Adam J

I am probably not going to post on this again until I can get some real world comparison images. However you put it that is the only test that is going to actually matter. Am open to suggestions about targets and exposure settings though. Am also of two minds as to if I should cool the cameras in the cool box for the test. Problem is that as I only have the one cool box it will mean a long delay in changing between cameras. So I am thinking ill just do the test at ambient temperature.

Ah not its not a test for intensity these have been processed to attempt to examine the signal to noise ratio, i.e how much detail can be extracted from the image.....although as the noise level is almost identical between the two cameras you could in fact. say that the level of detail is a indication of intensity or to be more exact the signal level itself. I have never shared RAW files before as they are quite large. Ill take a look into how I might do that. I am assuming drop box or something like that, although I dont actually have an account. I am going to try super pixel mode on the mono data next.

Your right it will let a small amount if broad band light past the filter. However, I already considered this, due to the narrower pass band of the single red pixel in the RGB camera it will let allot less broad band light through to the detector than in the case of the mono which is seeing everything. So yes its not a 100% pure test, but it is a test that is in fact biased in favor of the mono camera not the RGB camera. As a result it did not concern me as its likely to make the mono appear better than it really is in comparison to the RGB not worse and hence would not change the result. The second thing that makes me suspect that this is not an issue is that the signal level in the blue and green channels of the RGB image was a good 20dB below the peak of the red channel. See BackyardEOS histogram below, indicating that it is mostly noise. In this experiment I am looking at signal to noise. In this case the noise is mostly going to be bias / read noise as the exposures are very short. However, while the signal to noise ration in any given image is likely to change with different exposures (at least until the thermal noise becomes dominant) the ratio of the signal to noise ratios (that is a mouthful) between the two cameras is likely to remain fixed. I am 100% open to being wrong on this still, or I would not be planning to do the real world test against an emission nebula. I am just stating the facts based on testing up to this point. I have not finished my analysis yet. Yep I am seeing better performance from the Mono when the CLS filter is used. Would be good for higher resolution images of galaxies. But I am starting to feel its going to be better to use the RGB camera for narrow band. I think that there is a new coma corrector on the marked that increases back focus enough that it allows you to use a filter wheel with a DSRL on a fast newt without effecting the focal length. https://www.firstlightoptics.com/coma-correctors/baader-rcci-rowe-coma-corrector.html

With the filter in place the same amount of 656.28nm (+ or - 3.5nm) light is getting through the H-a filter and reaching each of the sensors. With the H-a filter in place the bottle in the image is effectivly a h-a source in so far as the camera is concerned. A full resolution image will have the same signal to noise as image 1 but at a higher resolution.

Ok I have a set of comparison images. Some baby food bottles on the side in my kitchen but it will have to do. Each image is a 1/50th of a second exposure through my Baader 2" 7nm filter fitted to the front of a 50mm lens ISO800 F1.8 (although as discussed short forcal lengths may have an effect on the mono sensitivity). From left to right: 1) Mono Camera Single Red Channel Only Extracted. 2) Mono Camera all four pixels extracted (2x2). 3) RGB Camera Red Channel Only Extracted (Green and Blue Removed). I think that the clear winner in this test is the original OSC camera it simply has the best signal to noise ratio. Now I will still be doing the real world test on a Ha nebula as soon as possible as you could convince me that this may be due to the short focal lenght of the lens....but I would not bet on it. You could also convince me that ultimately with longer exposures / integration I would get more detail out of the mono when processing it for full resolution as opposed to binning it. But from what I can see here I would expect to have to increase the integration time by about a factor of four to achieve the same signal to noise level as in the Red channel only of the RGB camera.....I have seen this done by someone with a mono camera and the results are very good but the integration times are crazy (10's of hours). This leaves me of the opinion that the camera is (baring a a big change in the real world test) not going to give me what I am looking for and I would be better off taking H-a and OIII data with the bayer intact.

I disagree I have seen the effect of white balance on raw images especially when processed as full resolution mono. However, I don't have pixsinaight so don't know what that work stream would involve. I agree that CCD cameras are now on borrowed time but I am not so sure about a mono dslr coming close to a 8300 due to the loss of the micro lenses. Perhapse you could post some recent example images of weak h-a nebula with your exposure settings? Last night I set the camera up and just got a single 3 min frame of the soul nebula with the mono 1000D (I did not have time for the cooling). Assuming that I was pointing in the right place (ill plate solve it tonight)....but no real reason why not, then I got no indication of the nebula at all through my Baader 7nm H-a. Although I would have done a 15 min cooled exposures for that target if cloud cover had allowed me, i might have expected a wisp of nebulosity despite sub optimal conditions.

If you have the cash get the ASI i am only doing this because my total sensor budget is under 200 pounds.

Yes I think this is the real advantage is (luminance). Have you ever done a Mono vs RBG comparison with a H-A filter? Also do you cool your camera? I always remove the green and blue channels In so far as those results are concerned I am no longer sure that they are correct, mostly because while those results where using different parts of the same sensor with the perimeter for the non mono readings the readings for the second normal RGB camera do not yield the same results. I am going to fully wright this all up once I have some real world H-A results.

