Catanonia

Over a few of my posts, I have had contrasting statements about what is best to use with my RASA 8 and ZWO 2600MC Pro setup.

Some say a few seconds imaging at 1x bin as I will flood the camera with background and loose resolution.

Others are saying I should use 2x or more bin as I will not loose resolution at this FL and setup.

I am currently using 2xBin and 2 - 4 min subs. - I like the quick and deep captures I get compared to 1xbin.

So now I am totally confused.

So with  

• RASA8 at 400mm FL
• ZWO 2600MC Pro 
• lEnhance 2 inch filter
• Bortle 5 - 6 skies

What should I be using for optimum images ?

Thanks

3 hours ago, The Lazy Astronomer said:

Actually, by binning you are potentially losing resolution, depending on the quality of your seeing on the night. The sampling rate of your setup at bin 1 is ~1.9"/px. On nights of average to good seeing, this would be a proper sampling rate. 

Using bin 2 on those nights will get you a higher SNR for a given integration time, but at the cost of resolution.

Another thing to consider is that with a couple of exceptions (e.g. cameras which use the IMX492 sensor), binning in CMOS cameras is done after each pixel has been read out. This means there is practically no difference between binning at capture and binning in post.

It would therefore be more advantageous for you to capture at bin 1 and consider binning during processing - you can use the measured FWHM of stars in your stacked image to determine if your conditions on the night mean binning is required.

And, while a longer exposure will capture more photons, once you've reached the point where your sky background has swamped the camera read noise, using longer exposures follows a law of diminishing returns.

The optimal exposure length for your setup, at bin 1 and gain 100, and assuming a fairly typical bortle 5 sky, is somewhere in the region of a few seconds, not minutes.

 

interesting and contrasting statements made in my other thread about reducing the F Stop of the RASA 8

Totally confused now.

5 hours ago, iantaylor2uk said:

To be honest, with that set-up, I would go for 30 second subs (even with the L-enhance filter on) and bin 1x1 (you can always bin 2x2 in software later if you want). 

Several reasons

• I will not loose resolution at 2x bin due to chip size and pixel size on the 400mm RASA 8
• 2xbin is 4x photon gathering and so effectively 4 times as fast as 1xbin and on an F2 that is a lot
• More photons = more data and as longer exposure than say 30sec = better detail.
• Longer exposures reduce the noise massively with the 2600
• A lot less files to store and process.

13 minutes ago, Chris said:

This is brilliant! Super clean for a single stretched sub, and that detail can't be from a light stretch....or maybe actually with the RASA. 

You will have to trust me, this was only histogram stretched and converted to JPG.

This is the RASA 8 @F2 at work here as a light bucket. The great noise is down to the ZWO2600MC Pro at gain 100.

5 hours ago, Adam J said:

Very impressive in terms of signal from such a short exposure. The thing that has put me off a RASA though is the spot diagrams which show spots of 8um or more at the centre of the FOV, hence not too sharp for such a large aperture. Can you or Olly or Gorann maybe comment on sharpness in comparison to some of the optically slower alternatives?

I do note that this is 2xbin though. 

Adam 

I am still learning this scope and camera combination. But I would also agree with Olly, this scope is not for close in detailed work. It is all about the "bigger" picture.

I still have the 183MC Pro that I can use if I want even smaller pixel sizes, but to be honest that is probably wasted on the RASA8 as the FL of 400 generically means I will not be getting in close to galaxies or the like and with the 183MC, all I am really doing is sacrificing FOV in the final image.

For the 1st time ever, I had 2 hours of clear skies for new equipment on the day / night it arrived   Yeeha

Very impressed with the 2600 and the data it captures along with the wide APC Sensor FOV you get to bring out the maximum benefits of the RASA8.

I got this setup for the very limited dark opportunities I get just south of Manchester and the M6 Motorway and every opportunity I get I want to maximise.

So here we have 20x 4min subs at 2x bin on the RASA8 / ZWO2600MC Pro / ASI Air Pro and NEQ6 Pro  (not too shabby for under 1.5 hours)

I was using a lEnhance 2 inch filter in Bortle 6 skies and this was processed entirely in PI with Darks, Flats and Bias frames (not that the subs really needed them)

Now 2 issues I have and could do with some advice on as I would like to sort them out

• Stars to some corners are elongated and probably down to either tilt or spacing / backfocus that I need to sort out
• Stars are loosing their colours, either down to the lEnhance filter or the 100 gain I am using on the 2600. I might try to take a separate set of subs with gain 0 just for the star field.

I hope you like, I certainly have a lot more tinkering to do, but a good 1st light for a change and I am certainly happy with the progress so far.

4 hours ago, ollypenrice said:

Like you, I'm knocked out by this combination.

Interesting that you're at 100 gain. We've yet to try that.

Olly

Yeah, a lot of forum searching showed this to be the most recommended gain setting of 100 due to the extra high mode the camera goes into. As long as you don't completely fill the wells, it is ok I guess. Hard to do with such deep wells even 4mins at 2xbin.

I am using the ASI Air Pro and so I can't play with the offset.

Creating the final image now with 20x good subs I got last night and will post soon.

12 hours ago, Stuf1978 said:

Yet another reprocess as I've been working on trying to produce bicolour images from OSC data for months without much success until now

 

 

Try this video - you may be able to get the techniques and apply to the software you are using

oh this is nice, great colours and detail. Love it

That is so beautiful, crisp, even the diffraction spikes are spot on. 

A lot of time / hours in the data too.

