M53 with new Camera

[gonzostar]

Hello

This was my first opportunity to use the ZWO 385MC camera with a optolong l-eNhance filter for deep sky objects

Telescope used was the ES102mm APO AT f7

I chose M53 as it was at reasonable high above the horizon and could be easily found near Arcturus with my navigation. Also first use for deep sky with this camera. Used it before for lunar 

Gain 300

Exposure 45 minutes using 60s subs

15X Darks

25x BIAS

Processed in PS

Sorry no flats at the moment. Used Sharpcap, havent got the pro version yet. Do I need pro to dither? Also is gain/ exposure okay for this object? Also not sure which colour setting to use

 

Sorry for all questions Cheers

Dean 

 

[wimvb]

Very nice. One question: why do you use bias frames for calibration? With cmos cameras, bias frames can differ from the bias signal contained in darks and lights. The general rule is to shoot darks and flats at the same settings as lights (temperature, gain/offset, and for darks: exposure time), in order to get consistent calibration masters.

Edited April 16, 2023 by wimvb

[Budgie1]

You may not even need Darks with the ASI385 MC.

You will still need Flats & Flat Darks, but that may be about it. Worth trying with & without Darks and see what the difference is between the two stacks.

As for gain, 300 may be a little on high side. Looking at the graphs for the camera, there's a nice drop in Read Noise + a lift in dynamic range at a gain of 60 and Unity Gain seems to be at 135 (if I've read it correctly). Experiment with it and see what works best for your setup.

Lastly, you mention using the L-eNhance filter, this doesn't really work that well on broadband targets like star clusters, galaxies & reflection nebula. It can actually remove or block some of the signal you need for these objects. Where this filter does come into it's own is with emission & planetary nebula with lots of Ha & Oiii.

If you're not using the L-eNhance filter, then make sure to use at least a UV/IR Cut filter, assuming you don't use any sort of light pollution filter. This stops the star from looking a bit bloated.

[gonzostar]

5 hours ago, wimvb said:

Very nice. One question: why do you use bias frames for calibration? With cmos cameras, bias frames can differ from the bias signal contained in darks and lights. The general rule is to shoot darks and flats at the same settings as lights (temperature, gain/offset, and for darks: exposure time), in order to get consistent calibration masters.

Thanks Wim, Only used the ASI385 so far with moon shots, and m53 practice.  Awaiting planetary season. So decided to move away from DSLR and try on a faily bright object I could find. So used bias as still in DSLR  mode. 😁

If its the same object say M51, and i choose to do over several evenings. Does this mean i need a set of dark and flats (with same settings etc) for each evening

[gonzostar]

4 hours ago, Budgie1 said:

You may not even need Darks with the ASI385 MC.

You will still need Flats & Flat Darks, but that may be about it. Worth trying with & without Darks and see what the difference is between the two stacks.

As for gain, 300 may be a little on high side. Looking at the graphs for the camera, there's a nice drop in Read Noise + a lift in dynamic range at a gain of 60 and Unity Gain seems to be at 135 (if I've read it correctly). Experiment with it and see what works best for your setup.

Lastly, you mention using the L-eNhance filter, this doesn't really work that well on broadband targets like star clusters, galaxies & reflection nebula. It can actually remove or block some of the signal you need for these objects. Where this filter does come into it's own is with emission & planetary nebula with lots of Ha & Oiii.

If you're not using the L-eNhance filter, then make sure to use at least a UV/IR Cut filter, assuming you don't use any sort of light pollution filter. This stops the star from looking a bit bloated.

Thankyou Martin for your time and detailed response much appreciated. 

