rsarwar

Running a proper mock session on the heat nebula with readmode=1, gain = 56 and offset = 25. this would be my standard setup. this is approx 2. compared to D700 at iso800 (3.3 * unity gain) the brightness is exactly the same (runing 600 sec subs). however, the level of detail is still as impressive as before thanks to DR and bit depth in my opinion.

14 hours ago, MarsG76 said:

what makes me happy is that you're comparing 300s QHY subs to 600s DSLR subs.. and the QHY subs have more signal... so that is at least more than half the exposure time... possibly 4 time quicker, as you said that a 1200s DSLR exposure was not as bright at the 300s test...

I dont want to deflate you however, the 1200 sec from D7000 was "brighter" than QHY. What i suggested was that It did not have comparable detail (i.e. qhy had more detail) - possible due to superior bit-depth and dynamic range.

I am comparing 300s QHY with 600s DSLR, however, the operative consideration there is that qhy was operating in 6.6 * unity gain whilst DSLR was on 3.3 * unity gain. It's like comparing two DSLR at ISO 400 vs ISO 800. the one with the higher ISO will have more signal and hence half the exposure time, however will sacrifice dynamic range and welldepth. with 6.6 * unity gain, qhy manage to saturate 30% of the stars, so the gain i ran the test on is not a usuable gain in most case.

i calculated a reduction of exposure time by a factor of 1.36. yours will depend on the QE and pixel size of your dslr.

I have to state - QE does not indicate performance of a camera. it is just another arbitary param (look at the QE curve from ASI2600M and QHY268M, their curves vary vastly for the same chip). asi294 and asi2600 has almost the similar QE (infact asi294M has better QE compared to asi2600M), however asi2600 will outperman a asi294 given it is 16-bit. For example, nikon and canon camera have comparable QE. however I would never pick a canon camera as my primary interest is night time photography - because of the poor dynamic range of canon cameras. you just can pull out details. things that matter are read-noise, dark current, dynamic range, bit depth and well dept

Okay I did some testings on the heart nebula. very rough ones. but using the same target and same telescope (130 pds). I live is bortle 6.

DSLR: D7000, 16 MPix APS-C IMX071 (same was ASI071) with full spec modd + custom firmware to disable onboard post processing, i.e. true darks + no star eating stuff. The pictures (always the right hand side of each screenshot) were taken a weeks ago (zero moon with the nebula fairly high in the sky) when i got the M48 Astronomik 12 nm Ha filter and wanted to see how well it worked and how an OSC handles it. ISO was set at 800 and time was 600 sec. according to the link sharkmelley gave, and according to this link, it equates to a gain of approx 3.3 * unity. ambient temp was about zero. only showing the red channel here - as it is  a Ha filter

QHY268M with the same filter, no moon, and readmode=0, offset=25 and gain=56 (6.6 time unity) but took a 300 sec frame (i was having issues with backfocus and wanted to investigate it so wanted a shorter exposure - it did saturated some of the stars). so I did not frame the target - just point and shoot. camera cooled to -15 C. image was taken when the nebula was fairly high in the sky.

Firstly, the autostreched images on PI. the left image, taken by qhy is clearly shows more detail and is brighter.

Secondly, same images but zoomed in to the core; ignoring the obvious backfocus/focus issues the Max value of a pixel on the nebulocity was 0.178 and 0.131 for the qhy and d7000 respectively. that makes the qhy 1.36 times faster. [D7000 is 4.7um with an eff of 35-40pc, so i was would have expected 1.20 times better.] However the level of detail is phenomenal in my opinion. qhy has less noise. so less stacking is needed. I also have a 1200 sec frame from the D700, and it is still not able to match the level of details

final picture is that of the same images, but using the same stretch.

@MarsG76 I dont think you will be disappointed

5 hours ago, KSteve said:

Hi all,

I recently decided to attempt to astromodify an old Canon 450D, adding in the Baader Astro-Conversion filter - I followed the modification procedure on Gary Honis' website and managed to swap the filters and reassemble the camera, however when it came to switching the camera back on I get no response.

I've tried reseating and repositioning all ribbon cables that are unclipped during the process - including cleaning all contacts with isopropyl alcohol to make sure nothing is messing with the connection. I've lost count of the amount of times I've tried doing this, and even removed the rest of the body to make reseating ribbon cables I and J easier. I've tried with different batteries just incase, and have noticed that if the battery is left in and the camera is switched on, they do drain over time - so I expect the issue lies elsewhere.

Has anyone had any experience with this, and if so I would love to hear any recommendations of what I should do next!

check the ribbons sockets, see if you bent any of the pins. they are usually difficult to fix if they are indeed bent.. I once ruined a phone whilst trying to change the display and ended bu bending some pins.

