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alan potts

Can anyone tell me?

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2 hours ago, alan potts said:

Alan and Dave,

I don't know if you can assess this it is only 3 frames stacked that I got the other night, I now have 70cms of snow outside and it could well be some time before I can get the Obsey open. Golly it was clear last night, no power and utterly Black sky before they got some power back on, 24hrs we were off, lots of damage all around.

So I have loaded this on the off chance it will do, I think it is reasonable focus but that really causes me problems with so short a scope. To me the stars look better.

Hope you have some joy.

Alan from a very snowy Bulgaria.

Hi Alan,

Hope you're keeping safe and haven't had any damage yourself. We're due to have a storm hit over the weekend, but no snow forecast for me this far south (yet).

On a quick check your latest image is much better with good star shapes all over. The elongated red stars on the right of your previous image are now much improved. The red channel is still more out of focus compared to the green and blue but again better than the previous image. I'll do a CCDI analysis later and post the results.

Alan

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11 minutes ago, symmetal said:

Hi Alan,

Hope you're keeping safe and haven't had any damage yourself. We're due to have a storm hit over the weekend, but no snow forecast for me this far south (yet).

On a quick check your latest image is much better with good star shapes all over. The elongated red stars on the right of your previous image are now much improved. The red channel is still more out of focus compared to the green and blue but again better than the previous image. I'll do a CCDI analysis later and post the results.

Alan

Alan, Maybe at this here is where the scope could benefit from the stronger L3 filter, F 4.3 is very fast even with the name Borg on it. I guess with wide field which is what it is aimed at the effects of the red being out are less noticeable. I bought the 183mc for this scope and maybe should have asked site for advice before taking the plunge. However at x 2 binning it will be good on my M/N 190mm, it not bad on my 805mm APO with reducer for getting close-ups too. Fancy the new 26mb camera from Zwo, only 1900 quid, I order half a dozen. I do like the wide field shots.

Still not got full power back 2 days now, can't cook but we are warm which is something. Sirius last night was as still as I have ever seen it not a flicker, shame I can't get near the obsey.

Alan

 

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Here's the results of your latest image through CCDI. I don't know if they're more of a help or a hinderance. Looking at each channel at full size in Photoshop or similar I think tells you more than CCDI does. :smile:

The curvature and 3D plots implies large large focus variation top to bottom in Red, but in reality the variation is not that great. CCDI scales best to worst in black to pink so a large or small variation can result in the same graph shape. Between black and dark blue the difference is slight. The blue channel is showing fairly consistant focus over the whole frame though. The small variation in FWHM indicates this.

All the stars are very slightly oval so I think there was a slight tracking/polar alignment error causing the rather high aspect scores overall. Blue has uniform aspect ratio stars over the whole frame.

As you say getting the narrower UV/IR bandwith filter could well help with the red. Your focusing seems to be optomising for blue, so maybe offset the focus in a direction which helps the red without upsetting the blue too much. trial and error will be needed to do this.

Curvature

1548779878_CCDICurvature.jpg.0c59043adb91b7066019f674a6b3a8a5.jpg

3D Curvature

559790_CCDI3DPlot.jpg.cc0b31e1282f1c3876ba989453d91c0b.jpg

Star Aspect Ratio

3303699_CCDIAspect.jpg.6a149d3f59e1ab21ddc9307cf0c5bcde.jpg

Hope you get your full power back again soon.

Alan

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10 hours ago, symmetal said:

Here's the results of your latest image through CCDI. I don't know if they're more of a help or a hinderance. Looking at each channel at full size in Photoshop or similar I think tells you more than CCDI does. :smile:

The curvature and 3D plots implies large large focus variation top to bottom in Red, but in reality the variation is not that great. CCDI scales best to worst in black to pink so a large or small variation can result in the same graph shape. Between black and dark blue the difference is slight. The blue channel is showing fairly consistant focus over the whole frame though. The small variation in FWHM indicates this.

All the stars are very slightly oval so I think there was a slight tracking/polar alignment error causing the rather high aspect scores overall. Blue has uniform aspect ratio stars over the whole frame.

