Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.


New Members
  • Content Count

  • Joined

  • Last visited

Community Reputation

5 Neutral

About coenie777

  • Rank

Profile Information

  • Gender
  • Location
    Pretoria - South Africa
  1. Matt, pretty sure at this time as I have photographic proof that my tweaking with the secondary produced either more or less of the effect. I also check the images with CCD Inspector and can see that where the field is not flat is where the stars do not look round. By changing things in the adjustments I have made to date I was able to reduce the coma shapes of the outer stars significantly. So it is definitely something sitting on the optical axis as moving this around I can exagerate or improve the results. What are you thinking?
  2. This question relates to my MN190 but I guess the technical principals at play here may be the same for all Newts. In trying to tweak my MN190 to show round stars all the way to the edge (I have them round up to around 90% of the edge at this time), I need some advice please. I build myself a 2" Cheshire sightube and tried my best to get the cross hairs exactly square. They are within 0.5mm I would say. I started off by trying to get the marking on the secondary mirror centred on the Cheshire. Here I need the first bit of advice; - For fear of extending the secondary mirror down too much and risking a mirror drop, I also loosened the focuser and moved it up and down the tube. - I got the crosshair close to the marking, but it was lower than the horizontal crosshair. To explain this, if I moved the focused up and down the tube after loosening the screws, the centre dot would move left and right of the vertical cross hair. The position relative to the horizontal line is not affected by this. Moving the focused only moved the mark left and right (if I do not twist it laterally off course). - I then figured out that by tilting the focuser on one side, I can actually get that horizontal offset aligned. I added some padding to the one side of the focused and got the dot centred. So I raised the lower fixture point, tilting the focuser to one side. First question is if tilting the focuser by adding padding is a good idea or not? Second question is if this scope should actually be able to have the dot centred without having to tilt the focuser. Once i got the dot centred, it looked like the secondary image circle under the focuser were not 100% following the roundness of the Cheshire. To my eyes it looks like the mirror needed to be dropped further down the tube. I can see all three primary clips and they actually seem to extinquish at the same time. It is just that the circle looks to be slightly shifted towards the upper end of the tube (towards the corrector lens). Before trying to drop the secondary down in order to try and make up for the above, would this be recommended? If the centre dot of the secondary is under the crosshairs now, can it still be a case of the secondary being too high up the tube? Surely if I drop it down now, it would move the dot away from the crosshair centre? Clouds are going to not see me being able to image anytime this week so I hope someone can share some experience or maybe advice that I can try in the mean time. I am fairly confident that the secondary twist is correct as I used a laser and got the dot actually on the primary centre dot, taking care while tightening the lock down nut to not twist it again.
  3. I have taken my mount apart twice now. The first time round I made a sketch of the placement of the spacer rings on the shaft (their order). I unfortunately lost this sketch. When I took the mount apart for the second time I for some reason (arrogance?) did not make the best notes of the order of the spacer rings. I now sit with a situation where I am not sure if I am placing the rings back in the correct order. Can someone perhaps tell me if there is a specific order that all these mounts' spacers follow or is it different for each mount? I have the mount that required three spacers in total. I am 100% sure that the first ring goes down the shaft first before the lower bearing. What I need some guidance on are the two red spacers on the sketch below. Should they go on top of each other or maybe one between the two bearings and the other on top of the last bearing? I am also pretty sure that I have the correct one in the first position on the bottom (they are not all the same thickness). The mount comes together without any major gaps evident but I am wondering if my bad RA tracking is maybe due to the incorrect insertion order of the two red spacers.
  4. I removed the primary cell and indeed this was the cause of the "thumb" when rotating the tube. The rubber holders were very loose, so much so that I could move the mirror around the cell with some side pressure. I tightened these down in line with Ronin's suggestions and the movement were gone. Took some time to re-do the focuser alignment and for the first time I have a good picture through the Cheshire (or maybe it is psychological : - ) ). Now for the long wait for a clear night but I suspect I cleared up a major issue on this scope.
  5. Thanks for the reply Ronin I am pretty sure that the movement is not coming from the laser or focuser. I also notice that when putting the scope on the mount or taking it off; when you turn it through 90 degrees as you position it for carry/placement on the mount, there is a small "thud" sound, like something moved ever so slightly. Sounds like I will need to remove the mirror cell after all to now for sure.
  6. I use the above method to collimate the primary of my MN190. I noticed today that if I put the tube horizontally pointing say left, and align the laser donut and then proceed to turn the tube through 90 degrees, the just now collimated donut "jumps" slightly off the mark. If I move the tube horizontally pointing right now, and re-do the collimation, it would shift again as I move it through 90 degrees to point the other way (this is with the scope on my EQ mount). Would this behaviour be caused by a loose primary mirror cell or what would you say should be the first thing to fault find to try and cure this issue?
