1,000 to 1,500 frames depending on the camera.

Taking long exposures of 2 minutes will acquire more light but this is the Sun we are imaging, we have plenty of that. Longer overall exposures may have great individual frames but when stacked they will become blurred. Remember the solar surface when you started the exposure will look different 2 minutes later.

So, the key factors are;

1) Exposure time - typically milliseconds.

2) Gain - a higher gain setting will allow you to reduce exposure time. You might ask won’t increasing gain increase noise? Well, the total exposure time is around 10 seconds so no.

3) FPS - needs to be as high as possible. Low exposure times help. Reduce ROI helps. Imaging in 8-bit rather than 12 or 16 bit will help. At a gain of 250 and exposure time of 7ms I can achieve c130FPS with the ASI174mm with a double stacked Lunt and 4x Powermate. FPS increases to c160 with a 2.5x or 3x Barlow as I can use an even lower exposure time as the image is brighter.

4) Appropriate settings in your acquisition software will help generate high FPS but your computer needs to be able to keep up. USB 3 and writing to an SSD is a must otherwise you will just ‘drop’ frames resulting in a longer overall capture time and lower FPS.

5) Camera - mono over colour is preferred. Cameras with high FPS like the ASI174mm and Player One solar cameras fit the bill. Large pixel size also helps (the 174 has 5.86um pixels, the top Player One camera for solar is near twice that of the 174).

The 585 I believe has a max. FPS of 46 so you facing a challenge here. So, initially you will need to tweak 1 to 4 above to reach this unless you want to purchase a different camera.

 

John

 

PS - I image in H-alpha and just seeing the post from Elp notice you are referring to white light. Certainly play around with exposure and gain and use the histogram to make sure you are not blowing out any of the highlights. Points 3 and 4 remain relevant whether imaging in white light or H-alpha.

 

 

Edited June 28 by Hughsie

[Elp]

That was another query for me as to the desired goals.

As it's an SCT it'll be close up imaging so camera size is a factor but the OP is using their existing.

With WL you can use a green filter to help improve contrast which may help with SCT optics, the other option is a Baader solar continuum filter in front of the camera nosepiece, I believe these help more with refractors due to the glass refraction.

Edited June 28 by Elp

[Hughsie]

3 minutes ago, Elp said:

As it's an SCT it'll be close up imaging so camera size is a factor but the OP is using their existing.

Camera pixel size with this scope combo will result in a slight over-sampling in good ‘seeing’ conditions. Binning 2x2 might also be tried.  Seeing at 200mm aperture will also be a challenge to acquiring a good image. Whilst nothing can be done to change the ‘seeing’ I prefer imaging in the morning when temperatures are lower and none of my neighbours roofs have warmed up!

[Elp]

Do you think stopping the aperture down to increase the f ratio will help with contrast, or just do it in post process?

[JonHigh]

Hi and thank you for your time and help! 

I have a Baader SC filter stacked with a UV/IR which has made a big difference to the camera being unfiltered. For Solar, it's only white light as I can't afford or justify anything else right now as I just got the EdgeHD so working on what I have for the time being. My exposure time is was roughly 30ms. Gain was 252 but maybe I should up that to increase exposure times. I always shoot Solar, Lunar and Planets in 8bit RAW, Ser video format. However unless I'm working at 640x480 my fps is no where near that of the 174! LOL ...  I use Autostakkert 4 as the stacking program on my main PC but I'm currently using a Lenovo e580 laptop for all my AP captures. It has USB3 ports but I would have to look up which version. Also has a M.2 NVMe on the motherboard and an 1Tb internal SSD but again I'm not too sure what the bus speed is so that could be a bottleneck!? I will try binning 2x2 next time as I didn't think about using that feature. I know that using the EdgeHD for solar maybe not be the best and I think I got cleaner images from my ETX90 which was one reason I was thinking about reducing the FL with the reducer so I was being a bit kinder to the scope and scrubbing off some of the magnification and reducing the effect of seeing conditions plus increasing the FPS using a small capturing area. 

When I have the time I do Solar imaging in the morning as well also and especially during the 'Summer'  as I don't want to start melting the lubricants or greases or possible other mount issues (warping the belts etc). However, I am always surprised just how cool the scope and mount are after a hour.

I guess it comes back to my other post regarding OSC to Mono and selling the 585 in favour for a Mono!!!  Maybe of a used ASI174MM or alike comes up I'll grab it!!

Edited June 28 by JonHigh

[JonHigh]

If I was to use a reducer would I have to apply the 105mm back focus for either solar or lunar? As I understand back focus doesn’t apply to solar system objects.