angryowl

Thanks to all who took the time to reply. I have found a QHY5L-IIC which should be delivered any day now. This has a 1.25" body so should be perfect for my setup.

Hi Nikolas, I appreciate you taking the time to reply, but unfortunately the price is a bit out of my range and what I'm willing to spend on this since it'll only be used for polar alignment using SharpCap.

Yes, that's exactly it. A mate of mine found someone selling a QHY5L-IIC which is perfect and am currently communicating with the seller. If this materialises then I'm sorted.

I see, I've attached an image to my original post of my 60mm modified guidescope to better illustrate where the guidecam imaging chip needs to be.

Thanks for replying, but I updated the Ad with more information. I have seen that DMK21 and I also have a DMK41, but these can not be inserted into a 1.25" focuser enough to reach focus with my guidescope.

Looking for a guide camera (CCD or CMOS) with a 1.25" barrel size that could slide into my guidescope focuser. To reach focus with my guidescope the guidecam imaging chip will need to be positioned inside the 1.25" focuser so the camera will need to be inserted almost all the way inside the focuser hence the need for a 1.25" body. Examples of compatible cameras are QHY5 series, Lodestar guide cameras, ZWO ASI 120 mini. This is my guider and roughly how much the camera needs to be inserted into the focuser to reach focus Any make and model considered. Thanks for looking

When I tried the OAG lent to me by @souls33k3r I did manage to get the spacing right and guiding gave me pinpoint stars in all exposures. So far the OAG is the only thing I tried that actually works and currently I’m in the process of building a DIY one. The reason I’m not going with a commercial one is that the guide camera body and USB cable get in the light path of the scope and cause weird diffraction spikes whereas with a DIY one, I’m hoping to avoid that. Chip moving inside the camera…wow that’s scary! Glad you got that one sorted as I can see it being hard to solve. Seeing as the images in my OTA and guidecam drift the same direction and amount I’m inclined to believe the guidecam/chip is securely attached and not moving relative to the main OTA. At least not by any significant amount anyway. But a really good suggestion, thanks.

Oh yeah, that I will do given the opportunity. Perhaps when Ahmed gets his one finished he'll let me throw it on top for a quick test ?

Managed to get out during a clear night last week and tried guiding with the refractor piggy backed on top of the RASA and also with the 60mm guider clamped onto the bottom dovetail of the OTA. I also cleaned up the residual adhesive on the tripod head and sanded the bottom plate of the Mesu down which resulted in a much larger contact area with the tripod head. The results are not really what I expected, but a lot better than before and guiding is more consistent. That being said, guiding with either the 60mm guider or the refractor still doesn’t produce round stars. The elongation is much smaller than before and looks like guiding is now actually correcting for most of it, but still not completely. Not sure why this is as the elongation direction and amount are now very similar in both guide and main images. The guided subs are now almost usable, but I’d still very much like to get as close to perfectly round stars and just don’t see this happening with the current guider. Therefore I’ve started designing an OAG using a right angle prism and will be using the bare CMOS board from a QHY5L-II-C camera to avoid obstructing the light path with either the camera body or the USB cable. I have most parts and it’s just a matter of finding a way to mount them. I won’t be troubleshooting this any longer as I’ve spent far too many clear nights on this and I now know that an OAG will certainly solve the problem. I really wanted to get to the bottom of this but it just seems like it’s not practical at the moment. Will update this thread once the OAG is complete Some examples of what elongation looks like now

Hi Jakub Welcome to SGL, you’ll find the very helpful and experienced people here will provide invaluable assistance and guidance when dealing with issues such as yours. Don’t yet have a final word on this, but so far it seems like the PTFE pads were only part of the issue and although I can now guide most of the elongation out, it’s definitely still present in most guided subs. In response to your question, I’ve tried anything from 1 second exposures all the way to a minute in most directions in the sky and no elongation whosoever was present in these short exposures. I find that in subs up to 3-5 minutes I usually see no sign of elongation wherever I’m pointed. That being said, the first thing I’d suggest is rotating your camera 90 degrees to see if the direction of elongation changes by 90 degrees. If it doesn’t, that could point to the camera not being completely orthogonal. This would explain seeing elongation during such short exposures and also remember when pointing at the zenith the gravity would no longer be pulling the camera/imaging train to one side to such an extent and would explain why stars come out fine. Apart from this, we’d need to know a lot more before anyone on here can offer any meaningful advice on troubleshooting this. Please let us know how you get on with this as I’m very much interested in what this’ll turn out to be.