Probably, but it will be dependent on the ratio of the height of the pixel to its width and although most diagrams I have seen show this to be one to one I am not sure if this is a true representation of what is happening on the chip itself.

Well this is part of the issue, you cant do a comparison based on short daylight exposures only as its only part of the story. You don't get much thermal noise in short exposure, only the read noise....although this is also the case in a 10 min exposure when the camera is cooled. The other interesting thing is that the effectiveness of the micro-lenses will also be dependent on the angle of incidence of the light against the CMOS sensor at least for conventional front illuminated sensors. Back illuminated sensors would not see that effect. So part of my issue is that I am using a fast 50mm lens to do my experiments and so the light cone will be very tight, meaning what with no micro lens allot more light will miss the light sensitive area and hit the copper...or at least that is my theory. There is of course a range of angles in any given focal point however the point is that the spread is higher for short focal lengths leading to greater light loss without micro-lenses. Again at least in theory...

There have been other quantitative studies, however for the most part people have done these with partially removed coatings rather then by a comparison between two camera with and without. Essentially what I am seeing is that she very short daylight exposures (1 second or so) through the H-A filter the RGB has the clear advantage. However, once I move to longer exposures in a dark room the results reverse and the mono is superior. What I have seen though is that the mono will provide a significant performance boost when Luminance is shot through my CLS filter. Kinda makes sense as all the pixels are sensitive to all wavelengths and so each pixel is receiving 3 to 4 times the amount of light as it would normally against a broadband target like a Galaxy or a reflection nebula. This is counter to what other people have suggested...everything I have read so far indicates that people think the biggest boost will be when using narrow band, but I do believe this to be completely correct due to the loss of per pixel sensitivity.

I dont think that anyone has ever done an A6000...well not that I have read about. It would be a jump into the unknown. I am not even really familiar with the model. What I have heard is that the sensors do get more delicate as the pixel count increases, I would not do this to an expensive sensor first time out. I am going to post a real world comparison soon. I have two identical 1000D's one Mono one not. I am getting some very very confusing results from them. Under some exposure conditions the mono looks marginally better, under other conditions the RGB is hugely superior despite only using 1/4 of the pixels. I have decided that the only way to know for sure is to point each at the California nebula for 10 x 5 min exposures each and see how the two images compare. I JUST NEED SOME CLEAR SKY I HAVE HAD THE MONO FOR OVER A MONTH NOW!!

I always de-noise then sharpen or you just make the noise worse. I then do that in two or three cycles. I wish I had a CCD then I would not have to muck about mono-modifying DSLR's but they are just so expensive and I am having to save for a new family car as it is anyway Heck I would take that ability to use a filter wheel with my DSLR on a 130PDS but you simply don't have sufficient back focus when using the Baader MPCC MKIII

There might be something very slight there but to be honest if it is that then its not a twist its a defect / dint in the vane...not sure if skywatcher would do anything about that after 9 months of ownership...

Mine was almost entirely towards the rear end of the scope on the current screws even without changing the current screws I just moved if forward about 6mm. Might that explain something? What was it that prompted you to do it?

I am assuming that i do that by winding in the adjustment screws....if i go too far will the primary fall off? I dont want that to happen lol

Thats why I tried to place the center of the secondary mount in the center of the primary so that in theory the vane would appear to vary in width if twisted. Or at least that was my theory. What i need is a short flat surface to lay on top of the vane so that I can see if it is flat against its entire length.

Yes but not quite as pronounced....i see it on several DLSR pictures in this thread so it makes me suspect that the cause may be the ingress of the focus tube due to the DSLR back focus I cant find an example on a CCD image.

I have a little play but it looks ok to me here are some pictures for you guys to look over. I added a straight line to show that they are straight. Let me know what you guys think. The thing that confuses me is that the unwanted spikes are much dimmer. The focus tube is in the same position i locked it off in for focus with the M45 picture. It looks to me like it may be clipping the very edge of the optical path. Am actually looking at it now wondering if the secondary is slightly rotated anti-clockwise....

Ok here is a good question, assuming it is a twist that I have missed, what is a good way to test for it? I am basically eyeing it up against a steal ruler and cant see anything. Is there a better method? To help me out, given that it is the vertical spike in the image that is doubled and that the camera was mounted with the long axis of the sensor parallel with the OTA, am I correct in thinking that with the focuser pointing straight down as I look at it will be the horizontal pair of vanes that I need to be looking at?

I would agree with this. I just dither to remove dust and hot pixels from the image and even out the color noise takes about 16 frames to be effective. I do use a chunk of Bias frames normally about 24, but as I cooled my DSLR to -10c in my M45 at 300s bias is actually the bigger noise component not thermal.

How much twist are we talking about here? I cant see any at all...so unless we are talking fractions is a mil differenct from each end then I am not sure. Its a DSLR so the focuser is almost fully retracted into the tube and is within the light path. Ill pist a picture of the vanes later tonigt.

I am not sure but I think you are trying to say that the weight attached to the skin of the scope may be causing flex in the tube wall close to the secondary mounting points making them flex? Problem is that they look straight with everything attached and I am already mounting my finder guider over the rear tube ring. But ill have a look and see.

Just boosted the blue channel a little. I am going to try and get another 75 frames over the next few weeks.

Tried to correct the Halos.