Hassaan Zaheer:
andrea tasselli:
Hassaan Zaheer:
i removed the primary and did thighten it up a bit.
it does spin around with some force applied but as for some sort of huge movement i doubt it.
i did test with a laser collimator. When i point it at the center donut and slew it does move away from the center. I tightened the secondary veins a bit and it did help but not alot.
so i think the issue is with the secindary
Fair enough. Your best bet is to replace the entire spider assembly, not just the vanes. TS makes a pretty good replacement spider assembly, should you look for one.
https://www.aliexpress.com/item/1005006713885101.html?spm=a2g0o.home.0.0.650c76db5Ds6bL&mp=1
What about this?
This looks solid too
I fitted this spider too my 200pds , excellent quality fits perfectly,I didn’t buy the apeture mask as I fitted one by deepskydad that also lips over the primary slightly to eliminate reflections, also recommended 👍 cleans up spikes very well and I fitted a Steeltrack focuser too .
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Dave B:
Hassaan Zaheer:
andrea tasselli:
Hassaan Zaheer:
i removed the primary and did thighten it up a bit.
it does spin around with some force applied but as for some sort of huge movement i doubt it.
i did test with a laser collimator. When i point it at the center donut and slew it does move away from the center. I tightened the secondary veins a bit and it did help but not alot.
so i think the issue is with the secindary
Fair enough. Your best bet is to replace the entire spider assembly, not just the vanes. TS makes a pretty good replacement spider assembly, should you look for one.
https://www.aliexpress.com/item/1005006713885101.html?spm=a2g0o.home.0.0.650c76db5Ds6bL&mp=1
What about this?
This looks solid too
I fitted this spider too my 200pds , excellent quality fits perfectly,I didn’t buy the apeture mask as I fitted one by deepskydad that also lips over the primary slightly to eliminate reflections, also recommended 👍 cleans up spikes very well and I fitted a Steeltrack focuser too .
That settles it, ill go for this for now and hopefully results will be better.
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Hassaan Zaheer:
That settles it, ill go for this for now and hopefully results will be better.
It's the same of TS so you should be all-right.
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I once had a similar issue and spent a lot of time searching what caused it. Finally I realised that it was a security camera over my setup with its infrared beam!
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I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
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Hassaan Zaheer:
I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
What camera are you using out of interest?
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Dave B:
Hassaan Zaheer:
I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
What camera are you using out of interest?
Nikon D5100
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Hassaan Zaheer:
Dave B:
Hassaan Zaheer:
I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
What camera are you using out of interest?
I wonder if it’s the camera, I say that as there is a ring artefact which can affect the D5300 I will see if I can find the posts and solution to that and post links , have you tried another make of camera to see if it gives same results ?.
This chap came up with a soloution have a read through
https://www.markshelley.co.uk/Astronomy/NikonConcentricRings/nikon_lossy_compression.html |
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Dave B:
Hassaan Zaheer:
Dave B:
Hassaan Zaheer:
I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
What camera are you using out of interest?
I wonder if it’s the camera, I say that as there is a ring artefact which can affect the D5300 I will see if I can find the posts and solution to that and post links , have you tried another make of camera to see if it gives same results ?.
This chap came up with a soloution have a read through
https://www.markshelley.co.uk/Astronomy/NikonConcentricRings/nikon_lossy_compression.html
Yes i suspected as much.
I was using a redcat before but this never happened.
but im sure it has nothing to do with the scope
I used multiple flats ranging from 1/5 from the left of the histogram to exactly the middle of the histogram
The one which was the least exposed gave the faintest circles.
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Hassaan Zaheer:
Dave B:
Hassaan Zaheer:
Dave B:
Hassaan Zaheer:
I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
What camera are you using out of interest?
I wonder if it’s the camera, I say that as there is a ring artefact which can affect the D5300 I will see if I can find the posts and solution to that and post links , have you tried another make of camera to see if it gives same results ?.
This chap came up with a soloution have a read through
https://www.markshelley.co.uk/Astronomy/NikonConcentricRings/nikon_lossy_compression.html
Yes i suspected as much.
I was using a redcat before but this never happened.
but im sure it has nothing to do with the scope
I used multiple flats ranging from 1/5 from the left of the histogram to exactly the middle of the histogram
The one which was the least exposed gave the faintest circles.
Yes as mark explains in his post a lot to do with background values and combinations of fl ,iso etc , I have a D5300 and switched to a swo533 mc .
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It isn't the camera as I have the same and nothing like this happens. And I don't use any compression in my raws.
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andrea tasselli:
It isn't the camera as I have the same and nothing like this happens. And I don't use any compression in my raws.
