PadrePeace

As an update for all I have sent the scope down to APM UK where Rupert is looking at it. I’ll report back on what he manages to find and importantly do about it.

Thanks for this link. Though not for refractors it detailed the common optical issues which is always really helpful.

Pity, as that had the makings of a nice image. Thanks for chiming in.

Thanks David, really appreciate you efforts. I guess even a feather touch won’t guarantee a tilt free image although this could be the sensor. That won’t be what's causing these odd star shaped across the field though would it? The fact that the Flame is worse and being that it was at a low elevation suggests some droop perhaps. M109 by contrast was virtually at the zenith and chosen for that reason so I’ve learned something about the rig if not what I would like to fix. Many thanks again.

Just had an interesting reply from a fellow in the US on Cloudynights. He said he had a similar problem with the same model scope and APM advised him to slacken or remove the 9x peripheral grub screws that were likely pinching the optics as they didn't need to be there to hold the cell lenses in alignment. Sounds strange but he said he did what APM suggested and the issue fixed itself. I guess his cell hasn't fallen apart yet or he'd have mentioned that you would expect. What would hold the lens cell together if theses grub screws are removed?

Skipper Billy. Did you find the fits images I pointed out? They are in the imaging forum as I first thought that would be most appropriate. Needless to say I had no comments there so moved over to this forum. I’ve reposted the .fits here. If you need any more just ask. Thanks for the offer of support.

1parsec The scope lives in the garage on the mount so is never more than a couple of degrees away from ambient temperature. It was out for 9 hrs until 4 in the morning with temps at 2 deg C with no change of star shape from the start of that session. Bottom line, the scope is always cooled.

All My buddy AdanJ posted this elsewhere on this site which was his take on the issue: Glad you posted this mate. Ill kick off with my interpretation. 1) I can see the star is pear shaped pointing downwards in the image. 2) You dont mention it but its very important to note that from memory rotating the focuser resulted in the distortion rotating relative to the camera and remaining fixed relative to the object being imaged. For me that rules out sensor tilt in the camera as a cause. I also know you have confirmed that the focuser is aligned using a laser colimator. 3) Its only visible when viewing the image at full size, so not the worst I have ever seen (some horrific star issues get posed on here) but still something is not right for a scope in that price range. I dont think that the flame is the best example of this as poor seeing has disguised the issue a little. The better example is M109 where you can see something is wrong even with the smallest stars. 4) I dont see anything obvious in the star test, although it might be worth re-doing with the star less defocused and with shorter exposures. I have seensome people use a guide camera and then stack the results as you would a planetary image to resolve more detail in the rings. Seeing can also effect the result. You are aiming for something more like this (my Esprit 100): Using a shorter exposure and in better seeing shows many more rings in more detail making it easier to judge collimation, 10 rings are visible or more. Although this is still probably more de-focused than is ideal. Something like a 0.05s exposure from my ASI1600mm pro, not sure what the min exposure is for your ATIK460EX, hence maybe use a guide camera. On the whole, from the shape I think it might be a case of pinched optics. But as you know I dont have sufficient experience of refactors yet to be sure or to rule out something like coma or a colimation issue. So hopefully someone else will be able to comment. Adam Edited March 10 by Adam J

Skipper Billy. Thanks for the support. I posted this thread here but got no response. It has four raw fits files for you to choose from. If you want any others get back to me.

Kathleen no changes to the imaging rig at all. The Artificial star was resting on top of a SW tripod hence the other random stuff in the shot.

Equipment: APM 107/700 triplet with a 3” Feathertouch focuser, Atik 460EX mono, ZWO EFW, and for these images an Astrodon Lum 1.25” filter was used. Both HEQ5Pro and AZEQ6 GT mounts with steady guiding have both been tried under the scope with no change to the star shape. It occurs whether or not I’m guiding, and also with flattener/reducers in or out of the optical path. What’s telling is that the shape appears well formed on 10sec to 600secexposures so I have discarded trailing. I’ve uploaded two star test shots and some raw Lum images taken at both low and high elevations to discount droop. Can anyone shed light on what will be causing this star shape across my images and how I might fix it? I've added jpegs if these are more suitable than the original .fit files. The first image is a Cheshire collimator shot of the coherence of the lenses. Second image is a slightly defocused image of an artificial star test I did over the weekend. Added the other extra x 2 and intra x2 focus images from a clear sky session the following night. You clearly have to zoom into the other two image to see the pear shape stars I’m concerned with. Many thanks for your experienced comment in advance.

