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HenryNZ

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About HenryNZ

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  1. Mod: i wonder if it is more appropriate to move this thread to discussion / whole scope set up forum which seems to have similar discussions.
  2. Thank you. Please keep comments coming. I am leaning towards a Samyang 135 at the moment, what sample images I could see have all been good. Even with adaptors and focus contraption it will probably be about half the price of a kitted our FS60cb and be faster. It can be had for even better price thru gray import but I am adverse to buying optics without warranty due to my past experience. So far I have only come across one report of a bad sample... I am partial for the Takahashi, and if the reducer is not this expensive I would probably have gone for it for the peace of mind and ease of use. However a kitted out Tak would be about twice the price of an OTA alone
  3. I am trying to put together a portable setup for wide field imaging. My main considerations are either a Takahashi FS60cb with a reducer for ~250mm, versus a camera lens either a Canon 200 mm f/2.8 or a Samyang 135 mm f/2. I have also considered a Borg 55FL with its 0.8 reducer for ~ 200 mm. I have trawled through as much as I could on online forums and it seems opinions vary which one would be better. The Takahashi is attractive - because well, it is a Takahashi and it is a telescope so I don't have to deal with focusing a camera lens. However to get to the focal length I want I will need to use it with the dedicated reducer which is almost 70% of the price of the OTA and thats not including the CAA and other adaptors. I have also read about blue bloat with the baby Tak. The Borg 55FL is also a telescope and it seems to be a bit cheaper than the Tak, but image examples I have seen online seems to show malformed stars at the corners even for just APS-C. That would be rather disappointing. I have seen some nice images from Canon 200 f/2.8 and Samyang 135 f/2 but it is difficult to really get a good gauge how well it performs at the corners looking at the reduced images online. Trying to rig up an auto focus mechanism is a concern too. Moreover I am worried about unit to unit variability for mass produced items like these. I would like to gather comments / comparisons about these options especially for those who have use some or all of them before. Areas I would like comments on in particular: 1. How good are the stars at the corner for 4/3 size sensor, APS-C size sensor and full frame sensor? 2. How much CA / colour bloat is there? 3. For camera lens - how do you focus? 4. For camera lens - do you find unit to unit variability? 5. Which one would you recommend and why? Any comments much appreciated!
  4. I know this is an old thread but is there any update on this matter. Also did you re-collimate with the reducer on?
  5. Yes, you are right. It should be camera>FW>OAG. I have corrected my first post. Question is still the same though...
  6. I have recently purchased a second hand SX FW+OAG to go with my Atik 460ex camera, it is still in the mail but alas I think I might have made the wrong purchase!! I already have an Atik FW and OAG but the Camera+OAG+FW back focus requirement is in the order of 61mm (13 mm camera+22 mm FW +24mm OAG +2 mm for the adaptor to the focal reducer) which is way out of spec for two of my reducers. So I thought since SX OAG + FW including the adaptors have a back focus of 42 mm, this would be perfect for my Atik camera (total 55 mm). But then I started reading about how the OAG may not be able to reach focus if I simply go camera>FW>OAG>reducer because the OAG is designed expecting the main camera to have a back focus of 17 mm. In other word, with my Atik camera, the guide cam will not reach focus (the focal plane is still inside the stalk). To make it work I have been told I may need spacer to increase the back focus of my Atik to 17 mm'sih, but then this negates this whole exercise of buying the SX as I am literally back to square one! Someone please tell me this isn't true... I am just hoping that the guide cam focuser of the OAG can be adjusted enough to still allow it to focus when using my Atik camera. My guide cam is a original Lodestar BTW.
  7. Yeah I figure there is something wrong with it. Unfortunately I bought it on a trip to the States so servicing will likely need to return to base which will be expensive, probably costs more than half what the scope is worth. As I have nothing to lose, I will likely open the OTA to try to fix the problem once the retailer confirms my suspicion (that I will need to send it back to the States to get servicing). For those who are interested and for posterity, please see my test results here: http://www.cloudynights.com/topic/565341-cant-get-consistent-round-stars-with-my-edgehd-at-native-f10/?p=7693688 Basically, the symptom is identical to a severe case of mirror flop that is bad enough to change collimation, however this is not helped a slightest bit by mirror lock indicating the flop is not the usual type but more likely indicates something loose inside the OTA.
