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Hi,
I'm having an issue with guiding.? I'm using an ONAG with ASI462 and have bloated stars which limits my guiding.? I suspect I'll be able to get sharper stars using a mono camera with higher binning.? I'm reluctant to buy a new camera unless I know it will help.?
My image below as taking with guiding around 0.9 to 1.1 arc second and the image scale is 1.09 arc sec/pixel.? My understanding is i'm leaving resolution on the table.? ?Does anyone here have a 174 standard or mini camera which I could try with my setup for a few minutes?? I can offer cold beer and geeky astronomy talk while doing the experiment.
Whirlpool Galaxy? - Integration time ~ 5H
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Hey Greg,
If you’re willing to drive out to my place in White Lake on some night, I’d be happy to let you try out my ASI174MM Mini.
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On Mar 24, 2022, at 9:28 AM, gregz12@... wrote:
?Hi, I'm having an issue with guiding.? I'm using an ONAG with ASI462 and have bloated stars which limits my guiding.? I suspect I'll be able to get sharper stars using a mono camera with higher binning.? I'm reluctant to buy a new camera unless I know it will help.? My image below as taking with guiding around 0.9 to 1.1 arc second and the image scale is 1.09 arc sec/pixel.? My understanding is i'm leaving resolution on the table.? ?Does anyone here have a 174 standard or mini camera which I could try with my setup for a few minutes?? I can offer cold beer and geeky astronomy talk while doing the experiment. Whirlpool Galaxy? - Integration time ~ 5H
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Hi Greg! Can you clarify one thing...is this the MC or colour version of the camera. I am checking online and there does not appear to be a mono version of this camera. The question I have...what is the makeup of this image...single long exposure or stacked short exposures. This would make a significant impact on the resolution. The pixels are very small on this camera so it should provide good resolution. What is your focusing regimen??
Cheers, Chris.
On Thursday, March 24, 2022, 09:28:43 a.m. EDT, gregz12@... <gregz12@...> wrote:
Hi,
I'm having an issue with guiding.? I'm using an ONAG with ASI462 and have bloated stars which limits my guiding.? I suspect I'll be able to get sharper stars using a mono camera with higher binning.? I'm reluctant to buy a new camera unless I know it will help.?
My image below as taking with guiding around 0.9 to 1.1 arc second and the image scale is 1.09 arc sec/pixel.? My understanding is i'm leaving resolution on the table.? ?Does anyone here have a 174 standard or mini camera which I could try with my setup for a few minutes?? I can offer cold beer and geeky astronomy talk while doing the experiment.
Whirlpool Galaxy? - Integration time ~ 5H
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Chris, If you’re referring to the ASI174, I can assure you there is a monochrome version (at least in the mini form factor) — I own 2 of them! :)
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On Mar 24, 2022, at 12:04 PM, Chris T via groups.io <thuemen_cm@...> wrote:
?
Hi Greg! Can you clarify one thing...is this the MC or colour version of the camera. I am checking online and there does not appear to be a mono version of this camera. The question I have...what is the makeup of this image...single long exposure or stacked short exposures. This would make a significant impact on the resolution. The pixels are very small on this camera so it should provide good resolution. What is your focusing regimen??
Cheers, Chris.
On Thursday, March 24, 2022, 09:28:43 a.m. EDT, gregz12@... <gregz12@...> wrote:
Hi,
I'm having an issue with guiding.? I'm using an ONAG with ASI462 and have bloated stars which limits my guiding.? I suspect I'll be able to get sharper stars using a mono camera with higher binning.? I'm reluctant to buy a new camera unless I know it will help.?
My image below as taking with guiding around 0.9 to 1.1 arc second and the image scale is 1.09 arc sec/pixel.? My understanding is i'm leaving resolution on the table.? ?Does anyone here have a 174 standard or mini camera which I could try with my setup for a few minutes?? I can offer cold beer and geeky astronomy talk while doing the experiment.
Whirlpool Galaxy? - Integration time ~ 5H
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On Thu, Mar 24, 2022 at 12:04 PM, Chris T wrote:
the MC or colour version of the camera. I am checking online and there does not appear to be a mono version of this camera. The question I have...what is the makeup of this image...single long exposure or stacked short exposures. This would make a significant impact on the resolution. The pixels are very small on this camera so it should provide good resolution. What is your focusing regimen??
