Anthony RS

Hello,

I've recently had some issues with my ASI 1600mmPRO that I noticed while taking 10 minute darks at gain 200. The camera is not 1 year old yet.

Before I explain what I did, all the test were done in exactly the same conditions, same laptop etc... I tried using different USB cables, different capture software and a different PC with the same results.

My main issue is that the mean ADU of my darks are not stable. They start at ADU 920 for example, go up slowly till about 970 and then drop back to 915 or so. This does not happen at gain 75, only gain 200 (did not test other gains yet). 

I have plotted a graph showing the mean value of each frame for 5 minute and 10 minute darks at gain 200. The x-axis is the frame number, the y-axis is the mean value.

I compared these darks with my older darks, and the old darks' mean was extremely stable (+- 1 ADU difference between frames).

The cooler power seems to be stable with no big fluctuations (just 1 or 2% max and it rarely changes).

I am currently in the process of taking 3 minute darks at gain 200 to see if the same trend happens. So far the mean appears to be stable. I will update this info once capture has finished.

Still waiting for ZWO support to reply so I'd appreciate if anyone has any insights or if someone else had this issue just so I save myself some time and trouble.

Cheers,

Anthony

3 minutes ago, globular said:

If you turn the mask over does the odd effect flip too (which might suggest a dodgy mask) or do you get the same effect with the same orientation (which might suggest collimation).

hmm I'm not entirely sure but I think it always the same effect no matter the orientation. I never knew collimation error could show in the spikes 😕 although collimation looks fine with my collimation tools. 

Hello,

I'm using a Bahtinov mask made for a 6 inch aperture on my 6 inch F4 Newtonian. However, The Central spike doesn't appear to be straight. I'll share an image I drew to simulate what I see. What could be the cause of that? Is it a bad Bahtinov mask or something with the optics? The star is in the center of the frame.

1 hour ago, Ricochet said:

You should adjust it so that it appears central. The offset is towards the primary, your secondary appears to be too far away from the primary.

Assuming that TS calculated the correct length of secondary collimation bolts and collimated your telescope as stated, I would start by looking at the focuser and checking whether it is square on the tube and pointing at the correct point on the opposite tube wall. If it has taken a knock during transit it is possible that it is no longer pointing where it should. The point where the focuser connects to the adaptor plate is probably a weak point so I would loosen off the grub screws around the outside of the plate, reseat the focuser and tighten them up again to see if it makes any difference. 

I loosened the grub screws and reseated the focuser, nothing changed. I'm not sure how to square the focuser and how to check if it's pointing to the correct point. 

Here are some images for the scope.

Hello, I've already posted this issue on cloudy nights but I'll post it here also maybe someone has some other ideas.

I just received the TS UNC 6" F4 newtonian. According to TS,The scope is perfectly collimated before shipping, but will probably need to be recollimated before use.. However when checking the scope, I noticed that the secondary mirror is way off center and slightly elliptical (attached image). Is it normal for the secondary to be in such a position in an F4 or should I adjust it so it 's centered in both the x and y axes? According to TS, they calculate the perfect offset for the scope, and I'm not sure if that's the result.

My main problem is it's impossible to get the secondary mirror to appear at the center of the drawtube. The reason being when I loosen the diagonal's center screw as far as I can, first the spring between the holder and the diagonal gets too loose to the point where it's useless, secondly, the 3 adjustment screws won't even reach the diagonal even when fully tightened. The furthest I could position the diagonal is around 3/4 the way the the center. I'm not sure if "offset" has anything to do with it but from what I know, offset is automatically set once I center the secondary under the draw tube. 

The diagonal is an oversized 70mm mirror and here's a link to the scope https://www.teleskop-express.de/shop/product_info.php/info/p5881_TS-Optics-UNC-150-mm-f-4-Newton-Teleskop-mit-Carbontubus.html. According to TS, they manufactured the scope specifically to give full illumation with my ASI 1600mm and SW F4 Aplanatic Coma Corrector.

I've shared two images. The first one is just an image of how I received the scope taken through the draw tube with my phone without a cheshire or a collimation cap showing how far the diagonal is from the center ( I know it's not a reliable way, but the diagonal was so far off that it's really apparent). Note that the manufacturer claims to collimate and test the scope before shipping. I do trust TS, I love everything I purchase from them, but I feel there's something really wrong going on.

The second image is after doing my best to center the secondary (which remained far off-center) and collimate the scope. I took the image using my asi 120mc with its lens inside the focuser and used mire de collimation for the crosshair layout. The green circle is the current position of the diagonal, the purple when is where it should be.

The third image shows a test image I've taken with my DSLR though sincec I haven't received the ASI yet. It shows all the edges and the center of the image. The stars are terrrible. Guiding error was less than half my image scale so it's not the issue. Backfocus spacing for the coma corrector and DSLR needs to be 52mm but I have it at 55mm since I can't adjust it without a thinner t-ring but I don't think it's the cause for this since even the stars at the center are elongated.