As you say getting the narrower UV/IR bandwith filter could well help with the red. Your focusing seems to be optomising for blue, so maybe offset the focus in a direction which helps the red without upsetting the blue too much. trial and error will be needed to do this.

Curvature

1548779878_CCDICurvature.jpg.0c59043adb91b7066019f674a6b3a8a5.jpg

3D Curvature

559790_CCDI3DPlot.jpg.cc0b31e1282f1c3876ba989453d91c0b.jpg

Star Aspect Ratio

3303699_CCDIAspect.jpg.6a149d3f59e1ab21ddc9307cf0c5bcde.jpg

Hope you get your full power back again soon.

Alan

Thank you for doing that Alan, I recall now I did really rush this and guiding was poor on one of the frames with me moving about in the observatory, for sure the guide line in PHD 2 did go to almost 2 pixels which is way outside where it would normally be , it rarely goes about half a pixel. So that may well account for the shapes. I feel I would use my 071 on this scope the most or if I buy one the new Zwo at APS C size. The results at the wider field are fairly pleasing to my at least. All that you have done is much appreciated and if nothing else turned me on to something I had forgotten in the locking of the focus. It is surprizing how easy it is to forget such things but I guess I will not be the last. May well get that L3 as well, how stupid I was getting two L 2's.

Alan

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Happy to help Alan. :smile: Locking the focus seemed to have produced the biggest improvement and the flat blue field indicates no tilt and no curvature worth mentioning. Normally blue is the most critical for getting a flat field. You could always run a 'shrink stars' photoshop action (or similar) on just the red channel to reduce the red halos on the composite image as the red focus 'bloating' is similar over the whole field.

Good luck with the L3 filter or new camera if you get them. I like widefield images too but they are more hassle to get good over the whole frame. :smile:

Alan

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17 hours ago, symmetal said:

Happy to help Alan. :smile: Locking the focus seemed to have produced the biggest improvement and the flat blue field indicates no tilt and no curvature worth mentioning. Normally blue is the most critical for getting a flat field. You could always run a 'shrink stars' photoshop action (or similar) on just the red channel to reduce the red halos on the composite image as the red focus 'bloating' is similar over the whole field.

Good luck with the L3 filter or new camera if you get them. I like widefield images too but they are more hassle to get good over the whole frame. :smile:

Alan

Alan

I tried make stars smaller a few time with the action package I have, this seemed to give a very dark background that looked un-natural. It is a good while since I used any of them in truth. I prefer the views given by the 071 on this short F4.3 Borg and even when for sure things were not set up correctly it still gave a reasonable result, I did this a week before (no correct spacers) and for sure the focus was not locked but was in a slightly different sky area so maybe bent in a different direction.

1639287300_WideField236229234237.thumb.jpg.94e7ca3acdfe6826b29a4af00591e0dd.jpgr

 

I am still getting this blacker than black on the rightside of frame, this suggests to me the the focal plain is still off in the same way as most of my other images. There is still a good amount of out of control red spread about but when shooting these SH-2 areas I find it difficult to work out if this is a fault or faint nebular coming through. This is a shot of 20x 4 mins at zero gain on the 071 and Borg 330mm. I've seen worse.

Alan

 

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That's actually pretty good focus wise. The red focus is actually similar to green and blue. The jpg compression does make assessment more difficult. Have you used flat frames as that would normally take care of the right side darkening. :icon_scratch: The right hand side has ended up being over processed as the bright blue stars have red halos clipped to black and the top right nebula has green clipped to black.

Overall it's a good image though.

What diameter extension tubes have you used? With my 071 with the WO Redcat51 or ZS61 I've used M48 extension tubes (as that's the thread on the rear of the scopes, and put the M48 to M42 adapter right next to the camera. With your fast borg scope M42 spacers several cm in front of the camera may cause more noticible vignetting. it's just a thought.

Alan

 

Edited by symmetal

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Hi Alan,

Just letting you know that I havent given up on you!

Since chiming in and trying to help I have been away in our campervan and without comms - this storm has been unbelievable!

Just found a wee hotspot and dropped you a line but thats it again now for a while as we have 400 miles to go through blizzards today!

