27 replies to this topic

[bluesilver]

Hi,  Bit of an odd question here,

I basically have three OTAs,  Skywatcher Esprit 150,  Skywatcher Esprit 100 and Celestron C14 with a V3 Hyperstar.

All using the same camera  asi2600mc

I am in a Bortle 3 area.

I was just thinking if it would be worth while trying to use the Hyperstar to image the galaxies this season,  I have always use the Esprit 150,  only just received the Esprit 100 so haven't played around with that one much yet.

And also only just managed to pick up the Hyperstar not long ago also.

We don't get many clear nights this time of year, and all of this is working of say 4 hours of imaging time for the one night.

 

I am only very basic at this side of things,  but

The Hyperstar is at f1.9 and 684mm FL,  and the resolution works out to be 1.13 " / pixel

The Esprit 150 is f7 and 1050mm FL,   and the resolution works out to be 0.74 " / pixel

The Esprit 100 is f5.5 and 550mm FL,  and the resolution works out to be 1.41 " / pixel

 

Not too sure on how all that works out in simple terms though.

I know the Esprit will give a narrower filed of view and more of the galaxy will be on the asi2600s chip compared to the other two.

But as the Hyerstar at f1.9 is roughly 12 times faster that the Esprit at f7,  would I get more detail and a sharper image of the galaxy using the Hyperstar compared to the Esprit 150 if imaging for say 4 hours.

I am thinking this because I would be getting more light and also more frames using the Hyperstar compared to the Esprit 150.

 

For the Esprit, I generally take 180 second subs, I can do 300 and 600 second subs with no issues.

Not sure if I should be taking 60 second subs or less or more for that matter with the Hyperstar,  I am guessing that I would need to be using gain 0 on the asi2600mc if using the Hyperstar?

 

I have also just installed Sharpcap for another reason not related to this,  but just noticed it has a smart brain function that samples an area of the sky you are imaging and gives a read out on recommended exposure settings,  not sure how good this is,  i am only just now seen it.

 

Sorry for the long drawn out question, just trying to give as much information as I can to hopefully get some advice.

Thanks.

Edited by bluesilver, 20 April 2025 - 12:52 AM.

[rgsalinger]

For best detail I'd use the longest focal length scope no matter what the target. Stil, in your case I'd certainly give the hyperstar a try and aggressively dither and drizzle the results. 

[bokemon]

Theoretically, it is the total number of photons you capture from an object that determines its image quality.  (until the ojbect is too large to fit in the frame, or its features becomes smaller than the pixel size).  This is just proportional to the aperture size.  It's independent of things like pixel size, using barlows or reducers, etc.  In real life, these other factors matter in terms of ease of image processing / guiding, etc. 

[ayadai]

Match the scope to the target using Stellarium to determine framing. 

For many smaller galaxies, you may get the best results using the C14 without the Hyperstar. For larger galaxies and groups, shorter focal lengths would be indicated; for larger targets, the C14 with the Hyperstar would give you much more data (and hence, more detail) for a given period of time than the Esprit 100, but the Esprit 100 may give a bit sharper overall image.

 

In terms of gain and exposure on the C14 with the Hyperstar, I'd leave the camera at unity gain and shoot 20-30 second exposures to start.

Edited by ayadai, 20 April 2025 - 04:37 AM.

[BucketDave]

I'd expect the C14 hyperstar to reveal more feint features than the Esprit 150 but those features might be larger (or more blurry).

It might be interesting to add the images together. The C14 hyperstar revealling the dim outer reaches of galaxies with the Esprit 150 highlighting the small features in the brighter regions.

[smiller]

There are two factors that determine the number of details you’ll see in a galaxy:

 

1) The signal to noise ratio.    Here the C14 clearly wins because of the larger aperture, catching more photons per second of your target.  People will talk a lot about F ratios, but with respect to SNR that just determines the field of view and how the photons are distributed amongst the pixels… that is not as important for SNR as long as you aren’t read noise limited.  The C14 collects roughly (14/6)^2 =5.4 times the number of photons per second per square unit of sky (a bit less due to central obstruction and perhaps more optics loss) .  That’s a pretty big deal!

