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Focusing Help

Astrophotography Beginner
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#1 scharles

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Posted 22 September 2022 - 05:48 PM

Hi All, 

 

Couple of questions for folks. I've been using a skymax 127 cas mak OTA to start a humble beginning in astronomoy and astrophotography and I've been loving getting involved. I've been out for a few evenings of late and have noticed a couple "issues" that I've been having repeteadly and wondering if I'm being hardware limited or that I'm doing something a little wonky. 

 

I've found when finding planets visually (mainly saturn / jupiter) and bringing them into focus I've been doing a good job. (Using either a 10 or 25mm EP with and without a 2x barlow) but when I get the planet centred and tracking properly I'll switch over to my camera and refocus / recentre on the sensor. I've been targetting saturn mainly lately just because its higher in the sky earlier in the night and I've been using a 1.5 barlow on my OTA for it. I've been having a really rough time focusing and getting a nice crisp image on my laptop screen during the capture, its usually very grainy / granulated. Ive been aiming for 10 +/- 5ms exposure times then aiming to have the rgb histograms around 70% (I can put some screenshots in if people would like). Then when i go to process and stack the images, I am getting quality curves in autostakkert that are relatively flat and steady but sits on the 30% quality line (again can provide screenshots if needed). I tried capturing a couple times without the 1.5x Barlow and the image "quality" was better but still quite low.

 

I guess I'm just wondering if 

 a) live capture image on screen is supposed to be quite granulated / grainy / unfocused? 
 b) can I do anything to help "focus" the planets better on my camera sensor

 c) what can I expect on a small cas mak ota

 

n.b most sessions have been on relatively good seeing conditions


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#2 FRANKVSTAR

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Posted 22 September 2022 - 06:16 PM

I assume you can view images on your laptop as you say. If so can you view the images one at a time as you take them, if so that is how I find it easier to get the proper focus, or at least the best that can be done. Just change focus slowly back and forth as your viewing the still images till you reach the sweet spot.

 At my age the viewfinder on my Canon does me no good at all, and I am waiting on the correct cable to arrive so I can connect Canon to ASIAIR PLUS and view images as I take them , that how I will get a better focus. Now I am just guessing as I am no expert, so I suggest waiting on other to reply.



#3 Tulloch

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Posted 22 September 2022 - 06:28 PM

Focusing is hard, there are a couple of tips in section 14.2 of the FAQ at the top of the page, but it is a difficult thing to do. With Saturn, try to get the Cassini division as dark as possible, on Jupiter try for the darker cloud banks.

https://www.cloudyni...ated-july-2022/

 

What camera are you using, that will help suggesting a barlow to use?

 

To watch how I capture and process the planets (after already spending a few minutes going forwards and backwards with the focus knob) with a C9.25, 2.5x Powermate and ASI224MC, watch here.

https://youtu.be/yUPhM2kdxNI?t=81

 

Andrew



#4 scharles

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Posted 22 September 2022 - 06:48 PM

Focusing is hard, there are a couple of tips in section 14.2 of the FAQ at the top of the page, but it is a difficult thing to do. With Saturn, try to get the Cassini division as dark as possible, on Jupiter try for the darker cloud banks.

https://www.cloudyni...ated-july-2022/

 

What camera are you using, that will help suggesting a barlow to use?

 

To watch how I capture and process the planets (after already spending a few minutes going forwards and backwards with the focus knob) with a C9.25, 2.5x Powermate and ASI224MC, watch here.

https://youtu.be/yUPhM2kdxNI?t=81

 

Andrew

I'm using the same camera as you the ASI224MC, I'll definitely watch your video as well. 
I guess my biggest gripe or confususion point is that there is such a difference in view between eyepiece and camera view mode



#5 Tulloch

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Posted 22 September 2022 - 06:54 PM

I'm using the same camera as you the ASI224MC, I'll definitely watch your video as well. 
I guess my biggest gripe or confususion point is that there is such a difference in view between eyepiece and camera view mode

Yep, in fact since I mostly just image, I keep the focus point set for my camera, then align my scope with an eyepiece using the out of focus donuts. It's actually easier to centre the donuts in the eyepiece :)



#6 Lacaille

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Posted 22 September 2022 - 07:04 PM

Hi there

 

I guess I'm just wondering if 

 a) live capture image on screen is supposed to be quite granulated / grainy / unfocused? 
 b) can I do anything to help "focus" the planets better on my camera sensor

 c) what can I expect on a small cas mak ota

 

n.b most sessions have been on relatively good seeing conditions

It is likely that imaging in S Australia in these past few weeks the seeing was probably not that great!  But yes, the live feed can be quite granular even under pretty good conditions.  