All for now

David.

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24 minutes ago, Skipper Billy said:

Hi Alan,

Just letting you know that I havent given up on you!

Since chiming in and trying to help I have been away in our campervan and without comms - this storm has been unbelievable!

Just found a wee hotspot and dropped you a line but thats it again now for a while as we have 400 miles to go through blizzards today!

All for now

David.

Thanks Dave, many would give up on me. I am a hopeless case.

Alan

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15 hours ago, symmetal said:

That's actually pretty good focus wise. The red focus is actually similar to green and blue. The jpg compression does make assessment more difficult. Have you used flat frames as that would normally take care of the right side darkening. :icon_scratch: The right hand side has ended up being over processed as the bright blue stars have red halos clipped to black and the top right nebula has green clipped to black.

Overall it's a good image though.

What diameter extension tubes have you used? With my 071 with the WO Redcat51 or ZS61 I've used M48 extension tubes (as that's the thread on the rear of the scopes, and put the M48 to M42 adapter right next to the camera. With your fast borg scope M42 spacers several cm in front of the camera may cause more noticible vignetting. it's just a thought.

Alan

 

Alan,

I am fairly sure the focus was not locked when I took this so I am, maybe wrongly, assuming that the blackness is cased by the slight bend in the optical alignment. I also seem to have gone through a period of clipping blacks I never had when using my other scopes. Why I have no idea.

Extension tube wise I am just using those supplied with with the 071, unlike yourself I have M42 on the rear of the Borg adapter, at least I think I have. I can't check now due to snow still. There is just the one sleeve in the mix as I was told I need 37.5mm of backspace and the chip is recessed 17.5mm. So there is just the 20mm sleeve. I see the vignette on most images and at the moment do not have a software to remove them though I do try a vignette removal in Raw Camera Adjustment a part of PS, which helps.

I will have a look at this in the next day or so as things are melting a bit and sort of getting back to normal.

I am using flats and dark flats too but they could be dark on that side too as I may have had the focus lock untightened, dare say Darks are the same..

Been and checked!!, the M42 20mm fitting/spacer that is in now is much larger internally than the Zwo 21mm fitting and this shot was taken with the Zwo 21mm, so things should now be better. May have a go tonight if clear.

Alan

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The 77EDII is claimed to cover full frame sensors, so the M42 rear fitting should be fine for the 071. What size Astronomik filter are you using and where is it fitted. They do an M42 version which would possibly cause vignetting if fitted significantly in front of the camera. Or do you have a 2" filter fitted in the scope which would be fine.

If your flats were also showing the same darkening on the right, then when calibrating with them it should have corrected the problem. The result of excessive vignetting calibrated with same vignetting flats should still be a flat frame. The visible effect after calibration should be increasing noise seen on the right as more gain is effectively applied there to correct the light loss. That is as long as the flats or image are not clipped to black anywhere on the right side. Likewise check the darks aren't black clipped anywhere too. The default offset on the 071 is fairly high at 65, and I've checked mine and they are well clear of black clipping at that offset value. Check your value hasn't been changed inadvertently.

If the focuser was tilted by not using the locking screw I would have thought the focus across the frame would be more sevely affected than the vignetting. The focus on your last post is pretty even over the whole frame and doesn't show significant tilt effects.

Alan

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15 hours ago, symmetal said:

The 77EDII is claimed to cover full frame sensors, so the M42 rear fitting should be fine for the 071. What size Astronomik filter are you using and where is it fitted. They do an M42 version which would possibly cause vignetting if fitted significantly in front of the camera. Or do you have a 2" filter fitted in the scope which would be fine.

If your flats were also showing the same darkening on the right, then when calibrating with them it should have corrected the problem. The result of excessive vignetting calibrated with same vignetting flats should still be a flat frame. The visible effect after calibration should be increasing noise seen on the right as more gain is effectively applied there to correct the light loss. That is as long as the flats or image are not clipped to black anywhere on the right side. Likewise check the darks aren't black clipped anywhere too. The default offset on the 071 is fairly high at 65, and I've checked mine and they are well clear of black clipping at that offset value. Check your value hasn't been changed inadvertently.