 

2) The spatial resolution of your capture.  In this case case the longer focal length and smaller pixel scale wins as long as you are not limited by your atmospheric seeing.  In this case, your larger refractor wins as long as your atmospheric scene is reasonably good.  I shoot galaxies at 1.09” and 0.69” pixel scales and on a night of below average seeing, there is no resolution difference between these two options because I am limited by my atmosphere.

 

But on nights a very good atmospheric scene, I can get a better capture and more details at 0.69”.  And I live in an environment that does not get very good seeing on average… so if you are in a place that gets good seeing I would suspect you’re smallest pixel scale will do well for you.

 

So my answer is if you collect an abundant amount of data so that both the refractor and your hyperstar C14 both collect plenty of photos to get good SNR ratio then I think you’re refractor will get a better shot because it has a smaller pixel scale.

 

But if you are in a rush and only have a small amount of time to image and your quality of your capture is going to be limited by your single to noise ratio, then the abundant photo collecting power of your C14 will win out, especially on nights of inferior seeing. (But on nights of inferior seeing you should be shooting some dim extended target anyway not focusing on galaxies)

 

Since you are in Bortle 3 and I suspect you aren’t in a rush, you are going to get a very good signal noise ratio fairly quickly so I think your refractor will do better in general.  Plus the optical quality of your refractor may be a bit higher (just a guess), and if true, that will help too.

 

My money is on the refractor!   Ok, who’s going to bet against me… betting is now open!

 

 

 

As was noted earlier by another, the refractor might do better on the core brighter regions of the galaxies, but if you’re talking about the dim dusty outer regions that are hard to capture even from B3 then your C 14 will render those with less time.

Edited by smiller, 20 April 2025 - 10:11 AM.

[KGoodwin]

I think the C14 without the Hyperstar would be the best solution.  One of the advantages of the SCT is the flexibility to use or not use Hyperstar depending on your needs.  Perhaps use a reducer/corrector assuming it's a non-edge version.

[smiller]

I think the C14 without the Hyperstar would be the best solution.  One of the advantages of the SCT is the flexibility to use or not use Hyperstar depending on your needs.  Perhaps use a reducer/corrector assuming it's a non-edge version.

Dang, I missed that option, that might be the winner.   How did I miss this?

 

Although that teeny tiny pixel scale could be overkill.  However, perhaps the C14 with a high quality Starizona reducer at F6.7 and 2365mm focal length and 0.33” pixel scale may be a great combo.  Certainly smaller than most seeing conditions and guiding parameters.

[PhilHoyle]

I took the hyperstar off of my C14 and just use a 6.3 reducer.

[ayadai]

For many smaller galaxies, you may get the best results using the C14 without the Hyperstar.

I think the C14 without the Hyperstar would be the best solution. 

Dang, I missed that option, that might be the winner.   How did I miss this?

I think that the answer is in the echoes...
 

[KGoodwin]

0.33" is a good pixel scale for galaxies in the age of BlurX since it helps to be a bit oversampled to recover more through the deconvolution.  Perhaps it's sort of like how dithering lets you recover more detail with drizzling.  I do my galaxies and PNs at 0.31" and it's great.  If your seeing is consistently bad you can always down sample 1.5x or 2x or if you want to save storage space and know the seeing is always going to be fairly poor you can bin 2x.  I wouldn't do that unless you're certain the seeing will be worse than about 1.8" on a consistent basis, though.

[bluesilver]

Thanks for all the replies and advice,  just been going over it a few times re reading them

The C14 with the asi2600mc actually works out to be .02 " / pixel if I am correct ( i am using the astronomy.tools site for this information).

Not sure if this is too much or not?

With a reducer, this bring it back to 0.31" / pixel

It is the non edge C14,  i don't have any reducers for it at the moment though.

I generally only image when the jet stream is little to none. ( using the global jet stream map )

Edited by bluesilver, 20 April 2025 - 08:12 PM.

[rjkrejci]

Thanks for all the replies and advice,  just been going over it a few times re reading them

The C14 with the asi2600mc actually works out to be .02 " / pixel if I am correct ( i am using the astronomy.tools site for this information).

Not sure if this is too much or not?

With a reducer, this bring it back to 0.31" / pixel

It is the non edge C14,  i don't have any reducers for it at the moment though.