On 08/03/2021 at 09:06, Deeko said:

Hi Rsarwar, the photo shows exactly that. In the photo the M54-M48 adaptor is bolted onto the camera first, then the T2-T2 adaptor (with the M42-M48 ring) to make it T2-M48, so the M48 side screws into the cameras M54-M48 adaptor and the other T2 end straight into the EFW. I admit it is quite confusing and tool me some time to figure it out until I had the camera and adaptors in my hand.

Hi @Deeko - Finally got my qhy268m yesterday. still waiting for some M48 extenders to use with FF/CC for 55mm. However I wanted to ask you about the BF. Looking at the engineering drawing of the device, did you take the backfocus to be 12.5 mm or  12.5 + 1.8mm. I am not sure if that 1.8 mm extrusion is absorbed within the QHY FIlterwheel or is accounted by some other way. The confusion arises because no one seemed to have mentioned it in all the writeup i have read - they all say backfocus is 12 .5mm, when it appears to be 14.3 mm

3 hours ago, sharkmelley said:

This site gives you the ISO for unity gain (i.e. 1e-/ADU): DxOMark Derived Sensor Characteristics (photonstophotos.net)

The QHY268 gain setting for unity gain (1e-/ADU) will be available probably in the documentation.  You can then adjust upwards and downwards from there.  You will want to choose a gain where both DSLR and QHY268 are operating in the same mode i.e. high gain or low gain.

Mark

Thanks Mark. I will have a read through it after work. 

I am using my ASI EWF, so have to wait for some M48 extentions for my flattenern but i would definately try to work this out

So i got my QHY268 earlier today. 

but cloudy outside. 

Was wondering if anyone knows how to map ISO values from DSLRs are to be mapped onto the Gain scale. Without the right mapping, this comparision will not be possible.

17 hours ago, MarsG76 said:

Do you know this for a fact or are you speculating/estimating like me?

 

 

Speculation as i still dont have the camera, but i am confident. 

Qhy268 has smaller pixel and lower read noise and thus will have better SNR. So to achieve the same level of SNR seen in a DSLR, you will need stack less number of frames to achieve the same level of detail /SNR as a DSLR. 

also your new camera is 16-bit, that will also play a major part in bringing out more detail. 

What i am saying is there is no comparision to be had between QHY268/ASI2600 and a DSLR - it will whip the floor with any DSLR from any generation. However, your comparison based on exposure time needed for each frame, is not a the right one to be looking at.

On 01/04/2021 at 00:44, MarsG76 said:

I'm starting to think that I'll have minimal benefit from the camera as my DSLR is active cooled.... only hope I have now is detail captured due to no bayer matirx on the mono camera. Also hoping for faster photon aquisition.

 

 

Dont forget you will get less noise - meaning to get to the same quality as a DSLR, you would need to stack far less frames. i.e. your exposure time for a single frame will not shorten by more than 1-1.5 times, but the total integration time will be lot shorter, albeit you need 3-4 channels to work with.

I am still awaiting for my QHY268. got some clear skies today with quater moon only rising at 5 am. 

One also has to consider that large pixel size would result in softer images. So you can't simply start using a camera with the largest pixel size

It will still be better than 1600 which is what most people will compare with as they have similar pixel size.

Also you have to consider that you would have to stack less frames. What I suggested us that having a 2600 camera will not create a significantly brighter image for a given exposure time.

Having said that - i am secretly hoping that i am wrong and that you are correct.

the main reasons i have considered a didcated astro camera is to go mono, cooling and shutter shake.

I doubt you will see anywhere near what you are expecting. The math is very simple really if you are to only consider filters, pixel size and qe

Say you have 100 ha emission photons coming in per second per 1 micro meter squaeree (area in 1 um²) With 60 pc efficiency on Ha, you would capture 60 of them per second per um². Similarly for 40d, you would get 25 of them per second per um². 

Now consider pixel size. With 3.7 um pixel size, asi2600 would capture 60*3.7*3.7 or 821 photons per second per pixel. Similarly for 40d, that value is 812 (5.7 um).

For peak transmission,  asi2600 is 1095 vs 40d is 1137 photon per second per pixel

Pixel size matters. that is why we use large pixel sizes with long focal lenght (after considering undersampling/oversampling reasons)

This however does not take into account improvements in the readout electronics. Also since your new sensor has smaller pixel, it will have less noise, so you would need to stack less frames

The impact of color bayrr matrix is minimal on efficiency, as the debayering algorithm interpolate and fill in missing photons due to the filters.