I'm not sure, but the lower left corner does suggest some pinched optics as well?

Am I doing something wrong, or is the scope defected? 

I will share some images below of the scope, maybe they could be helpful.

Cheers!

Anthony

18 hours ago, RodAstro said:

Hi Anthony

I am also looking at one for EAA

I have used the 8" version for several months in my observatory so have some experience.

People went on about collimation on the 8" I just think it was rough handling and not that good at collimating.

The one I used stayed in collimation for months in a fixed position, piggybacked to my main scope, in my observatory. The secondary was the most vulnerable because of the thin spider  so the 6" should be better because of the smaller diagonal and shorter spider arms but that's what you pay for having thin spider vanes.

I can see balance will be a problem depending on the camera used and I would say a small weight added to the back of the dovetail bar would be a good option, in my view better than a long springy SW/Vixen dovetail bar.

Focuser was good for the money I had no problem with it.

You are always going to get coma on a F4 newt even with a CC, maybe if you spent a few hundred more than the scope cost on a CC you may get rid of it. Visually you should not notice it if the objects you are looking at are interesting. Photography wise fix it in your processing.

As for should you get it, well there is nothing else at f4 at this price range, (other than the same scope under a different name) double that and you may get rid of the coma totally but that's a gamble.  

Thanks for the info! I actually decided to go with the TS UNC 6 inch F4. which is a step above the photon. I own the Skywatcher F4 Aplanatic coma corrector, do you think it's good enough to eliminate coma in an F4? I really hate coma.

Hello,

Is anyone here using the TS Photon 6" F4 newtonian? I'm about to purchase it but I have some doubts and questions:

1- Does it hold collimation well, at least in a single session?

2- Is it impossible to balance in DEC due to its small dovetail or is it possible but harder?

3- Is the focuser rigid enough or does it introduce tilt?

4- Will collimating it be a nightmare?

5- I'm really picky when it comes to coma, should I expect some coma on edges even while using the Skywatcher Aplanatic F4 CC?

6- All in all, do you advice me to buy it or have some other option in the same price range.

Cheers!

Anthony

6 hours ago, michael8554 said:

I see "choose guide star" in several of the preceding replies. 

You don't choose the star, PHD2 does that with the Auto Select. 

That way you don't get double stars selected, or stars too close to each other, or bloated stars, or underexposed stars. 

Of course, if you think you know better than PHD2 what constitutes a suitable star, go right ahead....... 

Michael 

I always let PHD choose the star. That's not the issue.

8 minutes ago, glowingturnip said:

another thing to check - don't choose a guide star close to any other star in PHD, eg don't choose one of a binary pair.  PHD can get confused between the two stars and keeps flipping from one to the other as its centroids change.  PHD won't report anything wrong, and the guiding graphs will look good, but the subs will all show a smear in the same angle and magnitude as those binary guide stars.

I didn't think of that thank you! But i doubt this is the issue since I've tried many different targets and different stars to guide on. But I'll keep that in mind. Thanks!

11 minutes ago, almcl said:

Can't answer that one, I am afraid, but it happened to me after some weeks of blameless guiding, suddenly, there it was.   It might have been 'mirror flop', or guide scope flexure or a combination.  If the PHD2 graph is solid for an image with bad stars, my money is on one or both of the two foregoing.

Incidentally, now that I've had a chance to plate solve your image of the Veil, it looks as though the two bottom images are erring in Dec, while top left has jumped in RA:

Balancing'east heavy' can be tricky close to the zenith (if that is where the scope was pointing) and can produce this effect, but so too can failing to rebalance after a meridian flip (ask me how I know!)

One more thing if you don't mind, how did you plate solve the image and how did you know where the DEC and RA directions point?

6 minutes ago, almcl said:

Can't answer that one, I am afraid, but it happened to me after some weeks of blameless guiding, suddenly, there it was.   It might have been 'mirror flop', or guide scope flexure or a combination.  If the PHD2 graph is solid for an image with bad stars, my money is on one or both of the two foregoing.

Incidentally, now that I've had a chance to plate solve your image of the Veil, it looks as though the two bottom images are erring in Dec, while top left has jumped in RA:

Balancing'east heavy' can be tricky close to the zenith (if that is where the scope was pointing) and can produce this effect, but so too can failing to rebalance after a meridian flip (ask me how I know!)

Btw how does pointing to the Zenith cause this effect if east heavy balancing isn't as it should. If you mean it could cause the RA axis to wobble, then that should appear in the guiding graph but it's not. 