If the focuser was tilted by not using the locking screw I would have thought the focus across the frame would be more sevely affected than the vignetting. The focus on your last post is pretty even over the whole frame and doesn't show significant tilt effects.

Alan

Alan,

I have decided to do a complete set of new darks and flats, maybe tomorrow I will have a clear sky, last night was not going to be any good, and cleared in part only for a short time.

The Borg 77EDll has it's own filter draw infront of the reducer lenses, it is a 2 inch Astronomik's L2, which we have said may not be quite strong enough. I have been shooting on zero gain settings and I think the off set is also zero, I use the same on both cameras.

I am going to persist with the 183mc for the moment so I can see if we get that right. I am sure it is me causing these issues as Borg is meant to be somewhat better than the normal run of the mill scopes, I didn't pay this but this scope combo would have cost about 2000 USD, so should be decent, unless something else is not correct that we don't know of. The shot with the 071 on the Flaming Star and partner to me at least suggests things are not so far away.

I am not sure what to really look for on these Darks so I will post one up for you when I manage another image to look at. As I am sure you know all these darks, I shot 4 sets, have amp glow in this right side area, though this does not apply to the 071.

Thank you so much for your time and help Alan.

 

Alan

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Do you really mean zero gain and offset or did you mean to say unity gain (the default option I believe). The 071 unity gain is gain 90 with offset 65. Clicking on the camera Ascom driver setup icon in your capture software should let you check. You probably need to click the 'advanced' tick box in order to view the offset. If your offset actually was zero that would give black clipping.

As your Borg has a 2" filter drawer that rules out the filter causing vignetting.

There is a slight amp glow on the 071 on longer exposures but it's generally along the top and bottom rather than the right. The Flaming Star/Tadpoles 071 image looks like the 183 darks have been applied instead of the 071 darks if the 183 has amp glow on the right. The darks are subtracted from the lights, so a dark with amp glow will subtract more where the glow is. As they are different resolutions the stacking software shouldn't allow that though. You could recalibrate your Flaming Star 071 image without using darks and see what results. Or post your current dark and flat masters here. :smile:

Alan

Edited by symmetal
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12 hours ago, symmetal said:

Do you really mean zero gain and offset or did you mean to say unity gain (the default option I believe). The 071 unity gain is gain 90 with offset 65. Clicking on the camera Ascom driver setup icon in your capture software should let you check. You probably need to click the 'advanced' tick box in order to view the offset. If your offset actually was zero that would give black clipping.

As your Borg has a 2" filter drawer that rules out the filter causing vignetting.

There is a slight amp glow on the 071 on longer exposures but it's generally along the top and bottom rather than the right. The Flaming Star/Tadpoles 071 image looks like the 183 darks have been applied instead of the 071 darks if the 183 has amp glow on the right. The darks are subtracted from the lights, so a dark with amp glow will subtract more where the glow is. As they are different resolutions the stacking software shouldn't allow that though. You could recalibrate your Flaming Star 071 image without using darks and see what results. Or post your current dark and flat masters here. :smile:

Alan

The Gain is set to zero on both cameras, as it comes up in settings at best dynamic range, I thought this was best and have done it pretty much since I got them. I believe there are 3 pre-sets, Best Dynamic range, Unity and Lowest read noise, this equats to zero, just below mid-way and max on the slider.

 I don't believe I have mixed the darks as I keep them in different folders now, have done it in the past though. Here is an 071 dark and a 183 dark. These are from the old darks at minus 5 not the new one I did yesterday.  

183mc

D_2019-10-12_13-09-50.fit

 071.

D_2019-10-12_10-29-52.fit

Alan

 

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Ahh OK. Zero gain is fine as you have much more clear skies generally than us in the UK so can use longer subs without running out of time. :D Your offset won't be zero though but I'm sure it's right if you haven't changed it.

Here are your darks heavily stretched. The 071 dark looks fine showing a slight sign of amp glow top and bottom. The 183 Dark is something else though. :smile: I think you had some light leakage while taking them and it should have made your 183 images exhibit a dark diffraction pattern from the centre right as well as a slight dark halo in the centre.