Ps, I am expecting my qhy268 in the next couple of weeks and be happy to test against d7000, unless you get yours first and post results

On 02/03/2021 at 11:50, tooth_dr said:

Seems to be working fine last night, apart from mist/cloud issues.  I’m only cooling to -10 deg C though.

I just wanted to add an update on attaching the camera to an Atik EFW3. Currently the only way was to use the M48 adapter, which added 5mm. This meant the total back spacing of the camera is 19.5mm

The Atik EFW3 is designed to mount directly to an Atik 16200 camera. Both seem to have a similar spacing of bolts.

Indeed it’s very close and in fact I only had to widen the holes by 0.15mm using 3.5mm drill bit) to let me screw the EFW3 plate directly onto the QHY268.

5mm doesn’t seem like much, but it means I can use my ZWO OAG (16.5mm) and Atik EFW3 (22mm) with my Baader MPCC mk1, and still maintain the correct back spacing (56mm).

Plus it is a secure flat fit 👍🏻

 

 

Hi.

I am in a similar situation and want to keep using my zwo ewf, which means I will be increasing the sensor to efw distance to 17.5mm.

I was wondering if you saw any problems with your 19.5mm spacing? I guess I should prepare myself to drill some wholes as well.

if you wish to take a luminus shot, sure 12x at 450 nm in terms of exposure time. or about 8x at Ha in terms of exposure time. but when you add a filter, red/blue/green, you would only see about 2x on Ha in terms of exposure time assuming you are using modded cam. that is the theoretical max.

going back to 40d, that sensor has larger pixels sizes compared to asi2600/qhy268. so some of what you gained through QE will be lost there.

so i personally would not expect the exposure time to be smaller than 1.6-1.8x shorter when using a red filter/Ha filter

In terms of resolution however, you will see a mark improvement, at least 5 times

13 minutes ago, ollypenrice said:

Hi Rashed, I'm not sure what the two contradictory points are...? (I'm not being evasive, After re-reading the thread I just don't know.)

I never said that mono is four times faster, however. (At least I hope I didn't! Because it isn't.) The broadband equation is roughly thus: Luminance: All object photons. Each colour, 1/3 of all object photons. So in 4 hours LRGB you have 3+1+1+1 = 6. In RGB/OSC you have 1+1+1+1 = 4.  That makes the mono advantage 6 to 4, not 4 to 1. It is not that simple, though. The OSC filters don't, in fact, cut off sharply between colours so each one does pass more than 1/3 of the signal. What adds complexity is that some targets, with extremely faint parts, are not going to yield any colour with present technology but may yield a bit of signal - which they will do best in luminance, not through colour filters. The LRGB speed advantage is not going to go away but it is target-variable.

Meanwhile, back in the real world, there are stunning new OSC CMOS cameras and ingenious dual band filters for OSC which have changed the OSC/mono debate since I made the earlier points in this thread. Would I buy a modern OSC CMOS?  You bet I would.  I had the good fortune to be invited to post-process Yves Van den Broek's mega-mosaic of the galactic equator. Even without a dual band filter his CMOS/OSC data went deeper than my CCD in HaLRGB, though he did not find any significant OIII. (The Squid in what is otherwise his image came from my CCD data.) With a dual band filter he would have found the Squid for sure. See Gorann's RASA images on here.

Yves' image with my scrap of OIII thrown in:  https://www.astrobin.com/g82xf7/B/?nc=user

I'm happy to clarify further any earlier points I made if I can.

Olly

Thanks Olly, Much appreciated. That is a brilliant 32 frame picture. 

I may have misread you on 4:1 ratio, i did not realize when you said "6 to 4" you meant it like a ratio - makes more sense now. So what you are suggesting is a mono image with 1 hr worth of data in LRBG will be theoratically equal 1.5 hrs of OSC? That is not much but still quite tangible.

I see you comment on the latest CMOS sensors - in fact one of my more experienced friend is of the same mind as you - that he is considering getting a qhy268c after discounting CMOS/OSC for similar reasons for a while.

I live in a suburban area with moderate to high LP. I feel i can get decent images with IDAS V4 on its 50+nm Ha bandpass. and takes a lot of work at post to get the details when using a standard IDAS P2 LP filter.

So i think i need to go narrowband really. With that in mind, I am seeing two options for myself:

1. get a qhy268M with SHO filters (and LRGB to get the star colour)

2. get a qhy268C with Dualband + SII filter and create SHO images from there. (thats two filters for SHO - not sure if that is even possible as the O will get split between B and G 😜)

if you were in my shoes what would you prefer if you were primarily interested in nabulas? i.e. would you recommend using a QHY268C for SHO? Would the individual exposure time and total integration time be comparable between OSC/Mono?