1 minute ago, almcl said:

Can't answer that one, I am afraid, but it happened to me after some weeks of blameless guiding, suddenly, there it was.   It might have been 'mirror flop', or guide scope flexure or a combination.  If the PHD2 graph is solid for an image with bad stars, my money is on one or both of the two foregoing.

Incidentally, now that I've had a chance to plate solve your image of the Veil, it looks as though the two bottom images are erring in Dec, while top left has jumped in RA:

Balancing'east heavy' can be tricky close to the zenith (if that is where the scope was pointing) and can produce this effect, but so too can failing to rebalance after a meridian flip (ask me how I know!)

That's very interesting Thank you! Most of my images tend to be similar to the 2 bottom images so perhaps I'm having some Dec issues. But what's confusing me is that my guide graph looks normal 😕  Here's a screenshot I took, unfortunately I don't have one showing the whole graph and the logs won't be of much help. I guess I'll have to narrow it down to flexure and/or dec error. Thank you that really helped.

16 minutes ago, david_taurus83 said:

I'd say its guiding error or as above, flexure. Your imaging at 1" so in an ideal situation youd want your guiding to be sub 0.5"RMS and that includes the peaks! Can you check a few guide logs? Ignore the average RMS and take note of the peak errors. It only takes one jump to 2.0" to give issues.

I've never had this issue even before I hypertuned the mount. I used to have >1.2" error with huge 4" spikes in the RA, and never got this exact issue. Now i have sub arcsec guiding with no spikes (very few spikes now and then but they do not always coincide with the bad images). Plus my reasoning is that even if there are spikes, they are usually really short and not enough to register such a bright second star?! It looks more like the scope moved entirely during image acquisition with no guiding correction which does not seem to be the case according to the guiding graph. 

27 minutes ago, almcl said:

If the guiding graphs are good with no sudden excursions, and the scatter plot in PHD2 is reasonably round yet you get star trails, flex between guide scope and imaging scope is a possibility.  

You mention guide scope rings, are these the ones with plastic tipped locating screws?  If so, these alone are sufficient to introduce the sort of flex displayed in your post above.  Solid guide scope rings might help, or, better, switching to an Off-Axis Guider (there are Canon specific ones) would help to eliminate flexure between guide scope and imager.  An OAG will also help if the mirror is moving in its cell as, for example, when the scope tracks through or close to the zenith.

Can you post a guidelog from a session where you got the weird stars?  

Yep the rings have those plastic tips. My main issue is that I've been imaging with the same gear without any problems and suddenly I got this. Why would flexure suddenly appear out of nowhere. I always make sure the screws are extremely tight to avoid flexure. I will try to post some logs but the problem is that I was messing with the scope while guiding (checking for loose stuff, cable drag, etc...) so the log will have huge spikes that we won't be able to distinguish from actual guiding spikes and me messing up with the scope.

Hello!

I've been having this issue for a while now, and I've been trying to find the culprit with no success. This is driving me crazy. For some reason, I've been having weird stars in my image, where it's not a typical star trail, but the stars are actually doubled or tripled in more than 50% of my images. I've attached an image with different previews from different images, one of the images in these previews has good stars while the others have weird stars which seem to go in different directions in each image.

Here are some notes:

-I'm using a celestron AVX with the 8 inch newtonian telescope, Canon 500D with SKywatcher aplanatic coma corrector, 60mm guidescope with zwo asi 120mc-s.

- My guiding looks normal, I'm having the issue with guiding error of 0.8" and my image scale is 1"/px. I've had no problems before even when my guiding error was 1.2"

- The dec graph seems to swing from north to south sometimes due to backlash but the error is always below my image scale. I think I've tried to guide with dec guiding off and had the same issue but I'm not sure (been a while since I've tested). Plus, I believe that if the problem was strictly due to the Dec behaving strangely, the star "trails" wouldn't be in a different direction in different images. Correct me if I'm wrong please. EDIT: After reviewing all the images. It seems like the trail of doubled stars is mostly in the same general direction (in most images but not all).

- My RA is always below 0.8"

- I'm positive my PHD2 settings are correct in terms of focal length, pixel size etc...

- I'm using a cheap 8 inch newtonian (celestron). I always collimate before the imaging session. I even checked collimation after the imaging session just to check if the mirrors are moving during imaging, causing this problem, but collimation always seem to be spot on after I'm done.

- I have tried to extremely tighten everything and all the screws you can think off. All the adapters, guidescope rings screws, literally everything. 

- I tried a different camera.

- I've tried different exposure times from 180s to 300s, and different PHD2 parameters. I have yet to try exposure times of less than 180s.

- It gets cold really fast during the night at the location where I'm imaging, maybe that could be causing the scope or the mount to cause this problem in some way.

- I tried to image with dithering off. I first suspected that maybe APT was sending dither commands randomly during the image (although that should appear as a larger error in PHD2 guiding error)

- I thought it might be the focuser or focuser's draw tube moving due to the weight of the camera but that would mean that I'm losing focus so I've checked focus several times during the night with a Bahtinov mask and it never changed.