071 Dark

50960958_071Dark.jpg.c57d4d71cf9600acb0c1e23af50b3ff0.jpg

183 Dark

1105961645_183Dark.jpg.c40000f589366f5ef9632880527bf8a0.jpg

It's worth posting the 071 flat you were using as I'd like to know what's causing the right darkening on the 071 images.

Alan

Edited by symmetal

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12 hours ago, symmetal said:

Ahh OK. Zero gain is fine as you have much more clear skies generally than us in the UK so can use longer subs without running out of time. :D Your offset won't be zero though but I'm sure it's right if you haven't changed it.

Here are your darks heavily stretched. The 071 dark looks fine showing a slight sign of amp glow top and bottom. The 183 Dark is something else though. :smile: I think you had some light leakage while taking them and it should have made your 183 images exhibit a dark diffraction pattern from the centre right as well as a slight dark halo in the centre.

071 Dark

50960958_071Dark.jpg.c57d4d71cf9600acb0c1e23af50b3ff0.jpg

183 Dark

1105961645_183Dark.jpg.c40000f589366f5ef9632880527bf8a0.jpg

It's worth posting the 071 flat you were using as I'd like to know what's causing the right darkening on the 071 images.

Alan

I tried this myself on the 183mc a good while back and stretched the image in APT and seen this on darks, end up pretty much like the one you have worked on. I feel I have given you a very early 2 minute Dark here where I see this fault too, maybe I was not careful back then, there is no light leak as far as I can see now I have changed my method.    First the Obsey is dark with lights off, the lens cap is on the scope and I cover the lens cap with a very thick cloth, then cover the whole scope with a thick velvet curtain. I would have said now leaks were impossible. I don't cover the camera for fear of loss of cooling.  I think I made a mess of these and have not dumped them, sorry to have wasted your time.

Here is a flat for the 071, would it be better for you I post Masters for you? This is a single.

 

F_2020-01-04_13-02-26.fit

 

Here is a shorter 2 min dark that I took with the 183mc a good while ago

 

D_2019-10-12_14-30-28.fit

 

Here is a Dark I took yesterday with the 183mc, this is 3 minutes at minus 10 (getting adventurous) see if that the same, it looks better as I see it. For the life of me if it is I can't think what I did to cause that on the other one other than me not being careful then..

D_2020-02-10_13-18-42.fit

 

Many thanks,

Alan

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Hi Alan,

The flat of the 071 you posted is totally over exposed and white clipped, ADU 65528 over the whole frame, so would have had no effect on correcting any vignetting from your scope. Maybe you posted the wrong file, but post the master you used just to be sure.

You didn't waste my time with the old darks. I didn't analyse them properly. :redface: The newer 183 darks posted are similar to your previous dark though the newer 3min one doesn't have the halo. Actually examining the original ADU values of the highly stretched image the white 'star' like pattern coming in from the right probably is just amp glow and is in reality only just brighter than the rest of the frame. For your newest 3 min 183 dark, the average ADU on the left is 640 while the brightest part of the the 'star' pattern on the right is 704 ADU. Not much difference really. It's shape led me to think it was light leakage and I didn't go any further. I should have checked the ADU values before assuming it was light leakage. Not sure what the cause of the halo on the older darks was though it could just be slight 'amp glow' from components on the sensor which are masked by the longer dark to the point where they are not significant. Also, the newer longer dark has lower ADU values so reducing the temperature has been beneficial. It just looks more noisy because it has been stretched more.

So I'd say the 183 and 071 darks are fine. Just need to see a proper 071 flat now. :smile:

Older 183 2 min dark (range 800 to 1070 ADU)

 453812574_183OldDark.jpg.0c0aad381d3df72ab99f80df6aa9c05b.jpg

Latest 183 3min dark (range 640 to 704 ADU)

1072834591_183NewDark.jpg.5f52956cd9e1fd1279587cf344cfc453.jpg

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13 hours ago, symmetal said:

Hi Alan,

The flat of the 071 you posted is totally over exposed and white clipped, ADU 65528 over the whole frame, so would have had no effect on correcting any vignetting from your scope. Maybe you posted the wrong file, but post the master you used just to be sure.