What is the difference between gain, and unity gain? If gain is low would i need to increase exposure? Or am falling into a trap. My mount is a AVX mount and just concerned if it can cope with longer exposures as guiding errors will be easily spotted with a more sensitive camera 

Have replaced filter with the UV/IR one. Will try m51 and compare to image on DSLR 😁👍

 

Cheers

Dean 

 

[wimvb]

37 minutes ago, gonzostar said:

Does this mean i need a set of dark and flats (with same settings etc) for each evening

if you have the cooled version, you can reuse darks at the temperature which you use for lights. If the temperature is stable between nights, you can also reuse darks. But if you shoot without cooling, and the temperature differs more than a few degrees, darks may not work. Otoh, it never hurts to try. Also if your camera doesn't have amp glow, you may do without darks. Bias frames are never used with cmos. And darks can't be scaled to be used at different exposure times. What stacking software do you use? DSS and PixInsight both have what is called "cosmetic correction", which is a way to get rid of hot pixels, without having to use darks. So if your camera doesn't have amp glow, you can use that in stead of darks.

[gonzostar]

I use DSS, Not used the "cosmic correction" though At moment researching gain and exposure time. Getting to conclusion integration time is critical

 

Although confused with charts in camera manual  The charts for the ASI385MC suggest read noise gain 60, and another chat suggests 135 (-adu).

Which do i start with in shapcap? 

Cheers

Dean 

[Budgie1]

1 hour ago, gonzostar said:

What is the difference between gain, and unity gain? If gain is low would i need to increase exposure? Or am falling into a trap. My mount is a AVX mount and just concerned if it can cope with longer exposures as guiding errors will be easily spotted with a more sensitive camera

There is no difference between Gain and Unity Gain. Unity Gain is the Gain sweet spot between minimum Read Noise and good Dynamic Range. On the older CCD cameras gain and offset were pre-set at the factory and you can't alter them, but in CMOS cameras you can alter the gain to your own setting.

When I use my ASI294MC Pro, I use a gain of 120 for broadband imaging and 200 when I have the L-eNhance  or other narrowband filter fitted. In either setup I choose the exposure setting I feel is best on the night, New Moon will tend to have a longer exposure (180 - 360 seconds) and for a Full Moon or bright object I'll use 45 - 180 seconds. 

In your case, a lower gain level is better suited to longer exposures and with short exposures you can turn the gain up. It's all about learning what works best for your setup, there's no "one size fits all".

The AVX mount should be fine for guided imaging, as long as you have some sort of guide camera setup running with the likes of PHD software. If you don't have a guide camera & scope fitted, then slowly increase your exposure times until you see the stars starting to trail and then reduce it back again to find the ideal exposure time. If you're using 60 second exposures then just take lots of them, for good deep sky images you're normally talking about hours of subs to get the most out of it. You can obviously spend less time on the likes of clusters because they are quite bright objects, but you'll see some members on here taking 24 hours or more of subs on a single target.  

Edited April 16, 2023 by Budgie1

[gonzostar]

Cheers Martin A good clear explanation

So if your target was requiring say 12 hours intergration time over a few nights. Would you take dark frames for each night or just a master dark? 

However am i presuming sum of those nights you may have moon at different phases hence different exposures, would require different dark frames? 

I'm happy with phd2 as i've used this with the DSLR and manage to get 5minute light frames

Cheers

Dean 

[wimvb]

42 minutes ago, gonzostar said:

However am i presuming sum of those nights you may have moon at different phases hence different exposures, would require different dark frames? 

Keep life simple and don't worry about the moon. As long as it's not near full or doesn't show (as now), it won't have any effect. When the moon is more prominent, it will increase the overall brightness, but not deteriorate much untill it's almost full and near your target. With cmos, you want to keep the exposures as short as possible, in order not to overexpose the stars. Just make sure that you can't see banding in your images, because that means that you are exposing near the read noise floor. The old rule of thumb for DSLRs that you should have the histogram at about 1/4 or 1/3 from the left edge, doesn't apply to cmos.

I have my exposure times set such that I only can see the very bright stars in the linear image. The target is never visible (unless it's a star cluster) in the non-stretched sub frames.

[gonzostar]

Cheers Wim for all this exciting info, Now the bit we cant control. Waiting for  those clouds to disappear!