Hi Chris,? The imaging camera is an ASI2600MC which was paired with an Optolong L-pro filter.? I was taking 1 minute subs and stacked using Pixinsight.? My focus regiment is NINA's auto focus routing.? HFR for this session was around 2.2 to 2.5 which is what I get with my edge HD 8 and low-average seeing from my Bortle 8 back yard.?The image camera is binned 2x2 which produces an image scale of 1.09 arc seconds per pixel. My issue is with the guide camera.? I use an on axis guider from Innovation Foresight and my planetary camera ASI462MC.? The stars in my guide camera are always very bloated.? The FWHM jumps between 8 and 12.? I suspect this is responsible for my poor guiding >1 arc second RMS.? As an experiment I connected PHD2 to my 2600 which produced FWHM of ~ 4.? The guiding error dropped to 0.6 to 0.8 arc seconds RMS.? My mount is an Ioptron CEM 70 and from what I've read I should be able to get down to an error of 0.4.? My understanding which may be wrong is I need to get my guide error to be about 50% of my image scale.? This would mean guiding at 0.5 arc seconds which should be achievable for the mount. I've attached an image of the bloated stars as measured in PHD2.? The reason I want to try the ASI174 is it has larger pixels and should help with the guider focus.? The ASI462 is also very sensitive in IR and I suspect this is contributing to the bloating stars. Greg
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I find this thread interesting even though I'm not an
astrophotographer. I would have thought that "camera" would be the
last entry on the list of suspects causing bloated stars. I would have
guessed the priority order of things to check would be:
- focus
- atmospheric seeing
- spherical aberration of the telescope
- position/config of coma corrector
- scope collimation (less likely if your star images are round)
- scope vibration (less likely if your star images are round)
- diffraction limit of scope aperture ( A 56mm scope scope has star
images about 2 arcseconds across)
All these can be checked with an eyepiece.
-ad
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On Thu, Mar 24, 2022 at 1:23 PM <gregz12@...> wrote:
On Thu, Mar 24, 2022 at 12:04 PM, Chris T wrote:
the MC or colour version of the camera. I am checking online and there does not appear to be a mono version of this camera. The question I have...what is the makeup of this image...single long exposure or stacked short exposures. This would make a significant impact on the resolution. The pixels are very small on this camera so it should provide good resolution. What is your focusing regimen??
Hi Chris,
The imaging camera is an ASI2600MC which was paired with an Optolong L-pro filter. I was taking 1 minute subs and stacked using Pixinsight. My focus regiment is NINA's auto focus routing. HFR for this session was around 2.2 to 2.5 which is what I get with my edge HD 8 and low-average seeing from my Bortle 8 back yard. The image camera is binned 2x2 which produces an image scale of 1.09 arc seconds per pixel.
My issue is with the guide camera. I use an on axis guider from Innovation Foresight and my planetary camera ASI462MC. The stars in my guide camera are always very bloated. The FWHM jumps between 8 and 12. I suspect this is responsible for my poor guiding >1 arc second RMS. As an experiment I connected PHD2 to my 2600 which produced FWHM of ~ 4. The guiding error dropped to 0.6 to 0.8 arc seconds RMS. My mount is an Ioptron CEM 70 and from what I've read I should be able to get down to an error of 0.4. My understanding which may be wrong is I need to get my guide error to be about 50% of my image scale. This would mean guiding at 0.5 arc seconds which should be achievable for the mount.
I've attached an image of the bloated stars as measured in PHD2. The reason I want to try the ASI174 is it has larger pixels and should help with the guider focus. The ASI462 is also very sensitive in IR and I suspect this is contributing to the bloating stars.
Greg
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Hi Greg:
I don't think having larger pixels on your guide camera will
improve anything - you will likely still have the same size (in
arcsec) guide stars, you just won't be able to resolve them as
well.
I think Attilla has given a good summary of potential issues.?
Have you done a very careful focus of the guider camera itself,
separate from the main camera?
With the on-axis guider are you not guiding on the infrared?? I
wonder if maybe the scope is badly corrected in the IR and giving
you the bloated stars.? I would be concerned that the 174 camera
may have a lower response in the IR than the 462 and you may find
your guide stars are dimmer.? On the other hand the 174 mono
should be more sensitive so that may balance out.
I can check with a friend who has an on-axis guider and see how
his stars look?? Or perhaps just put you in contact with him
directly if you'd like and he's willing.
Rick
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Hi,
I'm having an issue with guiding.? I'm using an ONAG with ASI462
and have bloated stars which limits my guiding.? I suspect I'll be
able to get sharper stars using a mono camera with higher
binning.? I'm reluctant to buy a new camera unless I know it will
help.?
My image below as taking with guiding around 0.9 to 1.1 arc second
and the image scale is 1.09 arc sec/pixel.? My understanding is
i'm leaving resolution on the table.? ?Does anyone here have a 174
standard or mini camera which I could try with my setup for a few
minutes?? I can offer cold beer and geeky astronomy talk while
doing the experiment.