Ill try to trace the problem
maybe internal reflections that might go away by flocking
But i will trace the issue
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Just a remark - when I was working for an optical instruments company in the 80´s, the design engineers always needed to check the path of the reflection rays from all surfaces from the entrance to the exit. Most of the time, they needed to design special coatings for at least one or two of the many surfaces to get rid of circular reflections in the image plane.
I have a similar situation with my Sharpstar (Hypergraph6) - the mirrors are OK, all potential surfaces are either blackflocked or covered with black velvet and still there are weak circular reflections in the image plane - the producer of them is the coma corrector, which is built-in. I found out by (removable of course) paint part of the lenses with black paint and the resulting reflex mirrored by partial covering.
Another problem is linked to the usual procedure of taking the flats - we all, at least most of us, are using either a white shirt or an illuminated screen. The problem is that the screen (and the t-shirt) produce a homogenously illuminated surface from which the light is emitted in all possible directions. This is absolutely different from our normal imaging situation with stars and galaxies or even nebulae - those light sources never emit rays into all directions into the OTA - they are too far away. I hope my English lets you understand what I mean - proper flats would imitate the same inclination angle which we have in the imaging situation. Maybe taking flats during the night with full clouds would come closer to the situation we have during imaging stars and nebulae. Just an idea...
CS
Georg
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Georg N. Nyman:
Maybe taking flats during the night with full clouds would come closer to the situation we have during imaging stars and nebulae. Just an idea...
That won't help in most instances as the clouded sky isn't quite that uniform. I tried several times (no lack of clouds here) with little to no success. The only way about it, for restricted FOVs (2-3 degrees tops), is to take dusk flats in clear skies.
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Georg N. Nyman:
Just a remark - when I was working for an optical instruments company in the 80´s, the design engineers always needed to check the path of the reflection rays from all surfaces from the entrance to the exit. Most of the time, they needed to design special coatings for at least one or two of the many surfaces to get rid of circular reflections in the image plane.
I have a similar situation with my Sharpstar (Hypergraph6) - the mirrors are OK, all potential surfaces are either blackflocked or covered with black velvet and still there are weak circular reflections in the image plane - the producer of them is the coma corrector, which is built-in. I found out by (removable of course) paint part of the lenses with black paint and the resulting reflex mirrored by partial covering.
Another problem is linked to the usual procedure of taking the flats - we all, at least most of us, are using either a white shirt or an illuminated screen. The problem is that the screen (and the t-shirt) produce a homogenously illuminated surface from which the light is emitted in all possible directions. This is absolutely different from our normal imaging situation with stars and galaxies or even nebulae - those light sources never emit rays into all directions into the OTA - they are too far away. I hope my English lets you understand what I mean - proper flats would imitate the same inclination angle which we have in the imaging situation. Maybe taking flats during the night with full clouds would come closer to the situation we have during imaging stars and nebulae. Just an idea...
CS
Georg
i get your point
Definitly the issue is with reflective sirfaces inside the tube. And i will rry to take flats at dawn too to see the effect.
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Sharpness looks good
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Hassaan Zaheer:
I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
Re collimation: I agree with Andrea in that you may want to look at the primary first. On my Sharpstar 130 HNT f/2,8, I found out that the primary mirror floated around laterally in it's cell due to insufficient felt on the side of the mirror clips. I'm not sure if your scope has the same mirror cell design, but adding enough felt to stabilize the mirror laterally (also centering it), allowed me to achieve stable collimation. I'm assuming this will also be helpful in achieving a repeatable calibration procedure.
Re calibration: Agree with Georg, calibration procedure plays an important role. If I take flats outside near any stray light, I get over correction or embossed/ring effects. Breaking down my setup down and taking the flats indoor resolved this. Careful in making sure the that mirror doesn't fog up when bringing inside because it will also produce flats with similar characteristics. Moving things around like this presents more challenges, like introducing dust or having dust move around. However, of all my sessions, this hasn't been a problem for me. So maybe trying to take flats inside might help you. You'll have to address the movement of your primary though, because if the mirror moves as you move your equipment, you'll continue to have the same problem.
Hope I could help,
Kice
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Markice Stephenson:
Hassaan Zaheer:
I have pretty much resolved that mirror issue by not moving the scopes orientation after imaging session and taking flats in the same orientation.
I have ordered the spider veins and will replace them as soon as i get them as they are the source of all the problems.
collimation has been pretty much perfected.
Now i can see some green concentric circles which i think are due to flats.
i shot a session with iso at 100 and they were very strong
last night i took this session with iso 400 and they seem to be fainter.
