Edge hd imaging issues

Hello Dan,
I have the same equipment as you and recently photographed M81 and M82 without any problems in an urban environment. See my astrobin post (https://www.astrobin.com/fs9tp5/) . When the Moon is out, it's important to have a dew shield: Celestron's aluminum ones are perfect!

Loïck

See my equipment below on my garden terrace.

Im experimenting with a used C6 at F10+
I was bricking taking flats but a nasty old strip of once white t-shirt, £8 led  tracing panel and Nina flat wizard seems to have made them comically easy.

Better flats should remove the donuts/dust bunnies. They did for me.

Apart from having a dew shield in place which might help somewhat you have also an issue with vignetting which renders flattening more difficult but you can use one (or few) of of the light frames to create a sky flat which would allow to remedy some of the obvious flaws and possibly salvage the final stack (to an acceptable level). Needless to say the reason for this behavior is the reducer and you'll be better off binning the camera and image a f/10 if the target fits in the FOV.

I could go on describing how to do but not sure if it is a waste of time so if there is some interest I might do it.

Andrea 

I image at f5 with my refractor so I was trying the reducer for the f7. Do you think bin 2 with the 2600mc and exposure lengths 2-5min will be ok for small galaxies and PN?

I have been imaging for a few years with my refractor and just got my sct a few months ago and have been slowly tweaking it as the clouds allow and it has been a much larger learning curve for sure.

I'm not sure about the Edge 8 reducer but the Edge 11 and Edge 14 reducers performed poorly in my case and I ditched them (this was once I was running the F14 and it was upon the very good advice of John Hayes). Running at a long focal length (3910mm in my case) can be quite rewarding once you've pinned a few things down - dithering is definitely of paramount concern and seeing conditions can wreck what appears to be a perfectly clear night that may offer no problems on a short FL meaning that patience is required. I have been running at Bin 2 until recently but I am now experimenting with Bin 1 and do see some improvments (John also told me that Bin 2 produces 14 bit as opposed to the native Bin 1 16 bit; at least on the ASI6200). Your M81 would do well on Bin1 I think.

The Reducers on the 8HD are hot garbage. I've seen 50% increases in spot size, leading to massive sharpness issues. I've also noticed that the ADU's are nearly equal at the same exposure lengths with the F/7 reducer, as if the increase of glass leads to an equal speed as F/10. Regardless, I've found F/10 to be sharper, and more friendly to APS-C and larger sensors. The 8HD can nearly correct the entire field of view if it werent for the vignette.

Nothing should really change at F/10, go for about 1.25x the integration you would have gone for just for safe measure.

I would also downsample your images to about 0.6"/px.

If you decide to stay at F/7, with the flats you want to try to match the background brightness across the flats and lights. It's super sensitive to invariance.

Although my camera is a 533mm being the only difference.

This makes all the difference though.

Jan Erik Vallestad:

Although my camera is a 533mm being the only difference.

This makes all the difference though.

My reply was aimed at the dust bunny's,  irrespective of camera.  Donuts like in image linked is cleaning of sensor area and filter ( if the filter is super close to the sensor). Some one kindly pointed in my early days, that donuts appear very close to sensor. And actually 533mm/mc( i have both) is way worst than the 2600mc.

Lots of useful info for the poster being posted, which always good. It's interesting re the reducer I've heard alot about them not being effective. I've never tried mine without,  something I may try and remove and see the difference.

I used my IMX533 with the reducer which was just fine. Everything calibrated as it should and I never really knew about these issues, which are sensor-size dependant. Hence the "533 vs 2600 makes all the difference" comment, it was not meant in a bad way! I get what you're saying about the dust motes, but they were also part of the symptoms I saw when troubleshooting on my own - without there being anything wrong with the actual flats.

Sadly I've lost most of the data from back then, but this is a 20 second sample (1x5s each of LRGB) with the 533MM, calibrated:


Then there's the calibrated 2600MC stack of about 12 hours:



The only change was the sensor size. Same scope, same reducer and the same image train more or less as well as still shooting broadband data. Clear circles where the light has reflected on the bright inner sides of it and left over dust motes (even though they were in the flat frames). As soon as the reducer was removed every dust mote got calibrated and no more circles. If I was still using my IMX533 in stead of IMX571 cameras still I would probably not have this issue at all. I was told that NB data would probably not have those reflections either- but I have not done any more testing. Clear, dark nights are too few to be spent messing around with that reducer  

Personally I didn't remove it due to lack of sharpness, I thought the data looked quite good besides the obvious issues. I was also told by Celestron that the reducer was faulty, which implies that they do make ones that aren't. Maybe its a early batch problem, but I'm not tempted to test that theory as long as most people I talk to seem to have the exact same experience.

Hello Dan,
I noticed that on your 5th image, the donuts from dust are present on the image.

This should normally be removed by flats.

This same problem occurred to me long time ago, and the reason was that the bias (or offset) of either my flats or my images was not properly removed.

On your images the dust donuts appears white, meaning that your flats are overcorrecting the image. I think this can happen when image bias is not fully subtracted or when flat bias is over substracted.

Hope this could help you …

Daniel

Dan,
You’ve received a lot of good advice here but I’m going to toss in my two cents anyway.

1) In my experience, reducers are almost always problematic.  A few work but most introduce excessive optical aberration, stray reflections, or extreme vignetting.   So, my first recommendation is to get rid of the reducer.  You certainly don’t need it for imaging M82—or for that matter, most galaxies.

2) It looks like you have a combination of too much vignetting and perhaps some internal stray reflections.  Removing the reducer will probably fix the vignetting problem.  Make sure that all of the internal surfaces of your connector tubes are well blackened.  Also make sure that there are no light leaks anywhere in your imaging train.

3) Dust motes appear for only two reasons:  A) something moved (or changed) causing a registration problem or B) your calibration data is not being properly applied.  First, clean out all that dust!  Take everything apart in a clean environment, wear gloves and a face mask, and blow out ALL of the dust.  Examine the surfaces under a bright light to make sure that there are ZERO particles on the optics and sensor.  Then reassemble the system and use high quality vinyl tape to seal any gaps so that dust cannot get in.  Then make sure that you are properly calibrating your data using flats, matched darks, and bias.

Get everything working flawlessly without the reducer and then if you want to go back to try it again, you’ll be able to more easily isolate problems that it might be causing.  Again, I don’t recommend using a reducer.   It is much better to get a bigger sensor to gain FOV.

Good luck with it!

John

I'm having a similar issue with my EdgeHD800 (no reducer) where my flats are waaaay overcorrecting. Instead of uncorrected dark spots, I have white donuts as dust bunny's and a complete reverse vignette. This only started when I moved to Voyager though. Never had this problem with NINA and the Flat Wizard. On Voyager, I have tried Sky Flats and flats with a normal panel as well with no change. I just got an EL panel which I am going to try tommorow.

One interesting thing I find between NINA and Voyager is that my ASI2600 has a different horizontal resolution, at least when I am BIN'd 2x2. NINA is 3120x2088 and Voyager is 3124x2088. I need to look back through some old data but I dont believe this is the case at 1x1.

Loïck VIGER:
Hello Dan,
I have the same equipment as you and recently photographed M81 and M82 without any problems in an urban environment. See my astrobin post (https://www.astrobin.com/fs9tp5/) . When the Moon is out, it's important to have a dew shield: Celestron's aluminum ones are perfect!

Loïck

See my equipment below on my garden terrace.

Completely off-topic but..... that's a pretty glorious set-up you've got there :-)