Clarkey

I have been pondering a though which I am sure has a very simple answer. However, my old and naddled brain is not coming up with the answer. (Physics was never my strong point). Why does focal length dictate the FOV of a scope? For example, a simple refractor of a given focal length will show a certain amount of sky. Why could you not alter the lens shape to focus the same area of sky at a different point? Same with a mirror system. Any guidance to put me out of my misery would be appreciated. (Be aware, I do have a penchant to miss the glaringly obvious 😀).

I have used stellarium without issue. If the mount starts in the home position it is normally approximately right for the first slew. I think the alignment positions are held in EQMOD when synched. As more stars are synched it gets more accurate (normally). Maybe the data is not clearing from EQMOD? Do you shut your PC / Stellarium down between uses?

I would check, but I think this may be what you are looking for. https://www.firstlightoptics.com/skywatcher-focusers/astro-essentials-2-dual-speed-low-profile-crayford-focuser-for-newtonian-telescopes.html I think the hacksaw option is the 'standard' route.

Not something I can agree with. I have PI, but I find it like playing pass-the-parcel with boxing gloves on😁 I assume your camera is not modified. This would really help picking up the Ha signal. But if you have good stars at 300s that's good. I would not bother with darks with the 200d as it will probably add more noise than it removes, especially with 4.

Not sure I would try threading anything made out of cheese.

I would agree. Adjust your back focus until at least one corner is right. After that it is probably tilt. Looking at the image, I think if you get it close enough you probably won't notice any tilt unless you pixel peep.

I had just started a reply. Beat me to it! 650nm is a very low cut off point. Not only loosing Ha and SII but half the red spectrum. Strange for an astrocam?!

No. The IR/UV wavelengths are removed by the NB filters. You only need this for normal OSC imaging.

I think you need to check your priorities 🤣

Look on the bright side - you can save the money by turning off your heating while you are outside imaging in the winter. Every cloud....😁

Mine stopped talking to me years ago.🤣 Definitely. Excellent scope for the money.

I got my SM 90mm just before new year (and the price increase). Although at this point I was largely using my longer FL scopes for galaxy imaging, I did use the SM a few times. In most areas I think it is excellent. It is well made with a focuser that works for AP - most of my other scopes have not been so good. The made-to-measure flattener reducer is also excellent. Optically it is also very good with no visible CA. My only question with it is the cooling. I set it up along side my ED80 on my dual rig (first and only use so far) and the SM focus drifted way more than the ED80 which stayed pretty constant. As I put my scopes out in plenty of time, the only reason I can see for this is cooling of the optics being very slow. I will be trying it again soon with the new season starting so I can see if will always be a potential problem. If you are using it on its own with an auto-focuser I would not hesitate to get one (especially if you can get one of the ex-demo models cheap). These images are using the SM90. The top one is LRGB plus Ha - something like 8 hours total integration using the F4.8 flattener. The second was a combination of ED80 with a Canon 600D plus Luminance with the SM90. The final image was the SM90 only at F6 using the SM flattener. I did not use any star reduction on these images so you can make your own decision on how 'good' the stars are. To be honest the processing was fairly minimal -as was the set up. On the last image the flattener probably needed to be moved out a fraction, but on the California nebula it was plug and play.

Rising Cam IMX571. Pretty much the same camera but half the price. Slight gamble with warranty but much better value. There other manufacturers selling it under a different name at low prices too.

Back today!!! Yey!!!!😄😄😄

As far as I know there is not much between them optically. Focusers and other bits might be slightly different, but as far as I'm aware pretty much the same. My only question is regarding cool down time with carbon tubes. My 90mm Stella refractor is very slow to cool.

On your own there. I still have the ZWO filters. Astronomik and Antila seem to get good reviews. Depends on how deep your pockets are....

I would agree with @scotty38 that the 7 slots is a definite benefit (even more so if using unmounted filters). You don't want to be opening up your filter wheel to keep changing filters. If you only do RGB or narrowband you would be OK. As for filter sizes, I think for the 533, 1.25 are fine. For the APS-C you would probably get away with 31mm filters - but it will depend a bit on the scope and set up. I would check on the Astronomy tools website which has a filter size calculator. If you are using 'cheaper' filters then it might be worth going larger as the cost difference is small. I think you are probably better off spending the extra on better filters rather than larger.

I think maybe you are over-thinking this! The 'back-focus' is just the focus point as with any other scope. For normal AP I use the four extensions provided (100mm) and then the focuser and focus normally - but the focus point is a long way back. As the primary and secondary mirrors are not moving you are not changing anything in terms of the optics. Although the supplier focuser is OK, I did change mine to a Baader ST just to make sure everything was rock solid. Not sure it was necessary really but it was nice, new and shiny😁. I don't have my rig set up at the moment, but here is a picture of roughly where my RC8 focuses (there is a tilt adjuster too which adds about 20mm). As @Len1257 says the weight is far back. I use a combination of guidescope and homemade power box to balance.

The is also a Stella Mira flattener that might be suitable. It's design for f5 to f7 which suggests it should be ok.

Hey it's a start. It is focus and the stars are pretty round. Good start I would say. 800 iso is probably about right for the Canon. I would forget the darks and run some bias frames and flats plus increase the integration time. In terms of framing, have a look on Stellarium or similar for some interesting areas of sky.

Perhaps if your tone was a little less patronizing and condescending you would get a better response? In terms of what you are saying, whether you are right or wrong is irrelevant, you can not accuse everyone with a different view to yourself as being ignorant savages. This forum openly encourages friendly discussion and debate. If someone has a completely different view to everyone else that is accepted - not condemned or ridiculed.

How about a sky-tee with a ST120 for wide field and pick up one of the many 2nd hand 200p's for a couple of hundred pounds. Should be about on budget.

From the back of the scope to the back of the camera - making allowances for cables and approximate point of focus - is about 43cm. Bearing in mind the back heavy nature of the scope and the width, I have never had a problem with it hitting the tripod. This is with an AZ-EQ6.

You can't use the dovetail itself as it is too close to the tube you could probably attach risers or add a handle. I actually use mine to guide with an ST80 mounted on top towards the front. Helps with the balance a bit too as the RC8's are very back-heavy once loaded with photo gear. WRT the collimation - once set it needs very little, if any adjustment. Mine was pretty good from delivery and only really required a minor 'tweak' to give a slight improvement. In fact the images in my earlier post were taken before I collimated the scope. I wanted to wait until the end of Galaxy Season to start messing with it - just in case!

As I said in my post above - I don't disagree at all, I was just giving options. I would still question the FPL-51 vs FPL-53 mainly down to the manufacturing tolerances at this price point - not specifically down to design but down to individual scopes. I have an ED80 which is FPL-53 and this gives a fair bit of blue bloat and generally this is deemed 'good' optically for the money. Mine was also optically checked by FLO.