I too am 1st lighting my ZWO2600MC Pro (colour) and am super impressed with its noise levels and photon gathering capabilities.

I am running mine at 100gain and -10 temp, what are you doing ?

Just now, paul mc c said:

Can't seem to see it. 

edited the post

For once, new kit arrives and I have a few hours clear skies to try it out   I must have done something good this week

So replacing the ZWO 183MC Pro with the ZWO 2600MC Pro as I want that large FOV

The 2600 has almost twice the fov with the APC sensor size.

• Zero amp glow compared to the 183
• Only slightly bigger pixel sizes
• Large x by y resolution
• Much deeper wells to capture those photons
• And is twice as expensive

So here is 1 single sub from the RASA 8 and the ZWO 2600 MC Pro

• Single Sub at 4minutes guided and 2xbin
• No Darks, Bias or Flats applied
• lEnhance 2inch filter
• Gain 100 on the 2600 and -10 temp
• No processing other than a stretch, image horizontal flip (as RASA images in reverse due to camera on the front of the scope) and convert to JPG to make it visible on the forum
• Taken from less than impressive Bortle 6 skies and not even properly dark yet.

This is almost as good in a single sub as my pictures before I left the hobby 7 years ago. How much tech has changed.

I am very impressed and the images are rolling in now.

Still loving and getting used to the RASA8.

But returning to the hobby has proved expensive after just shelling out for a ZWO 2600 MC Pro as I want that large chip size on FOV.

But here is a couple of hours (5min subs) on the Eastern Veil using the ASI Air Pro, NEQ6 Pro with the RASA 8 and ZWO 183MC Pro.

Will put the 183mc pro up for sale if the 2600 works out well.

I am finding the lEnhance filter to be excellent in Bortle 5 skies. I think the lExtreme would have been overkill and lost me HA data

Definitely want to get a mosaic of this whole region done before the winter sets in.

1 hour ago, Catanonia said:

Shame the 2600 is 17.5 sensor to plate compared to the 1600 and 183 that is 6.5mm .

On a RASA 8 this leaves no room for a filter drawer

Looks a cracking camera and like the fact it is large sensor, good pixel size and has zero amp glow.

Quoting myself, using this https://www.teleskop-express.de/shop/product_info.php?products_id=11535#cs that I already have, I can use my filter and get the 2600 in focus.

Grrrrr, more money

27 minutes ago, vlaiv said:

One with the largest sensor size that can be covered by RASA8 corrected circle and highest QE.

Since RASA8 can cover 30mm - that means APS-C sensor size. ASI2600 seems like logical choice as it has higher QE than ASI071MC.

Any ZWO camera you choose will need binning since all have small pixels.

 

Shame the 2600 is 17.5 sensor to plate compared to the 1600 and 183 that is 6.5mm .

On a RASA 8 this leaves no room for a filter drawer

Looks a cracking camera and like the fact it is large sensor, good pixel size and has zero amp glow.

1 hour ago, vlaiv said:

snip

 

So what would be the best ZWO camera in your opinion that would suit the RASA 8 with respect to pixel size / sampling ?

1 hour ago, vlaiv said:

snip.....

From SNR point of view - it is better to have properly sampled image than over sampled.

So yes, I'd say that with RASA8 - you actually bin x3 rather than by x2 as it is closer to 6.7µm pixel size if you are working with 2.4µm pixel camera as 2.4µm x 3 = 7.2µm.

 

wow, so basically you are saying, with the 183 OSC, I should be imaging at least with Bin2 and almost reducing my capture time in 1/2 ?  I could even go bin 3

mmmm, I am planning a 6 panel mosaic and I think I will give this a go as I should be able to get 6 panels done in 1 night.

With the mosaic, I can live with the 1/ 2 resolution

Thank you so much for this.

17 hours ago, vlaiv said:

In case of RASA8 and ASI2600 - it does not.

Telescope itself has spot diagram that matches better with ~6.7µm pixel size than with 3.76µm.

 

So I am using a ZWO 183MC (colour) with my RASA 8 and always using bin1.  Should I be using bin 2 for even faster captures and not loose resolution ?

Yeah for the last week I have been opening each image in PI to check it and decide whether to keep or reject it in the stack

Open the image, apply a screentransformation on it, zoom in and check and rinse repeat until your eyes bleed

Well until today when I discovered the Blink Tool in PI

Well that is easier

12 hours ago, vlaiv said:

I have to say that RASA8 is simply most cost effective solution to a particular problem.

snip

 

Interesting read and thanks for taking the time to put this together. Spent too long on TS website, but luckily my wallet survived

Knew it was a weird question and I would concur that the cost / practicalities are too high

Get another scope if you want more FL

Taken the other night on my RASA 8 / ZWO 183MC with lEnhance filter from Bortle 6 skies.

I managed to grab a little over 3 hours in 5min subs with the OSC.

Still getting tracking errors around the meridian flip which lost me about 20mins of data.

Quite pleased how this worked out and really getting to grips with the new RASA 8 / ASI Pro setup ready for the dark session.

Hope you like it

I am still being amazed at the Rasa8.

This is a single 10m 1xbin shot with the ZWO  183MC direct from ASIPro in Bortle 6 skies.  

No processing, it is actually a screenshot from my iPad ASI Pro screen posted direct to the forum.

You can also see the characteristic ZWO 183MC amp glow on the middle right. This processes out ok with proper darks.

On 01/09/2021 at 16:55, nephilim said:

I'm not sure if this really counts but I am imaging at f2-f4 with the Samyang 135ED Lens

Sure it counts