That makes a lot of sense now, but didn't know any better two years ago when I built the tripod. Looked at the EQ8 and saw that the tripod they sell had PTFE pads and the mount is rated at 50kg, I thought adding 0.5mm thick pads on mine would be a safe bet. However, I'm thinking the EQ8 might have more contact area with those pads than my Mesu did which would make a difference.

Hehehe, thanks mate. Don't want to get too excited as I said it could be only part of the issue, but further testing should confirm.

Forgot to mention the subs above were taken with the mirror unlocked.

Thanks for the suggestion.I mounted the guidescope as close to the mount as I could during one of my latest sessions and it drifted in the same direction and the same amount as the main OTA. Turns out this may have been caused by the PTFE pads between the tripod and mount, but further testing is needed to confirm this.

Some more progress on this. Piggy backed the refractor on top of the RASA using a very solid adapter plate made of steel profiles welded together. I’m pretty sure the plate does not introduce any flexure in the mix. Started by guiding the RASA using the refractor and QHY camera. I also guided without sending corrections to the mount and just monitoring the guide star in PHD and this showed the star drifting in the exact same direction as it did in the main OTA. I wasn’t able to get a single sub to guide properly using the refractor as all subs showed substantial drift. I also ran the other test of taking short exposures with both refractor and RASA at 10 minute intervals to see the direction of elongation and amount in both scopes. The direction was always similar in both scopes and the drift amount in arc seconds was always lower in the refractor. At the same time I also had the 60mm guide scope mounted on the bottom dovetail bar of the OTA. This is as close I could get it mounted to the mount plate and still have the full weight of the RASA on the mount. Again I measured the drift which was the same in direction and amount and tried guiding through it with no success. I then moved the Atik camera to the refractor and took some unguided exposures and these also show elongation even at 5 minutes. It was clear that the issue was now pointing at either the mount or tripod. I started looking at the tripod. As I have the two plates on top, separated by six M10 bolts (not the best design I know) I thought I’d eliminate potential flexure coming from the bolts by sandwiching some washers between the two plates and tightening everything up. Although I tried this some months ago, I also placed some large wooden boards underneath the 70mm diameter tripod legs as I was thinking the legs may be sinking into the ground due to the additional weight of the OTA. Neither of these made any difference and the drift was very much the same. I took things inside and securely attached a small laser module on the mount head plate with the RASA mounted and balanced. Then I pointed in some positions I know the drift occurs and marked the laser position accurately as it was projected on a wall. After about 30 minutes, in almost all positions I tried, there was a relatively small but visible movement in the laser position. I started pressing and tugging on different parts of the mount and tripod and to my surprise the only thing that moved the laser point on the wall considerably was me squeezing the bottom plate of the mount to the top plate of the tripod. The only thing that would allow this compression is the 0.5mm thick PTFE self adhesive pads I had on. Upon inspection of the mount bottom plate and PTFE pads it was clear that the contact area of the mount plate is actually rather small only around the edge as can be seen in the images. Plus, when inspecting the PTFE pads, the self adhesive glue was almost completely dry and I was able to remove them easily with a thin blade. Additionally, it looks like when the adhesive dried the pads started lifting up slightly in places. After taking the pads off, I remounted the RASA and pointed the laser in the same positions only to find that even after an hour the position of the laser didn’t move at all. It was clear for a few hours last night so thought I’d test again and I only had time to take a few subs before the clouds rolled in. I still observed some elongation in unguided subs, but mainly when pointing West and the good news is I was able to easily guide it out using the 60mm guide scope mounted on top of the OTA. Also my PHD RMS numbers are higher now at about 0.7” compared to the 0.3” I was getting constantly when guiding before and still getting the drift. I sort of rushed things last night getting out so didn’t have time to completely remove the residual adhesive on the tripod head and I think I’ll also look at sanding the mount bottom plate so it has more contact area with the tripod plate. As it stands now, it seems like the issue could have been the PTFE pads all along. I added them when I built the tripod to allow for easy azimuth adjustment when polar aligning, but during PA last night I didn’t observe any difficulties or significant stiction when making adjustments. I’ll do more testing after cleaning the glue and levelling the mount plate but hoping that the ageing adhesive combined with the low contact area were the root of my problems. The PTFE pads Mount bottom plate Adhesive residue Unguided/guided 600s exoposures pointing West Unguided/guided 600s exoposures pointing SE