I generally only image when the jet stream is little to none. ( using the global jet stream map )

If you get a reducer for your non-edge, I'd consider the Starizona ones, particularly the LF one for your 14"    The spot sizes are far superior, better than the edge by a bit, and can cover FF if you may want that in the future.

[bluesilver]

When you say the LF version,

Do you mean this one from Starizona

https://starizona.co...34ec869fb&_ss=r

Not this one 

https://starizona.co...-coma-corrector

I am using a Moonlite focuser on the C14,  Not sure how the Starizona adapts to this,  might ask Starizona on this.

Edited by bluesilver, 20 April 2025 - 09:27 PM.

[smiller]

Thanks for all the replies and advice,  just been going over it a few times re reading them

The C14 with the asi2600mc actually works out to be .02 " / pixel if I am correct ( i am using the astronomy.tools site for this information).

Not sure if this is too much or not?

With a reducer, this bring it back to 0.31" / pixel

It is the non edge C14,  i don't have any reducers for it at the moment though.

I generally only image when the jet stream is little to none. ( using the global jet stream map )

0.2” pixel scale is almost certainly smaller than required or desired.  That’s getting close to the planetary lucky imaging pixel scale range. 

 

Also your field of view is tiny at only 0.34° in the long access which means that you can’t even frame half dozen of the largest galaxies.  Not even M101 or Bode’s Galaxy and even M 51 really doesn’t fit, let alone getting a little bit of the interesting starfield around a galaxy.  And unless you are always rotated correctly, even more galaxies may not fit well.

 

Plus from Bortle 3 at F11 you might be surprised to find that read noise, even in high gain mode, will start to become an issue unless your exposures are fairly long.  But at such a small pixel scale, it may be hard to hold a very long exposure time accurately, and realize much advantage from such a small pixel scale.    My calculations indicate that at F11 in B3 in high gain mode you’ll need 400 second exposures to have read noise at 5% or lower.  400 seconds may be challenging at 0.2” with the C14.

 

Conventional wisdom says “just say no” at doing deep sky at F11 and 0.2” pixel scale from B3 and at 3910mm focal length.

 

0.33” is plenty plenty tiny for deep sky galaxy imaging.  Plenty tiny.

 

Plenty

 

Tiny.

 

On the other hand, feel free to experiment with your various options:  Shoot a small detailed galaxy with your refractor, C14 with Hyperstar, and C14 with either nothing or a reducer and compare.   One problem will be seeing changes all the time and can vary quite a bit night to night, or even hour to hour... so it's tough doing a controlled experiment unless you are imaging with all the scopes at the same time.    

Edited by smiller, 21 April 2025 - 12:57 PM.

[rgsalinger]

There are "many many" interesting galaxies to shoot using a small FOV. There are maybe 25 galaxies that are larger that 20 arc minutes. It's a hoot to image at 4 meters IF you have the rest of the system up to the task. Otherwise, it's an exercise in futility. Much better off with a smaller focal length and perfected processing workflow. 

[Spaceman 56]

 

The Hyperstar is at f1.9 and 684mm FL,  and the resolution works out to be 1.13 " / pixel

 

The Esprit 150 is f7 and 1050mm FL,   and the resolution works out to be 0.74 " / pixel

 

The Esprit 100 is f5.5 and 550mm FL,  and the resolution works out to be 1.41 " / pixel

 

I shoot Galaxies at 1484mm with a 10 inch RC. before this I used a 530mm Takahashi.

 

of these 3 options I cant see why you would not shoot with the Esprit 150, as it has the highest focal length of the mentioned systems.

 

the Hyperstar may be quicker, but the objective of galaxy imaging (for me) is to cover as much sensor space as possible with the target. for this to work you need focal length, and the more the merrier.

 

you can get good SNR but if the target is a tiny dot in the middle of a large sensor, then no amount of cropping or trickery will make it look great.

you want the target to look big in the sensor, and then not crop at all if possible, which is why focal length is beneficial. 

 

just an opinion. 

[ayadai]

Conventional wisdom says “just say no” at doing deep sky at F11 and 0.2” pixel scale from B3 and at 3910mm focal length.