On 15/06/2017 at 20:25, ollypenrice said:

2) The increase in resolution by using all the pixels in a mono is actually trivial. The debayering routines are very sophisticated and interpolate (make an educated guess) about the 'missing' information remarkably well. I advocate mono but not for reasons of resolution because I have found very little or no gain in resolution when using mono over OSC on the same make of chip in the same telescope. 

3) You do not need more time with a mono camera, you need less. An OSC camera shoots through colour filters all of the time so it can never capture more than a third of the incident light, ever, under any circumstances. However, when a mono camera is working in its luminance mode it is capturing all of the incident light  and obtaining a massive speed advantage over colour. This cannot be less than a 6 to 4 time advantage and can easily rise to being twice as fast. The LRGB system was invented to save time.

6) Mono cameras can capture narrowband efficiently, Ha opening up many nights of moonlight to the imager.

 

Hi

Sorry to dig this up from the past. however, i am trying to decide between qhy268c/qhy268m (my move from D7000 which uses sony 071 chip) so i was doing my research when i noticed your post. firstly thank you for articulating your view so nicely.

I was trying to connect the two points that you make and to me they seem to be contradictory to each other. Maybe you would be kind enough to clarify.

I follow that one in every four channel is attributed to red. and i agree that when doing narrowband, we are only using 1/4 of the sensor and the rest is just dead space. However, if you also claim, rightly so, that the debayering routines are able to interpolate the red values for the "dead" pixels well enough, how can you say that mono is 4 times faster than, i.e. a 10 second exposure on mono is equivalent to 40 sec in a OSC, because the debayering algorithm has filled in the missing gaps. Yes photons are wasted, and we are making approximations, and given that a debaying routines are so good, that a 26 MPixel camera will probably behave comparible to 16+ MPixel mono in terms of resolution (maybe more - maybe a resolution comparison between qhy268c and asi1600m would confirm this).

However I donot follow why mono needs less time. in my view, the intensity registered in the R channel will be quasi-similar between an OSC and mono /w red filter. is that not so? 

Dont get me wrong, i want mono to be faster as then i would get the mono camera and get the benifit of higher resolution (i can get a EFW and i made already myself a autofocuser and processing seems similar except for one one extra step of LRGB combination module in PI). i am hoping you could clarify your statement. Ideally if someone has access to both qhy268m and qhy268c could probably do a shootout and put to rest this question.

Thanks

Rashed

3 hours ago, Deeko said:

Hello, unfortunately I didn't get a chance to go out, not sure when that will be next. There are a few photos below on how I connected the camera to the ZWO EFW with 55mm back focus. 

For connecting the 268m to the EFW I used the T2-T2 male adapter that came with the EFW and bought a ZWO M48-M42 ring adaptor (https://www.firstlightoptics.com/zwo-accessories/zwo-m48-to-m42-adapter-ring.html) to screw onto it. This gives one side of the T2-T2 adaptor an m48 thread that I could screw directly onto the camera plate with the  other side screwing onto the EFW.

Before screwing the T2 adaptor with M48 ring onto the camera plate:

 

After screwing in the T2 adaptor with M48 ring, which can then screw into the EFW:

For the Telescope side you will need to source adaptors that work for your setup and the reducer/flattener. For my setup I used a T2 extension and rotator to make up the remaining back focus, the EFW takes up 20mm:

 

HTH

perfect thanks. this fives me confidence that it can be done

could you not have use the M42-M48 to connect the EFW directly onto the M54-M48 adaptor that gets bolted on to the 268M.

Which retailer did you get the camera from - i usually do FLO, but they done seem to do QHY268M. would be nice to get it from within the UK.

Best Regards

On 05/03/2021 at 20:01, Deeko said:

Hey, I have posted up some images in this thread: 

However, they were all done under a full moon so not a great test yet! I had some vignetting but I think this may have been caused by the full moonlight and possibly over compensated flats. I need to wait on a clear night with no moon to do some more testing.

Brilliant pitctures indeed. 

weather has been really bad lately, but did you manage to take any pictures last night (was moonless) - it was clear between 2300 and 0300 hr for a while where i am, in oxfordshire?

may i ask how you did your spacings with ZWO EFW and how you connected it all?

Thanks

On 24/01/2021 at 09:25, Deeko said:

Been reading about the 268m on CN. There does not appear to be any solid information on the camera connector, and that it wont come with the dovetail like the 268c. Does anyone have any confirmed info and how it could connect to a ZWO EFW 7x 36mm filter? ta!

HI @Deeko - Just wondering if you went ahead with that arrangement and what your results were like. I have a ZWO 7x36mm as well and considering getting a QHY268m. But i am worried about vignetting. Also may i ask how you arranged it all.

I may be simpler to just get a new QHY EFW, but if its possible than i rather not.