Whirlpool Galaxy? - Integration time ~ 5H
|
Hi Oscar!
I was referring to the Greg's guiding camera.
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Greg!
I am going to ask what may appear to be a dumb question...the image you posted...is this from the primary imaging camera...at this point I am thinking yes. And...is this the full frame image or a crop?
Attila makes some good points regarding focus and respective of that, what telescope are you using and are you using a field flatner? I may be going out on a limb here but my experience is that the hardcore DSO imager is traditionally using a dedicated guide scope and there may be very good reasons for that. An OAG guider is working on the edge of the field and this edge is notorious for the potentiality of edge of field anomalies that even a field flatner can't deal with. You may be experiencing this very problem. Maybe your OAG is not aligned with the imaging axis of the scope. My first suspicion is that you are not getting good focus with your guide camera. It may be a worthwhile exercise to take a few dedicated images, on axis, with the guide camera to see what kind of resolution you are getting, of course taking your usual care to get a fine focus. If the images are sharp, then I would be looking at the OAG and also study your edge of field to see if you have some edge of field issues. Do let us know how you make out. I suspect that this is good information for many!!
Cheers, Chris.
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Hi Rick,
If you're friend is willing to speak to me I would be very interested in picking his brain on optimizing the ONAG.? I bought it used to guide at high focal lengths.? Many people claim it's easy to setup.? I've been struggling to get good guiding results with the system.? I assume my problems are due to PHD2's centroid detection struggling with my bloated stars.
My offer stands for any seasoned imagers to join me in the dow's lake area one clear night with a bucket of cold beer.
Thanks,
Greg
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Hi Chris,
The galaxy image is from my main camera.? It's been cropped significantly.? It's my first Whirlpool galaxy and I wanted to share it.? I got lazy and didn't remove the stars when processing.? They have been stretched significantly.? I'll reprocess it properly later.
The PHD2 image is from the guide camera.? The scope is an edge HD 8 and it does not have an external field flatner.? I'm not using an OAG, it's an ONAG which uses a dichroitic beam splitter to provide a full frame guiding in near IR.? The issue is not with field curvature of the scope.? The focus on my guide camera is as dialed in as possible.? The ONAG does provide astigmatism but I am not seeing other users reporting such a high FWHM.? I'm borderline over sampled on the guide scope which is why I was thinking larger pixels may help.? Seeing in Ottawa is not great in the winter which can really hurt if oversampled.
Greg
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Hi Greg! Sorry I missed that...I was not aware of this ?system of guiding...will need to get familiar with the technicalities of that equipment! I just don’t see the guide camera being the issue. I will follow up after I do some reading!
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On Mar 24, 2022, at 5:13 PM, gregz12@... wrote:
?Hi Chris,
The galaxy image is from my main camera.? It's been cropped significantly.? It's my first Whirlpool galaxy and I wanted to share it.? I got lazy and didn't remove the stars when processing.? They have been stretched significantly.? I'll reprocess it properly later.
The PHD2 image is from the guide camera.? The scope is an edge HD 8 and it does not have an external field flatner.? I'm not using an OAG, it's an ONAG which uses a dichroitic beam splitter to provide a full frame guiding in near IR.? The issue is not with field curvature of the scope.? The focus on my guide camera is as dialed in as possible.? The ONAG does provide astigmatism but I am not seeing other users reporting such a high FWHM.? I'm borderline over sampled on the guide scope which is why I was thinking larger pixels may help.? Seeing in Ottawa is not great in the winter which can really hurt if oversampled.
Greg
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Hi Greg, I own a ONAG and it can work very well although it does take a lot of room in the optical train. You can sometimes tell if the guider image is focused by the shape of the stars in the guide image. The arms of the star crosses should be the same length. You can rule out the size of pixels as the cause of guider bloated stars! Have a great day. Bob
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Hi Bob,?
The ONAG does take up most of my BF.? In fact I'm 2mm over ideal BF on the imaging camera.? What guide camera are you using?? I'm wondering if my camera's high IR sensitivity is causing the bloat.? I'll try the 2600MC on the guider port to rule out the my guide camera.
Greg
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Hi Greg!
I just watched a video about the ONAG manufactured by Innovations Foresight...very informative. The item that struck me the most is the need to get a strong IR emitting star and having a guide camera sensor that had sufficient IR sensitivity. ASI's sensitivity charts do not extend into the IR so it is difficult to get a gauge on the IR characteristics of your guide camera. That is the thing I would investigate first. The issue of locating a suitable IR emitting star within your guide camera's field may be a bit more problematic. Stars that emit more IR tend to be dimmer stars towards the red spectrum.