  8. Thanks for all the ideas. I have done quite extensive tests last few nights. I now believe the main problem is collimation change from significant mirror flop. It would appear that the bad star image I took was on the opposite side I collimated on. I have since reproduced the problem on multiple tests and every time the scope changed orientation the collimation change. So the collimation change has nothing to do with secondary mirror or temperature, or if it does the effect is small. There is probably something else contributing to the problem unrelated to collimation but it is difficult to pinpoint / decipher as the miscollimation is dominant and this is compound by the built in flattener mixing things up. I do not have a defocused star image as I forgot to keep one, but on one side of meridian the defocused star is textbook and the other side is obviously skewed. There is very obviously a problem of mirror flop which surprisingly wasn't helped with mirror lock. I now wonder if there is an particular orientation I should collimate in such that the mirror flop effect is minimised.
  9. The scope was out whole day under telegizmo cover on that first collimation atttempt, out for may be 2 hours when that image of the bad star was taken and out for may be three hours when I did the recollimation last night. The ambient temperature was very similar in all three nights.
  10. I have posted about my problem and some updates on cloudynights, but here is what I have found: last night seeing was acceptable so I checked the collimation and found that it was off. I recollimated and tightened the screws at the same time, since it had obviously changed between the two nights. However that gave me trefoil pattern of diffraction ring in focus and stars were triangular. Obviously something was pinching. I loosened the collimation screws in steps until the trefoil pattern was almost gone and the stars became nice and round across the entire field. I took a bunch of exposures and the stars were best I have seen from this scope. I then slewed the scope some 45 degree away, and to my great disappointment the triangular stars returned in full force. I then remembered I had the mirror lock on so I unlock the mirror and refocused. After that most of the triangular deformities disappeared but a slight hint could still be discerned. My conclusion: the cause of the problem was collimation shift, exacerbated by a bit of pinching of the secondary. Recollimation and loosening the screws fixed the problem at one particular location. However slewing and mirror lock both can introduce problem with star shapes . There was still some pinch at the second location after loosening the mirror lock. I don't know whether that was residual from the lock or residual from the secondary mirror. I am surprised the collimation can change so much between two nights with minimal moving in between. If this is an ongoing problem I really don't know if I can keep this scope as collimation significantly eats into imaging time.
  11. I have been struggling to get my 8" EdgeHD to perform properly. The thing is I know my EdgeHD is capable of producing nice round stars across the field of a APS-C DSLR. I have seen good image from this scope before. My problem is that the EdgeHD does not seem to perform consistently. For example: 2 nights ago I did my last collimation using Metaguide with 2x barlow. The resultant image is quite acceptable to me. However when I took it out again last night, all stars across the field are triangular. I have not touched a single collimation screw, have not knocked the scope or made any other change to the optical chain. I can understand slight shift of collimation from time to time, but I am at loss to what causes such dramatic change in performance between two nights of similar conditions. Is it because something is loose allowing the collimation to shift (I think the screws are quite tight)? Is it because of different degree of thermal equilibrium? Is it because of pinching? I don't mind collimating once a while but if I have to collimate every time I take the scope out it will eat into my imaging time very significantly. What have I missed here?
  12. I won't be able to refund coz I got it from a Hong Kong dealer. I suspect it is actually a gray market one he sold me. He has already washed his hand. I am already counting my lucky star that Japanese factory has taken it back once for recollimation, I guess because it was so bad out of the box. So I am stuck with it unfortunately. My dilemma is whether to spend more money in a potential futile attempt to "fix" it based on an anecdote that a Feathertouch fixed it for someone (lightvortexastronomy blog) or whether I should cut my losses and sell it to recuperate cost.
  13. I have eventually sent the telescope back to Japan factory for recollimation. They determined that a spacer has come loose. I have received the recollimated scope back and ran some more tests, but it seems there is ongoing problem with elongated stars at the corners. Unlike before though the elongation is now symmmetrical at all four corners. I have emailed the factory again and they replied that it is performing to factory specification and merely suggested focusing between centre and edge. Needless to say I am not very happy with that. Also so I should add that the test images I posted above are from a small chip size CCD (atik 460). I have since get myself a DSLR and the problem is distinctly worse with its larger chip size. Not it sure what to do now.
  14. The way I see it is, if the tilt or mal alignment is after the correcting element, It should be remediable with a better focuser or some shimming of the focuser. If the misalignment is ahead of the corrector towards the objective then it is no good and will need factory adjustment. My question is, how can one tell? Correct?
  15. Here are the eccentricity plots for the tests done at 60-70 degree. It is quite telling: From CAA knob at 12 o'clock: To: 3 o'clock: To: 6 o'clock To: 9 o'clock However, at Zenith, the plots look different: 12 o'clock: 3 o'clock 6 o'clock: 9 o'clock: Does it mean that the tilt is behind the CAA (camera), at the CAA or in front of the CAA (i.e. focuser and OTA)? Does it mean that there is focuser sag, since being at Zenith eliminates the tilting axis?
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