You didn't waste my time with the old darks. I didn't analyse them properly. :redface: The newer 183 darks posted are similar to your previous dark though the newer 3min one doesn't have the halo. Actually examining the original ADU values of the highly stretched image the white 'star' like pattern coming in from the right probably is just amp glow and is in reality only just brighter than the rest of the frame. For your newest 3 min 183 dark, the average ADU on the left is 640 while the brightest part of the the 'star' pattern on the right is 704 ADU. Not much difference really. It's shape led me to think it was light leakage and I didn't go any further. I should have checked the ADU values before assuming it was light leakage. Not sure what the cause of the halo on the older darks was though it could just be slight 'amp glow' from components on the sensor which are masked by the longer dark to the point where they are not significant. Also, the newer longer dark has lower ADU values so reducing the temperature has been beneficial. It just looks more noisy because it has been stretched more.

So I'd say the 183 and 071 darks are fine. Just need to see a proper 071 flat now. :smile:

Older 183 2 min dark (range 800 to 1070 ADU)

 453812574_183OldDark.jpg.0c0aad381d3df72ab99f80df6aa9c05b.jpg

Latest 183 3min dark (range 640 to 704 ADU)

1072834591_183NewDark.jpg.5f52956cd9e1fd1279587cf344cfc453.jpg

Alan,

This is all getting very technical, on the flats I run the APT flat helper. This basically suggest I need not less than 500ms and not more than 2 seconds, now that's a fair range. Thinking back I may well have done a combination of these times so probably selected a longer one, I've posted the master. All of these need to be redone now anyway, so any advice you can give would be great.

I tried to get a shot last night but was often with very thin cloud, it's a poor image and I am far from pleased with it. In fact I feel this Borg is better with the 071 and overall I am not pleased with it at all. I know I am not a great imager but i feel this scope is a lot of money new for not great results, well at least from me. I intend in March to buy the new FLO 85mm Stella Mira.

So this is Master Flat minus 5, maybe I need to do them again when I put the 071 back on

MasterFlat_ISO0.tif

 

This is a frame of the 25 I took , at minus 10, maybe the focus is again off, this really is so so hard to get right. It is a shot of the Cone Neb, at least I think it is.

L_2020-02-13_21-06-07.fit

 

Weather is turning a bit now so maybe no clear sky for a few days.

 

Many thanks Alan,

Alan

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Hi Alan,

Your 071 Master flat is again almost totally white clipped :sad2: so would have no effect on combating vignetting. I loaded yours and my 071 flat into APT (as that's what you use) to show what the histogram should look like. The APT histogram  seems to only display from the min to max ADU values in the image and not the full histogram from 0 to 65535 ADU which is a bit annoying.  Maybe there is a way to show the full histogram but I couldn't find it. Here are yours and my 071 flats in APT. Note your flat shows a peak but the range is 64076 to 65034. The peak is all squashed up at an average value of 65004. As it's a colour camera there should be three peaks corresponding to the response of the three colours and the actual colour of your light source. Note my flat has a range of 17358 to 47490, which is in the middle of the full range of 0 to 65535 so no clipping of data. The width of each colour hump indicates the amount of vignetting in the image. The wider the hump the more the vignetting.

1930531495_Alan071FlatAPThistogram.jpg.e7fd2c7b1057450d7d56df582aa21240.jpg 1147117339_My071FlatAPThistogram.jpg.5675af1ddd386e7c315660b6fcaff408.jpg

Here are your and my flats loaded into SGP which has a full 0 to 65535 top histogram display. Your flat doesn't really show on the top histogram as it's all effectively crammed into a single vertical line on the right. If I move the black point slider under the top histogram to the right the bottom histogram shows the values from 61503 to 65535 similar to what APT shows. My flat on the right shows the three colour humps nicely sitting in the middle of the full histogram. When taking flats you always really just want to see the full histogram and not have to analyse what the range values are and interpret the real result from them. Note that APT seems to debayer the preview image so it shows as green being brightest (the right hump of the three). SGP doesn't debayer the images so always shows the image as grey. 