Re collimation: I agree with Andrea in that you may want to look at the primary first. On my Sharpstar 130 HNT f/2,8, I found out that the primary mirror floated around laterally in it's cell due to insufficient felt on the side of the mirror clips. I'm not sure if your scope has the same mirror cell design, but adding enough felt to stabilize the mirror laterally (also centering it), allowed me to achieve stable collimation. I'm assuming this will also be helpful in achieving a repeatable calibration procedure.
Re calibration: Agree with Georg, calibration procedure plays an important role. If I take flats outside near any stray light, I get over correction or embossed/ring effects. Breaking down my setup down and taking the flats indoor resolved this. Careful in making sure the that mirror doesn't fog up when bringing inside because it will also produce flats with similar characteristics. Moving things around like this presents more challenges, like introducing dust or having dust move around. However, of all my sessions, this hasn't been a problem for me. So maybe trying to take flats inside might help you. You'll have to address the movement of your primary though, because if the mirror moves as you move your equipment, you'll continue to have the same problem.
Hope I could help,
Kice
i have ordered the flocking velvet and the veins. As soon as they arrive im gonnna tear everything down and apply all of the suggestions.
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flocking done.
Awaiting spider veins
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Hassaan Zaheer:
flocking done.
Awaiting spider veins
Address the light leak from rear of primary , fit an apeture mask over primary to stop reflections I used a deepskydad one , excellent fit and lips edge to stop reflections from mirror edge too if you go to his website deepskydad.com in his shop go to accessories then scroll down until you see apeture masks , and blacken inside of drawtube , you could probably felt that too .
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Dave B:
Hassaan Zaheer:
flocking done.
Awaiting spider veins
Address the light leak from rear of primary , fit an apeture mask over primary to stop reflections I used a deepskydad one , excellent fit and lips edge to stop reflections from mirror edge too if you go to his website deepskydad.com in his shop go to accessories then scroll down until you see apeture masks , and blacken inside of drawtube , you could probably felt that too .
Dave B:
Hassaan Zaheer:
flocking done.
Awaiting spider veins
Address the light leak from rear of primary , fit an apeture mask over primary to stop reflections I used a deepskydad one , excellent fit and lips edge to stop reflections from mirror edge too if you go to his website deepskydad.com in his shop go to accessories then scroll down until you see apeture masks , and blacken inside of drawtube , you could probably felt that too .
yes i use a wool cap to block the loght leak from the back. Works perfectly for me and helps a bit in balancing too:p
As for the drawtube
I think Cuiv the lazy geek showed that even a single coat on the inside of the drawtube does not allow the cc to enter.
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 Assembled everything back, got good collimation and it holds thanks to the new veins. The Flats were perfect also.
Happy with the results
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OK as one who has seen similar with a Maksutov newtonian...
This problem arises from the way you make your flats. Don't ask why, it's too complicated to explain in a short post here. Don't futz with the scope, don't futz with flocking or anything.
I suggest you try this workflow:
1. At the end of a session on a target, slew to some nearby part of the sky with no nebulae (just stars) and shoot a frame with the exact same exposure you used for your subs, with the scope in the exact same configuration. The scope and camera must be in exactly the same configuration you used to shoot the subs, with the same gain and exposure duration.
2. Stack all your subs as usual, using your weapon of choice (I use Astro Pixel Processor). With no flats.
3. Using that frame from step 1, make a "fake flat", using Affinity Photo as follows:
- obliterate all extended objects (nebulae, galaxies) and the dozen brightest stars using the INPAINT tool.
- use MEDIAN BLUR with a radius of 100 pixels to smooth the rest into oblivion. This should give you a nice "fake flat".
- Export that as "FAKE FLAT.PNG" (note Affinity will save in its own format, so use Export... to get a PNG or JPEG).
4. In Affinity, open your stacked image from step 2 and then subtract the FAKE FLAT using subtraction. The processes is described by James Ritson at
https://www.youtube.com/watch?v=kBV6p5T_Xkk
Watch carefully from 29:00 onwards.
I'm sure you can do similar in Photochop.
Even if you didn't shoot a chunk of sky with no nebulae, you can use the INPAINT tool to remove extended objects (nebulae or galaxies) and still produce a good flat. But ... it is avctuyally better to slew to a nearby chunk of sky which doesn't have any extended objects.
NB... if you have to do the impossible - such as imaging a target near the full moon, you're going to get a nasty gradient which traditional flats cannot remove. But... this method will fix this type of gradient.
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2.81
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7.76
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Assembled everything back, got good collimation and it holds thanks to the new veins. The Flats were perfect also.
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