?
Do you have an auto focuser or are you simply setting best focus and then running with it for the entire imaging session? Are you using a focus mask during your focus routine and does your ONAG have the ability to focus the guide camera separately?
?
So...based on my newly acquired knowledge I will amend my earlier comment? and suggest that your guide camera may be the weak link here...but you do need to contact ASI to see if they can provide you with information regarding the camers's IR sensitivity. I do understand the simplicity/maybe more compact guiding system that ONAG might provide but I do not think it provides the flexibility of having a dedicated guiding scope.?
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I'll be very interested in what you find from ASI regarding the IR sensitivity.
Cheers, Chris.
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Hi Chris,
Thanks for taking the time to look into this.? ASI does publish QE data in the NIR spectrum up to 1000nm.? My camera is very sensitive in NIR >750nm.. I have used it along with an IR pass filter to take IR luminance images of planets with good success.
When I connect the guide camera to my scope directly without ONAG it does produce bloated stars.? I have used a UV IR filter for planetary imaging and this does help with star bloating.? I suspect there is something going on with the high IR sensitivity and bayer matrix of the camera.? I'll try the 2600 connected to the guider port of the ONAG to rule out the high IR sensitivity/color camera.? I'm still hoping to borrow a mono camera from someone to try before I buy.
Greg??
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Hey Greg,
Not sure if it got lost in the thread somewhere, but you’re welcome to try out my AS174mm — I live about 40 minutes west of Ottawa in White Lake, if you’re able to get out here, or I could meet somewhere like the RASC’s Fred Lossing Observatory outside Almonte, or in Almonte itself..
For what’s it’s worth — I also have a CEM70, and I guide it with the as174mm through an OAG on the back of an 11” EdgeHD. On a night with good seeing, I can get my guiding error down to around 0.4-0.5” RMS.. more typical values are around 0.6-0.7.?
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On Mar 25, 2022, at 11:29 AM, gregz12@... wrote:
?Hi Chris,
Thanks for taking the time to look into this.? ASI does publish QE data in the NIR spectrum up to 1000nm.? My camera is very sensitive in NIR >750nm.. I have used it along with an IR pass filter to take IR luminance images of planets with good success.
When I connect the guide camera to my scope directly without ONAG it does produce bloated stars.? I have used a UV IR filter for planetary imaging and this does help with star bloating.? I suspect there is something going on with the high IR sensitivity and bayer matrix of the camera.? I'll try the 2600 connected to the guider port of the ONAG to rule out the high IR sensitivity/color camera.? I'm still hoping to borrow a mono camera from someone to try before I buy.
Greg??
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Hi Greg!
Sometime last year I read an article that discussed the down side of having too small a pixel size…of course I can’t remember where I saw it. But I did find a few articles online….I am sure there are many more…that discuss the impact of pixel size. The more pertinent link below is the one by Diffraction Limited, an Ottawa based firm.
Cheers, Chris.
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Near ?the bottom of the page you will find a graph that tells you how your optics and pixel size match up. I am guessing that you are over sampling because you are getting bloated stars. I don’t know if you can bin your tracking camera.
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Hi Oscar,
I did see your kind offer.? I live about 1 hour from you.? It would be pretty tough to put my young kids to bed and make it out there with my gear.? I'll ping you if I'm going to be out that way.
Greg
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Problem solved!? The bloated stars were related to pixel size and the central obstruction on the C8.? The pixels on the ASI462 are 2.9um and with 2x2 binning they are still very small causing over sampling.? I tested with a ASI174 mini and the guide stars focused well with FWHM around 3 to 4.? The improvement in FWHM allows PHD2 to make a proper centroid estimate. Guiding improved from 1.0 to 1.3arc seconds to 0.5 to 0.6 arc seconds.
Thank you all for the help.
Greg
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That’s great news...something to be learned for everyone!!
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On Apr 10, 2022, at 2:48 PM, gregz12@... wrote:
?Problem solved!? The bloated stars were related to pixel size and the central obstruction on the C8.? The pixels on the ASI462 are 2.9um and with 2x2 binning they are still very small causing over sampling.? I tested with a ASI174 mini and the guide stars focused well with FWHM around 3 to 4.? The improvement in FWHM allows PHD2 to make a proper centroid estimate. Guiding improved from 1.0 to 1.3arc seconds to 0.5 to 0.6 arc seconds. Thank you all for the help. Greg
<Guiding Update.png>
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Chris T