  7. I need to align my secondary again after it twisted when I loosened the fourth locking screw on the secondary attachement. It basically rotated the secondary cell inside the corrector cell. I tried the laser and a home made Cheshire but just cannot get it to produce good stars to the edge. CCDInspector is used to analyse the final result. Is there a way that I can take flats against a lit wall (setting the DSLR to AV as you do with sky flats) and then somehow figure out from that via CCDI if I have the required rotation set correctly? Would this be a good way of getting the rotation set correctly? I do not think that there are any issues with the lateral positioning of the secondary. It appears well centred under the focuser. I just cannot seem to get the rotation set correctly. I would appreciate any advice on what has worked for you or what I can tick off the list as not even having to try this or that. Are there any commercial products available that can be recommended as the sole tool you require to get this scope tuned collimation wise to its full potential? (secondary setup as well as primary) Any advice or views would be greatly appreciated. Coenie
  8. I recently bought a second hand MN190 (from first owner). I get images that appear to show coma in the upper and lower right hand corners: Here is a single sub, unprocessed with a Canon 40D (1.18"pixel resolution): And here is what the extreme lower right corner looks like: In contrast, the left upper and lower corners look way better: CCD Inspector looks like this on most of the subs: My question is: - Does it look like just bad collimation resulting in these terrible corners? - When I pick up the scope and turn it on its back (I mount it with the eye piece down so need to turn the tube lenght wise 180 to store it), there is a slight thumb. I am not sure if this could be the primary mirror flopping around. Does this sound like an issue? - When you focus with the standard focuser and want to lock focus with the set screw below the focuser, I see quite a bit of image shift. I want to know how tight you need to turn this as turning it in fully it actually move focus completely out. Should you just lightly tighten this? Once tightened, does this then disable the fine focuser knob from making any adjustments? - Lastly, when I collimate the secondary and loosen the fourth screw (lower one), it results in the secondary turning. I tried tightening the round knurled srew a bit but do not want to do something that may damage anything. Are these secondaries prone to turning when being adjusted?
  9. Could someone with technical know how on guiding please comment on what I hope could be a shot that could answer the following: - Is my guiding/mount good enough for decent long exposure images of Deepsky objects? - Is my scope good, very good or average in terms of how it presented the image. The first shot is a crop of the extreme lower right hand side of the 1200" image I took under heavy light pollution. I tried to minimize it a bit with PS levels but the histogram has three humps for each channel and I did not want to tweak too much. I reduced ISO to 100 to combat the LP. I also include the uncropped full frame shot without any darks or flats added. I would appreciate any comments. Guiding was via Orion Mini 50mm with SSAG under PHD2 and ST4 mode at 1x for RA and DEC. Focal length was only 420mm so that must help a huge lot. Crop: Full frame:
  10. I see there is a n RGB histogram option as well. Here it is clear that on the 180" shots I pushed the red channel off the histogram probably clipping it before I even started processing. Hopefully this post could serve as advise for someone in a similar situation as me. The 45" histogram sits well within the 40% band (I think): But the 180" show clearly why I could not process these images to something respectable:
  11. Thanks Mike, 800 or 1600 iso was what I was aiming for. I used to image at 400 after misreading a Craig Stark review of a 350d and advising 400 as optimal. Somehow I thought this applied to 40d too and just kept shooting at 400 until fairly recently. For the 45sec shots the histogram looked like this in Canon's DPP: The 180sec looked like this: I will make sure to read this histogram to know where 40% is as I would prefer to not have to check the back of the camera after the test shots.
  12. Thanks Mike What would work best, reducing ISO or exposure time? You are right, looking at the histogram in DPP (Canon software) the histogram is over to the extreme right. I will aim for the 40% mark you mention next time.
  13. I have been imaging for just on a year now and still need to learn a lot. I recently started to image exclusively with my AT65EDQ apo. I shot some nice unguided images before my guider arrived about a month ago. I thought that once I would do 300", the results I have seen on 45" and 90" so far would far be exceeded. This is however not happening. I would appreciate some advice on what could possibly be the result of these mediocre results, guided. I image without any filters and with an un-modded Canon 40D. My image site is at best mag 4 skies with plenty of light pollution right round me. My image used in the compilation of these images were all tight stars with slight elongation on the unguided shots on around every fourth one. Again, to my eye I got a better image from that than the round star guided images. The first shot is badly colored but I am looking more at detail now than getting the color right. It was a combination of two session's data. I shot 30 x darks, 30 x flats and 30 x bias frames. The second shot was a combination of 46 x 300" and 39 x 180" guided with FWHM reported by DSS to be below 4.1. Sensor temp were a bit high with EXIF data showing 27 - 29 degrees. I shot darks x 20, flats x 30, flat darks x 30 and 30 bias. Histogram were pushed very far right with three shots actually not making it due to the drop off in FWHM due to excessive light. To my eye I got more detail from the 45" shots than the guided shots. I used Startools for processing and tweaked in CS6. Any views/advice would be appreciated. Image 1 : http://www.astrobin.com/195204/B/ Image 2: http://www.astrobin.com/212273/
  14. I used the following grease on my mount: Loctite White Lithium Grease which is made by Henkel I see. Here is the link to the technical chart for this: https://tds.us.henkel.com/NA/UT/HNAUTTDS.nsf/web/4EF7A95478A9ED0085257E4300685592/$File/LB%208042-EN.pdf Any views on its efficacy for the intended use (although it is now too late for me )
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.