640904600_Alan071FlatSGPhistogram.jpg.bf87d611d3cb82b9632d1124ae9942d0.jpg 229788008_My071FlatSGPhistogram.jpg.e3cd654a185ef7e83fab2112d1e9f3bc.jpg

I should ignore the APT flat helper, as it doesn't seem to help, and just vary the exposure until you get three humps similar to what mine shows. Also check the range ralues are at least 5000 ADU (ideally more if you can), from the limiting end values of 0 and 65535. If you're still too overexposed at 0.5 second exposure put some sheets of paper over the front of the lens, or in front of the light box if you're using one.

Your latest single image is pretty good focus wise. Here it is debayered (rough colour balance), and just black lifted, not stretched, to avoid clipping too many stars. Just the stars on the left are slightly elongated (on all colours) showing very slight tilt or the camera not fully on axis. As the vignetting was generally on one side I would suspect the latter. However the image here shows no vignetting. The red is still slightly less focused overall compared to the green and blue but not enough to cause too much worry. The focus on all three colours does hold well into the corners though so the scope is good in that respect.

Hope this all helps Alan. :smile:

C_L_2020-02-13_21-06-07.thumb.jpg.6640388b2e012fe5daca5413128f9c9c.jpg

Alan

 

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Many thanks Alan, I will try what you suggest when I get a chance to use the scope again, I can't do flats again until I change the camera over and focus on a new target. I use a T shirt stretched over the front of the scopes and a photographic light box, clearly I have been exposing too long and will try to aim for what you suggest next time I do them. Weather is not great at the moment but there looks like a break coming Tuesday.

Many thanks,

Alan

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On 14/02/2020 at 20:01, symmetal said:

Hi Alan,

imageproxy.php?img=&key=127fb0a7147957bfYour 071 Master flat is again almost totally white clipped :sad2: so would have no effect on combating vignetting. I loaded yours and my 071 flat into APT (as that's what you use) to show what the histogram should look like. The APT histogram  seems to only display from the min to max ADU values in the image and not the full histogram from 0 to 65535 ADU which is a bit annoying.  Maybe there is a way to show the full histogram but I couldn't find it. Here are yours and my 071 flats in APT. Note your flat shows a peak but the range is 64076 to 65034. The peak is all squashed up at an average value of 65004. As it's a colour camera there should be three peaks corresponding to the response of the three colours and the actual colour of your light source. Note my flat has a range of 17358 to 47490, which is in the middle of the full range of 0 to 65535 so no clipping of data. The width of each colour hump indicates the amount of vignetting in the image. The wider the hump the more the vignetting.

1930531495_Alan071FlatAPThistogram.jpg.e7fd2c7b1057450d7d56df582aa21240.jpg 1147117339_My071FlatAPThistogram.jpg.5675af1ddd386e7c315660b6fcaff408.jpg

Here are your and my flats loaded into SGP which has a full 0 to 65535 top histogram display. Your flat doesn't really show on the top histogram as it's all effectively crammed into a single vertical line on the right. If I move the black point slider under the top histogram to the right the bottom histogram shows the values from 61503 to 65535 similar to what APT shows. My flat on the right shows the three colour humps nicely sitting in the middle of the full histogram. When taking flats you always really just want to see the full histogram and not have to analyse what the range values are and interpret the real result from them. Note that APT seems to debayer the preview image so it shows as green being brightest (the right hump of the three). SGP doesn't debayer the images so always shows the image as grey. 

640904600_Alan071FlatSGPhistogram.jpg.bf87d611d3cb82b9632d1124ae9942d0.jpg 229788008_My071FlatSGPhistogram.jpg.e3cd654a185ef7e83fab2112d1e9f3bc.jpg

I should ignore the APT flat helper, as it doesn't seem to help, and just vary the exposure until you get three humps similar to what mine shows. Also check the range ralues are at least 5000 ADU (ideally more if you can), from the limiting end values of 0 and 65535. If you're still too overexposed at 0.5 second exposure put some sheets of paper over the front of the lens, or in front of the light box if you're using one.