Equipment: APM 107/700 triplet with a 3” Feathertouch focuser, Atik 460EX mono, ZWO EFW, and for these images an Astrodon Lum 1.25” filter was used. Both HEQ5Pro and AZEQ6 GT mounts with steady guiding have both been tried under the scope with no change to the star shape. It occurs whether or not I’m guiding, and also with flattener/reducers in or out of the optical path. What’s telling is that the shape appears well formed on 10sec to 600sec exposures so I have discarded trailing. I’ve uploaded two star test shots and some raw Lum images taken at both low and high elevations to discount droop. Can anyone shed light on what will be causing this star shape across my images and how I might fix it? I've also added jpegs if these are more suitable than the original .fit files also loaded here. L_Lum_Flame_Bin1x1_120s__-10C_2020-03-02_21-44-34.fit L_Lum_Star Test focus_Bin1x1_1s__-10C_2020-02-20_21-49-36.fit L_Lum_Star Test focus_Bin1x1_1s__-10C_2020-02-20_21-50-51.fit L_Lum_M109_Bin1x1_180s__-10C_2020-03-02_22-29-37.fit

I’m so pleased you have finally shared this image with others. As a friend I’ve been watching this amazing image grow over many months of dedicated work in the face of many kit and weather setbacks. It has now finally done what it was destined to do. Stunned and inspired us as only great images like this can. Well done fella, coffee’s on me....

Ref the last comment here back in July (aatdalton). Any updates from anyone on how/if we can polar align through the ASPS/APT software?

Spec info and words on exposure times of 15mins on the 304 CMOS offering from SX. http://www.iankingimaging.com/show_product.php?id=1858 Sorry, just noticed this data had already been posted by AdamJ. I hadn’t got to page 2 of the thread before diving in.

David Adam and I have been mulling over my issues for several weeks and tried many things. You seem to have similar star issues. Try taking a single sub (long enough to get a solid star field) and then rotate your camera through 90 degs. take another shot and rotate again. Do this to get four images and then compare where the bad stars are on each image. If the bad stars rotate (so start in BLH corner and next appear TLH corner if rotating clockwise) then your tilt is in the scope/up-scope of your focus tube/rotator. If the bad stars remain in the same corner of each frame (so in my example the BLH corner) then the tilt is rear of your focus tube/rotator. Knowing this will help you work out where your tilt adjuster needs to be in the optical train; either up-scope of the rotator/end of the focus tube or....on the camera side of the rotator/end of the focus tube. Hope that makes sense.

Dave. I’ve not been able to test without the flattener/reducer in play. The FLT 6A (previous version to yours) is pitched as a doublet but is in fact a TRIPLET (see pic with a green laser revealing each lens face) Would this be relevant?

Thanks Adam. Good timing as here are tonight’s laser collimator tests with the cross hair paper disk fixed directly to the front of the lens cell (dew shield removed). The first image is my rig if anyone is interested. Comprises TS Optics rotator, Baader clicklock, WO 0.8 flattener/reducer FLT 6A. TS Optics Tilt adjuster, ZWO FW. 460EX. Next is the laser test rig mounted in the clicklock. I rotated the laser using the TS Optics rotator during the video. I also tried other combos of compression ring adaptors I have including the original WO 2” screwed directly into the focus tube but the results were variable and generally worse than the clicklock set up. So, is this centring error excessive? Given Adam’s calcs I would not expect it is, which clears the focus tube and rotator clicklock rig alignment as a suspect. Thoughts anyone? 9D263A52-177A-419A-BF1C-EB27F7D802A6.MOV

Olly, I have done this using a representatively (simulate the 460EX) weighted collimator firing the laser through both the filter wheel and Flattener/Reducer. I'll post an image, but in essence the red dot was within 1mm of the centre (which was a close to the centre of the OTA as I could reasonably tap it. When I rotated the laser it ascribed a slight circle within 1mm offset from paper circle cross-hairs centre throughout the full travel of the focuser. I also did this without the optical 'gear' by mounting the laser directly into the focuser tube with very much the same results. Thinking about that now, I taped the paper disc to the Dew Shield which was fully extended but intentionally seated against its stops. I should retry it with the Dew Shield removed and the circle taped directly over the Lens Cell to eliminate dew shield tilt. Thanks for making me rethink that one.

I have a WO 0.8 Flattener Reducer 6A (so scope running F4.7 at a FL of 336mm vice F5.9 420mm unreduced) in the optical train which I would have expected to have given me a much flatter field across such a small sensor as the Atik 460EX (12.5 x10 mm). Back focus has been adjusted from the factory advised 54.8mm through 55.8mm (to allow for the Astrodon Filter correction of 1mm) out to 56.5mm with no significant improvement in star shape in the problem areas. This includes the 13-13.5mm BF built into the 460EX.

As Adam said above, I have used CCD Inspector to try to adjust my way through this problem. Here are a few shots from that research along with the Airy Ring focus images that show the triplet lens cell is well set up as a unit. CCDI frames as I rotate the camera through each cardinal bearing starting at 360 in the top LH corner (read clockwise so top RH corner is 090 etc). Airy Shots x 2. NGC1333 stack showing poor star shape on LHS.