Perhaps, but I do love the framing at 3910mm for the current challenge object:

 

[mayhem13]

When you say the LF version,

Do you mean this one from Starizona

https://starizona.co...34ec869fb&_ss=r

Not this one 

https://starizona.co...-coma-corrector

I am using a Moonlite focuser on the C14,  Not sure how the Starizona adapts to this,  might ask Starizona on this.

In the case of a fixed mount focuser, you’ll need to use the type 4 reducer slipped in to the drawtube…the prescription distance of the reducer to the camera chip is fixed at 90.3mm +/- .2mm for the flattest field and highest resolution.

 

This option offers the highest potential all else being equal……but there are questions to be considered like have you modded the 14 with mirror locks?…do you collimate to a high level of precision?…….how’s your mount with the 14 and are you proficient with off axis guiding? 

 

Given the performance limiting factors, personally I’d not image at such extreme focal lengths without an observatory environment……I have a fixed pier at least for my C9.25 and imaging at 1600mm is extremely challenging to say the least.
 

Me?…..I say pick up a used cooled IMX183 chip camera and use the Hyperstar 14 to match the resolution of the Esprit 150……my reasoning is based on your Bortle 3 skies where sky noise is a huge plus combined with the fast optics of the Hyperstar……..each frame can be dramatically reduced in time reducing noise and the effects of less than perfect guiding. The smaller chip of the 183 will still be enough to frame most galaxies and is far less susceptible to tilt often associated with Hyperstar.

[rgsalinger]

Oh dear. I assumed that the OP had an appropriately mounted system and was not planning to use a tripod at 4 meters of focal length. 

[rjkrejci]

When you say the LF version,

Do you mean this one from Starizona

https://starizona.co...34ec869fb&_ss=r

Not this one 

https://starizona.co...-coma-corrector

I am using a Moonlite focuser on the C14,  Not sure how the Starizona adapts to this,  might ask Starizona on this.

Yes.  The first one (LF) is more future proof and seems to have smaller spots.     Much better than an Edge with reducer.

[bluesilver]

Appreciate all the replies and advice,

Yes, I should have mentioned I am in a permanent roll off roof observatory with a permanent concrete pier,  no tripod here.

Mount is the iOptron CEM 120 mount, so can handle the C14 no drama.

At the moment I am trying to find some images of either a C14, C11, C9.25 with a Starizona reducer and Moonlite focuser all connected up.

I can't see how the two can go together yet and no reply from Starizona as of yet.

Not sure what a type 4 reducer is, never heard of this before, 

The IMX183 sensor like the asi 183mc would bring the Hyperstar to around 0.92 " / pixel,  so this could be worth looking into.

and if using the asi2600mc it would be close to what the Esprit 100 is at with the asi2600mc

Edited by bluesilver, 23 April 2025 - 06:45 PM.

[mayhem13]

Appreciate all the replies and advice,

Yes, I should have mentioned I am in a permanent roll off roof observatory with a permanent concrete pier,  no tripod here.

Mount is the iOptron CEM 120 mount, so can handle the C14 no drama.

At the moment I am trying to find some images of either a C14, C11, C9.25 with a Starizona reducer and Moonlite focuser all connected up.

I can't see how the two can go together yet and no reply from Starizona as of yet.

Not sure what a type 4 reducer is, never heard of this before, 

The IMX183 sensor like the asi 183mc would bring the Hyperstar to around 0.92 " / pixel,  so this could be worth looking into.

and if using the asi2600mc it would be close to what the Esprit 100 is at with the asi2600mc

https://starizona.co...-coma-corrector
 

You install the focuser directly to the visual back of the scope and then slip the reducer into the focuser…..the  reducer and sensor distance is fixed and must not change….the entire assembly must be moved to achieve focus.

[bmcclana]

It looks like the large format reducer threads directly to the back of the scope, it doesn’t insert into a visual back. Then you can attach whatever you like to the back of the reducer with the same thread. It just has to fit into the 146mm back focus specification.

Can you make your moonlite + other optical train fit?

[bluesilver]

Yes, It will all fit with ease, 

Going with the large format reducer that screws directly onto the rear cell and the focuser screws directly onto this, I think I will have at a very rough guess around 58.5mm to fill up with spacers.