SO could the problem be the mount behaving strangely and not showing in PHD graph? some movement in the scope? bad collimation? flexure somewhere in the imaging train or guidescope? 

I'm really our of ideas so I was hoping someone could have some ideas or experience with this. The image I've attached might help in the analysis hopefully.

I'd appreciate any insights and recommendations.

Clear skies,

Anthony

1 minute ago, Adam J said:

I would have thought that the problems that you are introducing with colour balance would not be worth any gains from using a LP filter in those sky conditions. 

I understand that but my worries is star bloating since the CLS-CCD is also a UV/IR Cut filter. My camera still has LPF#1 but I'm not sure it's enough.

1 minute ago, wimvb said:

I moved to a Bortle 4 place, and haven't used my light pollution filter since. I do suffer from Stockholms light dome about 30 km to the south, but that only affects objects that are low in the sky.

is you DSLR modded without removing LPF#1 filter? If yes, are you seeing some star bloat?

Thanks

Hello,

I've modified my Canon 500D (t1i) following Garry Honis' video; however, I did not replace the IR cut filter with a clear glass filter. I just removed the IR filter and put back together all the other filters. I'm using a Newt. with the Skywatcher Aplanatic coma corrector.

Here's my issue, I already have the Astronomik CLS-CCD filter which is a light pollution filter as well as an IR blocking filter but I will be shooting M81/82 in bortle 4 skies this weekend so I'm not sure if using the CLS-CCD is a good idea. First, I'm in relatively dark skies with low light pollution, second, I'm shooting a galaxy, which as far as I know, and please correct me if I'm wrong, the CLS-CCD will do more harm then good blocking probably some of the details or requiring much longer exposures to get the same details as without the filter. I could remove the filter since i'm not worried about light pollution, but would that cause bloated stars since I'm using a coma corrector? or are the remaining filters in the DSLR enough to block IR?

If removing the CLS-CCD does mean I'm going to get bloated stars, the question is can I remove the filter to get as much detail as possible from the galaxies and deal with the stars in processing, or is keeping the filter not that detrimental to galaxies?

Appreciate any insights and opinions especially if you have any experience with this.

Cheers,

Anthony 

Hello,

I've modified my Canon 500D (t1i) following Garry Honis' video; however, I did not replace the IR cut filter with a clear glass filter. I just removed the IR filter and put back together all the other filters. I'm using a Newt. with the Skywatcher Aplanatic coma corrector.

Here's my issue, I already have the Astronomik CLS-CCD filter which is a light pollution filter as well as an IR blocking filter but I will be shooting M81/82 in bortle 4 skies this weekend so I'm not sure if using the CLS-CCD is a good idea. First, I'm in relatively dark skies with low light pollution, second, I'm shooting a galaxy, which as far as I know, and please correct me if I'm wrong, the CLS-CCD will do more harm then good blocking probably some of the details or requiring much longer exposures to get the same details as without the filter. I could remove the filter since i'm not worried about light pollution, but would that cause bloated stars since I'm using a coma corrector? or are the remaining filters in the DSLR enough to block IR?

If removing the CLS-CCD does mean I'm going to get bloated stars, the question is can I remove the filter to get as much detail as possible from the galaxies and deal with the stars in processing, or is keeping the filter not that detrimental to galaxies?

Appreciate any insights and opinions especially if you have any experience with this.

Cheers,

Anthony 

Major Update: I removed the mirror and tightened the clips till they touched the mirror basically. Tried collimating again and the collimation didn't even budge a hair. So I guess I'll have to experiment to see how much can I loosen the clips without messing  the collimation and pray that the clips don't cause any pinching... But that makes me wonder, every single post or site mentions how the clips shouldn't be tight and shouldn't be touching the mirror and that they're there just to keep the mirror from falling but that doesn;t seem to be the case here; and I wonder how many of u guys tried to do the test I've done which is to move the scope around while collimating and check what happens. I'd be interested to hear the results.

If I use the laser with the barlow, the same thing happens but what's interesting is that the dot on the primary doesn't move when i move the scope which I think eliminates any slop in the focuser, laser, adapters... which means the primary mirror or the cell is the issue...

Just now, John said:

It's the same as the Skywatcher Explorer 200P - made by the same manufacturer.

I wonder if the mirror cell is moving around rather than the primary mirror itself ?

I've owned a couple with this design and they hold their collimation well usually. I generally collimate with the scope at around a 45 degree angle.

The cell looks sturdy enough. It's definitely the mirror moving.

1 minute ago, John said:

What scope are we discussing ?

 

Celestron's 8 inch newtonian f5

2 minutes ago, Anthony RS said:

I don't know what that means ? I'll upload a couple of photos in a bit