 

Your approach to capture as described in your post looks pretty sound.

 

If you are using Firecapture, there are things you can do to improve the focus process:  

 

First, increase the feed sampling rate (1 in the screen shot) to about 30 FPS; it seems to default to 10fps which is adequate but if you have a decent computer it will handle a higher rate. This does not affect your capture fps settings.

 

Second, try using the screen adjustment settings (no. 2 on the screen shot). This again does not affect the capture settings, just the live feed. I usually find I get best contrast with gamma slid way over to the right and the brightness adjusted to your liking and the ambient condiitons.

 

Third, find the autoalign button - I have it on my vertical tool bar (number 3 on the screenshot) - if it is not visible you can call it up from the + button at the bottom of the vertical tool ba and turn that on while you focus, to hold the planet steady while you focus. You need good tracking so the planet is not moving too much on the sensor while you do this. You need to spend time getting the feel for the sweetspot

 

Firecapture.jpg

 

Your last question - you can expect good results with your scope, if you put the time in to capturing in good conditions, learning the ropes with Firecapture etc.  I had a  Celestron 127 Mak Cass in my flat in France and got good results with the planets very low, at 20-30 degrees altitude. I used a 2X Barlow, a ZWO224MC, and an ADC (of course!).  I had an electric focuser on the primary mirror focuser, which helped too. I also placed a counterweight at the front end as there was a lot of weight at the back end  for such a small mount. Check your balance point with the imaging train in place, and if necessary fashion a counterweight - I used coins in a ziploc bag!

 

Best of luck!

 

Mark

 

 



#7 JMP

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Posted 22 September 2022 - 07:04 PM

Saturn has a low surface brightness compared to the moon or Mars. You might try 20 mS exposure, reduce gain to give a 50% histogram, and go for a 5 or 6 minute AVI. Use cassini as your focus indicator. That last little bit of focus is so tiny, I like to say I touch the focus knob lightly and think about turning it.

 

It takes patience and practice to get the best results.



#8 scharles

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Posted 22 September 2022 - 08:00 PM

FWIW here is a couple images of my Autostakkert views with the best frames / frame quality graph 

 

Pic 1 best jupiter capture

jup1.png

 



#9 scharles

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Posted 22 September 2022 - 08:00 PM

Best saturn capture 

 

sat1.png



#10 Kokatha man

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Posted 23 September 2022 - 04:38 AM

I'd advise you to forget about using an ep for planetary imaging - with any finder scope aligned to the main scope there shouldn't be any trouble getting the target onscreen in your camera, but cranking up the gain will assist with hunting down your targets - once aligned you should be fine but if you bang your scope around between each session you might need to do it regularly!

 

Always collimate after you have aligned your finder, using a semi-bright star for collimating...obviously use a bright planet like Jupiter or the Moon to align said finder first. Collimation must be done with the camera at the f/l you wish to image at, ie, with the barlow in place also.

 

Have FireCapture set to the "Max" screen refresh rate (usually 60Hz for most screens) & if you wish to focus using a smoother image increase the exposure time which will lower the fps & display a smoother planetary image onscreen.

 

As mentioned, altering the gamma to get a darker & more contrasting image is a good ploy but of course you will need to increase the gain so the image isn't too dark then - but capture at gamma = 50 of course!

 

When focusing on Saturn it is when the Cassini Ring is blackest that you have best focus...for Jove it is when you can see the whispiest of detail in the shape of festoons in the EZ region, or greatest contrast variations in the 2 main bands, or the sharpest white storm ovals or dark spots...& with Mars it is the best contrast between the darker features & the reddish (sandy) background, looking at the borders of these 2 different aspects.

 

Some sort of focusing assistance mechanism is handy & this can range from a crude lever extension to a basic "Accufocus" device, where you can fit a small dc motor to your focuser & operate it via a hand controller going back & forth to find best focus, the motor is driven by an internal 9V battery in the h/controller...these work very well with a colour camera btw.

 

Go to our website which is linked to in my signature at the bottom of this post...in the tutes (which do concentrate upon the ASI224MC funnily enough wink.gif ) you can get additional information, especially about star-collimation.

 

We've been planetary imaging in Adelaide from Sellicks Beach for many years btw..! lol.gif




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