First Dive into Imaging (in progress) !

[jpoulette]

36 minutes ago, Lee_P said:

Specific advice here for @jpoulette -- one of the things that makes the Askar FRA400 a neat little 'scope is that there are no backfocus requirements; so long as the image is in focus, the backfocus is automatically correct. However, if you use the reducer then be aware that you will need to get your backfocus just right (probably 55mm or thereabouts) otherwise you'll get streaky corner stars. I'm not saying don't use the reducer, but it's just something to be aware of. Speaking personally, I never used a reducer with my Askar FRA400. 

Regarding "fast" optics in general, I try to sidestep the whole issue by treating astrophotography as a marathon rather than a sprint. My previous 'scope (the FRA400) was f5.6, and my current 'scope (Askar 130PHQ) is even slower, at f7.7. But *shrugs* it's fine, I just keep plugging away until I collect enough data. Granted, I might change my mind on this topic if I ever use a speed demon like a RASA 😁

Good advise - thanks. I picked up the reducer mainly because it was available - it seems to be 'out of stock' for quite a while. I need to acquire some data first and then evaluate (see the results with my own eyes), and adjust if necessary. The reducer may work perfectly at some point, given that the object is properly placed in the center of the image.

I've had a little experience with the classic Petzval design - I'm hoping that the inherent sharpness of the center area of the exposure will help, given the objects I'll be looking at. I'm not quite sure what the function of the 5th element in the FRA400 is - but a few images should enlighten me on that. 😀

I have a good 180 degree view centered due north from home - so there are several objects that I've had my eye on for imaging. I'm hoping Stellarium images like this one will give me a decent representation of the stock lens - detector relationship.

Edited February 2, 2023 by jpoulette

[Adam J]

6 hours ago, ollypenrice said:

Sorry, I'm not with you on this. A target focal length at a given aperture does not allow for any variables so what are we comparing with what?

Olly

So imagine two scopes. 

1) Triplet 80mm aperture with flattener @ 400mm focal length giving F5.

2) Triplet 80mm aperture @500mm focal length, but now using a 0.8x reducer to give 400mm effective focal length. 

Scope #2 will not only out perform scope #1 in terms of correction / spot size quality being equal. It will also be cheaper to make. Hence why most optically fast scopes archive this using a reducer instead of just a faster objective. 

That final point was less about the 'myth' and more about the usefulness of reducers. 

Adam

Edited February 3, 2023 by Adam J

[ollypenrice]

8 hours ago, Adam J said:

So imagine two scopes. 

1) Triplet 80mm aperture with flattener @ 400mm focal length giving F5.

2) Triplet 80mm aperture @500mm focal length, but now using a 0.8x reducer to give 400mm effective focal length. 

Scope #2 will not only out perform scope #1 in terms of correction / spot size quality being equal. It will also be cheaper to make. Hence why most optically fast scopes archive this using a reducer instead of just a faster objective. 

That final point was less about the 'myth' and more about the usefulness of reducers. 

Adam

OK, this may be true, though some reducers bring image quality issues of their own. Extra glass means extra dispersion and the risk of internal reflection, both of which we've seen on SGL in the past.  My earlier aim was to challenge the overly simple notion that F ratio alone determines exposure time in digital imaging.

Olly

[jpoulette]

Yet another newbie question: 😀

I'm told that all frames, light, dark, flat, & bias" should preferably all be taken "at the same temperature".

Is this ambient or detector temperature? I see the ASIair app has a few temperature options for the main camera and I wonder if you can trick the camera into thinking it's actually outside.

Example:

indoor temperature is 16.5°C, camera (run for an hour) reads 0°C (in ASIair ap) - a Δ of -16.5°C

outdoor temperature is -12°C - can I assume the camera temperature could be scaled to (-12°C + -16.5°C) = -28.5°C ?

If so, I could take dark and flat frames indoors at a camera temp set to -20°C, and use them with images acquired outside at ambients of ~ -5°C with the camera set to 0°C.

It's clearly not ideal (and I can't imagine the ambient not having an effect on the optic train) - but I'm just wondering if it's at all workable.

[Lee_P]

4 minutes ago, jpoulette said:

Yet another newbie question: 😀

I'm told that all frames, light, dark, flat, & bias" should preferably all be taken "at the same temperature".

Is this ambient or detector temperature? I see the ASIair app has a few temperature options for the main camera and I wonder if you can trick the camera into thinking it's actually outside.

Example:

indoor temperature is 16.5°C, camera (run for an hour) reads 0°C (in ASIair ap) - a Δ of -16.5°C

outdoor temperature is -12°C - can I assume the camera temperature could be scaled to (-12°C + -16.5°C) = -28.5°C ?

If so, I could take dark and flat frames indoors at a camera temp set to -20°C, and use them with images acquired outside at ambients of ~ -5°C with the camera set to 0°C.

It's clearly not ideal (and I can't imagine the ambient not having an effect on the optic train) - but I'm just wondering if it's at all workable.

It's sensor temperature. You're using a cooled camera, so this is easy. Don't overthink it  Just tell the ASIAIR to set your sensor to your desired temperature (I always use -10 deg C), then when it's cooled you're good to go.