Your latest single image is pretty good focus wise. Here it is debayered (rough colour balance), and just black lifted, not stretched, to avoid clipping too many stars. Just the stars on the left are slightly elongated (on all colours) showing very slight tilt or the camera not fully on axis. As the vignetting was generally on one side I would suspect the latter. However the image here shows no vignetting. The red is still slightly less focused overall compared to the green and blue but not enough to cause too much worry. The focus on all three colours does hold well into the corners though so the scope is good in that respect.

Hope this all helps Alan. :smile:

C_L_2020-02-13_21-06-07.thumb.jpg.6640388b2e012fe5daca5413128f9c9c.jpg

Alan

 

Alan,

I have changed the camera on this scope for one night and was not happy with the results so I have removed it from the mount for the time being to try out my better apo with reducer to see what that offers. I did however come across this image of M45 taken with the Borg and the 183mc that I thought looked half decent, can you run this, if you have time, to see what you think, it was taken a while back before I got the correct spacers. It just look much better than almost all the other shots.

L_2019-12-18_18-35-36.fit

 

Many thanks,

Alan

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13 hours ago, alan potts said:

Alan,

I have changed the camera on this scope for one night and was not happy with the results so I have removed it from the mount for the time being to try out my better apo with reducer to see what that offers. I did however come across this image of M45 taken with the Borg and the 183mc that I thought looked half decent, can you run this, if you have time, to see what you think, it was taken a while back before I got the correct spacers. It just look much better than almost all the other shots.

Many thanks,

Alan

Hi Alan,

This image isn't as good as those you posted since you used the focus lock. The spacing is wrong as you say so there is noticeable 'coma like' smearing towards the edges particularly on the left, different for each colour, and misshapen stars, again different between red and blue on the right. Green is the best focus overall and the red has 'halos' all over, not out of focus as such, as the star shows brighter in the middle of the halo. I assumed the bayer pattern was the same as the 071. I just lifted the blacks to avoid too much star clipping.

I think the spacing error is the root cause of these effects so it's hard to be sure about other causes. View the image below at full size.

C_L_2019-12-18_18-35-36.thumb.jpg.efbd0a686cc102730950faf7d6aaa2f2.jpg

Alan

 

Edited by symmetal

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12 hours ago, symmetal said:

Hi Alan,

This image isn't as good as those you posted since you used the focus lock. The spacing is wrong as you say so there is noticeable 'coma like' smearing towards the edges particularly on the left, different for each colour, and misshapen stars, again different between red and blue on the right. Green is the best focus overall and the red has 'halos' all over, not out of focus as such, as the star shows brighter in the middle of the halo. I assumed the bayer pattern was the same as the 071. I just lifted the blacks to avoid too much star clipping.

I think the spacing error is the root cause of these effects so it's hard to be sure about other causes. View the image below at full size.

C_L_2019-12-18_18-35-36.thumb.jpg.efbd0a686cc102730950faf7d6aaa2f2.jpg

Alan

 

Alan ,

Many thanks for all you have done for me, I thought at least to look at, this was a better shot, appears not, my eyes are lying to me.

I have taken up enough of your time, this again was a shot with the 183mc and was not spaced correct as we said, at least we appear to have solved that one. For the time being I am going to forget the Borg until such time I decide whether to buy a L3 filter, which we both feel may help, or just get rid of it. For what one of these did cost new I can't say I am that impressed, I would have thought it should perform a little better than it has, maybe it can and it's just me. I may try it with a Canon camera as I have an adapter for it at a later date.,

I had the longer APO working last night with the .79 reducer and again even though the spacing was correct, at no small cost, it was not good for the corners. I added a 0.2mm and things did look a little better but still not spot on. This is so much easier to focus than the Borg and I feel is a better scope in any case even though it was dropped a few years back and maybe not perfectly aligned any more. I am beginning to feel that native F/L and a flattener is the best way to use scopes, I still intend to get one of FLO's 85mm Stella Mira's at 560mm. So lets see how that performs when I buy it, come April.

Again many thanks you have been so helpful.

Alan

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