[jpoulette]

3 minutes ago, Lee_P said:

It's sensor temperature. You're using a cooled camera, so this is easy. Don't overthink it  Just tell the ASIAIR to set your sensor to your desired temperature (I always use -10 deg C), then when it's cooled you're good to go.

Hey - I overthink everything ! 😎

So, on the temperature side - it's OK to take lights outside, and other reference frames inside (as long as the camera is cooled to the same temperature) ?

I only ask because we're forecast for plunging temperatures the next few days (-20F / -30°C) tonight with wind chills to -50F. Not ideal for being outside.

[Lee_P]

49 minutes ago, jpoulette said:

Hey - I overthink everything ! 😎

So, on the temperature side - it's OK to take lights outside, and other reference frames inside (as long as the camera is cooled to the same temperature) ?

I only ask because we're forecast for plunging temperatures the next few days (-20F / -30°C) tonight with wind chills to -50F. Not ideal for being outside.

Yep, a-ok!

[DaveS]

On 02/02/2023 at 09:35, ollypenrice said:

Also, plenty of giant professional telescopes have slow F ratios but capture images in astonishingly short times. That's because they have large pixel cameras in the back. What matters is not the F ratio but the flux per pixel - which goes up if you bin your pixels or use larger ones.

Olly

 

For illustration I present Stephan's Quintet. Single 2 min subs in RGB From the Liverpool Telescope on La Palma. 2m mirror, f/10 but effectively 30 micron pixels and 90% QE.

[ollypenrice]

1 hour ago, DaveS said:

For illustration I present Stephan's Quintet. Single 2 min subs in RGB From the Liverpool Telescope on La Palma. 2m mirror, f/10 but effectively 30 micron pixels and 90% QE.

Exactly!

Olly

[jpoulette]

Progress report (as of 06 Feb 2023):

Since the weather has been so bad (another winter weather advisory tonight) - I switched over to getting a grip on the stacking / processing side.

Completed the first two freebie tutorial videos from Masters of PixInsight, and downloaded the free frame sets they offer. There are three free 45 minute videos that I would highly recommend to beginners who are learning PixInsight. With these I was able to Blink a set of light frames, use the Weighted Batch Pre-Program Script, do a Star Alignment, and Integrate the frames into an image. A good start (for me).

Finally experienced the "amp-glow" phenomena first hand while generating darks - wow, what a nuisance that is. But, I've read that it's perfectly normal with the ASI180MC pro.

I was able to take 3 'sets' (1 set at each detector temperature, 0, -10, and -20C) of darks, flats, and dark-flats. I took 30 @ 120" of each type for each 'set', and then integrated the darks and dark-flats into a master, and calibrated/integrated the flats into a master also (for a total of 9 masters). Basically an exercise, but hopefully I can use them at some point.

I think the more you use PixInsight the less overwhelming it becomes - at least on the stacking, integrating, and calibrating side. I suspect a lot of the "magic" will come from post-processing.

Onward and........upward ! 😎

 

 

[jpoulette]

OK, my first DSO image ever ! I'm reasonably happy with the first attempt - but you don't really know 'what you don't know' in PixInsight until you start using it. Wow!

Stacked in PixInsight with very little processing (Frankly, I have no clue how to do any meaningful post-processing yet....)

Tracking was good (~1' total pretty much all night, even with a little wind). I spent a ridiculous amount of time on the PA, and got it down to ~10" on both axis.

Started with 60 lights, blinked out 10 of those (shooting stars & planes all over the place), and WBPP kicked out another 8 for some reason. So I was left with:

42 Lights @ 120"

30 Darks

30 Flats

30 Dark-Flats

Now that I have at least one image up I'll modify my signature with my set-up. This is a simple jpeg but I think it shows enough detail to give you an idea if what I'm doing is on or off track.

Comments are encouraged - it's the only way I'm going to figure this out ! 😀

 

[jpoulette]

My 'second' astro image (M101) - taken 09 Apr 2023 (we've had REALLY bad weather for WEEKS)

80 60-sec lights, 40 each of Darks, Flats, and Dark Flats - stacked but unprocessed.

It clearly needs work but I'm very happy with this - and the AM5 is giving me 0.5' tracking pretty consistently. (but I do obsess on level and PA)

(reduced here ~1:10)

Edited April 11, 2023 by jpoulette

[ollypenrice]

The big improvement here is that you did not black clip the image. That's to say that you you did not bring the black point in too far. The sky is lighter and the faint arms have been preserved, not clipped out.

Olly

[jpoulette]

50 minutes ago, ollypenrice said:

The big improvement here is that you did not black clip the image. That's to say that you you did not bring the black point in too far. The sky is lighter and the faint arms have been preserved, not clipped out.

Olly

Yes - I'm starting to understand that. This was last night's 3-hour capture (M106). It's amazing how all the little galaxies come alive in the background if you're careful.

Thanks for the feedback! 😀

 

 

Edited April 11, 2023 by jpoulette

[Lee_P]

Very respectable images!